Biostratigraphy and conditions of formation of Albian and Cenomanian deposits on the south-western slope of the Ukrainian Shield (Middle Dnister region)

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Biostratigraphy and conditions of formation of Albian and Cenomanian deposits on the south-western slope of the Ukrainian Shield (Middle Dnister region)

Leonid Kyselevych, National Museum of Natural History, NAS of Ukraine; Oleksandr Kovalchuk, University of Wroclaw

Abstract

Data from a comprehensive study into the lithological composition and lateral distribution of Albian and Cenomanian deposits in the Middle Dnister region (Ukraine), in the watersheds of the Smotrych-Tarnava-Studenytsia-Ushytsia-Kalyus-Zhvan-Lyadova-Nemiya-Murafa-Rusava-Markovka rivers, are presented in the paper. Cretaceous deposits of Volyn-Podillia are part of the terrigenous-carbonate subformation of the Jurassic-Cretaceous carbonate formation (J3-K_x) and the glauconite Cretaceous formation, which includes gaizeous, siliceous-chalk and marl-gaizeous subformations. Cretaceous deposits of the Middle Dnister region are represented by the lower (Albian stage) and upper parts (Cenomanian stage).The study is focused on the distribution of micro- and macrofauna (e.g. molluscs, calcareous nannoplankton) in the Albian and Cenomanian deposits and their facies affiliation, as well as on the quantitative analysis of organic remains and palaeoecological conditions. Differences in homogeneous conditions of sedimentation within the epicontinental sea basin of the modern Middle Dnister region at the Early-Late Cretaceous boundary were insignificant. Due to a study of Cretaceous macro- and microfauna, its facies distribution, quantitative analysis, and palaeoecological conditions, it is possible to trace slight differences between close homogeneous conditions of sedimentation within the relatively homogeneous sea basin of the Middle Dnister region on the verge of the Early and Late Cretaceous. This shallow epicontinental sea was characterized by normal salinity and well-aerated warm waters with temporary strong bottom currents within shallow water and with maximum depths up to 150-200 m in some areas and soft muddy bottom of deepwater areas. Phosphatisation of the early-middle Cenomanian fauna is evidence for the important role of the Carpathian upwelling at that time. Geochemically active phosphorus is concentrated on shelf due to changes in salinity, temperature, pH, CO₂ content and other parameters of the aquatic environment, which were characteristic for this region of Volyn-Podillia.

Key words: stratigraphy, biochronology, palaeoecology, sea, Cretaceous, Ukraine.

Резюме

Біостратиграфія та умови формування відкладів альбу і сеноману на південно-західному схилі Українського щита (регіон Середнеього Подністер'я)

Леонід Киселевич, Олександр Ковальчук

У статті представлено результати комплексного дослідження літологічного складу та Латерального розподілу альбських і сеноманських відкладів у Середньому Подністер'ї (Україна), на вододілах річок Смотрич-Тарнава-Студениця-Ушиця-Калюс-Жван-Лядова-Немія-Мурафа-Марківка. Крейдові відклади Волино-Поділля є частиною теригенно-карбонатної підформації юрсько-крейдової карбонатної формації та глауконітової крейдової формації, що включає опокову, кременисто-крейдяну і мергельно-гезову підформації. Крейдові відклади Середнього Подністер'я представлені нижньою (альб) та верхньою частинами (сеноман). Дослідження зосереджено на розподілі мікро- та макрофауни (молюсків, нанопланктону) у відкладах альбу і сеноману та їх фаціальної приналежності, а також кількісного аналізу органічних решток та палеоекологічних умов. Відмінності в однорідних умовах седиментації в епіконтинентальному морському басейні сучасного регіону Середнього Подністер'я на межі ранньої та пізньої крейди були незначними. Завдяки вивченню крейдової макро- і мікрофауни, її фаціального розподілу, кількісного аналізу та палеоекологічних умов можна простежити незначні відмінності між близькими однорідними умовами осадконакопичення у межах морського басейну.

Це мілководне епіконти- нентальне море характеризувалося нормальною солоністю і добре аерованими теплими водами з тимчасовими сильними донними течіями на мілководді та максимальною глибиною до 150-200 м у деяких районах і м'яким мулистим дном на глибоководді. Фосфатизація фауністичних решток раннього та середнього сеноману є свідченням великої ролі карпатського апвелінгу. Геохімічно активний фосфор концентрується на шельфі внаслідок зміни солоності, температури, рН, вмісту СО₂ та інших параметрів водного середовища, характерних для Волино-Поділля.

Ключові слова: стратиграфія, біохронологія, палеоекологія, море, крейда, Україна.

Introduction

In the Early Cretaceous, most of the territory of modern Ukraine was a landmass with a weakly dissected relief, local depressions comprising continental terrigenous formations, and coastal-lagoon deposits in its outskirts. Shallow temporary epicontinental isolated seas with sandy, sandy-clayey, clayey-carbonate or siliceous sediments existed on the periphery (in the Dnipro-Donets Depression, Crimea, Black Sea region, Moldavian Depression, and Volyn-Podillia). The Early Cretaceous was characterized by the appearance of mostly continental formations, except for Valangian and Albian, when the accumulation of marine sediments took place. Because of a rather complex palaeogeo- graphic situation in Volyn-Podillia during the Cretaceous, in particular numerous transgressions and regressions associated with ocean eustatic processes, there is a mosaic lateral distribution of lithological facies of different stratigraphic units. Sediments of the Cretaceous system in Volyn-Podillia with a clear stratigraphic inconsistency transgressively lie on the blurred surface of geological formations of different age -- Neoproterozoic, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Jurassic.

The surface of pre-Cretaceous formations is inclined from east to west and gradually deepened, having a sharp bend on the border with the Pre-Carpathian Depression, which causes an increase in thickness of Cretaceous deposits in this direction: from several tens of centimetres within Volyn- Podillia to 1000-1400 m within the Lviv Depression and further to the west.

The study of the palaeogeographic situation during the Barremian-Early Albian shows that clay- carbonate sediments have formed in shallow bays of the palaeoshelf within Volyn-Podillia and in the adjacent part of the modern Pre-Carpathian Depression as a result of water runoff from land, which supplied terrigenous material to the branched isolated basin on the northern mainland outskirts of the Tethys. The almost complete absence of Berriasian-Aptian deposits on the south-western slope of the East European platform, including Volyn-Podillia, is due to global regression associated with a significant amplitude of falling ocean levels.

Analysis of earlier biostratigraphic studies and previous publications

Eichwald (1830) published the first paper containing specific data on the Cretaceous deposits of the Middle Dnister region, in particular the description of outcrops with Upper Cretaceous rocks. Kner (1848, 1852) studied fossils in this area, including Cretaceous molluscs from the Seret River basin. The age of fossils is not clearly defined, although Ammonites varians Sow. described by the author indicates the Cenomanian stage of fossil-bearing rocks.

Zar^czny (1874) analysed faunal remains from the Seret and Stryp rivers in more detail. In the geological part describing the scheme of the Cretaceous system, the author attributed sandy marls and sandstones to the Cenomanian and distinguished four horizons of different age. Dunikowski (1888) also studied the Cenomanian fauna, although he considered the horizons proposed by Zar^czny as facies of the same age. Radkevich (1891, 1897, 1898) allocated the northern and southern parts of this area. South of the Dnister-Southern Bug watershed, there are widespread Cenomanian deposits with faunal remains of all biozones, including Actinocamax plenus. Large species lists were presented by this researcher along with comparing the Cenomanian lithology and fauna of Podillia with those of Western Europe.

In the first half of the 20th century, Cretaceous deposits of the Middle Dnister region were studied by Vyrzhykivsky (1927, 1931, 1932), and the results were presented in a number of publications. Kokoszynska (1920, 1928, 1931, 1939) provided fauna lists and a description of numerous Cenomanian outcrops. Based on the study of rocks in this area, she identified five facies some of which are important stratigraphic horizons (sandstones, calcareous sandstones with sea urchins, green sands, marls, and white limestones), three lower of which the author refers to the Lower Cenomanian, and the two upper -- to the Middle and Upper Cenomanian, respectively. The section of Cretaceous rocks near Soroky (Moldova) was studied by Vascautanu (1923), who collected fossils from each layer and described the Cenomanian part of the outcrop. O.V. Savchynska studied the fauna of the Middle Dnister region from 1939 and concluded that there is `... a fairly strong confirmation of the presence of Albian deposits'

Despite the many studies, several issues of the stratigraphy of Cretaceous deposits of the Middle Dnister region remained unknown or required clarification. The most important of them were the following: identification of the full thickness of the Upper Cretaceous in general and of its individual stages, the study of the lithological nature of sedimentation, and facial changes within each stage. Complete lists of fauna have not yet been compiled making it difficult to compare and correlate with already studied areas. Earlier outcrops were studied only along the Dnister valley and its tributaries, but the wide application of drilling works allowed passing full section wells of Upper Cretaceous rocks, to study Cretaceous formations in continuous sections, to clarify the lateral distribution of sediments, and to study the microfauna.

In the late 1940s, research covered the Southern Bug basin. It was found that the Upper Cretaceous section begins with the lower Cenomanian formation; visible traces of the break between the Cenomanian and Turonian stages are not observed. Cenomanian deposits are absent in the raised areas of Palaeozoic rocks. In general, Cenomanian sediments are represented by various rocks: coarsegrained glauconite sandstones, marls, spongioliths, sandy limestones, and others. Pasternak (1957, 1959, 1962a, 1962b, 1966) studied Cretaceous formations of the Middle Dnister region, in particular the section from Volodymyr-Volynskyi to the Dnister River (Pasternak 1956a), the distribution of Albian and Cenomanian deposits and biostratigraphy of the Upper Cretaceous of the Volyn-Podillia Plate (Pasternak 1956b, 1957, 1966; Pasternak & Gavrylyshyn 1956, 1964). Pectenids are widespread in Upper Cretaceous deposits of the Middle Dnister region. Their ecology and taxonomy was considered and studied by Sobetsky (1961).

The lithological specificity of the Upper Cretaceous rocks drew the attention of researchers to the issues of lithogenesis (Senkovsky 1962, 1963a, 1963b, 1977; Sergeev 1964).

Mineralogical and petrographic characteristics of the Albian and Cenomanian stages were provided along with the discussion of genesis of sillicites. The issues of biostratigraphy of Cenomanian deposits of the Middle Dnister region are considered in detail by Kyselevych et al. (1987, 1988), Yakushyn (2006), Leshchukh et al. (2012), Ivanik et al. (2013), and others. Based on a list of fauna collected (Pasternak et al. 1987; Maryash & Kurepa 2013; Maryash 2015; Kyselevych & Ogienko 2018; Maryash 2019), the conditions of formation of these deposits were clarified (Kyselevych 1991, 1992, 1999; Danyliv 2017, 2019). Zonal biostratigraphic dismemberment of three substages of Cenomanian deposits in the Middle Dnister region was carried out, and they were correlated with formations of the same age of Western Europe and Central Asia.

Results and Discussion

Cretaceous deposits of Volyn-Podillia are part of the terrigenous-carbonate subformation of the Jurassic-Cretaceous carbonate formation ("-&) and the glauconite-Cretaceous formation ї©ЃAЋџ»з- K2), which includes gaizeous ї©…»з€кЃ–»з), siliceous-chalk (ЎЈґА€кЃ–‰Љ) and marl-gaizeous (^sn-^rn) subformations (Chebanenko et al. 1990). Cretaceous deposits of the Middle Dnister region (Fig. 1) are represented by the lower (Albian) and upper (Cenomanian) parts.

Cretaceous system K Lower section K Albian stage K_tal Middle Albian substage Kpl]

Stratigrap hy. The sandy facies of coastal zone of the middle Albian sea has been preserved in small areas of the south of Ternopil Oblast and is mainly distributed in depressions of the pre-Cretaceous relief. Lithologically, it is represented by clayey sands and sandstones with admixtures of glauconite, gravel, black flint and quartz, phosphorites, and pebbles of Silurian argillites in contact with Silurian rocks. Undoubted middle Albian fauna was found only near Melnytsia-Podilska in outcrops on the banks of the Dnister River (Pasternak et al. 1968).

On the blurred surface of Silurian rocks (near Khudykivtsi) it forms a thin layer of conglomerate (0.1-0.2 m), the saturation of which with washed and phosphatized faunal remains in some places reaches more than 50% of the cementing rock. The following taxa were identified in the conglomerate Here and further--fossils were identified by L. Kyselevych.: Nuculapectinata Sow.,Leda bergi Arkh., L. baueriNoetl., Area dupiniana (Orb.), Barbatia marul- lensis Park., Cucullaea glabra Park., C. mailleana (Orb.), Grammatodon carinatus (Sow.), Glycymeris sublaevis (Sow.), Limopsis mulleri Holzapf., Pteria sp., Entolium orbiculare (Sow.), Chlamys cf. his- pida (Goldf.), Lima rhotomagensis Orb., L. sp., Plicatula gurgitis Pict. et Roux, Lopha carinata (Lam.), Amphidonte conicum (Sow.), A. lateralis (Nilss.), Linotrigonia cf. spinosa (Park.), Cardita tenuicostata (Sow.), Cyprina ligeriensis Orb., C. lineocostata (Sow.), Lucina downesi Woods, Thetironia laevigata (Sow.), Cyprimeria faba (Sow.), Cardium proboscideum (Sow.), Dosinopsis caperata (Sow.), Panope gurgitis (Bron.), Pleurotomaria ewaldi Tissen, Littorina lubrica Woll., Turrilites sp., Confusiscata cf. dupiniana (Orb.), Gyrodes gaultina (Orb.), Natica ervina Orb., N. sp., Ringinella inflata (Sow.), Avellana cf. incrassata (Sow.), Fustiaria strehlensis (Gein.), Nautilus sp., Puzosia mayoriana (Orb.), Hoplites dentatus (Orb.), H. latesulcatus Spath, H. bailey Spath, and Anahoplites planus (Mant.). In addition, there are phosphated sponges, shark teeth, sea urchin needles and tree fragments. The given faunal assemblage, in particular hoplites (species-index Hoplites dentatus) evidenced the middle Albian age of the conglomerate layer. It should be noted that some researchers (Sobetsky 1978; Rozumeiko 1988; Leshchukh 1992; Leshchukh & Maryash 2009) doubt the presence of middle Albian deposits within the Middle Dnister region and suppose re-deposition of the faunal content in younger formations (Maryash 2007; Bakayeva 2010). According to I. Maryash (pers. comm.), remains of the middle Albian index species H. dentatus were most likely re-deposited.

Fig. 1. Study region with collection points of paleontological material. 1 -- Bilche-Zolote; 2 -- Mykhalkiv; 3 -- Khudykivtsi; 4 -- Melnytsia-Podilska; 5 -- Hrynchuk; 6 -- Malynivtsi; 7 -- Demshyn; 8 -- Bakota; 9 -- Velyka Kuzheleva; 10 -- Stara Ushytsia; 11 -- Tsykove; 12 -- Nova Ushytsia; 13 -- Kucha; 14 -- Struga; 15 -- Sloboda Shcherbovetska; 16 -- Balabanivka; 17 -- Zhytnyky; 18 -- Murovani Kurylivtsi; 19 -- Khonkivtsi; 20 -- Yaryshiv; 21 -- Sloboda-Yaryshivska; 22 -- Mohyliv-Podilskyi; 23 -- Ataky; 24 -- Otach; 25 -- Oklanda; 26 -- Mykhailivka; 27 -- Oksanivka; 28 -- Dzyhiv Brid; 29 -- Porohy; 30 -- Soroky.

In the current stratigraphic scheme for the Lower Cretaceous of Volyn-Podillia, the phosphorite layer from Khudykivtsi is referred to the upper part of the upper Albian substage, upper part of the Mortoniceras inflatum zone -- the Stoliczkaia dispar zone (Ivanik et al. 2013).

Palaeoecology. The coastal zone of the middle Albian sea received a sufficient amount of organic detritus, and the bottom waters were quite rich in oxygen and food, which were necessary for the existence of a number of benthic organisms. The systematic composition of faunal remains is represented by 40 species (Pasternak et al. 1968). Taxonomic composition and species richness indicates the highest distribution of bivalve molluscs (92.0% of the processed specimens), of which 56.0% are Taxodonta. The portions of other groups are as follows: gastropods -- 5.5%, cephalopods -- 1.1%, sponges €к 0.8%, sea urchins and fishes €к 0.6%. Cucullaea glabra Park. and Glycymeris sublaevis (Sow.) predominate by the number of individuals. Among the ecological groups, there are mobile benthos (92.3%, of which 13% are free-floating organisms (mainly ammonites and less often bel- emnites), and sedentary benthos (7.6%) represented by sponges, some species of Ostrea, Lopha, and Amphidonte. In addition, there were lithophagous organisms, the quantification of which is difficult, but common drilling traces in Silurian argillites indicate their widespread distribution and abundance. A number of bivalve shells have holes drilled by zoophagous gastropods (Natica).

The nature of the burial and the state of preservation of organic remains indicate that they were washed, re-deposited and represent an orictocoenosis. Almost all of the fossils are phosphatised, rolled and partially broken. Molluscs have remained in the form of nuclei. Significant clusters of fauna are often found, which are cemented with phosphate substance, and together with phosphorite pebble and phosphated wood remains form a phosphorite layer.

Based on ecological characteristics of certain groups of the fauna, in particular molluscs, as well as the lithological composition of rocks, it is possible to conclude on the physical and geographical conditions of this part of the Albian sea: the middle Albian fauna developed under favourable conditions -- sufficient light, good bottom water aeration, favourable gas regime, normal salinity, high water temperature, etc. The normal water salinity is indicated by the large number of stenohaline species represented by numerous Glycymeris, Limopsis, etc., which do not tolerate any deviations from normal salinity. The large number of thermophilous forms (e.g. Exogyra, Ostrea, Glycymeris, and Chlamys) indicates that water temperature was not lower than +17...+20°C. High water temperatures are also confirmed by oxygen isotope analysis in calcite rosters of belemnites. The presence of molluscs capable to drill bottom rocks indicates a slow sediment accumulation at the initial stages of development of the Albian sea basin, or a significant hydrodynamic activity of waters and the presence of strong bottom currents that removed the newly formed sediments.

Upper Albian substage K_tal₃

Stratigraphy. Upper Albian deposits are lithologically diverse, well characterized by fauna and widespread in the Middle Dnister region, where they are exposed (Pasternak et al. 1968). Separate layers with faunal remains are allocated in their structure (from bottom to top):

quartzose-glauconitic sands, containing gravels, sometimes conglomerates, and in eastern Podillia -- re-deposited phosphorite Neoproterozoic nodules in the lower part. The fauna is poor and represented mainly by Amphidonte conicum (Sow.), A. lateralis (Nills.), Lopha cf. carinata (Lam.), Plicatula gurgitis Pict. and Roux, etc. Neohibolites cf. minimus (Miller) was found near Mikhalkiv, and phosphatized nuclei of Aucellina gryphaeoides (Sow.), A. krasnopolskii Pavl., and A. stuckenbergi Pavl. in Mohyliv-Podilskyi. The basal sands of the upper Albian form separate lenses (up to 2 m thick) on the surface of the Neoproterozoic or Lower Palaeozoic deposits. Presumably, this horizon includes glauconite-quartz sandstone of Yavoriv district;

bryozoan-echinoderm, organogenic-detrital limestones composed mainly of fragments of bryo- zoans, sea urchins, and molluscs with an admixture of quartz and glauconite grains. Molluscs suitable for identification are very rare. Among them are Amphidonte conicum (Sow.), A. lateralis (Nills.), Lopha sp., Entolium orbiculare (Sow.), and Chlamyspuzosiana Woods. Colonial and solitary corals are relatively frequent. The rocks are quite varied, contain terrigenous material (sand grains) and often turn into calcareous sandstones, in places with oblique stratification (Bilche-Zolote village). In the eastern regions, they contain chalcedony pseudoconcretions and flint (Ustya and Kolodribka), as well as sand layers (Mykhalkiv). In Pylypche village, limestones are represented by coarse- and mediumgrained, often re-crystallized deposits with fragments of bryozoans and impurities of glauconite and fragmentary quartz grains.

These limestones (`sea urchin limestones,' according to Zarїмczny 1874) form a wide 8-10 m thick lens in Podillia. They are common near the mouth of the Seret River, but also known in Bilche-Zolote, Horodenka, and Horodnytsia. Their total thickness reaches 28 m in Pidluby;

gaizes and opal spongioliths, often containing chalcedony contractions, and in some places flints (Hrynchuk, Malynivtsi, and Bakota). The fauna is not phosphatised and is represented mainly by Amphidonte conicum (Sow.). Less common are Entolium orbiculare (Sow.), E. cf. balticum (Dam.), Chlamys hispida (Goldf.), C. cf. puzosiana (Math.), Lima cf. gaulnina Woods, Dosinopsis cf. subrotun- data (Sow.), D. cf. parva (Sow.), and Linotrigonia spinosa (Park.). The latter is quite often observed in the lower opal sillicites (Malynivtsi, Darabany, and Melnytsia-Podilska). In addition, single specimens of Parahibolites tourtiae were found in the outcrops of Melnytsia-Podilska and Khudykivtsi (Weigner 1910). Gaizes and opal spongioliths (0-18 m) are distributed mainly in the Middle Dnister region. Senkovsky (1962) also reported these rocks from near Zaboloty. Late Albian sillicites were found near Kamyanka-Buzka.

Based on previous observations, it can be stated that Albian deposits are distributed almost exclusively on the western and south-western edges of the Volyn-Podillia Plate and in adjacent depressions. In the part of Volyn-Podillia with the highest uplifts of the Palaeozoic surface, no marine Albian deposits were found and some signs indicate the presence of Lower Cretaceous continental formations that occur in the form of small lenses.

Upper section K2 Cenomanian stage Ks

Stratigraphy. The Late Cretaceous epoch was generally marked by the development of large- scale transgression and an increase in the depth of marine epicontinental basins. It is evidenced by the wide lateral distribution and facial features of Cenomanian formations in the composition of mainly shallow terrigenous sediments (early Cenomanian). At the early-middle Cenomanian boundary, regression took place, which manifested in breaks of sedimentation and in the appearance of phosphorite facies. The accumulation of carbonate sediments began in the second half of the Cenomanian age. The Carpathian Basin with a moderately deep-water zone and a deep shelf developed along the periphery of the south-western edge of the East European platform. Carbonate-clayey, silt, silty-siltstone deposits with sands formed there. The presence of inoceram remains indicates good water aeration and normal salinity.

At that time, there was no large landmass near the Volyn-Podillia Sea. In the east, the surface of the Ukrainian Shield, levelled by prolonged denudation, rose above the water in the form of large islands. In the southwest, the Volyn-Podillia Sea bordered the Carpathian Sea, separated from the Carpathian folded region by a shaft. In the north, there were several small islands. As a result, little terrigenous material entered the water basin and sedimentation occurred mainly due to erosion and processing of the weathering crust by the water mass.

Cenomanian deposits were formed under conditions of active hydrodynamic regime of the shallow epicontinental sea, which developed and caused significant vertical and horizontal lithological- facial variability of its sediments under the influence of rather intense bottom currents.

Two sedimentation areas are allocated in the Cenomanian sea basin (Sobetsky 1961): north-western shallow zone with terrigenous sediments (sublittoral) and south-eastern, relatively deep-water zone with carbonate-clayey and carbonate sediments. The boundary between these lithofacial zones is indistinct and the lithological change of sediments occurs as a result of sequential-pulsating (transgressive-regressive) `wedging' and wedge-shaped layering of marls with sands (Vorobiev et al. 1971). This was reflected in the gradual increase in the clay content of marls towards the Ukrainian Shield until their transition into carbonate clay, and then, as a result of increasing sand and glauconite content, into dense quartz-glauconitic sands.

In the north-western part of the Middle Dnister region, west of the Kalyus-Zhvan watershed, Cenomanian sediments lie directly on the blurred surface of Silurian deposits and are represented by coarse-grained sandstones and clayey shales. Dark green glauconitic sand with basal conglomerates lies in the base of the Cenomanian section. There are wood fragments (Struga) and re-deposited phosphorite nodules (Rudkivtsi) in basal conglomerates. The sand is fine-grained and dense with remains of sponges and bryozoans. Small clumps of grey flints are evenly scattered throughout the section. The thickness of the basal formations is 0.3-3.0 m.

Upward in the section, there are sandy gaizes interbedded with opal-glauconite-quartz sands and opal-chalcedony spongioliths. Opals comprise rare Entolium orbiculare Sow., E. balticum (Dam.), Chlamys hispida (Goldf.), and Parahibolites tourtiae (Weign.). In some places (Malynivtsi, Darabany, and Stara Ushytsia), there is a limestone layer (0.5-1.0 m), in which Amphidonte conicum (Sow.), Trigonia pavlovi Strem., and Lima sp. were found. The thickness of sandstone is about 10 m. A. conicum (Sow.), Venericardia tenuicosta Sow., Cucullaea aff. mailleana (Orb.), Parallelodon cartero- ni (Orb.), and Chlamys cf. hispida (Goldf.) were identified from deposits of the same age exposed near Demshyn. Further upward, there are sands (Kalius river basin: Nova Ushytsia, etc.) and marls (Verbivka river basin: Balabanivka).

There are uniform fine-grained, greenish-grey glauconitic-quartz sands (0.2-1.0 m) on the watershed between Kalius and Studenytsia. This sandy layer is enriched with numerous phosphatised remains of molluscs, detritus, and shark teeth. Sands are often interbedded with gaizes, formed due to secondary separation of carbonate rocks (Senkovsky 1973). Fossilization of remains is due to groundwater, which had reached this level (Vorobiev et al. 1971).

The lower border of glauconitic-quartz sands is clear. At the very contact with the underlying formations, there is a layer (0.1-0.15 m) of viscous olive-green clay with a small admixture of sand. The roof of sands is wavy and apparently reflects the relief of the seabed. The upper part of the sand section (0.5 m) is enriched with fragile iron contractions of semi-circular shape. In this part, along with faunal remains, a chain of shallow lenses of greyish-cream marls is observed. From above, in a layer of greenish-grey glauconitic-quartz sands, finger-like flints enter to a depth of 0.5 m. The thickness of glauconitic-quartz sands is 15-20 m.

The most complete set of the fossil fauna was collected in greenish-grey glauconitic-quartz sands near Nova Ushytsia: Cyprimeria faba (Sow.), Cucullaea mailleana (Orb.), C. subglabra (Orb.), Venericardia tenuicosta Sow., Avellana cassis Orb., Trigonia aliformis Park., Plicatula inflata Sow., Pl. gurgitis Pict. et Roux, Myoconcha cretacea Orb., Natica lyrata Sow., Trigonarca orbigniana (Math.), Chlamys cf. hispida (Goldf.), Ch. (Merklinia) aspera (Lam.), Ch. cf. fissicosta (Eth.), Аmphidonte conicum (Sow.), Grammatodon carinatus Sow., Terebratula striatula Reuss, Cretirhynchia subhercynica (Tsn.), Rhynchonella grasiana d'Orb., Nairiella cf. tenuicosta Plamad., Nodosiella cf. nodosa (Roem.), Neithea sp., Donax sp., Pleurotomaria sp., numerous fragments of belemnites, bryozoans, corals, vertebrae and teeth of Platypterygius? sp. (Kyselevych & Ogienko 2018), and shark teeth. A scale of the ganoid fish Scheenstia (Actinopterygii, Holostei) was also found there (Kyselevych & Kovalchuk 2019). Phosphatization has led to good preservation of fossils and their structural details.

The best preserved in this section are cephalopods represented by Cymatoceras deslongchamp-sianum (Orb.), Turrilites costatus Lam., Hypoturrilites aff. tuberculatus tuberculatus (d'Orb.)Ј¬Puzosia mayoriana Orb., P planulata (Sow.) var. odiensis Kossm., Arrhaphoceras variabile Renz, Acanthoceras cf. rhotomagense (Defr.), Sharpeiceras aff. schluteri Hyatt., Mantelliceras mantelli (Sow.), Schloenbachia varians Sow., S. varians subvarians Spath, S. varians subtuberculata (Sharpe), S. varians ventriosa Stiel., S. coupei quadrata Spath, Ammonites sp., and Turrilites acutus Passy. In addition to these species, Gryphaeostrea canaliculata (Sow.), Trajanella aff. muniari Popov-Hatzeg, Chlamys robinaldina (Orb.), Entolium noetlingi Sob., E. orbiculare (Sow.), Neithea quiquecostata (Sow.), Hypoturrilites man- telli (Sharpe), S. aff. coupei trituberculata Spath, and Spondylus sp. were identified in Balabanivka. Parallelodon carteroni (Orb.) and Lima podolica Sob. were found in Sloboda Shcherbovetska, Drilluta curta Peel. near Kucha, while Neithea cometa (Orb.) and Lima rhotomagensis Orb. were identified in materials from Velyka Kuzheleva.

The closest to the faunal assemblage of Nova Ushytsia is that from Lysyachy Yar (Tsykove), which, in addition to the previously listed species, includes Opis bicornis (Gein.), Gryphaeostrea canaliculata (Sow.), Capillithyris ex gr. capillata (Arch.), Mariella aff. essenensis (Gein.), and Turrilites aff. acutus Passy. To the west of the Zhvan River, the section of Cenomanian sediments ends with white finegrained trifles and marls with chalcedony flints.

In Balabanivka, flint lies in a sandy marl with a thickness of 5 m. The marl is very sandy in the lower part (1.5 m), up to the formation of dense carbonate sands. The number of flints increases upwards. In the lower part of the section, flint layer lies in greenish, viscous, carbonate, sandy clays. The thickness of flints increases westward and varies from 5 to 10 m.

To the southeast of the Zhvan River, the section of Cenomanian sediments changed -- there is a sand-carbonate stratum on basal conglomerates, which corresponds in age to spongioliths and glauconitic-quartz sands (Kraeva & Lypnyk 1958; Senkovsky 1963b). Some changes occur in the thickness of basal formations -- they are represented in Mohyliv-Podilskyi by glauconitic-sandy limestones with Amphidonte conicum (Sow.), Entolium orbiculare (Sow.), Neithea sexcostata Woodw., Plicatula gurgitis Pict. et Roux, and Neohibolites cf. ultimus (Orb.).

A 42 m thick layer of greyish-white dense sandy chalk-like marls with numerous black flints lies on basal formations (glauconitic sands with pebbles of Palaeozoic sandstones and mica clay shales) in Murovani Kurylivtsi. These marls yield the following fossils: Entolium orbiculare (Sow.), E. noetlingi Sob., Chlamys fissicosta (Eth.), Ch. cf. elongata Lam., Ch. (Aequipecten) aspera (Lam.), Neithea quin- quecostata (Sow.), Plicatula inflata Sow., Venericardia tenuicosta (Sow.), Trigonarca aff. orbignyana (Math.), Amphidonte conicum (Sow.), Cyprimeria faba (Sow.), Parallelodon carteroni (Orb.), Avellana cassis Orb., Pleurotomaria cf. panderi Gofm., Trochus duodecimcostatus Gofm., Neohibolites ultimus (d'Orb.), Rotularia damesii Noetl., Aucellina sp., and bone fragments. Cephalopods with outer shell (Nautilus laevigatus d'Orb., Puzosia aff. chivensis Arkh.(?), Schloenbachia varians varians Sow., S. vari- ans subvarians Spath, S. varians subtuberculata (Sharpe), S. coupei costata (Sharpe), and S. coupei quadrata Spath.) are also widely represented in this section.

The species list of Cenomanian cephalopods from a new section near Murovani Kurylivtsi was recently supplemented with Schloenbachia sharpei Semenov, S. ventriosa Stieler, Phylloceras sp., Forbesiceras sp., Hyphoplites cf. costosus Wright et Wright, Mantelliceras mantelli (Sow.), M. tuberculatum (Mantell), M. cantianum Spath, Acompsoceras cf. inconstans (Schluter), Puzosia mayoriana d'Orb., Puzosia sp., Austiniceras cf. austeni (Sharpe), Mariella sp., Turrilites scheuchzerianus Bosc, Stomohamites simplex (d'Orb.), Sciponoceras baculoides Mantell, Pseudocenoceras fittoni (Sharpe), Eutrephoceras sublaevigatum (d'Orb.), Praeactinocamax plenus Blainville, and Praeactinocamax sp. (Maryash & Kozlovsky 2019). Among them, Mantelliceras mantelli is an index species of the lower part of the lower Cenomanian (Ivanik et al. 2013), while Praeactinocamax plenus represents the Upper Cenomanian zone within the entire subtier for Volyn-Podillia (Maryash & Kozlovsky 2019).

In Yaryshiv, 20-25 m thick greyish-white, dense, homogeneous marls with iron inclusions and a gradually increasing number of flints lie on basal conglomerates. The marls are significantly clayey in the lower part of the section, being sandier in the middle part. The entire layer contains rare fragments of sponges and small pectenid shells.

Numerous fossil faunal remains were found 1-2 cm of the marl roof. This part of the section contains rare grains and small black flint pebbles. The fauna is numerous and diverse: Chlamys (Aequipecten) aspera (Lam.), Ch. robinaldina Orb., Ch. fissicosta (Eth.), Ch. aff. elongata Lam., Entolium orbiculare (Sow.), E. noetlingi Sob., Neithea quinquecostata (Sow.), Venericardia tenuicosta (Sow.), Cyprimeria faba (Sow.), Trigonarca orbignyana (Math.), Plicatulagurgitis Pict. et Roux, P inflata Sow., Parallelodon carteroni (Orb.), Cucullaea cf. subglabra (Orb.), Myoconcha cretacea Orb., Amphidonte conicum (Sow.), Gryphaeostrea canaliculata (Sow.), Ostrea aff. vesicularis Reuss, Exogyra lateralis Nills., Trigonia pav- lovi Strem., T. cf. aliformis Park., Terebratula striatula Reuss, Terebratulina podolica Zar., Avellana cassis Orb., Cyathophyllum articulatum Wahl., Scyphya fenestrate Goldf., Ventriculites coewicornis d'Orb., Rhynchonella grasiana d'Orb., Inoceramus crippsi Mant., Ceprina ligeriensis d'Orb., Spondylus striatus (Sow.), S. aff. dutempleanus d'Orb., Parsimonia ex gr. antiquate (Sow.), Serpula aff. ampul- lacea Sow., Pleurotomaria sp., Dentalium sp., Cymatoceras deslongchampsianum (Orb.), Mantelliceras mantelli (Sow.), Puzosiaplanulata (Sow.), Forbesiceras largilliertianum (Orb.), Turrilites costatus Lam., Schloenbachia varians subvarians Spath, S. varians subtuberculata (Sharpe), S. varians ventriosa Stiel., S. coupei quadrata Spath, S. coupei trituberculata Spath, and Sharpeiceras sp. In addition, Natica lyrata Sow., Arcuatothyris arcuata (Roem.), and Lima podolica Sob. were found in Khonkivtsi.

Chlamys (Aequipecten) aspera (Lam.), Trigoniapavlovi Strem., Cyprimeriafaba (Sow.), Venericardia tenuicosta (Sow.), Schloenbachia varians subvarians Spath, and Ostrea sp. were identified along with shark teeth from 17 m thick limestones of Mohyliv-Podilskyi.

Light gray marls with glauconite are exposed on the right bank of the Dnister River near Otach (Republic of Moldova). Pebbles of Palaeozoic rocks are found in the lower part of the section (0.25 m). Fossils found in this layer represent Inoceramus crippsi Mant., Lima gaultina Woods, Entolium orbiculare (Sow.), E. noetlingi Sob., Isocardia ex gr. karabakhensis Bobkova, Chlamys elongata Lam., Chlamys (Merklinia) aspera (Lam.), Spondylus striatus (Sow.), Plicatula gurgitis Pict. et Roux, Ostrea sp., and Schloenbachia aff. coupei quadrata.

Glauconite content is sharply decreased 5 m upwards. Marls of this part of the section comprise Entolium orbiculare (Sow.), Plicatula inflata (Sow.), Inoceramus crippsi Mant., Neithea quinquecostata (Sow.), N. cometa (Orb.), N. sexcostata (Woodw.), Chlamys robinaldina (Orb.), and Lima gaultina Woods. In 3 m above, the marl is enriched with numerous inoceram fragments indicating a significant mobility of waters within the sedimentation basin. Inoceramus crippsi Mant., I. orbicularis Noetl., Neithea quinquecostata (Sow.), Plicatula inflata Sow., Entolium orbiculare (Sow.), Gryphaeostrea canaliculata (Sow.), Chlamys cf. fissicosta (Eth.), Terebratula cf. striatula Reuss, and Rhynchonella sp. were collected there. The upper part of marls (15 m from the base) with numerous flint concretions contains Entolium noetlingi Sob., E. orbiculare (Sow.), Plicatula inflata Sow., Lima podolica Sob., Neithea quinquecostata (Sow.), Chlamys (Aequipecten) aspera (Lam.), and Inoceramus crippsi Mant. The Cenomanian section in Mohyliv-Podilskyi area ends with inoceram (5 m) and siliceous (6 m) limestones and trepels (5 m) with flint. Their age is confirmed by findings of the Cenomanian fauna. The presence of Turrilites cf. scheuchzerianus Bosc., Schloenbachia varians Sow., S. subvarians Spath, S. cf. scharpei (Sem.), S. cf. ventriosa Stiel., Turrilites costatus Lam., and Schloenbachia sp. in the assemblage allows to refer these deposits to the lower part of the Middle Cenomanian.

In the southern part of the Middle Dnister region, Cenomanian deposits are observed in the outcrops of Okland-Soroky, where they lie on the blurred surface of Riphean and Palaeozoic rocks, and are represented by pebbles and fragments of underlying rocks (0.4-0.5 m), dense quartz-glauconitic, clayey, fine-grained sands (1.5 m), and clayey marls (1.0 m). Greyish sandy marl (visible thickness 3.5 m) in Kobzhanka ravine near Soroky comprises Inoceramus crippsi Mant., I. orbicularis Noetl.,

Entolium orbiculare (Sow.), E. noetlingi Sob., Gryphaeostrea canaliculata (Sow.), Chlamys puzosia- na (Math.), Ch. robinaldina Orb., Ch. fissicosta (Eth.), Lima podolica Sob., Plicatula inflata (Sow.), Neithea quinquecostata (Sow.), and Cyclothyris cf. schloenbachi (Dav.). This marl upwards gradually turns into a very dense, chalk-like marl with a thickness of 2 m with small-sized Entolium noetlingi Sob., E. orbiculare (Sow.), Chlamys fissicosta (Eth.), Ch. robinaldina Orb., Ch. puzosiana (Math.), Neithea quinquecostata (Sow.), Plicatula gurgitis Pict. et Roux, Lima podolica Sob., and Inoceramus sp. This marl is covered by 4 m thick dense, fine-grained, essentially clayey marl containing Inoceramus crippsi Mant., I. orbicularis Munst., Entolium noetlingi Sob., E. orbiculare, Chlamys fissicosta (Eth.), Ch. robinaldina Orb., Neithea quinquecostata (Sow.), Plicatula gurgitis Pict. et Roux, Lima podolica Sob., Gryphaeostrea canaliculata (Sow.), Ostrea sp., and Mantelliceras mantelli.

There is a 5 m thick greyish, fine-grained, sandstone-like marl lying upward. The following fossils were collected there: Entolium orbiculare (Sow.), E. noetlingi Sob., Gryphaeostrea canaliculata (Sow.), Limagaultina Woods, L. podolica Sob., Neithea quinquecostata (Sow.), N. sexcostata (Woodw.), N. cGmeta (Orb.), Chlamys aff. fissicosta (Eth.), and Ch. robinaldina.

This layer is covered by a 10 m thick dense oolithic marls with nest-like clusters of fossil fauna represented by Entolium orbiculare (Sow.), E. noetlingi Sob., Gryphaeostrea sp., Neithea quinquecosta- ta (Sow.), and Chlamys robinaldina Orb. In the upper part of the section, there are Gryphaeostrea canaliculata (Sow.), Amphidonte conicum (Sow.), Parsimonia antiquata (Sow.), Plicatula inflata (Sow.), Chlamys aff. robinaldina Orb., Entolium orbiculare (Sow.), and E. noetlingi Sob. The sandy marl gradually turns into an olive-green clay-carbonate rock with traces of bioturbations and containing Gryphaeostrea canaliculata (Sow.), Entolium orbiculare (Sow.), Neithea quinquecostata (Sow.), and Plicatula inflata (Sow.). The Cenomanian section ends with 5 m thick dense, slightly silicified white marls with rare brown-grey flints the number of which increases upward. Two specimens of Inoceramus sp. were found in this layer.

Further north (between Soroky and Kobzhanka ravine, Moldova), there is a Cenomanian section, which is similar to the previous one. The following taxa were found in its lower part: Entolium orbiculare (Sow.), E. noetlingi Sob., Lima gaultina Woods, Plicatula inflata (Sow.), Inoceramus sp., Ostrea sp., and sp. Somewhat higher, there are Plicatula inflata (Sow.), Inoceramus sp.,

Ostrea sp., small fragments of belemnites and poorly preserved brachiopods. Chlamys robinaldina Orb., Ch. (Aequipecten) aspera (Lam.), Entolium orbiculare (Sow.), E. noetlingi Sob., Amphidonte conicum (Sow.), Gryphaeostrea canaliculata (Sow.), Plicatula inflata (Sow.), Parsimonia ex gr. antiquata (Sow.), Neohibolites ultimus (d'Orb.) were collected in the upper part of the section. Similar faunal remains were identified north of Soroky, in Dzyhiv Brid, Porohy, Oksanivka, and Mykhailivka. In addition to the above species, Cucullaea mailleana (Orb.), Venericardia tenuicosta (Sow.), Trigonarca orbignyana (Math.), Avellana cassis Orb., Cyprimeria faba (Sow.), Schloenbachia varians subvarians Spath, fragments of sponges, characteristic of the northern, shallower part of the Middle Dnister region, were found in Okland (Moldova). South of Soroky, Cenomanian sediments are represented by ash-grey fine-grained marls with a thickness of 20-25 cm (corresponding to fine-grained marls with marcasite in Kobzhanka ravine), containing Neohibolites ultimus (d'Orb.), Plicatula gurgitis Pict. et Roux, P inflata (Sow.), and Inoceramus crippsi Mant.

Age and biostratigraphy of the Cenomanian of the Middle Dnister region Lower Cenomanian ‹yјТ

Lower Cenomanian deposits are widespread almost everywhere in the Middle Dnister region, and numerous outcrops are known from the Ternava River in the west to the Markovka River in the east, which led to the most complex paleontological characteristics of this region.

Lithology. In the Middle Dnister region, there is a lithological change of facies: from shallow glauconitic-quartz sands of the littoral zone of open shallow shelf in the northwest to deep carbonate- clayey formations of the middle and upper sublittoral in the southeast.

Molluscs. Cephalopods with external shells are widespread in lower Cenomanian deposits of the Middle Dnister region, especially in its north-western part -- on the Ushytsia-Liadova watershed. Mass gatherings of this fossil fauna were made in vicinities of Nova Ushytsia, Tsykove, Velyka Kuzheleva, Verbivtsi, Struga, Kucha, Balabanivka, Zhytnyky, Murovani Kurylivtsi, Khonkivtsi, and Yaryshiv. In the south-eastern direction, there is a sharp reduction in species and quantity of cepha- lopods, and isolated findings are known in Mohyliv-Podilskyi and in the Republic of Moldova -- in Ataky, Okland, and Soroky. The following taxa are the most common among the ammonoids (Kyselevych 1991): Schloenbachia varians varians (Sow.), S. varians subvarians Spath, S. varians subplana (Mant.), S. varians subtuberculata (Sharpe), S. varians ventriosa Stiel., S. coupei quadrata Spath (Nova Ushytsia), S. aff. coupei trituberculata Spath (Balabanivka), S. varians varians (Sow.), S. varians subvarians Spath, S. varians subtuberculata (Sharpe), S. varians quadrata Spath (Murovani Kurylivtsi), S. varians subvarians Spath, S. varians subtuberculata (Sharpe), S. varians ventriosa Stiel., S. coupei quadrata Spath, and S. coupei trituberculata Spath (Yarishiv). In the south-eastern part of the Middle Dnister region, there are isolated Schloenbachia varians subvarians Spath in Mohyliv- Podilskyi, S. aff. coupei quadrata Spath in Ataky, and S. varians subvarians Spath in Okland.

In the north-western part of the Middle Dnister region, Schloenbachia is confined to a thick layer of glauconitic-quartz sands with a large number of phosphated mollusc remains. Phosphatization of remains led to their good preservation in the fossil state with details of the external sculpture and internal structure. Near Nova Ushytsia, Schloenbachia was found together with Mantelliceras mantelli (Sow.) -- an index species of the upper zone of the lower Cenomanian -- and with Turrilites costatus Lam., which is characteristic for the middle Cenomanian. Balan (1973) suggested that representatives of Schloenbachia, due to the presence of transitional forms and the high rate of prochoresis, were probably ecological subspecies. Atabekyan (1985) believed that in the south of the former USSR they are characteristic only for the upper zone of the lower Cenomanian. However, Marcinowski (1983) provided data about lower Cenomanian sections, which shows that the nominative and other subspecies of Schloenbachia varians (Sow.) were common in the lower and middle Cenomanian, and the first representatives of S. coupei (Brongn.) appeared only during the Middle Cenomanian.

Mantelliceras mantelli (Sow.), an index species of Lower Cenomanian (Kyselevych et al. 1987; Kyselevych 1992; Ivanik et al. 2013), is widespread in the Middle Dnister region. Its findings are known in the sandstones of Nova Ushytsia and Yaryshiv (our data), in the marls of the Soroky district (Kobzhanka ravine, Republic of Moldova), as well as in Bernadivka, Butsniv (Maryash 2016) and Murovani Kurylivtsi (Maryash & Kozlovsky 2019). The allocation of Mantelliceras mantelli zone in the Lower Cenomanian deposits of the Middle Dnister region is also tentatively confirmed by findings of Hypoturrilites aff. tuberculatus tuberculatus (d'Orb.) in Nova Ushytsia, H. mantelli (Sharpe) in Balabanivka (both these species have the same stratigraphic distribution according to Monnet & Bucher 2002) and Mariella aff. essenensis (Gein.) (Tsykove). According to Atabekyan (1985), all three these species are characteristic for the Cenomanian of England and France, as well as for the middle and upper parts of Mantelliceras mantelli zone of the North Caucasus, Mangyshlak, Tuarkir, and Kopet-Dag. In addition, the lower Cenomanian of the Middle Dnister region is characterized by the presence of poorly preserved Sharpeiceras aff. schluteri Hyatt., S. sp., and Forbesiceras largilliertianum (Orb.). Arrhaphoceras variabile Reuz, known from the upper Albian deposits of Turkmenistan, was found, apparently, in a re-deposited state near Nova Ushytsia (Kyselevych et al. 1987).

The oldest ammonites known in the Late Cretaceous seas of the eastern Central European province (Balan, 1973) represented the genus Puzosia Bayle, 1878. In the early Cenomanian sea of the Middle Dnister region, there were P planulata (Sow.) (Yarishiv), P. mayoriana d'Orb. (also recorded from the middle Cenomanian of Volyn-Podillya; Maryash & Kurepa 2014), P planulata (Sow.) var. odiensis Kossm. (Nova Ushytsia), P aff. chivensis Arkh. (Murovani Kurylivtsi). In addition to their distribution in Turkmenistan, species of the genus are known in the sediments of the lower Cenomanian Anglo-Paris and Polish-German basins, North Africa, Madagascar and Japan. Next to them, Nautilus laevigatus d'Orb. and Cymatoceras deslongschampsianum d'Orb. of the same age were found in the Middle Dnister region.

Most fossil molluscs are confined to the phosphatized faunal layer in the north-western part of the Middle Dnister region. In this area, many groups have varying degrees of importance, but, in general, it is possible to note certain patterns. The most common among bivalves are Cyprimeria faba (Sow.), Cucullaea mailleana (Orb.), C. subglabra (Orb.), Venericardia tenuicosta Sow., Trigonia aliformis Park., Plicatula inflata Sow., P gurgitis Pict. et Roux, Myoconcha cretacea Orb., Grammatodon carina- tus Sow., Parallelodon carteroni (Orb.), Trigonia aliformis Park., Amphidonte conicum (Sow.), A. cana- liculata (Sow.), and Lima sp., while Avellana cassis Orb., Natica lyrata Sow., Pleurotomaria sp., and Trochus sp. predominate among gastropods. There are rare Nodosiella cf. nodosa (Roem.), Nairiella cf. tenuicostata Plamad., Trajanella aff. muniari Popov.-Hatzeg, known in western Europe, India, and Japan. Among brachiopods, the most common member of assemblages is Terebratula striatula Reuss.

Bivalves and gastropods are represented by phosphatised nuclei, often with preserved carbonate shells with their outer sculpture, less often with phosphatised nuclei. Forms that are partially or completely buried in the living state in the bottom substrate (Cyprymeria and others) are represented in the fossil state by whole nuclei with remains of shells. They did not acquire any lifelong orientation, except Amphidonte conicum (Sow.) which formed oyster banks near Stara Ushytsia. Much less common in the northwest are Chlamys (Aequipecten) aspera (Lam.), Ch. cf. hispida (Goldf.), Entolium cf. noetlingi Sob., and Neithea sp.

A decline in species composition of bivalves is observed in the south-eastern direction. In the Yaryshiv area, pectenids are quite common €к Chlamys (Aequipecten) aspera (Lam.), Ch. fissicosta (Eth.), Ch. robinaldina Orb., Ch. elongata Lam., Entolium orbiculare (Sow.), E. noetlingi Sob., and Neithea quiquecostata (Sow.). Large Pectinacea shells indicate favourable living conditions. Of the pectenids, the most common are large Syncyclonema noetlingi Sob. and smaller S. orbiculare. Further to the southeast, there are only Entolium orbiculare (Sow.), E. noetlingi Sob., Chlamys fissicosta (Eth.), Ch. robinaldina Orb., Chlamys elongata Lam., Ch. puzosiana (Orb.), Neithea quiquecostata (Sow.), N. sexcostata (Woodw), N. cometa (Orb.), Lima gaultina Woods, L. podolica Sob., Plicatula inflata (Sow.), P gurgitis Pict. et Roux, Inoceramus crippsi Mant., I. pictus Sow., I. orbicularis Munst., and Ostrea sp.