INSTITUTUL DE GEOLOGIE ȘI GEOFIZICĂ i BUCUREȘTI 1976 -i Institutul Geologic aI României \K5r/ Responsability of the paper content gets exclusively over the author INSTITUTUL DE GEOLOGIE Șl GEOFIZICĂ ANUARUL INSTITUTULUI DE GEOLOGIE ȘI GEOFIZICA VOL. XLVIII BUCUREȘTI 197 6 Institutul Geological României Institutul Geological României CONTENTS P>«e Drăgănescu A. Lower Cretaceous Carbonate and Carbonate-Evaporitc Se- dimentation in the East-Wallachian Sector of the Moesian Platform (Eastern Romanian Plain)........................................... 5 Pop Gr. Origin of Some Mesozoic Basinal Limestones from the Reșița Zone (South Carpathians)..................................................... 57 Popescu B. Lower Gypsum Formation West of Cluj — A Supratidal Evaporite; Petrographycal and Sedimentological Features....... 97 Popescu B. Sedimentology of Priabonian Carbonate Rocks, Jibou Area, N—W Transylvanian Basin.......................................... 117 Rusu A., Drăgănescu A. Facies-Zoned Carbonate Sedimentation at the Hoia Limestone (Upper Tongrian) in NW Transylvania (Romania) 141 Institutul Geological României LOWER CRETACEOUS CARBONATE AND CARBONATE-EVAPO- RITE SEDIMENTATION IN THE EAST-WALLACHIAN SECTOR OF THE MOESIAN PLATFORM (EASTERN ROMANIAN PLAIN)1 BY ANDREI DRĂGĂNESCL’2 with an appendix by S. RĂDAN Abstract A Lower Cretaceous autochthonous sedimentation of a carbonate-evaporite type is des- cribed in the eastern part of the Romanian Plain on the basis of petrologie material provided by drillings. The concerned sedimentary sequence may be subdivided in 3 complexes : I) the micritic limestone complex, including mainly micrites accoininodating in places allochemical varieties of limestones; II) the facies-zoned complex, exhibiting a very complicate constitu- tion, consisting of three, isochronous, laterally interfingering, petrogenetic systems : the tidal- flat system (of a carbonate-evaporite consistence), the carbonate-lagoonal system (mainly limestones of a bahamite type) and the reef system (skeletal and oolitic limestones); III) the reefal limestone complex consisting mainly of skeletal limestones of a coralgal, brialgal and algal type. Tire main petrogenetic processes pointed out by the studied sedimentary sequence are : syngenetic processes including deposition of calcareous sediments on account of inorganic or biogenic extraction of CaCO8 from seawater as well as evaporite and dolomite formation in relation with sabkha cycles, and the diagenetic processual sequence — a new diagenetic line — involving dolomitization-dedolomitization-aggrading recrystallization responsible for most of the spar calcite in the analysed material. Particularly worth mentioning are 4 very interesting petrologie aspects discussed in the paper : 1) the microcoprolithic (fecal pellet) limestones, abundant in the tidal-flat system of the 2-nd sedimentary complex and consis- ting of very well-preserved fecal pellets ascribed to crustaceans, gastropods and polychaete annelids; 2) the anhydrite-after-gypsum pseudomorphs exhibiting two textura! types; 3) the 1 Received on January 12th 1973 and presented in the Meeting of March 9th 1973. 2 Institutul de geologie și geofizică, str. Caransebeș 1, 7000 București. Institutul Geologic al României 6 A. DRAGANESCU 2 peneconteinporaneous, submarine neomorphism of some mioritic fabrics to fine microspar; 4) the replacement origin for almost all spar calcite in studied material by a new diagenetic line; dolomitization-dedolomitization-aggrading recrystallization. CONTENTS Page General Statement................................................................... 6 ). The Micritic Limestone Complex.................................................. 11 II. The Facies-Zones Complex................................................ 17 A) The Zone of Carbonate-Evaporite Facies............................. 19 1. Țăndărei Sector.............................................. 19 2. Cireșu Sector................................................ 31 3. Amara Sector................................................. 38 B) The Zoneof Bahamite Facies......................................... 40 1. Smirna Sector................................................ 40 2. Gura lalomiței Sector........................................ 42 C) The Zone of Skeletal-Oolitic Facies ............................... 43 1. Zăvoaia Sector............................................... 43 2. Berlescu Sector............................................. 43 III. The Reefal Limestone Complex........................................... 44 1. Berlescu Sector............................................. 45 2. Zăvoaia Sector.............................................. 45 3. Smirna Sector............................................... 46 General Conclusions................................................................ 46 References......................................................................... 48 Appendix — Clay Mineral Study of Some Neocomian Cores in Țăndărei Dril- ling by S. R ă d a n................................................... 53 GENERAL STATEMENT The area considered in the present paper is located in the east- Wallachian sector of the Moesian Platform3, geographically lyingin the eastern part of the Romanian Plain, bounded by the localities : Hîrșova, Brăila, Smeeni and Călărași. The work relies on the petrologie data provided by the sedimentary sequence stratigraphically interposing between the Upper Jurassic dolomitized reefal limestones and theHaute- rivian variegated marly-calcareous series in the drillings performed in the following sectors: Bordeiu Verde (drilling no. 1), lanca (drilling no. 2), Berlescu (drillings no. 3, 4 and 5), Zăvoaia (drilling no. 6), Smirna (dril- 3 The Moesian Platform is the geological platform, generally epihercynian in age, placed between the Carpathian and Balkanian Orogens, geographically assembling the teritories of the Romanian Plain (= Wallachian Plain), Central and Southern Dobrudgea (all in Southern Remania) and the pre-Balkanian Plateau (northern Bulgaria). The Romanian part of the Moesian Platform is usually divided in four sectors : the west-Wallachian sector, the central Wallachian sector, the east-Wallachian sector and the Dobrudgean sector. Institutul Geological României Fig. 1. — The Neocomian sections crossed by the drillings in study area. IV = the variegated marly-calcareous complex (out of discussion); III = the reefal limestone complex; II = the facies-zoned complex; I = the micritic limestone complex, x = position of the mechanical cores extracted from the Neocomian sections. Institutul Geological României 8 A. (DRĂGĂNESCU 4 ling no. 7), Gura lalomiței (drilling no. 8), Cireșu (drilling no. 9) and Țăndărei (drilling no. 10) (the drilling numbering is convențional) (Fig. 1 and 2). The concerned stratigraphic interval includes deposits resulted from an autochthonous sedimentation, consisting of limestones, dolo- Fig. 2. — Facies map in the east-Wallachian sector of the Moesian Platform (eastern Romanian Plain) including the drilling locations, the ancient and present extents of the I and II Neoco- mian sedimentary complexes, and the sedimentary facies distribution during the deposition of II complex. mites and evaporites; the terrigeneous supply is represented only by rare and weak influxes of silty quartz grains and argillaceous material. The age of this sequence may be established by analising the supra- and subjacent formations as well as by interpreting the data provided by studied sequence itself. Thus, as the variegated marly-calca- reous series, overlying the under-discussion sequence, is assigned to the iGRy Institutul Geological României 5 LOWER CRETACEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION <) Hauterivian stage (by comparison with Southern Dobrudgea and nort- hern Bulgaria; Patrulius and Tocorjescu, 1962; D r ă g ă- n e s c u , 19714), and the Upper Jurassic limestones and dolomites, stan- ding for the basement of the coneerned sequence, eertainly include, besides the Oxfordian stage, the Kimmeridgian one (by comparison with central Dobrudgea as well as on faciological and paleontological grounds; Patrulius, unreported data; Drăgănescu, 19715), the dis- cussed sequence results to be placed in the Tithonian-Valanginian time range; but, inasmuch as there are suffieient reasons to accept also the presence of the Lower Tithonian (Danubian) substage within the Upper Jurassic dolomitized limestone series (Patrulius, unreported data; Drăgănescu, 1971 6), the sequence under-discussion appears restric- ted to the Upper Tithonian (Ardescian) ?-Berriasian-Valanginian range. This opinion is also supported by evidence provided by discussed sequence itself: the basal term, represented by micritic limestones bearing dolo- mite rhombohedra and considered as the first term of the Neocomian section in different areas of the Moesian Platform (Patrulius, 1964 a; Patrulius, unreported data), contains, in Zăvoaia sector (drilling no. 6, 2 295—2 296 m depth interval), an assemblage of calpionelids [Crassicollaria massutiniana (C o 1 o m), C. parvula B e m a n e, Tintin- nopsella carpathica (Murg, and Fii.), Crassicollaria cf. intermedia (Durând D el ga)] corresponding to the Crassicollaria biozone and suggesting an Upper Tithonian age(calpionelids determination by Pop); the uppermost term is represented by reef limestones, whose facies is analogous to that of the Valanginian beds of Southern Dobrudgea. Accordingly, the most plausible age for the entire under-discussion sequ- ence, in present author’s opinion, is the Berriasian-Valanginian one, possibly Upper Tithonian for its lowermost part. This assignation is in a good agreement with the more general point of view advanccd by most of the previous researchers, according to which the discussed sequence belongs to the Neocomian stage. A short bibliographic review reveals that the different studies bea- ring on the Neocomian sequences crossed by drillings in the east-Wal- lachian sector of the Moesian Platform pointed to the occurrence of some marine calcareous facies and of a peculiar one; this latter facies consists of coprolithic limestones, dolomites and evaporites and was thought the product of the temporary installation of some evaporite-lagoonal condi- tions in connexion with the emerged neighbouring territory of central and northern Dobrudgea. General remarks appear in the synthesis 4 A. Drăgănescu. Studiul forajelor adinei Țăndărei și Gura lalomiței din plat- forma moesică (The Study of the Deep Drillings of Țăndărei and Gura lalomiței in the Moesian Platform; unpubl. report). 1971. Arch. I.G.G., Bucharest. 6 Op. cit. 4. 6 Op. cit. 4. Institutul Geological României 16 R/ 10 A. (DRĂGĂNESCU 6 study made by B a r b u et al. (1966)7 and in the the paper of P o p e s c u et al. (1967). Summary and strictly descriptive lithological-petrographi- cal studies (bulletins of analysis and unpublished reports) were made also by some departments for petrographical analysis. Analysing the Neocomian series pierced by drillings in the Southern central-Wallachian and east-Wallachian sectors, Patrulius (1964, and unpublished data) concludes that in some areas marine calcareous sequences have been accumulated, while in others — alternating marine limestones and coprolithic limestones bearing dolomite and sulfates have been deposi- ted. This author estimates the latter lithologic assemblage as an expres- sion of a marine facies including evaporite-lagoonal episodic reccurren- ces. In the lithofacies map of the Romanian territory for the Neocomian stage, elaborated in collaboration with Ștefănescu, Patrulius (1969) achieved the first areal figuration of the facies in the east-Walla- chian sector; he distinguishes a mixed, marine-hypersaline lagoonal, carbonate-evaporite facies as a strip generally oriented NW-SE, bounded to the east by the mainland of central and northern Dobrudgea and to the west by normal marine, calcareous facies. The researches that I undertook (Drăgănescu, 1969 a8, 1969 b9, and 197110) on the drillings performed in the Moesian Platform revealed to me a lot of details giving much complication and somehow altering the previously accepted general image concerning the types and the distribution of the sedimentary facies during the Neocomian time interval in the east-Wallachian sector. This is the reason which deter- mined the present author to resume this stratigraphic interval in a syste- matic study purposing to establish as detailed and exact as possible the lithostratigraphic sequences crossed by the mentioned drillings and then to correlate them in order to obtain, on the basis of a minutious petrolo- gical analysis, the picture of the sedimentary pattern for each lithostra- tigraphic unit over the discussed area. Finally comparing these sedimen- tary patterns with doubtless data supplied by recent carbonate and car- bonate-evaporite marine sediments (and also by some ancient similar formations), the author attempted clearing upthe genetic significance of these patterns. In addition, besides the approach of the depositional aspects, the main diagenetic processes are outlined. 7 C. B a r b u, E. V a s i 1 e s c u, A. S terescu, T. D o i ci n, C. Paraschiv, O. Oprea, S. Dicescu and Gh. Dumitrescu. Studiul geologic complex al platformei moesice (The Complex Geological Study of the Moesian Platform; unpubl. report). 1966. Arch. I.C.P.G., Bucharest. 8 A. Drăgănescu. Studiul stratigrafie al forajelor din sectorul nord-estic al plat- formei moesice (The Stratigraphical Study of the Drillings Performed in the NE of the Moesian Platform; unpubl. report). 1969 a. Arch. I.G.G., Bucharest. 9 A. Drăgănescu. Studiul forajelor adinei Cireșu, Smirna și Zăvoaia din plat- forma moesică (The Study of the Deep Drillings of Cireșu, Smirna and Zăvoaia in the Moesian Platform; unpubl. rep.). 1969 b. Arch. I.G.G., Bucharest. 10 Op. cit. 4. ' t Institutul Geologic al României igr/ 7 (LOWER CRETACEOUS CARBONATE AMD CARBaNATIE-EVAPORITE SEDIMENTATION H Although the petrologie material examined was quantitatively not rich, the total number of the cores extracted from the Neocomian inter- vals reaching only a few tensu, the results provided many interesting and conclusive data as regards the manner of development of the Neo- comian sedimentation in the east-Wallachian sector. In the Neocomian section of the east-Wallachian sector, present author distinguishes 4 lithostratigraphic units (from bottom to top) (Fig. 1) : I, the micritic limestone complex; II,the facies-zoned complex; III, the reefal limestone complex; IV, the variegated marly-calcareous complex. The purpose of present paper is to describe only the first three complexes, that is, the Upper TithonianUBerriasian-Valanginian inter- val, which displays an autochthonous sedimentation The variegated marly-calcareous complex, Hauterivian in age, is out of discussion. The considered deposits are highly variable in thickness, decrea- sing radially from about 900 m in Smirna sector to about 100—300 m in Berlescu, Bordeiu Verde, Zăvoaia, Amara, Țăndărei and Gura lalo- miței sectors. Each of the component series (complexes I, II and III) displays variable thickness too. The variations in thickness were caused by temporal and spațial changes in the subsidence intensity as well as by a subsequent, parțial or total, removal of Neocomian upper terms in some areas owing to the erosional stages installed in connexion with the Austroalpine and Early Austrian movements. The diastrophic and sub- sidential aspects in the east-Wallachian sector are discussed in detail by present author in the above-mentioned unpublished reports. Present paper approaches only the aspects of a petrologic-faciologic order. Worth specifying is that the Neocomian sedimentation represents a distinct cycle bounded by two depositional disconformities : the lower disconfor- mity lies at, or slightly below the Jurassic/Cretaceous boundary, under- lined in placed by an erosional gap lying in the Upper Jurassic series; the upper disconformity, which is manifest in the Hauterivian-Aptian range, is partly a depositional gap and partly an erosional one. I. THE MICRITIC LIMESTONE COMPLEX This complex stands for the first term of the Neocomian sedimenta- tion and overlies the erosional-sculptured surface of the Upper Juras- sic reef limestones and dolomites. It was identified in the following sectors : Smirna (about 500 m in thickness), Cireșu (at least 60 m), Zăvoaia (about 300 m), Țăndărei-Gura lalomiței (about 50—100 m) and Berlescu-Bor- deiu Verde (50—200 m) (Fig. 1 and 2). Directly west of all these sec- tors, namely in Amara and Ciochina sectors, the drillings pointed to the lack of this complex (the drillings no. 11 and 12); here the Upper Ju- rassic dolomitized series underlies either the facies-zoned complex (drilling no. 11) or the Hauterivian marly-calcareous complex (drilling 11 The lithologic control between the cored marchs was offered by the electric logs and sieve samples. Institutul Geologic al României (GR 12 A. DRĂGĂNESCU Fig. 3. — Comparison between the present-day carbonate sedimentation on the Great Bahama Bank and the Neocomian sedimentation in the east-Wallachian sector of the Moesian Platform during the depo- sition of II complex. 1. skeletal facies; 2. oOlitic facies; 3. bahainite facies; 4, tidal-flat facies. Institutul Geological României 9 LOWER CRETA CEO US CARBONATE ANO CARBONATE-EViAPORITE SEDIMENTATtON 13 no. 12). This finding claims accepting the existence of a threshold of the Upper Jurassic morphologic surface at the time of the mioritic complex deposition, this threshold bordering the discussed depositional area to the west andSW. The threshold, oriented NW—SE, is thought to have been aligned lengthways the localities of Căldărușanca—Ciochina—Amara —Mărculești. This threshold behaved as an undepositional area, slightly higher elevated relatively to the surrounding bottoms, either in a sub- merged position or in an emerged one as a low, wide ridge. Inasmuch as central and northern Dobrudgea were emerged during the Neocomian time interval, according to the present general opinion, the discussed depositional area appears as a large bay clossed to the west, South and east, and widely opening towards the north. The micritic limestone complex consists mainly of micrites, most of them more or less dolomitic, and subordinately of skeletal, micritic limestones, skeletal, micritic, pelletal limestones, micritic pelletal limesto- nes, and other allochemical varieties in quite minor amounts (nomencla- ture B i s s e 11 and Chilingar, 1967) 12. The micrites are usually homogeneous, seldom grumous, and con- sist of cryptocrystalline calcite particles (less than 4 micra in size). Do- lomite rhombohedra frequently occur within the micrite matrix lending a slighter or a stronger dolomitic character to the limestone. The dolo- mite rhombohedra-bearing micrites represent the commonest petrogra- phictype within complex I (Pl. III, Fig. 1—5 ; Pl. VI, Fig. 1—2 ; Pl. VIII, Fig. 1—2 ; Pl. XIII, Fig. 1 — 4). The dolomite rhombohedra are usually 30—125 micra in size. They occur in variable amounts within micrite, from seattered crystals to compact aggregates. The dolomite crystals are either apparently clear, free from impurities, or turbid, including cal- careous dust dispersed in an approximately even distribution within crystals; a few micrite layers contain rhombohedra displaying only the cores occupied by rhomb-shaped patches of fine-grained lime dust; all these fine calcareous inclusions represent relict micritic material and suggest a replacement origin for the dolomite crystals. The skeletal, micritic limestones are sporadically spread throughout the micritic limestone complex. They are mainly fossiliferous micrites and subsidiary sparse biomicrites (nomenclature F o 1 k, 1962) (PI. I, Fig. 1—2 ; Pl. IV, Fig. 1; Pl. VI, Fig. 3); both of these petrographic types show the skeletal grains floating within micrite matrix. Dolomite rhombohedra occur, in a variable proportion up to 50 volume percent, as seattered crystals or aggregated in irregular-shaped patches (often evolved to very fine spar calcite by dedolomitization). The biogenic material consists of ostracods, echinoderm plates, calcispheres (partly being calcitized radiolarians), fibrospheres (cadosinids and stomiosphae- 12 In order to term the carbonate rock types as suggestive and exact as possible, I used in each situation the most adequate name, able to express at best the main features of the rock; the names proceed chiefly from F o 1 k's (1959, 1962), D unham ’s (1962) or B i s- s e 11 and G h i 1 i n g a r ’s (1967) classifications. Institutul Geological României ICR 14 A. DRĂGĂNESCU 10 rids), calpionelids and Aptychus debris. The ostracods, the calcispheres and the echinoderm ossicles occur over the entire depositional aiea, while the Aptychus debris, the calpionelids and the fibrospheres have been encountered only in the northern part of the studied ai ea, suggesting that the depositional environment gets more pelagic in facies northward (a fact confirming the interpretation on the northward opening of the depositional area). For the entire depositional area, the described skeletal material suggests a sedimentation in a relatively low turbulence (at least at the sediment/water interface) marine environment; the water depth is thought to have varied from several meters in the Southern part up to at most 100 m in the northern part of the depositional area. The pelletal limestone varieties were encountered only in the nort- hern sector, where they occur either as the main constituent of the mioritic complex section in drilling 3 Berlescu or as episodic reccurrences in the dolomitic micrites of the complex I in drilling 1 Bordeiu Verde. As a rule, they are represented by more or less fossiliferous pelmicrites (mi- critic, pelletal limestones, micritic-pelletal limestones, and skeletal, micritic, pelletal limestones in B i s s e 11 and C h i 1 i n g a r’s 1967 nomenclature) consisting subordinately of skeletal grains (fibrospheres, calcispheres, and ostracods) and mainly of pellets of a cryptocrystalline grain type (probably originating from the hardening of some mud-aggre- gates — nomenclature P ur d y, 1963), spheroidal or slightly ovoidal in shape, 130—150 mici a in size and with a homogeneous micritic internai structure, embedded in a grumous micrite matrix; in places, the pellets are directly merged into one another (as small levels and lenses of pel- letal limestones „cemented” by replacive spar calcite; see details in Pl .II, Fig. 4—5). Minor amounts of pellets are bound together in irregular- shaped lumps up to 500 micra in size. Small patches of pelletal-intraclastic limestones (intramicrites and intrasparites) occur within the pelletal limestones, as co-associated micro- facies, where the pellets and the lumps (if present) are accompanied to a variable extent by elongate, angular to moderately rounded, arenite or microrudite in size, intraclasts with an internai micritic structure (micrite containing scattered fibrospheres — Pl. I, Fig. 5—8). Associated to the „intraclastic phenomenon”, the oolitic accretion phenomenon manifested, the end-product of this microfacies type being some micro- lenses of “sparry”, oolitic, intraclastic-pelletal limestones; the oolitic grains vary from superficial ooliths to true ooliths, as nudei serving pellets or finaly arenitic intraclasts (Pl. I, Fig. 6—8). The spar calcite within the above-mentioned „sparry” alloche- mical varieties of limestone although apparently looks like a pore-filling calcite, actually stands for a replacement product formed by a diagenetic sequence involving dolomitization-dedolomitization-aggrading recrystal- lization (see details in the explanation to Pl. I—II). Worth emphasizeing is that this diagenetic sequence stands for a new postdepositional proces- sual line and was noticed by present author in numerous limestone series of different ages; it results in dedolomitic microspar and dedolo- Institutul Geological României \IGRZ 11 LOWER CRETACEOUS CARBONATE ANtD CARBCUNATE-EVAPORITE SEDIMENTATION 15 mitic pseudospar (new terms) which highly mimmic the neomorphic as well as the precipitative (orthospar) calcite varieties (Drăgăn eseu, in preparation)13. Another conclusive example for this new diagenetic sequence, offered by the allochemical limestones of complex I (drilling no. 3 Berlescu), is represented by which seems to be at first sight a- „depositional perturbation facies”, consisting of a gradual scale of petro- graphic terms from „disturbed” pelmicrites with irregular-angular spar calcite eyes („dismicrites”) up to completely “broken” pelmicrites into equidimensional, angular or subangular, arenitic or ruditic in size, „intra- clasts” embedded in spar calcite (“intrasparites”); this gradational suit may be watched in thin-sections along one or two centimeters, and actually it represents the product of the above-mentioned diagenetic sequence, where the dolomitized patches have undergone a dedolomiti- zation (replacement of dolomite by microspar) followed by an aggrading recrystallization of dedolomitic microspar to larger pseudospar (Pl. IT, Fig. 1—3). The mioritic limestones, more or less free from allochems, were also affected in places by the dolomitization-dedolomitization sequence resulting in a microspar varying in participation and distribu- tion from tiny patches irregularly scattered within micrite (leaving the appearence of a clotted texture) to a network enclosing some unaffected areas (pseudointraclasts) (Pl. I, Fig. 1—4). But, as already stated, most of the mioritic limestones have undergone dolomitization only, without to be further submitted to dedolomitization. As regards the micrite in this complex, it occurs as both inde- pendent rock (micrite = calcilutite — mudstone) and matrix in some allo- chemical limestones. It originated from the lithification of a former lime mud; this mud has most probably resulted from physico-chemical precipi- tation processes and seems to represent an ancient equivalent of the recent aragonite muds occuring in the inner, sheltered paits of the Ba- hama Banks, particularly of Great Bahama Bank. On the Bahama plat- forms the aragonite muds form in shallow, quiet, warm water environ- ments by Chemical precipitation, without any biogenic influence, on account of the slight increase in the seawater salinity over the banks in response to the restrictions in water circulation and to the strong eva- poration caused by the warm and dry climate (C 1 o u d, 1962). This slightly increased salinity is enough to bring the seawater at the supersa- turation level, with respect to its calcium carbonate content, required by CaCO3 precipitation in the mineralogic form allowed by the seawater Mg/Ca ratio ; calcium carbonate separates from the seawater mass as cryp- tocrystalline aragonite needles only (C 1 o u d, 1962 ; T a f t, 1967 ; W i n- 1 a n d, 1969; etc.). Inasmuch as the climatic conditions prevailing over the Moesian Platform during the Neocomian time were of a tropical- 13 A. Drăgănescu. Dolomitization-dedoiomitization-aggrading Recrystalliza- tion — a New Postdepositional Processual Sequence in the Shallow-water Marine Limestones and its Petrological Implications (in preparation). Institutul Geologic al României 16 A. ©RAGANSSCU 12 subtropical type (as revealed by the reefal faunas occurring on the Romanian territory in the Upper Jurassic-Aptian strat igraphical range) such depositional processes were quite possible. Furthermore, the semi- closed and epicontinental character of the depositional area discussed in present paper suggests a total similitude with regard to the depositional environment, conditions and processes and consequently to the mineralogic consistence of resultant sediments, between most of the discussed area and the inner parts of the Bahama Banks. Thus the mioritic limestones of complex I are thought to represent ancient aragonite muds formed in a quiet, relatively shallow water environment and express a typical lime mud facies (sensu P u r d y, 1963). The skeletal material, by its coinposition and distribution, also suggests sheltered depositional condi- tions with basinal influences in the northern part of discussed area. As regards the episodic pelletal facies and its associated microfacies, occuring in the mioritic section of the northern part of the studied area, their depositional conditions seem to have been slightly different from those previously discussed. The tendency of mioritic mud to agglutinate into pelletal grains, the occurrence of more or less washed pelletal and intraclastic episods, and the manifestatien of the oblitic accretion pheno- menon, all these facts suggest a higher energy level for the depositional environment comparatively to the (more or less skeletal) mud facies previously commented. Mineralogically, the deposits of the complex I are thought to have been initially aragonitic in consistence, except for the skeletal grains (mainly calcitic). But as long as the aragonitic sediments are maintained under the seawater influence they preserve their rhombic, metastable mineralogic form; in this state the sediments may undergo dolomiti- zation by penecontemporaneous or early diagenetic (at shallow depths of burial) replacement of aragonite by dolomite (111 i n g et al., 1965 ; Deffeyes et al., 1964, 1965 ; S h i n n et al., 1965 ; Lucia, 1968 ; M u r r a y, 1969; etc.). The dolomitization noted in the limestones of complex I seems, taking into account the large size of the dolomite crys- tals comparing with the extremmely small crystal size of present-day penecontemporaneous-replacement dolomites, to stand for a case of early diagenetic dolomitization brought about probably by a process of seepage refluxion (sensu A d a m s and R h o de s, 1960) completed by a further increase of the Mg/Ca ratio in the seawater-derived, Mg-rich, dolomitizing, interstitial Solutions percolated into the calcareous sedi- ments. Later on, the dolomite was submitted in places to a late diage- netic sequence: dedolomitization-aggrading recrystallization (that is, replacement of dolomite by dedoloinitic microspar and aggradation of this microspar to larger pseudospar). Faciologically, the complex of mioritic limestones expresses a marine sedimentation in a shallow, quiet water environment under a lime mud facies (sensu Purdy, 1963), with reccurrences of episodic pelletal and intraclastic-oblitic facies suggesting a more agitated environment. The last two facies temporary replace in places the lime mud facies in the northern part only of the east-Wallachian sector, in other words exactly v 'A Institutul Geological României XjgrZ 13 LOWER CRETACEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 17 in that part where the depositional area widely opened up being largely linked to the rest of the Neocomian basin. Therefore, the sedimenta- tion took place on an extensive inner platform domain (= inner shelf domain) under a prevalent lagoonal, lime mud facies, with some local tendencies of accumulation under outer platform facies in the northern part of the depositional area. The occurrence of calpionelids and stomioS’ pherids in the northern part of the area suggests some basinal influences in the northern sectors of the carbonate platform; hence, the possibility for the inner platform domain to have been directly linked to the basinal one, the outer platform domain (outer shelf domain) having been slightly manifest only in places at the join of the two extreme domains. II. THE FACIES-ZONED COMPLEX The facies-zoned complex, laid down apparently in depositional conformity with the underlying, lower complex, displays a variable thickness: 100—200 m thick in Țăndărei and Gura lalomiței sectors, about 400 în in Smirna sector, at least 300 m in Amara sector, about 150 m in Cireșii sector, at least 100 m in Zăvoaia sector and 50 — 100 m in Berlescu sector (Fig. 1). The Căldărușanca-Ciochina-Mărculești threshold continues to behave as an undepositional risen area (the Upper Jurassic limestones and dolomites directly underlie the Hauterivian marly-cal- careous complex along this threshold). Unlike the lower complex, present complex exhibits a large petro- logie variety, the sections crossed by the borings pointing to an interes- ting and evident facies zonation (Fig. 2) : laterally interfingering facies zones succeeding as belts that parallel the Căldărușanca—Ciochina — Mărculești threshold, each of them observing a semicircular alignment with the concavity facing NNE. Their drawing relies on the finding that from S and SW towards N and NE the following petrologie assemblages sueceed : evaporites subordinately containing dolomite and micrite inter - calations (Amara sector); evaporites, micrites, dolomites and microco- prolithic-microoncolitic calcarenites (Cireșu and Țăndărei sectors); poorly skeletal micrites and microcoprolithic-lumpal, sometimes oblitic, caî- carenites (Smirna sector); poorly skeletal, lumpal-pelletal calcarenites (Gura lalomiței sector); oblitic calcarenites, bioconstructed and corpus- cular skeletal limestones (Zăvoaia and Berlescu sectors). This succession, displaying a notable gradual scale of substitution of the terms from an assemblage to the next one, argues for distinguishing 3 laterally inter- fingering facies zones, disposed from the “Ciochina” threshold (the margin of the discussed depositional area) towards the interior of the discussed depositional area (that is, towards N and NE) as follows : A) the zone of carbonate-evaporite facies; B) the zone of bahamite facies; C) the zone of skeletal-oblitic facies. From genetic point of view these facies zones are thought to have the following significances : A) The deposits included in the carbonate-evaporite facies zone represent a tidal-flat System being the product of a cyclic sedimentation m Institutul Geological României IGRy 18 A. draganbscu 14 under a dry, warm climate on the Coastal plain extending on the north- eastern flank of the “Ciochina” threshold and submitted to the mean sea-level periodic fluctuation. B) The bulk of the deposits of the bahamite facies zone makes up a carbonate-lagoonal system, resulted from a marine sedimentation on an inner platform domain (sheltered, shallow water environment). C) The deposits of the skeletal-oolitic facies zone make up a reefal system, evolved from a marine sedimentation on an outer platform do- main (agitated, shallow water environment). Therefore, from the emerged “Ciochina” threshold towards NE, that is, towards the off-shore parts of the discussed depositional basin, 3 depositional domains extended : the shore zone was occupied by the tidal-flat domain; this was followed seaward by the protected, inner do- main of the continental shelf; this latter domain was contiguous seaward with the unsheltered, outer domain of the shelf. All these three domains stretched on a shelf whose surface was near the mean sea-level in the south-western (peripheral) parts of the discussed depositional area, and slowly sank towards N and NE, but keeping at very shallow depths (depths more probably in the range of meters than of tens of meters). The disposition of these 3 domains is similar to that noted in the present-day low latitude areas with a marine, shallow water, carbonate sedimentation. This similitude is striking especially when compared with the Andros Platform (Great Bahama Bank), whose facies pattern and asymmetric morphology (the flank west of Andros Island very extensive and exhibiting all of the 3 foregoing sedimentary domains, unlike the flank east of the island much shorter and displaying the reefal facies nearly joined to Andros Island) seem to be reproduced by the present case (Fig. 3). Thus, data provided by drillings point to the fact that direc- tly west of “Ciochina” threshold the stratigraphie interval eorresponding to the facies-zoned complex is occupied by a reefal, skeletal-oolitic facies (the borings of Călărași, Urziceni, etc.). Consequently, a cross section made SSW—NNE through the discussed area shows a carbonate platform with an oblong flank (the north-eastern one) exhibiting the complete carbonate depositional pattern developed on the flank west of Andros Island, and a short flank (the south-western one) confined to a reefal facies only, similarly to the flank west of Andros Island; the equivalent of Andros Island seems to be the “Ciochina” threshold. From another angle, the facies distribution displays typical features of a carbonate platform of a bahamian type, as it was synthetically conceived by Purdy (1963), the bahamite (nomenclature B e a 1 e s, 1958) facies zone representing the sheltered, inner platform facies placed between the two, outer plat- form, skeletal-oolitic facies (to these ones, the tidal-flat facies adding as the product of the interaction between a risen area occuring within the inner platform domain and the cyclic oscillation in the mean sea-level). Further on, the petrologie data which have served as a basis for the afore exposed sedimentological interpretations are presented; the 3 'A Institutul Geological României jgr/ 15 LOWER CRETACEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 19 facies zones will be successively approached in the following order : the carbonate-evaporite facies zone, the bahamite facies zone and the skele- tal-oblitic facies zone. A) The Zone of Carbonate-Evaporite Facies The carbonate-evaporite facies, recorded in Țăndărei, Cireșu and Amara sectors, lies directly east of the undepositional area of the “Cio- china” threshold, parallel and closely joined to it. This facies includes limestones, dolomites and sulphates (mainly of calcium). In Țăndărei sector (drilling no. 10) clayey micrites, microoncolitic- microcoprolithic calcarenites with Favreina salevensis, evaporites and dolomites occur (Pl. VII-XII and XVII-XIX). In Cireșu sector (drilling no. 9) micrites, pelmicrites, microcoproli- thic calcarenites with Favreina salevensis, and evaporites were intersected (Pl. XIII—XVI). The Favreina salevensis-bearing calcareous-evaporite facies of Cireșu was already briefly reported by Patrulius (1964 b) on the occasion of the study undertaken by this author on the Neocomian microcoprolithic limestones containing Favreina salevensis from Atîrnați drilling (the central-Wallachian sector of Moesian Platform) : the mentio- ned author used the association between the coprolith Favreina saleven- sis and evaporites at Cireșu as an argument supporting the interpretation that Favreina salevensis biofacies corresponds to a marine environment with an abnorma!, slightly increased salinity, interpretation initially infered from the lack of typical marine organisms in the section of Atîrnați. In Amara sector (drilling no. 11) a sequence consisting of evaporites with minor amounts of dolomite and micritic limestone was crossed. For present work a petrologie study was accomplished only on the carbonate-evaporite series of Țăndărei and Cireșu sectors, the petrologie material from Amara sector having not been available to the author. 1. In Țăndărei sector, the carbonate-evaporite sequence (crossed within the 526-about 700 m depth interval by the drilling no. 10) was mechanically cored in the depth intervals of 574—575 m, 620—621 m and 634 — 635 m. a) At the depth of 574—575 m, a sequence of greenish, clayey, micri- tic limestones imbued with gypsum occurs; it contains, at several levels, evaporite intercalations as irregular-shaped lenses or nodules consisting of gypsum, anhydrite and celestite. The clayey micrites “invaded” by gypsum (Pl. VIII, Fig. 3—4) consist of cryptocrystalline calcite particles (in present case less than 3 micra in size) and clayey material, and contain rare ostracods. Gypsum occurs within host clayey micrite as colourless or whitish, flattened crys- tals varying from less than 1 mm to 1 cm in length; the crystals occur either solitary or twinned or aggregated in small bodies whose angular outlines are given by crystallographic faces (crystallotopic structure of % Institutul Geologic al României IGR/ 20 A. DRĂGĂNESCU 16 Maiklem et al., 1969 u). The gypsum crystals appear either pure, clear, or impurified with calcareous dust as disseminations. Some parts of the host micrite appear “broken up”, “expanded”, with the constitu- tive micritic particles slightly distanced from one another and poikili- tically entrapped within gypsum cement optically representing single large crystals. Other parts of the micrite are obviously mechanically disso- ciated by the growth of gypsum crystals. In others, the micrite is comple- tely invaded with gypsum crystals either disposed in random orientation or merged into irregular bodies ; these networks and aggregates of gypsum crystals completely dismember the host micrite that appears partly enclosed as calcareous pieces or particles within large gypsum crystals and partly entrapped as calcareous tails and pieces (calcareous streaks in nomenclature of M a i k 1 e m et al., 1969) betweenmerged gypsum crys- tals. AII these observations suggest that: the clayey micrite was settled as clayey calcareous (probably aragonitic) mud containing scattered ostra- cods ; the gypsum formation took place later, subsequently to the clayey lime mud deposition; the gypsum was laid down from interstitial super- concentrated Solutions, within the still soft, clayey calcareous mud, either by carbonate replacement or, mosț frequently, by interstitial precipita- tion accompanied by mechanical displacement of the host mud, the gyp- sum crystals having grown by entrapping or by pushing aside the soft clayey calcareous mud. Therefore, two depositional generations may be distinguished wit- hin a calcareous layer, belonging to two successive stages and representing two lithogenetic units : the calcareous unit (unit a), standing for the pro- duct of the first depositional stage, and the gypsum unit (unit Ș), repre- senting the product of the second stage. Unit p is developed within unit a. The lensoid or nodular evaporite intercalations, up to several cm thick, display either a nodular-mosaic to a mosaic internai structure or a massive one (nomenclature Maiklem et al., 1969), and consist of gypsum, anhydrite and, subordinately, celestite. The gypsum occurs as flattened crystals 50—500 micra on the long side (therefore, much smaller than the gypsum crystals imbueing the micrites), aggregated into masses with a blockv texture (nomenclature Maiklem et al., 1969). The anhydrite masses occur as irregular-shaped zones within the gypsum masses. Under the microscope they display a blocky-fibrous texture (new term) consisting of a mosaic of approximately rectangular or parallelogramic aggregates 50—500 micra long associated in a blocky texture, each aggregate exhibiting a parallel-fibrous internai texture made up of parallel lath-shaped crystals disposed perpendicularly to the long side of the aggregate. The anhydrite lath-shaped crystals are 30—100 micra in length by about 3—5 micra in diameter (Pl. VIII, Fig. 5). Between the anhydrite masses and the gypsum ones there are mineralo- 14 In present paper the fabric nomenclature for anhydrite masses of Maiklem et al. (1969) was successfully used for gypsum masses too. Institutul Geological României 16 R 7 17 LOWER CRETACEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 21 gically mixed zones consisting of both gypsum and anhydrite. Undei’ the microscope, these zones reveal interesting and eloquent facts concerning the anhydrite genesis : the gypsum crystals, approximately rectangular or parallelogramic in shape, are aggregated in a blocky texture and con- tain inside them variable amounts of lath-shaped anhydrite crystals; the anhydrite prisms accommodated within a gypsum crystal appear developed with their long axes approximately perpendicular to the large faces (010) of the host flattened gypsum ciystal (that is perpendicular to the long sides of the gypsum crystal in thin-section); the anhydrite prisms within a gypsum crystal are neither exactly parallel to one another nor exactly perpendicular to the f010) faces of the gypsum crystal; a gradual scale of terms was noticed from gypsum crystals bearing a few anhydrite prisms through gypsum crystals “invaded” by anhydrite prisms up to anhydrite aggregates (with parallel-fibrous internai texture) similar in shape and size to the gypsum crystals. These observations support firstly that the gypsum-anhydrite association does not represent a syn- genetic paragenesis (depositional concrescence) but an alteration assem- blage caused by the replacement of gypsum by anhydrite, and secondly that the rectangular or parallelogramic aggregates making up the anhy- drite masses represent anhydrite-after-gypsum pseudomorphs, each aggre- gate of fibrous anhydrite crystals corresponding to a single inițial gypsum crystal. The turning of gypsum crystals into pseudomoiphic anhydrite aggregates was already noticed or assumed in both present-day marginal- marine carbonate-evaporite deposits (B u 11 e r, 1969; K i n s m a n, 1969; K e n d a 11, S k i p w i t h, 1969 ; etc.) and ancient evaporite-bearing rocks of a different age (S te w a r t, 1953 ; Hen d er son, 1959 ; K er r, Thomson, 1963 ; M u r r a y, 1964 ; etc.). The present material supplies convincing arguments for the anhydrite-after-gypsum pseudomorphic replacement in ancient rocks and the same time, it allowed establishing the exact manner which the replacement proceeded by to yield pseudo- morphs of a textural type representing, to the author‘s knowledge, a new type of internai arrangement of the replacive anhydrite prisms wit- hin the replaced host gypsum crystal. The gypsum masses locally contain abundant colourless or light-blue bipyramidate, short celestite prisms. The celestite prisms are 60—150 micra long by 30—60 micra in diameter, and appear developed in or between the gypsum crystals, suggesting a genesis quite similar to the anhydrite, i.e. by gypsum replacement (Pl. VIII, Fig. 6 — 7). Therefore, the lensoid or nodular evaporite intercalations consist of primary gypsum, of a direct precipitation, and secondary anhydrite and celestite, proceeding from gypsum replacement, all these evaporites suggesting a deposition from hyperconcentrated Solutions. The complex evaporite intercalations of each lithologic level make up an apart litho- genetic unit, formed during a stage subsequent to those responsible for the formation of the gypsmn-bearing clayey calcareous mud accommoda- ting the respective level. The occurrence of severa! levels bearing complex evaporite inter- calations (gypsum-anhydrite-celestite nodules or lenses) within the cal- Institutul Geologic al României \lGRy 22 A. DRĂGĂNESCU 18 careous-clayey-gypsum section suggests a cyclic sedimentat ion expressed by a succession of cyclothems. A complete cyclothem is assumed to be represented by a calcareous-clayey-gypsum layer enclosed between the tops of two successive levels bearing complex evaporite intercalations; consequently, a cyclothem would consist of a calcareous-clayey-gypsum layer displaying at the top of a level accommodating complex evaporite intercalations; a such cyclothem appears consisting of 3 lithogenetic units, corresponding to 3 successive depositional stages (this genetic interpretat ion keeps valid even if the accolades combining the lithologic elements into cyclothems within the discussed mechanical core are other- wise drawn) : a) the (more or less clayey) micrite unit; Ș) the gypsum unit, developed within unit a; y) the gypso-anhydrite unit, deposited within and/or over unit a. Within a cyclothem, a consistent upward increase in the concentra- tion of the depositional Solutions (that is, an increase in the restriction of the depositional conditions) is markedly evident. The interpretation of the foregoing data themselves as well as the comparison with the present-day marginal-marine carbonate-evaporite sediments of Persian Gulf, Madre Lagoon (Texas), Baja California (Me- xico), Bonaire Island (Netherlands Antilles) (C u r t i s et al., 1963 ; Shearman, 1963; Evans, Shearman, 1964; 111 ing et al., 1965 ; B u t le r, 1964, 1969 ; K i n s m a n, 1969 ; K e n d a 11, S k i p - w i t h, 1969 ; M a s s o n, 1955 ; F i s k, 1959 ; P h 1 e g e r, 1969 ; L u c i a, 1968) lead to the conclusion that the formation of cyclothems may be explained by two ways : either by a permanent supratidal sedimentation with periodieal influxes of clayey-calcareous mud from the subtidal mari- ne shallows owing to the flooding of the supratidal surfaces by seawater during the highest spring tides or storms, thus the requirement of the cyclic fluctuation in the salinity of depositing Solutions being satisfied (every seawater influx meaning a dilution and a supply of lime mud, and the time interval elapsed between two consecutive floodings correspon- ding to a stage of drastic increase in salinity and evaporite deposition), or by a cyclic sedimentation of a tidal-flat type due to periodic oscillation in the mean sea-level. I accepted the latter genetic pattern as the inost natural and plausible in present case. In accordance with the embraced genetic model, the lithogenetic units of a cyclothem fonned as follows : a. The deposition of the calcareous unit consisting of lime mud containing rare ostracods and clayey (most probably wind-blown) material, took place in a shallow-subtidal, protected, marine environment with a relatively normal-marine salinity. p. The gypsum unit, precipitated within the soft mud of unit « from superconcentrated interstitial Solutions, suggests intertidal genetic conditions, possibly upper intertidal. This genetic assigning relies on several facts. Firstly, in the present-day marginal-marine carbonate-evaporite sedimentation, gypsum precipitation as the first evaporite terni from interstitial supersaline marine-derived Solutions starts in the upper inter- tidal zones, going on upward, that is landward. Secondly, both the existence of a calcareous imit previously formed and that of a complex evaporite JA Institutul Geological României igr/ 19 LOWER CRETA CEO US CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 23 unit laid down subsequently and under more restrictive saline eonditions, restrict the genetic environment to (upper) intertidal eonditions. Thirdly, the large size of gypsum crystals supports salinities less drastic than those specific to a supratidal environment, pleading for an intertidal origin too. y. The gypso-anhydrite (complex evaporite) unit represents a ty- pical supratidal product, laid down from seawater-derived hyperconcen- trated brines accumulated over or within the clayey calcareous sediments of unit a (brought onto a supratidal position). The much more drastic values in concentration of depositing Solutions under supratidal condi- tions caused the formation of complex evaporites, where, besides gypsum, the anhydrite and celestite occur. The inițial mineral, directiv precipi- tated from the hyperconcentrated Solutions, was gypsum, which, owing to the high values of solution superconcentration, formed as tiny crystals, much smaller than those of the unit The anhydrite and celestite for- med at the expense (by penecontemporaneous replacement) of gypsum. The anhydrite formation by gypsum replacement, as the genetic manner invoked in present case, represents a process ascertained on a large scale in the recent carbonate-evaporite sediments of the supratidal marginal- marine areas. The celestite formation relates, in the present-day carbonate- evaporite marginal-marine sedimentation around the Persian Gulf (Evans, S h e a r m a n, 1964 ; K i n s m a n, 1969), to the apparition within the supratidal carbonate-evaporite sediments of some seawater-derived pore- filling brines strongly enriched in strontium; this enrichement is related to some processes such as replacement of aragonite (7 000—9 000 ppm Sr) by dolomite (600 — 700 ppm Sr) or gypsum, and inversion of aragonite to calcite (less than 1 000 ppm Sr). The considerable amounts of stron- tium released into the hypersaline interstitial fluid by these processes, in the presence of SOf ions, generate celestite, either by direct precipi- tation from the solution or by replacement of previously formed gypsum ; the gypsum substitution by celestite is favoured by the lower value of the celestite solubility product as against that of gypsum. In the present case the oceurrence of the celestite as prisms disseminated within gypsum masses suggests a replacement process of gypsum by celestite under su- pratidal eonditions, on account of the reaction of gypsum with seawater- derived hyperconcentrated and strontium-enriched interstitial Solutions (enrichment probably resulted in the present case from replacement of aragonite of the host calcareous sediments by dolomite and/or gypsum, processes quite liable to have occurred taking into account the general depositional context). b) At the depth of 620—621 m in Țăndărei sector, a sequence of thick (1—5 dm) and thin (0.2—1 dm) gypsum beds spaced by interbedded limes- tone beds 0.1—1.5 dm thick invaded by gypsum was transected. The thick gypsum beds (1—5 dm thick) (Pl. VIII, Fig. 8—9; Pl. XVII, Fig. 4—6) consist of gypsum masses of ten associated with or em- bedded in greenish clay (the volumetric participation of the clayey material is usually highly subordinated to that of the evaporites). These gypsum U; Institutul Geologic al României igr/ 24 A. drăgănescu 20 beds display several structures (nomenclature M a i k 1 e m et al., 1969): massive structure, mosaic structure, nodular-mosaic structure and nodular structure. While the massive structure is nonnodular and free from clayey material, the last 3 structures belong to the “nodular” type and consist of gypsum nodules up to a few cm in size and clayey material filling the internodular spaces (these 3 “nodular” structures are defined in terms of the spacing of gypsum nodules within clayey mud). Texturally, these gypsum masses consist of flattened, small crystals 100—300 micra on the long side by 40—80 micra in thickness, aggregated in blocky, felted or aligned-felted textures (as they appear under the microscope) (nomen- clature Mai klem et al., 1969). These thick gypsum beds are analo- gous to the gypso-anhydrite levels of the previously described core, and suggest deposition from seawater derived superconcentrated Solutions on the surface of a supratidal area; the clayey material was probably derived from an eolian or coluvial redistribution of some possible residual clayey deposits born on the threshold of Căldărușanca-Ciochina-Mărculești. The masses of nodular, nodular-mosaic, or mosaic gypsum (Pl. XVII, Fig. 4—5) seem to have formed by precipitation as irregular-shaped no- dules within the clay mud, roughly simultaneously to the deposition of this latter one; growing, the nodules reached finally different degrees of spacing or merging. The masses of massive gypsum (Pl. XVII, Fig. 6) suggest to have been laid down on the supratidal surfaces where or when- ever the clay influxes were missing; consequently, they formed as pure evaporite soft sediments set down on the depositional surface and net as hard bodies grown within a sedimentary framework (clay muds) as is the case of the “nodular” types. The thin gypsum beds (2—10 cm thick) (Pl. XVII, Fig. 1—2 ; Pl. XVIII, Fig. 4 — 7) are free from clayey material, display only nodular or nodular-mosaic structures and contain, between the gypsum nodules, calcareous fragments (sensu Maiklem et al., 1969) of the same petro- graphic type with the supra- and subjacent calcareous beds ; the gypsum crystals are small and clear, devoid of calcareous material. These observa- tions suggest that these thin gypsum beds (displaying “nodular” structu- res, lacking clay material and containing calcareous fragments) have formed under supratidal conditions similar to the thick gypsum beds, but unlike these latter ones they were born within previously formed quasiconsolidated calcareous sediments and not above them (as is the case of the thick gypsum beds that lack calcareous fragments, containing clay material in the “nodular” varieties instead). Accordingly, the thin gyp- sum beds represent intercalations within a limestone layer, even though now they appear as evaporite beds developed between limestone beds. Therefore, two or three limestone beds (0.1—1.5 dm thick) separated from one another by thin nodular nodular-mosaic gypsum beds actually (genetically) represent a single calcareous layer, subsequently dissociated by growth of supratidal thin evaporite beds inside it. The limestone beds (subsequently invaded by gypsum of another generation than the foregoing gypsum beds) (Pl. IX—XII; Pl. XVII, Fig. 1—3 ; Pl. XVIII) are represented by calcarenites consisting of two. A Institutul Geological României JGRZ 21 LOWER CRETACEOUS CAIRBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 25 types of allochems : microoncolites and fecal pellets (microcoprolithes). These calcareous grains contribute in variable proportions to the limestone bulk, leading to different petrographic rock types : pelletal calcarenites, pelletal microoncolitic calcarenites and microoncolitic calcarenites. Both of these grain types, initially of an aragonitic consistence (comparing to the similar recent products), display a micritic internai structure 1—2 micra in crystal size ; some grains show the constituent micrite partly or totally aggraded to a fine microspar (5 — 6 micia in crystal size). The microoncolites (Pl. IX), thought as algal products of schyzo- phycean (blue-green) algae, appear either monoenveloped or polienvelo- ped, with the nudei, when preserved, represented by approximately spheroidal pellets. The microoncolites are 150—400 micra in diameter, usually lying in the 300—400 micra size range. The concentric micrite laminae making up the envelopes doubtless stand for algal products. As regards the origin of pelletal nudei, I fed they cannot represent fecal pellets owing to the following reasons : the nudei, more or less spherical, are completely different in shape from the fecal pellet types occurring in the limestone; the oncolite-producing algal activity was concomitant to the production of pellets, inasmuch as the latter do not bear the hallmark of the algal activity, appearing devoid of micritic envelopes or other pe- culiar traces suggestive of an algal intervention. The pelletal nudei pro- bably originated from processes of algal precipitation-agglutination and seem to represent the embryo-colonies of the blue-green algae which subsequentîy yielded the oncolite-type deposition. The nudei may be defined as algal mud-aggregates. The nucleus often is missing, its place being occupied by an area, apparently monocrystalline, of gypsum ; the gypsum deposition have been accomplished by replacement of the nucleus or by infilling of the void resulted from a previous leaching of the nucleus. In many microoncolites, the micrite laminae of the envelopes are distanced from one another on account of the development of concen- tric or wedge-like gypsum strips between them; in a more advanced stage the envelopes appear disrupted, radially cracked, the voids between the resultant fragments being filled up with gypsum ; further on, in extreme cases, the microocolites, completely dissociated, dismembered within a gypsum mass, appear as phantomatic dusty cvasicircular bodies consis- ting of spaced calcareous particles. In all above-described situations, the gypsum areas developed within microoncolites display single optical orientations over large surfaces in thin sections. The fecal pellets (Pl. X and XI) belong to 3 types : a) large, keg-sha- ped fecal pellets, €00—800 micra long by about 300 micra in diameter, exhibiting internai longitudinal tubes and belonging to the species Fa- vreina salevensis (P a r 6 j â s), considered to represent coprolithes of de- capode crustacean (P a r 6 j â s, 1935,1948 ; B r o n i m a n, 1955); b) small ovoidal fecal pellets probably produced by worms (polychaete annelids); c) small, dongate-cylindrical fecal pellets probably standing for dejections of gastropods (the last two fecal pellet types were genetically assigned by comparison with the fecal pellets described in the recent carbonate sedi- 'A Institutul Geologic al României IGR// 26 A. ©RAGANESCU 22 ments of the Great Bahama Bank; K o r n i k e r, P u r d y, 1957 ; 01 o ud, 1962). The binder of the calcarenites is represented by both micrite matrix and spar gypsum cement (instead of spar calcite cement). The micrite matrix fills about 30—40 volume percent of the inter- corpuscular space and display, when unaggraded, a crystallinity equal or slightly larger than that of calcareous grains (1—3 micra). Much of the micrite matrix as well as some of the allochems are evolved (Pl. XII) to a fine microspar (5—6 micra in crystal size). A short parenthesis is required for discussing briefly this microspar, which stands for a worth analysing case as it might contribute, by its particular features, to a better understanding of both the manner and the moment of develop- ment of one of most important and still rather obscure processes: the mi- crite-to-microspar neomorphism. Present microspar patches do not stand for a depositional material but represent the product of a postdepositio- nal process, because they occur developed within both micrite matrix and calcareous grains, often transecting the depositional fabric, i.e. lying at the same time on several close grains or on grains and the matrix between them; the preferentially replaced material seems to have been the micrite matrix. On the other hand, the above mentioned gypsum ce- ment has obviously formed subsequently to the enlargement of the mi- crite fabrics to microspar, because now the sulfate cement dissociates at different degrees the microspar patches from pieces with torn outlines to crystal-by-crystal dismeinbrations with the tiny microspar crystals floating within gypsum cement, this latter often consisting of a single large crystal. Accordingly, at least the recrystallization (without inversion of aragonite to calcite) of the micrite particles to microspar crystals pro- ceeded before the sediment cementation by gypsum has taken place, that is certainly before the calcareous sediment be taken out of the seawater influence. But as long as the calcareous sediment was kept under seawa- ter influence, it preserved its aragonitic consistence and soft state. There- fore, the microspar resulted from an extreinely early (penecontempora- neous?) aggrading recrystallization of the cryptocrystalline aragonite particles composing the calcareous mud and grains. This process must logically resulted in a soft, aragonitic microspar. Probably this early aggra- ding recrystallization in soft, aragonitic state was followed much later, during late diagenetic stages, by the aragonite-to-calcite inversion. Con- sequently, this microspar raises several problems difficult to explain such as : the aragonite micrite-to-aragonite microspar recrystallization in soft state and within a soft sediment kept under the seawater influence; the aragonite-to-calcite inversion in isolated microspar crystals already entra- pped within crystalline media such as the large gypsum crystals in present case (Pl. XII). Corning back to the micrite matrix, this one occurs in uneven dis- tribution within a limestone bed (Pl. XVII, Fig. 1), resulting in an irre- gular alternation of calcarenites (grainstones), devoid of micrite matrix, and lutaccous calcarenites (packstones and wackstones), displaying the intercorpuscular spaces filled up with micrite. The micrite matrix shows Institutul Geological României IGR 23 lower cretaceous carbonate AND CARBONATE-EVAPORITE SEDIMENTATION 27 no preferențial association to one or other of the two calcareous grain types — the pellets or the microoncolites. The vertical variation in the micrite matrix participation seems to mirror rather the variation in the pelleting rate of the mud by the pellet-makers and the variation in the supersaturation level of the seawater with respect to its CaCO3 content, than the variation in the energy level of the depositional environment. The micrite matrix is analogous to the marine aragonite muds forming now, mainly by physico-chemical precipitation, in protected shallow water environment (the carbonate-lagoonal environments in Bahamas, Persian Gulf, etc.). Some calcarenite levels contain large, elongate and flattened intra- clasts (1—2 cm long by 3—5 mm thick) consisting of micrite bearing scattered fecal pellets and microoncolites, therefore displaying features characteristic of flat-pebbles (Pl. XVIII, Fig. 1—3). They probably re- sulted from the penecontemporaneous reworking of some of the calcareous sediments that, accumulated on the intertidal flats, have undergone a slight consolidation by compaction and, further, by deshydration, have broken down into flattened pieces ; the merely semiindurated state of the pebbles at the moment of redeposition is demonstrated by the obser- vation that the calcareous grains of the host calcarenite have imprinted themselves on the pebbles surface, slightly penetrating them. The core from the depth of 620—621 ni shows also, at the bottom of a limestone bed (Pl. XVII, Fig. 1; Pl. XVIII, Fig. 3—6), theoccurrence of a level 2—3 cm thick consisting of lutaceous calcarenites displaying a slightly waved, laminar structure with thin, elongate laminoid fenestrae developed in places between the laminae (laminoid fenestral fabric, type A? ; T e bb u t et al., 1965); each of the laminae is made up of the same, above-described fecal pellets and microoncolites entrapped within a dense (when unaggraded) micrite matrix. This level, displaying features of an algal stromatolite, points to the existence, in places, within the sedimen- tary succession, of the deposit usually typical of the tidal-flat domain namely the stromatolitic algal mats. The laminoid fenestrae are disposed almost horizontally or slightly waved, upward converging only in the small protuberances of the algal crust (Pl. XVII, Fig. 1 and Pl. XVIII, Fig. 3, just below the calcarenite/stromatolite contact). The limestone beds express a carbonate-lagoonal sedimentation of a pellet mud facies on a sheltered, inner platform domain in shallow sub- tidal and lower intertidal environments with salinities slightly exceeding the normal marine one (by comparison with the present-day depositional areas displaying similar sediments ; 111 i n g, 1954 ; O 1 o u d, 1962 ; P u r d y, 1963 ; 111 i n g et al., 1965 ; K e n d a 11, Skipwit h,1969 ; etc.). Most of the binder in the limestone beds (about 60 — 70 volume percent of the intercorpusclar space) is represented by a sparry gypsum cement (Pl. IX—XI). This gypsum, developed inside (and not between) the calcarenitic beds, occurs as cement, small lenses and thin bands, and consists of flattened, large gypsum crystals (0.1—1 cm on the long •A Institutul Geological României igr/ 28 A. DRĂGĂNESCU 24 side) which appear juxtaposited, approxiinately parallel to each other, consequently exhibiting approximately the sameoptical orientation (under the microscope). The large size as well as the approximately single optica! orientation of the gypsum crystals account for the behaviour of the gypsum cements, lenses and bands as monocrystal on large surfaces in thin sections. In accordance with the microscopic evidence, the development of gypsum within the host calcarenite took place as follows : gypsum passive preci- pitation as spar cement of a single optical orientation within available intercorpusclar spaces, between the oncolite laminae, into the molds left by leaching of oncolite nudei and into the empty internai tubes of the Favreina salevensis fecal pellets; displacive and/or replacive further growth of gypsum crystals and/or patehes at digfferent intensities resul- ting in local consumption of calcareous grains to different extents, deta- chment of the calcareous grains from one another, dissociation of the oncolites or pellets and/or replacement of some oncolite nudei or envelopes by gypsum; stil further, local growth of gypsum patehes yielding com- pact bodies of gypsum as small lenses and/or thin bands both of them less than 1 cm thick and fibrous in texture, consisting of juxtaposited flattened crystals of the same optical orientation and identical to that of gypsum crystals belonging to the interstitial cement. These small compact bodies of gypsum display a streaky massive structure (nomen- clature Maiklem et al., 1969), containing disseminations, patehes and transversal bridges of mioritic or corpusclar calcareous material (more or less dismembered into the constitutive micrite particles) (Pl. XIII, Fig. 1; Pl. XVIII, Fig. 1); the gypsum crystals are not clear, but include torn calcareous material (Pl. IX, Fig. 6—7); the gypsum body/host limestone boundary is not as Sharp as is the case of the already-descri- bed thin gypsum beds with nodular or nodular-mosaic structures ; in the case of present small bodies of gypsum with massive structure the passage from host limestone to gypsum body is gradual, the limestone undergoing a gradual disintegration from a limestone with gypsum cement up to gypsum body enclosing calcareous material floating within or bet- Aveen the gypsum crystals. Therefore, this generation of gypsum formed within unconsolidated calcarenitic sediment, evolving from the cementa- tion of host sediment to the strong dissociation of the latter by a local excessive growth of gypsum patehes to form massive structures of small gypsum bodies; it suggets, considering its large crystal-size, the soft state of the host sediment, as well as the data reported on present-day marginal- marine sedimentation, a deposition under upper intertidal conditions from seawater-derived brines. A second gypsum generation noticed within the calcarenitic beds and Crossing the above-described first gypsum generation is represented by quasivertical gypsum veinlets (0.1 — 1 cm thick) of a fibrous structure, consisting of crystals disposed perpendicular to the veinlet walls (Pl. XVII, Fig. 3). The gypsum crystals are devoid of calcareous impurities. In places angular fragments of limestone are enclosed. These veinlets seem to have formed by the infilling of some dessication cracks(or other types of cracks) born in the Consolidated gypso-calcareous sediment duringits exposing JA Institutul Geological României igr/ 25 lower cretaoeous carbonate and carbonate-evaporite sedimentation 29 to subaerial conditions on supratidal areas. The veinlets may affect one ■or more calcar enitic beds (and the interstratified gypsum beds). Concluding on the 620—621 m depth interval in Țăndărei sector, worth underlining is the cyclic pattern of the sedimentation, suggesting a deposition of a tidal-flat type. A complete cyclothem seems including 3 lithogenetic units : a) the calcareous unit; 0) the early gypsum unit; y) the late gypsum unit. The whole above-discussion suggests the follo- wing genetic pattern for the 3 units : a. The calcareous unit represents the shallow subtidal-lower inter- tidal unit, suggesting a calcareous sedimentation of a protected, inner shelf type in a pellet mud facies with local formation of flat-pebbles and algal stromatolites on the intertidal flats. 0. The early gypsum unit represents the upper intertidal unit, including the first gypsum generation (deposited inside the still unconso- lidated unit a, that is, the gypsum cement and the small gypsum bodies of a streaky massive structure developed within the calcarenitic beds. y. The late gypsum unit is the equivalent of the gypso-anhydrite unit described in the cyclothem type section of the previous core, repre- sents the supratidal unit and consists of the thick gypsum beds (accu- mulated over the unit a, the thin gypsum beds of a mosaic or nodular- mosaic structure (developed inside unit a, quasiconsolidated) and, if cor- rectly interpreted, the gypsum veinlets. The supratidal unit clearly prevails over the other units within the lithologic section of the core. c) At the depth of 634—635 m in Țăndărei sector, the drilling no. 10 intercepted dolomites only (idiotopic mosaic texture and 40 — 90 micra in crystal-size), displaying a laminar structure consisting of irregularly waved laminae separated from each other by rows of elongate laminoid fenestrae (laminoid fenestral fabric = LFF, type A; T eb b u tt et al., 1965) (Pl. XI, Fig. 8; Pl. XIX). The colour of the laminae varies from yelow to blackish green, the dark tinges being due to a blackish matter, thought to be of an organic nature, finely disseminated within the dolomite crystals. The darker laminae (corresponding to those consisting of organic matter-rich dolomite rhombohedra) exhibit a finer crystal-size than the light coloured laminae. Therefore, the dolomites display features of an algal stromatolitic deposit, formed during an intertidal stage and dolomi- tized during the next, supratidal stage. The petrographic arguments for an early dolomitization are: the preservation of the depositional fabrics (LFF, A); the presence of the organic matter and its uneven distribution from a lamina to the other; the reverse dependance of the dolomite crystal- size upon its content in organic matter. The causes responsible for the supratidal penecontemporaneous dolomitization in Țăndărei sector are, I think, those generally involved in such situations (111 i n g et al., 1965 ; K i n s m a n , 1969; etc.): evaporative superconcentration of the interstitial seawater-derived solution, implicitely bringing about a strong increase in the absolute eoncentration in magnesium ions ; the impoverish- ment of interstitial fluid in calcium ions, therefore the increase in Mg/Ca Institutul Geological României IGR/ 30 A. DRĂGĂNESCU 26 ratio of the pore waters, on account of aragonite and gypsum precipit ation ; the propitious mineralogic constitution of the calcareous sediments (ara- gonitic alone) in Țăndărei sector, the aragonite exhibiting a remarkable afinity to dolomitization, as the present-day littoral areas with marine carbonate-evaporite sedimentation argue. But, inasmuch as, on the one hand, the modern penecontemporaneous dolomitization always yields extremely fine dolomite and, on the other hand, the discussed core shows- both well-preserved laminoid fenestral fabrics and a reverse correlation between the crystal-size and the amount of organic matter accommodated within the crystals, it is to conclude that the dolomitization undei’ discussion proceeded by two steps : the first step, previously discussed and represented by penecontemporaneous supratidal dolomitization, gave rise to an extre- mely fine dolomite preserving the depositional fabrics and largely retai- ning the inițial, algal, organic matter; later, during the second step (pro- bably early diagenetic) this dolomicrite undeiwent an aggrading recrystal- lization, partly inhibited in places by the presence of the organic matter, evolving to the present 40 — 90 micra crystal-sized dolomite. This core has a double importance. On the one hand, it confirms the occurrence of the deposit indicative for the intertidal areas, namely the stromatolitic algal mats, in Țăndărei sector, supporting the carbonate- evaporite sequence in this sector as a tidal-flat deposit. On the other hand, this core directly demonstrated that during the supratidal stages, besides and in close relation to the other main processes as gypsum preci- pitation, anhydrite and celestite formation, the process of penecontem- poraneous dolomitization of the shallow subtidal-lower intertidal calca- reous deposits brought onto a supratidal position was manifest. This. process intensely takes place today on the western coast of Quatar Penin- sula (111 i n g et al., 1965), where the lagoonal aragonitic pelletal muds and the intertidal algal stromatolitic deposits, brought onto supratidal position on the Coastal flats, react with the interstitial seawater-derived magnesium-rich brines, getting gradually replaced by dolomite land- ward. The electric log and sieve samples (chips) certify that the same carbonate-evaporite lithology maintains over the entire section of the facies-zoned complex in Țăndărei sector. Synthesizing all the core data, an ideal complete cyclothem in Țăndărei sector appears to Consist of: a. calcareous, shallow subtidal — lower intertidal unit; 9. gypsum, upper intertidal unit; y. complex evaporite-dolomite, supratidal unit. Inasmuch as both the gypsum unit and a part of the complex dolo- mite-evaporite unit are accommodated inside the calcareous unit, the lithologic column of a complete cyclothem never exhibits a sequence of 3 lithologic levels corresponding to the 3 lithogenetic units, but at the best it consists of two lithologic levels: a lower, calcareous level bearing eva- porites and/or dolomite, and an upper, evaporite level (representing just a part of the third, supratidal unit, namely the supratidal evaporite de- Institutul Geologic al României 27 LOWER CRETIACEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 31 posit accumulated upon the mass of the calcareous unit and not inside it). I estimate the mean thickness of a cyclothem averaging within several dm—1 m range. 2. 1 n C ir e ș u sector, the carbonate-evaporite sequence (traversed by drilling no. 9 within 2 160-about 2 300 m depth interval) was mecanically cored within 2 208—2 209 m and 2 279—2 280.80 m depth intervals. a) At the depth of 2 208—2 209 m, a sequence of micrites (contai- ning pelmicrites and dismicrites as local microfacies) and pelletal (micro- coprolithic) calcarenites occur, accommodating evaporites (gypsum and anhydrite) as both intercalations (lenses and irregular-shaped strips) and disseminations (seattered crystals and microaggregates). The micrites (Pl. XIII, Fig. 5) display a homogeneous or clotted (grumous) texture and contain scarce ostracods and dassycladacean algae (genus Actinoporella; determination Patrulius , 1965). Gypsum occurs disseminated within micrites as tiny crystals (crystallotopic struc- ture of M a i k 1 e m et al., 1969) or irregular-shaped microaggregates consisting of crystals of identical optical orientation (the nodular structura of M a i k 1 e m et al., 1969). The gypsum microaggregates and crystals are developed only between the clots within those microscopic fields dis- playing a clotted texture, suggesting to have formed subsequently to the host micrite by interstitial precipitative ordisplacive growth (accompanied or not by a replacement of calcareous material) within the most porous parts of the lime mud. It is to be assumed that the clotted texture in pre- sent micrites is a primary fabric, derived from a depositional floccular texture, so that the superconcentrated Solutions had to circulate within original lime mud only through the more porous, interfloccular spaces (between the present clots), laying down gypsum within these spaces only. To be more exact, the clotted texture represents, I feel, a depositional fabric subsequently accented by diagenetic neomorphic processes (which led to a larger aggradation of the interfloccular mud in comparison with that of the micrite particles composing the floccules). The subsequent deposition of gypsum as against the time of calcareous sediment formation is also suggested by the observation that the cavities of the alga Acti- noporella are filled with micrite, while the gypsum appears developed only within the skeleton wall of the alga (by replacement, microscale solution- precipitation and/or mechanical displacement ? of the test). Within some clotted-textured areas of the micrites, the clots, more sharply outlined, appear as spheroidal pellets of a mud-aggregate type (nomenclatura Pur dy , 1963, alias friable aggregateof 111 i n g , 1954). The microvolumes made up of such pellets embedded in a micrite matrix displaying a crystallinity slightly larger than that of pellets (but both of them less than 4 micra in crystal size) stand for the mentioned pelmi- crite lenses accommodated within the micritic limestones. The dismicrites (Pl. XIII, Fig. 6) occur also as microlevels or micro- lenses irregularly dispersed within micritic limestones. They consist of dense micrite with vaguely clotted texture and extremely fine crystal- Institutul Geological României 32 A. iDRAGANEISCU 28 linity (features of algal calcilutite), containing ocular or vermicular birds’ eyes. Therefore the dismicrites display a pronounced character of an algal deposit. Some eyes are filled with equant spar calcite cement, others- — with gypsum, "and others — with both of these minerals (it is difficult to establish the genetic sequence; apparently, calcite is the first generation and gypsum — the second, inasmuch as the calcite shows corrosions at the contact with the euhedral gypsum crystals). The pelletal (microcoprolithic) calcarenites (Pl. XIV; XV; XVI, Fig. i—4) consist of the 3 types of fecal pellets already described in Țăn- dărei sector (Favreina salevensis large, keg-shaped fecal pellets with in- ternai longitudinal tubes; small, elongate-cylindrical pellets ascribed to gastropods; and small, ovoidal pellets probably excreted by worms) embedded in a spar calcite usually 8—20 micra in crystal size. The pellets are composed of micrite particles less than 1 micron in size; the outer parts of the pellets often display a coarser micrite texture 2—3 micra in crystal size, which, in contrast with the extremely fine micrite making up the central parts of the pellets, leaves the appearence of microspar rims. These rims probably proceeded from the aggradation of the original extremely fine micrite composing the pellets. As regards the „intercor- pusclar” spar calcite, the petrographic evidence supports a replacement origin by dolomitization developed mainly along the grain boundaries followed by dedolomitization and local aggrading recrystallization ofdedolo mitic microspar to larger pseudospar (the new diagenetic sequence already mentioned in section I; for details see explanations to Pl. XIV-XVI). Other fabrics (contact Solutions, grain deformations) suggest that the original pelletal sands were submitted to rather strong pressures be- fore and during the development of the first step of the above-mentioned diagenetic sequence (the dolomitization) (Pl. XIV—XV). Consequently these pelletal limestones represent grainstones resulted from some pelletal sands assumed to have undergone the following postdepositional proces- ses: early pore-compaction (penecontemporaneous process) accounting for a good merging of the pellets; enlargement of the extremely fine micrite composing the pellets to coarser micrite (penecontemporaneous process developed inside the pellets, from their surface inwards) on account of the interstitial circulation of the seawater-derived Solutions; more or less strong grain-compaction as a result of the continuation of the compaction process (early diagenetic process) illustrated by the mentio- ned compression fabrics, and concurrently to this latter process the net- work-like dolomitization in response to the apparition of some seawater- derived, magnesium-rich Solutions (Solutions also responsible, together with the active externai pressures, for the contact solution phenomena noticed in these limestones); dedolomitization followed by local aggra- ding recrystallization (both of them presumed as late diagenetic processes) probably at the moment when the seawater-derived, magnesium-rich Solutions were replaced by magnesium-poor, connate waters (for arguments and details see explanations to Pl. XIV—XV). The apparently total lack of the micrite matrix in these grainstones may be ascribed" to the high activity of pellet-makers. L- Institutul Geologic al României 29 LOWER CRETACEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 33 AII these calcareous sediments characterize the present-day shallow subtidal and lower intertidal areas of the marginal-marine domains with quiet water, carbonate sedimentation. The limestone beds are crossed by veinlets (Pl. XIII, Fig. 7) composed of calcite, anhydrite and, subordinately, gypsum. The calcite represents the first precipitated generation, appearing largely crystallized, either in a parietal position or desaggregated and enclosed as angular fragments within sulfate mass. The sulfates stand for the second precipitated genera- tion, displaying a felted texture and occupying the central parts of the veinlets. The veinlets are supposed to represent originally hard fillings (as against the soft ones in a subsequently described core) of some dessication cracks formed within the hardened calcareous sediment brought onto a supratidal position. In these cracks the marine-derived superconcentrated Solutions laid down salts in the order of the increase of their solubility: primarily — calcium carbonate, and then — the sul- fates. The anhydrite obviously prevails among the sulfates; it occurs as small lath-shaped crystals in random orientation, lacking any relationship with gypsum and offering no evidence for a genesis by gypsum replace- ment, suggesting a direct precipitation from superconcentrated Solutions. The large participation of the anyhdrite comparatively to gypsum and its primar character (direct precipitation) involve extremely high values (at supergeneous scale) of concentration and temperature (at least35—40°C) for the precipitating solution (as the experimental data and the theore- tical estimates suggest; P o s n j a c , 1938, 1942 ; M a c D o n a 1 d , 1953; Mur ray, 1964). The sulfate intercalations incorporated into the calcareous sequence occur as lenses or irregular-shaped strips some centimeters thick and consist of anhydrite alone, or of anhydrite (at least 80 volume percent) and, subordinately, gypsum. They display either a streaky nodular- mosaic structure, or a massive one, or a contorted bedded one (nomencla- ture M a i k 1 e m et al., 1969); the crystallinity varies from 30 micra to 1—2 mm. The evaporite intercalations of a streaky nodular-mosaic structure contam calcareous (mioritic in consistence) tails and pieces with tom outlines (calcareous streaks) floating between sulfate nodules; the no- dules, more or less merged, are composed of anhydrite and subordinately gypsum, and exhibit a blocky-fibrous texture (idem Pl. VIII, Fig. 5). The anhydrite displays all the features already remarked in Țăndărei sector (core from 574 — 575 m depth) for the type of gypsum replacement: pseudomorphs of anhydrite after gypsum, as rectangular or parallelogramic aggregates (in thin section), each aggregate consisting of parallel lath- shaped small anhydrite prisms ; some gypsum crystals appear only partly replaced by the tiny anhydrite prisms. Therefore these evaporite interca- lations were initially composed of gypsum only, subsequently undergoing anhydritization. They suggest to have formed within unconsolidated or semiconsolidated calcareous sediment by gypsum precipitation (from interstitial supraconcentrated Solutions) as nodules, whose growth led 3 - o. 11 >. Institutul Geologic al României IGR/ 34 !A. DRĂGĂNESCU 30 to their parțial merging and to the dissociation of host sediment to calca- reous streaks. The evaporite intercalations of a massive structure show a lath- shaped texture (nomenclature Maiklem et al., 1969) and consist exclusively of large, lath-shaped anhydrite prisms 1—2 mm long in ran- dom orientation (idem Pl. XVI, Fig. 8). These intercalations are free from calcareous streaks. The anhydrite of these intercalations seems to be a primar sulfate, laid down by direct precipitation from marine-derived hyperconeentrated Solutions of high temperatures (over 34°C after M a c- D on al d , 1953 ; over 42°C after Conley, B u n d y , 1958). The problem concerning the direct precipitation of the anhydrite in the na- tural environment is still an unsolved question, despite the affirmative answer suggested by the positive results of the laboratory experimenta and by the theoretical computations. So, although the physico-chemical requirements are accomplished in some present-day marginal-marine supratidal areas with carbonate-evaporite sedimentation no conclusive evidence was obtained for the direct precipitation of the anhydrite versus its replacement origin at the expense of gypsum. Thus, K i n s m a n (1969) shows that the anhydrite formation on the supratidal flats of the Trucial Coast (Persian Guîf) initially takes place by the relatively pene- contemporaneous replacement of gypsum crystals in the upper 4—5 cm of the sabkha „giving- rise to well-formed pseudomorphs”. But K i n s m a n goes on stating that ,, the pseudomorphs begin to lose their shape with time, and primary diagenetic anhydrite (anhydrite with no gypsum pre- cursor) is precipitated upon and between the older pseudomorphs, produ- cing as an end product the larger ovoid and variously shaped anhydrite nodules” (K i n s m a n , 1969, p. 834). Unlike Kin s m an , B u 11 e r (1969), studying the same supratidal deposits of the Trucial Coast, assu- mes that the anhydrite is entirely of a secondary origin, derived from gypsum, and that “ there is no conclusive evidence to suggest that any anhydrite has formed by direct precipitation from concentrated sea water” (B u 11 er , 1969 p. 81). In the present case the petrologie data support a direct precipitation origin for anhydrite. The evaporite intercalations of a contorted bedded structure exhibit an aligned-felted texture (nomenclature Maiklem et al., 1969) and consist of crystals of anhydrite and subordinately gypsum, 30—300 micra long (Pl. XIII, Fig. 8). These evaporite intercalations are devoid of calcareous streaks too, but contam angular calcareous fragments (sensu Maiklem et al., 1969). The anhydrite within these intercalations suggests, by its micrographic features, both genetic possibilities : it seems to have partly formed by gypsum replacement and partly — by direct precipitation concurrently with gypsum from superconcentrated Solutions. The last two types of evaporite intercalations, both of them lacking calcareous streaks, reveal, by contrast to each other, two different genetic lines. The anhydrite intercalations of a massive structure suggest to have originated from gravitațional accumulation of free crystals in an open space, while the gypso-anhydrite intercalations of a contorted bedded structure seem to have grown by deposition and replacement (gypsum-to- Institutul Geological României 31 LOWER CRETACEOU-S CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 35 anhydrite conversion) as originally hard bodies in a limited, close space (the formation in close space is probably responsible for the distortion of evaporite body structure). AII of these structural-textural, mineralogic and genetic findings guide to the conelusion that the evaporite intercalations devoid of calca- reous streaks originated under supratidal conditions, namely : the massive, exclusively anhydrite intercalations settled, as soft sediments consisting of free crystals, on the floor of some standing bodies of hypersaline water, while the eontorted gypso-anhydrite intercalations were laid down from interstitial Solutions as originally hard, clean lenses or strips within quasi- consolidated host sediment. Thus, the hyperconcentrated Solutions accu- mulated on supratidal surfaces have exclusively precipitated anhydrite, owing to the extremely increased values in their salinity and temperature, while the interstitial Solutions, exhibiting relatively lower concentrations and temperatures, have yielded both gypsum and anhydrite (by both direct precipitation and gypsum-by-anhydrite replacement). The calcareous streaks-bearing gypso-anhydrite intercalations, whose anhydrite appears to be exclusively of a gypsum replacement type, have formed in an original mineralogic configuration somehow different of that one exhibited now (initially consisting only of gypsum) and probably during a stage preceeding the stage of clean evaporite intercalations for- mation (namely concurrently with the deposition of interstitially dissemi- nated gypsum described within micrites and dismicrites). These interca- lations, initially consisting of gypsum only, have subsequently under- gone an anhydritization, probably during the stage of clean evaporite intercalations formation, that is during a supratidal stage. I interpret the stage of formation for the interstitial-disseminated gypsum and the calcareous streaks-bearing evaporite intercalations, both these deposit types accumulated (as already stated) within still unconsolidated calca- reous sediment, as representing an upper intertidal stage. Synthesizing the presented material, the following genetical image concerning the sequence from the 2 208—2 209 m depth may be infered : the sedimentation develops a cyclic pattern of a tidal-flat type ; a complete cyclothem appears to consist of 3 lithogenetic units: a. The calcareous, shallow subtidal-lower intertidal unit deposited in a marine environment of a carbonate-lagoonal facies with relatively normal-marine salinity, includes ostracods-bearing micrites, algal dismic- rites, pelmicrites containing mud-aggregate-like pellets, and fecal pellet sands. (3. The gypsum unit was precipitated under upper intertidal con- ditions from marine-derived superconcentrated interstitial Solutions that imbued the unconsolidated calcareous sediment (= unit a; some processes took place (within the calcareous sediment) : precipitation of calcium carbonate and gypsum as disseminations within the calcareous sediment, and formation of gypsum hard bodies of a streaky nodular-mosaic struc- ture. y. The gypso-anhydrite unit points to its having originated under supratidal conditions, reflecting a drastic increase in concentration values df Institutul Geologic al României \ IGR/ 36 A. 'DRĂGĂNESCU 32 foi* the marine-derived Solutions, for both those interstitial and those accumulated at the surface of the supratidal area; the following processes took place : depositions of anhydrite soft bodies at the surface of the sup- ratidal areas (above the bulk of the calcareous unit), depositions of hard, gypso-anhydrite lenses and strips inside the quasiconsolidated calcareous unit, replacenients of gypsum by anhydrite in both supratidal-deposited gypso-anhydrite bodies and upper-intertidal-formed gypsum bodies, formation of calcite-gypsum-anhydrite veinlets as fillings of some dessi- cation cracks within calcareous sediment. b) At the depth of 2 279—2 280.80 m, micritic limestones occur, containing anhydrite intercalations (each of them some cm thick). The micritic limestones contain variable amounts of ostracods, varying from fossilifereous micrites to biomicrites; angular silty quartz grains (probably wind-blown material) occur in a low proportion giving concentrations at some microlevels (Pl. XVI, Fig. 5). The limestones in- clude micronodules of sulfate and are crossed by sulfate veinlets. The sulfate micronodules (Pl. XVI, Fig. 6) are rectangular or paral- lelogramic in shape, 200 micra to 2 mm long, and consist of anhydrite prisms arranged in felted texture (nomenclature Maiklem et al., 1969); in places the nodules contain small gypsum patches. These micro- nodules strongly suggest inițial large gypsum crystals partly or totally replaced by aggregates of tiny anhydrite prisms, a repetition of the anhy- drite-after-gypsum pseudomorphs already described within previously examined cores (but, unlike these previously described ones displaying an internai parallel-fibrous texture, in the present case the pseudomorphs exhibit an internai felted texture). The veinlets (Pl. XVI, Fig. 7), 50—500 micra wide, consist of lath- shaped crystals 150—300 micra long of anhydrite and, subordinately, gypsum; the veinlets display a relatively aligned felted texture (nomen- clature M a i k 1 e m et al., 1969) oriented either parallel to veinlet walls or perpendicular to them; in each of these two fabric types (types liable to replace one another even within the same veinlet) the sulfate crystals are neither perfectly parallel to one another, nor do they indicate growths from the wall towards the interior of veinlet; they suggest a gravitațional accumulation, initially unconsolidated, of free, anhydrite and gypsum crystals inside some dessication cracks. The sulfate crystals are thought to have precipitated from the superconcentrated Solutions which were infilling the dessication cracks. The precipitated crystals settled down in the dessication cracks in a position depending on the ratio between the crystal size and the crack width : the large crystals, with the long side exceeding the crack width, settled in a relatively parallel position to the crack walls (vertical in the case of flattened gypsum crystals, and indif- ferent within the plan paralleling the crack walls in the case of anhydrite prisms), while the crystals equal to or smaller than the crack width set- tled in a quasihorizontal position (with the long side in an indifferent orien- tation relatively to the walls position). These two accumulative types yielded the two textural types of sulfate veinlet: the first accumulative ir- Institutul Geologic al României 33 LOWER CRETA.CEDUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 37 type gave rise to the felted texture quasiparallel to veinlet walls, while the second accumulative type originated in the felted texture quasiper- pendicular to veinlet walls. After deposition, the evaporite crystals often kept on with growing, as demonstrated by some anhydrite prisms in the perpendicular textura! type which protrude from the veinlet space pene- trating, often rather deep, the walls of host micrite. These observations also suggest that during veinlet formation, the host calcareous sediment was merely semiindurated permitting the in-situ-growing sulfate crystals to penetrate it. The evaporite intercalations accommodated within the mioritic sequence display a bedded massive structure (nomenclature Mai kl e m et al., 1969) and consist of 1—2 mm long anhydrite prisms only, disposed in a lath-shaped texture (nomenclature Maiklem et al., 1969), with the lath-shaped crystals either in random orientation or in a slightly aligned quasihorizontal position (Pl. XVI, Fig. 8). These intercalations are similar to those exclusively anhydritic described in the previous core, and suggest open-space accumulations of originally soft sediment on supra- tidal surfaces by direct precipitation of free anhydrite crystals from stan- ding bodies of marine-derived hypersaline Solutions. Therefore, the 2 279—2 280.80 m depth interval provides a sedimen- tary sequence displaying a cyclic pattern of a tidal-flat type; a complete cyclothem includes : a. The calcareous unit consisting of ostracod-bearing lagoonal micrites, and corresponding to the shallow subtidal (-lower intertidal?) stage; 0. The gypsum unit, represented by large gypsum crystals (sub- sequently evolved to anhydrite) accommodated within the micritic limes- tones of unit a, formed probably under upper intertidal eonditions (upper intertidal stage); y. The gypso-anhydrite unit composed of the anhydrite interca- lations (laid down upon the calcareous unit, and not within it), gypso- anhydrite veinlets and pseudomorphs of anhydrite after intertidal gypsum, and suggesting a supratidal depositional environment (supratidal stage). Concluding on Cireșu sector worth underlining is the strong simili- tude in facies with Țăndărei sector. The sedimentation, cyclically developed under a tidal-flat regime, consists of a sequence of relatively identica! cyclothem s, each of them containing, when complete, three lithogenetic units: a) the calcareous, shallow subtidal-lower intertidal unit; 0) the gypsum, upper intertidal unit; y) the gypso-anhydrite, supratidal unit. The three lithogenetic units of a cyclothem appear strongly inter- penetrated spatially, the calcareous unit accommodating both the gyp- sum unit and a large part of the gypso-anhydrite unit; this fact makes a complete cyclothem to exhibit two lithologic levels only : a lower, cal- careous level containing gypsum disseminations (as single crystals — some of them anhydritized —, or microaggregates) and gypso-anhydrite inter- calations (as lenses and irregular-shaped strips); an upper, exclusively anhydritic level representing a part of the supratidal unit, namely the M Institutul Geological României JGR/ 38 A. DRĂGĂNESCU 34 sulfates (primary anhydrite) settled down upon, not within, the calca- reous unit. 3 . 1 n Amara sector (drilling no. 11), according to the data mentioned in different unpublished reports, the sequence is almost enti- rely made up of anhydrite and gypsum, suggesting that the evaporite stages were plainly dominant; the carbonate material, utterly subordi- nate, consists of micritic limestones and dolomites. Unfortunately, the petrologie material from this sector was not available to the author for study. The foregoing petrologie data suggests the following conclusions concerning the development of the sedimentation in the carbonate-eva- porite facies zone : The sedimentary succession in the carbonate-evaporite facies zone was born by the superposition of a great number of cyclothems; a com- plete cyclothem is lithogenetically made up of a calcareous unit and two evaporite units, one gypsic and another complex evaporitic (anhydrito- gypso-dolomitic). As already mentioned, the conditions and processes pointed out by this cyclothem type suggest a sedimentation of a tidal-flat type. This conclusion is also supported by the regional sedimentary pattern : the areal configuration of this facies zone and the vicinity of an emerged rise. Therefore, the carbonate-evaporite facies zone represents an ancient tidal-flat domain. A complete depositional time-cycle consisted of a shallow subtidal- lower intertidal period corresponding to the stage of the calcareous unit sedimentation, and of an upper intertidal-supratidal period corresponding to the two stages responsible for the deposition of the evaporite units (gypsum unit and anhydrite-gypsum-dolomite unit). During the shallow subtidal-lower intertidal period, calcareous deposits have formed under sheltered, inner platform conditions, belon- ging to lime mud facies, pellet mud facies and skeletal mud facies (sensu I m b r i e , Pur dy, 1962 ; Pur dy, 1963), with local participation of intertidal algal mats. During the upper intertidal-supratidal period the entire area gra- dually became a belt of Coastal salt flats, equivalent to present-day coasta! sabkhas developed around the Persian Gulf. Exactly as on the modern sabkhas, on these fossil sabkhas sedimentation proceeded under the direct influence of marine-derived brines. So, on the one hand, the sea-derived waters imbued the marginal-marine calcareous deposit lifted in upper intertidal or supratidal position, their renewal having probably been accom- plished either by flood recharge (sensu B u 11 e r , 1969) or by landward interstitial capilar migration ; on the other hand, the seawater accumulated on the supratidal surfaces on account of capilar ascension of marine- derived interstitial waters or by direct flooding of these surfaces by sea waters during storms or high spring tides. The interstitial waters are assu- med to have got superconcentrated by the process of capilar concentration (sensu M iii Ier, 1960 ; F r i e d m a n , Sanders, 1967). The ma- rine waters accumulated on the supratidal surfaces were also submitted 'A Institutul Geological României IGR/ 35 lower cretaceous carbonate and carbonate-evaporite SEDIMENTATION 39 to a process of high concentration by strong evaporation. Thus, all the marine waters migrated into upper intertidal and supratidal areas evol- ved to brines, whose concentration was increasing landward, so that in the upper intertidal flat space they were precipitating gypsum, while in the supratidal flat space they were laying down gypsum and anhydrite; in places, simultaheously to these last products the calcareous sediments have undergone dolomitization (not to confuse this penecontemporaneous dolomitization with the early diagenetic dolomitization ascertained in many limestones in present paper and displaying no relation to sabkha cycles); all these processes were sometimes accompanied by celestite formation as a supratidal by-product of the calcium carbonate repla- cement by sulfate (gypsum) and/or dolomite. In the upper intertidal zones the evaporite deposition took place, from the interstitial brines, within the previously formed and still soft calcareous (sometimes more or less cla- yey) sediments. In the supratidal zones, evaporite depositions occurred both within the previously formed and already hardened calcareous (more or less clayey) sediments, and over them (in this latter case the eva- porite deposition being sometimes accompanied by clayey mud accumu- lation); within the calcareous sediments, evaporite and dolomite formation took place from the interstitial brines; over the calcareous sediments, evaporite settled down as soft sediments from the standing bodies of supra- saline -water accumulated on the supratidal flats (brine pools and brine pans). The evaporite veinlets are assumed to have formed also during the supratidal stages by infilling with salts the dessication cracks opened within the quasiconsolidated calcareous sediments. As regards the evaporite minerala genesis with relation to the sabkha cycles in the studied area, it is to conclude : — gypsum appears always as the first mineral laid down from the marine-derived Solutions (usually by direct precipitation, but some- times by replacement of calcareous material); it is an upper intertidal and supratidal product; — anhydrite is mainly a secondary mineral, formed by replacement of gypsum, only a few situations suggesting a primary origin by direct precipitation from brines; the anhydrite seems to be only a supratidal product; — celestite appears as a secondary, replacement mineral formed under supratidal conditions at the expense of gypsum; — dolomite is also a secondary mineral, supratidally formed by calcium carbonate (probably aragonite) replacement. The lack of halite within the studied area suggests that the salinity of precipitative brines has not exceeded values of 250—300 %0, inasmuch as the halite precipitation requires concentrations (salinities) at least as low as 300 %0 (S c h m a 11 z , 1966). On theoretical grounds, it is to be expected that the sedimentary sequence across the carbonate-evaporite facies zone should display a substanțial horizontal variation in lithology, from an almost comple- tely evaporitic composition landward to a mainly calcareous one seaward, Institutul Geological României A. (DRĂGĂNESCU in accordance with the presumption that the upper intertidal-supratidal sedimentation prevails landward and the shallow subtidal-lower intertidal one — seaward. This theoretical assumption is consistent with the field evidence; so, watching the variation in sedimentation across the carbonate- evaporite facies zone (using the data provided by the 3 drillings), one may ascertain that generally from SW towards NE (that is from „Ciochina” land towards the sea) the participation of evaporites decreases and that of limestones increases. On the whole, the carbonate-evaporite deposits of this facies zone appear outlined, in the vertical section of the east-Wallachian sector, as an well-individualized sedimentary system : the tidal-flat system. B) The Zone of Bahamite Facies This facies zone parallels the previous one, lying directly NW of it. The bahamite facies is represented by skeletal-lumpal-pelletal, muddy calcareous facies in Smirna and Gura lalomiței sectors. 1. In Smirna sector (drilling no. 7), the calcareous sequence contains poorly skeletal-pelletal, micritic limestones (1239—1 240.30 m depth) and lumpal-oolitic limestones (1 338.50 — 1 339 m depth). The poorly skeletal-pelletal, micritic limestones (fossiliferous, pel- let-bearing micrites; in Folk’s 1959 nomenclature) consist of scarce skeletal grains and fecal pellets floating in homogeneous or grumous micrite (Pl. VI, Fig. 4). The skeletal grains are represented by ostracods and spiral or biseried foraminiferids; the fecal pellets belong to both the Favreina salevensis type (crustacean fecal pellets) and the elongate-cylin- drical, small type (probably molluscan fecal pellets). The limestones con- tam angular, silty, quartz grains in minor amounts (about 10 volume per- cent). Therefore, this limestone type resembles some of the limestones of the carbonate-evaporite facies zone, expressing the same quiet, shallow marine environment illustrative of the protected, inner platform domain. The foraminiferids exhibit strong tendencies of micritization (grain- diminution of O r m e , B r o w n , 1963 ; W o 1 f , 1965 a) which may be ascribed to the algal boring-inorganic infilling mechanism deseribed from modern sediments (B a t h u r s t, 1966 ; K e n d a 11, S k i p w i t h, 1969; A1 e x a n d e r s s o n , 1972), the former ones appearing more or less turned into cryptoerystalline grains (nomenclature Purdy, 1963). The terrigeneous quartzose material probably resulted from an eolian transport. The lumpal-oolitic limestones (Pl. VII) consist of oolitic grains (= ooids=ooliths) and pseudodlitic grains (= pseudooids = pseudooliths) embraced by a finely or very finely crystalline spar calcite often displaying features of a basal binder. The microscopic examination suggests that this spar calcite is a diagenetic pseudospar resulted from replacement of calca- reous grains and possibly some micrite matrix; it seems to represent the product of the new diagenetic sequence (already mentioned in section I) involving dolomiztization-dedolomitization-aggrading recrystallization (for details see explanations Plate VII). Institutul Geological României «;r7 37 LOWER CRETACEOUS CARBONATE Al© CARBONATErEVAPORITE SEDIMENTATION 41 The pseudoolitic grains (= the nonoblitized grains accompanying the oolitic grains, the same time representing the source of nuclei for these latter) are represented by pellets and grapestone lumps. The pellets, 100 — 500 micra in size, belong to the fecal pellet type as well as to the cryptocrystalline grain type. There are two kinds of fecal pellets : fecal pellets of the Favreina salevensis type (crustacean fecal pellets) and small ovoidal fecal pellets (probably produced by worms). The spheroidal to irregular-ovoidal pellets seem to be of a cryptocrystalline grain type, probably proceeded from the hardening of some mud aggrega- tes (nomenclature P u r d y , 1963). The grapestone lumps (nomenclature 111 i n g , 1954 ; P u r d y , 1963) are composed of pellets, smaller grapestone lumps (consisting of pellets too) and/or obliths. The lumps reach up to 2 mm in size and are made up either of one (monogeneous) or of more (poligeneous) of the enumerated component types. The coexistence of the pellets or some small lumps and the obliths within the large grapestone lumps proves that the processes of pelletal and lumpal accretion took place concurrently with the oolitic accretion processes. The oolitic grains, representing more than 90 volume percent of the allochem bulk, mainly belong to the superficial oblith type, each of them usually possessing a large nucleus (0 5 — 1.5 mm in diameter) and a single thin chcumlamina of oolitic accretion; in minor amounts true obliths occur, whose small nuclei (100—150 micra in diameter) bear thick oolitic envelopes consisting of numerous laminae (some of them partly or completely micritized probably by the algal boring-inorganic infilling mechanism described by Bathurst (1966) and A1 e x a n d e r s s o n (1972) in modern shallow-marine sediments). The nuclei are represented by pellets and lumps. Th< pellets have yielded, by oolitization, both super- ficial obliths and true obliths. The lumps, owing to their large size, under- went a superficial oolitic accretion only; they appear as an ancient equi- valent of pi esent-day botryoidal lumps (111 i n g , 1954 ; P u r d y , .1963 ; K e n d a 11 , S k i p w i t h , 1969). The obliths with pelletal nuclei were frequently aggregated, along with or without other grain types, in grapestone lumps (consisting of 2—4 aggregated grains), which, in their turn, were submitted to a new oolitic accretion, finally resulting in superficial obliths bearing complex nuclei (these obliths are also equi- valent to modern botryoidal lumps). This fact supports the opinion that the processes of pclletal-lumpal accretion and oolitic accretion developed concurrently. The obliths are 1—1.5 mm in diameter, therefore rather uniform in size comparativcly to the large range of nucleus size; the pre- sent data confirm the fact, already described by different authors, that the oolitic accretion tends to homogenize the grain size by a higher rate of oolitic accretion on the smaller pseudoolitic grains. In the last analysis one may assert that the processes of oolitic ac- cretion concurred with the processes of pelletal lumpal accretion, the grains bearing, at the moment of burial, the prinț of this concurrence and ।nstitutul Geological României IGR/ 42 A. •draganescu 38 falling into the oblith class or pseudoblith clasa in accordance with the last procesa undergone : oblitic accretion or lumpal type accretion. The simulta- neous development of the lumpal-pelletal and oblitic accretion» suggests that the sedimentation took place in no case within an oolitic facies area, but within a grapestone facies area (sensu P u r d y , 1963) submitted to the influences of a neighbouring oblitic facies. Therefore, Smirna sector belonged to an inner platform domain, where the deposition developed under skeletal-pellet mud facies and gra- pestone facies, that is, under a calcareous bahamite facies (sensu B e a 1 e s , 1958 : the ancient analogous of all present-day facies distinguished within the sheltered, inner areas of the carbonate platforms). Along the same line, worth mentioning is that bahamite facies and bahamite rock should be regarded as two distinct notions which must not be confused : the term of bahamite facies encompasses the lime mud facies, skeletal/pellet mud facies and grapestone facies, that is the facies prevailing in the sheltered, inner domains of the carbonate platforms and bordering seaward upon the skeletal-oolitic facies specific to the agitated, open environment of the outer domains of the carbonate platforms, whereas the bahamite rocks stand for the petrologie group represented by limestones varying from calcilutites to calcirudites and consisting of calcareous mud and/or allo- chems of a micritic consistence suggesting to have originated from physi- co Chemical precipitation-accretion-aggregation processes only. The transient manifestation of some oblitic facies influences (outer platform facies) in Smirna sector suggests the existence of a lateral shif- ting in facies perpendicular to the direction of the facies zones develop- ment, probably in correlation with the lateral movements within tidal-flat domain lying directly S and SW. 2. In Gura I al o mi ț ei sector (drilling no. 8 : 220—226 m depth core) medium and coarse lumpal-pelletal calcarenites were iden- tified (Pl. III, Fig. 6—8). The alloehems are chiefly represented by gra- pestone lumps (consisting of pellets) and pellets (of a cryptocrystalline grain type, possibly mainly proceeding from mud-aggregates); coated grains subordinately occur, bearing micrite envelopes and varying from monoenveloped to polienveloped (microoncolitic) grains ; in minor amounts finely arenitic skeletal grains occur (ostracods, echinoderm ossicles, milio- lids). The alloehems are embedded within a microspar matrix, thought as derived from a former micrite matrix. These limestones express a baha mite facies (sensu B e a 1 e s , 1958) of a grapestone facies type (sensu Purdy, 1963). The presented bahamite facies fully corresponds to a shallow marine calcareous sedimentation developed within an inner platform domain under its specific, carbonate-lagoonal facies analogous to the present-day lime mud facies, pellet mud facies, skeletal mud facies and grapestone facies ținitially outlined on Great Bahama Bank, Andros lobe ; I m b r i e, Purdy, 1962; Purdy, 1963); sporadic influences of the N and NE outer platform facies were felt in places. The bulk of bahamite deposits of this facies zone at present makes up the carbonate-lagoonal sedimentary system. Institutul Geological României 39 LOWER CRETA CEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 43 0) The Zone of Skeletal-Oolitic Facies This facies zone stretches parallel to the previous one, lying di- rectly NEandNof it. Inasmuch as the facies-zoned complex is missing NE of the line joining the localities of Hîrșova and Berlescu, being removed by erosion, a little part only of the skeletal-oblitic facies zone preserved until today. Thus, calcareous skeletal and/or oblitic facies (both of them sensu P u r d y, 1963) were encountered in Zăvoaia and Berlescu sec- tors only. 1. I n Zăvoaia sector (drilling no. 6) oblitic calcarenites (2 033—2 033.40 m depth core) and skeletal limestones (1 956—1 956.50 m depth core) occur. The oblitic calcarenites (oosparites) consist of true obliths (several oblitic laminae) whose nudei are represented by pellets of a cryptocrys- talline grain type; minor percents of pseudobliths (pellets of a crypto- crystalline grain type) occur. The rock is a medium-grained calcarenite (note : the thin sections were not available for a detailed study and for taking photographs). These limestones express a typical oblitic facies of open, outer platform environment. The skeletal limestones are extremely complex, consisting of bioli- thite masses and allochthonous skeletal masses (Pl. IV, Fig. 2—3). The biolithite masses include an assemblage of coraligeneous structures, algal structures and encrustingforaminiferic structures of a „nubecularian” type (sensu E 11 i o t, 1966); the algal structures are prevalent and belong to the pseudostromata type (sensu W o 1 f, 1965 b, 1965 c), consis- ting of extremely dense and various-textured (from homogeneous to pel- letoid) algal calcilutite (schyzophycean calcilutite): the foraminiferic structures occur as nodules within the algal structures. The allochthonous skeletal masses (sensu C a r o z z i, 1960) include biomicrites and biopel- micrites; they consist of a micrite matrix containing numerous skeletal grains (fine shells of pelecypods, ostracods and rare calpionelids), algal pellets about30 micra in size made up of extremely dense calcilutite (algal mud-aggregates), and microoncolitic algal nodules centrated or not by a ske- letal grain. These skeletal limestones express a skeletal facies of a coralgal type (sensu Purdy, 1963) typical of an unprotected, outer plat- form environment. There is no doubt that they stand for an ancient reef complex. 2. I n Berlescu sector (drilling no. 3), pelletal, skeletal calcarenites (2 128.90—2 129.20 m depth core) (biosparites to biopels- parites — Pl. II, Fig. 6 — 7) occur. The skeletal grains are the main con- tributor to the limestone bulk and consist of echinoderm plates. The pellets appear ovoidal or spheroidal in shape, 60 — 150 micra in size and belong to the cryptocrystalline grain type. Irregular-shaped lumps, made up of pellets, subordinately occur. These limestones express a skeletal facies (sensu Purdy, 1963). Both the pellets and the lumps seem to have formed by algally (schyzophycean) induced precipi- tation-aglutination-aggregation processes, inasmuch as on the one hand it is very difficult to accept the occurence of some pure physico-chemical Institutul Geologic al României 1GR 44 A. DRĂGĂNESCU 40 processes of this kind, without any organic intervention, under a skeletal depositional facies, and on the other hand the constitutive micrite ap- proaches the algal calcilutite (as it was defined by W o o d, 1941; Ca- ro z z i, 1960; W o 1 f, 1965 b, 1965 c). The spar calcite „cement” ex- hibits clear features of a pseudospar resulted from the diagenetic sequence including dolomitization-dedolomitization-aggrading recrystallization (ar- guments : scattered or grouped dedolomitized rhombohedra, angular out- lines of micrite grains, parțial or total consumption of grains, rhombohedra obviously penetrating the grains of a mioritic consistence). The calca- renites of Berlescu sector may be ascribed to a skeletal facies of an echi- nalgal type (skeletal facies including limestones consisting of echinoderm pieces and corpuscular algal products of blue-green algae, the latter also termed algal grains of the Oncolithi Group; sensu W o 1 f, 1965 c). Therefore, the skeletal-oblitic calcareous facies corresponds to a reefal sedimentation within an outer platform domain under coralgal, echinalgal and oblitic facies. As a whole, the deposits belonging to this facies zone make up, at present, the reef sedimentary system. The facies-zoned complex, on the whole, represents the sedimen- tary product of a highly facies-differentiated, carbonate platform. The depositional area within discussed perimeter was sketched as a large bay widely opening northward and closed on the other three sides by the mainland of Dobrudgea and „Ciochina”rise15. Three sedimentary do- mains, semicircular in shape, stretched within this area from S to N, that is, from a near-shore position towards an off-shore position : the marginal-marine domain, the inner shelf domain and the outer shelf domain. Three depositional facies were corresponding to these three do- mains : the carbonate-evaporite facies, the calcareous bahamite facies and the. calcareous skeletal-oblitic facies. The simultaneous development of these three facies led to the accumulation of a sedimentary body — the facies-zoned complex — consisting of three lateral-interfingering petrogenetic Systems : the tidal-flat system, the carbonate-lagoonal system and the reef system. These three Systems succeed now in the above- mentioned order from S and SW towards N and NE. III. THE REEFAL LIMESTONE COMPLEX This complex was recognized only in the central part of the studied area, in Berlescu (about 50 m thick), Zăvoaia (50 — 60 m) and Smirna (20—30 m) sectors, overlying apparently in depositional conformity the 15 The carbonate-evaporite facies zone eventually has its continuation towards SE, in south Dobrudgea, where prof. Bănci lă reccntly described (,,On the presence of a Purbe- kian — Wealdian gypsiferous formation in the Fetești-Constanța region” — in Romanian; in press) a thick evaporite sequence stratigraphically interposing between the upper Jurassic limestones and the Lower Cretaceous ones, sequence dated by mentioned author as belonging to the uppermost part of the L’pper Jurassic. \ IGR Institutul Geologic al României 41 LOWER CRETACEOUS CARBONATE AND CARBOîNATiEHEVAPORITE SEDIMENTATION 45 facies-zoned complex. The absence of this complex in all the other sectors seems to be connected with the very active postneocomian-prealbian erosion. Only in Ciochina sector it seems to be a depositional gap and not an erosional one (because here the Hauterivian complex does exist, directly overlying the Upper Jurassic limestones and dolostones). 1. In Beri eseu sector (drilling no. 3: 2 078—2 079 m depth core) biodolomicrites occur, consisting of a dolomicrite matrix containing many, arenite-sized, skeletal grains : pieces of echinoderms, tests of dassycladacea» algae (genus Aetinoporella), briozoan, pelecypod and brachiopod debris, and scarce foraminiferids. The dolomicrite matrix consists of a micrite matrix of extremely fine crystallinity (algal calcilu- tite ?) invaded by dolomite microrhomboheara (at most 8 micra in size) (possibly of a penecontemporaneous replacement of the calcareous mud under submarine conditions). I consider these limestones as representing a skeletal facies of a brialgal type (skeletal facies including limestones consisting of algal material and zoogeneous material characterized by the presence of frequent briozoan remnants and the lack of coral debris). 2. I n Zaro ai a sector (drilling no. 6 : 1 906 —1 906.50 m depth core), gresous, pelletal, lumpal calcarenites and microcalcirudites occur, consisting of lumps, pellets and angular quartz grains (the last ones in amounts of 10—20 volume percent and 60—90 micra in size) (Pl. IV, Fig. 4 —6; Pl. V). The lumps, made up of pellets and/or smaller lumps, are of a grapestone lump type (nomenclature 111 i n g, 1954) and of a micritic lump type (new term : lump displaying either a homo- geneous-micritic consistence, in present case on account of a perfect merging of the component allochems also micritic in consistence, or a slightly nonhomogeneous-micritic consistence, in present case owing to the parțial merging only of the component grains). The pellets, up to 125 micra in size, ovoidal or spheroidal in shape, and of a homogeneous- micritic consistence, display features of cryptoerystalline grains (nomen- clature P u r d y, 1963). Within „intercorpuscular” spaces, diagenetic equant spar calcite occurs, suggesting to represent, by its fabrics, an allochem-replacive calcite, resulted from the already-mentioned diage- netic sequence involving dolomitization-dedolomitization-aggrading re- crystallization (for details see explanations to Pl. V). Therefore, this spar calcite stands for former patches of grouped dolomite rhombohedra; scattered dedolomite rhombohedra occur disseminated within the micrite of the calcareous grains too. The micrite composing the allochems exhi- bits features of an algal calcilutite (extremely fine crystallinity less than 1 micron, extremely dense and compact texture) corrcsponding to the descriptions given by W o o d (1941) and W o 1 f (1965 b, 1965 c). The calcareous grains display strong tendencies of merging to each other, often welding to yield pseudodismicritic microvolumes (see explanations to Pl. V). These observations suggest an algal origin for the calcareous grains; the author considers them as algal pellets and algal lumps (calca- reous grains of a micritic consistence formed by algally (blue-green algae) produced or induced processes of precipitation-flocculation-agglutination- Institutul Geological României 16 R 7 46 'A. •DRAGANESCU 42 aggregation). Therefore, in present case the pelletal-lumpal limestones do not express a bahamite facies (sensu B e a 1 e s, 1958) of a grapestone type (sensu Pur d y, 1963): pure physico-chemical accretion-aggrega- tion ; they suggest a skeletal facies (sensu Purd y, 1963) of an algal type, represented by allochthonous limestones (sensu C a r o z z i, 1960) made up of algal calcilutite organized in corpuscular productions (= algal grains). 3. In Smirna sector (drilling no. 7 : 1 183.50—1 184.50 m depth core), gresous biomicrites occur consisting of abundant skeletal grains and angular silty quartz grains (in amounts of 10 — 20 volume percent) embedded within a micrite matrix (Pl. VI, Fig. 5 — 7). The mi- crite matrix often displayes enlargement to microspar. The skeletal material is represented by : foraminiferids, fragments of briozoans, corals, dassycladaceans, pelecypods and echinoderms; all the skeletal grains exhibit micrite envelopes representing supposingly the product of the algal boring-inorganic infilling mechanism reported from recent sedi- ments by Bathurst (1966) and Alexandersson (1972); the foraminiferids display different stages of grain-diminution to an in- ternai micritic texture (this process is thought to have proceeded by the same boring-infilling mechanism above-refered to). The limestones of Smirna sector indicate a skeletal facies (sensu Purd y, 1963) of a coralgal type. As a general conclusion, the calcareous reefal complex, as much as it is preserved, suggests a strong homogenization of the depositional conditions in comparison with the previous complex, the sedimen- tation taking place under a general skeletal facies, the whole area dis- playing features of an outer platform domain; within this general reefal facies, some differentiations may be noted depending on the biocoenosis type which yielded the calcareous deposits: coralgal facies, brialgal facies and algal facies. Taking into account that in Cernavoda sector (western-Southern Dobrudgea) the same skeletal facies develops over- lying the carbonate-evaporite facies of the facies-zoned complex (as the data presented by B ă n c i 1 ă suggest16), one may conclude that the sedimentation of the calcareous reefal complex proceeded under a skeletal facies of outer shelf domain over the entire eastern part of the Romanian Plain (that is, also in those sectors where this complex now appears eroded). Probably the rise of Ciochina-Mărculești was lowered to a submerged position, having lost its role of threshold during the de- position of this third complex, even though sqme of its sectors, such as Ciochina sector, possibly behaved as undepositional areas. GENERAL CONCLUSIONS The petrologie study of the Neocomian sequences crossed by drillings in the eastern Romanian Plain emphasizes the following general conclusions: 18 Op. cit. 15 Institutul Geological României XICRZ 43 lower cretaceous CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 47 During the Upper Tithonianî-Berriasian-Valanginian time in- terval, an autochthonous, carbonate and carbonate-evaporite sedimen- tation developed, originating in 3 sedimentary complexes : the lower, micritic limestone complex; the middle, facies-zoned complex; and the upper, reefal limestone complex. The complex of micritic limestones generally expresses a marine sedimentation in a lime mud facies within a sheltered, inner platform environment. The facies-zoned complex represents the product of a sedimentation on a carbonate platform with strong facies differentiations; this complex includes 3 isochronous petrogenetic Systems which laterally interfinger succeeding from S towards N as folows : the tidal-flat system, the car- bonate-lagoonal system and the reef system; these 3 Systems represent the products of the 3 sedimentary facies — the carbonate-evaporite fa- cies, the bahamite facies and the skeletal-oolitic facies — typical of the 3 depositional domains of any marine carbonate platform under warm and dry climate: the marginal-marine domain (or the tidal-flat domain), the inner shelf domain and the outer shelf domain. The complex of reefal limestones on the whole represents, as its name reveals, a reefal system formed on an extensive outer shelf domain under coralgal, brialgal and algal facies; this complex suggests the rec- currence of the uniformity of the depositional eonditions over the entire studied area, as is the case with the first complex. The general sequence of the main petrogenetic processes noticed in the whole studied material appears as follows : The syngenetic processes consisted in : direct deposition of calca- reous (mainly aragonitic) sediments by physico-chemical or organogenous extraction of CaCO3 from seawater; direct precipitation of gypsum and possibly anhydrite; anhydrite-after-gypsum replacements, sometimes of pseudomorphic types (two textural types of pseudomorphic replace- ment are described, in both of them each gypsum crystal being replaced by an aggregate of tiny anhydrite prisms); celestite formation probably also by gypsum replacement; penecontemporaneous, extremely finely crystalline dolomitization. All these processes, except the calcareous se- diment formation, took place with relation to sabkha cycles. The early diagenetic stages (diagenesis after some burial, but still undei’ seawater influence) include the main bulk of dolomitization, deve- loped as finely or medium crystalline rhombohedra. The late diagenetic stages (diagenesis after rather deep burial and developed under the influence of connate waters) were responsible for the dedolomitization-aggrading recrystallization processual sequence ascer- tained in many cores. A worth mentioning fact is the total lack of the pore-filling calcite (=orthospar=calcite cement) in the examined petro- logie material; so, all the spar calcite, apparently calcite cement in many instances, actually represents microspar or pseudospar usually of a dedo- lomitic type (proceeding from the diagenetic sequence of doîomitization- dedolomitization-aggrading recrystallization) and seldom of a neomorphic Institutul Geological României 48 A. .drăgănescu 44 type (direct aggrading neomorphism of some depositional mioritic fabrics to larger calcite). As regards the age of each sedimentary complex, accepting that these complexes conformably overlie each other, that the calpionelid assemblage of mioritic limestone complex in Zăvoaia sector suggests an Upper Tithonian age and that the complex of reefal limestones is the equivalent of the Valanginian reefal limestones of Southern Dobrudgea (Cernavodă sector), present author put fonvard the following presump- tive chronostratigraphic assignation : I. The mioritic limestone complex is Upper Tithonian?-Lower Ber- riasian in age; II. The facies-zoned complex belongs to the Upper Berriasian- Lower Valanginian time-interval; III. The reefal limestone complex stands for the Upper Va- langinian terni. REFERENCES Alcxandersson T. (1972) Micritization of Carbonate Particles : Processes of Precipi- tation and Dissolution in Modern Shallow-Marine Sediments. Bull. Geol. Inst., Uni- versity Uppsala, new series, 3/118. Uppsala. A d a m s J. E., Rhodes M. L. 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Chicago. IGR/' Institutul Geologic al României 47 LOWER CRETACEOUS CARBONATE AND CARBONATE-EVAPORITE SEDIMENTATION 51 Orme G. R. B r o w n W. W. M. (1963) Diagenetic Fabrics in the Avonian Limes- tones of Derbyshire and North Wales. Yorkshire Geol. Soc. Proc., 34/1/3, p. 51 — 66. Leeds. P a râ j a s E. (1935) "L’organisme B” de E. Jukpwski et J. Favre. C. R. Soc. Phys. Hist. Nai. Geneve., 52/3. Genăve. — (1948) Sur quelques coprolithes de Crustaces. Arch. Sci. Soc. Hist. Nat. Geneve., 1, p. 512—520, Geneve. P a t r u 1 i u s D. (1964 a) Studiul stratigrafie al depozitelor inezozoice și paleozoice traver- sate de forajul de la Cetate (partea de vest a Gîmpiei Române) D. S. Com. Geol. XLIX/1 (1961-1962). București. — (1964 b) Asupra prezenței unor calcare cu coprolite de crustacei decapozi (Favreina salevensis P a r e j a s) în Neocomianul inferior din platforma moesică (Cîmpia Română). D.S. Com. Geol. L/2 (1962 — 1963). București. — (1965) Inventar sumar al algelor calcaroase neojurasice și eocretacice din Carpații Ro- mânești și Platforma Prebalcanică D.S. Com. Geol. LI/2 (1963-1964). București. — Tocorjescu M a r i a (1962) Studiul stratigrafie al depozitelor neogene, cretacice și neojurasice străbătute de forajul de la Atîrnați (Cimpia Română) D.S. Com. Geol. XLVII (1959-1960). București. — Ștefănescu M. (1970) Lithofacies Map of the Romanian Territory at the Neo- comian Time (Lower Cretaceous) scale 1 :2 000 000. Geol. Inst. Publ. București. Phleger F. B. (1969) A Modern Evaporite Deposit in Mexico. Bull A.A.P.G. 53/4, p. 821 — — 829. Tulsa. Popescu M., Pătruț I., ParaschivD. (1967) Stadiul actual de conoașteregeo- logică a platformei moesice de pe teritoriul românesc. Petrol și gaze., 1/18. București. P o s n j a k E. (1938) The System CaSO4-H2O. Am. J. Sci., 235 - A, p. 247-272. — (1940) Deposition of Calcium Sulfate from Sea Water. Am. J. Sci., 138, p. 559 — 568. Purdy E. G. (1963) Recent Calcium Carbonate Facies of the Great Bahama Bank. J. Geol., 71, p. 334-355, 472-497. Chicago. Sanders J. E., Friedman G. M. (1967) Origin and Occurrence of Limestones. In : G. V. Chilingar, H. J. Bissell and R. W. Fairbridge (Editors). Carbonate Rocks, Elsevier. 9A, p. 169—265. Amsterdam. Schmalz R. F. (1966) Enviromnents of Marine Evaporite Deposition. Mineral Industries, 35/8, p. 1—7. Park. Pennsylvania. — (1969) Deep-Water Evaporite Deposition. A Genetic Model. Bull. A.A.P.G., 53/4,p. 798—823. Tulsa. Ser u ton P. C. (1953) Deposition of Evaporites. Bull. A.A.P.G. 37, p. 2498 — 2512. Tulsa. Shearman D. J. (1963) Recent Anhydrite, Gypsum, Dolomite and Halite from the Coastal Flats of the Arabian Shore of the Persian Gulf. Proc. Geol. Soc. London. 1607 — 63.65. London. Shinn E. A. (1968) Practicai Significance of Birdseye Structures in Carbonate Rocks. J. Sed. Petr. 38/1, p. 215-223. Tulsa. Shinn E. A., Ginsbur g R. N., Lloyd R. M. (1965 a) Recent Supratidal Dolo- mitization in Florida and Bahamas. Geol. Soc. Am. Spec. Papers. (abstract) 82, p. 183 — 184. Boulder. — (1965 b) Recent Supratidal Dolomite from Andros Island Bahamas. In : L. C. Prax and R. C. Murray (Editors ) Dolomitization and Limestone Diagenesis, a Symposium. Soc. Econ. Paleont. Mineral. Spec. Publ., 13, p. 112—123. Tulsa. Institutul Geologic al României igr/ 52 A. ERAGĂNESCU 48 — (1969) Anatomy of a Modern Carbonate Tidal-flat, Andros Island Bahamas. J. Sed. Petr. 39/3, p. 1202-1228. Tulsa. Stewart F. H. (1953) Early Gypsum in the Permian Evaporites of North-eastern England. Proc. Geol. Assoe. 64, p. 33 — 39. Taft W. H. (1967) Physical Chemistry of Formation of Carbonates. In : G. V. Chilingar, H. J. Bissell and R. W. Fairbridge (Editors) Carbonate Rocks, Elsevier. 9 B, p. 151 — 167. Amsterdam. Tebbutt E. G., C o n 1 e y D. C., B o d y D. W. (1965) Lithogenesis of a Districtive Carbonate Rock Fabric Wyoming Geol. Survey Contrib. Geol. 4/1, p. 1—13. Textoris D. A. (1968) Petrology of Supratidal, Intertidal and Shallow Subtidal Carbo- nates, Black River Group, Middle Ordovician, New York U.S.A. XXIII Internai. Geol. Congr., 8, p. 227 — 248. Thompson A. M. (1970) Tidal-flat Deposition and Early Dolomitization in Upper Ordo- vician Rocks of Southern Appalachian Valley. J. Sed. Petr. 40/4, p. 1271—1286. Tulsa. Wells A. (1962) Recent Dolomite in the Persian Gulf. Nature, 194, p. 274 — 275. Wentroth C. K. (1922) A Scale of Grandes and Class Terms for Clastic Sediments. J. Geol., 30, p. 377-392. Chicago. Winland H. D. (1969) Stability of Calcium Carbonate Polymorphs in Warm, Shallow Seawater. J. Sed. Petr., 39/4, p. 1579-1587. Tulsa. Wolf K. H. (1960) Simplified Limestone Classification. Bull. A.A.P.G. 44, p. 1414—1416. Tulsa. — (1965 a) „Grain-Diminution” of Algal Colonies to Micrite. J. Sed. Petr. 35/2, p. 420— - 427. Tulsa. — (1965 b) Petrogenesis and Paleoenvironment of Devonian Algal Limestones of New South Wales. Sedimenlology. Elsevier. 4, p. 113—178. Amsterdam. — (1965 c) Gradational Sedimentary Products of Calcareous Algae. Sedimenlology. Else- vier. 5, 1 — 37. Amsterdam. — (1965 d) Littoral Environment Indicated by Open-space Structures in Algal Limestones. Paleogeogr. paleocllmat. paleoecol. 1, p. 183 — 223. W o o d A. (1941) „Algal Dust” and the Finer Grained Varieties of Carboniferous Limestone. Geol. Mag. 78, p. 192-200. QUESTIONS M. Sandulescu: How does the author explain the lack of some facies zones es- pecially that of carbonate-evaporitic facies in the area stretching towards the north-Dobrudgean mainland ? Answer : The mainland probably included both the northern and central Dobrudgea (according to the annexed facies map). The present-day lack of facies zones towards the Dobrud- gean mainland is accounted for both diverse erosional phases installed subsequently to the Neocomian time, and probable original disposition under an intricated pattern of the facies zones at the contact with the Dobrudgean shore. Institutul Geological României 49 LOWER CRETACEOUS CARBONATE AND CARBtXNATE-EVAjPORITE sedimentation 53 DISCUSSIONS M. Sănduleseu. When emphasizingthe scientifical and practicai quality of the paper drawn up at an up-lo-date level, and presented by our colleague A. Drăgănescu, I should like to remark that the explanation of the asyminetrical character of facies zones, and hence their lack towards the north-Dobrudgean mainland may be found if taken into account the occurrence of some tectonic accidents of a transcurrent fault type (strike slip faults) which would have cut the primary depositional zones, shifling towards north-west the north-Dobrudgean compartment < faults trending NW—SE). However, such strike slips have been already noticed in the Pecenega-Camcna fault zone by our late colleague O. M i- r ă u ț ă. This structural control of the present pattern of the facies zones is underlined by the perfect parallclism between the Ciochina threshold and the Fierbinți fault. APPENDIX CLAY-MINERAL STUDY OF SOME NEOCOMIAN CORES IN ȚĂNDĂREI DRILLING BY SILVIC RĂDAN1 Method Two samples from the cores at 574 — 575 m depth (sample Ă) and 620 — 621 m depth (sample B) wereprepared for X-ray diffraction analysis aiming at the knowledge of their elay-mineral composition. With a view to satisfy this purpose, each sample was treated with HC1 0,1 N in order to remove the carbonate fraction, thcn washed and shaked in distiled water. The suspension containing the fraction less than 2 microns was collected and two slides of oriented aggregates were prepared. Three X-ray diffractograms were obtained from each slide: untreated, exposed to a saturated atmosphere of ethylene-glycol and heated at 550°C. Calculation of the relative amounts of clay minerals in each of the samples, on the basis of these diffractograms was, achieved using Biscaye’s method (1965). Results TABLE Claij-mineral composition of the samples Sample Depth Clay-mineral composition Ulițe (%) Chlorite (%) Mixed-layer structures A 574 —575m 620-621 m 90 85 • 10 15 10-14 M, 14 C-14 M 1 Institutul de geologie și geofizică, str. Caransebeș 1, 7000 București. i Institutul Geologic al României 54 'A. DRĂGĂNESCU 50 The illite displayes a good crystallinity in both samples, and I (002)/I (001) ratio shows rather high values (0.46 in sample A and 0.58 in sample B), typical of Al-rich illites. The chlorite of sample A is of a poor swelling, Fe—Mg-rich type, while the chlorite of sample B is of a Mg-rich type and belongs to the CM type, according to L u c a s classification (1962). The random mixed-layer structures belong to 10—14 M and 14C—14M types (according to L u c a s classification, 1962) and were identified only in sample B. They are believed to have resulted from degradation of illite (10 — 14 M) and chlorite (14C—14 M). Discussion The mineralogic composition of clay fraction in both samples is characteristic, as a rule, of the deposits laid down undei' dry climate, where the physical wethering prevails. The lack of mixed-layer structures in sample A suggests aggrading action, rather drastic insolation and ca- tion abundance, as the main features of the original depositional envi- ronment. The sample B, in oposition to the former, expresses an environ- ment submitted to a larger circulation of the water or to a stronger in- fluence of the shore proximity, where degraded minerals were not able to get back to their original structure. The clays of sample A suggest a subtidal depositional environment, while those of sample B seem to stand for an intertidal or supratidal product. Some processes specific to the deep-burial stage of diagenesis are thought to have been superposed to the transformations developed du- ring the above-commented, marine, pre-burial stage of diagenesis. So, this opinion is supported by the fact that the illite, though Al-rich in both samples, is however sligthly Fe-enriched in sample A, and the chlo- rite is Mg-rich in sample B and slightly Fe -enriched in sample A. The gradual enhance in aluminium content of the illite and magnesium con- tent of the chlorite with increasing burial depth of sediment in present case are in a very good aggrement with Dunoyer’s data (1969). EEFERENCES Bisca y e P. E. (1965) Mineralogy and Sedimentation of Recent Deep-Sea Clay in the Atlantic Ocean and Adjacent Seas and Oceans. Geol. Soc. Am. Bull., 76, p. 803 — 832. New York. Dunoyerde SegonzacG. (1969) Les mindraux argileux dans la diagendse. Passage au mdtamorphisme. Mem. Serv. Carte giol. Als. Lorr. 29. Strasbourg. L u ca s J. (1962) La transformation des mindraux argileux dans la sedimentation. Etudee sur les argiles du Trias. Mem. Serv. Carte geol. Als. Lorr. 23. Strasbourg. PLATE I (a, b) Institutul Geological României PLATE I (a, b) Berlescu sector. Complex I. Thin scctions in the core from 2 182.15 — 2 182.90 in depth in drilling no. 3 Fig. 1 — 2. — Fossiliferous clolted micrites bcaring frequent fibrospheres (cadosinids and sto- tniospherids) and calcitized radiolarians. The clotted texture seems to be due to an irregular, slight dolomitization followcd by dedolomitization resulting in a microspar network enclosing micrite clots. Fig. 3 — 4. — Fossiliferous (fibrospheres) micrite or pelmicrite With pseudointraclastic micro- facies resulted from an irregular dolomitization-dedolomitization leaving intra- clast-like patches of relict micrite embeddcd within a dedolomitic microspar network. Fig. 5. — Intramicrite as microfacies within micritic limestones, consisting of a fibrosphere- bearing pelmicritic groundmass containing micritic intraclasts. Fig. 6—8. — Oblitic, intraclastic microfacies within micritic limestones, represented by patch- like, „sparry” or micritic, pellelal, oblitic, intraclastic calcarenites (i = large intraclasts consisting of fibrosphere-bearing pelmicrite; o1>2 = obiiths). The intercorpuscular spar calcite seems to be a pseudospar resulting from a network- like dolomitization (on eventually interestitial micrite, tiny grains and margins of larger grains), follow’ed by dedolomitization (replacement of dolomite by dedolomitic microspar) and more or less aggrading recrystallization (aggradation of dedolomitic microspar to larger pseudospar) (arguments : grains with poligonal outlines, abnormally loose packing, spar „cement” with angular outlines consis- ting of straight and rather long segments linked at different angles while its com- ponent calcite crystals are anhedral in shape and very small in size). All photographs under plane polarized light. Institutul Geological României CO DrăgănEscu. Lower Cretaceous Carbonate and Carbonate-Evapoi’ite Sedimentation. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României X IGRZ Institutul Geologic al României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Ib Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic al Românie \JGR/ PLATE JT (a, b) Berlescu sector Thin scctions in the cores from drilling no. 3 Fig. 1 — 3.— Complex I (2 182.15 — 2 182.90 m depth). The pseudo- "depositional per- turbation facies” consisting of pclmicrites, „disturbed” pehnicritcs, „dismicri- tes” and „intrasparites”. The photo 3 shows a vertical passage from fossilifer- ous pehnicritcs(top) to „dismicrites” (bottom). All spar calcite eyes and patches, responsible for such an interpretation at first sight owing to their pore-filling appearence, actually represent a diagenetic product of the dolomi- tization-dedolomitizalion-aggrading recrystallization sequence. Arguments : all sparry areas, although „filled” with tiny anhedral calcite crystals, are large- angular in shape strongly suggesting former dolomite patches; many spar calcite areas display angular-scrrate outlincs whose component segments, gro- uped by twos, threcs or fours, close more or less completely in small rhomb-sha- ped spaces the marginal zones of these sparry areas; within spar calcite areas, micrite relicts occur exhibiting diffuse, angular outlincs. Conscqucntly, this „depositional facies” actually stands for a diagenetically acquired fabric. Fig. 4 — 5. — Complex I (1 182.15 — 2 182.90 m depth). Fine alternation of fossiliferous pehni- crites and pelsparites, containing in places (Fig. 5, lower half) micritic intra- clasls (some of them displaying sparry coatings : oolitic envelopes or diagenetic fine spar calcite rim?). The pelsparites are corrcclJy termed with relalion to their probably perfect washing, although their calcite „cement” exhibit strong features of the type described from Fig. 1 — 3, present plate (probably an early pore-eom- paction of the original grainstonc followed by the diagenetic sequence of dolo- milization-dedolomitization-aggrading recrystallization developed mainly along the grain boundaries). Fig. 6 — 7. — Complex II (2 128.90—2 129.20 m depth). Pelletal, crinoidal calcarenites (bio- sparites and biopelsparitcs), whose spar calcite “cement” displaycs clear fe- atures of a replacement spar calcite by the diagenetic sequence of dolomiti- zalion-dcdolomilizalion-aggrading recrystallization (arguments : many seattered or grouped dcdolomized rhombohedra, angular outlincs of the grains). All photographs under plane polarize.d light. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Ila. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României Carbonate anei Carbonate-Evaporite Sedimentation. Pl. Ilb. A. Drăgănescu. Lower Cretaeeous 2mm 0 0,25 0,5 Anuarul Institutului de geologie și geofizică, voi. XLVIII. 16 R/ Institutul Geological României PLATE III (a., b) Berlescu and Gura lalomiței sectors Thin sections in the corcs from drilljngs no. 4 and 8 Berlescu sector (drilling no. 4) Fig. 1 — 2. — Complex 1 (2 372 — 2 373.20 m depth). Dolomite-bearing micrite. The dolomite rhombohedra exhibit rhomb-shaped nudei of relict micrite. Gura lalomiței sector (drilling no. 8) Fig. 3 — 5. — Complex I (313 — 313.50 m depth). Micrite invade d by dolomite rhombohedra each of them displaying rhombic nudei of relict micrite. Fig. 6—8. — Complex 11 (220—226 m depth). Lumpal-pellelal calcarenites consisting of grapestone lumps (composed of pellets), pellets and rare skeletal grains embedded within a microspar matrix, locally aggraded to larger pseudospar (probably dolomitization-dedolomitization-aggrading recrystallization on the mi- crite matrix and the smallest grains). All photographs under plane polarized light. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. lila. Anuarul Institutului de geologie și geofizică, voi. XLVIII. 1GR Institutul Geological României Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Illb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. < Institutul Geologic al României x igrV PLATE IV (a, b) Fig. 1 Fig. j Fig. 4 Zăvoaia sector Thin sections in the cores from drilling no. 6 .— Complex 1 (2 295—2 296 m depth). Fossiliferous micrite containing scattered dolomite rhombohedra. The skeletal material consists of echinoderm pieces, liny ostracods and (not visible in the photo) calpionelids. — 3. — Complex II (1 956 — 1 956.50 m depth). Skeletal limestones including biolithite masses (coraligenous structures, algal structures and foraminiferic structures) (Fig. 2:a) and interbiolithitic sediments (biomicrites, and biopelmicrites, Fig. 3). — 8. — Complex 11! (1 906—1 906.50 m depth). Algal calcarenites and calcirudites va- rying from pelletal, lumpal limestones (grainstones) (Fig. 4 — 6), some of them exhibiting the algal grains partly merged (Fig. 7), to pseudodismicrites of a complete or almost complete merging of the grains (Fig. 8) (see also the next plate). AU photographs under plane polarized lighl. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate aud Carbonate-Evaporite Sedimentation. Pl. IVa. Anuarul Institutului de geologie și geofizică, voi. XLVIII. \lGRZ Institutul Geologic al României Institutul Geological României Drăgănescu. Lower Cretaeeous Carbonate and Carbonate-Evaporite Sedimentation. Pl. IVb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE V (a, b) Zăvoaia sector Thin scctions in the core from 1 906—1 906..50 m depth (Complex III) in drilling no. 6 Fig. 1—1a. — Pelletal, lumpal algal calcarenites (idem PL IV, Fig. 4 — 6). Fig. la represents an enlargement in Fig. 1. Fig. 2 —2a. — Algal pseudodismicrite resulted from an almosl complete merging of the algal nodulcs, pellets and lumps. Fig. 2a stands for an enlarged part of the Fig. 2 The spar calcite „cement” (this Plate and Fig. 4 — 8, Pl. IV) displays evident features of a replacive type formed at the expense of depositional petrographic constitucnls, probably by doloniilization-dcdolomitization-aggrading recrystallization developed mainly on the tiny grains and along the margins of larger grains (arguments : the rhombohedral-shaped margins of the spar areas, relict angular patches with micritic internai structurc floaling within spar- areas, angular outlincs of algal grains, seattered dedolomite rhombohedra consisting of dedo- lomitic microspar). These algal limestones (this Plate and Fig. 4 —8, Pl. IV), originally algal sands, suggest to have undergone an early merging of Ihe calcareous grains owing to a penecontemporaneous algal aggregalion followed by a very early diagenetic pore-compaction; conscqucntly, in a first stage, grainstones exhibiting an apparently perfect welding of the component grains resulted; subsequently, by a dolomitization-dedolomitization-aggrading recrystallization developed mainly along the grain boundaries, the welded grainstones evolved to the present „loosely packed” grainstones (Pl. IV., Fig. 4 — 6; Pl. V, Fig. 1—la) or, if this diagenetic sequence rc- sulted in a patch-like spar calcite, to the present pseudodismicrites (Pl. IV, Fig. 7 — 8; Pl. V, Fig. 2-2a). All photographs under plane polarized light. L- Institutul Geologic al României A. Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Va. 1 0 0,25 0,5 1 I----1----1--------F 2 mm Anuarul Institutului de geologie și geofizică, voi. XLVIH. C > Institutul Geologic al României X igr/ Institutul Geological României A. Drăgănescu'. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Vb. 0 0,25 0,5 1 I---------1---------1-------------------F 2 mm > Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE VI (a, b) Smirna sector Thin sections in the cores from drilling no. 7 Fig. 1 — 2. — Complex 1 (1 983.50 — 1 987.50 m depth). Dolomite rhombohedra-bearing mi- crites. Fig. 3.— Complex I (1 856—1 856.50 m depth). Micrite containing calcispheres, oslracods and other small skeletal debris. Fig. 4. — Complex II (1 239.50—1 240.50 m depth). Micrite containing foraminiferids (most of them submitted to a strong micritization), fecal pellets (Fanreina salevensis, noted „f" in the photomicrograph) and quartz grains. Fig. 5 — 7. — Complex III (1 183.50—1 184.50 m depth). Greseous biomicrite containing abundant skeletal grains (foraminiferids, fragmente of corals, briozoans, echino- derins, etc.) submitted to a strong algal action (micritic envelopes and micritiza- tion). In the photomicrograph 7, some large limeclasts (intraclasts or lumps?) occur, including tiny pellets, micritized foraminiferids, quartz grains, etc. Most of the micrite matrix is evolved to fine microspar. AII photographs under plane polarized light. £ Institutul Geologic al României \ IGRZ . DrăgĂnescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. PI. Via. E E ou Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României A. Drăgănescu. Lower Cretaeeous Carbonate and Carbonate-Evaporite Sedimentation. Pl. VIb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE VII (a, b) Smirna sector Thin sections in the core from 1 338.50— 1 339 m cleplh (Complex II) in drilling no. 7 Fig. 1—3. — Lumpal-oolitic limestones consisting of: grapestone lumps (1, 12), many of them displaying superficial oolitic envclopes (bothryoidal lumps : Ij), ooliths (o), pel- icts of a fecal pellet type (Favreina salevensis = p, pv and ovoid fecal pellets = p2) and of a cryptocrystalline grain type. The pellets and the ooliths are most frequently bound together within compositc grains=grapestone lumps (13). The calcite „cement” exhibits strong features of a rcplacive, diagenetic spar calcite (pseudospar) : abnormally loose paeking, the „cement” patches cut, transect and partly or totally assimilatc the allochems. In addition, other features (the „cement” patches show fre- qucnl angular outlines bula xenotopic structure, in places penetrating the preserved grains as rhombohedral-shaped protrusions; the small size of the pseudospar crystals aligned along the margins of the pseudospar arcaș as against the large Icngthof the straight segments composing the angular outlines of the pseudospar areas) suggest that the pseudospar proceeded from a nelwork-like dolomitization (of some allochems and possibly some former micrite matrix) fol- lowed by dedolomitization and. in most instances, recrystallization of dedolomitic microspar to larger pseudospar. All photographs under plane polarizcd lighl. Institutul Geologic al României Anuaiul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României A. Drăgănescv. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Vllb. 0 0,25 0,5 ' 1 2 mm I---1---H2-----1-----------;---1 Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE VIII (a, b) Țăndărei sector Thin scctions in the cores from drilling no. 10 Fig. 1--2. — Complex I (728—729 m depth). Dolomite-bearing micrite. Plane polarized light. Fig. 3—4. — Complex II (574—575 m depth). Gypsum mash-bearing clayey micrite. The gypsum grew as large cuhedral crystals (the white areas) dissociating the soft host mud (the grey areas) in pieces and particles entrappcd within or between the sulfate crystals. The large size of these gypsum crystals belonging to litho- genctic unit 3 stroifgly conlrasts with the small size of gypsum crystals of litho- genetic unit y (Fig. 5—7, this Plate). Origin of the thin section : clayey micrites imbued with gypsum. N -Ț. Fig. 5.— Complex II (574 — 575 m depth). Anhydrite with blocky-fibrous texture. Each of the anhydrite aggregatcs (some of them outlined with dashed line) consists of quasiparallel, neddle-Iike, anhydrite prisms and represents a single inițial gypsum crystal subsequently replaced by anhydrite. Origin: lensoid evaporite intercala- tion with mosaic structure. N + . Fig. 6—7. — Complex II (574 — 575 m depth). Celestite prisms (c) seattered within a finely crystalline gypsum mass blocky to microcryslallinc in texture. Origin : lensoid evaporite intcrcalation with mosaic structurc. Plane polarized light. Fig. 8 — 9. — Complex II (620 621 m depth). Gypsum displaying a texture varying from blocky to felted or aligncd-fcllcd. Origin : thick gypsum bed with mosaic struc- ture. N -|-. XjGR Institutul Geologic al României Dragănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. VlIIa. Anuarul Institutului de geologie și geofizică, voi. XLVIII. \IGR/ Institutul Geologic al României Institutul Geological României Anuarul Institutului de geologie și geofizică, voi. XLVIII. Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Institutul Geologic al Românie IGR> PLATE IX (a, b) Țăndărei sector Thin section in the core from 620—621 m depth (Complex II) in drilling no. 10 Fig. 1 — 8. — Pelletal (microcoprolithic) and/or microoncolitic calcarenites (grainstones) or lutaceous calcarenites (packstones and wackestones) displaying various fabrics and textural relationships between their petrographic components. The calcareous material consists of microoncoliles(abundantin Fig. 3,4,5), fecal pellets (a- bundant in Fig. 1,2,6 —8) and micrite matrix (most of the micrite matrix and many of the grains exhibit their constituent micrite evolved to microspar as in Fig. 1,6,8). AII the light spaces in the photographs represent gypsum patehes as void-or pore-filling cement or as replacive or displacive growths within or between the grains (the latter case led finally to thin gypsum lenses or strips (g) with massive structure, as in Fig. 6,7). Most of the microoncolites lack the original calcareous nucleus, exhibiting a central patch of gypsum instead; some of them show gypsum growths between the micritic laminae of their envelopes (Fig. 3, 4). Some well-visible fecal pellets of the Favreina saleucnsis type, either well-preserved or cracked to brocken by gypsum growth, occur in the photos 1, 3, 6 and 8 (some of them outlined with dashed line). The photo 1 also shows very clear, small, cylindrical fecal pellets ascribed to gastropods. Some details concerning the infilling of porc spaces by gypsum followed by its displacive or replacive growth between or within the calcareous grains are seen in Fig. 5 (enlargement in the left of Fig. 4): the pores are filled up with gypsuțn ; some microoncolites (m) show gypsum patehes instead of nudei; the calcareous grains (both microoncolites, m, and Favreina saleucnsis fecal pellets, f) „imbued” with gypsum display various degrees of dismembration. AII photographs under plane polarized light. Institutul Geological României Dbăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR Institutul Geological României Drăgănescv. Lower Cretaceous Carbonate and Carbonate-Evaporitc Sedimentation. Pl. IXb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. ksr/ Institutul Geological României PLATE X (a, b) Țăndărei sector Thin sections in the core from 620—621 m depth (Complex II) in drilling no. 10 Fig. 1 — 8. — Various fabrics and lexlures in the same pelletal (microcoprolilhic) and/or micro- oncoli tic calcarenites or lutaceous calcarenites presented in Pl. IX. The intercor- pnscular spaces filled with micrite matrix (moslly evolved to microspar) or gypsum cement. The pellets belong to 3 types : a) large, keg-shaped fecal pellets of erusta- ceans (Favreina salevensis) (clearly visible in Fig. 1, 5, 6, 8); b) small, elongate- cylindrical fecal pellets probably excreled by gastropods (typical in Fig. 7); e) small, ovoidal fecal pellets ascribed to polychaete annelids (abundant all over the photomicrographs). Note : for other petrographic aspects see explanations to Pl. IX, XI and XII. All photographs under plane polarized light. Institutul Geological României Anuarul Institutului de geologie și geofizică, voi. XLVIII. Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Xa. X Institutul Geologic al României X IGR/ Institutul Geological României Dkăgăkescv. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Xb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României yiGRZ PLATE XI (a, b) Țăndărei sector Thin sections in the cores from drilling no. 10 l'ig. 1 — 7. — Complex II (620—021 m depth). Delails in the pellctal-microoncolitic limestones presented in Pl- IX—X, purposing to illustrate especially the dismembration of the original lime sands or muddy sands by gypsum displacive or replacive growth : Fig. 1 — (detail in Fig. 4, Pl. X) : Pelletal lutaceous calcarenitcoverlainby pelletal calcare- nite cemented by gypsum. The pelletal lutaceous calcarenite consists mainly of small, ovoidal fecal pellets (worm dejections) cmbedded in an originally micritic matrix; almosl all micrite matrix and most of the pellets aggraded to fine micro- spar 5—6 micra in crystal size; the unaggraded pellets surrounded by microspar rims. The pelletal calcarenite is cemented by gypsum displaying single optical orientation (the same orientation of the cleavage over the entire gypsum net- work); the fecal pellets belong to the alrcady-mentioned Favreina type, small elongate-cylindrical type and small ovoidal type; the displacive growth of gyp- sum accounts for the local abnormally loose packing; many pellets arc more or less rcplaced or dissociated by gypsum. Fig. 2. — (detail in Fig.8,Pl.X) Pelletal calcarenite consistingof the3above-mentionedfecal pellet types and minor amounts of microoncolites cemented by gypsum (of a single optical orientation). Gypsum assimilates partly or totally many pellets; many microoncolites display subepidermal circular narrow gypsum rims. Fig. 3. — idem Fig. 2. Note the marked tendency of gypsum to replace, disintegrale, or break the calcareous grains. The preferentially disintegrated grains are those evolved to microspar. Fig. 1—5. — (Fig. 5 shows a detail in Fig. 6, PI. X) Pelletal lutaceous calcarenites conlaining patch-like pelletal calcarenites cemented by gypsum. Frequent, large Favreina fecal pellets occur more or less cross-seclioned. Most of micrite matrix and many grains display aggradations to microspar 5—6 micra in crystal size. A gradual passage. is noted between microspar arcaș and gypsum patehes, the former under- going a particle-by-particle Progressive disintegration within gypsum. Fig. 6. — (detail in Fig. 7, Pl. X) idem to Fig. t —5. Typical, lengthwise-sectioned, elon- gate-cylindrical fecal pellets (ascribcd to gastropods) occur. Fig. 7. — Microoncolitic limestone strongly affecled by subsequent energic development of gypsum. Ahnost all calcareous material shows the component micrite particles enlarged to microspar. The gypsum highly dismembers the limestone by vigurous displacive and replacive growth between and within the calcareous grains. Al present, remnants of allochems as well as shapeless microspar patehes floal within a gypsum mass. Fig. 8.— Complex II (634 —635 m depth). Dolomite consisting of euhcdral rhombohedra more or less stained by dark organic maller. The more the organic maltcr within the crystals, the finer the crystallinily. All photographs under plane polarized light. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. PI. Xla. Anuarul Institutului de geologie și geofizică, voi. XLVIII. 'jAr Institutul Geologic al României ig r/ Institutul Geological României Dbăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Xlb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. IGR> Institutul Geological României PLATE XII (a, b) Țăndărei sector Thin seclions in the core from 620—621 m depth (Complex II) in drilling 10 — Details at high magnilude, under plane polarized light, in the limestones pre- senled in Pl. IX —XI, illustraling the microspar problem — l'ig. 1-2. — Pelletal calcarenites consisting of fecal pellets and rare microoncolites embedded within a gypsum mass. Most of the pellets are replaced by microspar (as irregular- shaped patches and fringing rims) which in its turn appears more or less disso- ciated within gypsum mass as individual microspar crystals or shapeless micro- spar patches. The microspar rims surrounding the calcareous grains are often separated from the respective grains by narrow gypsum rings. The pellets show disintegrations within or replacements by gypsum, they appearing sometimes as phantomalic or torn patches. Xote the single orientalion of the clcavage (single optical orientalion) of gypsum in each photograph. Fig. 3,5 and 7. — Calcarenite showing microspar 5—6 micra in crystal-size developed as large patches covcring numerous calcareous grains; the preserved calcareous grains (mainly fecal pellets) ) exhibit an internai micritic structurc partly replaced by microspar as peripheral rims or small patches. The microspar arcaș and the preser- ved grains float within a gypsum mass of a single optical orientalion in each photo- graph. The gypsum penetrates the microspar areas, gradually dismembering them from microspar fields containing irregular-shaped gypsum patches to microspar blebs with torn outlincs accommodated within gypsum mass and still furlher to individual microspar crystals seattered within gypsum fields. Fig. 1, 6 and 8 — I.ulaccous calcarenite consisting of a former micrite matrix (now almost entirely aggraded to microspar 5 — 6 micra in crystal size) and calcareous grains ma- inly of the fecal pcllel type (most of them partly or lotally cvolved to microspar). Al present, the aggraded micrite matrix and pellets makc up a microspar ground- mass containing unaffccled pellets (displaying a micritic consistence). These relict grains appear surrounded by microspar rims probably formed at the expense of former micrite matrix. All these facts suggest that the microspar resulted from an approximalely penecontem- poraneous aggradation of micrite fabrics (matrix and grains), before gypsum ccmcntation took place. By all means, this microspar must be considered as formed al a moment when the calca- reous sediments were still soft and under the seawater influence. Thcrcfore, its formation procccded in soft state and under aragonitic form (considering the sediments as originally ara- gonilici by comparison with their present-day analogous). Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. Xlla. Anuarul Institutului de geologie și geofizică, voi. XLVIII. ICR Institutul Geological României Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonat e-Evaporite Sedimentation. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României \ igrZ PLATE XIII (a, b) Cireșii sector Thin scctions in the cores from drilling no. 9 Fig. 1—4. — Complex I (2 351 — 2 353 m depth). Micrite invaded by dolomite rhombohedra as disseminations. crowds and thin strips. Plane polarized light. Fig. 5. — Complex II (2 208 —2 209 in depth). Clotted micrite containing rare ostracods, Ac- tinopordla tests (A) and tiny gypsum microaggregates and crystals (the white spots inside the micrite). The hclinoporclla. test consists of gypsum (of a replacive type). Plane polarized light. Fig. 0. — Complex 11 (2 208 — 2 209 m depth). The same clotted micrite containing dismicrite textures (exhibiting strong features of an algal product) (d). The sparry eyes in dismicrite patchcs are filled with gypsum and/or calcite. Plane polarized light. Fig. 7. — Complex 11 (2 208-2 209 m depth). Photomicrograph showing the contact between a calcite-evaporite veinlet (upper right half of photo) and the host micrite (lower left half of photo). The veinlet consists of anhydrite (a) in a central position and calcite (c) in a parietal position including some gypsum patches (g). The host mi- crite contains tiny gypsum micro-aggregates (the white spots) and is pierccd by a fine calcite veinlet. N + • Fig. 8. — Complex II (2 208 — 2 209 m dcptli). Evaporite inlerealation with contorted bed- ded structure and aligned-felted texture, consisting mainly of anhydrite and subordinately of gypsum. N + . Institutul Geological României Drăganescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. PI. XlIIa. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României Drăgănescu. Lower Cretaeeous Carbonate and Carbonate-Evaporite Sedimentation. 1’1. X Anuarul Institutului de geologie și geofizică, voi. XLVIII. 40^ Institutul Geological României IGR ■’ PLATE XIV (a, b) Cireșii sector Thin seclions in the core from 2 208 — 2 209 in depth (Complex II) in drilling no. 9 Fig. 1, 3, 5 and 7. — Pelletal (microcoprolithic) calcarenites. Textural and structural general features. Plane polarized light. Fig. 2, 4, 6 and 8. — dclails in the pelletal (microcoprolithic) calcarenites presented in Fig. 1, 3, o, 7. Plane polarized light. The pelletal calcarenites consist of fecal pellets (belonging to the same 3 types described in Țăndărei drilling, Pl. IX—XI : crustacean, large, keg-shaped, Favreina salevensis fecal pellets; small, elongatc-cylindrical fecal pellets ascribed to gastropods; and small, ovoidal fecal pellets probably excretcd by worms) embedded in a very finely or finely crystalline spar calcite. The fecal pellets consist of micrite particles less than 1 micron in size; the outer parts of the pellets appear often aggraded lo a coarser micrite 2 3 micra in crystal size; in some pellets this larger micrite replaces the whole fine micrite. The limestones often show an abnormally loose packing. The „intercorpuscular” spar calcite is 8 — 20 micra in crystal size in places enlarged to 30—60 micra crystal size; the spar calcite displayes a granulai- texture, scldom showing slighl tendencies towards a drusy texture; usually, the larger the spar patch, the larger its crystallinily; the contact between the spar calcite „cement” and the calcareous grains (either finely micritic or coarser micritic in consis- tence) is sharp, no gradual passage existing from the pellet crystallinity to the spar calcite one; the spar „cement" cuts and transects the pellets and their internai fabrics, often lending them new and angular outlincs; sometimes, the pellets appear more or less „disolved”, assimi- lated within the spar „cement” ; a caretul observation of the spar calcite network shows that most of ils outlincs arc angulăr-serrate consisting of short, straight segments associaled in poli- gonal forms slrongly suggesling rhombohedra margins. In many instances the pellets show the deslruction of their outer paris along the contact between them ; in these cases the contact between them is usually masked by a thin strip of spar calcite (as in Fig. 6, lower left). All hese observations support the opinion eoncerning the replacement of the „intercorpus- cular” spar calcite’’by the diagenetic sequence of dolomitization-dedolomitization-local ag- grading j-ccrystallization : nelwork-like dolomitization develope on the small grains and margins of larger grains; dedolomitization leading to dcdolomitic microspar 8—20 in crystal size; local aggradalion of this microspar lo 30—60 micra pseudospar. The contact solution phenomena suggested by the deslruction of the pellets along their contacls involve a rather strong compaction before and during the circulation of the Solutions responsible for the „intercorpuscular” dolomitization. As regards the aggradalion of the originaEcxlremely fine micrite composing the outer paris of the pellets lo larger micrite, this process developed from pellet surface inwards and is thought to have taken place before the development of the above-mentioncd diagenetic se- quence, that is, it represents a penecontemporaneous process. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XlVa. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României \iGRy Institutul Geological României DrĂGĂNESCU. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XlVb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE XV (a, b) Cireșii sector Thin scctions in the core from 2 208 — 2 209 m depth (Complex 11) in drilling no. 9 p'ig. 1 — 8. — Details in the same pelletal grainsfones presented in thePl. XIV. Thereplacement origin of the spar „cement” by the diagenetic sequence of dolomitizalion-dedo- lomilization-local recrystallization is more obvious than in the previous plate : the pellets arc reoutlined, cut, more or less assimilaled or invaded by the „intercor- puscular” spar calcite; the edges of the spar calcite areas display angularilics suggesling margins of former dolomite rhombohedra. Many large pellets (Fig. 3, I. 8) show marked deformalions by fracturing followed by slipping of the resul- tant fragments along the fraclurc plancs, as well as parțial „melling”(obYious in Fig. 1, 3, 5) on account of contact solulion phenomena, proving that the pel- letal grainstones were submitted to rather slrong pressures before and during the development of the network-like dolomitization. The pholomicrographs, fol- lowing from Fig. 1 through Fig. 8, show an increasing in the intensity of the dia- genetic sequence, exhibiting Ihe resultant network-like spar calcite inscribing in a gradual scale from thin strips along the grain boundaries (Fig. 1) lo a spar groundmass accommodaling more or less deslroyed fecal pellets (Fig. 8). The eluslcr of pellets in the left of Fig. 2 represenls a relict, undismembered. small part of the original pelletal sand as it looked after the pore-compaetion and the aggradalion of the outer parts of the pellets lo coarser micrite have laken place and before the „intercorpuscular” dolomitization has starled. AH photographs under plane polarized light. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. cS Anuarul Institutului de geologie și geofizică, voi. XLVIII. 1GR Institutul Geologic al României Institutul Geological României Drăgănescu. Lower Cretaeeous Carbonate and Carbonate-Evaporite Sedimentation. PJ. XV Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR PLATE XVI (a, b) Circșu sector Tliin scclions in the cores l'rom drilling no. 9 i-'ig. 11. — Complex II (2 208 2 209 in depth). The same pelletal ealcareniles presenled in 1’1. XIV XV. The limeslones appcar slrongly ‘Tecryslallized” with pelletal relics floaling in a vcry finely or finely cryslalline calcilc; thcy stand for the extreme case ascertained within these pelletal ealcareniles, where the diagenetie sequcnce of dolomilizalion-dcdolomilizalion-reeryslallizalion reached the highest intensily, deeply penetrating the large pellcls and almosl completele’ consuming the smaller ones. Plane polarized lighl. l-'ig. 5. Complex 11 (2 279 —2 280.80 m depth). Micrile containing frequenl oslracods and numerous quartz grains. Plane polarized lighl. l-'ig. 6.— Complex 11 (2 279—2 280.80 m depth). Micrile containing large anhydrile micro- nodules (a) with felled texture. A large micronodule appears in the middlc left of the pholomicrographs, and other two micronodules are partly visiblc in the left and lower left of Ihe photomicrograph. Plane polarized lighl. l-'ig. 7. Complex 11 (2 279 2 280.80 m depth). Micrile(containing tiny quartz grains) crossed by a tliin evaporite veinlel (v) consisting of anhydrile and gypsum cryslals dis- posed quasiperpendicular lo the veinlel walls; the evaporite cryslals are noi parallel lo one anolher; some of Ihcm pierce Ihe veinlel wall. penetrating the hosl micrile. These observalions supporl a gravilalional aceumulation of frec cvaporile cryslals within a dessicalion crack, followed by in place growlh of some of the evaporite cryslals, those of an excessive growlh managing to exceed in Jength the veinlel widlh and lo penelralc the hosl micrile. N-p. l-'ig. 8. — Complex 11 (2 279— 2 280.80 m depth). Anhydrile exhibiling lalh-shapcd lexlure. Origin : anhydrile inlercalation of a bedded massive structure. X -J-. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XVIa. Anuarul Institutului de geologie și geofizică, voi. XLVIII. < Institutul Geological României \iGRy 0 Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XVIb. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic al României IGR/ PLATE XVII (a, b) Țăndărei sector Cote specimens from 620 -621 m depth (Complex II) in drilling no. 10 Fig. 1. — Core specimen showing a calcareous sequence containing three thin gypsum inlerca- lalions: the upper one (g,) with monocryslal heliăviour dîsplays streaky massive structure, while the two lower intercalations (g,and g3) arc obviously polycryslal- line and exhibit nodular to nodular-mosaic structure. The limestone consists ol a lower, stromatolitic level (s), and an upper, calcarenitic sequence (c) composed of microoncolilic-microcoprolilhic (fecal pellets) calcarenites with micrite matrix or gypsum cement. Fig. 2. — Core specimen consisting of two thin gypsum beds with nodular-mosaic structure dcveloped within the microoncolitic-microcoprolilhic ealearcnite (this last one preserved as a thin slrip in the middle of the core specimen, as remnants at the top and the botlom of the core specimen, and as calcareous fragments entrapped within gypsum beds among the gypsum nodules). Fig. 3. — The oposite side of the core specimen (upper half) presented in Fig. 1, showing the microoncolitic-microcoprolithic limestone and the thin gypsum intercalation with streaky massive structure (gt) cut across by a quasivertical, slightly wa- ved gypsum veinlet (v) containing rare angular calcareous fragments. Fig. 1. — Core specimen provided by a thick gypsum bed with nodular-mosaic lo mosaic structure. The inlernodular spaces arc filled up with greenish clay material. Fig. 5. — The oposite side of the upper half of the core specimen in Fig. -1, showing a well-visible gypsum nodulc (n). 1 ig, 6. — Core specimen proceeding from a thick gypsum bed with massive strm ture. This gypsum bed type is frec from clayey material. V Institutul Geologic al României c3 Anuarul Institutului de geologie si geofizică, voi. XLVIII. Institutul Geological României Institutul Geological României .. Drăgănescu. Lower Cretaeeous Carbonate anei Carbonate-Evaporite Sedimentation. Pl. XVIIb. <3 Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic al României PLATE XVIII (a, b) Țăndărei sector Details in the cores specimens presented in Pl. XVII, Fig. 1 — 2. Complex II, 620 — 621 m depth Fig. 1. — Detail in the upper middle of the core specimen presented in Pl. XVII, Fig. 1. The microoncolitic calcarenite, bearing a flat-pebble type, large intraclast (i), contains gypsum as cement and as a narrow baud (g^ of a streaky massive struc- ture (resulted from the local exccssive growlh of the gypsum cement). Fig. 2. — Detail in the upper part of Fig. 1, this Plate : microoncolitic calcarenite bearing a large intraclast (i) whose surface appears moulding the grains of the host sediment. The imprinting of the grains of the host calcarenite on intraclast surface proves the merely semiindurated state of the intraclast at the moment of its reworking and burial within microoncolitic sand. Fig. 3. — Detail in the middle of the core specimen in Pl. XVII, Fig. 1, showing the stroma- tolite (s)/calcarenite (c) contact. The calcarenitic sediment contains large intra- clasts of a flat-pebble type (1). Fig. 4 —6. — Details in the lower part of the core specimen in Pl. XVII, Fig. 1 : stromatolilic laminae (s) enclosing a thin gypsum bed of a nodular-mosaic structure (g3). Fig. 5—6 are enlargements in Fig. 4. Fig. 7. — Detail in the middle of the core specimen in Pl. XVII, Fig. 2 : two thin gypsum beds of a nodular-mosaic structure (g) separated by a thin calcarenite level (c) and containing calcareous fragments resulted from the disruption of the host calcarenite. Institutul Geological României Drăgănescu. Loiver Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XVIIIa o 1 2 3 4- 5 mm Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR Institutul Geologic al României A. Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XVIIIb. Fig.5,6:? ] j Șmm 7 1 cm Anuarul Institutului de geologie și geofizică, voi. XLVIII. 6 Institutul Geological României PLATE XIX (a, b) Țăndărei sector Core specimens from 631 — 635 m depth (Complex 11) in drilling no. 10 Fig. 1 — 2. — Core specimens of dolomite exhibiting waved laminar slruclure, the laminae being separated by rows of laminoid feneslrae. The slabs suggest former calcareous stromatolitic deposits subsequently dolomilizcd. Fig. 3 — 5. — Details in the dolomitized stromatolitic sequence from 63-1 — 635 m depth. The laminoid fencslral fabric is conspicuous in photos 3—4. The alternalion of dark and light levels, depending on the amount of organic maller entrapped within dolomite crystals, is clearly dcmonstraled by photo 5. Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XIXa. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României Institutul Geological României Drăgănescu. Lower Cretaceous Carbonate and Carbonate-Evaporite Sedimentation. Pl. XlXb- LO co Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României Institutul Geological României ORIGIN OF SOME MESOZOIC BASINAL LIMESTONES FROM THE REȘIȚA ZONE (SOUTH CARPATHIANS)1 BY GRIGORE POP2 Abstract Within the Reșița Zone the typical basinal carbonate sequence is represented by the Upper Oxfordian — Berriasian Valea Aninei, Brădet and Marila Limestones. Valea Aninei Limestones are differing from the other carbonate units due to the high frequency of alioda- pic limestones as well as banded and nodular cherts. Brădet Limestones occur in the marly nodular limestone facies, and the Marila Limestones are essentially made up of pelagic micrite containing calpionellids. In all these limestones micrites of pelagic origin are predominant, and their share increases from older to younger limestones and from east to west. The depo- sition of carbonate sediments took place in the outer part of the Reșița Trough, within its basinal margin and slope, bellow aragonite compensation depth and over that of calcite, through accumulation of pelagic particles as well as redeposition of some sediments, initially formed in shallow marine environments of the adjacent threshold (Semenic). Redeposition of non-consolidated sediments and reworking of the semi-consolidated ones occured through various submarine „flows” (slidings, semi-fluid flows, turbidity currents); owing to the sub- marine transport, sediments of diverse origin were mixed in various proportions and modes. Lithification of basinal sediments, selectively displayed as a function of their fabrics, has taken place through the compaction, neomorphism, parțial replacement by silica of bioge- nous origin, cementation, and locally dolomitization processes. Compaction, partially neomor- phism and cementation of sediments as well as their replacement by silica had occurred during a very early diagenetic stage. CONTENTS Page Introduction............................................................................ 58 Basinal Limestones ..................................................................... 59 Lithostratigraphic Units ................................................. 59 Constituents of Basinal Limestones ....................................... 65 1 Received on 23rd July 1975 and accepted for publica tion on July 30th 1975. 2 Institutul de geologie și geofizică, str. Caransebeș 1, 7000 București. 58 GR- POP 2 Genesis of Basinal Sediments ........................................................... 70 Main Types of Sediments and their Origin............................. 70 Mineralogical Nature of Carbonate Sediments.......................... 72 Deposition and Redeposition of Sediments............................. 73 Depth Deposition of Sediments........................................ 74 Paleogeographic and Paleotectonic Aspects............................ 76 Lithification of Carbonate Sediments.................................................... 81 Lithification of Carbonate Oozes..................................... 81 Genesis of Modular Limestones........................................ 83 Lithification of Allochthonous Allochemical Sediments................ 85 Silicification of Sediments.......................................... 87 Dolomitization of Sediments ......................................... 88 Conclusions .................................................................... 88 References.............................................................................. 91 INTRODUCTION Within the South Carpathians the Jurassie and Cretaceous carbonate formations occur in some areas known as „sedimentary zones”, and generally represent the Middle Jurassie to Aptian interval. In each of these main zones carbonate formations have a certain lithologic constitution and some lateral and vertical facies variations involving important petrological implications. The Reșița Zone is the innermost sedimentary zone within the South Carpathians and is located in the inner part of the Getic Reahn thus bordering to the west upon the Supragetic Unit. Within this zone the Upper Paleozoic and Mesozoic formations (Triassic, Jurassie and Lower Cretaceous) make up several frequently asymmetric and faulted longitudinal anticlines and synclines (Fig. 1). As a whole the Jurassie and Cretaceous sedimentary sequence consists of Lower Jurassie lacustrine conglomerates, sandstones and bituminous shales (< 500 m thick), Middle Jurassie to Hauterivian pre- dominant basinal limestones and marls (600—1000 m thick), Barremian- Aptian shallow water limestones (especially algal boundstones and grainstones) (300—600 m thick) and Albian and Cenomanian? glauconitic and calcareous sandstones (< 200 m thick) (see : Năs t ăs eanu, 1964). A few years ago the author began petrological investigations of the Mesozoic basinal and shallow water carbonate formations from the Reșița Zone; the results of this study, partially recorded in two unpubli- shed reports (Pop and Jeana lonescu, 1972 3; Pop, 19734), 3 Gr. Pop and Jeana lonescu. Petrological Study of the Mesozoic Carbonate Deposits from the Central Part of the Reșița Zone. 1972. (in Romanian) Arch. Inst. Geol. Geo- phys., Bucharest. 4 Gr. Pop. Petrological Study of Mesozoic Carbonate Deposits from the Northern Part of the Reșița Zone. 1973. Arch. Inst. Geol. Geophys., Bucharest (in Romanian). Institutul Geological României 3 IMESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 59 are going to be presented in several papers. The first paper will include the data concerning the sedimentary environments and some diagenetic aspects of the Upper Oxfordian-Berriasian basinal limestones. BASINAL LIMESTONES Lithostratigraphie Units The typical basinal carbonate deposits from the Reșița Zone are successively represented by the Valea Anin ei Limestones (Upper Oxfor- dian-Kimmeridgian), the Brădet Limestones (Lower Tithonian), and the Marila Limestones (Topmost Lower Tithonian-Upper Berriasian pro parte) Fig. 1. — General distribution of the Mesozoic sedimentary for- mations in the Reșița Zone (South Carpathians). Fig. 2. — Basinal carbonate sequence from the Reșița Zone. (Răileanu et al., 1957, 1964 ; M u t i h a c, 1959 ; Năstăseanu, 1964 ; Aurelia Bădăluț ă-N ăstăseanu, 1965 5; Pop, 1974) (Fig. 2; PL, Fig. 1). 5 A u r e 1 i a Bădăluț ă-N ăstăseanu. Geology of the Anina Area with Parti- cular View on Jurassic (Reșița Zone, Banat). 1965. Summary of the Dissertation Thesis (Unpu- blished, in Romanian). Institutul Geologic al României 60 GR- POP 4 Between these limestones there is a gradual passage. The basinal carbonate sequence is passing in the same manner both to the older Tă- mașa Marls (Upper Callovian-Lower Oxfordian) and to the younger Crivina Marls (Upper Berriasian pro parte-Valanginian). Only in the eastern part of the Reșița Zone the Valea Aninei Limestones transgres- sively and unconformably overlie older sedimentary formations as well as the metamorphic basement. The thickne. s of basmal limestones di play longitudinal and, par- ticularly, transversal variations. Thus in the central part of the Reșița Zone their thickness attains its maximum while in the marginal areas of this zone (eastern and western) it is decreasing. The three basinal carbonate units may be easily recognized owing to the higher or lower frequency of certain limestone types and also of cherts. Valea Aninei Limestones. This lithostratigraphic unit lithologically 6 is the most varied being made up of different pelagic and allodapic limestones 7 as well as transitional fabrics between the two main group of limestones and frequently bedded and nodular cherts(Pl. I, Fig. 2 ; Pl. II, III, IV, Fig. 1; Pl. VII-IX, X, Fig. 1-4). Pelagic limestones having the highest share especially consist of micrite and biomicrite containing corresponding skeletal grains (calci- tized radiolaria and sponge spicules and scarce thin-shelled bivalves, cadosinids, Globochaete and belemnite guards), micrite nodules (intra- clasts) and pelletoid particles, and subordinately nodular limestones (intramicrudites or nodular packstones) which also include certain fraction of some of the above mentioned allochems. Allodapic limestones representing almost half of the bulk of the Valea Aninei Limestones are composed of skeletal, intraclast, pelletoid and pelletal grainstones-packstones whose allochems consist of more or less sorted and micritized crinoids, pelecypods, benthonic foraminifera, algal crust and structure grains, shallow water and basinal intraclasts (s.l. F o 1 k, 1962), pelletoids and pellets. These allochems and also the pelagic fraction ent-ail various mixtures thus resulting different hcmo- geneous to non-homogeneous carbonate fabrics. In the eastern part of the Reșița Zone the crinoid biosparites are very frequent. Generally the frequence of allochemical limestones decreases from east to west. Locally in these deposits early diagenetic dolomitized limestones are encountered (Vîsoki Hill, Caraș Valley) (Fig. 3). AII these basinal limestones usually occur as clear-cut strata lying in direct contact or being separated by a shale pellicle and/or by banded cherts. Frequently the contact between two successive strata is of sty- lolite nature; such contacts are more frequently encountered among 6 In this paper is essentially used the F o 1 k’s (1962) and D u n h a m’s (1962) carbonate rock classification terminology. ’ Allodapic limestones (M e i s c h n e r, 1964) here designate all the limestones resul- ting from carbonate sediments formed in shallow water, and then transported and resedimented in basinal areas. Institutul Geological României 5 MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 61 allodapic limestones or between these limestones and the pelagic micrites. Allodapic limestones often display parallel and oblique laminae and oc- casionally graded bedding. Fig. 3. — Parțial sequences in the Valea Aninei Limestones froin the Visoki Hill (lower (I) and middle (II) parts) and from north of Anina (basal (III) and middle (IV) parts). 1, pelagic micrite and biomicrite sometimes containing pelagic micrite nodules (intraclasts) (a) and nodular micrite (b); 2, allodapic packstones-grainstones including pelagic micrite intra- clasts ; 4, pelletal and pelletoid packstones-grainstones; 5, banded and nodular cherts; 6, dolomitized allodapic and pelagic limestones; 7, moderately dolomitized limestones; 8, stylo- lites; 9, parallel and oblique laminae. Institutul Geological României 62 GR. POP 6 The thickness of strata shows a certain tendency depending on the limestone fabrics; in this way the highest frequency is niarked by strata whose thickness ranges from 16 to 32 cm, and which are predominantly built up of micrites; as the thickness of beds decreases they are to an ever larger extent represented by micrites of pelagic origin. Beds whose Fig. 4. — Thickness frequency of beds and their fabrics in the Valea Aninei Limestones. a, pelagic sometimes nodular micrites and biomicrites; b, allo- dapic packstones-grainstones containing pelagic micrite intra- clasts ; c, allodapic pelletoid, pelletal and skeletal grainstones- packstones including pelagic micrite intraclasts; d, dolomitized allodapic and pelagic limestones. thickness exceeds 32 cm are rather made up of allochthonous allochems (Fig. 4). In the Valea Aninei Limestones there are two or three massive limestone intercalations which are not reef limestones (Năstăseanu, 1964) but represent basinal heterogeneous mixtures of various shallow water and pelagic carbonate grains, wherein the latter often constitute a large fraction (Pl. I, Fig. 2 ; Pl. III, Fig. 3). Valea Aninei Limestones often exhibit synsedimentary simple to intricate slump-folds and gravitațional slidings; slump-fold aspects and the westward dip of slide planes in relation to bed surfaces point out Institutul Geological României 7 IMESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 63 almost always a corresponding dipping of the sea floor, inclusively in the innermost part of the Reșița Zone (Ciudanovița). B rădet Limestones. This lithostratigraphic unit also known under the name of „nodular limestones” is made up to a great extent of Fig. 5. — Parțial sequence in the Brădet Limestones from the Miniș Valley (south-west of Anina). 1, nodular limestones; 2, nodular micri- tes and biomicrites; 3, marly nodular limestones; 4, marls: 5, banded and nodular cherts; 6, biopelsparites. pelagic limestones and only scarcely of allodapic ones (Fig. 5). The pelagic limestones are represented prevalently by typical grey and greenish no- dular limestones and subordinately by nodular micrites and biomicrites. These limestones are more or less argillaceous and the matrix of the nodules is occasionally weakly to moderately dolomitized. Besides mi- crite and biomicrite nodules, the alloehems of these limestones consist of skeletal grains and rare pellets. The skeletal particles are represented by common to abundant Saccocoma and Globochaete, rare thin-shelled bivalves, calcitized radiolaria and accidentally some benthonic foraminifera. These 64 GR. POP 8 limestones locally contain ammonite moulds and opercules {Aptychus), belemnite guards and brachiopods {Pygope and others). Allodapic intercalations are built up of generally well sorted and in some cases poorly washed pelsparites and crinoid biopelsparites. These Fig. 6. — Thickness frcquency of beds in the Brădet Limestones. a, pure and marly nodular limestones; b, nodular micrites and bioinicritcs; c, marls. limestones are relatively scarce or are missing, only in the eastern part of the Reșița Zone they are more frequently encountered. The Brădet Limestones include thin mari and silty mari interca- lations with frequent irregular micrite and biomicrite nodules. Cherts are much less frequent than in the Valea Aninei Limestones and occur as nodules and lenses and only rarely as thin beds (Fig. 5). Although apparently the Brădet Limestones consist of a relatively small number of carbonate fabrics the transitional structures among them, the different content of the limestones in argillaceous matter and the presence of the mari intercalations amplifies their rock variety (Pl. IV, Fig. 2 ; Pl. V, VII; Pl. X, Fig. o, 6 ; Pl. XI, Fig. 1-4). Generally the Brădet Limestones occur as well bedded limestones whose average thickness is ranging from 16 to 32 cm (Fig. 6); the more conspicuous their bedding the smaller their content in argillaceous matter. The upper part of some limestone beds is richer in argillaceous matter and commonly contains micrite nodules ; in other cases in the same upper part of a bed the carbonate fraction shows the tendency to form an incipient nodular structure. In such situations either the upper surface of beds is less distinct or the limestones display a transition to- wards the covering mari intercalations which usually show subdeci- metric thicknesses (Pl. IV, Fig. 2). 9 (MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 65 The Brădet Limestones present various synsedimentary gravita- țional deformations (slump-folds, sliding planes) which constantly indi- cate slidings towards the western part of the Reșița Zone (Pl. V, Fig. 2). Marila Limestones. These limestones are the most homo- geneous basinal carbonate deposits and are prevailingly formed of micrites of pelagic origin bearing calpionellids. Subordinately, especially in their lower part, there are some intercalations of nodular micrites and almost typical nodular limestones, occasionally weakly or moderately dolo- mitized; this lithostratigraphic unit also includes allodapic well sorted pelsparite and crinoid biopelsparite intercalations, sometimes intraclastic, and in their upper part — thin marls and shales. The Marila Limestones scarcely contain nodular and lens-like cherts (Pl. XI, Fig. 5, 6 ; Pl XII). The petrographic monotony of the Marila Limestones is doubled by their stratonomic uniformity, the average thickness of the limestone beds being close to 20—40 cm. Locally these limestones display at some stratigraphie levels westward oriented synsedimentary slump-folds. Constituents of Basinal Limestones The major carbonate and non-carbonate constituents of rocks dis- play both common and peculiar aspects in the three above described lithostratigraphic units. These constituents are microcrystalline calcite, allochems, sparry calcite, dolomite crystals, siliceous minerals and ter- rigenous particles. Microcrystalline calcite. The very fine-grained calcite is the principal constituent of micrite and of certain allochems and their matrix, forming the basinal allochemical limestones. In pelagic limestones such calcite occurs under the form of a non- homogeneous microcrystalline mosaic wherein the calcite crystals display a varied size-range in the limits corresponding to this end member of car- bonate rocks (F o 1 k, 1959, 1962). Occasionally in micrites there are encountered irregular patches bearing no relation to the bedding in which calcite has been converted entirely into microspar (< 10 p.). The size varia- tions of the microcrystalline calcite are more pronounced in biomicrites. In micrite limestones containing argillaceous matter from the Brădet Limestones and from the upper part of Marila Limestones such calcite particles are more fine-grained and more uniform in size. These rela- tionships seem to be general in the case of studied basinal micrite limestones, so one may admit that as the content of argillaceous matter decreases the microcrystalline calcite displays ever more varied shapes and sizes. In contrast with calcite from pelagic micrite, the microcrystalline calcite from allochthonous allochems is more fine-grained and more uni- form in size; this is the result of micritization processes of allochems in original shallow water environments. Allochemical grains. In basinal limestones these grains in- clude nodules, intraclasts, bioclasts, pelletoids, pellets and rarelyooliths. Allochems here named „nodules” are always made up of micrite and biomicrite of pelagic origin and are the major constituent of the so- - o. 11 Institutul Geologic al României igr/ 66 GR. POP 10 called „nodular limestones”; likewise these allochems are often encoun- tered as subordinate constituents in other basinal limestones of pelagic and allodapic origin. In many cases the nodules may be distinguished from their micrite and biomicrite matrix through their more finely grain- sized microcrystalline calcite, the differences in density and orientation of skeletal particles and their slightly different colour due to a certain content of argillaceous matter, organic substance and ferromanganese impregnations. Their contours are either sharp, sometimes partially or entirely outlined by neomorphic microsparite pellicles, or diffuse; the former display varied shapes (irregular, angular to rounded), and are poorly sorted although in each case taken separately most of them are comprised among certain dimensional limits. In some cases the nodules present an internai compound nodular structure indicating intraformational rework of such cohesive sediments, and other times they are surrounded by a more or less developed micrite coat of oncolithic type which is more dense and clouded and sometimes includes calcitized radiolaria and other planktonic calcite bioclasts ; some nodules do also contain ammonite moulds and tabular bioclasts inter- sected by their edges, a fact proving their detrital origin. When the mi- crite matrix of the nodular limestones has been more or less dolomitized the nodules did undergo dolomitization only to a very insignificant extent. In allodapic limestones (especially in the Valea Aninei Limes- tones) nodular grains are associated in varied proportions with shallow water allochems from which they may be easily distinguished through their pelagic micrite fabric and planktonic microorganism content; at the contact with other allochems, nodular grains present varied mecha- nical deformations. In nodular limestones the internodular contacts often are stylolitic. Nodular grains frequently include the same planktonic microfauna as their micrite and biomicrite matrix; this fact is more conspicuous in the Brădet Limestones and in the lower part of the Marila Limestones where both these grains and their matrix contain the same Saccocoma, and, respectively, calpionellid assemblages (Pl. V, Fig. 1; Pl. VI, Fig. 1; Pl. VII, Fig. 3-6 ; Pl. VIII, Fig. 1; Pl. IX, Fig. 3,5 ; Pl. X, Fig. 6 ; Pl. XI, Fig. 1-4,6 ; Pl. XII, Fig. 1-5). Basinal limestones contain both nectono-planktonic skeletal par- ticles, some of them specific to certain stratigraphic intervals and alloch- thonous bioclasts initially formed in shallow marine waters. The first group of skeletal grains includes more or less frequent cal- citized radiolaria and sponge spicules, pelagic crinoids of Saccocoma type, Globochaete, calpionellids of the Crassicollaria, Calpionella and Calpionel- lopsis Zones, fine bivalves, cadosinids, ammonite moulds and opercules (Aptychus), brachiopods, belemnite guards, very rarely benthonic fora- minifera and in addition other skeletal fragments of unknown origin. These bioclasts occur only in the pelagic limestones or fractions. The second group forming allodapic limestones consists of crinoid monocrystallindicalcite associated with polycrystalline molluscan frag- ments, benthonic foraminifera (textularids, miliolids), algal micrite Institutul Geologic al României \ksrz 11 MESOZOIC BASINAL LIMESTONES. — REȘIȚA ZONE 67 crusts and structures, corals and rarely bryozoans. All these bioclasts are more or less micritized some of them to an extent that does not allow to recognize their particular aspects. Among skeletal grains from allodapic limestones only crinoid particles reach corresponding abun- dance to form peculiar fabrics such as the crinoid biosparites, which are very frequent in the Valea Aninei Limestones from the eastern part of the Reșița Zone. Occasionally the tabular molluscan bioclasts underwent some intrastrata] fragmentations during the compaction of sediments. Allochthonous allochems are also built up of micrite, pelsparite and biopelsparite intraclasts commonly poorly sorted and variably shaped. These intraclasts represent fragments of algal crusts and of very early lithified carbonate sediments and eventually „lump”, „grapestone” and „micrite aggregate” type structure, originated ih shallow marine waters. Pelletoids and pellets are often encountered in different allodapic limestones and are the major constituent of pelmicrites, pelsparites, and biopelsparites scarcely occuring in the three lithostratigraphic units. These grains are of varied origin (see : B e a Îs, 1965), however, most of them represent micritized allochthonous bioclasts. In the Brădet and Marila Limestones there are some pelletal limestones wherein these grains are of smaller size (30—40(4) and better sorted. 8 p a r r y calcite. Calcite from basinal limestones occurs under the form of microspar and coarse spar. Microspar is encountered as patches in micrite matrix of some al- lochemical limestones, within some allochthonous grains and as liant in intergranular and intraskeletal spaces. In the last case the microspar is inade up of relatively uniform-sized crystals or forms finely bladed and fibrous crusts covering allochems and filling intrasveletal voids. These crusts are limited outside by equant microspar or coarse spar and by the micrite matrix (Pl. VIII, Fig. 6; Pl. IX, Fig. 1—4). The coarse-sparry calcite mainly occurs in intergranular spaces of better sorted allochemical limestones where it forms varied-sized crystals and overgrowths in lattice continuity, especially on the crinoid monocrys- talline grains. Such calcite crystals either entirely occupy the intergranular spaces or are limited outside by equant or radial-fibrous microspar. In some cases one may observe two or three generations of overgrowths and their „zig-zag” boundaries (Pl. VIII; Pl. IX, Fig. 1, 4). Dolomites. In the lower and middle part of the Valea Aninei Limestones there are dolomite rocks which form either compact intervals ofvariablethickness,occasionally reaching 50-70m (VîsokiHill),or subor- dinate intercalations. These rocks are built up of equant anhedral to euhedral dolomite mosaic containing some relics of inițial sediments (finely disseminated clouded argillaceous and (or) organic matter, calci- tized radiolaria and rarely benthonic foraminifera). Dolomite crystals (100—500 p) do often have zoned rhombohedral shapes. In some strata the distribution of relics is variable and imitates the arrangement of parallel and oblique laminae of original carbonate sediments. Intercrystalline spaces are filled with calcite as shown by Alizarin Red S staining. In dolomite rocks one may observe some joints where •;M Institutul Geologic al României \IGRZ 68 GR. POP 12 intersected dolomite crystals are regenerated ; regenerated parts of these crystals are lacking relics and are bordered by calcite filling the joints. Dolomite rocks show the same bedding as limestones and contain banded and rarely nodular cherts. Sometimes the dolomite intervals have parallel limits in relation to the bedding of the limestones, but in other cases these limits seem to intersect some limestone beds. In dolo- mite intervals slump-folds or other synsedimentary gravitațional defor- mations have not been observed (Pl. IV, Fig. 1). In some nodular limestones from the Brădet and Marila (lower part) Limestones the matrix usually contains up to 30 per cent of rhorn- bohedral fine crystalline dolomite. Accidentally such crystals do also occur in the nodular grains. In some cases dolomite crystal spaces are oecuppied by „dedolomite microspar”; likewise, dolomite rhombohedra are very seldom replaced bv microcrystalline calcedony (Pl. XI, Fig. 2,3 ; Pl. XII, Fig. 3-5). Cherts. Siliceous rocks occur as bedded, lens-like and nodular cherts. Bedded cherts appear as thin bands between limestone beds and within some micrite ones. Lenticular and nodular cherts display a similar distribution ; nevertheless these cherts seem to be chaotically distributed in micrites and more orderly distributed in allodapic limestones where thev are situated on the planes of some parallel and oblique laminae (Fig. 3; Pl. II, Fig. 1; Pl. III, Fig. 1,2). Cherts are composed of microscrystalline or fibrous quartz and probably cristobalite. AII the cherts are diagenetic products and resulted from silicification of carbonate sediments (Pl. X, Fig. 2). Bedded cherts are frequently encountered in slump-folds ; likewise the presence of graded nodular cherts in some allodapic limestones from the Anina Valley (Valea Aninei Limestones) is to be noticed. In some biosparites the crinoid grains are occasionally substituted by silica. A o n-c arbonate terrigenous particles. These par- ticles are present in a small amount in the basinal limestones under the form of sand — to silt-sized grains and clayey minerals. The terrigeneous grains are represented by quartz, feldspars (some- times secondarily regenerated), muscovite and very seldom amphiboles (hornblende). They are met only at certain stratigraphic levels and are commonly associated with allochthonous carbonate grains (Pl. X, Fig. 1). Generally, in the eastern part of the Reșița Zone the content of th e limestones in terrigenous grains is higher and at more stratigraphic levels than in the western one ; this rise in terrigenous content from west to east is accompaniecl by an increase in grain-size. Thus the crinoid bios- parites from the lower part of the Valea Aninei Limestones occuring in the eastern part of the Reșița Zone contain up to 30 per cent of sand- sized non-carbonate terrigenous grains. Clay minerals are widespread in almost all basinal rocks, especially in the mari intercalations and limestones from the Brădet and Marila (upper part) Limestones. 16 R/ Institutul Geologic al României 13 MESOZOUC BASINAL LIMESTONES — REȘIȚA ZONE 69 Taking into account the manner under which the major consti- tuenta of the basinal limestones from the Reșița Zone occur, one may notice that within these limestones fine-grained calcite particles prevail, especially representing nannoplankton skeletons; these particles are relatively non-uniform sized in chemically purer limestones and more uniform-sized and finer grained in the limestones containing more than about 2 % argillaceous matter. As a. whole, the amount of microcrystalline calcite from the basinal carbonate units increases from the older limestones to the younger ones. Allochthonous allochemical grains are generally poorly sorted and associated in different manner with pelagic microcrystalline calcite. As the sorting of these grains increases their liant is made up of coarser calcite and the micrite intraclasts show ever more pellet shapes; also as the amount of such allochthonous grains and their sorting increase, the al- lodapic limestone beds tend to become thinner and present more fre- quently parallel and oblique laminae. Dolomite crystals from the Brădet and Marila Limestones, usually euhedral and finely crystalline are found more frequently in the micrite matrix of nodular grains, which has often a small content of argillaceous matter and silty grains. In basinal limestones one may notice a positive relation between the frequency of cherts and the amount of calcitized radiolaria. The same positive relation is found between the frequency of allochthonous allo- chems and those of silt and sand terrigenous grains. As regards fabric and stratonomical aspects in time one may state in the basinal carbonate sequence a decrease in the amount of allochthonous carbonate grains accompanied by an increase of their sorting degree, gradual uniformity of pelagic composition and bedding of the limestones, the diminution of chert frequency and calcitized radiolaria and a decrease of the number of synsedimentary gravitațional deformations. At the boun- dary between the Valea Aninei and the Brădet Limestones a rather sudden diminution of the allodapic frequency takes place. In space starting from the outer part (east) towards the inner part (west) of the Reșița Zone one may observe a lowering of the number of allodapic intercalations concomitantly with the increase of grain sorting diminution of bed thickness, also involving the massive intercalations from the Valea Aninei Limestones, and the decrease in frequency of the synsedimentary gravitațional deformations (distal aspects). Thus, the Upper Oxfordian-Berriasian basinal limestones generally display a slope facies in the outer and central parts of the Reșița Zone and a basin margin facies in the inner part of this zone (see also W i 1 s o n , 1970). GENESIS OF BASINAL SEDIMENTS Petro logica! aspects of basinal limestones from the Reșița Zone are indicative of the source of the sediments, their original mineralogica! setting and the sedimentary environments. ||hy Institutul Geologic al României IGR/ 70 GR- POP 14 Main Types of Sediments and their Origin Following up the share of various carbonate structures in basinal limestones it may be readily stated that their sediments Avere made up of carbonate ooze, nodular ooze and of allochthonous allochemical sedi- ments (Fig. 7). Brac/et i/mestones ,Va/ea Anine/ Limestones( Aia/or cartonate depos/tiona/ environments Sas//? Basin s/ope Sheif or thresMd Fig. 7. — Deposition environments and the main sources of the basinal sediments from the Reșița Zone. a, pelagic particles ; b, shallow marine sediments redeposited as a result of submarine transport; c, reworking of the basinal sediments; d, detrital particles originated in some littoral and landmass areas and subsequently deposited in the basinal areas by the eolian transport. Carbonate oozes. The formation of such oozes characte- rized the basinal sedimentation; they are usually proceeding from the accumulation of planktonic microorganism skeletons, espacially of coc- coliths. Nowadays it is known that the so-called „pelagic limestones” do, to a great extent, consist of nannoplakton skeletons (see : G a r r i s o n , 1967 ; G a r r i s o n and F ischer, 1969 ; F ii g e 1 et al., 1968 ; F a - r i n a c i, 1969 ; J e n k y n s , 1970 a, b, 1971, 1972 ; B ernoulli, 1971, 1972 ; B e r n o u 11 i and J e n k y n s , 1970 ; and others). On ac- count of this fact, one may assume that the basinal fine-grained carbonate sediments from the Reșița Zone chiefly consist of nannoplankton skeletons. A certam amount of carbonate oozes probably originated in the adjacent shallow marine areas where they initially formed through gene- rally known processes (M a t h e w s , 1967 ; S t o ckm an et al., 1967). It is presumable that at least a part of the dolomite crystals from the Brădet and Marila Limestones have detrital cores which previously for- med in the same areas. The non-uniform fine-grained character of carbonate oozes has been, to a great extent, determined by the inițial sizes of skeletal parti- 15 MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 71 cles o f pelagic origin to which have also contributed repeated resedimen- tation phenomena, through which these particles were partially desinte- grated in their component parts, eventually their parțial solution at the water/sediment interface and subsequent neomorphism processes. Nodular sediments. As a w’hole the micrite nodules from the nodular limestones are considered to be of an early diagenetic nature. Undoubtedly, the observations on nodular limestones from the Reșița Zone pointed out that in the genesis of nodular structures an essential role was played by the early lithification of carbonate ooze. Howeve, the study of nodular limestones and of other types of limestones including micrite nodules supplies us with evidence that a large part of these nodules are intraclasts and to a lesser extent the products in situ of a specific diagenetic process affecting the carbonate oozes. The intraclastic nature of nodular structure is illustrated by follo- wing aspects : — compound structure of some nodules and their occurrence along with homogeneous micrite nodules in the same bed; — association of nodules with allochthonous allochems in allodapic limestone beds with current laminae and graded bedding; — a usually chaotic mixture of nodules with other types of sedi- ments within the massive intercalations of the Valea Aninei Limestones where portions of some slump-folds are also recognized; — different density of bioclasts and the chaotically variation of colours of nodules in the same bed, aspects which also distinguish the nodules from their micrite matrix; commonly the density of bioclats is less pronounced in nodules than in their matrix; — occurrence in some nodules of skeletal elements truncated by the contour of the nodules ; — the frequently finer-grained character of the nodules in compa- rison with their micrite matrix and their local presence only at some levels or within the whole bed of micrite or biomicrite, practically pure from the Chemical viewpoint, and with no signs of diagenetic segregation. The contacts among the nodules or between these and |their ma- trix, the shape and size of nodules are rather varied; they are controlled both by the different coherence degree of sediments in course of conso- lidation, reworked as nodules, and by the subsequent lithification of nodular sediments. For this reason, the parțial or whole transitional contacts between nodules and maxtrix or between two nodules, for ins- tance, do not exclusively prove the formation in situ of nodules but also the possibility that the latter should represent reworked grains which have been diagenetically welded with the surrounding mass of sediments. Consequently, the intrabasinal reworking of some pelagic more or less Consolidated carbonate sediments led to the formation of nodular sediments with a fine-grained matrix. The micrite nodules probably arose through reworking of some nodules and nodular sediments already diagenetically formed or in course of formation and through the fragmen- tation of some crusts or beds of more or less lithified micrite sediments, with subsequent transport and deposition of the carbonate clasts. The M Institutul Geologic al României JGR/ 72 GR. POP 16 last case is particularly evidenced by the existence of some intercalation of micrite breccias in the Brădet Limestones also containing some al- most rounded micrite grains (Pl. VI, Fig. 2). Such grains at least should be at the origin of some nodular structures. Moreover in many cases the well bedded carbonate sediments, including the nodular ones, represent the effect of resedimentation. Allochthonous shallow water sediments. The genesis of pelagic sediments was accompanied by the accumulation of some allochemical sediments previously formed in adjacent shallow marine environments. Their redeposition has been very frequent during the deposition of the sediments of Valea Aninei Limestones, and progres- sively more seldom, during the accumulation of those of Brădet and Marila Limestones. The allochthonous sediments were to a large extent composed of marine shallow water bioclasts and compound grains (intraclasts s.l., F o 1 k, 1959,1962), pellets and pelletoids and rarely coated grains (ooliths, oncoliths). These allochemical sediments have been almost always mixed in various proportions with the pelagic ones through reworking and redeposition of the latter as matrix or intraclasts. The share of the diverse allochems was different determining the formation of sediments with frequently non-homogeneous fabrics. As a whole, however, during the Upper Oxfordian and the Kimmeridgian the supply in intraclastic (s.l.) and skeletal sediments (particularly crinoidal ones), prevailed especially in the eastern part of the Reșița Zone, whereas during the Tithonian and Berriasian in the basinal areas chiefly pelletal and pelletoid sediments have been redeposited. N o n-c ar b o n at e sediments. The accumulation of both pe- lagic and shallow water sediments was accompanied by the deposition of planktonic siliceous skeletons and of some terrigenous clayey, silty and sand-sized particles. The siliceous particles accumulated as radiolaria skeletons and sponge spicules and they sometimes were an important constituent of carbonate oozes. According to the frequency of calcitized radiolaria and of cherts in basinal limestones, the climax in prolificity of the siliceous organisms (particularly of radiolaria) coincided with the formation of the Valea Aninei Limestones, subsequently their amount noticeably decreasing. The terrigenous sediments have originated in some land and littoral areas from which they were transported in basinal environments, some of them together with shallow water carbonate sediments. The deposition of argillaceous particles has been probably more intense during the Lower Tithonian and since the Upper Berriasian. Mineralogical Nalure of Carbonate Sediments The mineralogical composition of inițial carbonate sediments may be generally estimated relying on major constituents of basinal limestones. Thus the fine-grained sediments of pelagic origin were composed of Institutul Geologic al României igr/ 17 MESOZOTC BASINAL LIMESTONES — REȘIȚA ZONE 73 low-magnesian calcite which formed the skeletons of the nannoplankton and other planktonic microorganisms (probably calpionellids, Saccocoma, cadosinids and others). Belemnite guards, ammonite opercules and bra- chiopod shells, sporadically encountered in these limestones, are made up of the same mineral species. The high-magnesian calcite constituted a reduced fraction in the pelagic sediments, being included in the tests of rare benthonic forami- nifera met with especially in the Brădet Limestones ; the aragonite with a similar content was present in the ammonite shells which have been, however, dissolved under submarine or intrastratal conditions very soon after their deposition. The shallow marine carbonate sediments redeposited in the basinal area were probably formed to a great extent from aragonite and high- magnesian calcite. The inițial pelagic sediments comprised likewise numerous opaline skeletons (especially radiolaria), which in a certain time interval (Upper Oxfordian — Kimmeridigian) have been an important constituent of car- bonate oozes. Deposition and Redeposition of Sediments The structures, textures and bedding of basinal limestones are sug- gesting that the accumulation of sediments represent a single effect or in many cases a combined one of several „mechanisms” such as : partide by partide deposition, resedimentation and submarine slidings of semi- consolidated sediments. The planktonic skeletal particles have accumulated through par- tide by partide deposition ; in the same way a part of the argillaceous and other terrigenous particles has been deposited as a result of eolian transport from land areas in marine ones. Owing to the slow and pro- bably discontinuous deposition the carbonate and non-carbonate particles have accumulated as relatively thin strata of homogeneous composition. In many cases, however, the particles deposited through the general processes of pelagic sedimentation were resedimented by several types of submarine „flows” ; the redeposition has been particularly con- trolled by the submarine slope and its relief, by the subsidence regime (conjunction with certain fractures probably situated between trough and threshold) as well as by the physical properties of the sediments. Under the influence of these factors the non-consolidated fine-grained sediments were frequently drawn into submarine semifluid flows often evolving into turbidity currents ; the more or less Consolidated sediments have been submitted in many cases to gravitațional slidings accompanied by various deformations. The redeposited non-consolidated sediments have been systematically retextured, and the submarine slidings gave rise to varied styles of simple to intricate, plastic to ruptural deforma- tions ; in the case of weekly Consolidated sediments these deformations have sometimes caused the destruction of their inițial fabrics and the UL- Institutul Geologic al României 16 RZ 74 GR. POP 18 formation of news ones, aspects already known in such limestones (B e r- noulli, 1971). One of the more striking effects of the resedimentation has been the transport of sediments formed in shallow marine areas and their rede- position in basinal environments. Their transport in deeper marine areas has been chiefly carried out by turbidity currents which led to the formation of allodapic limestones frequently displaying gradded bed- ding and parallel and oblique laminae. The fabrics of these limestones also point out the fact that the transport of shallow water sediments also involved a various amount of non-consolidated and semi-consolidated sediments of pelagic origin from the higher parts of the basin slope towards the deeper ones. Subsequently these pelagic sediments have been rede- posited as matrix of shallow water grains, as intraclasts with varied con- tours depending on the eompetence of reworked sediments, and as parti- cles in the fine-grained intervals from the upper part of turbidite beds. Accordingly, under control of the basin slope and of the movements to which it was submitted, the sediment bodies, exceeding a certain cri- ticai volume, have undergone slidings; these sediment slidings being at the origin of many resedimentation processes have often evolved into semifluid and turbulent flows determining the formation of fluxoturbidite and, respectively, turbidite limestones. The various ways of submarine reworking of sediments were probably interrelated, so that the display of one of them could have induced a ,,chain reaction” owing to which the sediments were affected by several types of submarine flows. Some of these combined submarine flows were recognized in two or three massive intercalations from the Valea Aninei Limestones which are in fact basinal heterogeneous limestones, a chaotical mixture of pelagic and shallow water sediments displaying slump-folds, formed by wide-scale redeposition of such sediments. The frequency of effects caused by gravitațional slidings and rese- dimentation is differing from an area to another and also from one stra- tigraphic interval to another suggesting certain variations of the submarine relief. Generally, however, one may notice their decrease from east to west and also from the bottom to the top of the sequence; likewise the allodapic Ihnestones have in the same sense the tendency to show a distal aspect. These facts reflect a corresponding attenuation of submarine slope and progressively a more distant redeposition of sediments from their source. Depth Deposition of Sediments The interpretation of depth deposition of basinal carbonate sedi- ments is so far a most delicate probleme since this depth implies not only paleogeographic aspects and their tectonic control but also its influence on the sedimentation of previously deposited sediments. Upper Oxfordian-Berriasian limestones from the Re.șița Zone were commonly considered of bathyal origin taking into account the classical criteria, chiefly the presence of ammonite moulds and of planktonic 19 MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 75 microfauna (see : E ă i 1 e a n u et al., 1957). Aetually, one may notice the pelagic nature of these limestones as well as the absence of features pointing to deposition in shallow marine environments; in these limes- tones one may observe lack or scarceness of some aragonite shells (which could have been replaced by calcite) owing either to their solution on the sea floor or in intrastratal conditions under a certain depth, scarceness of benthonic organisms, especially as a result of lack of food, presence of chert and allodapic limestones and, in general, the lateral persistence of beds. AII these elements evidence the bathyal depth of formation of basinal limestones. However, these criteria have a relative character and hence the above mentioned aspects of limestones are likewise reflecting relative depths (H a 11 a m, 1971). For this reason basinal limestones with similar facies as a whole were considered to have formed at depths of some hun- dred to about a thousand meters (Be r n o u 11 i and J e n k y n s, 1970 ; B e r n o u 11 i, 1971, 1972 ; W i 1 s o n, 1969) or even exceeding 4 000 meters ( (G a r r i s o n, 1967 ; G a r r i s o n and F i s c h e r, 1969). When appreciating the deposition depth of ancient carbonate se- diments, in most cases data relating to the depth accumulation of recent pelagic carbonate oozes have been considered. When estiinating the ionic activity products it has been stated that the superficial marine waters are saturated and supersaturated with respect to all CaCO3 phases and are undersaturated in this respect with increase of their depth owing to increase of total pressure and CO2 pressure and decrease of temperature (Berner, 1965; Pytkowicz, 1965), facts subsequentlyverified in the waters of Central Pacific (Pete r s o n, 1966 ; B e r g e r, 1967). According to Huds on (1967), if the solubility product of aragonite changes like that of calcite as a function of pressure and temperature, aragonite becomes thermodynamically soluble in ocean waters at a shal- lower depth than calcite, a fact later proved by L i et al. (1969), and assigned to the different amounts of CO2 dissolved in these waters. This differences in saturation of marine waters with respect to CaCO3 as well as of solubility of aragonite and calcite would have accounted for the scarceness of aragonite organisms, preserved only as moulds, and the preservation of calcite skeletal grains (ammonite opercules, belemnite guards, brachiopod shells, crinoid pieces and others), which only very seldom present irregular traces of corrosion. If we take into account the fact that in warm seas, as those of the Jurassic, the aragonite and calcite solution rate might have been higher than nowadays, and that these mi- nerals were submitted to an essential solution at comparatively shallower depths, we have grounds to admit depths of probably some hundredto about a thousand meters, for the accumulation of the Upper Oxfordian- Berriasian carbonate sediments. Besides, as noticed by Hudson (1967) and Jenkyns (1970), it seems that traces of submarine solution of carbonates from ancient fossils and sediments are not necessarily indica- tive of great depth of sea waters. JA Institutul Geological României igr7 76 GR. POP 20 The mere fact of the increase of depth does not implicitely mean a corresponding solution of carbonates in sea water, the formation of car- bonate particles and their accumulation showing a complex character. In near-surface sea waters (photic zone), where organic production of pelagic particles is taking place, the CaCO3 is in a supersaturation state and, consequently of desequilibrium; this state has been assigned to the inhibition effect of Mg in solution on the precipitation of carbonates (P y t k o w i c z, 1965), to the complexing of Ca and CO3 ions by the dissolved phosphorus and organic compounds as well to the inactivation of the CaCO3 nudei by the dissolved organic matter which is faster ad- sorbed from sea water onto their surface than the precipitation of CaCO3 onto the same surface (C h a v e , 1965 ; C h a v e and S u e s s , 1967, 1970). The carbonate particles protected by their organic coatings may reach and accumulate at great depths; the adsorbed organic molecules prevent or inhibit the reactions between carbonate particles and the undersaturated deeper sea waters (S m i t h et al., 1968). The solution of such particles, probably displayed selectively (B erger, 1967, 1968), may take place through the removal of their organic coating as a result of repeated resedimentation and bacterial activity. Hence, if one admits the existence of such factors in the Upper Oxfordian-Berriasian environmental sedimentation within the Beșița Trough, it results that carbonate sediments of the Valea Aninei, Brădet and Marila Limestones have deposited about or under the aragonite compensation depth and over the calcite compensation depth, the two limits being probably situated at shallower depth than at present. Undei* these conditions, as also assumed by J e n k y n s (1970 b), if large ara- gonite and, occasionally, calcite skeletons have been dissolved, smaller particles with greater reaction surfaces have also to be dissolved; it is probable that metastable shallow water carbonate sediments, particu- larly the aragonite ones, redeposited in basinal environments, have under- gone essential Solutions intrastratally and on the sea bottom. Solution of these carbonate particles probably led to the increase of the concen- tration in Ca and CO3 ions of interstitial fluids and subsequently — through their reprecipitation — to the early lithification of basinal sediments. The high frequency of bedded and nodular cherts in the Valea Aninei Limestones does not indicate essential depths; the abundance of diagenetic cherts is in connection with the inițial amount of biogenous silica which had resulted from prolific spreading of opaline organisms (especially radiolaria), an almost general phenomenon in the alpine peri- Mediterranean areas. Paleogeographic and Paleotectonie Aspects At the beginning of the Jurassic the South Carpathians area like the central Mediterranean zone (see : B e r n o u 11 i, 1971, 1972) had been predominantly submitted to longitudinal block-faultings, probably as a result of spreading of the central part of the Tethys. In connection -hC Institutul Geologic al României \ igrZ 21 MESOZOIC BASINAL LTMESTONTlS — REȘIȚA ZONE 77 Institutul Geological României 78 GR. POP 22 with these fractures there began a gradual separation of some elongated basins and swells under the shape of troughs (Reșița, Svinița, Severin, possibly Coșuștea) and thresholds (Dognecea, Semenic, Mehedinți) (C o - darcea and Pop, 1970 ; P o p , 1973) which have afterwards variously persisted up to the end of the Lower Cretaeeous (Pop, 1967) (Fig. 8)8. A long time, the Reșița Zone was interpreted as a „sedimentation zone”, notion also implying basinal marine conditions relying on the pre- sence of ammonite-bearing formations (Middle Jurassic-Neocomian) clas- sicaly considered of bathyal origin. The areal significance of this zone was evidenced later by Codar cea (1940, 1964) who pointed out that is was bordered by thresholds. Subsequent stratigraphic investigations have revealed lateral facies variations of the Mesozoic sedimentary for- mations, thus distinguishing central deeper water facies and marginal shallow water (locally littoral) ones (B o 1 d u r and Bol dur, 1962; Năstăseanu and Dincă, 1962; Năstăseanu, 1963, 1964; Răileanu et al., 1964). According to this interpretation whose starting poi"t has been the analysis of facies of Middle Jurassic formations (Bol dur and Boldur, 1962), the maximum depth of the basin corresponded to the central part of the present-day Reșița Zone, where the sedimentary for- mations build up a continuous thick sequence in fine-grained facies; the borders of the basin were located in the marginal parts (eastern and western) of this zone, where the Mesozoic sequences frequently display neritic facies, smaller thicknesses and at certain levels stratigraphic gaps and a transgressive position (Năstăsea nu, 1964 ; R ă i 1 e a nu et 8 These block-faulting structures, some of them so far under discussion (Coșuștea Trough) or with a uncertain paleogeographic position (Severin Trough), had each a specific geologic evolution and a certain morphology, which determined the formation of some sediments with corresponding facies and stratigraphic relationships, as well as with some common aspects. Thus the troughs and thresholds (considered under the form of those from Fig. 8) progressively separated ones in relation to others and within each of them certain morphological variations did exist which subsequently have gradually attenuated ; these aspects are reflected by lateral facies variations — more frequent in the Lower and Middle Jurassic formations and less fre- quent in those of the Upper Jurassic and Lower Cretaeeous. Nevertheless in the Svinița Trough, for instance, some intrabasinal swells were preserved which led to the formation of some con- densed sequences and to frequent redeposition of sediments. During the first stage of the sepa- ration of troughs and thresholds (Lower and partially Middle Jurassic) the sedimentation within them displayed a terrigenous character — firstly lacustrine and then marine, and from the Middle Jurassic onwards a generalization of carbonate sedimentation with varied intensity had started. The facies of sedimentary formations are suggesting, as a whole, a Progressive differentiated sinking of trough accompanied by a higher or lower deposition rate of sediments, phenomenon which has also cpisodically and partially affected the swells especially in the course of the Neocomian. Thus, for instance, the Mehedinți Threshold which during the Middle and Upper Jurassic presented typical shallow marine environments of Bahamas carbonate platform type, displayed in the Neocomian a tendency to sinking, as shown by deposition of micrites with scarce calpionellids. Such sinking movements also gave rise to the Severin Trough wherein sediments of the Sinaia and Comarnic Beds have accumulated (P o p, 1973). Institutul Geological României igr/ 23 MESOZOTC BASINAL LIMESTONES — REȘIȚA ZONE 70 al., 1964). A similar interpretation was given to the thickness variations, stratigraphie relations and to the facies of the Upper Oxfordian-Berriasian limestones. Data regarding fabrics, bedding, thickness, facies variation, strati- graphic relations and the regional geological framework of Upper Ox- fordian-Berriasian limestones grouped into the Valea Aninei, Brădet and Marila Limestones point out that their sediments accumulated in basinal environments of the Reșița Trough. The same data are also indi- cative of the fact that these sediments were restricted to the outer part of the Reșița Trough corresponding to the eastern basin margin and slope9 (see also W i 1 s o n, 1970). The deposition of sediments in dipping basinal areas is firstly indicated by the slump-folds and sliding planes which in all encountered cases point to a slope with westwards dipping inclusively in the innermost outerops of such limestones (Ciudanovița); the same submarine morphology is evidenced by the presence of allodapic limestones whose share in the basinal sequence is decreasing from east to west, as well as by the increase and afterwards decrease of thickness of the three lithostratigraphic units in the same direction. The more reduced thicknesses of the synchronous sequence from the western part of the Reșița Zone, previously considered as an element of the shallower facies, its pelagic more homogeneous composition and the slump-folds are indicative in fact of a greater depth than in central or outer parts of this zone. Consequently, the Upper Oxfordian-Berriasian limestones generally illustrate the sedimentation in the outer part of the Reșița Trough, and those corresponding to its inner part are missing from the Reșița Zone; the latter have been probably entirely or partially removed through ero- sion subsequent to post-Neocomian diastrophisms or tectonically overlain by the Supragetic Unit presumably at the end of the Upper Cretaceous. On this account, the outline of the Reșița Trough is difficult to be rendered, as we can only admit that its outer part mainly represented a wide basin slope with certain variations of submarine relief which have influenced the sedimentation, redeposition as well as gravitațional sliding of non- consolidated and semi-lithified sediments. The Reșița Trough was bordered by the Dognecea and Semenic Thresholds (C o d a r c e a and P o p, 1970). Nowadays within the thresh- olds areas Mesozoic formations of certain ages (Middle Jurassie) occur only in a few very small, areas so that their paleogeographic aspects are mainly indirectly inferred from the facies analysis of basinal formations. During the Lower Jurassie in the Reșița Trough there were lacus- trine environments and subsequently basinal marine ones; at the be- ginning of the Upper Jurassie the depth of this trough increased, thus determining the formation of a typical basinal sequence successively cor- responding to the Tămașa Marls, Valea Aninei, Brădet and Marila Limes- tones, the Crivina Marls and Hauterivian biomicrites (pro parte). ________________ / 9 Here there are accepted only two major carbonate depositional environments; basin and shelf (shallow water); the slope environments are included in the basinal ones. JA Institutul Geological României igr/ 80 GR. POP 24 In the threshold areas shallow marine conditions were more wides- pread during the Oxfordian and the Hauterivian and more restricted during the Kimmeridgian-Valanginian—as a result of their parțial sinking. The Hauterivian biomicrites showing an essential reduction of basin depth, progressively grade upwards into algal boundstones and grainstones of Urgonian type (Barremian-Aptian), which are indicating the extension of shallow marine environments within the trough area. Thus the austroalpine diastrophism led to uniformization of shallow marine environments over the whole inner part (Supragetic Unit and Getic Realm) of the South Carpathians (C o d a r c e a and Pop, 1970). In the basinal carbonate sequence the Valea Aninei Limestones with frequent allodapic intercalations and slump-folds illustrate an active subsidence regime connected with some longitudinal fractures, probably a marked depth difference between the trough and the adjacent Se- menic Threshold, and a relatively varied and periodically regenerated submarine relief. The allochthonous carbonate material from these limes- tones originated in the shallow marine environments of thethreshold which presumably represented an open carbonate platform. Crinoid grainstones, abundant in the eastern part of the Reșița Zone, previously interpreted as a neritic-littoral facies, represent a slope facies; these limestones with reworked pelagic sediments (chiefly as intra- clasts) deposited in the upper parts of the basin slope but below the level at which pelagic carbonate oozes still accumulated. Brădet Limestones do commonly occur in the „marly Ammonitico Rosso” facies of A u b o u i n (1964) and likewise evidence a basinal slope. A much lower number of allodapic intercalations as compared to the Valea Aninei Limestones is indicative of a diminishing of the morpho- logical difference between trough and threshold and at the same time a removal of the source of shallow water carbonate sediments. This situa- tion is probably due to the parțial sinking of the Semenic Threshold. These nodular limestones are at all events evidencing greater depth than the condensed so-called „carbonate Ammonitico Rosso” which characterizes the intrabasinal swells or seamounts (A u b o u i n, 1964 ; J e n k y n s, 1971; Bernoulli, 1971, 1972). In the South Carpathians such con- densed nodular limestones are very well exposed in some areas from the Svinița Zone (inner part of the Danubian Realm). Marila Limestones are generally occurring in the facies of the Majolica Limestone widely spread in the central and western Mediter- ranean provinces (see: Bernoulli, 1971, 1972); lithologically they are more homogeneous than the older basinal limestones from the Reșița Zone, show less synsedimentary gravitațional deformations, contain relatively scarce allodapic intercalations but still do present frequent evidences of intrabasinal redeposition. These limestones suggest more pronounced deepening movements and increased pelagic carbonate supply — probably rather due to the prolific development of nannoplankton during the Middle Tithonian-Berriasian than to the decrease of sedi- ment deposition depth ( N 6 e 1, 1965 ; H a Ham, 1971). Institutul Geological României 25 MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 81 The sinking of the adjacent threshold areas led to attenuation of the morphological difference between basin and thresholds and probably to the extension of the pelagic sediment accumulation area. During the late Berriasian and the Valanginian, the supply of pelagic carbonate sediments diminished concomitantly with a slightly increase of the share of argillaceous ones, which determined the formation of the Crivina Marls. This evolution of the basinal sedimentation took place without any important changes of the sediment deposition depth. LITHIFICATION OF CARBONATE SEDIMENTS The lithification of the Upper Oxfordian-Berriasian sediments from the Reșița Zone was especially achieved by neomorphism, ce- mentation, silicifieation and dolomitization processes. These processes generally had a selective character, depending on the fabrics of sediments, and mainly operated at different burial depths of sediments under the water/sediment interface and sometimes in basinal submarine environ- ments. Lithification of Carbonate Oozes At present, it is admitted that the transformation of carbonate oozes into monomineral (low-magnesian calcite) microcrystalline aggre- gates (micrites) is the result of several complex processes comprised in the „aggrading neomorphism” concept (F o 1 k, 1965). According to this concept, the lithification of the primary porous, wet, multiminera- logic and highly reactive carbonate oozes, should take place by the solu- tion of finet particles and the proeminences of the larger grains, the con- version of aragonite into calcite and the high-magnesian calcite recrystal- lization accompanied by the transfer of Mg2+ into interstitial fluids, the pressure-solution at grain contacts, the cementation of carbonate particles by CaCO3 precipitation under the form of syntaxial overgrowths on their surfaces and the corresponding decrease in porosity and interstitial fluids, and eventually by the allochthonous influx of Ca2+ and COi" in these sediments (F o 1 k, 1965; Bathurst, 1970). The share of these processes in the lithification of carbonate oozes probably depended on many factors such as : mineralogical nature of carbonate particles, their shapes and sizes, sedimentation rate, burial depth of sediments and their content in argillaceous matter and organic substance, and others. The Upper Oxfordian-Berriasian carbonate oozes of pelagic origin were to a great extent composed of low-magnesian calcite, their parti- cles were relatively non-uniform sized; they accumulated under a low sedimentation rate and by frequent redeposition and some of them contained certain fractions of argillaceous matter, organic substance and opaline microfossil skeletons. For this reason, the aragonite conversion into calcite and high-magnesian calcite recrystallization were minor pro- o - c. 11 Institutul Geological României IGR/ 82 GR. POP 26 cesses ; also aragonite solution from the autochthonous and allochthonous particles, under a low sedimentation rate, probably took place pene- contemporaneously with the sediment accumulation due to the subsa- turation state of the deep sea waters with respect to aragonite. It results that the solution of finer supersoluble particles, pressure- solution, precipitation of calcite under the form of syntaxial overgrowth cement on the microfossil skeletal particles and eventually the calcite recrystallization constituted important factors for the lithification of basinal carbonate oozes of pelagic origin. Generally the achievement of such processes probably depended on burial depth and age of the sedi- ments and their insoluble content, as a matter of fact these aspects being noticed in the lithification of some Upper Cretaceous and Ceno- zoic carbonate oozes from certain deep sea and oceanic areas (see : B e rg e r and von Rad, 1972 ; P a c k h a m and L i n g e n, 1973 ; Matter, 1974). As a result, the compaction of the carbonate oozes (usually now imperceptible) under the influence of lithostatic pressure, even if it was considered as having a minor implication, could play a certain role in pressure-solution at the contact points of grains and their welding. Syntaxial overgrowth carbonates resulted from the dissolving of finer particles and from the pressure-solution at the intergrain contacts (see also Matter, 1974), from the solution of aragonite particles of shallow water origin and their conversion into calcite, through the for- mation of early diagenetic stylolites (B a t h u r s t, 1970), as well as from the replacement of carbonate sediments by silica. Transformation of carbonate oozes into compact and rather uni- forin-sized monomineral aggregates has been recently explained by F o 1 k (1974) through Mg2+ adsorbtion from interstitial fluids on the surface of calcite particles which should prevent from their normal growing over the equilibrium sizes of 2—4 microns, representing the average length of the original particles ; this should be a chemically-induced limitation of the growing of calcite particles determined by a small amount of inter- stitial Mg2+ proceeding from sea water and fine high-magnesian calcite particles. As it was shown in the previous chapters, the basinal micrites have their particles of smaller and more uniform sizes when they contain argillaceous matter tending to get the „minimicrite” fabric of F o 1 k (1974). These fabrics were previously explained by the fact that a con- tent of argillaceous matter greater than about 2% in carbonate sedi- ments should promote more intense compactions, at the same time inhi- biting their early lithification by cementation (Z a n k 1, 1969). More intense compaction and slower lithification of such sediments were also observed in the case of Cenozoic sediments from some deep sea areas (see: Matter, 1974). Basinal carbonate oozes from the Reșița Zone containing argil- laceous matter do not seem to have had initially a higher content of high-magnesian calcite than those chemically purer, from which a greater amount of interstitial Mg2+ resulted. For this reason, the eventually greater amount of Mg2+ could be retained in the interstitial fluids pro- < ’i Institutul Geologic al României XjGR/ 27 MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 83 bably by the semipermeable membranes of clay particles which braked free moving of these fluids and their ions ; Mg2+ concentrated in this way and adsorbed on the surface of calcite particles inhibited the forma- tion of the overgrowth cement. The clay particles had probably a si- milar inhibiting role as they partially or integrally isolated the calcite particles from the interstitial fluids. Although the lithification of basinal carbonate oozes was conditioned, among other factors, by the burial depth of sediments and their age, however, at least their local lithification in submarine environments oi' near water/sediment interface cannot be excluded. At present, several cases of submarine lithification of the recent carbonate oozes predomi- nantly of pelagic origin are known (M i 11 i m a n, 1966, 1969 ; F i s- c h e r and Garr ison, 1967 ; Garr is on and F i s c h e r , 1969). The frequent synsedimentary gravitațional deformations of sedi- ments and the presence of micrite intraclasts at numerous stratigraphic levels in the basinal carbonate sequence from the Reșița Zone prove the early lithification of carbonate oozes, in some cases possibly even in submarine conditions; almost unanimously, it is believed that the sub- marine lithification of such sediments was favoured by their long exposure on the sea bottom due to a very low sedimentation rate accompanied by solution and reprecipitation of carbonates. The greater frequency of the synsedimentary gravitațional deformation in the Valea Aninei Limes- tones could be caused not only by a more marked and labile slope but also by an earlier lithification of the sediment as a result of more intense neomorphism of metastable carbonate particles of shallow water origin redeposited in the basinal area. Genesis of Nodular Limestones The origin of nodular limestones focused the attention of many petrologists and continues to be one of the most delicate problems of the carbonate rock petrology. Such limestones, known under the name of „Ammonitico Rosso”, “Knollenkalke” or “calcaires noduleux” are fre- quent in the Tethyan Jurassic sequences and have many common fea- tures as to their fabrics, and also certam local petrographic aspects which have led to more or less different interpretations regarding their genesis10. 10 C a y e u x (1935) considered some nodular limestones as an ,,o)d pudding breccia”. L u ca s (1955 a, b) admitted the formation of such limestones by the parțial cementation of pelagic carbonate oozes having a high content of argillaceous matter, under the shapc of no- dules with clear or sometimes diffuse contour; the sediments surrounding these nodules under- went intense differential compaction and dissolution, leading to an important reduction of their thickness and to deformations of stylolite type of the nodules. The same author also admi- tted the possibility of nodule formation in submarine environments, where currents could have removed their matrix, and accidentally their subsequent reworking. Atanasov (1958) considered Gallovian and Kimmeridgian nodular structures from the Balkans of early diagenetic nature being made up by the concentration of the carbonate matter around some bioclasts Institutul Geological României 84 GR. POP 28 In their formation a main part should. have been played by : early ce- mentation and differential compaction of more or less argillaceous car- bonate oozes (L u c a s, 1955 a, b), submarine solution known under the narne of “subsolution” (H o 11 m a n n , 1962, 1964), diagenetic segregation in a broad meaning (H a 11 a m, 1967), subsolution accom- panied by shrinkage-cracking (Garrison and F i s c h e r, 1969), ,,flow” of semi-consolidated sediments in some cases and burrows (B e r- n o u 11 i, 1972). Consequently, almost in all cases one may notice a certain content of argillaceous matter in the nodular limestones and as result various ef- fects of compaction of the inițial sediments ; under the influence of the lithostatic pressure the nodules and their matrix underwent plastic and pressure-solution deformations. Also, most of the authors admitted the formation of nodular structures by early diagenetic lithification of pe- lagic oozes, sometimes even in submarine conditions. The early lithifica- tion of these carbonate sediments do represent a condition for the forma- tion of nodular structures. In the nodular limestones from the Reșița Zone there are no obvious elements which can attest the nodule formation by differential solution and/or shrinkage-cracking of some carbonate crusts or semi-consolidated ooze strata or by burrows. In exchange, within marly intercalations as well as in limestones with higher content of argillaceous matter one may notice incipient nodular structures in which the nodules have diffuse contours and gradually pass to their matrix. These nodular structures seem to be formed in situ generally by diagenetic segregation; their under the influence of a certain argillaceous content; the compaction of their more argillaceou matrix was deduced from its moulding aspects around the nodules and from the fact that the ammonites from the matrix are flattened while those from nodules are undcformed. H o 11- in a n n (1962, 1964) interpreted the nodular structures from the Ammonitico Rosso from the Southern AIps, which bcar evidences of some intense submarine solution, as relics of some carbonate strata already formed and then distroyed through a process called „subsolution”. According to A u b o u i n (1961) the nodular facies is of syngenetic origin and resulted from discontinuous and slow pelagic sedimentation, interrupted by periods of submarine dissolution; nodular limestones often stratigraphically condensed should characterize the deep swells and their slopes. Ha Ha m (1967) assigned the nodule formation to an early diagenetic segrega- tion ; the same processes should also control the genesis of limestone-marl alternations from the Ammonitico Rosso deposits. Analyzing the origin of nodular limestones, especially the Adnet ones, Garrison and F i s c h e r (1969) admitted that they reflect the periodical deposition of carbonate oozes followed by solution stages in the same place, accompanied by lithification and shrinkage-cracking; by the combination of these factors, the carbonate ooze strata evolved to nodules, partly embedded within a red fossiliferous clay matrix. B er- n o u 11 i (1972) has found that many nodules from the Ammonitico Rosso limestones were formed in some places by „diagenetic flow” of semiconsolidated sediments, and in other places the nodular aspects should have resulted from burrows; the nodular aspects were in many cases accentuated by postdepositional intrastratal Solutions. JA Institutul Geological României igr/ 29 MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 85 consolidation took place probably similarly to the lithification of oozes containing argillaceous matter. Consequently, the nodule formation is the effect of neomorphic solution and differential cementation of the calcite particles, especially by syntaxial overgrowth on these particles. In some cases, the influence of inițial random distribution of carbonate and argillaceous particles, as a result of sediment redeposition, on the nodule „nucleation” is not to be excluded. The nodule formation was favoured by long time exposure of these sediments on the sea floor as a result of very low rates of sediment accumulation. Redeposition of the sediments, which through such an early dia- genetic evolution contained more or less lithified nodules and an uncon- solidated argillaceous matrix, probably led to the formation of nodular sediments in which the nodules were laid down as detrital grains. Conse- quently, such primary in situ formation of nodular structures and their frequent redeposition as intraclasts had probably a major role in the genesis of nodular limestones from the Reșița Zone. The fragmentation of semi-consolidated crusts or beds of carbonate oozes by submarine sli- dings and the reworking of their fragments had also subordinately con- contributed to the formation of nodular limestones. In many cases, the nodular structures were amplified by com- paction and subsequent neomorphic lithification. Lithification of Allochthonous Allochemical Sediments Lithification of these sediments was also achieved by compaction^ neomorphism and cementation. Subsequently to their accumulation in the basinal area, the alloch- thonous carbonate sediments were more or less affeeted by submarine and intrastratal Solutions (especially aragonite particles) and by com- paction. The sediment compaction had as important effects the welding of some allochthonous micrite allochems (mainly pellet and pelletoid grains) and mechanical deformations such as various intergrain contacts resul- ting from their different consistence; also the compaction produced deformations of muscovite lamella from crinoid biosparites and breakage of some tabular skeletal grains. These deformations were probably accom- panied by pressure-solution and tended to the formation of some stable frameworks of the sediments, concomitantly with an increase in intensity of their neomorphism and cementation. In these sediments, the micrite allochems and also their fine-grained matrix usually of pelagic origin, generally underwent neomorphic lithi- fication specificai to the carbonate oozes, subsequently evolving to microspar or even to sparry calcite. Also of neomorphic nature are the radial-fibrous crusts and the conica! crystals perpendicularly grown on some bioclasts, which developed by replacement of the surrounding fine- grained matrix and sometimes of some micrite allochems (see : F o 1 k, 1965) (Pl. VII, Fig. 2). A Institutul Geologic al României IGR 86 GR. POP 30 Adjoining allochems generally with .similar micrite fabrics are fre- quently met, but some of them have radial-fibrous crusts on their surface. Radial-fibrous crusts have neomorphically formed presumably only on allochems which displayed the same mineralogical nature. On the intra- clasts made up of pelagic micrite such crusts have never been noticed; the low-magnesian calcite of these intraclasts prevented from the nucle- ation of. carbonate crystals of the crusts which formed in another mineral phase(probably high-magnesiancalcite) (Pl. VIII, Fig. 6 ; Pl. IX, Fig. 1—4). Syntaxial neomorphic overgrowths on monocrystalline grains had an important role in the lithification of allochemical sediments since crinoidal grains often constituted a significant fraction of these sediments. These overgrowths were made up by replacement of the fine-grained car- bonate matrix and partially of micrite allochems especially pelletal and pelletoid particles; there are cases when such grains were wholly repla- ced by the calcite overgrowths, being recognized only due to the distri- bution of organic and argillaceous inclusions previously contained by these grains. There are also cases when the syntaxial overgrowths par- tially replaced some micrite allochems after they underwent intergrain deformations. Often, the boundaries of syntaxial overgrowths are saw- toothed, and sometimes the distribution of insoluble inclusions within them points out two or three generations of calcite, and consequently the discontinuity of neomorphic overgrowth formation (see : Evamy and Shearman, 1965, 1969). In a single case a crinoid grain was met presenting two generations of syntaxial overgrowths : a first generation with its externai part micritized in shallow marine environments (see: B a t h u r s t, 1966 ; Alexandersson, 1971) and a second one which arose after the redeposition of this grain in the basinal area. In all cases, the relations between radial-fibrous crusts and neomor- phic syntaxial overgrowths demonstrate that the former were made up before the latter. The neomorphism also led to frequent replacement of the primary fabrics of bioclasts by more or less coarse sparry calcite. The lithification of allochemical sediments, especially of the well sorted and washed crinoid ones, also took place by Ca2+ and COI" precipi- tation as cement from the interstitial fluids within intergrain and intras- keletal voids. Cementation first took place under the form of radial-fibrous crusts, more or less developed on the surface of some allochems, and then as sparry crystals whose sizes usually show a centripetal increase within intergrain spaces. Sparry calcite from cements seems to be clearer than those considered of neomorphic origin. The precipitation of radial-fibrous crusts had a selective character, their crystal nucleation occurring only on certain allochems, probably depending on their mineralogical nature. The sparry calcite and radial-fibrous crusts were also formed within the voids resulted from the solution of some aragonite bioclasts and within the chambers of some bentonic foraminifera. In the latter case, it is possi- ble that the radial-fibrous crusts formed, at least partially, in shallow marine waters where these skeletons initially originated. A Institutul Geologic al României XIGR/ 31 MESOZOTC BASINAL LIMESTONES — REȘIȚA ZONE 87 The cementation of these sediments took place frequently by preci- pitation of calcium carbonate as syntaxial overgrowths on the crinoid grains. In sediments with a greatei’ content of such grains, the cementa- tion by syntaxial overgrowth had a major role in their lithification. In the early stage of diagenesis, the allochemical sediments under- went compactions and formed neomorphic and cement radial-fibrous crusts and at least a part of overgrowths on monocrystalline calcite grains. The radial-fibrous crusts and a part of the syntaxial overgrowth originated in this early diagenetic stage by CaCO3 crystallization probably under the form of high-magnesian calcite. This has been presumably due to a favou- rable Mg/Ca ratio in the interstitial fluids (see: F o Ik , 1974). The for- mation of the two morpholgical types of high-magnesian calcite took place probably after their incipient burial, and locally even in submarine environments. In the subsequent diagenetic stages, the formation of neomorphic and cement syntaxial overgrowths in conditions of deeper burial of the basinal sediments did continue. Under these conditions probably arose a great part of microspar from the matrix and sparry calcite as orthos- par and pseudospar. During the later diagenetic stages, the dominant mineral forming phase of calcium carbonate was probably the low-magne- sian calcite. Siliciîication of Sediments This process had an important role as to the basinal carbonate sedi- ment lithification from the Reșița Zone, especially of the Upper Oxfor- dian-Kimmeridgian ones. The existent positive relation between the amount of calcitized radiolaria from limestones and the frequency of bedded and nodular cherts represents an incontestable argument that silica is of biogenous origin resulting from the solution of opaline skeletons of planktonic micro- fossils. Silica from interstitial fluids, having predominantly such an origin, has probably precipitated as cristobalite which replaced the carbonate particles and filled the intergrain voids of sediments (Pl. X, Fig. 2). The cherts from the basinal carbonate sequence from the Reșița Zone are mainly made up of calcedonic and fine grained quartz and subordi- nately of cristobalite, thus they represent quartz-rich cherts, an end pro- duct of the reaction : biogenous opal —> cristobalite -> quartz chert (see also H e a t h and M o b e r 1 y , 1971; W i s e et al., 1972 ; W i s e and W ea ver, 1974; B erger and von Rad, 1972 ; and others). Dis- solution of opaline microfossils and subsequent silicification of carbonate sediments took place probably in a very early stage of diagenesis; this fact results from the presence of bedded cherts in slump-folds and from graded redeposition of some nodular cherts. However, some cherts, espe- cially the nodular ones, seem to have been also formed in the later diage- netic stages by silica remobilization. Following up the relic fabrics of the silicified sediments, one may notice that the bedded cherts are more frequently formed through sili- Institutul Geologic al României igr/ 88 GR. POP 32 cification of allochthonous carbonate sediments than of pelagic ones; it is probable that their metastable carbonate composition favoured the early and intense silicification of these sediments. Silicification of carbonate sediments released a relatively great amount of Ca2+ and CO|“ which subsequently participated in their early lithification. Dolomitization oî Sediments In the basinal carbonate sequence from the Reșița Zone, dolomites occur as tiny crystals in the nodule matrix of the Brădet and Marila (lo- wer part) Limestones, and as medium to coarse crystals in the Valea Aninei Limestones. The genesis of fine dolomite crystals from the pelagic limestones and Cenozoic to Recent deep sea carbonate sediments was assigned to different causes (see : B erger and von Rad, 1972 ; Pa c k a m and L i n g e n , 1973). In the Brădet and Marila Limestones such crystals occur in the matrix of nodules which has almost always a certain con- tent of argillaceous matter and silty detrital quartz; this assemblage suggests that at least part of the dolomite crystals was formed by regeneration in basinal sediments of some fine grained detrital dolomite initially originated in inter- and supratidal environments. This fact does not exclude the possibility of in situ forming of a certain part of these crystals (see also Thompson et al., 1968; S c h o 11 e , 1971). The coarser crystalline dolomites from the Valea Aninei Limestones are of diagenetic nature, and resulted from the dolomitization of basinal carbonate sediments subsequently to an important stage of their silici- fication under the form of bands. These dolomites were formed by local dolomitization of different basinal carbonate sediments through processes of ,,seepage refluxion” type (see : D ef f ey es et al., 1965). CONCLUSIONS The typical basinal carbonate sequence from the Reșița Zone is successively represented by the Valea Aninei, Brădet and Marila Limes- tones (Upper Oxfordian-Berriasian). The Valea Aninei Limestones are made up of different types of pelagic limestones (micrite, biomicrite and sometimes nodular ones), allo- dapic limestones (packstones-grainstones), and of limestones with mixed fabrics, banded and nodular diagenetic cherts and rarely dolomites. The Brădet Limestones do predominantly consist of Saccocoma nodular limes- tones, occasionally with a dolomitized matrix, which includes scarce allo- dapic intercalations. Marila Limestones are essentially built up of calpio- nellid micrites including rare allodapic intercalations and, in their lower part, nodular micrites. 33 MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 89 Beginning with the lower part of this basinal sequence and tracing it upwards, one may generally state an increase in the pelagic limestone share concomitantly with a decrease in frequency of allodapic limestones, of cherts and calcitized radiolaria and also of synsedimentary gravitațional deformations ; in the same time it is noted an increase of the sorting degree of allochthonous allochems from allodapic limestones. From east to west of the Reșița Zone one may observe a lowering of allodapic intercalations and an increase of their grain sorting, diminution of bed thickness (inclu- sively of massive intercalations from the Valea Aninei Limestones) and the decreasing frequency of synsedimentary gravitațional deformations of carbonate sediments. Basinal limestones resulted from the lithification of three main types of sediments : carbonate oozes, nodular oozes and allochthonous allochemical sediments. Carbonate oozes proceed from the accumulation of planktonic microorganism skeletons (especially of nannoplankton), and subordinately from the redeposition of some oozes previously formed in shallow marine areas. Nodular oozes, which led to the formation of a great part of nodular limestones, have arisen due to the reworking of early diagenetic previously formed nodules or those in course of formation, and of some crust or bed semi-consolidated ooze fragments resulted from submarine erosion and slidings. Allochthonous sediments formed through the redeposition within basinal areas of some shallow water sediments, constituted of bioclasts (especially the crinoid ones), ccmpound grains (intraclasts, s.l.), pelletoids and pellets and scarcely coated grains (ooliths, oncoliths). Pelagic oozes were to the greatest extent composed of low-magnesian calcite, and subordinately of opal contained in the siliceous microorganism skeletons while the allochthonous sediments were predominantly made up of aragonite and high-magnesian calcite. The accumulation of sediments involves a peculiar effect, and in many cases a combined one of the partide by partide deposition, rede- position of such sediments and of those originated in shallow marine areas, as well as of submarine slidings of basinal sediments. Redeposition of sediments which is especially determined by the exceeding of a certain criticai volume of sediment bodies under the influence of tectonic move- ments, of submarine relief and of a certain sedimentary rate took place through submarine slidings, semifluid flows and turbidity currents. These reciprocally connected main transport modes led to the gravita- țional deformations of sediments, their retexturation, and to the for- mation of some turbidite and fluxoturbidite limestones. Carbonate sediments accuinulated under the aragonite compensation depth and over that of calcite probably situated at shallower depth than today, and at the depth of several hundred to about a thousand meters. In these conditions aragonite particles accuinulated in basin areas, under- went important dissolution before to be buried at various depths under the water/sediment interface. The high frequency of cherts (all of diage- netic origin) within the Valea Aninei Limestones does not imply a greater depth of sea waters, but is rather reflecting a prolific widespread of opaline 'jX Institutul Geologic al României 90 GR. POP 34 organisms; likewise essentially micritic and homogeneous Marila Limes- tones suggest an increase of the supply of carbonate particles which had been sooner determined by a prolific development of nannoplankton than by the decrease of sea water depth. Petrological data are suggesting that sediments of the Upper Oxfor- dian-Berriasian basinal sequence from the Reșița Zone have accumulated under basinal eonditions in the outer part of the Reșița Trough (especially in the basinal margin and slope areas). Sediments formed in the inner part of this trough have been subsequently eroded and/or tectonically overlain by the Supergetic Unit. The Reșița Trough was bordered by Semenic Thresholds outside and the' Dognecea one inside that during the Tithonian and Berriasian had displayed a tendency to- parțial sinking, thus determining the rise of the accumulation area of pelagic sediments and the diminution of the supply of shallow water carbonate sediments. The lithification of basinal sediments took place through compac- tion, neomorphism, cementation, silicification and, locally, dolomitiza- tion processes which had selectively operated (as a function of their struc- tures) at various depths under water/sediment interface, and partially in submarine environments. Carbonate oozes have been submitted to lithification by neomorphic processes within which dissolution of finer supersoluble particles, pres- sure-solution, precipitation of syntaxial calcitic overgrowths on skeletal particles, and eventually recrystallization of calcite constituted essential factors. Likewise the formation of micrites has been probably conditioned by Mg2+ adsorbtion on calcitic particles which limited their growth to the corresponding sizes of these rocks. The formation of overgrowths on calcitic particles from sediments including argillaceous matter has been more limited as a result of their isolation by surrounding clayey particles, and of Mg2+ adsorbtion on their surfaces; Mg2+ concentrated in interstitial fluids under the influence of the same clayey particles, which played the part of semi-impermeable membranes. The differential neomorphism of such more or less homogeneous sediments determined the in situ formation of nodular structures under the eonditions of a long-lasting exposure on sea bottom as a result of a very low sedimentation rate; these structures have been subsequently amplified owing to their compaction and neomorphic lithification. The lithification of allochemical allochthonous sediments took place through compaction under whose influence their grains had undergone weldings and varied pressure-solution and mechanical deformations, neo- morphic processes especially obvious under the form of thin radial- fibrous crusts, microspar and pseudospar, and cementation through equant and radial-fibrous microsparry calcite, sparry calcite (medium to coarse crystalline) as well as through syntaxial overgrowths. Banded and nodular cherts did predominantly form during an early diagenesis phase through dissolution of opahne planktonic skeletons, and afterwards replacement of carbonate sediments; silica has probably precipitated as cristobalite which subsequently graded, to a great extent, Institutul Geological României igr/ 35 'MESOZOIC BASINAL LIMESTONES — REȘIȚA ZONE 91 into quartz. It would seem that lithification affected more intensely allochthonous carbonate sediments with a metastabile mineralogical com- position. 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Petrology, 38, 4, p. 1305-1312. Tulsa. W i 1 s o n J. L. (1969) Microfacics and Sedimentary Structures in „Deeper-water” Lime Mudstones. Soc. Econ. Paleontologists Mineralogists, Special Publ., 14, p. 4 — 19. Tulsa. — (1970) Depositional Facies Across Carbonate Shelf Margins. Transactions — Gulf Coast Assoe. Geol. Soc., XX, p. 229—233. Institutul Geologic al României 39 (MESOZOIÎC BASINAL LIMESTONES — REȘIȚA ZONE 95 Wi s e S. W., Buie B. F. andWeaver F. M. (1972) Chemically Precipitated Sedi- mentary Cristobalite and the Origin of Chert. Eclogae geol. Helo., 65/1, p. 157—163. Basle. W i s e S. W., Weaver F. M. (1974) Chertification of Oceanic Sediments. In: Pelagic Sediments on Land and under Sea. Spec. Publ. int. Assoc. Sedimentologists 1, p. 301 — 326. Oxford. Zankl H. (1969) Structural and Textura! Evidence of Early Lithification in Fine-grained Carbonate Rocks. Seciimentology, 12, p. 241 — 256. Amsterdam. Institutul Geological României PLATE I Fig. 1. — Basinal limestones froin the Reșița Zone, a, Valea Aninei Limestones; b, Brădet Limestones; c, Marila Limestones. Northern slope of the Caraș Valley (about 3 km north-east of Carașova). Fig. 2. — Valea Aninei Limestones displaying relatively thin bedded pelagic and allodapic limestones and banded cherts (white ones) (a) and a thick intercalation of limestone (b) initially made up by the redeposition of a mixture of pelagic and shallow marine carbonate sediments. North of Anina (near the viaduct). Institutul Geological României Gr. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. I. Anuarul Institutului de geologie și geofizică, voi. XLVIII. K fGR7 Institutul Geological României PLATE II Fig. 1. — Detail of the Valea Aninei Limestones. a, pelagic micrites; b, laminated allodapic limestones; c, cherts; d, stylolites. Visoki Hill (on the Anina — Carașova road). Fig. 2. — Two successive beds of coarser (a) and finer (b) grained allodapic limestones sepa- rated by a horizontal megastylolite surface (c). Valea Aninei Limestones. North of Anina (near the viaduct). Fig. 3. — Crinoid biosparite layers showing multiple graded intervals; in their lower parts, these intervals are made up of sandy biosparites (cloudy parts). Lower part of the Valea Aninei Limestones east of Secul (on the Reșița — Văliug road). Gr. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. II. 1 2 Anuarul Institutului de geologie și geofizică, voi. XLVIII. 3 Institutul Geological României IGRZ PLATE III Fig. 1. — Parallel and oblique laminae in a fine grained allodapic limestone (a) and banded cherts (b). Middle part of the Valea Aninei Limestones. About 3 km north of Anina (on the railway). Fig. 2. — Laminations in an allodapic limestone bed including conformably distributed nodular cherts (a); this limestone overlies a nodular limestone layer. Middle part of the Valea Aninei Limestones from the Vîsoki l lill (on the Anina — Carașova road). Fig. 3. — Thick basinal limestone intercalation pointing out somesynsedimentary gravitațional deformations (see arrows). Valea Aninei Limestones at about 4 km north of Anina. Gk. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. III. Anuarul Institutului de geologie și geofizică, voi. XLVIII. A Institutul Geologic al României IGR/ PLATE IV Fig. 1. — Dolomitized basinal limestones containing banded and rarely nodular cherts (whitish ones); the carbonate sediments were partially replaced by silica previously to their dolomitization. Lower part of the Valea Aninei Limestones from the Vîsoki Hill area (on the Anina — Carașova road). Fig. 2. — Nodular micrite beds upwards gradually passing into nodular marls. Brădet Limes- tones from the Miniș Valley (south-west of Anina). Institutul Geological României Gb. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. IV. 1 2 Anuarui Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE V Fig. 1. Fig. 2. — Typically thin beddcd marly nodular limestones. Brădet Limestones from the Miniș Valley (south-west of Anina). — Slump structure in the Brădet Limestones from the Miuiș Valley (soulh-west of Anina). JA Institutul Geologic al României IGRZ Gk. Pop. Mesozoic Basinal Limestones — Reșița Zone. Anuarul Institutului de geologie și geofizică, voi. XLVIII. M Institutul Geologic al României IGR/ PLATE VI Fig. 1. — Nodular limestones wherein the nodules (clouded ones) are embedded in a more argil- laceous and weakly to moderately dolomitized micrite matrix. Brădet Limestones from the Brădet plateau (Bibel quarry, west of Anina). Fig. 2.— Intraformational carbonate breccia intercalation in the Brădet Limestones; the grains and their matrix are made up of Saccocoma biomicrite and micrite. Lindina Mare Valley (tributary of Nera River). Gr. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. VI. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic al României \ igrZ PLATE VII Fig. 1. Micrile conlaining calcilizcd radiolaria and sponge spicules. Valea Aninei Limestones. Norlh of Anina (near Ihe viaduct). Fig. 2. — Allodapic inlraclastic packslones with a malrix mainly ol' pelagic origin. On the surface of elongated calcite hioclast perpendicularly grown neomorphic conicul cal- cite cryslals. Valea Aninei Limestones from the Vîsoki I lill area. Fig. 3. — Allodapic inlraclastic and skelctal packstone-grainstone including some rounded pelagic micrile inlraclasts (a). Valea Aninei Limestones from the casierii border of the Beți (a Zone (Comarnic). Fig. 1. — Allodapic inlraclastic and skelelal grainstone bearing some irrcgularly cdged pelagic micrite inlraclasts (a); the liant of this limestone predominanlly consists of ncomor- phic synlaxial overgrowlhs (on the crinoid grains) (b) and microspar (c). Valea Aninei Limestones. Norlh of Anina (near the viaduct). Fig. 5. — Allodapic inlraclastic grainstone-packstone conlaining irregularly edged pelagic mi- crite inlraclasts (a); belwccn these inlraclasts and other allochems Ihere are diffe- rently shaped conlacls formed under the influence of compaclion. Valea Aninei Li- meslones. Norlh of Anina (near the viaduct). Fig. 6. — Inlraclastic wackestone. Somelimes the inlraclasts are made up of very fine-grained pelagic micrile and their borders arc probably impregnated with ferromanganese oxides. Valea Aninei Limestones. Visoki Ilill. Gr. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. VII. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României Tgr PLATE VIII Fig. 1. — Crinoid grainstone containing defonned pelagic micrite intraclasts (a) and intensely micritized crinoid grains (b) without syntaxial overgrowths; the grain liant is pre- dominantly made up of neomorphic and partially cement syntaxial overgrowths. Valea Aninei Limestones from the eastermnost part of the Reșița Zone (Comarnic). Fig. 2. — Allodapic intraclastic and skeletal grainstone. The coarse crinoid grain displays dis- continuous neomorphic syntaxial overgrowthsprobably under the formof three genera- tions, marked by their insoluble inclusions. Also the pelletoid and micrite intraclastic grains are often welded similarly to those lithified in undisplaced shallow marine sediments. Valea Aninei Limestones from the Reșița-Văliug road (east of Secul). Fig. 3. — Allodapic intraclastic and skeletal grainstone. Syntaxial overgrowths on the crinoid grains formed by neomorphic replacement of some micrite alloehems often show saw-toothed boundaries. Valea Aninei Limestones from the Comarnic area. Fig. 4. — Pelletoid packstone-grainstone. Some crinoid grains (a) underwent corrosions and incrustations with ferromanganese oxides before to be redeposited in the original place of this sample. Valea Aninei Limestones. North of Anina (near the viaduct). Fig. 5. — Allodapic intraclastic and skeletal grainstone. In this limestone the micrite alloehems are often welded and the syntaxial overgrowths on the crinoid grains are very deve- loped cementing many adjacent alloehems and thus displaying a poikilotopic fabric. Valea Aninei Limestones. North of Anina (near the viaduct). Fig. 6. — Allodapic intraclastic grainstone; the liant of their alloehems ispredominantly cons- tituted of neomorphic syntaxial overgrowths on crinoid grains and some micrite grains present recrystallized thin radial-fibrous crusts. Valea Aninei Limestones from the Comarnic area. Institutul Geological României Gr. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. vin. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE IX Fig. 1. — Allodapic intraclastic grainstone. The radial-fibrous crusts selectively formed on the ccrlain micrite allochems, followed by the overgrowlh neomorphism and cemenla- tion of the carbonate grains. Valea Aninei Limestones. East of Secul area. Fig. 2. — Allodapic wackestone. Sonic micrite or micritized allochems of shallow marine origin present on their surface lypically neomorphic radial-fibrous crusts. Valea Aninei Limestone. Visoki Hill area. Fig. 3. — Allodapic intraclastic and skeletal packslone including deformedpelagic micrite intra- clasts and some shallow water micrite allochems prescnting thin radial-fibrous crusts on their surface. Valea Aninei Limestones. North of Anina. Fig. 4. — Algal boundslone fragment (a) containing internai micrite (b) and a crinoid grain (c), sedimented in their original shallow water environmcnts; the internai sedimen talion was followed by the neomorphic formalion of a relativei}' thick radial-fibrous crust (d) and subsequenlly by the overgrowlh of syntaxial calcitc on the crinoid grains. This crust is comparativei}' more developed than those formed within basinal sedi- menls. The boundslone fragment was encountered in a thick predominanți}' al- lodapic limestone inlercalation from the Valea Aninei Limestones outcropping in the eastern border of the Reșița Zone (Comarnic). Fig. 5. — Pclletoid and skeletal (crinoid) grainstone or biopclsparile conslituled of well-sorted shallow marine allochems and of some pelagic micrite intraclasls sometimes irregu- larly edged. Valea Aninei Limestones occurring al north of Anina (near the viaduct). Fig. 6. — Well-sorted and fincr-grained pelleloid and crinoid grainstone (biopclsparile) (dislal facies) occurring as rare intercalations in Ihe Valea Aninei Limestones from the western border of the Reșița Zone (Giudanovița). Gk. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. IX 3 500JI 4 500)4 Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României Tgr PLATE X Fig. 1. — Sandy grainstone made up of different shallow marine allochems and coated detrital quartz. Basal part of the Valea Aninei Limestones from the Reșița-Văliug road (east of Secul). Fig. 2. — Partially silicified allodapic intraclastic packstone from the Valea Aninei Limes- tones. The silicified part (upper part of the picture) occurs as banded chert within the middle interval of this limestone layer. Vîsoki Hill area. Fig. 3. — Medium to coarsely crystalline dolomite resulted from the dolomitization of some basinal carbonate sediments containing previously calcitized radiolaria (a). Valea Aninei Limestone occurring in the Vîsoki Hill area (on the Anina-Carașova road). Fig. 4. — Medium to coarsely crystalline dolomite. The dolomite crystals are rich in insoluble inclusions pre-existing in the basinal carbonate sediments subsequently diagenctically dolomitized. Intercrystalline voids were then fillcd by calcite. Valea Aninei Limes- tones from the Caraș Valley (abolit 3 km north-east of Carașova). Fig. 5. — Saccocoma biomicrite in the Brădet Limestones from the Brădet plateau (Bibel qua- rry, west of Anina). Fig. 6. — Nodular micrite bearing fine bivalves and some Saccoma pieccs. The nodule (a) is made up of more fine-grained micrite than its matrix and only partially edged. It is probably of detrital origin. Brădet Limestones from the Miniș Valley (south-west of Anina). Institutul Geological României Gr. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. X. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic al României PLATE XI Fig. 1. — Nodular micrite containing calcitized radiolaria. Nodules are ol detrital nature sho- wing different fabrics in relation lo their malrix. Brădet Limestones from the Bibcl quarry (Brădet platcau). Fig. 2. — Moderately dolomilized nodular micrite from the BrădetLimestones. Dclritic micrite nodules sometimes containing Saccocoina are comprised in a partially dolomilized micrile matrix. Easl of Livadica (on Ihe Danube).) Fig. 3. — l’arlially dolomilized nodular micrile. The nodules are of deli i lai origin and display different fabrics among them and as against their moderately dolomilized micrile malrix. Brădet Limestones from the Miniș Valley (soulh-west of Anina). big. 1. — Allodapic wcll-sorted pelleloid and skelelal (crinoid) grainstone (biopelsparitc) forming a distinct bed in the Brădet Limestones from the Miniș Valley. Fig. o. — Relative homogeneous micrile conlaining calpionellids (here Calpionella alpina) from the Calpionella alpina subzone (late Upper Tithonian). Marila Limestones from the Mindrișag Valley (tributary of Miniș River). Fig. 6. — Nodular micrile from Ihe lower part of Ihe .Marila Limestones including rare caici- lized radiolaria, benthonic foraminifera and traces of burrows. In this case Ihere is no conneclion belwecn the detrital nodale and burrows. Marila Limestones from the .Mindrișag Valley. PLATE XII Fig. 1. -■ Nodular micrite containing some pelmicrite to pelsparitc patches where the fabric difference between the nodules and their matrix is obvious proving the detrital na- ture of these nodules. Marila Limestones from the Livadica area (northern slope of Danube). Fig. 2. — Nodular pelmicrite. In some well-rounded nodules the marginal micrite allochems are intersected by the nodule botmdary, thus showing detrital origin of these nodules. Marila Limestones from the Livadica area. Fig. 3. — Moderately dolomitized nodular micrite from the lower part of the Marila Limestones. The nodules are hardly distinguished from their undolomitized matrix. Mindrișag Valley (south-west of Anina). Fig. 4. — More intenscly dolomitized nodular micrite from the lower part of the Marila Limes- tones. Lindina Mare Valley (tributary of Nera River). Fig. 5. — Moderately dolomitized nodular micrite from the lower part of the Marila Limes- tones. Some nodules have their margins finer-grained and more clouded probably as a result of their impregnation with insoluble matter; the nodules and their matrix contain the same calpionellid assemblagc (Crassicollaria Zone). Mindrișag Valley. Fig. 6. — Allodapic pelletoid grainstone-packstone from the Marila Limestones occurring in the Mindrișag Valley (south-west of Anina). Institutul Geological României Gr. Pop. Mesozoic Basinal Limestones — Reșița Zone. Pl. XII. LOWER GYPSUM FORMATION WEST OF CLUJ-NAPOCA - A SUPRATIDAL EVAPORITE; PETROGRAPHYCAL AND SEDIMENTOLOGICAL FEATURES1 BY BOGDAN POPESCU 2 Abstract A supratidal sequence of evaporites (Lutetian in age) is described here. The petrogra- phic evidences lead us to presume the following diagenetic event; replacement of carbonate sedi- ments by 1—5 p doloinicrite; recrystallization of dolomicrite to 5 — 10 p dolomicrosparite and leaching of siltic and arenitic skeletal and nonskeletal grains; filling of pores and vugs by gypsum. Thus, the gypsum filling and the gypsum nodules growth take place in an already replaced and eVen recrystallized sediment. Then, in the early diagenetic stage, only euhedral dolorhombs, larger than 10 p, fare formed around the pores. The complete sedimentological study shows that there have been many penetrations and retreats of the sea leaving behind thin sediments. By a supratidal exposure they underwent a penecontemporaneous sabkha diagenesis. CONTENTS Page Introduction........................................................................... 97 Studied Area............................................................... 98 Work Techniques........................................................... 98 Ceological Setting .................................................................... 98 Petrographical Approach .............................................................. 100 Discussions on the Environment of Deposition.......................................... 110 Conclusions ............................................................................ 113 References.............................................................................. 114 Introduction Evaporite formations from the Transylvanian Basin have since long focussed the scientific interesț-of many a geologists. Due to their 1 Received on 2nd February 1973 and presented in the Meeting of March 9th 1973. 2 Institutul de geologie și geofizică, str. Caransebeș 1, 7000 București. 7—e. 11 Institutul Geologic al României 98 B. POtPESCU economic importance, the earlier studies have dealt with deposit condi- tions, physico-Chemical features and ways of evaluation of these rocks. There have been issued works covering a large range of problems concerning evaporite genesis (Paucă, 1967; D r a g o ș, 1969; and many others), or detailed works treating mineralogical and regional cor- relation aspects. Reminding that well developed evaporites occur at three strati- graphical levels; Lutetian, Priabonian and Badenian in age, in this work we are going to describe only the major petrographical and sedi- mentological characters of the Lower Gypsum Formation (Lutetian) west of Cluj. Studied Area We have chosen as a study zone a rectangular area lying in the Finului and Viilor Valley basins, bordered north by the Nadaș Valley and south by the Căpușului Valley (Fig. 1). Most complete outcrops in the Lower Gypsum Formation can be found in this area, this being also the only area where one can follow the sequence of evaporite facies from the crystalline basement of the Gilău Mountains (south) up to the zone where this strata go deep under younger formations. It may be mentioned that two quarries are to be found north and south of Leghia village. They offer excellent continuous outcrops where detailed field observations can be done in the area of maximum thickness of our evaporite formation. W o rk Techniques We have examined severa! profiles in the field, more than 150 samples being collected. 80 the sections and 14 polished samples have been studied in labora- tory; 10 thin sections have been stained with Alizarine Red, following the F r i e d m a n (1959) techniques in order to establish the exact tex- tural relations between calcite and dolomite; 8 Roentgen analyses have been made for calitative and cantitative evaluation of mineralogical com- ponents (Tab. 1) Geological Setting The stratigraphy of Eocene deposits of the Transylvanian Basin have been studied since the last century. Koch (1894) was the first one to make a modern pattern of the Tertiary stratigraphycal sequence in Transylvania, including our study area as well. He separated two gypsum „horizons” : lower gypsum horizon and upper gypsum horizon. R ă i 1 e a n u and Saulea (1956) have first noticed that the Eocene suit can be symmetrically divided in two marine sequences of deposits separated by an intercalated continental sequence. According to these authors the evaporite formations are the first „horizons” in both Institutul Geological României 3 LOWER GYPSUM FORMATION WEST OF CLUJ-NAPOCA 99 marine series; the lower gypsum and Anomia bearing marly limestones horizon and the upper gypsum and oolitic limestone horizon respectivelly. TABLE i Percentage of dolomite and calcite in Lower Gypsum Formation; Foidaș quarry. No. Sample no. CaCO3 % CaMg (CO3)2 % Other componenls 0/ /o 1 4177/10 94-96 2-4 2-4 2 4177/12 90-92 5 — 6 2-3 3 4177/13 5 — 6 88-92 6-8 4 4177/17 4-6 90-96 1-3 5 4177/21 10-12 82-84 6-8 0 4177/24 2-4 90-96 2-5 7 4177/26 6-8 45—50 40-45 8 4177/28 2-4 94-96 2-6 In the present study only the Lower Gypsum Formation (Lute- tian in age) is dealt with, which, as it has been mentioned above, attains TABLE 2 Generalized stratigraphic succession of the Eocene deposits west of Cluj-Napoca Age Lithostratigraphic units Priabonian Hoia Formation Bryozoan Mari Formation Cluj Limestone Formation Upper Gypsum Formation Upper Red Clay Complex Leghia Limestone Formation Mortănușa Mari Formation (emend) Nummulites perforatus Beds Lower Gypsum Formation Lutetian Ypresian- ?Paleocene Lower Red Clay Complex 100 B. POPESCU 4 the maximum development in the studied region. Table 2 shows the frame of the Lower Gypsum Formation in the Eocene suit west of Cluj-Napoca 3. We pointed ont that the stratigraphical terminology is still in development, many other schemes being proposed. The Lower Gypsum Formation is getting thicker and thicker (from 10 to 40 in) from south to north, where it disappears under younger deposits right near the Nadașu Valley. Petrographical Approach The petrographic descriptions are mainly based on the two excellent outcrops of the Leghia and Foidaș quarries as of other additional profiles in the Finului and Viilor Valleys (Fig. 1 and 2). In our latter disscutions concerning the sedimentogenesis of evaporites some other incomplete successions scattered over the studied area will be taken into account. Generally speaking (Fig. 2), three main lithological types can be noticed in the Lower Gypsum Formation; gypsum, gypsum-bearing rocks and dolomites alternating in different manners along the studied profiles. In the lowermost part of evaporite sequence, above the red clays ■with intercalated microconglomerates, pebbles and scattered lens of quart- zitic sandstones there lays a thin dolomitic bed, the first sign of evaporite regime. The dolomite is yellow-redish, porous, 75—85 cm thick (Fig. 2, 3621/14). It is made up of a 5—10 g dolomicrospar4 wherein there are scattered quartz grains and muscovite. The porous dolomicrosparitic mass is partly cemented by gypsum (Pl. I, Fig. 1,2). The dolomicrospar is light brown with curved crystal boundaries, marked by a thin cryptocrystalline film, probably of an argillaceous 3 B. Popescu. Stratigraphical Study of Paleogene Deposits between Căpușul Mic and Aghireșu. 1970. Arch. of Institute of Geology and Geophysics. B. Popescu. Stratigraphical Study of Paleogene Deposits between I Ticu-Mihăiești Zone and II Valea Chioarului Zone. 1971. Arch. of Institute of Geology and Geophysics. 4 This term would describe the same neomorphic features as those already pointed by F o 1 k (1965) in the neomorphic transformation of the micritic calcite to microspar. In this work we try to demonstrate that after the replacement of the calcium carbonate (aragonite or Mg-calcite) sediments by dolomite; there results a dolomicritic mass (less than 5 p in size) which passes via recrystallization to dolomicrospar (5 — 10 p in size). All this processes are penecontemporaneous with the sedimentation of the lagoonal deposits as it results from the analogy with the recent evaporitic environments correlated with our petrographical data. The dolomicrospar is characterized by the great uniformity of the crystal size (5 — 10 p) and by the ubiquity of the clay and organic ? impurities. The crystals have curved to plane boun- daries and form equant blocks. Tiny clay rims around the dolomicrosparitic crystals are fre- quent. The next step in this order of the dolomite recrystallization will be (probably in the early stages of diagenesis) the aggradation of the dolomicrosparite to dolopseudosparite. It is necessary to point out the genetic signification of these terms in opposition with the descrip- tive signification of T o o d’s microdolosparite and dolosparite (1966). Institutul Geologic al României X igr/ Fig. 1. Geologic map of^e ^dief d***; 3, Lower Gypsum Formalii; 4, Lower Red Clay Complex; 5, erystalline basement. 102 B. POPESCU 6 nature. This film was perhaps bom within the recrystallization process of dolomicrite to dolomicrospar, the argillaceous matter being pushed aside to the crystal borders (Pl. XI, Fig. 2). The ferrous ion that is all- ways present in our dolomitizing Solutions gives the brown colour of dolomicrosparite crystals. This ferrous ion is also present in Solutions that follow the penecontemporaneous dolomitization as it is clearly noticed by cryptocrystalline patches of limonite which obscure the texture, co- vering both dolomicrospar and the gypsum cement. Around the pores, 15—20 si euhedral dolorhombs can be generally noticed, contrasting with the 5 —10 p dolomicrosparite mass. The larger pore dolorhombs have palimpsest structures. The outer clear dolomite envelope is built around a cryptocrystalline nucleus probably of an organic or clay nature. There are also 50—75 p dolorhombs with a 15—20 p brownish dolomite nucleus (the same as those formerly described), which grades into clear dolomite cover at this 50—75 p crystal size. At high magnification on can notice that these crystals are not perfectly euhe- dral in shape, the growth of the clear dolomite cover being made at the expense of the dolomicrospar mass around it (Pl. XI, Fig. 3). Dolomi- crosparitic inclusions are kept within the gypsum cement. Larger surfaces of these cement have the same optical arrangement. Petrographical evidences as well as, we shall see, the sedimentolo- gical ones entitle us to suppose that this dolomite is the result of the penecontemporaneous dolomitization of upper intertidal and supratidal sediments. Dolomitization is the effect of capillary concentration of the interstitial solution. The fresh-marine waters moving landward become more and more concentrated being able to precipitate gypsum and to dolomitize the carbonate muds. This kind of process is common only for hot and dry regions where evaporation exceeds precipitation plus runoff. Nowadays, the recent sediments of the Persian Gulf (111 i n g et al., 1965; B u 11 e r, 1969; K i n s m a n, 1969; Kendall, S k i p- with, 1969) or those of the Andros Island (Shinn et al., 1965) are the sites of the above mentioned process. Gypsum precipitation precedes or is simultaneous with dolomiti- zation (B u 11 e r, 1969). As the result of this first process a dolomicritic (less than 5 p) mass with gypsum nodules and cement arises. Next to it, subaerial or submarine, that is directiv influenced by the marine waters, the agrading recrystallization of dolomicrite to dolomicrospar takes place. This is a proper time when the argillaceous and organic ma- terial mixed with carbonate material in the inițial sediment is pushed aside. Dolorhombs larger than 50 p with brownish 15—20 p dolomite nucleus are perhaps the last effect of the diagenetic event of this basal dolomite. This diagenetic event and field data strongly suggest that we may speak about a transgressive level (=basal transgressive supratidal dolos- tone — Friedman, Sanders, 1967). Landward dolomitization is thus the effect of a slow covering process of the supratidal areas by the transgressive sea. 'A Institutul Geological României igrA columns Forma- I Foidaș Fig. 2. — Lithologic < through Lower Gypsum tion of the Leghia and quarries. 1, red clays; 2, marls; 3, silty marls; 4, gypsiferous marls; 5, dolomites; 6, gypsum beaung do- lomites; 7, clayey dolomites; 8, limestones; 9, oolitic limesto- nes; 10, bioclastic limestones; 11, nodular and bedded massive gyp- sum ; 12, stromatolites; 13, num- ber of the analysed sample. Foidaș quarry £ 12 13 « 16 Leghia quarry 3621. 77 18 13 20 25 26 O 1 2 3 4m Institutul Geological României 104 B. POPESCU 8 To the upper part of this dolomitic level, the detritic supplies in- crease; quartz grains become larger up to 5 mm in diameter showing a poor sorting and muscovite quantity is sensibly high (Pl. I, Fig. 4). There comes without any transition a thin pebble and sand layer with oblic stratification, and next to it red clays with lens shaped laminae of sands and silts. Above this short terrigeneous episode there comes the first gypsum episode. This is a 5 m streaky-bedded mosaic5 getting in the upper part nodular mosaic. The streaks are dark coloured of an argillaceous or bituminous origin. The texture of gypsum nodules is random or aligned felted, with patches of blocky mosaic textures. There follows a 2.5—3 m thick allternance of finely laminated dolo- mites with nodular gypsum-bearing dolomites and nodular gypsum. The dolomites are very porous chalky, yellowish or light brownish in colour. If hammered they spread a bituminous smell. In the lowermost part of this dolomitic bed there is to be found a very thin lamination (Pl. I, Fig. 1,4) due to the larger quantity of mixed iron oxides, clay and organic matter, which was in suspension in the fresh marine waters of depocenter. The laminated dolomites pass gradu- ally to unlaminated white-greyish dolomites with some clay and ferru- ginous impurities but with gypsum diaclases and micronodules (Pl. I, Fig. 1 B). Above this already described microcycle one can find other microcycles of this kind or incomplete ones, always separated by a little erosional surface (Pl. I, Fig. 1D). Sometimes the lamination may be disturbed, the next microcycle moulding this relief. This disturbance is probably the effect of water movements in sedimentary medium, due to the high spring tides or abnorma! storms. The gypsum diaclases are normal to the bedding surface and are found either under the erosional surfaces or may transect (less common) more microcycles being larger than the former ones (Pl. II, Fig. 1). These structures suggest shrinkage cracks made up under subaerial ex- posure of dolomitized and gypsum bearing sediments. The resulted cracks have been subsequently filled by gypsum precipitated from concen- trated waters of supratidal pans. Overlaying the laminated dolomites alternance there are chalky, brown-yellowish gypsum nodules bearing dolomites or dolomites with 5—15 cm thick laminae. There can be also found gypsum diaclases of ten connecting the scattered gypsum nodules. The quantity of clay and fer- ruginous impurities is smaller here giving the rock a mottled aspect (Pl. IV, Fig. 1). At microscope study we may notice the presence of gypsum only as ce- ment within the fine varved brownish dolomites (Pl. XI, Fig. 2). The quantity of gypsum increases upwards within the microcycles where gypsum is to be found only as micronodules. They are mostly of an ovoidal or pris- -----------:----1 . 1 5 In this work we follow the Maiklem et al. (1969) terminology proposed for anhy- drite structures and textures. This is successfully applied by us in the field of gypsum structures and textures. Institutul Geological României (GR 7 9 LOWER GYPSUM FORMATION WEST OF CLUJ-NAPOCA 105 matic shape of 75 to 500 p. in size and are ,, floating” in a 5—10 p. dolomi- crosparitic mass (Pl. II, Fig. 2, 3). Around these micronodules as well as around the ernpty pores there are transparent 15—25 p. euhedral dolo- mites (Pl. XVI, Fig. 1). Some of these crystals have dark coloured, cryp- tocrystalline nucleus, probably of a clayey and/or organical nature (Pl. XVI, Fig. 1). In nodular-mosaic gypsum beds and in nodular gypsum bearing dolo- mites we may find the same ovoidal and prismatic voids, subsequently f illed by gypsum. The ovoidal micronodules have been considered as dissolved pel- lets or oblites and the prismatic ones as dissolved bioclasts. The dissolution of the sand and silt sized particles occurs in the last phases of the dolomi- tization process (111 i n g et al., 1965 ;Deffeyes et al., 1965 ; M u r - r a y , 1969). We may watch all the phases of pellet dolomitization. First larger anhedral dolomite crystals with palimpsest structures appear in dolomicritic pellets, leavinga porous mass behind. Then, this anhedral dolo- mite is pushed aside by gypsum infilling. Thus the photomicrograph 3 of Plate V is very instructive in this respect. One can see in it the following succession : under streaky nodular gypsum there is a thin pelletal bio- clastic dolomicrospar; within this dolomicrospar the pellets dolomitized bearing larger 10—20 p. dolomite crystals with palimpsest structure ; other pellets are completely filled by gypsum. In the underlying pelletal do- lomicrite, there can be seen gypsum filled fissures (probably former mud- cracks) and pores, as well as the thin rims of dolomicrospar around them (see also Pl. XIV, Fig. 4, Pl. XIII, Fig. 1,2). The nodular-mosaic gypsum beds are intercalated at different levels in the dolomites. The gypsum nodules are of centimetric size and the clayey impurities lend them a grey colour and a dull luster. The dolo- microsparite was pushed aside by the growth of gypsum nodules. More nodules are often joined together, thin dolomicrosparitic streaks being left among them (Pl. V, Fig. 2,4). The gypsum nodules have a blocky mosaic and more seldom a felted texture. Sometimes in the dolomites there are to be found gypsum rosettes. The acicular gypsum of rosettes is mostly anhedral in shape but there are also well shaped crystal boundaries. Unaffected dolomicrospar is found within acicular gypsum (Pl. IV, Fig. 2,4). Out of what we have mentioned above it results that the first step in dolomitization of carbonate sediments is the transformation of clay sized sediments into 1—5 p. dolomicrite. An advanced dolomitization causes the dissolution of dolomitization resisting particles (e.g. bioclasts and the great majority of pellets). Concomitently or just before there takes place the dolomicrite to dolomicrospar recrystallization. The resul- ting pores were subsequently filled by gypsum precipitated from supra- tidal highly concentrated waters. These transformations take place in the wet sediments in the penecontemporaneous stage of diagenesis. During the early diagenesis the precipitation of dolorhombs larger than 10 p oc- cured. This was probably possible owing to a long interaction of the dolo- microspar with interstitial Solutions or by precipitation from the residual Mg-rich solution resulted after the gypsum precipitation. Thus the penecontemporaneous dolomitization and recrystallization occured at )X~ Institutul Geologic al României IGRZ 106 B. POIPESCU 10 the same time or immediately before the gypsification procesa. In the early diagenesis only the larger dolorhombs will precipitate. Unlike the first dolomitic level (3621/14, Fig. 2) atthislevel (3621/12-8, Fig. 2), due perhaps to a longer subaerial exposure the evaporitic diage- nesis is more advanced. There occurred the dissolution of the resistent dolomization particles, the growth of gypsum nodules, and the subse- quently filling of the resulted vugs by gypsum. In both quarries as well as in other outcrops a thin varved mari with gypsum lenses of about lo cm thick beds overlies the lithological sequence already described. There follows the main gypsum mass of the Lower Gypsum Formation. It is bedded massive (1—2,5 m thickness of beds) with thin varved green or blackish clay joints. The gypsum is chalky white, seldom greyish or reddish with black, probably bituminous laminae. The upper part of the main gypsum mass is blocky nodular-mosaic not bedded structure. Kandom felted and blocky mosaic textures occur. In the upper nodular gypsum the streaks are greyish and felted and blocky mosaic textures are quite common. Over the main gypsum mass in Leghia quarry there is a gypsum bearing, finely laminated green clays. In the gypsum lens zones the lamination of the clays is disturbed due to the gypsum growth within muddy sediment. In Foidaș quarry over the main gypsum mass there follows a 5 cm thick alternation of dolomites, gypsum bearing dolomites and gypsum nodules bearing marls as well (4177/26—19, Fig. 2). In the first 2 in there are white-yellowish chalky dolomites having variable amounts of clay and gypsum and nodules. There follows a white porous dolomite of 1 m thickness (4177/25, Fig. 2). Here, within a dolomicrospar of 5—10 u. in size, around the pores, clear euhedral dolorhombs of 15 p and larger are to be noticed as well. There can be also found mica, quartz and feldspar grains probably of an eolian origin. This texture is often obscured by argillaceous patehes. The white porous dolomite is overlain by a 10 cm thick brownish dolomite with smaller than one centimeter lenses of green-grayish pelletal dolomite (Pl. VII, Fig. 1). A large number of 100—500 ți ovoidal pellets, a smaller quantity of quartz grains (less than 5%) clay and limonite are to be found within the 5—10 u. dolomicrosparite mass. Most of the dissol- ved pellets are gypsum filled and the undissolved ones exhibit a different stage of dolomitization. The dissolved pellets leave ovoidal vugs which before gypsum filling are covered inside by a thin limonitic film (Pl. XIV, Fig. 1,2). After the gypsum filling this appears like a brownish cryptocrys- talline envelope. Around the pores, as we have already mentioned before, there are the euhedral dolorhombs with or without palimpsest relicts. In the dolomicritic tongues most of the pellets are undissolved (Pl. VII, Fig. 2,4) but for those on the dolomicrite/dolomicrospar boundary which are gypsum filled. The pellets of dolomicrite tongues are cryptocrys- talline with scattered dolorhombs whose nuclei are dark probably of a mixed clay and organic nature. Institutul Geological României XJGR/ 11 LOWER GYPSUM FORMATION WEST OF CLUJ-NAPOCA 107 Gypsum microdiaclases start from dolomicrosparite to the dolo- micritic tongues (Pl. VII, Fig. 2). They transect gypsum filled pellets or larger dolorhombs bearing pellets without no ehange in their texture. Such being the case it results that this pelletal dolomitic bed is a review of all the diagenetic changes having occurred in the already des- cribed dolomites. Summing up the petrographical descriptions and ultimately the textural relations between different component» of the mentioned dolomitic rocks, we can presume the following diagenetic events: 1. The dolomitization of carbonate mud which turn into a 1—5 ia dolomicritic mass. Penecontemporaneous recrystallization of dolomicrite to dolomicrosparite is supposed to occur in the unlithificated wet dolo- micritic sediments. The capillary concentration and the seepage refluxion are suspected to be responsible with. 2. By the advancing of the dolomitization process, the resistant siltic or arenitic particles (all the bioclasts and some of the pellets) will be dissolved leaving an important vug porosity behind. Some of the undissolved dolomicritic pellets may bear larger dolorhombs with palimp- sest relics of an organic nature. 3. In the newly ereated porosity it can be found clay, organic and ferruginous impurities which imbued the walls of the pores. These impu- rities will be first lost by decantation from the brines that are to be found in supratidal pans and lagoons. Then, by seepage of highly concentrated brines gypsum can precipitate filling thus most of the pores, shrinkage cracks and other cavities. If the sediments were exposed, in the dolomi- critic but the most common in the dolomicrosparitic bulk of sediment the gypsum nodules will grow. 4. After a thin burial or due to the long contact of „residual” mag- nesium-rich Solutions resulting from gypsum precipitation, the precipi- tation of clear euhedral dolorhombs larger than 10 (a takes place around the filled and unfilled cavities. According to the latest dealing with supratidal „sedimentation” as well as with the changes occurring within the mass of such kind of se- diments we presume that the 1, 2, 3 phases of our diagenetic event are penecontemporaneous. There are many evidences that these transfor- mat ions take place in the soft wet sediment. The precipitation of clear euhedral dolomite larger than 10 is probably early diagenetic. Overlying this much discussed pelletal dolomite there is a 30 cm ■of nodular gypsum bearing marls. The expansion of nodules in the soft sediment has disturbed the inițial lamination. The muddy se- diment between the nodules has been expelled, remaining only as thin streaks (Pl. VIII, Fig. 1, Pl. XIV, Fig. 3). The nodules are alligned ■or random felted with blocky mosaic patches in texture (Pl. VII, Fig. 3). In this felted texture there are larger than 250 p. euhedral anhydrite laths. Generally speaking, the anhydrite is precipitated from high temperature (more than 35C)° and chlorinities (more than 145%) interstitial Solutions A Institutul Geological României J6R/ 108 B. POPESCU 12 (Butler 1969). These very restrictive conditions are met in inner sabkha during the dry and hot season (K i n s m a n , 1969). There follows a chalky yellowish free of gypsum dolomite bed. And here as we have always noticed up to now, within a 5—10 dolomicrospa- rite there are the common euhedral dolorhombs around the pores. As gypsum is missing here too, we may assert that in our supratidal sequence the first precipitate is dolomite. This fact is contradictory to the latest works on the recent sediments of the Persian Gulf (111 i n g et al., 1965 ; Butler, 1969 ; Kendall, S k ip w i t h , 1969). This free of gyp- sum dolomite might represent the supratidal sediment of inner sabkha (Butler, 1969). The brines with highest Mg/Ca ratio come from the hydrostatic level which have already precipitated gypsum in the outer sabkha. Neomorphism e.g. the recrystallization of dolomicrite to dolo- microsparite does not depend on gypsum precipitation. This dolomite is overlain by a 20 cm yellowish pelletal dolomite. The pellets are in different stages of dissolution (Pl. VIII, Fig. 4). The vugs thus created generally rimed by a thin limonitic envelope. Some of the pellets show a central relic surrounded by a gypsum envelope (Pl. XIII, Fig. 3, 4) suggesting a replacement of pelletal dolomicrite by gypsum. Bedded nodular gypsum of a 15 cm thickness and yellowish chalky dolomite of a 5 cm thickness overlie the pelletal dolomite. They have the same textures and structures as those described for subjacent beds (see the description made for 4177/23 and 4177 /22). Above them there lies a milky-white not bedded nodular-mosaic gyp- sum. The streaks between nodules are dark of an argillaceous-organic nature. And here the textures and structures are comparable with those of 4177/23, 4177/31, 3621/6, 3621/5 (Fig. 2). The 4177/18 may be correlated with 3621/5 and 3621/6 levels of the Leghia quarry. In the Foidaș quarry above the nodular-mosaic gypsum there follows a 4,25 m yellowish chalky dolomite and greyish clayey dolomite alternance. The dolomites are highly porous being pelletal and bioclastic dolomites with scattered quartz grains (Pl. IX, Fig. 1). The textures are largely obscured by an important amount of clay. The rock mass is less than 5 jx dolomicrite. Around the micropores and scattered in the dolomicrite there are, following the rule, dolomicrospar patches. Southwards, at the Leghia quarry, the equivalent of this dolomicrites is an alternance of chalky-clayey dolomites and greenish bearing gypsum nodule marls. In both quarries there follows a not bedded, 1 m thick nodular-mosaic gypsum. It is much like those already described but here the streaks are only of white chalky clayey dolomite (Pl. XV, Fig. 4). Further on the detailed references will regard only the Foidaș quarry as we have here the most obvious profile between the Lower Gypsum Formation and Nummulites perforatus Beds. In the Leghia quarry the uppermost part of the wall is blown off by the explosions during the ex- ploatat ion. /A Institutul Geological României igrA 13 LOWER GYPSUM FORMATION WEST OF CLUJ-NAPOCA 109 Thus in the Foidaș quarry the nodular-mosaic gypsum is overlain by a 1,80 m chalky, yellowish dolomite bed which gradually passes to clayey, brownish bioclastic dolomite. The bioclasts are dissolved and then filled with gypsum. Around the pores and the dissolved bioclasts there can be seen dolorhombs larger than 10 [x which markedly contrast with the dolomi- crosparitic mass (Pl. IX, Fig. 4). Some of the pores are imbued with limonite and clay impurities. Above the bioclastic dolomite is an oblitic bioclastic limestone of a 0,70 m thickness. The mud supported rock is a packstone according to D u n h a m ’ s (1962) nomenclature (Pl. X, Fig. 1). This level is stron- gly transgressive. Southwards, the oolitic limestone becomes devoid of mud matrix, the bioclasts are subordinate ; the cement is sparry calcite, the rock becoming a grainstone (Pl. X, Fig. 2). The scarce bioclasts play a sheltering role, the fabric under them being porous and incompletely cemented (Pl. XVII, Fig. 2). The oolits have a quartz, miliolid or pellet nucleus. As in the Foidaș quarry the oolits are less than 15% and the asso- ciated matrix and particles (pellets, lumps) suggest a lagoon environment, we consider that the oolits have been splashed from the oblitic shoals into the lagoon, thus resulting a mud supported rock. Therefore, we may sup- pose that the lagoon was basinward as compared to the oblitic shoals (we mention that the erystalline basement and hence the land was south- wards). Overlaing the oblitic limestone without any transition there is a 1,5 m greyish mari bed. The marls contam the mollusc molds and milio- lids. At the upper part the marls become more calcareous and highly bioclastic. The bioclasts are mainly forams, most of them being filled with sparry granular mosaic calcite. This kind of fabric is characteristic of modern-near shore calcareous sediments (Alexandersson, 1972), being abundant in turbulent environments. A thin stromatolitic level of 20 cm thickness ends the first cycle of Nummulites perforatus Beds. It is an ancient algal mat of „intertidal” origin6. Various kinds of grains, most common bioclasts are bound within the algal micrite (Pl. X, Fig. 4). Various neomorphic textures are to be found in these algal micrites (Pl. XVII, Fig. 3, 4). Thus the Nummulites perforatus Beds started with a transgressive oblitic limestone followed by a lagoon bioclastic marls and by near shore bioclastic and stromatolitic levels. Over this short „intertidal” episod there comes the main marly mass of Nummulites perforatus Beds with a net marine fauna; nummulites, echinoids and molluscs. 6 In the Eocene time, the Transylvanian Basin was an arm of the Pannonian Sea. The tides probably were of small amplitude and consequently the intertidal space was quasiabsent as results form the lack of intertidal-structure sediments in our lithological sequence. We used he supra-, inter- and subtidal terms for making them easier to understand when referring to the carbonate sedimentology works. Institutul Geological României (GR 7 110 B. POPESCU 14 Diseussions on the Environment of Deposition The interpretation of the environment of deposition is based broadly on petrographical and stratonomic evidences given us by the two reference sections : Leghia and Foidaș. We will try to reconstruct the major events of sedimentary environment in the deposition time of Lower Gypsum Formation also adding the supplementary information furnished by many other sections seattered over the study area (Fig, 1),. As we have already said, above the coarse deposits — microconglo- merates, pebbles, sands and sandstones with red clays intercalations — of terrigenous origin, there comes transgressively the first occurrence of an evaporite regime in the region west of Cluj. The basal transgressive dolo- mite (common in many other world wide regions — F r i e d m a n , S a n d e r s , 1967 ) is in fact a supratidal sediment which has become- dolomitized under the action of capillary eoncentration process of marine Solutions. The basal dolomite (3621/14, Fig. 2) is an inițial mixture of wind blown material (quartz and mica) and small amounts of carbonate sedi- ments of supratidal origin. The interstitial water loss due to the high rate of evaporation is counterbalanced by the continuous flow of ground waters from the adiacent sea and by occasionally flood recharges (capil- lary eoncentration vs. flood recharge). This kind of sedimentation and their penecontemporaneous diagenesis is known in sedimentological literature as sabkha cycle. It is knowm that in the supratidal spaces of hot and dry regions where evaporation exceeds precipitation and runoff, the eoncentration of interstitial solution is 10 times greater than that of fresh marine waters (Kinsman, 1969). Aragonite and gypsum can precipitate at this eoncentration and the replacement reaction between sediment and inter- stitial Solutions can occur (111 i n g et al., 1965 ; B u 11 e r , 1969 ; Kinsman, 1969). Due to the aragonite and gypsum precipitation the Mg/Ca ratio will become sensibly high because of using Ca+ + in CaSO4 and CaCO3 lattices. The growth of^magnesium eoncentration in intersti- tial Solutions will make possible the beginning of the carbonate mud dolo- mitization. 111 i n g et al. (1965) and B u 11 e r (1969) suggest that there is a direct quantitative relation between dolomitization and gypsum preci- pitation. Out of B u 11 e r ’ s statements it results that this relation may be written as follows : 2CaCO3 + Mg++ + SOr = CaMg(CO3)2 + CaSO4 sediment solution solution sediment sediment A microcrystalline or cryptocrystalline sediment will result out of carbonate mud dolomitization. The siltic and arenitic particles are’t resis- tent to dolomitization and will be leached by advancing of the dolomiti- 7 Op. cit. point 6. M Institutul Geological României igr/ 15 LOWER GYPSUM FORMATIOY WEST OF CLUJ-NtAPOCA 111 zation process (111 i n g et al., 1965 ; Deffeyes et al,. 1965). At the same time or just after, the penecontemporaneous recrystallization of dolo- micrites takes place. The newly created pores can be subsequently filled by gypsum. The basal dolomite records the first phases of penecontemporaneous diagenesis — the replacement of carbonate sediments by dolomite and its recrystallization to dolomicrospar. These are immediately followed by the cementation with gypsum (Pl. XII, Fig. 1). In the early diagenesis a precipitation of euhedral dolorhombs larger than 10—25 p takes place. Then, these euhedral dolorhombs acquire a clear dolomitic envelope at the expense of the surrounding dolomicrosparite (Pl. XI, Fig. 3). A new terrigenous supply is marked without any transition by cross laminated sands and pebbles. Above the sands there lies red clay, well laminated with sand lenses only. These deposits are thicker and thicker from north to the crystalline basement (south). The terrigenous deposits signify a regressive phase of the sea and the installation of con- tinental sedimentary conditions. Probably many lakes receiving the tor- rential apports from the Gilău Mountains mainland were formed in the supratidal flat. After this regressive episode the evaporite-marine regim is definiti- vely established in the studied area. Thus, it is only north to the Dumbrava village (Fig. 1) that there is a nodular gypsum bed (Fig. 2, 3621/13 and 4177/31). It is a typical supratidal deposit. By a long time persistence of the evaporative conditions in the mid and inner sabkha, gypsum will largerly precipitate. It will grow in clay and silt sized sediments expelling and digesting the surrounding sediment. If sediments are carbonates, the dolomitization and recrystallization occur first. In Plates XIV, Figure 4, and XV, Figures 1,2, we can notice the tiny streaks and isolated crystals of dolomicrospar within gypsum nodules. In its southward advance, the sea overlaps the nodular gypsum which will be overlain by subtidal pelletal and bioclastic muds. These deposits have about the same extent as the basal dolomite but not exceeding them. The first deposits are finely laminated, pelletal bioclastic dolomites, followed by unlaminated, gypsum nodules and micronodules bearing dolomites. The structures and textures of these sediments strongly resem- ble with those of the coasta! lagoon pans (K i n s m a n , 1969) and with well laminated brown clayey silts of the transition zone of the Colorado River Delta (Thompson, 1968). In the upper intertidal and supra- tidal area of the Colorado River Delta the gypsum is precipitated between the products of two floods. As in the Transylvanian Basin the tides where probably of little amplitude, the coasta! and supratidal lagoons had a greater stability leading to a rapid concentration of waters and thus to gypsum pre- cipitation. The petrographical sketches read that the dolomitization and then the recrystallization of the dolomicrite promotes from pores to the bulk of matrix (Pl. IX, Fig. 4, Pl. XII, Fig. 2). We presume that dolo- mitization started due to the seepage refluxion of thin films of suprasa- turated solution from the shifting supratidal lagoons. /A Institutul Geological României IGR/ 112 B. POPESCU 16 After a subaerial exposure desiccation cracks may occur. The pores, the leaching grains and the desiccation cracks are filled by gypsum of a flood recharge origin (Pl. XIV, Fig. 4). If a new supply is absent the gypsum nodules growth is allowed and that is why the dolomicrite and the clay „matrix” is pushed aside. Before the concentration of the new marine supplies in the already mentioned cavities and above the substratum the impurities carried in solution by this flooded waters will be laid down. The main gypsum mass evidences a new sea retreat, being deposited in a Coastal lagoon with permanent water layer due to the quite regular periodic influx. The gypsum is thinner southwards and dissapears north of Păniceni village (Fig. 1). Near the Leghia village it attains 20 m in thick- ness being bedded massive with clayey joints and dark varved lamina- tion. The varved and bedded structure suggests a stable evaporitic regime with periodic influxes. Each new marine supply was marked by the tiny clayey or clayey-bituminous laminae which represent the products of decantation of the suspended matter. The mixture of sediments with the organic matter is reported in many areas of evaporite deposition. The dark colour of these laminae are due to strongly reducing conditions which are revealed by H2S release (ex : Baja California, Phleger, 1969). On the upper part of bedded gypsum mass there appear the bedded nodular-mosaic structures which, as we have already said, are probably of an intertidal-supratidal origin. Thus, the lagoon filling leads its inclusion in the supratidal flat with its characteristic processes. Nortwards, i.e. basinward, pelletal muds are deposited (Fig. 2, 4177/26—24). If exposed, they undergo diagenetic changes already men- tioned. We may also say that in this pelletal dolomite the leached pellets coexist with the dolomicritic ones. 111 i n g et al. (1965) wrote about the occurrence of the same dolomitic mud fabric in the supratidal flats in the Persian Gulf. The leached pellets are subsequently filled by gypsum. The undissolved pellets are gradually digested and then filled by gypsum (according to the rule here presented, in early diagenetic stage arround the pores and the gypsum filled pellets, euhedral, clear dolorhombs larger than 10 |x were formed). In the Leghia quarry and southwards, this pelletal dolomite is mis- sing. This is in favour with the idea of a regressive phase which began at the same time with the main gypsum mass deposition. A new marine ingression, overlaying the sediment outcropping in both quarries but not extending far to the south, is represented by an alternance of marly dolomites and finely laminated marls. Due to a sub- sequent retreat of the sea, these sediments have been subaerially exposed. Within their mass a whole range of sabkha processes takes place. Nodular gypsum displacive structures are to be found in the upper part of this regressive sequence (4177/18 and 3621/5, Fig. 2). It is only 1 km south of the Leghia quarry that these nodular gypsum are overlain by the se- diments of a new marine ingression. Institutul Geological României IGR/ 17 LOWER GYPSUM FORMATION WEST OF CLUJ-NAPOCA 113 These ingressive sediments are subtidal bioclastic muds, in the north and pelletal dolomites with nodular gypsum intercalations in the south (4177/17 and 3621/2-4, Fig. 2). The last regressive phase in the time-span of the Lower Gypsum Formation emphasises the supratidal condition of deposition in the area. The scattered gypsum nodules within clay matrix are the only evidence left by this event. Anomia bearing dolomites overlie most of the underlaying sediments, Corning in direct touch with the main gypsum mass at the Dumbrava village and with the basal dolomite north of the Păniceni village. The Nummulites perforatus Beds started with a transgressive oblitic limestone having about the same extent as the AnomiaA)e&rmg dolomites. The oblites suggest us a near shore deposition. They are mud supported, mixed with lumps, pellets and bioclasts northwards (i.e. basinward) and grain supported, cemented by fibrous sparite southwards (i.e. in the vici- nity of the crystalline basement). A new eustatic oscillation is recorded in the studied carbonate area, that is a thin stromatolitic level (4177/9, Fig. 2) representing an ancient algal mat of a probably upper subtidal-lower intertidal origin. Conclusions 1. Petrographical and sedimentological evidences demonstrate the supratidal origin of the evaporites in the Lower Gypsum Formation. 2. Most of the carbonate sediments in this formation were deposited in normal marine waters. By supratidal exposure they underwent a sabkha penecontemporaneous diagenesis. 3. The diagenetic events seem to be the following: a) The penecontemporaneous dolomitization of carbonate muds are probably due both to capillary concentration and seepage refluxion phenomenon. In this first stage the lime muds are replaced by a micro - crystalline dolomite less than 5 p.. Unlike the penecontemporaneous supra- tidal diagenesis revealed by the recent sediments, the gypsum cement is seldom found in this stage. b) After a longer subaerial and may be submarine exposure, the dolomitization process goes on. The pellets, probably of an inițial ara- gonite mineralogy, will be dolomitized and the bioclasts will be dissolved. The recrystallization of dolomicrite (less than 5 (x) to dolomicrospar (larger than 5 [x but less than 10 jx) takes place in the same stage. c) The gypsum filling of the newly created pores, the replacement of dolomicrite or dolomicrosparite by gypsum and the gypsum nodules growth take place at the same time or immediately after the above men- tionated stage. d) Euhedral dolorhombs are formed around the pores and gypsum filled pellets and bioclasts after a thin burial, probably due to the long contact of high concentrated magnesium solution during the early diage- netic stage. There is no evidence for late diagenetic changes. 8 — c. 11 Institutul Geological României yiGRZ 114 B. POPESCU 18 4. Within the Lower Gypsum Formation there are recorded several penetrations and retreats of the sea which left behind thin sediments. The first and the last penetration of the sea (i.e. the basal dolomite and the Anomia-be&rmg dolomite) had the greatest extent. The regressive phases brought about the subaerial exposure of marine sediments -which bear the evaporite diagenesis. REFERENCES Alexandersson T. (1972) Granular Growth of Marine Aragonite and Mg-Cal- cite : Evidence of Precipitation from Supersaturated Seawater. J. Sed. Petr. 42,2, p. 441 — 460. Tulsa. Butler G. (1969) Modern Evaporite Deposition and Geochemistry of Coexisting Brines, Trucial Coast, Persian Gulf. J. Sed. Petr. 39, 1, p. 70— 89. Tulsa. Deffeyes K. S., Lucia F. J., Weyl P. K. (1965) Dolomitization of Recent and Plio-PIeistocene Sediments by Marine Evaporite Waters on Bonaire Netherlands Antiles. In : Dolomitization and Limestone Diagenesis. Ed. by L. C. Pray and R. C. Murray. Soc. Econ. Paleontologists and Mineralogists Spec. Publ. 13, p. 71 — 89., Tulsa. D r a g o ș V. (1969) Contribuții la cunoașterea genezei evaporitelor din bazinul Transilvaniei. St. Cerc. Geol. Geof. Geogr. ser. Geol, 14, 1, p. 163—181. București. D u n h a m R. (1962) Classification of Carbonate Rocks According to Depositional Texture. Am. Assoc. Petr. Geol. Mem. 1, p. 108—121. Tulsa. F o 1 k R. L. (1965) Some Aspects of Recrystallization in Ancient Limestones. In : Dolomi- tization and Limestone Diagenesis. Ed. by L. C. Pray and R. C. Murray. Soc. Econ. Pale- ontologists and Mineralogists. Spec. Publ. 13, p. 14 — 48. Tulsa. Friedman G. M. (1959) Identification of Minerals by Staining Methods. J. Sed. Petr. 29, 1, p. 87-97. Tulsa. — Sande r s J. (1967) Origin and Occurence of Dolostones in Carbonate Rocks. Ed. by G. V. Chillingar, H. J. Bissell, R. W. Fairbridge. Dev. in Sedimentology 9A, p. 264 — 347. Amsterdam. Illing L. V., Wells A. J., Ta y lor J. M. (1965) Penecontemporary Dolomite in the Persian Gulf. In: Dolomitization and Limestone Diagenesis. Ed. by L. C. Pray and R. C. Murray. Soc. Econ. Paleontologists and Mineralogists. Spec. Publ. 13, p. 89-111 Tulsa. K e n d a 11 C., S k i p w i t h P. (1969) Holocene Shallow-water Carbonate and Evaporite Sediments of Khor al Bazam, Abu Dhabi, SW Persian Gulf. Am. Assoc. Petroleum. Geol. Bull. 53, 4, p. 841-870. Tulsa. K i n s m a n D. J. J. (1969) Modes of Formation, Sedimentary Associations and Diagnostic Features of Shallow-water and Supratidal Evaporites. Am. Assoc. Petroleum. Geol. Bull. 53, 4, p. 830-840. Tulsa. Koch A. (1894) Die Tertiarbildungen des Beckens der Siebenburgischen Landsthiele. I Palâogen Abtheilung. Mitt. Jahresb. k. ung. geol. Anstalt. X, 6. Budapest. Maiklem W. R., B e b o u t D. C., Glaister R. S. (1969) Classification of Anhy- drite a Practicai Approach. Bull. Canad, Petr. Geol. 17, 2, p. 194—233. 19 LOWER GYPSUM FORMATION WEST OF CLUJ-NAÎPOCA 115 Murray R. C. (1969) Hidrology of South Bonaire, N. A, A. Rock Selective Dolomitiza- tion Model. J. Sed. Petr. 39,3, p. 1007-1014. Tulsa. P a u c ă M. (1967) Contribuții la cunoașterea zăcămintelor de săruri rniocene din România. D. S. Inst. Geol. Pom. LII, 2. București. P h 1 e g e r F. (1969) A Modern Evaporite Deposit in Mexico. A, Assoe. Petrol. Geol. 53, 4, p. 824 — 829. Tulsa. Răii ea nu Gr., Saulea Emilia (1956) Paleogenul din regiunea Cluj-Jibou. An. Com. Geol. XXIX, p. 271 — 308. București. S h i n E. A., Ginsburg N. R., Loyd R. M. (1965) Recent Supratidal Dolomite from Andros Island, Bahamas. In: Dolomitization and Limestone Diagenesis. Ed. by L. C. Pray and R. C. Murrray. Soc. Econ. Paleontologists and Mineralogists. Spec Publ. 13, p. 112-124. Tulsa. Thompson R. W. (1968) Tidal Fiat Sedimentation on the Colorado River Delta, NW Gulf of California. Geol. Soc. of America Soc. Mem. 107, p. 1 — 133. Boulder. Todd T. W. (1966) Petrogenetic Classification of Carbonate Rocks. J. Sed. Petr., 36, 2, p. 317—340. Tulsa. Institutul Geological României Institutul Geological României PLATE I Institutul Geological României PLATE I Fig. 1. - Dolomicrospar partly cemented by gypsum. In the dolomicrosparitic mass there are seattered quartz-and mica grains as well larger dolorhombs (with dashed line in the center of the photo) with palimpsest structures. N 4-. Leghia quarry, 3621/11. Fig. 2. — Same as Fig. 1. There are lo be shown the gypsum cement (while milky patches) and the quartz-and mica grains (white like small pin poinls). N //. Leghia quarry 3621/ÎL Fig. 3. - Dolomicrospar partly cemented by gypsum. Note the larger dolomicrilic intra- elast (lower right corner of photo). Basal transgressive dolomite. N//. Finului Valley. Fig. I. — Dolomicrite with large amount of quartz grains. Note the unsorling and the angu- larily of some grains. N //. Finului Valley. Institutul Geological României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. I. Anuarul Institutului de geologie și geofizică, voi, XLVIII. 16 R/ Institutul Geological României PLATE II Fig. 1. — Polished slab in fine laminated dolomite. A, B, C, D, E are intervals controlled by thin sections. The lamination is due to the large amounts of iron oxide, clay and organic matter. Note the increase in gypsum micronodules (in fact leached pellets subsequently filled by gypsum) on the upper part of lower microcycle. Under a little erosional surface (C) there are tiny microdiaelases filled by gypsum, interpreted as former shrinkage craks. The upper part of the photo is an inverse microcycle with disturbed lamination. Leghia quarry 3621/12. Fig. 2. — Dolomicrosparite with rare leached pellets. Note the large amount of cryptocrystalline clay and organic matter obscuring the dolomicrosparitic fabric. N//. Leghia quarry 3621/12 interval A in Fig. 1. Fig. 3. — Pelletal dolomicrospar. Same features as in photo 2. N//. Leghia quarry 3621/12, interval B in Fig . 1. Fig. 4. — Interval C in Fig. 1. The cryptocrystalline laminae arc of an iron oxides, clay and organic matter origin. N//. Leghia quarry 3621/12. Institutul Geological României B. Popesw. Lower Gypsum Formation West of Cluj-Napoca. Pl. II. 2 1 Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR PLATE III Fig. 1. — Dolomicrosparite. The dark laminae are a mixture of clay iron oxides and bituminous material. N//. Leghia quarry 3621/12, interval D in Fig. 1, Pl. II. Fig. 2. — Leached ostracods shells subsequently filled with gypsum. The dolomicrosparilic fabric is largely obscured by cryptoerystalline clay iron oxides and bituminous material. N//. Leghia quarry 3621/12, interval E in Fig. 1, Pl II. Fig. 3. — Same as Fig. 4. N +. Leghia quarry 3621/11. Fig. 4. — Bioclastic dolomicrosparite. The leached shells arc subsequently filled by gypsum. Note the definite boundary of the larger Shell and the clear euhedral dolomite (ar- rows). N//. Leghia quarry 3621/11. B. Popesci'. Lower Gypsum Formation West of Cluj-Napoca. Pl. III. 2 4 1 Anuarul Institutului de geologie și geofizică, voi. XLVIII. | W Institutul Geologic al României k igr/ PLATE IV Fig. 1. — Polished slab, Dolomite with gypsum nodules and diaglases. The nodules are former cavities or macropores enlarged by subsequent circulation of gypsum saturated Solutions. Note the fine channel bonds between nodules (lower part of photo). Leghia quarry 3621/10. Fig. 2. — Gypsum rosettes in dolomicrosparite fabric. Most of gypsum needles are partly anhe- dral in shape. N//. Leghia quarry 3621/10. Fig. 3. — Dolomicrosparite. The very porous fabric is partly ccmentcd by gypsum. N//. Leghia quarry 3621/10. Fig. 4. — Gypsum rosette. Within gypsum needle there are kept undigested crystals of dolo- microsparite. N//. Leghia quarry 3621/10. B. Popescu Lower Gypsum Formation West of Cluj-Napoca. Pl. IV. 1 2 Anuarul Institutului de geologie si geofizică, voi. XLVIII. Institutul Geological României IGR> PLATE V l'ig. 1. — Polished slab. Bedded nodular-mosaic gypsum within brown-yellowish dolomite. Note the definite upper contact between the two laminae and the irregular one in the lower part. The lower contact is due to the subacrial exposure and to the gypsum growth, the upper contact is due to the sea landward ingression. Leghia 3621/9. A, B, C, D intervals are controlled by thin scctions. big. 2. — Gypsum nodules. The streaks between nodules are made of dolomicrosparite. There are isolated dolomicrosparite crystals kept within gypsum nodules. Thus, the recrysta- llizalion take place before the growth of nodules. N //. Leghia quarry' 3621/9, interval A in Fig. 1. Fig. 3. — Transition from nodular gypsum bând (wite in the upper part of photo) to pelletal bioclastic dolomicrosparite and to the pelletal micrite (black in the lower part of photo). In the dolomicrosparilic layer most of the pellets arc leached and filled with gypsum. There are also pellets (arrows) with scattered dolorhombs having crypto- crystalline nudei. N//. Leghia quarry 3621/9, interval B in Fig. 1. Fig. -1. — Gypsum nodules with tiny' streaks of dolomicrosparite. The growth of gypsum nodules pushed aside the soft dolomicrospar around them. Compare with photo 2. N//. Leghia quarry 3621/9, interval G in l'ig. 1. Institutul Geologic al României B. Popescu. Lower Gypsum Formation West of Cluj -Napoca. Pl. V. 3 4 Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE VI l-'ig. 1. — Nodular gypsum. In the dolomicrosparilic fabric there arc „nudei” of futurc no- dules. By expansion they can join cxpelling Ihe dolomicrosparite around them. N//. Leghia quarry 3621/9, interval D in I-'ig. 1, Pl. V. l-'ig. 2. — Dolomicrosparite with an important vug porosity. Some of pellets kepp larger dolo- rhombs with palimpsest structures and are partly filled by gypsum. N//. Leghia quarry 3621/8. I-'ig. 3. — Pelletal dolomicrosparite. The pellets are leached and subsequenlly filled by gypsum. Some of them arc „weldcd” forming gypsum lenscs. N//. l-'oidaș quarry 4177/28. I-'ig. 4. — Same as l-'ig. 3. Here one can notice the line of penetration of the gypsum rich Solu- tions. In the upper part of photo there arc not filled pellets. N + . l-'oidaș quarry 4177/28. Institutul Geological României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. VI. 3 Anuarul Institutului de geologie și geofizică, voi. XLVIII. 4 «gr/ Institutul Geological României PLATE VII Fig. 1. — Polished slab. Brownish pelletal dolomicrosparite with lenses of slightly pelletal dolomicritc (with dased line). Foidaș quarry 4177/24. Fig. 2. — Fpper dolomicrosparite-dolonricrite boundary. Within the pelletal dolomicritc there arc leached and not leached pellets. Some of leached pellets arc subsequenlly filled by gypsum. From the pelletal dolomicrosparite start gypsum filled diaclases which transect the leached and then filled with gypsum pellets as well, not leached pcl- lets (arrows) leaving no tcxtural changes. Thus, the gypsum rich Solutions arc not related to the dolomitization process. X//. Foidaș quarry 4177/24. Fig. 3. — Lower dolomicritc-dolomicrosparite boundary. Note the well definite contact and the complete absence of pellets. N . Foidaș quarrry 4177/24. Fig. I. — Tcxtural delail in the nodular gypsum. Blocky texturc. N . Foidaș quarry 4177/23. Institutul Geological României B. Popesct. Lower Gypsum Formation West of Cluj-Napoca. Pl. vu. Anuarul Institutului de geologie și geofizică, voi. XLVIII 16 R/ Institutul Geological României PLATE VIII Fig. 1. — Polished slab. Nodular-mosaic gypsum. The growth of nodules have expelled the marly sediment surrounding them; some of the nodules joined together, leaving only tiny marly streaks. Foidaș quarry 4177/23. Fig. 2. — Dolomicritc in the lower part of the photo, passing into dolomicrospar. Noted the highly porous fabric in the resulted dolomicrosparite area. N//. Foidaș quarry 4177/22. Fig. 3. — Blocky gypsum mosaic. The euhedral prismatic crystals (arrows) are anhydrite. Foidaș quarry 4177/18. N +. Fig. 4. — Pelletal dolomicrosparite. There coexists leached, not leached and partly leached pellets (arrows). Some of them are filled with gypsum. N jl. Foidaș quarry 4177/21. Institutul Geological României B .Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. VIII. 1 2 Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României 16 R/ PLATE IX Fig. 1. — Clayey highly porous dolomite. Foidaș quarry 4177/17. Fig. 2. — Random felled gypsum texture. N 4-, Foidaș quarry 4177/16. Fig. 3. — Aligned felted gypsum texture. N +. Foidaș quarry 4177/15. Fig. 4. — Compact dolomicrite (dark area) passes into porous bioclastic dolomicrosparite. The shells remaints have been leached, leaving vugs. N//. Foidaș quarry 4177/13. Institutul Geological României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. IX. Institutul Geological României 16 R/ PLATE X Fig. 1. — OOlitic packestone. The mud matrix supports various kinds of grains: oolits, bio- clasts, lumps and pellets. N//. Foidaș quarry 4177/12. Fig. 2. — Oolitic grainstone. There are only normal or superficial oolits cementcd by sparry calcite. Viilor Valley, same level as in Fig. 1. N //. Fig. 3. — Polished slab. Stromatolite. In the lower part there is a bulbous massive stroma- tolite layer overlain by a planar stromatolite. Foidaș quarry 4177/9. Fig. 4. — Algal micrite with entrapped miliolid shell. Note the micritization of Shell walls and the sparry calcite cement inside. N //. Foidaș quarry 4177/9. Institutul Geological României B. Popescu. Lower Gypswn Formation West of Cluj-Napoca. Pl. X. 1 2 Anuarul Institutului de geologie și geofizică, voi. XLVIII. IGR/ Institutul Geologic al României PLATE XI Fig. 1. — Typical dolomicrospar. Crystal average are about 6—9 p. in diameter. Note the uni- formity o£ grain size and the cquant shape of crystals. N//. Foidaș quarry 4177/14. Fig. 2. — Dolomicrospar partly cemented by gypsum (arrows). Some of dolomicrosparitic crystals have palimpsest structures. N +. Leghia quarry 3621/8. Fig. 3. — Larger dolomite crystal (with dashed line) within dolomicrosparite fabric. Around an euhedral dolomitic nucleus of 25 u in size, there is a clear dolomitic cover. N + • Leghia quarry 3621/14. Fig. 4. — Dolomicrospar. In the lower right corner of the photo one can notice the cryptocrys- lalline material between the dolomicrosparitic crystals. It has been pushed aside by the recrystallization of dolomicrile to dolomicrospar. N //. Leghia quarry 3621/12. Institutul Geological României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. XI Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE XII Fig. 1. — Dolomicrospar largerly cemented by gypsum. The dolomicrosparite crystals „float” within gypsum cement. N //. Leghia quarry 3621/14. Fig. 2. — The transition from dolomicrite into porous dolomicrosparite. N 4-. Foidaș quarry 4177/13. Fig. 3. — Undissolved di. nicritic pelletal remnant within a highly porous dolomicrosparite. N +• Foidaș quarry 4177/21. Fig. 4. — The boundary between fine laminated dolomicrosparite and not laminated dolomicro- sparite. The lai linae are marked by the cryptocryslalline mixturc of clay, ferrous oxides and organic matter. Within dolomicrosparite the cryptocryslalline material is only as spols and patehes. N//. Leghia quarry 3621/12, interval B in Fig. 1 Pl. II. Institutul Geological României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. XII. 4 Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României 16 R/ PLATE XIII Fig. 1. — Pelletal bioclaslic dolomicrospar. The leached pellets and bioclasts are filled with gypsum. Note the high number of dolomite cryslals with cryptocrystalline nudei scattered within gypsum filled pellets and bioclasts. N//. Leghia quarry 3621/9, in- terval B in Fig. 1, Pl. V. Fig. 2. — Same as Fig. 1. N +. Fig. 3. — Partly leached pcllct. The vug has been filled with gypsum. An undissolved remnant is trapped within the gypsum filling. Note the cryptocrystalline envelope of this gypsum filled pellet. N//. Foidaș quarry 4177/21. Fig. 4. — Same as Fig. 3. N +. Institutul Geologic al României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca Pl. XIII. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR> PLATE XIV Fig. 1. — Doloinicrosparițe with gypsum fillcd porc. Note the cryptocrystalline „floor” of the cavity and the same nature of this rim and of cryptocrystalline patches around them. N//. Foidaș quarry 4177/24. Fig. 2. — Clear doloinicrosparițe with gypsum filled pellet. The wall of the leached pellet is iinbued with cryptocrystalline material. N//. Leghia quarry 3621/11. Fig. 3. — Tiny dolomicrosparitic streaks within nodular gypsum. N//. Foidaș quarry 4177/23. Fig. 4. — Under strcaky nodular gypsum there arc a thin pelletal bioclastic dolomicrospar above pelletal dolomicrite. 'Within the pelletal dolomicrite the pellets arc leached, some of them bcing fillcd with gypsum. There is any relation between the recrystal- lization of the dolomicrite and the gypsum filling. N //. Leghia quarry 3621/9 in- terval B in Fig. 1, PL V. Institutul Geologic al României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. XIV. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României îgrV PLATE XV Fig. 1. — Gypsum nodule growth within dolomicrosparite. Note the loose boundary between gypsum and dolomicrospar and the streaks of dolomicrospar left within the gypsum nodule. N4-. Leghia quarry 3621/9, interval D in Fig. 1, Pl. V. Fig. 2. — Not „digesled” isolated crystals of dolomicrospar within gypsum nodules. N //. Leghia quarry 3621/9, interval A in Fig. 1, Pl. V. Fig. 3. — Blocky texture with larger partely euhedral anhydrite crystals (arrows). N + . Foidaș quarry 4177/18. Fig. 4. — Felted texture. N-p. Foidaș quarry 4177/15. Institutul Geological României B. Popescu. Lower Gypsum Formation West of Cluj-Napoca. Pl. XV. Anuarul Institutului PLATE XI Fig. 1, — Oncolilic packstone. Matrix moderalely recrystallized lo microspar and pseudospar.. Hoia Formation, west of Mesteacăn village at the top of the Cozla Formation. Thin section, N//. Eig. 2. — Pelccypod? burrow within oncolilic wackestone. The burrow filling is also an oncolilic packstone bul moderalely or not recrystallized. ..Hoia Formation”, north of Vărai village al Ihe top of the Cozla Formation. Thin section, N //. Fig. 3. — Gastropod shell with an oncolilic coat within oncolilic packstone. Same locallily as in Figure 2. Fig. 1. - Corallinacean coral grainslone. Note the dose resemblance of the micritized corallines with fecal pellets. I loia Formation. upper part, wcsl of Ciocmani village. Thin section. N7/. Fig. 5. — Same as Figure 1. At higher magnificalion one may sometimes recognize the coral- linacean (C) or miliolitic (M) structure. Other corallinacean grains are wholly micri- lized (AP) becoming an algal pellet. v. Institutul Geologic al României B. Popescu. Sedimentology of Priabonian Carbonate Bocks. Pl. XI. Anuarul Institutului de geologie și geofizică, voi. XLVIII. ICR- Institutul Geological României BPOPESCU. Sedimentology of Priabonian Carbonate Rocks, Jibou Area, NW. Transilvanian Basin LITHOSTRATIGRAPHIC COLUMNS THROUGH THE PRIABONIAN CARBONATE FORMATIONS FROM JIBOU AREA 2-Giurgiului valley - Nr. of outcrop or quarry in fig. 1 3.572/l-Nr. of sample Skeletal wackestones and packstones Skeletal grainstones Coral and coralgal boundstones r 0 2 4 I i I 1 L 6 m j____i CURTUIUȘ FORMATION 6. Ciocmani W 13 14 g 11 12 <5 10. Cuciulot quarry 2597/ 1 Marls bearing skeletal wackestones HOIA Limestone 8 16 Marls 17 Sands and sandstones BREBI MARL J 18 FORMATION Fault 19 20 21 2146/ 22 23 24 OQ UJ CK □n 2 v FORMATION \ 2148 2 SG Imprim. Atei. Inst- Geol. Geof. ANUARUL INSTITUTULUI DE GEOLOGIE Șl GEOFIZICA VOL. XLVIII Institutul Geologic al României 2147 FACIES-ZONED CARBONATE SEDIMENTATION AT THE TIME OF THE HOIA LIMESTONE (UPPER TONGRIAN) IN NW TRANSYLVANIA (ROMANȚA)1 BY A. RUSU and A. DRĂGĂNESCU» Abstract La sidimentation carbonatique z o n n 6 e au niveau du C a 1 c a I r e de Hoia (Tongrien superieur) dans le NW de la Transylvanie. L’analyse petrologique des facies depositionnels au niveau du Calcaire de Hoia (Ton- grien superieur) des aires du Mezeș et de la Preluca (NW de la Tranylvanie) ont permis aux auteurs de mettre en evidence une interessante zonalite faciale. II faut souligner tout d’abord que le terme de ,,Calcaire de Hoîa” doit itre retenu seulement pour le facies calcaire coralli- gine des Couches de Hoîa (s.l.). En mime temps, on demontre que l’intervalle stratigraphique entre les Marnes de Brebi et les Couches de Curtuiuș de l’aire du Mezeș, de mime que son iqui- valent (le facies calcaire algal = Calcaire de Ciglean) de la pârtie terminale de la Sirie calcaire de l’aire de la Preluca, correspond au Calcaire de Hoîa ct ă Ia pârtie basale des Couches de Mera (y compris le niveau infirieur ă Scutella) de la region de Cluj-Napoca. Les coupes giologiques examinies relivent l’existence de trois zones faciales, ă savoir: la zone du facies sablonneux ă corallinacies, occupant la plate-forme du shelf; la zone du facies vaseux ă miliolides et coraux, qui longe la bordure du shelf; la zone du facies vaseux ă globigirines et bryozoires, correspon- dant au domaine pilaglque. Ce dernier facies est placi stratigraphiquement dans la pârtie terminale de Marnes ă bryozoires (Marnes de Brebi) des zones plus internes du bassin. L’image stratigraphique rigionale et la zonaliti faciale mises en ividence nous portent ă conclure que les dipâts du niveau du Calcaire de Hoîa correspondent il un moment de rigression rapide. Le contenii paliontologique du Calcaire de Hoîa et des dipâts iquivalents du bassin leur confire l’âge tongrien supirieur; ce laps de temps doit itre inclu soit â l’Oligocine moyen, si l’on con- sidire le Lattorfien en tanl qu’itage oligocine, soit ă la base de l’Oligocine — si cet itage se range ă l’Eocine supirieur. C’est cette derniire variante qui a iti adopție dans le prisent ou v rage. 1 Received on October 2nd 1974, accepted for publication on December 2nd 1974 and presented in the Meeting of January 17th 1975. 2 Institutul de geologie și geofizică, str. Caransebeș 1, 7000 București. 142 A. RUSU, A. DRĂGĂNESCU 2 CONTENTS Page Previous Work.......................................................................... 142 General Discussion on the Stratigraphy of the Interval Including the Hoia Limestones ............................................................................ 143 Description of Studied Scctions................................................ 146 The Sedimentary Facies of the Stratigraphic Interval of the Hota Limestone. . . 154 The Facies Zonation within the Stratigraphic Interval of the Hoia Limestone . . . 156 The Genetic Significance of the Distinguished Facies Zones...................... 159 Chronostratigraphic Aspects Related to the Age of the Hoia Limestone....................160 General Conclusions ................................................................... 163 Refcrcnces..............................................................................165 The Hoia Beds stand for one of most interesting and controversial lithostratigraphic units of the Paleogene sequence of the Transylvanian Basin. The achievement of a first facies zonation in the stratigraphic interval corresponding to the Hoia Limestone enables us to modify to a certain extent the previous manner of interpretation of this member. The region discussed in the paper lies in the northwestern part of the Transylvanian Depression, in the proximity of the crystalline moun- tains of Mezeș, Țicău and Preluca. The eoncerned sector reaches more than 80 km in length and is centred by the locality of Jibou (Pl. XXI). PREVIOUS WORK The fauna of the Hoia time interval was first recorded in the pioneer’s paper of Hauer and Stache (1863). Later, Hofmann (1879) separates at the base of the Oligocene sequence in the vicinity of Jibou, a distinct member under the name of „Untere marine molluskenreiche Schichten”, mentioning that it corresponds to the Hoia Beds of the Cluj- Napoca region. Thus it would be for the first time now, that the name of Hoia Beds appears in the literature, because the paper of Koch, the author which proposed it, was published an year later (1880, fide Koch, 1894). From 1881 on, Hofmann used this term in his papers too, specifying that in the Preluca area the lower part of the Hoia Beds consists of limestones containing corals and „Lithothamnium11 and theh* upper part — of limestones with molluscan shells. In his famous monograph on the Tertiary deposits of the Tran- sylvanian Basin, Koch (1894) describes the section exposed in the Hoia Hill (Cluj-Napoca) pointing out that there the Hoia Beds encom- pass two layers of breccia-like marly limestones containing molluscan shells, corals, balanids and small nummulitids. In addition this author records several other equivalent outerops in the Gilău area thus achie- ving the first correlation of the deposits in the stratigraphic interval of the Hoia Limestone. Institutul Geological României 3 sedimentation; AT THE TIME of THE hoia limestone 143 A fact interesting to be mentioned is the strânge opinion of Mi- h â 11 z which considered the Hoia Beds to be transgressive and in places even uncomformably overlying the Brebi Marls (while actually, as will be proved further on, the under-discussion beds correspond to a phase of regression). In 1956, Răileanu and Emilia Saulea correlated the eoraligenous limestone of the Hoia Hill with the Mera Beds (Oligocene) — actually younger —, while B arbu (1956) asserted on micropaleontolo- gical grounds that the sequence separated as Hoia Beds in the Jibou re- gion represents only a calcareous facies at the upper part of the Brebi Marls (Eocene). Thus we are confronted by two quite different interpre- tations, which led either to an erroneous correlation of these strata within the basin, or even to their elimination from the local stratigraphic sequence. R u s u, initially by unpublished works (1962 —1963) and then by two published papers (1967, 1968) resumes the study of the Hoia Beds in the Jibou region, opinating for their quality of stratigraphic entity. Subsequently, the situation in the stratotype area is clarified by the researches enterprised by M o i s e s c u (1968) and Meszâros and M a g d u n (1972), which supply many convincing, detailed data. Quite recently, M â s z â r o s et al. (1973) and soon afterwards M a r t i n i and Moisescu (1974) analyse the nannoplancton of the Hoia Beds, ascribing a Lattorfian and, respectively, a Lower Oligocene age to this member. In spițe of the lately achieved improvement of our knowledge on these strata, several aspects which led through the years to such different interpretations remained unclarified. Our belief is that the present paper will help to a better understanding of what represents and how must be interpreted the Hoia Limestone. GENERAL DISCUSSION ON THE STRATIGRAPHY OF THE INTERVAL INCLUDING THE HOIA LIMESTONE Inasmuch as the name of „Hoia Beds“ was used in a broader mean- ing designating deposits rather different in facies and sometimes even different in age in comparison with those of the stratotype, we prefer the term of „Hoia Limestone41 restricted exclusively to the eoraligenous facies of this stratigraphic interval. The type section of the Hoia Limestone was unfortunately ill-chosen because the outerop on the Hoia Hill (Cluj-Napoca) does not expose the boundary with the underlying Bryozoa Marls, and, on the other hand, a red clay facies invades the overlying Mera Beds to a rather low level. The Hoia Limestone is, instead, well defined paleontologically (molluscs, corals, echinoids, foraminifera, nannoplancton) so that any references to the Hoia Beds must take into account the faunal assemblage of the stra- totype. Three main depositional areas of the Paleogene were distinguished (R u s u , 1970) in the northwestern part of the Transylvanian Depression : ,'L Institutul Geologic al României IGRZ 144 A. RUSU, A. DRĂGANESICU 4 the Preluca area (developed around the crystalline massif of Preluca), the Mezeș area (flanking eastward the crystalline ridge of the Mezeș Mountains), and the Gilău area (bounding northward and eastward the crys- talline massif of Gilău). The present paper discusses the Hoia Limestone and its stratigraphic equivalents only in the Preluca and Mezeș areas (Pl. XXI). In the Jibou region (Mezeș area) two beds of limestones separated by a marly layer are individualized on a certain extension between the underlying Brebi Marls and the overlying Curtuiuș Beds ; the two limestone beds were together designated since Hofmann as Hoia Beds. The stra- tigraphical studies undertaken by Eusu pointed to the fact that only the lower, coral-bearing, limestone bed corresponds in age to the limestone of the Hoia Hill; thus, only this one may be termed „Hoia Limestone” ; the upper, molluscan shell-bearing, limestone bed, for which the idea that it would bemore typical for the Hoia Beds got accredited since Hof- mann (1881, p. 327), actually corresponds to the lowermost part of the Mera Beds of the Cluj-Napoca region (Gilău area), namely to their Scutella Lower Level (Fig. 1). The particular situation of the Jibou region (Mezeș area) was unjustly extended also to the Cluj-Napoca region (Gilău area), different authors rea- ching the erroneous idea of considering the Scutella Lower Level as the main element of the Hoia Beds in this latter region (Moisescu, 1968; Bombiță and Moisescu, 1968). Usually an equivalent of „Hoia” was looked for in the first sandy-calcareous deposits overlying the Bryozoa Marls ; but the nannoplancton analyses have established that the assemb- lage encountered at Cluj within the Hoia Limestone occurs, for instance at Mera, in the uppermost part of the Bryozoa Marls (M e s z â r o s et al., 1974). Koch (1894) intuited partly this fact, considering that at Mera the deposits 2,5 m thick underlying the Scutella Lower Level be- long to the Hoia Beds (p. 340), and showing that at Sard the place of the typical Hoia Beds is occupied by a layer of marly clays ( 2 m) contai- ning fossils of the „Bryozoaentegeîs” (p. 320). This interpretation was also put forward for the regions of the nort- hernmost part of the basin. So, Hofmann (1881) contemplates the possibility for the limestones with eorals and ,, Lithotha/mniu^ of the Preluca area to represent a littoral facies much reduced in thickness of the Brebi Marls, a possibility which, for lack of evidence, is rejected seve- ral lines further on (p. 327). B a r b u (1956) thinks that the strata separa- ted as Hoia Beds in the Jibou region would represent only a calcareous facies of the upper part of the Brebi Marls. Later on, Eusu (1967) correctly remarks that only the lower calcareous bed (that is even the Hoia Limestone) could stand for a calcareous facies of the Brebi Marls, but he as well as B ar b u leaves to be understood that in this case the true Hoia interval would not be involved. The recently undertaken studies led the present authors to the fol- lowing picture concerning the stratigraphic interval including the Hoia Limestone (Fig. 1). Institutul Geological României igr/ 5 SEDIMENTATION. AT THE TIME OF THE. HOIA LIMESTONE 145 In the Gilău area the Hoia Limestone Member is located strati- graphically between the Bryozoa Marls Member at the bottom and the Mera Beds (Member) at the top, the latter including in a subbasal position the Scutella Lower Level. In places the Hoia Limestone is lacking, being replaced by the Bryozoa Marls which rises up to the base of the Mera Beds ; in this situation the calcareous Scutella Lower Level, by its geome- trical position, gives the impression that it represents the Hoia Beds, a Fig. 1. — The Hoia Limestone position in the stratigraphie ensemble of the Transylvanian Basin in authors opinion. fact which often misled the previous researchers in the stratigraphie sepa- ra tion of the Hoia Limestone. Therefore in the Gilău area the Hoia Limes- tone represents the true Hoia overlying the Bryozoa Marls and underlying the Mera Beds. In the Mezeș area the „Hoia Beds” are located between the Brebi Marls Member (the northern equivalent of the Bryozoa Marls) at the bot- tom and the Curtuiuș Beds (Member) at the top ; but the lower boundary of the Curtuiuș Beds lies stratigraphically higher than the lower boundary of the Mera Beds (the Southern equivalent of the former), and the Scutella Lower Level is included in the uppermost part of the „Hoia Beds”. In other words, in Mezeș area the „Hoia Beds” occupy a larger stratigraphie interval than the true Hoia Beds of the Gilău area. As regards its compo- sition, the „Hoia Beds” in the Mezeș area appear heterogeneous, consisting of a lower calcareous coraligenous unit standing for the Hoia Limestone (the true Hoia Beds), and an upper unit composed of several marly beds with brackish-water faunas and crowned by the Scutella Lower Level, this upper unit as a whole representing the stratigraphie equivalent of the lower- most part of the Mera Beds. Therefore in the Mezeș area the Hoia Beds must be restricted to the Hoia Limestone Member, the overlying brackish member bounded between the Hoia Limestone and the Curtuiuș Beds Institutul Geological României 146 •A. RUSU, A. DRAGANEȘCU 6 representing a distinct stratigraphic unit. In places the Hoia Limestone disappears, being replaced by the Brebi Marls which are directly over- lain by the brackish member (the equivalent of the lowermost part of the Mera Beds). In other situations the Hoia Limestone and the overlying brackish member (underlying Curtuiuș Beds) are replaced by a calcareous corallinacean facies making up a single stratigraphic unit — the Ciglean Limestone — equivalent to the „Hoia Beds sensu lato“ (alias sensu Hofmann). In the Preluca area the Curtuiuș Beds (Member) are underlain by a comprehensive series — the Calcareous Series — including in its upper part corallinacean and coraligenous limestones standing for the strati- graphic equivalent of the Ciglean Limestone. Therefore the correspondent of the Hoia Limestone in this area must be stratigraphically placed in the subterminal part of the Calcareous Series, that is in the lower part of the uppermost interval of the Calcareous Series equivalent to the „Hoia Beds sensu lato”. In the present paper only the Hoia Limestone (the true Hoia Beds) interval in the Mezeș and Preluca areas will be discussed. DESCRIPTION OF STUDIED SECTIONS The main outcropping sections of the Hoia Limestone interval in the Mezeș and Preluca areas are described below. To have a systematic presentation, it is necessary to anticipate the next chapters and to state that in the Mezeș and Preluca areas three sinchronous, depositional, calcareous facies may be distinguished in the stratigraphic interval of the Hoia Limestone : a muddy, miliolid-coraligenous facies proper. to the actual Hoia Limestone ; and two colateral facies (standing for the facies of the stratigraphic equivalents of the Hoia Limestone), namely a sandy, corallinacean facies in the uppermost part of the Calcareous Series, and a muddy, globigerinid-bryozoan facies developed in those sectors where the stratigraphic equivalent of the Hoia Limestone is located at the top of the Brebi Marls. The outcropping sections of each of these facies are described further on (Fig. 2). A) The muddy, miliolid-coraligenous facies ap- pears in Mezeș area as a continuous strip following the line linking the locali- ties Ciocmani-Brebi-Moigrad-Stîna-Ciumărna-Treznea, and in the Preluca area as scattered patches accommodated within the mass of the sandy, corallinacean facies. In the Mezeș area there are three main sections within the mentioned strip of coraligenous facies : in the Jurteana valley (N of Stîna), în the Pîrîul Bercului valley (Ciumărna), and in the Groapa Stiavului valley (Treznea). In the section of the Jurteana valley (upper course, left side) it may be noticed that the Brebi Marls (a) are gradding upwards into Institutul Geologic al României Fig. 2. — The correlation of several sections in the Preluca and Mezeș areas. , chalky marls : 2, corallinacean limestones ; 3, coraligenous limestones ; l,coquina limestones ;5, marls; 6, clays ; 7, nummulitids ; 8, miliolids. Institutul Geological României 148 A. RUSU, A. DRĂGĂNESCU 8 b) an organogeneous, 50 cm thick, limestone containing corals of the Rhabdophyllia type, miliolids, nummulitids, Chlamys, small oysters, underlying, c) 50—150 cm of white-greyish marls with miliolids and varied ty- pical marine foraminifera, d) 60 cm of yellow-greyish marls with brackish microfaună and, in addition, marine foraminifera reworked from the underlying bed, e) 10 cm of greenish, fine clay, j) 50 cm of coquina limestone with Turritella, Ampullinopsis, Callista, Cardium, followed by clayey marls belonging to the Curtuiuș Beds (g). So far, the Hoia Beds were considered to encompass beds b-f. Aetu- ally only the limestone bed with corals (b) stands for the Hoia Limestone (true Hoia Beds), the upper, coquina limestones (bed ]) corresponding to the Scutella Lower Level of the Mera Beds. The interval of the beds d-e of brackish facies represents the equivalent of the lowermost part of the Mera Beds. It is quite possible that a sedimentary discontinuity exists between the two marly beds (c and d), as suggested by a compa- rison with other sections (i.e. Ciumărna) where the stratigraphic sequence between the Hoia Limestone and the Curtuiuș Beds includes more litho- logic terms, as well as by the reworking of marine microfaunas of the lower, marine bed (c) within the overlying, brackish bed (d). The possible sedimentary discontinuity between the two marly beds as well as the marine facies of the lower bed (c) versus the brackish facies of the upper one (d) give support to the affiliation of the lower, marine, marly bed to the Hoia Limestone interval. This marly bed displays a muddy, miliolid, calcareous facies strongly infested with clayey material; however, as will be seen later, the muddy, miliolid-coraligenous facies passes by gradual loss of the corals to a muddy, miliolidic variety ; thus, it is possible that the marly bed (c) stands for this coral-lacking variety and, consequently, from the facies point of view, its affiliation to the Hoia Limestone interval does not represent an impediment. In the Pîrîul Bercului valley (S of Ciumărna) the Brebi Marls (a), which end in calcareous marls containing Chlamys, Panope, small oysters and scarce nummulitids, are followed by b} 75 cm of bioconstructed coraligenous limestone with Rhabdophyllia and Hydnophyllia, c) 50 cm of green-greyish fine clays, which include at their bottom a centimetric crust of corals belonging to the Hydrophyllia type (that were stopped to keep developing by the unfavourable, brackish environ- ment which was just installed), and in the reinainder bed contain a brackish fauna consisting of individuala of Polymesoda and Tympanotonos, d) 40 cm of slighty slaty, coarse marls, e) 7 cm of sandy-marly limestone with Cardium transsilvanicum and scarce Polymesoda convexa, j) 75 cm of sandy marls with rare cardiids, g) 40—50 cm of sandy limestone with many individuala of Cardium transsilvanicum, hy Institutul Geologic al României igr/ 9 SEDIMENTATION AT THE TIME OF THE HOIA LIMESTONE 149 h) 15 cm of limestone with miliolids bounded by marly joints, i) 40 cm of coquina limestone with Turritella, Babylonia, Callista, and above, marls firstly with miliolids and then with brackish molluscs belonging to the Curtuiuș Beds (j). From the interval of the beds b-i ascribed by the previous authors to the „Hoia Beds” we keep as representing the Hoia Limestone (true Hoia Beds), only the bioconstructed coraligeneous limestone (bed b) and the lowermost, coraligeneous part of the suprajacent, marly bed (c). A fact to retain is that the sequence between the Hoia Limestone and the Curtuiuș Beds is more complete here than in the Jurteana valley. The interval of the beds c-i would represent an equivalent of the lowermost part of the Mera Beds, the bed i standing for the Scutella Lower Level. An interesting section is offered by the Groapa Stiavului valley (tributary to the Treznea valley, downstream the locality of Treznea). Here the Brebi Marls (a) ending in a hardened marly limestone with Chlamys, Panope, Nummulites, and a centimetric level of encrusting corals at the top, is overlain by b} 75—80 cm of massive, coraligenous limestone mainly with Bhab- dophy'llia, Hydnophyllia, etc., covered by a sandy mari. A little way upstream on the valley, after an observation gap 1 m thick corresponding to a soft rock, the section continues as follows : c) 20 cm of slaty, coarse marls with Cardium transsilvanicum, Panope angusta, which gradually passes upwards into d) 30 cm of gresous-marly limestone with Cardium transsilvanicum, Anodontia globulosa, Panope angusta, Sinodia incrassata, Ampullinopsis crassatina, another observational gap, but of a small ampleness (a few dm), and then e) 10 cm of slaty, coarse mari with miliolids, f) 15 cm of fine, marly limestone with small pelecypods, g) 17 cm of slaty, coarse mari with miliolids and scarce pelecy- pods, h) 35 cm of slightly coquina limestone with Turitella biarritzensis, T. granulosa, Tympanotonos labyrinthum, Callista villanovae, Polymesoda convexa, etc. and miliolids, followed by the marls accommodating brackish fauna of the Curtuiuș type (i). The Hoia Limestone may be easily recognized here (bed b); in this section it reaches the highest thickness for the Mezeș area. The sequence of the beds c-h stands for the equivalent of the lowermost part of the Mera Beds, here ending in the Scutella Lower Level (bed h). In the area of development of the muddy, coraligenous facies of the Mezeș area is included as well the outcrop of sandy limestone with corals in the Peștera valley at Hodiș (southernmost part of the Mezeș area). Between Treznea and Hodiș the relief transects the deposits synchronous 150 A. RUSU, A. DRAGANESCU 10 to the Hoia Limestone, situated inwards the basin and belonging to the muddy, globigerinid-bryozoan facies, the deposits of the coraligenous facies supposed to have developed westward being removed by the erosion. Approximately 1 km WNW of the alignement of the coraligenous strip (above discussed), the stratigraphic interval of the Hoia Limestone accommodates the already mentioned facies variety of the muddy, milio- lidic limestones. Outcrops cuting this facies variety occur NW of Ciumărna (on the left tributary stream of the Ciumărna valley), SW of Stîna (the uppermost course of Șipote valley), as iveli as in several points W of Moigrad. In the muddy coraligeneous facies as a whole, the eorals are repre- sented mainly by branching and lamellous forms, subordinately by digitate forms. R u s u determined among these : Rhabdophyllia tenuis R e u s s (branching eorals) (Pl. III; Pl. IV, Fig. 1), and Hydnophyllia cf. scalaria (C a t u 11 o ) (Pl. I, Fig. 1; Pl. II), Cyathoseris apennina gibossa (P r e- ver) (Pl. IV, Fig. 2—3), Stylocaenia sp. (Pl. I, Fig. 3) and Actinacis (Pl. I, Fig. 2) (lamellous eorals). The branching eorals occur as bush-like colonies, those lamellous — as planar or nodular, crust-like colonies or as largely open, small, flat-fans, and those digitate — as short, massive, crust-like colonies. The coral colonies are usually in situ, in growth position, originating in biolithitic fabrics (bioconstructed limestones); in the case of the colonies of lamellous or digitate eorals the biolithitic structure is continuous (welded biolithite), while in the case of the colonies of branching eorals the biolithitic structure may be either continuous if the calicia are tangent (welded biolithite) or discontinuous if the calicia are spaced (spaced biolithite). Thus, at Ciocmani occur colonies of branching and lamellous eorals, at Brebi and Moigrad — spaced colonies of bran- ching eorals, at Stîna — nodular, crust-like colonies of lamellous eorals, at Ciumărna and Treznea — fan-like colonies of lamellous eorals, crust- like colonies of lamellous or digitate eorals, and welded or spaced colonies of branching eorals. In the Mezeș area the coraligeneous colonies of the Hoia Limestone do not make up a continuous biostrome, but within the continuous strip of muddy miliolid-coraligenous facies they seem to be irregularly distri- buted, giving rise to local concentrations as small bioherms, which consi- dered at a regional scale may be assembled in a discontinuous biostromal level. In the Preluca area, the muddy, miliolid-coraligenous facies is repre- sented by scattered patches of bioconstructed coraligenous limestones consisting of colonies of lamellous (Hydnophyllia) and/or branching eorals ; such patches occur S of Soimușeni, in the quarry Letca (W of Toplița), N of Răstoci, N of Bizușa, and N of Dăbîceni; in places the coraligenous material appears triturated (i.e. E of Purcăreț). B) In the area of development of the sandy, c o r a 11 i n a - cean facies, which corresponds to the outeropping area of the Calca- Institutul Geological României 11 SEDIMENTATION AT THE TIME OF THE HOTA LIMESTONE 151 reous Series in Preluca area and may be watched southward up to Ciglean in Mezeș area, the sections are numerous but little various. In the Pîrîul Pietrii valley (SW of Ciglean) the typical Brebi Marls (a) underlie : b) 3,5 m of limestones with miliolids interbedded with marls, c) 4 m of corallinacean limestones stratified in beds variable in thick- ness (0,2 — lm); these limestones contain, besides coralline algae, nummu- litids, bryozoa debris, and scarce shells of Pycnodonta gigantica (Sol.). In the authors’ opinion the miliolidic limestone (level b) is attached to the Brebi Marls Member, the equivalent of the stratigraphic interval including Hoia Limestone + Scutella Lower Level (that is the „Hoia Beds sensu lato”) being represented by the corallinacean limestones (level c), for this latter we thinking that it is useful to be kept the name of Ciglean Limestone proposed by 11 i e s c u in an unpublished report (11 i e s c u et al., 1962)3. The Ciglean Limestone, essentially corallinacean, occurs also at N of Ciocmani, S of Piroșa, and in the quarry Băbeni. In the other points of outcropping of the uppermost part of the Calcareous Series, the Ciglean Limestone appears however atypical, strongly enriched in nummulitids. Thus, for instance : In the Someș Pivei’ cliff, N of Cliț, the coarse, nummulitic limestones typical of the Calcareous Series are overlain by : a) 3 m of limestones with Lithophyllum and Nummulites (the Ciglean Limestone enriched in nummulitids), b) 1 m of limestone with miliolids and shells of molluscs (correspon- ding to the Scutella Lower Level, here exhibiting lithological individua- lity). At Toplița, on the hill slope near the village, at the top of the Calca- reous Series 2—3 m of limestones occur containing abundant skeletons of Nummulites and Lithophyllum and subordinately echinoid remnants, some of them belonging to Scutella subtrigona (the Ciglean Limestone enriched in nummulitids, and clearly encompassing the Hoia Limestone unit and the Scutella Lower Level unit). In the locality of Glod, near the spring of the village, the nummulitic limestones of the Calcareous Series which gradually discharge upwards of nummulitids underly : a) 0,7 m of limestones with Lithophyllum and Nummulites (the Ciglean Limestone enriched in nummulitids), b) 2 m of greenish grey marls with Tympanotonos, Globularia, Poly- mesoda, etc. belonging to the Curtuiuș Beds, followed by skeletal limestones with sorted elements represented by nodules of Lithophyllum, pieces of balanids, skeletons of nummulitids, associated with shells of Tympanotonos, Globularia, Polymesoda, whole this skeletal material being embedded in a 3 O. 11 i e s c u, Aura Naghel, Gh. Mărgărit, Mari a Mărgărit, M. Gheorghian, M i h a e 1 a Ghe orghian, A. Naghel. Geological Report on the Prospections for Coal in Moigrad-.Jibou-Stejerea-Ileanda-Răzoare Region (in Romanian) (1962). Arch. of Institute of Geology and Geophysics, Bucharest. Institutul Geologic al României ig Ry 152 A. RUSU, A. DRAGANESCU 12 marly-calcareous matrix ; these limestones, which may be easily confused with the Ciglean Limestone, stand for reworkings of skeletal material of the Ciglean Limestone in the Curtuiuș Beds. We take advantage on this occasion to draw the attention to the fact that resedimentations and re- workings in the lowermost part of the Curtuiuș Beds stand for a common phenomenon, especially in the Preluca area, being obvious at Var (Pîrîul Cheții valley), in the vicinity of locality of Poienița, and W of Glod quarry ; in these places, at the base or interbedded with the basal marls of the Curtuiuș Beds, a material of Ciglean type, fragmented and sorted, may be noticed together with brackish molluscs typical of the Curtuiuș Beds; so far, this fact had not been pointed out, and often the limestone beds belonging to this type were erroneously taken for the Hoia Beds. An other fact worth mentioning is that in places, in the area of de- velopment of the sandy corallinacean facies, the algal limestones are replaced by coquina limestones (pelecypods and/or gastropods) where the thalli of coralline algae occur sporadically. That is the situation found in the uppermost course of Brebi valley (NW of Brebi), in Pîrîul Haiturii valley (NW of Ciocmani), N of Piroșa, near Purcăreți, W of Răstoci, E of Valea Chioarului, etc. From all these points Eusu determined the following species : Gastropoda : Turritella granulosa, T. biarritzensis, T. clumancensis, Tympanotonos labirintlmm, T. troMear diaboli, Ampulli- nopsis crassatina, Globularia aff. auriczdata, G. patula, Polinices catena archatensis, P. semperi, Thericium intradentatum, T. aff. globulosum, Babylonia caronis, JDiastoma costellatum elongatum, Pugilina bonnetensis, Bayania stygii, Architectonica subplicatula, Cancellaria excellens, Trochus trochlearis, Tectus lucasianus, Xenophora solida, Scaphander aff. jostisii, Collonia sp., Terebellum sp., Vexillum sp., Cassis sp., etc. Pelecypoda : Chlamys bellicostata, Callista aff. villanovae, Sinodia incrassata, Poly- mesoda convexa, Panope angusta, Cardium transsilvanicum, Crassostrea plicata, Pycnodonte gigantica, Anodontia globulosa, Bourdotia subornata, Glycymeris tenuisulcata, Caestocorbula henclceliusiana. Perna sp., Plega- ximis sp., Pinna sp., etc. C) T h e muddy, g 1 o b i g e r i n i d-b r y o z o a n facies outcrops only in the Mezeș area as a strip bounding at SE the strip of the coraligenous facies on its Hodiș-Treznea segment. It may be ascer- tained in several sections among which more important are those of Bozna and Bodia. In the village of Bozna, on a left tributary stream of Bozna valley, the Brebi Marls Member (a) ends in a coarser, indurated, calcareous mari, 0,5 m thick, macroscopically with miliolids and rare impressions of pele- cypods ; this mari seems to represent the equivalent of the Hoia Limestone, inasmuch as 25 cm higher (covered interval) there are b) 1,2 m of greenish grey marls with a faunal assemblage of Curtuiuș type (Tympanotonos, Pirenella, Cyrena), c) 35 cm of marly limestone with miliolids and fine pelecypods, d) 10 cm of marly limestone containing miliolids in the upper part, 'A Institutul Geological României igrA 13 SEDIMENTATION. AT THE TIME OT THE HOIA LUMESTONE 153 e) 35 cm of coquina limestone with Turritella, Callista, Ampulli- nopsis — the equivalent of the Scutella Lower Level, /) 100 cm of marls belonging to the Curtuiuș Beds. The interval of the beds b-e is considered the stratigraphic equiva- lent of the lowermost part of the Mera Beds. In the Bodia valley, 1,3 km upstream of the Jibou-Ciucea road, the following sequence may be noticed : a) the Brebi Marls are overlain by b) 25 cm of grey calcareous marls containing abundant, sorted, skeletal material consisting of small nummulitids of N. jabianii group, fragments of pelecypods especially Chlamys, pieces of balanids, and un- brocken shells of Chlamys bellicostata and Pycnodonte gigantica; towards the uppermost of the bed the first individuals of Tympanotonos and Cyrena make their appearence, c) 25 cm of bluish marls of Brebi type with small foraminifera, d) 40 cm of well-bedded coquina limestone containing pelecypods {Chlamys, small oysters of Cubitostrea group) and nummulitids, e) 5 cm of limestone with miliolids, /) 200 cm of bluish grey marls with several miliolidic levels, g) 40—50 cm of hard, skeletal limestone with miliolids, nummuli- tids, pelecypods, Turritella, plates of echinoids, etc., strongly suggesting to represent the equivalent of the Scutella Lower Level. h) interbedded limestones and sandstones containing the faunal assemblage of the Mera Beds. There is no doubt that a part of the deposits underlying the Scutella Lower Level stands for a correspondent of the Hoia Limestone Member. The intercalations bearing sorted skeletal material and occuring within a sequence of marls of Brebi type represent intraformational resedimenta- tions of materials reworked from the near-shore areas and transported over the coraligenous zone eastward. In the outeropping sector of the muddy, globigerinid facies in Mezeș area, the deposits, of the muddy, coraligeneous facies are missing, being removed by the erosion. The proof that these facies were initially juxta- posited is given northward, where the drillings performed east of the out- eropping strip of the Hoia-Ciglean Limestone, namely at Lupoaia and Jac, entered from the Mera Beds directly the Brebi Marls (M e s z â r o s et al., 1970). The Lupoaia boring was located approximately 4 km inward the basin from the outerops of Ciglean Limestone at Ciglean, and the Jac drilling was bored approximately 4 km E of the alignement of Hoia Limestone near Moigrad. In these drillings, the first, coarser deposits, with Turritella chtmancensis, Cardium tramssilvanicum, Tellina, etc., overlying the Brebi Marls stand obviously for the correspondent of the Scutella Lower Level, and consequently the interval equilvalent to the Hoia Limestone must be included in the subjacent marls, that is in the upper part of the Brebi Marls Member. 154 'A. RUSU, A. DRĂGĂNESCU 14 THE SEDIMENTARY FACIES OF THE STRATIGRAPHIC INTERVAL OF THE HOIA LIMESTONE The petrological study of the sequences lying in the stratigraphic interval of the Hoia Limestone in the Mezeș and Preluca areas allowed to distinguish 3 synchronous, calcareous, depositional facies : the muddy, miliolid-eoraligenous facies; the sandy, corallinacean facies; and the muddy, globigerinid-bryozoan facies. The sections analysed from each of these facies were discussed in the previous chapter. These facies are characterized by proper depositional petrologie features, each facies displa- ying peculiarities which individualize it sharply in comparison -with the other facies. The successive petrological analvsis of each facies is presented further on (Pl. VII-XX). A) The muddy, miliolid-eoraligenous facies is a marine, calcareous, muddy skeletal facies and represents the facies exhi- bited by the whole Hoia Limestone in the Mezeș area (alignement Hodiș- Treznea-Moigrad-Brebi-Ciocmani) (Pl. XIV, Fig. 3—6 ; Pl. XVI, Fig. 5—6 ; Pl. XVII, Fig. 1—3; Pl .XVIII—XIX), and by the limestones of several disparate patches (Soimușeni, W of Toplița, N of Eăstoci, W of Bizușa, Dăbîceni) in the Preluca area (Pl. XIII, Fig. 4—5). Texturally, the limestones of this facies are lime wackestones and packstones accommodating coral biolithitic structures. The depositional petrographic components of these limestones are represented by the coral biolithitic structures and by the sedimentary accummulations within the available spaces inside the former (intrabiolithitic fillings) or between them (interbiolithitic sediments); the sedimentary accumulations consist of micrite matrix (lime mud) bearing abundant miliolids, fine pelagic foraminifera (globigerinids and globorotaliids), ostracods, fine pelecypods and sporadically bryozoa debris and coral fragments, to which locally and in minor amount nummulitids, coralline debris and echinoderm plates are added if this facies stays under the influence of the sandy, corallina- cean facies. The skeletal grains show different degrees of micritization, the most micritized being sometimes the miliolid tests and allways the coralline fragments, both of them of ten appearing converted into crypto- crystalline grains. Though the main depositional components of these limestones are the coral biolithitic structures, the micrite matrix, the miliolids and the pelagic foraminifera, among these constituents only the micrite matrix and the miliolids stand for the all over spread and charac- teristic elements, because there are sectors where the corals and the pe- lagic foraminifera are missing (the zone lying west of the coraligenous alignement Treznea-Ciumărna-Stina); therefore, within the muddy, miliolid-eoraligenous facies a coral-lacking, miliolidic, muddy subfacies may be distinguished as variety. To conclude, one may assert that this facies is characterized by more or less sandy lime muds containing scattered and undisturbed (in" place) coral colonies. Institutul Geological României 15 SEDIMENTATION. AT THE TIME OF THE HOIA LIMESTONE 155 B)The sandy, corallinacean facies is a marine, skeletal calcareous facies and largely develops in the Preluca area occupying the whole mass of the uppermost part of the Calcareous Series equiva- lent to the Hoia Limestone (except those several seattered spots of a cora- ligenous facies) (Pl. VII—XIII), extending westward in the Mezeș area west of the coraligenous alignement up to Ciglean (the sector NW Brebi- Ciglean-W and N Ciocmani) (Pl. XIV, Fig. 1—2; Pl. XV: Pl. XVI, Fig. 1-4; PL XVII). Unlike the previous facies, this facies consists exclusively of lime grainstones (originally lime sands), calcarenitic to microcalciruditic in grain-size, whose general and usually prevalent depositional petrographic component is represented by entire or brocken corallinacean nodules (almost exclusively species of Lithophyllum (Pl. V) among which E u s u identified Lithophyllum simplex Lem o in e and L. symetricum L e - moine); as co-associated constituents are added in variable amounts : nummulitids and other large benthonic foraminifera (Asterigerina, Sphe- rogypsina, Rotalia), miliolids, echinoderms, pelecypods, gastropods, plates of balanids, and bryozoas (Pl. VI, Fig. 1—2). Several subfacies may be distinguished depending on the percentual participation of the secondary depositional constituents (varieties of the sandy facies) : the corallinacean subfacies where the corallinacean tests make up at least 75% of the limestone bulk (Ciglean, N of Ciocmani, S of Piroșa, Băbeni); the nummulitid-corallinacean subfacies standing for the commonest subfacies, where both groups of organisms are abundantly represented; the coquina subfacies encompassing skeletal limestones con- sisting completely or mainly of shells of pelecypods (i.e. NW of Brebi), of gastropods (i.e. Valea Chioarului), or of both of them (i.e. Fundătura- Creaca, NW of Ciocmani, W of Eăstoci); the miliolidic subfacies (W of Ciocmani, NW of Brebi on the uppermost course of the Brebi valley); and the oncolitic subfacies, a quite unusual subfacies, consisting of limes- tones whose skeletal grains appear coated with concentrical micritic layers and turned into pisoncoliths or macrooncoliths (to which microoncoliths are added in large amounts). All the skeletal grains show micritizations, among them the miliolids and the corallinacean algae being submitted to strongest micritization; sometimes they display total alteration to a micritic mass evolving to pelets and micritic lumps. The skeletal grains appear completely merged into each other, resulting in a strongly compacted structure lending to the rock the feature of welded grainstone. If the corallinacean tests lie in a direct contact each other, their total micrization and welding may give the impres- sion of micrite matrix in which different other skeletal grains (i.e. nummu- litids, miliolids, etc.) float, the rock leaving the appearence of wackestone or packstone. The rocks show not only a total pore compaction resulting in a perfect merging of the grains into each other but also a strong grain compaction supported by the numerous contact-solution phenomena (ascertained between the grains) joining the deformation, interpenetration, and faulting of the grains (accompanied or not by the displacement of the resulting fragments). Therefore the micritization of the skeletal grains i Institutul Geological României \ igr/ 156 A. RUSU, A. DRĂGĂNESCU 16- and mainly of the coralline tests was followed by a total pore compaction and then by a strong grain compaction, finally the rock displaying the grains,. mostly micritized, merged and even intermingled. The diagenesis gave rise to a microspar (replacive, very finely crystalline, spar calcite) which developed as patches or networks covering irregular-shaped, large fields replacing equally the micritized corallinacean tests as well as the other micritized skeletal grains, however apparently consumming only the micri- tized areas of the different skeletal grains. This microspar may represent a neomorphic product but, alternatively, it may stand for the result of the diagenetic sequence including dolomitization on the micritized areas followed by dedolomitization, in this latter case being a dedolomitic product (D r ă- gănes cu , in preparation). This microspar, in places aggraded to larger pseudospar, is very finely crystalline (5—15 microns in crystal size) and contains the remaining unaffected skeletal grains as scattered or grouped welded grains floating within this matrix-mimicing microspar, leaving for the rock the appearence of a lime wackestone-packstone with the matrix slightly aggraded; as already stated, this microspar „matrix” actually stands for microspar irregular-shaped networks or patches developed at the expanse of micritized areas of the merged skeletal grains. C) T h e muddy, globigerinid-bryozoan facies is- a marine, marly, muddy skeletal facies, and appears developed in Mezeș area directly east of the coraligenous alignement Hodiș-Treznea-Moigrad- Brebi; it outcrops at Bodia and Bozna, northward being encountered in the drillings of Jac and Lupoaia (Pl. XX). It represents the facies typical of the Brebi Marls Member and con- sists of marls with nummulitids, miliolids, globigerinids and globorotaliids embedded in a clayey-micritic matrix. Southward, in Gilău area, as will be seen later, this facies excels in the abundance of bryozoan tests accom- modated in a marly matrix too (the Bryozoa Marls), reason through which generalizing for the whole NW sector of the Transylvanian Basin we have termed this facies : the muddy, globigerinid-bryozoan facies. Within its framework two subfacies may be distinguished : a northern, globigerinic subfacies included in the series of the Brebi Marls, and a Sout- hern, bryozoan subfacies accommodated within the series synchronous to the former and termed the Bryozoa Marls. THE FACIES ZONATION WITHIN THE STRATIGRAPHIC INTERVAL OF THE HOIA LIMESTONE Watching the distribution of the three facies distinguished over the surface of the Mezeș and Preluca areas, one ascertains that in the Mezeș area they are disposed as juxtaposited strips oriented NE-SW, while in the Preluca area the coraligenous and corallinacean facies make up a mosaic. We present further on the analysis of the areal distribution of the facies distinguished in the stratigraphic interval of the Hoia Limestone (Pl. XXI). Institutul Geological României \ IGr/ 17 SEDIMENTATION. AT THE TIME OF THE HOIA LIMESTONE 157 In the Mezeș area the three facies form three, approximately par^Hel belts, oriented SW-NE, which from west to east succed as follows : the sandy, corallinacean facies zone; the muddy, miliolid-coraligenous facies zone; and the muddy, globigerinid-bryozoan facies zone. The muddy, miliolid-coraligenous facies zone may be folloived from the Southern extremity of the Mezeș area, from Hodiș, to its northern extremity, to Ciocmani; it appears as a continuous, muddy- miliolidic belt accommodating patches of eoraligenous colonies along the alignement Hodiș-Treznea-Ciumărna-Stîna-Moigrad-Brebi-Ciocmani; this zone is narrow (about 1,5 km wide) in the northern segment, in that Southern, starting from the locality of Moigrad southward, widening gradually up to at least 2,5 km (westward eroded) on account of the attaching, westward of the strip of muddy miliolid-coraligenous facies, of a strip of coral-lacking, muddy-miliolidic facies (subfacies) making up a facies subzone within the muddy, miliolid-coraligenous facies zone. In the Brebi-Moigrad sector the eoraligenous facies zone changes twice its direc- tion displaying a lock. Inasmuch as northward of the locality of Ciocmani we did not find the outeropping muddy, miliolid-coraligenous facies making up a continuous strip, and on the other hand because northward and east- ward of Ciocmani the sandy, corallinacean facies is present in outerops, one may conclude that it is possible that starting from the locality of Ciocmani the eoraligenous facies zone changes its direction and sinks under younger deposits, turning firstly towards SE (inscribing in a small gulf whose concavity is directed southward) and then directing eastward; alternatively, it is possible that this facies zone disappears directly north- ward of Ciocmani. The sandy, corallinacean facies zone lies directly west of the cora- ligenous zone, starting from the parallel of the locality of Ciglean towards north (southward being either eroded or, more probably, undeposited owing to the joining of the Southern segment of the eoraligenous facies zone to the mainland lying directly westward). This facies zone gets wider northward, largely linking to the facies of the Preluca area; actually this facies zone stands for the southwestern termination of the area of develop- ment of the sandy, corallinacean facies wdiich covers extensive portions within Preluca area. The muddy, globigerinid-bryozoan facies zone develops directly east of the eoraligenous facies zone, starting from the alignement Bodia- Bozna-Jac-Lupoaia and extending largely eastward, probably occupying the whole central part of the northwestern sector of the Transylvanian Basin. In the Preluca area the outerops show a single extensive facies zone — the sandy, corallinacean facies zone (represented mainly by the nummulitid- eorallinacean subfacies) — containng patches of muddy, miliolid-cora- ligenous facies as small, scattered islands dispersed within the sand- sized corallinacean-nummulitic mass. Therefore the two facies — corali- genous and corallinacean — make up together a mosaic in which the eoraligenous facies occurs as sporadic lenses floating in the mass of the corallinacean facies. The deposits of this facies zone occur starting from Institutul Geological României igrz 158 A. RUSU, A. DRĂGĂNESCU 18 the top of the Preluca massif southward approximately up to the parallel of the locality of Glod ; south of this locality the deposits of the concerned stratigraphic interval sink under younger sediments. But certainly south- ward these facies are replaced by the muddy, globigerinid-bryozoan facies. It is possible that at the limit between the corallinacean facies zone with islands of coraligenous facies and the muddy, globigerinid-bryozoan facies, a more or less continuous, muddy, coraligenous facies zone be developed, similarly to the situation encountered in the Mezeș area. As a conclusion, generally from NW towards SE one may consider that three facies zones are developed : an extensive, sandy, corallinacean facies zone able to rich more than 15 km in width in the Preluca area, geting thinner towards SW and disappearing south of Ciglean; a narrow, muddy, miliolid-coraligenous facies zone; and a broad, muddy, globi- gerinid-bryozoan facies zone covering all the remaining sectors of the central part of the NW Transylvanian Basin. The published geological data reveal that the facies zonation distin- guished in the Mezeș and Preluca areas verif ies in the Gilău area too. Thus, the breccia-like limestones bearing molluscs, corals (skeletons of Rhabdophyllia and Hydnophyllia), balanids, and nummulitids of the Hoia Hill as well as those, less coraligenous, of Mînăștur Wood(Cluj-Napoca) are obviously included in the muddy, miliolid-coraligenous facies zone, very poorly represented in the Gilău area. The muddy, globigerinid- bryozoan facies zone, consisting here of brvozoa-bearing marls included in the uppermost part of the Bryozoa Marls Member and directly over- lain by the Mera Beds (Member), is largely developed instead in this area, a fact which most often determined the previous researchers to separate, as Hoia Beds, deposits of the lowermost part of the Mera Beds. The stratigraphic equivalent of the Hoia Limestone starting from Cluj towards the interior of the basin (towards NW) would be placed in different points at the following levels (Pl. XXI) : At the mouth of the Popești valley, in an outcrop described by Koch (1894, p. 319—320) and Moisescu (1968, p. 493, 497), the stratigraphic equivalent of the Hoia Limestone lies under the Scutella Lower Level (lowermost part of the Mera Beds), that is in the interval 7—8 m thick consisting of an alternation of marls (of the Bryozoa Marls type) and skeletal marly limestones containing abundant fragments of Chlamys, balanids, crustaceans, solitary corals and nummulitids. Moi- sescu eroneously interpreted the Scutella Lower Level of the Mera Beds as representing the Hoia Limestone (true Hoia Beds). In the already classical section on the Berecoaia valley, at Mera (Koch, 1894, p. 339—340; Bombiț ă and Moisescu, 1968, p. 710—712), a nannoplancton fauna occurring in the Hoia Limestone in the type section, is placed here within the Bryozoa Marls, whose upper part would therefore stand for an equivalent of the Hoia Limestone (M e- s z â r o s et al., in press). Worth mentioning is the fact that Koch (1894, p. 340), although he eroneously considered the first, indurated and coarser Institutul Geological României 19 SEDSMENTATIONi AT THE TIME OF THE HOIA UMESTONE 159 deposits in this section as equivalent to the Hoia Limestone, correctly plaeed the base of the Mera Beds at the first bed bearing Scutella, bed which later will be unjustly included by some authors in the Hoia Beds. Following the same direction, at Șardu one ascertains, as Koch (1894, p. 320) correctly remarked already, that the place of the typical Hoia Beds is occupied by a level of marly clays 2 m in thickness containing the shells of the Bryozoa Marls and many balanids. Towards the center of the basin, in the drilling of Sîncraiu Almașului, molluscs-bearing sandstones of a Mera Beds type directly overlie the Bryozoa Marls, lacking any megascopical element allowing to separate an equivalent of the „Hoia”. In the ancient conception this equivalent would have been separated in the lowennost part of the Mera Beds; now it is proved that it must be plaeed in the uppermost part of the Bryozoa Marls. The problem concerning the correlation of the deposits in the strati- graphic interval of the Hoia Limestone is not completely cleared up. However the additional details and specifications which will be got hence- forth are expected not to change the general, here-proposed scheme of facies zonation. THE GENETIC SIGNIFICANCE OF THE DISTINGUISHED FACIES ZONES Taking into account the fact that the teritory of the Apuseni Moun- tains stood for a mainland area which included, in its northern part, the Gilău massif, the crystalline ridge of Mezeș and the Șimlcul Silvaniei Basin (where the drillings proved the lack of the eocene-oligocene deposits), as well as the fact that the crystalline massives of Preluca and Ticău were shallow submerged areas together making up a large ridge representing the prolongation towards NE of the western mainland, one may conclude that the sandy, corallinacean facies zone was in a position juxtaposited to the shore, and the muddy, globigerinid-bryozoan facies zone was in an off-shore position. The gradual loading in lime mud from the near-shore, corallinacean facies zone towards the off-shore, globigerinid-bryozoan facies zone, the high occurrence of the large benthonic foraminifera and of the coralline algae in the sandy, corallinacean facies zone and the high frequency of the globigerinids and globorotaliids starting from the outer part of the coraligenous facies zone and continuing in the globigerinid-bryozoan facies zone, the development of the hermatipic corals unde muddy facies being under the influence of both near-shore facies (the occurrence of the coralline algae and large benthonic foraminifera) and off-shore facies (the occurrence of globigerinids and globorotaliids), all these data suggest the following genetic interpretation on the three facies zones distinguished : a) the sandy, corallinacean facies zone corresponds to the shelf- platform large area, standing for a corpusclar (sandy) skeletal marine facies (skeletal lime sands) of shallow, agitated water; Institutul Geological României 1GR 160 A. RUSU, A. DRĂGĂNESCU 20 b) the muddy, miliolid-eoraligenous facies zone covered the shelf- edge and shelf-slope narrow areas, representing a muddy skeletal marino facies (coral bioherms in lime muds) of shallow, but quiet water; c) the muddy, globigerinid-bryozoan facies zone stands for a basinal marine facies expressing quiet, rather deep water. In other words, during the sedimentation of the Hoia Limestone, the shelf-platform areas were occupied by a sandy corallinaccan facies, the shclf-edge (4-slope?) areas were the sites of development of a muddy miliolid-eoraligenous facies, and the basinal areas accommodated a mud, globigerinid-bryozoan facies. The reccurrences of mud coraligenous facies within the area of the sandy eorallinacean facies zone may be explained by the occurrence of some small depressions with shallow, but quiet water which, reproducing the shelf-edge conditions, favoured the deve- lopment of the mud coraligenous facies as tiny patches. As a conelusion, the north western sector of the Transylvanian Basin represented, during the deposition of the Hoia Limestone, a gulf in whose center clayey-calcareous oozes of a basinal, globigerinid-bryozoan facies accummulated, and colaterally, on the margins, muddy, corali- genous deposits of a shelf-edge facies and skeletal (mainly corallinacean- nummulitic) sands were deposited, the latter covering the whole shelf platform between the shelf edge and the shore. Supposingly, the water depth of the sedimentary basin gradually increased from the sandy coralli- nacean facies zone (meters to a few tens of meters) towards the mud, globigerinid-bryozoan facies zone (50—60 meters or more). CHRONOSTRATIGRAPHIC ASPECTS RELATED TO THE AGE OE THE HOIA LIMESTONE Most of the researchers considered the Hoia Beds as representing the first Oligocene term of the Transylvanian Basin, terming them either Lower Oligocene (Hofmann, 1887), either Ligurian (Koch, 1894), or later on, Lattorfian. This age, established especially on the basis of the molluscan assemblage, seemed not to be in aggreement with that sug- gested by foraminifera. B o m b i ț ă , for instance, notes the occurrence in the Hoia Limestone of some evoluated forms of Nummulites fabianii standing for passage forms to N. intermedius, concluding that this limestone would represent a Priabonian member of passage to the Oligocene series (B o m b i ț ă , 1963 ; B o m b i ță and Moisescu, 1968). Quite recently, the Oligocene age of the Hoia Limestone was recon- sidered on the basis of the nannoplancton studies. Thus, M e s z â r o s et al. (1973) deseribe from this limestone a nannofloral assemblage, ascri- bing it a lattorfian age (estiinating the standard zone NP 21), and Mart i- n i and Moisescu (1974) point out the presence of the Hdicopontos- phaera rdiculata zone (the standard zone NP 22), which is included by the authors together with the zone NP 21 in the Lower Oligocene. Without having any doubt on the vcracity of this last biozonation, which otherwise for the Bryozoa Marls corresponds to the zonation pre- \ igr/ Institutul Geological României 21 SEDIMENTATION AT THE TIME OF THE HOIA LIMESTONE 161 viously accomplished by P o p e s c u and Gh eț a (1972), weintendonly to bring into the discussion the assigning of the standard zone NP 22 to the Lower Oligocene, a fact which in our opinion is wrong. It is well known the fact that the Latdorf Sands as well as the Sil- berberg Formation proposed as neostratotype for the Lattorfian contain the Ericsonia subdisticha zone (standard zone NP 21) (Martini, 1969 ; Martini and Ritzkowski, 1968). On the other hand, the Rupelian of D u m o n t encompasses as main component the Berg Sands and the Boom Clays, both of them included by M ii 11 e r (1970) on the basis of the nannoplancton in the Sphenolithus predistenthus zone (standard zone NP 23). But the Rupelian of Belgium does not follow directly the Lattor- fian, which here is separated under the name of Lower Tongrian (including the standard zone NP 21; Martini and Moorkens, 1969), between them being interposed the Upper Tongrian (containing in the Vieux Joncs Sands the nannoplancton assemblage of the standard zone NP 22; Martini, 1969). The question is where must the Upper Tongrian be attached, to the Lattorfian type or to the Rupelian type, or in other words where must this chronostratigraphic subdivision be included, in the Lower Oligocene or in the Middle Oligocene? To work out this question we remind the fact that B a t j e s (1958) proved, using the foraminifera, that the Upper Tongrian represents a lateral facies of the Early Rupelian, and that in Helmstedt region of Germany the deposits directly younger than the Silberberg Formation (Lattorfian) are for long time designated under the generic term of „Rupelton”. This latter, in Brick yard Alversdorf, contains the nannoplancton of the Cyclococcolithiis margaritae subzone (the lower part of the standard zone NP 22) (R o t h , 1970). Taking into account these arguments it is evident that the Upper Tongrian and the equivalent deposits must be included in the Middle Oligocene, and together with them the Helicopontosphaera reiiculata zone too (as already have proceeded some authors : R o t h , 1970 ; R o t h et al., 1971). In addition worth mentioning is the fact that this interpre- tation is in agreement with the original sense given by B ey r i ch to the Middle Oligocene. As a consequence of the above-mentioned facts, the age ascribed by M a r t i n i and Moisescu (1974) to the Hoia Beds on account of the presence of the standard zone NP 22 must be reinterpreted. They do not belong to the Lower Oligocene (Lattorfian), but to the Middle Oligocene (Rupelian s.l.) and correspond temporally to the Upper Tongrian of Belgium. We have to mention that this age was already put forward by R u s u in an unpublished report (p. 38)4 where the estimation was done as a result of the study of gastropods : the Hoia Beds and the Mera Beds belong 4 A. Rusu. The Stratigraphy of the Oligocene Deposits of Treznea-Poiana Blenchii Area on the Basis of the Gastropod Fauna, (in Romanian) (1967) Arch. of Institute of Geology and Geophysics, Bucharest. j- <.n Institutul Geologic al României (GR 7 162 A. RUSU, A. DRAGA.NESCU 22 to the Upper Tongrian (considered as the first terna of the Oligocene se- ries). In this sense, this author applied, then and later in a published paper (Eusu, 1972, Fig. 3), for the two members the term of ,,Lower Oligo- cene” (incorrectly used for the Upper Tongrian), considering the Lattor- fian as belonging to the Eocene period. An other problem to solve is the belonging of the Lattorfian to the Eocene or to the Oligocene; this matter keeps entailing much discus- sion and we think that the analysis of the Paleogene of the mesogean realm may bring some contribution to taking of a decision as adequate as possible. If it is proved that the Lattorfian corresponds temporally to the whole interval of the Priabonian type (the situation encountered in the Transylvanian Basin pleads for this opinion), it will be adequate to con- sider it as Eocene. For the time being it may be indirectly deduced that the Nummulites retiatusiproblematicus subzone which crowns the Pria- bonian (Cita, 1969), is equivalent to the Lattorfian. The above-men- tioned subzone of nummulitids corresponds in terms of planctonic fora- minifera to the Globigerina gortanii gortanii zone (Cita, 1969); but R o t h et al. (1971), who studied concurrently the nannoplancton and the pelagic foraminifera of several paleogene sections of Italy, ascertain that the Globigerina gortanii gortanii zone contains the assemblage of the Ericsonia subdisticha zone (occurring also in the Lattorfian type). For this reason the cited authors opinate for the exclusion of the Globigerina gortanii gortanii zone from the Priabonian definition, proposal which, given the situation in the mesogean realm, has little chance to be adopted. More suitable it seems to be the placement of the Lattorfian within the Eocene column, as already recommended by K r u t z s c h and L o t s c h (1957) and other authors, a fact which would be in a good agreement with the conception of Cavei ier (1968) also sta ted in the report of this latter at the Colloquium on the Eocene in 1968 at Paris ( ga v e 1 i e r , 1969). It is well known the fact that the West-German geologists hardly want to keep this stage included in the Oligocene period (maybe for this reason they broaden the Lower Oligocene interval unjustifiedly including here the standard zone NP 22 and thus giving to this subdivison a more oligoceneous appearence) and this situation is preserved as such sooner by virtue of the priority principie (the original definition of the Oligocene given by B e y r i c h ), because the character of the faunas does not plead for this interpretation. The adoption of the formula Lattorfian-Eocene would bring instead much advantage. On the one hand the Upper Eocene of the northern realm (Barthonian s.l.) would become equal to that of the mesogean realm (Priabonian), and on the other hand the delicate problem of the Eocene/ Oligocene boundary would be solved. So, this boundary would correspond to the bionomic threshold given by both the macro- and microfauna of the Mediterranean bioprovince, by the molluscan fauna of the boreal biopro- vince, and by the mammalian fauna („Grand Coupure” de Stehlin) of < jA Institutul Geological României \jGRy 23 SEDIMENTATION AT THE TIME OF THE HOIA LIMESTONE 163 Europe. Placed over the Lattorfian, the Eocene/Oligocene boundary coin- cides with that traced between Ludian and Stampian (including at the base the Sannoisian facies) in the Paris basin, between Lower Tongrian and Upper Tongrian (Henisian) in Belgium, between Kievian and Harko- vian in Southern Ukraina, and at the top of the Priabonian in the mesogean realm (Fig. 3) In the Transylvanian Basin this boundary would be placed, as sugges- ted by the nummulitids and macrofauna — at the base of the Hoia Lime- stone and of its stratigraphic equivalents, and as required by the nanno- Mesogean Realm Paris Basin Belgium ii. W. Germany S. Ukraina § 1 § Oligocen f Stampian U. Tongrian t Rupe Han s.l. Harkovian 5 D • , • Priabonian e । Ludian 1 L. Tongrian Lattorfian Kievian Fig. 3. —The chronostratigraphic correlation accepted in current paper around Eocene/Oligo- cene boundary. (A . Rus u). plancton—a few meters below, at the level of disappearence of Cyclococco- lithus formosus (if the limit between the standard zones of nannoplancton NP 21 and NP 22 is thought as representing the Lattorfian /Eupelian s.l. boundary). GENERAL CONCLUSIONS Emphasizing the fact that the content of the Hoia Beds must be restricted to the eoraligenous calcareous facies (the Hoia Limestone) and that the Scutella Lower Level, which all the recent papers use to include in the Hoia Beds, actually belongs to the Mera Beds, the authors establish for the first time that the deposits overlying the Brebi Marls Member and underlying the Curtuiuș Beds (Member) and usually separated as „Hoia Beds” in the Mezeș area correspond both to the Hoia Limestone of the Hoia Hill (Gilău area) and to the lowermost part of the Mera Beds (inclu- ding the Sctitella Lower Level) of their stratotype section (Gilău area too). The facies of Lithophyllum-beaxm^ Limestones, developed in the same stratigraphic interval starting from Ciglean northeastward, between Ciglean and Ciocmani being stratigraphically located between the Brebi Marls and the Curtuiuș Beds and from Ciocmani eastward representing the upper - most part of the Calcareous Series Formation directly underlying the Curtuiuș Beds, is proposed to be termed the Ciglean Limestone; it displayes an other stratigraphical extent, namely corresponding to the interval encompassing the Hoia Limestone and the Scutella Lower Level. There- fore in the area of development of the Calcareous Series (Preluca area) the jA Institutul Geological României \jgrz 164 ’A. RUSU, A. DRĂGĂNESCU 24 equivalent of the Hoia Limestone would be placed in a subterminal posi- tion, and the Scutella Lower Level — at the top of the Calcareous Series. Presenting the outeropping sections in the concerned stratigraphic interval, the authors draw the attention on the reworkings of skeletal material of the Ciglean Limestone in the suprajacent Curtuiuș Beds, ma- terial which is able to originate in calcareous beds giving the false impression of standing for the Ciglean Limestone. In the Mezeș area, the authors point out an obvious facies zonation including from the shore inward the depositional basin : the sandy, coral- linacean, marine facies zone covering the shelf-platform areas (correspon- ding to the Ciglean Limestone); the muddy, miliolid-coraligenous, marine facies zone expressing shelf-edge conditions (corresponding to the Hoia Limestone); and the muddy, globigerinid-bryozoan, marine facies zone occupying the basinal environments (corresponding to the uppermost part of the Brebi Marls in those sectors where these latter substitute the Hoia Limestone). Thus it is proved the fact that both the Hoia Limestone and the lower part of the Ciglean Limestone stand for correspondents of the uppermost part of the Brebi Marls, replacing the latter ones in the marginal sectors of the basin in the Mezeș area. The data of the literature suggest that the zonation ascertained in the Mezeș area keeps valid for the Gilău area too. In the Preluca area, a single facies zone outerops — the sandy, corallinacean facies zone — accommodating small islands of muddy, miliolid-coraligenous facies within its nummulitic-corallinacean sands; it is to be supposed that the other facies zones distinguished in the Mezeș area are continued in this area too, under younger deposits. Taking into account the genetic significance of the distinguished facies zones as well as the stratigraphic sequences in the investigated teritory, one may conclude that the deposits of the stratigraphic interval of the Hoia Limestone correspond to a phase of rapid regression, in which phase the basinal marly Brebi facies withdraws inwards the basin, being replaced shoreward by calcareous, shelf facies represented by lime muds accommodating small coral bioherms and by nummulitid-corallinacean lime sands. The analysis of the available data concerning the age of the Hoia Limestone and especially of those data provided by the nannoplancton studies (the standard zone NP 22 established by M a r t i n i and Moi- sescu, 1974), points to the fact that the Hoia Limestone stratigraphic interval is temporally equivalent to the Upper Tongrian, which must be inclu- ded either in the Middle Oligocene if the Lattorfian is considered as belon- ging to the Oligocene period, or in the lower part of the Oligocene if the Lattorfian is placed in the Upper Eocene. Noticing that the Lattorfian of the northern realm correlates with the uppermost part of the Eocene of the mesogean realm, Rusu opinates for the location of the Eocene/Oligocene boundary between the Lattorfian and the Rupelian s.l. (including the Upper Tongrian); in the Transylvanian Basin, this boundary would underlie directly the Hoia Limestone. M Institutul Geologic al României IGRZ 25 SED UMENTATIONi AT THE TIME OF THE HOIA LIMESTONE 165 REFERENCES Bărbii I. Z. (1956) Contribuții la studiul microfaunei din Paleogemil Transilvaniei de N —W. An. Univ. „C.I. Parhon”, Ser. șt. nat. 10, p. 155 — 163. București. Batjes D.A.J. (1958) Foraminifera of the Oligocene of Belgium. Mem. Inst. roy. Sc. nat., Belgique, 143, p. 1 — 188. Bruxelles. B 1 o w W.H. (1969) Late MiddleEocene to Recent Planktonic Foraminiferal Biostratigraphy. Proc. First. Internat. Conf. Plankt. Microfossils, I, p. 190—314. Leiden. B o m bi ță Gh. (1963) Contribuții la corelarea Eocenului epicontinental în R.P. Română. Ed. Acad. R.P.R. București. — Moisescu V. (1968) Donnfees actuelles sur le Nummulitique de Transylvanie. Mim. B.R.G.M. 58, Coli. Eoc. 1968, p. 693-729. Paris. Ca vel ier C. (1968) L’fiocene superieur et la base de I’Oligocene en Europe occidentale. Mem. B.R.G.M. 58, p. 509-526, Coli. Eoc. 1968. Paris. — (1969) La limite Eocăne — Oligocăne. Mem. B.R.G.M. 69, Coli. Boc. 1968, p. 431 —437. Paris. Cita M.B. (1969) Le Paleocene et l'Eocăne de l’Italie du Nord. Mem. B.R.G.M. 69. Coli. Eoc. 1968, p. 417—428. Paris, D u m i t r e s c u I. (1957) Asupra faciesurilor și orizontării Cretacicului superior și Paleogenului din bazinul Lăpușului. Lucr. Inst. de Petrol și Gaze, III, 1956, p. 19 — 44. București. Franca v lila F., Frascari Ritondale Spân o F., Z e c c li i R. (1970) Alghe e Macroforaminifcri al limite Eocene-OIigocene presso Barbarano (Vicenza). Gior. Geol. (2), XXXVI (1968), p. 653-686, Bologna. H a u e r Fr., S t a c h e G. (1863) Geologie Siebenbiirgens. Ed. W. Braumiiller, 636 p. Wien. H o f m a n n K. (1879) Bericht uber die im ostlichen Theile des Szilagyer Comitates wăhrend der Sommercampagne 1878 vollfiihrten geologischen Specialaufnahmen. Foldt. K6zl. IX, 5-6, p. 231-283. Budapest. — (1881) Bericht uber die im Nordwestsiebenbiirgischen Grenzgebirge und Ungebung im Jahre 1881 ausgefuhrtcn geologischen specialaufnahmen. Foldt. Kozl. XI, p. 317 — 329. Budapest. — (1887) Geologische Notizen uber die krystallinische Schieferinscl von Preluka und liber das nordlich und siidlich anschliessende Tertiărland. Jb. d. kgl. ung. geolog. Ansi. f. 1885, p. 31 — 61, Budapest. Koch A. (1894) Die Tertiărbildungen des Beckens der siebenbiirgischen Landestheile. I. Palăogene Abtheilung. Milth. a. d. Jb. d. kgl. ung. geolog. Anst. X. Bd. 6Hft. p. 177 — 399. Budapest. Kruts c h W., Lotsch D. (1957) Zur straligraphischen Stellung der Latdorfstufe im Palăogen. Geologie 6, h. 5, p. 476 — 501. Berlin. Martini E. (1969) Nannoplankton aus dem Latdorf (locus typicus) und weltweite Paralle- lisierungen im oberen Eozăn und unteren Oligozăn. Senckenbergiana lethaea 50. (2/3). p. 117—159. Frankfurt am Main. — (1971) Standard Tertiary and Quaternary Calcareous Nannoplancton Zonation. Proc. II Plankt. Conf. Roma 1970, p. 739-785. Roma Martini E., Moisescu V. (1974) Nannoplankton — Untersuchungen in oiigozănen Ablagerungen zwischen Cluj und Huedin (N—W Siebenbiirgisches Becken, Rumănien). AL Jb. Geol. Palăont. Mh, H.l, p. 18-37. Stuttgart 166 A. RUSU, A. DRĂGĂNESCU 26 — MoorkensT. (1969) The Type-Locality of the Sand of Grimmertingen and Calcareous Nannoplankton from the Lower Tongrian. Bull. Soc. belg. Geol. Paliont. Hydrol. 78, 2, p. 111-130. Bruxelles. — R i t z k o w s k i S. (1968) Was ist das „Unter-OIigocăn” ? Nachr. Akad. W’fss. Gottingen II. Math-Phys. kl.1968, 13, p. 231-250. Gottingen. Mastrorilli V.I. (1967) Nuovo contributo allo studio delle Corallinacee dell’Oligocene ligure piemontese: I reperti della Tavoletta Ponzone. Atti Ist. Geol. Univ. Genova 5,2, p. 153—406. Genova. M 6 s z ă r o s N., M a g d u n D. (1972) Beitrăge zur Prăzisierung der stratigraphischen Lage des Hoiaer Kalksteines am Hoia-Berg in Cluj (Klausenburg). Slud. Univ. Babeș-Bolyai, ser. geol.-miner. 1, p. 53 — 59. Cluj. — 1 li eseu O., Petre I. (1970) Unele considerațiuni asupra limitei Eocen-Oligocen în forajele de la Jac-Lupoaia (valea Agrijului, județul Sălaj). D.S. Inst. geol. LV/4, p. 165 — 173. București. — L e b e n z o n C., I a n o 1 i u C. (1973) Limita Eocen-Oligocen în dealul Hoia din Cluj, stabilită cu ajutorul nannoplanctonului. St. Univ. „Babeș Bolyai”, ser. geol.-miner. 1, p. 61 — 69. Cluj. — Lebenson C., I a n o 1 i u C. (1974) Limita Eocen/Oligocen la Mera, stabilită cu ajutorul nannoplanctonului (in press). Moisescu V. (1968) Cercetări geolog ce în împrejurimile orașului Cluj. St. și cerc, geol., geofiz., geogr., seria geol. 13, 2, p 491 — 503. București. Kl ii 11 e r C. (1970) Nannoplankton aus dem Mittel-Oligozăn von Norddeutschland und Belgien. N. Jb. Geol. Palăont. Abh. 135, 1, p. 82—101. Stuttgart. Popescu B., G h e ț a N . (1972) Nannoplanctonul calcaros din orizontul marnelor cu bri- ozoare de la vest de Cluj (bazinul Transilvaniei) D.S. Inst. geol. LVIII/3, p. 129—140. București. R ă i 1 e a n u Gr., S a u 1 e a E. (1956) Paleogenul din regiunea Cluj și Jibou (NW bazinului Transilvaniei). An. Com. Geol., voi. XXIX, p. 272 — 308. București. Roth P.H. (1970) Oligocene Calcareous Nannoplancton Biostratigraphy. Eclogae geol. Helv., voi. 63/3, p. 799-881. Basle. — Ba uman P., B e r t o 1 i n o V. (1971) Late Eoccne-Oligocene Calcareous Nanno- plancton from Central and Northern Italy. Proc. II Plankt. Conf. Roma 1970, p. 1069— 1097. Roma. R u s u A. (1967) Studiul geologic al regiunii Moigrad (nord-vestul bazinului Transilvaniei). D.S. Inst. geol. LIII/1 (1965-1966), p. 427-455. București. — (1968) Contribuții la cunoașterea stratelor de Hoia din regiunea Jibou. St. și cerc, geol., geof., geogr., seria geol., t. 13, 2, p. 511 — 519. București. — (1970) Corelarea faciesurilor Oligocenului din regiunea Treznea — Bizușa (N-W bazinului Transilvaniei). St. cerc. geol. geof. geogr., scria geol. 15, 2, p. 513—525. București. — (1972) Semnalarea unui nivel cu Nucula comta în bazinul Transilvaniei și implicațiile lui stratigrafice. D.S. Inst. geol. LVIII/4 (1971), p. 265 — 282. București. Șuraru N. (1970) Stratigrafia depozitelor terțiare din bazinul inferior al văii Almașului (NW Transilvaniei) cu privire specială asupra celor Miocen inferioare, Ph. D. thesis. București. Institutul Geological României 27 SEDIMENTATION. AT THE TIME OF THE HOIA LIMESTONE 167 QUESTIONS B. Popescu : 1. Why do you exclude the NP22 zone from the Lattorfian (Lower Oligocene according to M a r t i n i ’ s classification) ? 2. If the limestones with Scutella and Nummulites fabianii, N. intermedius, N. incrassatus, N. vascus from the terminal part of the Calcareous Series (Cozla Beds) do not represent an equi- valent of the Hoia Limestone, where might be found this equivalent within the Calcareous Series ? 3. What is the significance of the large amounts of matrix in the limestones of the coral- linacean sand facies which you consider to represent the materialization of an agitated environ- ment, hence where this matrix could not have resisted the „washing" ? Answer : 1. The Lower Oligocene, as defined by Beyrich, corresponds exactly to the Lattorfian stage, and the lattcr includes in its stratotypc only the association of the Nanno- plankton Standard Zone NP 21. To include the NP22 Zone, characteristic of the Upper Tongrian, in the Lower Oligocene is an error, since it was proved that the Upper Tongrian represents the Early Rupelian, and consequently should be placcd in the Middle Oligocene of Beyrich (or, in our acception, in the lowermost part of the Oligocene, provided the Lattorfian would be considered as Eocene in age). Hence the NP22 Zone should not be artificially enclosed in the Lattorfian. 2. The limestones with Scutella from the uppermost part of the „Calcareous Series" corres- pond to the Scutella Lower Level of the Mera Beds (Gilăul area), and the equivalent of the Hoia „Limestones" is located in the „Calcareous Series" directly below it, i.e .in a subterminal position. 3. In the opinion of the authors the corallinacean facies are composed solely of skeletal corpuscles, being devoid of micrite matrix ; the appearance of matrix is brought about either by micritization processes accompanied by the welding of the corpuscles, or by the development of very finely crystalline microspar as networks or irregular patches. This problem is approached in detail in the chapter reserved for the petrographic description of the sedimentary facies and illustrated in photo plates annexed to this paper. M . S ă n d u 1 e s c u : 1. The authors assert that the corallinacean facies closes towards south-west. How can be explained, according to this interpretation, the lack of the fore- going facies in the entire area south of Moigrad, where the coraligeneous muddy facies commes into a direct contact with the mainland (as interpreted by the authors) ? 2. Recently B. Popescu presented a different paleogeographic image which presumes; a westward prolongation of the facies zones oriented east-west. How do the authors consider this interpretation? Answer : 1. The authors do not assert but just assume the ending of the coralline facies towards south-west, in accordance with the petrological evidences. As shown also in the text of the paper, we think that the Preluca area, where the sandy corallinacean facies was largely developed, formed an extensive plateau covered by several meters of water and bordered westwards by a mainland with a low relief. These eonditions which favoured the formation of real „algal strands", were no more accomplished south of Moigrad. We assume that here the depth of the basin increased faster, and the sea shore was higher sup- plying the terrigenous material which from north to south got more abundant and coarser. In the same direction the corallinacean thalli get gradually scarcer in the rock finally vanishing in the Stina-Treznea sector. These data correlated with the outlines of facies zones suggest that here the corallinacean facies zone is missing, and the muddy coraligenous facies zone with miliolids directly joins the shore. Therefore, the rapid increase in the basin depth, and the development 168 A. RUSU, A. DRAGANESCU 28 of some shelf-edge conditions in the close vicinity of the land would have represented the chief factor responsible for the facies configuration under discussion. 2. The paleogeographic image implying the westward prolongation of the facies zones pre- sented by Popescu refers to the stratigraphic interval located beneath the Hoia Limestone. DISCUSSIONS V . Moisescu : We can refer the Hoia Limestone only to deposits cropping out in the Hoia Hill within the type section. A formation similar to it is no more encountered in the Transylvania Basin. I do not agree with the facies interpretation put forward by the authors for the Hoia Beds. It remains only a working hypothesis. Hoia Limestone is a regressive formation, still not marking a sharp regression. Hoia Limestone belongs to the Lower Oligocene (post-Lattorfian) and to the Middle Oligocene although the molluscan fauna are partially resembling those from the superjacent deposits. Taking into account its nannoplankton Hoia Limestone should pertain to the NP22 biozone, i.e. to the upper part of the Lower Oligocene. This biozone is confined to the Upper Tongrian, fact also admitted by the authors. The Upper Tongrian is, however, the chronostra- tigraphic equivalent of the upper part of the Lower Oligocene, and not of the Middle one as it is considered in this paper. Answer : We do not share the opinion of V . Moisescu, according to which the Hoia Limestone might be recognized only in the Hoia Hill. In our view any occurrence of eoraligenous facies at this stratigraphic level should be tabulated as Hoia Limestone, i.e. at Stîna, Ciumărna or Treznea, in the Mezeș area. Paleontological evidence bearing on the equivalence of Hoia Limestone with the terminal part of Bryozoa marls does exist even in the Gilău area. Thus Măszâros, I a n o 1 i u and Lebenson found the nannoplankton association of the Hoia Limestone from Cluj in the uppermost deposits of the Bryozoa marls (hence beneath the Scutella Lower Level) from the Mera type section (see also Moisescu, M 6 s z ă r o s , 1974, Plate VI). Therefore we are confronted with a facies variation from the border of the basin (coral-bearing miliolid linie muds) inwards (marls with globogerinids and bryozoas). It seems that I was not sufficiently explicit, but in the paper it is clearly argued why the Upper Tongrian cannot be assigned to the Lattorfian, between them being located the Lower Oligocene/Middle Oligocene boundary in the northern realm, or the Eocene/Oligocene boun- dary in the Mesogean realm (as it is also the case of the Transylvania Basin). B. Popescu: 1. From the parallelism you presented as an answer to my question it results that the Hoia Beds of the Hoia Hill with nummulites of fabianii-inlermedius and incras- satus-vascus type, corals still without Scutella have an equivalent in the sequence underlying the limestone of a similar paleontologic content but in additionwith Scutella from the terminal part of the Calcareous Series ( = Cozla Beds), which this time is parallelized with the lower- most part of the Mera Beds (Upper Tongrian-Rupelian s.s.) Thus you arrive at a conclusion entailing a situation unique of its kind, nowhere recognized, which implies the presence of forms of nummulites of the fabianii type in deposits assigned to the Middle Oligocene. 2. I likewise doubt as to existence of some reefs of the ,,patch reef“ type in the Hoia Beds from the Mezeș area. In the course of our investigations, which the last years have compri- Institutul Geologic al României 29 SEDIMENTATION AT THE TIME OF THE HOIA UMESTONE 169 sed this zone too, I never encountered in the Hoia Beds corals in growth position. Numerous examples even of colonial corals do exist, but these are brocken and form accumulations yielding limestones with corals. 3. Finally I consider that the corals quoted in the corallinacean facies zone could not develop in depression zones formed in the skeletal sands and muds, as asserted by the authors. In zones with present-day sediments where fine-grained carbonate sediments develop, coral colonies do not grow in excavations, where they may be readily overlain by carbonate mud transported by the water movements from this facies zone (agitated hydrodinamic regime in this zone, according to the authors of this paper). 4. The paper presented by mc last year led us to a different paleogeographic picture as regards the sedimentation of the Cozla Beds interval ( = Calcareous Series), the Cluj Limestone, the Bryozoa Marls, the Brebi Marls. It is noteworthy that the facies of the regressive Hoia Beds mark a curve following, in general, the present-day shape of the Transylvania Basin, fact also asserted by the authors of this work. According to our interpretation the significance assigned to these facies was somewhat different, as we consider the shore as being located in the Gilău Massif Zone with a terrigenous carbonate shelf nortlnvards. In front of the shelf a channel ( = shelf lagoon) with pelitic sediments (Bryozoa Marls, Brebi Marls) and farther northwards a platform with a pure carbonate sedimentation are found. Answer : We have to take into account that at the level of the Hoia Limestone, we are not anymore in the presence of some typical forms of N. fabianii; they actually stand for some mutations (according to Bombiță other than N. reliatus or N. problemalicus) which cannot be so far uscd as biostratigraphic arguments as even their age is to be established. The examina- tion of other groups of fossil organisms enables us to state that the deposits including these num- mulites correspond either to the Upper Tongrian of the nothern realm or to the lowermost Oligocene of the Mesogean realm. The outerops exposing the bioconstructed limestones are rather scarce and small, so that they may be easily overlooked. Gh. Bo mb i ță : The spirited character of discussions is explained by the bulk of data upon which each author is relying, data contained in their Ph. D. theses. In Romania the Transylvania Basin is the most representative domain for the strati- graphy of the Paleogene, and any discussion referring to this domain are welcome. The disagree- ments which persist in defining the Eocene/Oligoccne boundary are due to the frequcnt and exclu- sive utilization of one of the characteristic macro- and micro-fossil groups : mollusks, small or large foraminifera, nannoplankton, as well as the rigid use of data from some recent Works which approach this problem, and whose conclusions are sometimes only apparently and theo- retically definitive. ' M Institutul Geologic al României IGR/ PLATE I Fig. 1. — Hydnophyllta ct. scalarta (C a t u 11 o ) (xl,l) Hoia Limestone, Stîna. Fig. 2. — Aclinacis sp. (x 2), Hoia Limestone, Treznea. Fig. 3. — Stylocaenia sp. (x2), Hoia Limestone, Treznea. Institutul Geologic al României IGR/ A. Eusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. I. Anuarul Institutului de geologie și geofizică, voi. XLVIII. (GR Institutul Geological României PLATE II Fig. 1, 2. — Hydnophyllia cf. scalaria (Ca t u 11 o ) (xl) Hoia Limestone, Ciumărna. 1, the upper side. 2, the lower side. A. Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. II. Anuarul Institutului de geologie și geofizică, voi. XLVIII. «gr/ Institutul Geological României PLATE III Rhabdophyllia tenuis Rcuss (xl), Hoia Limestone, Treznea. Institutul Geological României A. Busu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. III. Anuarul Institutului de geologie și geofizică, voi. XLVIII. -LfĂDA Institutul Geological României X IGRZ Fig. 1. Fig. 2, t PLATE IV — Coraligenous limestone with Rhabdophyllia lenuis R eu sg (X1). Hoia Limestone, Brebi. 1. — Cyathoseris apennina gibbosa (Prever) (xl) Hoia Limestone, Treznea. 2, the upper side. 3, the lower side. Institutul Geological României A. Rusu, A. Dbăgănesctj. Sedimentation at the Time of the Hoia Limestone. Pl. IV. Anuarul Institutului de geologie și geofizică, voi. XLVIII. 1 Institutul Geological României IGR PLATE V ua GQ — Lithophyllum symetricum Lom o ine (x 64). Ciglean Limestone. Ciglean. — Lithophyllum simplex Lemoine (x 64). Ciglean Limestone. Ciglean. . 3, 4. — Lithophyllum sp. (x 64). 3, — Hoia Limestone, Brebi. 4, — Limestone Series, Glod. Institutul Geological României A. Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. PI. V. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic el României \ IGRZ PLATE VI Fig. 1. — Individuala of Globorolalia sp. in Hoia Limestone (x 64). Fundătura (Creaca). Fig. 2. — Bryozoan tests and Hotaliids in the uppermost part of the Limestone Series (X 64). Șoimușeni. Fig. 3. — Skeletal limestone with pelecypods and foraminifera (x 64). Hoia Beds sensu lato. The equivalent of the Sculella Lower Level of the Mera Beds. Slîna. Fig. 4. — Sandy limestone with miliolids (x 64). Hoia Beds sensu lato. The equivalent of the lowermost part of the Mera Beds. Ciuinărna. A. RUSU, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. VI. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR> PLATE VII The sandy, corallinacean facies zone. Top of Calcareous Series. Preluca area : Glod. Fig. 1—6. — Very coarseand coarse, numinulitid-corallinacean, weldcd grainstones consisting of coralline nodules (the black grains), nummulitids and other large benthonic foraminifera, echinoderm plates, bryozoas, miliolids. Corallinacean algae. miliolids and in places nummulitids are partly or wholly micritized. The grain welding most obvious in Fig. 2; hard grain compaction supported by grain interpenetration and contact-solulion phenomena. In all other photomicrographs the originar wclded texturc is more or less obliterated by a diagenetic replacive spar calcite (microspar to pseudospar) developed at the expanse of the micritized skeletons, the spar calcite nibbling into, penetrating or transecting the different (especially coralline) grains. Institutul Geological României A. Eusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. VII. Anuarul Institutului ele geologie și geofizică, voi. XLVIII. *GR Institutul Geological României PLATE VIII The sandy, corollinaccan facies zone. Top of Calcareous Series. Preluca area : Glod. Fig. 1—2. — Details in very coarse and coarse, nummulilid-corallinacean,welded grainstones consisting of coralline fragmenta, nummulilids, balanids (Fig. l),cchinoderm plates (Fig. 2), etc. The photomicrographs show the matrix-mimmicing microspar clearly developed on the skeletal (mainly coralline) grains, which appear reoutHncd and floating as isolated fragments into a microspar groundmass. Institutul Geological României A, Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. VIII. 0 0,5 ■ 1 mm I________________I________________J Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic al României PLATE IX The sandy, corallinacean facies zone. Top of Calcareous Series. Preluca area : Boiu Marc. Fig. 1. —2. —Very coarse and coarse, numinulitid-corallinacean, weldcd grainstones consisting mainly of coralline nodules and nummulitids, and subordinalely of bryozoas, miliolids, echinoderm plales. The wekled texture is obvious; strong grain compac- tion pointed out by grain interpenetration and conlact-solution phenomena. Fig. 3. — Detail in Fig. 2. Welding, solution and interpenetration of the skeletal grains is slrongly manifest. All the blaek areas showing or not line cellular fabrics stand for coralline algac. Fig. 4. — Detail in the same grainstones. The strong grain compaclion rcvealed by the welding of the grains, is highly obvious. Institutul Geological României A. Rusu, A. Drăgânescv. Sedimentation at the Time of the Hoia Limestone. Pl. IX. Anuarut Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE X The sandy, corallinacean facies zone. Top of Calcareous Series. Preluca area : Răstoci and Toplița. Fig. 1 — 3. — Răstoci. Fig. 3 is an enlargemcnt in Fig. 2. Coarse and very coarse, nummnlitid- corallinacean, welded grainstones. Welding of the skeletal grains obvious in Fig. 2 (delailed in Fig. 3), i.e. belween a coralline grain and a nummulitid, or belween bryozoan tests. Evident developinenl of replacive spar calicite on account of skcle- tons. Fig. 4 — 5. — Toplița. Fig. 5 is an enlargement in Fig. 4. Medium-grained, ntiininuIiUd- corallinaccan. welded grainstones. Obvious welded texture. In photo 5 malrix- like microspar (in places aggraded to larger pscudospar) developed al the expense of the micritized corallinacean and foraminiferal welded tests. Institutul Geological României A. Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. X. Anuarul Institutului de geologie și geofizică, voi. XLVIII. igrZ Institutul Geologic al României PLATE XI The sandy, corallinacean facies zone. Top of Calcareous Series. Preluca area : Purcăreț, Băbeni, Cliț. Fig. 1. — Purcăreț. Coquina welded grainstone consisting of gastropods, pelecypods, cora- lline tests, foraminifera. The gastropod cavities filled with skeletal grains too. Spar (pseudospar) calcite areas developed al the expense of the skeletal (mainly coral- line) grains. Fig. 2. — Băbeni. Coquina welded grainstone consisting chiefly of pelecypods and coralline fragments. The pelccypod shells often fractured, in place with the resultant frag- menls more or less displaccd suggesting a strong grain compaction. Network-like microspar, partly aggraded to larger pseudospar, developed on the micritized skeletal (mainly coralline) grains. Fig. 3 — 5. — N of Cliț. Fig. 5 is an enlargement in Fig. 4. Coarse to very coarse, nummulitid- corallinaeean, welded grainstones. Obvious welding, melting (contact-solution) and intermingling of the skeletal grains. Development of microspar areas by eon- sumption of the coralline nodules and nummulitids most manifest in Fig. 5; most of microspar in Fig. 2 aggraded to (mosaicate or monocrystalline syntaxial) larger pseudospar. Institutul Geological României A. Rusu, A. Drăgănescu. Sedimentation at he Time of the Hoia Limestone. Pl. XI. 0 0,5 1 mm Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României PLATE XII The sandy, corallinacean facies zone. Top of Calcareous Series (Ciglean Limestone). Preluca area : Băbeni and Piroșa. Fig. 1—2.— Băbeni. Very coarse, corallinacean, welded grainstones consisting chiefly of large nodules of coralline algae. The skeletal grains are welded, showing contact-solution phenomena and interpenetrations. The spar areas are rcplacive calcite mainly on coralline tests. Fig. 3. — Băbeni. Oncolilic welded grainstones consisting of microoncoliths and pisoncolilhs. The spar areas are spar calcite replacemenls on fields of welded microoncoliths. Fig. 4 — 5. — Piroșa. Fig. 5 is an enlargemcnt in the central part of Fig. 4. Coarse to medimn- grained, corallinacean, welded grainstone displaying the component skeletal (mainly coralline) grains completely merged into each other. Theabundance of the coralline tests, their stronger or slighter micritization and their perfect welding originated in an appearence of micrite matrix, al low magnifica lions; al higher magnificalions, as photo 5 proves, Ihe „matrix” dissociales oplically in welded coralline fragments. Institutul Geological României A. Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. XII. 0 OJ 1 mm Anuarul Institutului de geologie și geofizică, voi. XLVIII. 16 R Institutul Geological României PLATE XIII The sandy, corallinacean facies zone. Top of Calcareous Series. Preluca arca : Soimușcni. Fig. 1 — 3. — Fig. 3 is an enlargement in the botlom of Fig. 2. Coarse to very coarse, nummu- litid-corallinacean, welded grainstone. The skeletal grains show contact-solulion phenomena. The nelwork-like microspar in which the skeletal grains seem embed- ded is not a slightly aggraded micrite matrix but, as clearly pointed oul by Fig. 3, it stands for a replacive, very finely crystalline spar calcilc stiperimposed on the original welded skeletal grains (now more or less ,,melled” within the microspar groundmass). Fig. 4 — 5. — Island of mud ly, coraligenous facies within the sandy, corallinacean facies zone. Fig. 5 is an enlargement in the botlom of photo 4. Globigerinids- and globo- rotalliids-bearing wackestones, accommodating coral biolithitic structures. Institutul Geological României A. Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. 1’1. XIII. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geologic al României PLATE XIV Preluca area : Ciocmani. l-'ig. 1—2. — N and, respeclively, E of Ciocmani. The sandy, corallinacean facies zone. Ciglean Limeslone enriched in nummulitids. Medium-grained lo coarse, nummulilid- corallinacean, welded grainstone showing the skelelal grains apparenlly loosely packed owing lo Ihe development of a nelwork-likc replacive spar calcite (inilially microspar. subsequcnlly aggraded to larger pseudospar) which ingested many of the original, welded skeletal grains; the unaffected grains show contact-solution phenomena and slight interpenetralions, supporting the welded grainstone tex ture of the original rock. l-'ig. 3 — 6. — Loealily of Ciocmani. The muddy, coralligeneous facies zone. Hoia Limeslone. Coral biolilhites filled with allochem-free (algal?) micrite. Thin-sections in massif, cruslous colonics of digitale corals. Institutul Geological României A. Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. XIV. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR/ PLATE XV The sandy, corallinaccan facies zone. Ciglean Limestone. Mezeș arca : Ciglean. Fig. 1 — 6. — Coarsc to very coarsc, corallinaccan, welded grainstones consisting of merged corallinaccan nodules and fragments, and in minor amounts, foraminifera, echi- noderm plates (with replacive monocrystalline syntaxial overgrowths). The spar calcite areas, varying from very finely to medium crystalline, stand for replacive diagenetic calcite (microspar and pseudospar) formed on account of the coralline tcsls. Institutul Geological României A. Rusu, A. Drăganescu. Sedimentation at the Time of the Hoia Limestone. Pl. XV. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României 1CR PLATE XVI The Mezeș area. Fig. 1—1.— The sandy, corallinacean facies zone. Ciglean. Ciglean Limestone. Corallinacean wekled grainstones showing interpenetration of the grains and obvious contact- solution phenomena (Fig. 2) accounting for the infered strong grain compaclion. Fig. 5—6. — The muddy, miliolid-coraligenous facies zone. Brebi (Pîrîul Ortelec valley). Hoia Limestone. Lamellous coral biolithitcs accommodated in a micrite matrix be- aring miliolids and pelagic foraminifera (see photographic details on the matrix in next plate). Institutul Geological României PLATE XVII The Mezeș area : Brebi. Fig. 1 — 3. — Brebi (Pîrîul Orlelec valley). The muddy, miliolid-coraligenous facies zone. Hoia Limeslone. Delails in the malrix of Ihelimestones presented in Pl. XVI; Figs. 5—6. Wackestones consisting of miliolids, globigerinids, globorotaliids, ostracods and pelecypods embeddcd in a micrile matrix. Fig. 4.— NW of Brebi (uppermost course of Brebi valley). Top of Brebi Marls Member: packstone conlaining abundant miliolids, coralline fragments, pellets, fine-grained quartz, diverse foraminifera. Fig. 5. — NW of Brebi (uppermost course of Brebi valley). The sandy, corallinacean facies zone. (Hoia Limestone interval). Coquina welded grainstone consisting of mergcd pelecypod shells. Institutul Geological României A. Rt'sr, A. DrăgăNESCU. Sedimentation ai the Time of the Hoia Limestone. Pl. XVII. Anuarul Institutului de geologie și geofizică, voi. XLVIII. Institutul Geological României IGR/ PLATE XVIII The muddy, miliolid-eoraligenous facies zone. Hoia Limestone. Mezeș area : Moigrad, Slina and Ciumărna. Fig. 1—3. — Moigrad. Linie wackeslone» and packstones accommodating coral biolithitic structures. The host sediment consists of coral debris, miliolids, globigerinids, globorolaliids, etc. embcddcd in a micrite matrix. Fig. 4 — 5. N of Stlna (Jurleana valley). Coral biolithitic structures in a lime wackslone or packstonc composed of micrite matrix, miliolids, coral debris, nummulitids, etc. Fig. 6.— Ciumărna. Top of Brebi Marls, underlying direclly the Hoia Limestone. Mari containing nummulitids, pelagic foraminifera, ele. Institutul Geologic al României A. Rusu, A. Drăgănescu. Sedimentation at the Time of the Hoia Limestone. Pl. XVIII. 3 4 Anuarul Institutului rle geologie și geofizică, voi. XLVIII. Jp.. Institutul Geological României igr/ PLATE XIX The muddy, miliolid-coraligenous facies zone. Ifoia Limestone. Mezeș area : Treznea and Slina. Fig. 1-1. — Treznea. Coral biolithllic strnclnres accommodaled in lime wackestone or pack stone composed of micrite matrix. coral fragments, miliolids, pelagic foramini- fera, ele. Fig. 5—6. — Slina (Șipole valley). The muddy. pelecypod-miliolidic subfaeies consisting of lime muds conlaining chiefly pelecypods and miliolids (local variely of the muddy, miliolid subfaeies). A. Rusu, A. Drăgănescu. Sedimentation al the Time of the Hoia Limestone. Pl. XIX. Anuarul Institutului ele geologie și geofizica, voi. XLVIII. igr/ Institutul Geological României PLATE XX The muddy, globigerinid-bryozoan facies zone. Top of Brebi Marls (equivalent to the Hoia Limeslone). Mezeș arca : Bozna. Fig. 1 — 3. — Marls consisting of clayey micrite matrix (partly replaced by a microspar or pseudospar calcite) containing miliolids. pelagic foraminifera, ostracods, and cryptocrystalline grains (lumps and pelets, mainly proceeding from micritized miliolids). Institutul Geological României Â. Ersv, A. Drăgănesc t\ Sedimentation al the Time of the Hoia Limestone. Pl. XX. time KW Stîna rna Mera dlHo'a ‘°oPnW Ge°^0^ institutul 1HE ho^ ass wăhsxl ^C'E* H0RW ‘ ' R$eni O^,J‘ :c coq^'na and Corallinacean g Mi11olidic vadcestones -pachetenes /ens-shaped coral boundstones r wacKee nțpOSVnON oCoi'a opiroȘa Roma oBQdia de Meseș ©HUtO'N Valea O oBo»u oSas° ©JIBOU ® oBmodat'n9 rinid^3l°b0 Redactor: ILONA SANDU Traduceri: MARGARETA HĂRJEU Ilustrația: VIRGILIU NITU Dai la cules; decembrie. 1975. Bun de tipar; aprilie 1976. Tiraj; 950 ex. Hîrtie scris IA 70x100/56 g. Coli de tipar; 103/A. Com. 11. Pentru biblioteci indicele de clasificare 55(058). Tiparul executat la întreprinderea poligrafică ,,Informația", str. Brezoianu nr.23-25. București — România Institutul Geological României Institutul Geological României The Annuary oi the Institute of Geology and Geophysics has been edited in the course of time under following denominati- ons : Anuarul Institutului Geologic al României t. 1 -XV (1908-1930) Anuarul Institutului Geologic al României (Annuaire de l'ln* stitut Geologique de Roumanie) t. XVI-XXII (1931-1943) Anuarul Comitetului Geologic (Annuaire du Comite Geologi- que) t. XXIII -XXXIV (1950 -1964) Anuarul Comitetului de Stat al Geologiei (Annuaire du Co- mite d Etat pour la Geologie) t. XXXV-XXXVII (1966 -1969) Anuarul l-nstitutului Geologic (Annuaire de l'lnstitut Geo- logique) t. XXXVIII-XLII (1970 -1974 ) Anuarul Institutului de Geologie și Geofizica (Annuaire de l'lnstitut de Geologie et de Geopliysique) t. XLIII -1975 Institutul Geological României Institutul Geologic al României ' K3R