ISSN 0869-5938, Stratigraphy and Geological Correlation, 2019, Vol. 27, No. 3, pp. 339–360. © Pleiades Publishing, Ltd., 2019. Russian Text © The Author(s), 2019, published in Stratigrafiya, Geologicheskaya Korrelyatsiya, 2019, Vol. 27, No. 3, pp. 70–92.

Lectostratotype of the Maikopian Group in the Belaya River Section Upstream of the Town of Maikop (Western Ciscaucasia) in the Oligocene Part S. V. Popova, *, I. P. Tabachnikovab, A. F. Bannikova, E. K. Sytchevskayaa, T. N. Pinchukc, M. A. Akhmet’ev d, N. I. Zaporozhetsd, A. van der Boone, W. Krijgsmane, A. S. Stolyarovf, †, and J. Krhovskyg aBorissiak Paleontological Institute, Russian Academy of Sciences, Moscow, 117647 Russia bAll-Russia Geological Institute (VSEGEI), St. Petersburg, 199106 Russia cKuban State University, Krasnodar, 350040 Russia dGeological Institute, Russian Academy of Sciences, Moscow, 119017 Russia ePaleomagnetic Laboratory of Utrecht University, Utrecht, 3584 CD The Netherlands fFedorovsky All-Russian Scientific Research Institute of Mineral Resources (VIMS), Moscow, 119017 Russia gMinistry of the Environment of the Czech Republic, 100 Prague 10, Czech Republic *e-mail: [email protected] Received February 4, 2017; revised May 7, 2018; accepted April 12, 2018

Abstract—The section of Maikop deposits on the Belaya River upstream of the town of Maikop is character- istic of Western and Central Ciscaucasia; it is well exposed and well-studied and can be considered as the type section of the Maikop Group. The section shows a continuous transition from the underlying white marl of the Belaya Glina Formation to dark clay lying at the base of the Maikop Group. The lower Oligocene part of the section exposes an almost uninterrupted outcrop of the Pshekha Formation and shows unconformities at the base and top of the Polbian Bed. These are overlain by the lower non-carbonate and upper carbonate sub- formations of the Morozkina Balka Formation and the Batalpashinsk and undivided Upper Oligocene Septarian + Zelenchuk formations. This paper contains a detailed lithological description of the section with a summary of its fossils. The composition of the studied microphytoplankton and animal remains, including nannoplankton, planktonic and benthic foraminifers, mollusks, and ichthyofauna is described and paleo- magnetic study results are presented. The study of palynology and dinocysts from the same series of samples was previously completed. The history of the study of the Maikop Group and its subdivision into formations are discussed. This paper discusses the possibility of using the data for correlation and reconstruction of the depositional environment.

Keywords: Upper Paleogene, nannoplankton, dinocysts, foraminifers, mollusks, ichthyofauna, paleomagne- tism, stratigraphy, depositional settings DOI: 10.1134/S0869593819030043

INTRODUCTION 1960). The ichthyofauna was studied by Danilchenko (1960) and others. The term “Maikop Formation” began to be applied We studied the Maikop part of this section in the at the end of the 19th century by a group of geologists 1980s and then in 1994–1996, while working on Proj- who worked under the leadership of K.I. Bogdanovich ects MPGK nos. 174 and 326, when, along with the and was first published by Prokopov (1910, quoted in traditional fossil groups (foraminifers, mollusks, ich- Prokopov, 1937b, p. 32). The Maikop mollusks were thyofauna), the phytoplankton was studied for the first described by Korobkov (1937, 1939), Liverovskaya time, and a guidebook for an international excursion (1938), and Volkova (1962), whereas a microfaunistic was compiled (Akhmetiev et al., 1995). For the Belaya substantiation for the stratigraphy of the Maikop For- River Section, nannoplankton data were obtained by mation was provided by Bogdanovich (1960), Ter- Krhovsky et al. (1995) and others, while Akhmetiev Grigoryants (1961), and many others (see Grossheim, et al. (1995) and Zaporozhets (1999) studied dinocysts and spore-pollen assemblages, and E.K Sytchevskaya † Deceased. (in Akhmetiev et al., 1995; Popov et al., 2009; etc.)

339 340 POPOV et al. reviewed the ichthyofauna; fishes were described by Polba, and Morozkina Balka. The early authors did Prokofiev (2005, 2006; 2013) and were also collected not include the Khadum Horizon in the Maikop and studied by Bannikov (see Bannikov, 2010; Ban- Group, and it was considered as a transitional series nikov and Parin, 1997; etc.). In 2014–2018, the sec- from the carbonate “foraminiferal beds” to non-car- tion was studied by Russian geologists in collaboration bonate clay of the Maikop Group (Prokopov, 1937a, with an international group, which included special- p. 17); later, the Khadum Horizon was included in the ists from Utrecht University (Netherlands), who con- Maikop Group (Grossheim, 1960). Korotkov (1940, ducted paleomagnetic and cyclostratigraphic studies, unpublished) described the main sections and bore- and also colleagues from the Montanuniversität Leo- holes from the Kuban River to the Pshekha River and ben (Austria), who obtained and prepared for publica- in the middle Maikop recognized the Abadzekhskaya tion geochemical and isotopic data (Sachsenhofer and Voskovogorskaya formations. However, the man- et al., 2017). To ensure a correct stratigraphic and uscript remained unpublished, and short descriptions event interpretation of these data and biotic control of of these formations were later published by Grossheim the conclusions, we continue a comprehensive pale- and Gladkova (1953). ontological and lithological study of the section aim- Two competing stratigraphic schemes are used for ing to obtain a considerably more detailed biotic and the Maikop Group in modern publications on the sedimentological characterization of the recognized section of the Belaya River. Geologists conducting formations, to allow more precise definitions of their the geological mapping of the western Caucasus of boundaries and thickness, and to interpret deposi- 1 : 50000 scale in the 1950–1980s and 1995–2008 tional settings. At present dinocysts and spore-pollen used stratigraphic nomenclature close to Korotkov’s assemblages are most comprehensively studied scheme (Beluzhenko, 2010; Beluzhenko and Kova- (Zaporozhets and Akhmetiev, 2017) from samples col- lenko, 2006), considerably differing from Prokopov’s lected in 2014. Nannoplankton and foraminifers are scheme of Central Ciscaucasia (Fig. 2). The reason studied from the series of samples collected for paleo- for the proposal of various schemes was an inability magnetic study in 2015 and 2016. Both groups of sam- to directly trace the stratigraphic units of Central ples are reliably correlated (Fig. 1). Nannoplankton Ciscaucasia because of the presence of the delta was studied by I.P. Tabachnikova. In addition, data facies in the section of the Laba River above the obtained by J. Krhovsky as a result of studies of 1995, Batalpashinsk level. which were previously cited only in the excursion guidebook (Akhmetiev et al., 1995) and in summaries At the same time, geologists and lithologists of the of reports (Krhovsky et al., 1995; etc.), were used. For- Koltsov Expedition who were particularly involved in aminifers were studied by T.N. Pinchuk. studying potentially productive facies in the Maikop sediments showed that such tracking is quite possible if data from boreholes nearer the trough axis are used. FORMATIONS OF THE MAIKOP SECTION Therefore, they used Prokopov’s scheme, with a The formation stratigraphy of the Maikop Group refined Khadum part as proposed by Korotkov, and of Ciscaucasia was proposed by Prokopov (1937a, extended its subdivisions along the whole of Western 1937b) and Korotkov (1935). Prokopov subdivided the and Central Ciscaucasia (Semenov and Stolyarov, Maikop series from bottom to top into the Khadum, 1970; Stolyarov and Ivleva, 2004). We also use these Batalpashinsk, Septarian, Zelenchuk, Karadzhalga, more widely traceable formations for the upper part of Olginskaya, and “Ritsa” horizons on the basis of sec- the Maikop Group. tions of the Central Ciscaucasia, primarily on the sec- A.S. Stolyarov, an expert on the Maikop deposits of tion on the Kuban River near the town of Cherkessk. Ciscaucasia, Mangyshlak, and Kopetdag, compiled in Originally, the “Ritsa” Horizon was spelled “Rit- 1985 a full lithological description of the section on sevsky Horizon” by Prokopov and later by Grossheim the Belaya River. Stolyarov’s correlation of the upper (1960), and later major reviews and reference books part of the Maikop Group (Semenov and Stolyarov, began citing it as the “Ritsa Formation” (Neogeno- 1970; Stolyarov and Ivleva, 2004) used the tracing of vaya…, 1986; Paleogenovaya…, 1975; Stratigrafich- “fish facies” associated with anoxia: the Batalpashinsk eskii…, 1982), probably mainly from Ritsev (Ritsa) Formation in the Upper Oligocene and the Kara- Mountain in the southern vicinity of Nevinnomyssk. dzhalga Formation in the Lower Miocene, separated Korotkov (1935), while conducting research in the by a bed with sandy interlayers and septarian concre- Khadyzhensk and Neftegorsk districts, subdivided the tions. In this work, as well as in the guidebook of the Khadum Horizon into three subhorizons: Pshekha, excursion along the Belaya River (Akhmetiev et al.,

Fig. 1. Location of samples collected from the Oligocene formations in the valley of the Belaya River near the village of Abadze- khskaya (from a satellite image) and a lithological log showing the position of samples. Numbers of the beds (1–16) are on the left of the column; structure of the sediment is on the right.

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 341

Belaya River 230 Laba River Stavropol 45 Krasnodar N 225 3-N1 Samples

2015–2016 Maikop 220 BA292 Formations 288 Samples 2014 215 Scheme er Riv Cherkessk BA286 shown below 210 282 44 280

Greater CaucasusKuban 205 14 278 276 Sochi 272 BLACK 200 270 SEA 0 50 100 km 195 BA268 139 138 266 137 262 135 39 40 41 42 43 E 190 133 260 131 254 101–104 185 256 Boon al., 2017) et der (Van data Paleomagnetic Karadzhalga 13 250 246 180 96–100

175 BA244 1–18 242 170 240 12 239 130 BA363–368 BA369– 93–95 Fyuntv River 129 Batalpashinsk 165 235 372 229 128 127 BA328–362 Zelenchuk 160 227 126 + 221 125 BA316–327 155 BA223 124 Septarian BA294–315

150 BE383 123 386 122 5 m 121 145 11 389 115 BA288–293 BE392 117 140 BA282–287 Batalpashinsk Molochka BA270–281 135 BA220 Creek BA257–269 215 256 Abadzekhskaya BA246–255 210 130 BA244, 245 63 Village 205 BA223–243 114 61 62 125 BA200 113 BE382 112 Upper 375 111 Morozkina 110 BE383–393 120 369 109 Subformation 365 108 329–333 BA201–220 115 10 358 106 BE358–382 BE297–313 110 343–357 BE333 097 334–342 327 096 292–296

326 Subformation Morozkina Upper 105 314 105 287–291 Lower Morozkina Subformation 357 103 286 Polbian 351 102 BE277–285 100 347 101 BE259–276 343 Bed 342 BE231–258 Pshekha 95 339 100 216–230 BE337 099 209–215 193–208 90 334 BE192 Belaya Glina 0 150 300 m 85 313 095 9 094 80 309 093 304 092 300 299 090

75 tions 295 Forma- 70 BE296 082 Legend: 292 081 16

290 Samples 2016 Samples 2014

291 Subformation Lower Morozkina 65 289 079 157 Carbonate clay 8 286 076 Polbian Bed 285 156 283 072 Non-carbonate clay 60 7 278 070 5 m 068 280 275 066 BA Clay with fish remains 55 271 064 275 372 154 266 062 370 50 060 368 153 Clay with sand interbeds 261 270 366 BE260 365 152 Calcareous and septarian 45 363 151 265 355 concretions 6 BE257 058 33.2 ± 0.34 Ma 348 40 252 055 Bioturbations 054 260 342 35 248 053 15 338 and macrofaunal remains 243 052 255 332 Tuffite interbeds 30 239 050 328 234 048 250 231 046 Zelenchuk + Septarian Gaps 044 Pshekha 326 25 227 320 143 042 245 316 142 9 m 223 040 20 5 028 314 Structure 219 026 024 240 308 215 021 302 141 of sediment: Polarity: 15 4.5 019 298 140 4 m 210 235 208 017 294 Bedding Normal 10 016 3 7 m 203 230 Reversed 200 014 Biotur- 5 198 011 2 4 m 008 bated Uncertain 0 1 193 004 BE190 001 Belaya Glina Formation

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 342 POPOV et al.

1995), we accept this division of the section, using Stolyarov’s field book notes for a lithological descrip- tion and stratigraphy. Comparison of these two main Lithology m Beds Series competing schemes (Fig. 2) shows that, in the lower et al., 2014 et Scale, m Scale, Formations, Thickness, subformations Formations, in this paper

subformations part, they are almost identical, differing only in the after Beluzhenko, after 2010; Beluzhenko 2010; rank of units. The outcrop is excellently exposed and the boundaries of the Pshekha, Polba, and Morozkina 230 Balka formations are readily recognizable. 220 17 At the same time, we consider it important to sepa- rate the lower subsystem of the latter from the upper

210 Karadzhalga Voskovogorskaya

Lower Miocene Lower one, since the boundary between them corresponds to 300 Alkunian the transition from the brackish water Solenovian basin Horizon to a normal marine basin (Popov et al., 1993; Sachsen- 290 16 25 Alkun hofer et al., 2017; Zaporozhets and Akhmetiev, 2017). 280 The boundary at the base of the Batalpashinsk For- 270 mation in these two schemes is not unequivocally 260 interpreted. This part of the section contains a thin bed 250 40 (Bed 11, about 5 m thick cropping out near the suspen- sion bridge in the village of Abadzekhskaya), contain- 240 15 ing small carbonate nodules. The bed is assigned by 230 Septarian + Zelenchuk Septarian Beluzhenko et al. (2014) to the Batalpashinsk Forma- 220 tion on the grounds that the nodules are included in non-calcareous clay. 210 14 40 Now, with low water, the beds are well exposed, 200 showing that the host clay beds are calcareous, and 190 Batalpashinsk therefore we assign them to the uppermost part of the 13 0.7 180 upper member of the Morozkina Balka Formation. It was not possible to observe the boundary with the 170 12 36 Batalpashinsk non-carbonate Batalpashinsk Formation, but it is cer- 160 tain that it is in a very thin (about 5 m) covered interval 150 (Fig. 1). The greatest differences in the allocation of 11 5 formations and the position of their boundaries begin 140 with the top of the Batalpashinsk Formation as we cur- 130 rently interpret it. 120 Our opponents do not recognize the Septarian and 10 35 Zelenchuk formations on the Belaya River (Pismen- 110

Subformation naya et al., 2009; Beluzhenko, 2010; Beluzhenko et al.,

100 Morozkina Upper 2014), considering the level of the appearance of the 90 septarian nodules and sands in the sections to be non-

Subformation isochronous, and they assign the non-carbonate part 80 9 36 Morozkina Balka Morozkina

Lower of the sequence with nodules and sand beds to the top

70 Morozkina Subformation of the Batalpashinsk Formation. 8 0.5 Polb. Polb. 60 7 5 Prokopov, in the original description of the 50 Khadum “Septarian Horizon” (Prokopov, 1937b, pp. 34–35), 6 32 emphasized the tentative nature of the boundary 40 between the Septarian and Zelenchuk formations: 30 “examining the section from bottom to top and find- 5 9 ing septarian concretions, we can expect the appear- 20 Pshekha Lower OligoceneLower 4 4.5 Oligocene Upper ance of sandstone higher up, and vice-versa ….” Infre- 10 3 7 quent septarian concretions occur on the Belaya River 0 1–2 4 Pshekha Subformation along a considerable distance (40 m thickness near the road bridge in the northern vicinity of the village of Belaya Glina Abadzekhskaya), immediately above the Batalpash- Eocene insk Formation, as in the sections of Central Ciscau- casia. The main beds of fine-grained sand, as in the Fig. 2. Correlation of the subdivision of the Oligocene part of the Belaya River section (Beluzhenko, 2010, Beluzhenko Kuban section, appear on the Belaya River above the et al., 2014) and accepted in this paper. Polb.—Polbian Bed. level with septarian nodules. However, the lowermost

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 343 level of the appearance of sandy interbeds is indeed Kovalenko (2006; Beluzhenko, 2010, p. 42) that not consistent: thin sand beds already appear in the septarian concretions and possibly sands are fre- upper part of the Batalpashinsk Formation; higher up, quently present below and above the Alkunian level. In they alternate with clay with nodules. It is this gradual fact, on the Belaya River, there is a probable erosional increase in arenaceous content that Stolyarov consid- horizon above the upper level of concretions: the ered regionally consistent and considered it to be of dinocyst assemblage is here characterized by a pro- stratigraphic importance, emphasizing that the con- nounced redeposition with the presence of redepos- tent of the arenaceous material here remains very low, ited Paleogene and Cretaceous taxa, according to from a few tenths of one percent to a few percent Zaporozhets and Akhmetiev (2017). (Stolyarov and Ivleva, 2004, p. 268). Therefore we The Upper Maikop deposits are more uniform and consider it important to separate this regionally well- difficult to subdivide stratigraphically, so they will be defined level from the Batalpashinsk level and accept dealt with in a separate paper when the results of biotic it as an undivided Septarian + Zelenchuk Formation, and paleomagnetic studies become available. beginning from the level of the first Septarian concre- tions, approximately coinciding with the appearance of noticeable sandy interbeds (Figs. 1, 2). SECTION DESCRIPTION In his main study on the stratigraphy of the Maikop The outcrop of the Maikop part of the section Group, Prokopov (1937b, p. 35) noted the similarity begins south of the village of Abadzekhskaya, 1.5 km of the section on the Kuban River to the section on the below the highway and railway bridges, along the left Assa River: both sections contain the level of the first bank of the Belaya River (Fig. 1), and directly con- appearance of fine sands, underlined by a horizon tinues from the Eocene section (Cherkessk, Keres- with septarian nodules, in turn underlined by a “hori- tinsk, Kuma, and Belaya Glina formations; Popov zon of platy marl—arenaceous or dolomitic (Alkunian et al., 2018). Horizon).” Stolyarov considered the Alkun beds For the first time for this formation, remains of traceable only in eastern Ciscaucasia (Stolyarov and benthic fauna appear in the marl clays near the top of Ivleva, 2004, p. 267). The westward wedging out of the the Belaya Glina Formation (top 0.5 m). These are Alkun Formation was also shown by Kovalenko et al. the bivalves Propeamussium fallax and Nucula sp., (1977, unpublished, text-figs. 2, 3). remains of echinoids, imprints of bryozoans, and small bioturbations. The beds contain evidence of In the section of the Belaya River, the Alkun level massive redeposition of phytoplankton, indicating is traditionally recognized on the weakly carbonate regression and erosion. clay with nodules at the top of the septarian-sandy series (i.e., Septarian-Zelenchuk Formation in our Dinocysts show a high species diversity, dominated interpretation), exposed in the lower reaches of the by marine to open ocean chorate forms, including Fyuntv River (Figs. 1, 2) (Beluzhenko and Kovalenko, Impagidinium spiniferites, while Charlesdowniea clath- 2006; Beluzhenko et al., 2014; Dmitrieva et al., 1959; rata angulosa, a zonal index species characteristic of etc.). This carbonate level with foraminifers, nanno- the Priabonian, continues. plankton of the NP25–NN1 Zone, and a characteris- tic dinocyst assemblage, containing the first Miocene Pshekha Formation taxa, is currently traced in the sections of the Kuban River near the village of Karamurzinsky and in North (1) Clay greenish gray, overlying a distinct bound- Ossetia (Beluzhenko, 2010; Filippova et al., 2010, ary, thinly bedded because of alternation of gray cal- 2015). Our opponents refer to this level as to the Alkun careous clay with brownish fossils and barren greenish Formation and assign its lower, larger, non-carbonate non-calcareous clay. The bed contains infrequent fish portion with septarian concretions and sandy inter- remains: “Sardinella” rata, Thunnus sp. Thickness beds to the Batalpashinsk Formation (Fig. 2). We 0.4–0.5 m. agree with the importance of tracing this stratigraphic (2) Clay dark gray, weakly calcareous, micro- and level as a regional subdivision—marker beds with a dis- thin-bedded, with shells of planktonic pteropods of tinct faunal assemblage—and propose, following the genera Vaginella and Limacina (identified by Dmitrieva et al. (1959), to assign it to the Alkunian I.A. Gontsharova) on the bedding planes, with Regional Stage, which has a significant stratigraphic numerous fish remains, including boreal taxa. The importance according to the Stratigraphic Code assemblage is dominated by the Clupeidae “Sardi- (Stratigraficheskii kodeks, 2006, Article IV.4). In the nella” rata, Perciformes Anenchelum angustum and paper by Dmitrieva et al. (1959, p. 98, Fig. 3) the Palimphyes chadumicus, and Gadiformes Palaeogadus Alkunian Regional Stage, rather than the formation, is (five species) and Eophycis pshekhiensis; less common shown in a separate column at the level of the upper are isolated skeleton imprints and teeth of lamnoid part of the Batalpashinsk and Septarian formations. sharks (according to P.G. Danilchenko, E.K. Sytche- We are also prepared to agree with Beluzhenko and vskaya, V.F. Fedotov, and A.F. Bannikov). The leaf

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 344 POPOV et al.

Samples Lithology tions with nannoplankton Species of nannoplaknton Zones Beds Forma- 300 1–18 295 NP25–NN1 290 157 NP25 285 156 280 275 270 15 265 260 C. abisectus 255 250

245 rothii Pontosphaera Septarian + Zelenchuk Septarian 240 enormis Pontosphaera 235 euphratis Helicosphaera 230 carinatus Triquetrorhabdulus 225 220 sp.sp. 215 210 205 14 200 195 190 Cyclicargolithus floridanus Cyclicargolithus Transversopontis pulcher Transversopontis H. recta Reticulofenestra 185 13 BA256 NP25 180 175 Batalpashinsk 170 12 165 160 155 150 145 11 . sp.

140 Zigrhablithus bijugatus Dictyococcites bisectus bisectus Dictyococcites R BA220 135 BA214 130 BA208 NP24 125 BA200 120 BE371

10 ornata Reticulofenestra 115 BE358 Transversopontis pygmaeus Transversopontis 110 BE325 BE320 105 BE316 NP24

Upper Morozkina Subformation Morozkina Upper 100 95

90 sp. 85 80 9 75

Subformation 70 Lower Morozkina Lower Reticulofenestra lockeri Reticulofenestra multipora Pontosphaera 65 Trochoaster latus Tr. rectipons Tr. fibula Tr. pax Tr. Polb. 8 BE286 NP23 60 I. recurvus 7 R. umbilica 55 BE271 BE266 50 BE261 45 BE260 6 40 BE257 BE252 subdistichus Clausicoccus BE248 35 BE243 30 BE239 NP22

Pshekha 25 20 5 BE217

15 4 BE214 formosus Cyclococcolithus 10 BE208 3 BE202 5 BE200 2 BE198 NP21 1 BE193 m 0 BE190

Fig. 3. Stratigraphic distribution of nannoplankton species in the Belaya River Section and zonations of Oligocene–Lower Mio- cene deposits. Polb.—Polbian Bed.

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 345 flora is represented by Cryptomeria sp., Taxodium The upper part of Bed 6 and Beds 7–9 are exposed dubium, Castanopsis sp., Cinnamomophyllum sp., and in the next bend of the river, in the cliff of the left Myrica sp. (identification by M.A. Akhmetiev). The bank opposite the village of Abadzekhskaya (Fig. 1, bed contains nannoplankton of the NP20–21 Zone Sample ВЕ259–291): and small foraminifers Globigerina officinalis and (7) Clay dark, non-carbonate, in places and in G. bulloides. The dinocyst assemblage of the Phtano- lenses silty and micaceous, on the surface indistinctly peridinium amoenum Zone (D13) includes Deflandrea bedded, strongly jarositized, with rare fish remains. The phosphoritica, Homotryblium floripes, and Areospaerid- appearance of Batiacasphaera baculata and В. sphaerica ium pectiniforme. Thickness 3.5 m. in the dinocyst assemblage suggests the beginning of a (3) Similar dark gray clay with limacids, but in places decrease in salinity. The top (upper 0.5 m) contains bioturbated, containing diverse benthic fossils: bivalves clay with interbeds of sand and bioturbation traces. Pterolucina batalpaschinica (Korob.), Yoldiella chad- Thickness 5 m. umica (Korob.), Thyasira nysti (Phil.); gastropods Aporrhais speciosa Sch.; scaphopods Dentalium (Anta- lis) acutum parvum (Gonch.) (identified by I.A. Gont- Polbian Bed sharova); and tubes of the tube worm Spirorbis, i.e., a (8) Marl light gray, with lenticular and cross-bed- typical assemblage for the basal Oligocene. The ich- ding, inconsistent in thickness (0.1–0.5 m), with ferru- thyofauna is similar to that of the underlying bed. The ginous bed at the base, with lenses of sandy, glauconite, nannoplankton assemblage is also similar to that of the bony, and tuff material. The bed contains infrequent underlying bed, but does not contain Discoaster mollusks of a brackish-water endemic association of saipanensis or D. barbadiensis, whereas Sphenolithus Janschinella, Lenticorbula, and Cardiidae, character- pseudoradians is very uncommon (NP21 Zone). istic of the Solenovian Regional Stage, and ostracodes Thickness 7 m. of the Disopontocipris oligocaenica (Zal.) association. (4) Alternation of gray laminated calcareous clay The nannoplankton association belongs to the NP23 with Limacina and darker, less carbonate clay. Ben- Zone: Reticulofenestra ornata, Transversopontis fibula, thos is absent. The basal part of the bed contains nan- T. latus, and T. pax. The dinocysts belonging to the noplankton of the NP21 Zone, while in the overlying Wetzeliella gochtii Zone include Batiacasphaera part Clausicoccus subdistichus, C. fenestratus, and sphaerica, thin-walled Hystrichokolpoma and Glaphy- Cyclococcolithus formosus disappear, and the assem- rocysta, and acritarchs (Horologinella), indicating a blage belongs to the NP22 Zone, according to significant freshening of the basin. Toward the top, J. Krhovsky (Akhmetiev et al., 1995). The fish associ- marls become greenish marly clay with bioturbation ation is similar to that of the underlying beds. The pal- traces and lenses of quartz-glauconite sand. Thickness ynoassemblage is diverse, dominated by Taxodiaceae 0.2–0.6 m. over Pinaceae, and contains Rhus, Carpinus, Carya, Fagaceae, Corylopsis, Myricaceae, and Aralia. The dinocysts indicate the Phtanoperidinium amoenum Morozkina Balka Formation, D13 Zone (Zaporozhets, 1999). Thickness 4.5 m. Lower Morozkina Subformation (5) Clay dark gray and gray, thin-bedded, in places (9) Bed of dark gray, thin-bedded, non-carbonate calcareous, without Limacina. Nannoplankton clay, with fish detritus and scales, jarosite on the weath- belongs to the NP22 Zone. The ichthyofauna contains ered surfaces, overlying a distinct boundary. Dinocyst both coastal (Aeoliscus heinrichi) and numerous deep- species indicating brackish-water basin (thin-walled water taxa with photophores: Eovinciguerria obscura, Hystrichokolpoma, Batiacasphaera sphaerica) continue Scopeloides glarisianus, and Archaeolicus strictus (Aeo- to occur. However, in the middle part of the member, liscus assemblage with thermophilic tropical and sub- taxa of the brackish-water basins almost disappear, tropical taxa, such as Bregmaceros, Aeoliscus, and Fis- while the assemblage is dominated by cysts of open tularia (Sytchevskaya in Akhmetiev et al., 1995; Ban- marine species: Lejeunecysta spp., Wetzeliella gochtii nikov, 2010)). The deep-water assemblage indicates (index species of a regional zone), Selenopemphix depths to 1000 m. Thickness 9 m. nephroides, and Operculodinium. This suggests the (6) Clay dark gray, thin-bedded, along bedding influx of marine water in the basin, which was previ- planes calcareous owing to the carbonate inclusions ously suggested by Е.K. Sytchevskaya (Popov et al., (zooplankton coprolites with nannoplankton). The 2009, p. 69). The ichthyofauna includes sharks of the fish association is similar to that of Bed 5. Nanno- family Charcharinidae, bony fishes of the families plankton belongs to the NP22 Zone, and Wetzeliella Clupeidae, Osmeridae, Gadidae, Repropcidae, Pria- gochtii appears in the dinocyst assemblage, which is canthidae, Caproidae, Scombridae gen. indet., and characteristic of the second half of the Early Oligo- coastal Syngnathidae (Prokofiev, 2013; Sytchevskaya cene. The middle part contains several thin layers of and Prokofiev, 2013). The types of cysts that appear tuffites. Thickness 31–32 m. above indicate a reinstatement of the desalination

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 346 POPOV et al. regime. At the top, the clay becomes bioturbated in and Zygrhablithus bijugatus suggests that this assem- places. Thickness 35–37 m. blage belongs to the NP25Zone. Thickness 0.7–0.8 m. The upper part of Bed 9 and Bed 10 crop out in the (14) Clay gray and dark gray, non-carbonate, thin- high slope of the right bank above the suspension bedded and with fine cross-hatching, with fish bridge in the village of Abadzekhskaya (Fig. 1): remains. The middle part of the bed shows the appear- ance of thin interbeds of tuffite, fine-grained quartz micaceous sand, calcareous sandstone, and carbonate Morozkina Balka Section, material (described by Stolyarov in the channel of Upper Morozkina Subformation Molochka Creek). Thickness about 40 m. (10) Rhythmic alternation of gray and dark gray The cliff of the right and then left bank in the carbonate clay, in places with non-carbonate clay in northern vicinity of the village of Abadzekhskaya also the lower part and with carbonate material (coprolites shows clay of Bed 14 (Samples ВА270–293), replaced of zooplankton above). The nannoplankton belongs to (over a gap of 15 m) by Series 15 with nodules (Sam- the NP24 Zone (Nagymarosy and Voronina, 1993; ples ВА294–262): data from Tabachnikova, this paper). The bed con- tains a dinocyst assemblage with Wetzeliella gochtii and Chiropteridium partispinatum, characteristic of the Septarian + Zelenchuk Formation transition from the Lower to Upper Oligocene. The (15) Similar non-carbonate dark gray non-calcare- ichthyofauna contains marine pelagic Clupeidae, ous clay frequently with interlayers of brownish organ- Palaeorhynchidae, Gempylidae, and Scombridae. ics, with fish remains (in “fish facies”) shows the The middle part has several thin profiles of tuffite. appearance of horizons with small calcareous and Thickness 30–35 m. septarian concretions (up to 0.7 × 0.3 over 4–5 m), The left and right bank downstream of the suspension with septa composed of well-crystallized calcite (as in bridge shows an outcrop of Bed 11 (Samples BE383– the section on the Kuban River). The succession at the 393, 61–63). level of nodules sometimes contains interbeds of calcar- eous clay (up to 0.15 m). There are several interbeds of (11) Clay thin-bedded, carbonate, silty, with rare fine-grained glauconite-quartz (0.1–0.3, to 0.5 m) and carbonate nodules (up to 0.35 cm in diameter). The a sandy dike of the same sand. Thickness about 40 m. fish association is similar to that of the preceding bed. The dinocysts are taxonomically diverse and The same series continues to be exposed above and represent inhabitants of an open sea shelf. The below the road bridge in the northern vicinity of the appearance of Rhombodinium draco suggests that the village of Abadzekhskaya up to the Fyuntv River assemblage belongs to the Upper Oligocene. The (Samples ВА363–372, 93–95). bedding is almost horizontal or upturned. Visible The carbonate interbeds in the middle part of the thickness around 5 m. series contains nannoplankton: Cyclicargolithius flori- danus, large Helicosphaera euphratis, Pontosphaera Bed 12 crops out in a high slope of the left bank, enormis, P. rothii, Cyclicargolithus abisectus, Dictyococ- 1 km downstream of the suspension bridge (Fig. 1, cites bisectus (NP25 Zone, data from J. Krhovsky); there Samples ВА223–245): is a dinocyst assemblage with Chiropteridium partispina- tum and Deflandrea spinulosa (epibole) in the upper part Batalpashinsk Formation of the Chiropteridium partispinatum Zone. In the pal- ynoassemblage, Taxodiaceae are more abundant than (12) Clay dark gray, silty, non-carbonate, microl- Pinus, while angiosperms constitute approximately 25% aminated, with rare fish remains. The dinocyst assem- and include subtropical taxa: Engelhardtia, Castanopsis, blage belongs to the Chiropteridium partispinatum and Quercus ex gr. graciliformis. Zone. The palynoassemblage is dominated by the gymnosperms Pinus and Picea, indicating a cooling On the Fyuntv River, the upper part of the series episode. Thickness 35–37 m. contains nannoplankton: Coccolithus pelagicus, rare Pontosphaera enormis, Cyclicargolithus floridanus, one The mouth of Molochka Creek has an outcrop of specimen of Triquetrorhabdulus carinatus?, frequent the upper part of Bed 12 and Bed 13; upstream in the Cyclicargolithus abisectus (NP25–NN1 Zone, accord- river channel and on the right slope, clay of Bed 14 is ing to J. Krhovsky). The ichthyofauna is represented exposed (Fig. 1): by a relatively poor thermophilic association with Aeo- (13) Clay thin-bedded, light, carbonate, silty, liscus sp., Capros longispinatus, Repropca sp., and down and up the section gradually becoming dark “Sardinella” sp., whereas the dinocyst assemblage non-carbonate clay, with white mottles on the bed- includes Labirintodinium truncatum, Cleistrosphaerid- ding planes. The latter contains abundant nanno- ium thalassiphora, Paleocystodinium golzowense, Bitec- plankton dominated by Cyclicargolithus abisectus and todinium sp., and Selenopemphix nephroides. The paly- C. floridanus. The absence of Dictyococcites bisectus noassemblage is characterized by the Angiosper-

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 347 mae/Gymnospermae ratio = 3.5, by the greater 217), carbonate interbeds contain a nannoplankton abundance of Taxodiaceae over Pinaceae, and by the assemblage in which С. formosus is absent, Isthmo- dominance of Betulaceae over Fagaceae + Juglanda- lithus recurvus is dominant, and large specimens of ceae. This suggests a humid, moderately warm climate. Reticulofenestra umbilica are found only occasionally, These beds are followed by outcrops of the right which is characteristic of the NP22 Zone. and left banks downstream of the Fyuntv River, where In most of the Pshekha Formation (Fig. 3, Bed 6, the Miocene part of the Maikop Group about 300 m Samples ВЕ239–271), nannoplankton assemblages thick crops out, in outcrops that are somewhat less are composed of small Reticulofenestra and Isthmo- completely exposed. These beds are to be described in lithus recurvus and occasional Reticulofenestra umbil- a separate paper. ica, R. hillae, and Dictyococcites dictyodus, and very rare Cyclococcolithus formosus and correspond to the NP22 Zone. It needs to be said that Sample ВЕ250 MAJOR FOSSIL GROUPS contains a few representatives of the genus Transverso- Nannoplankton pontis (T. fibula, T. pulcher, T. sp.). Usually, the pres- ence of such endemic markers as T. fibula is character- Diverse nannoplankton assemblages of the Belaya istic of the Polba Formation and its equivalents Glina Formation in its upper part become less diverse, (NP22–23) in many localities of the Eastern Para- containing Coccolithus eopelagicus, Cyclococcolithus tethys. formosus, Chiasmolithus oamaruensis, Corannulus ger- manicus, and Discoaster tani; the amount of Discoaster Polba Formation. The nannoplankton assemblage sharply decreases. Sphenolithus pseudoradians (Martini, from the Polba marl is very distinct (Bed 8, Sample 1971), the index species of the NP20 Zone (=CP15 ВЕ286). This assemblage is dominated by small Retic- Discoaster barbadiensis, 15b Istmolithus recurvus ulofenestra ornata and contains numerous Transverso- Subzone according to Bukry, 1975), is still present. pontis fibula, T. pax, and T. latus and occasional Tro- choaster sp. J. Krhovsky assigned this peculiar assem- The uppermost horizons of the Belaya Glina For- blage to the NP23 Zone (Akhmetiev et al., 1995), mation (Sample ВЕ190) and the base of the Pshekha whereas Tabachnikova assigned it to the NP22–23 Formation (Fig. 3, Beds 1, 2, Samples ВЕ193, 196) zones (Muzylev and Tabachnikova, 1987). contain abundant Clausicoccus subdistichus, the explo- sion of abundance of which is in the Eocene–Oligo- Morozkina Balka Formation. The overlying non- cene boundary beds within the NP21 Zone or CP16 carbonate thinly laminated clay of the Lower Moroz- Zone (Gradstein et al., 2012). kina Subformation does not contain nannoplankton. The alternating carbonate and non-carbonate clay Pshekha Formation. The basal horizons of the beds at the base of the Upper Morozkina Subforma- Pshekha Formation (Beds 1, 2, Samples ВЕ193, 196) tion contain Reticulofenestra lockeri, Cyclicargolithus are still dominated by species continuing from the floridanus, Dictyococcites bisectus, Coccolithus pelagi- Eocene (Coccolithus eopelagicus, Dictyococcites bisec- cus, Pontoshaera multipora, and Transversopontis pyg- tus, and Reticulofenestra umbilica). We also found Dis- maeus and belong to the NP24 Zone, indicated by the coaster barbadiensis and D. saipanensis, one specimen last occurrence of T. pygmaeus and the first appear- each; the disappearance of these taxa defines the ances of Helicosphaera recta and Cyclicargolithus abi- upper boundary of the NP20 Zone (or CP15 Dis- sectus. Up the section (Bed 10, Samples ВЕ316–325), coaster barbadiensis Zone). However, this level shows abundant nannoplankton is represented by numerous mass redepositon of the microbiota (Zaporozhets, small Reticulofenestra spp., Cyclicargolithus floridanus, 1999); hence, isolated occurrences probably should Dictyococcites bisectus, and Pontosphaera multipora, not be considered as very important. and also by occasional (6–7 specimens) Helicosphaera Up the section (Bed 3, Samples ВЕ202–208), Dis- recta, the index species of the NP24Zone. This zone coaster saipanensis and D. barbadiensis completely dis- was also indicated for this locality by A. Nagymarosy appear, but the assemblages are still dominated by Ist- (Nagymarosy and Voronina, 1993). molithus recurvus, R. umbilica, and Clausicoccus subdis- In the middle part of the Upper Morozkina Subfor- tichus. Cyclococcolithus formosus, a species disappearing mation (Samples ВЕ358–373), the nannoplankton is at the upper boundary of the NP21 Zone, is represented similar to that of the previous assemblage, but contains by only a few specimens, so the association corresponds more Cyclicargolithus abisectus and includes Helicos- to the upper part of the NP21 Zone. phaera recta. Both of these species are characteristic of In Bed 4, the precise position of the NP21/22 the NP24–25 zones. Samples ВА200–214 from the boundary cannot at present be established above the upper part of the Morozkina Balka Formation contain Beds with Limacina because of the almost constant, abundant nannoplankton with numerous Dyctiococ- although rare, presence of Cyclococcolithus formosus cites bisectus, Cyclocargolithus floridanus, and C. abi- and also of redeposited specimens of Discoaster. In the sectus and with index species Helicosphaera recta, upper part of Bed 4 and in Bed 5 (Samples ВЕ214 and which is also characteristic of the NP24–25 interval.

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 348 POPOV et al.

Deposits of the Batalpashinsk Formation contain benthic taxa. The distribution of foraminifers along one carbonate bed (Fig. 3, Bed 13, Sample BA256), the section of the Belaya River is shown in Fig. 4. with abundant Reticulofenestra and dominated by Pshekha Formation. Foraminifers are found in Cyclicargolithus abisectus, and C. floridanus. The occa- most studied samples and are mostly represented by sional presence of Discolithina pygmaea and the benthic species, often as pyritized casts; tests are small absence of Dictyococcites bisectus and Zygrhablithus and thin-walled. The lower part of the section (Fig. 4, bijugatus suggest that this assemblage belongs to the Samples ВЕ193, 200b, 210, 220, 235, 252) contains an NP25 Zone. The assemblage is very similar to the alternation of interbeds with a small amount of ben- association described by Baldi-Beke (1984) from thic fauna and predominance of planktonic micro- Hungary in the upper part of the Kiscellian Regional fauna of the genera Globigerina, Сhiloguembelina, and Stage to Egerian Regional Stage in Borehole 33, which Pseudohastigerina and without microfauna, which was she assigned to the NP24–25 zones, also dominated apparently connected with the presence of carbon by С. abisectus and C. floridanus and with a noticeable dioxide and hydrogen sulfide of bottom waters and presence of Transversopontis cf. pulcher. dissolution of thinner shelled tests in the muddy waters Predominantly non-carbonate clays of the overlying of the upper layers of sediments. Septarian + Zelenchuk Formation lack nannoplankton. The upper part of the Pshekha Formation (Sam- It is found only in isolated weakly carbonated interbeds ples ВЕ240, 265, 279) is dominated by benthos, espe- with concretions in the upper part of the formation and cially frequently with Haplophragmoides aff. stavropo- is represented, according to J. Krhovsky, by Cyclicargo- lensis Ter-Grig., H. fidelis Ter-Grig., H. sp., Trocham- lithus floridanus, large Helicosphaera euphratis, Pontos- mina aff. complecta Ter-Grig., Asterigerina lucida phaera enormis, P. rothii, Cyclicargolithus abisectus, and (Min.), Cibicidina amphisyliensis (Andreae), and Cibi- Dictyococcites bisectus, assigned to the NP25 Zone. cidoides oligocenicus (Samoilova), but planktonic assemblages continue to be present. According to Ter- The uppermost beds of the Septarian + Zelenchuk Grigoryants (1964), who in the stratigraphic scheme of Formation (in the Alkunian Horizon) in an outcrop of the Maikop Group in the lower Khadum Horizon at the the Fyuntv River show a rhythmic alternation of non- level of the Pshekha Formation established biostrati- carbonate clay in places with carbonates and marl graphic units in the rank of local zones with Haplophrag- nodules. Here the composition of nannoplankton is moides fidelis and Asterigerina lucida as index species, similar to that described above (Coccolithus pelagicus, characteristic of the assemblage of Beds with Globiger- rare Pontosphaera enormis, Cyclicargolithus floridanus, ina officinalis, the assemblage of benthic foraminifers and C. abisectus), but the assemblage contains one from the Belaya River is similar in composition to the specimen of Triquetrorhabdulus carinatus?, which pro- assemblage from the Southern Stavropol Region. visionally dates this assemblage as the NP25–NN1 The Polba Formation Zone (Krhovsky in Akhmetiev et al., 1995). The over- in the section of the Belaya lying non-carbonate clay and silt of the Karadzhalga River does not contain foraminifers, but Sample ВЕ284 Formation do not contain nannoplankton. (0.2 m below the Polbian Bed) contains fragments of Spirorbis tubes, occasional Haplophragmoides fidelis Ter-Grig., Trochammina sp., and Cibicidoides oligoceni- (Samoilov). Sample ВЕ288 (0.5 m above the Bed) Foraminifers cus contains pyrite and siderite as rounded, fragmented, In the upper part of the Belaya Glina Formation, and not identifiable algal ossicles, test fragments, and the foraminiferal assemblage is replaced by an impov- casts of foraminifers. erished association with Globigerina officinalis, char- The Lower Morozkina Subformation (Samples acteristic of the Oligocene, and this change occurs ВЕ295, 328, 334, 340, 343), composed of noncalcar- below the lithological boundary between the Belaya eous clay, includes benthic and planktonic species of Glina facies and dark clay of the Pshekha Formation foraminifers, occurring in the underlying deposits of (with Sample ВЕ191), from the level of Beds with Pro- the Pshekha Formation, and the species Pseudoparella peamussium fallax, where nodosariids of the genera caucasica Bogd., appearing at that level. The foramin- Nodosaria, Lenticulina, Robulus, and Marginulina iferal assemblage of this subformation contains Rhab- begin to dominate, and representatives of Cibicidoides dammina cylindrica Glaessner, Saccammina variabilis appear. The planktonic assemblage is not diverse (spe- Bogd., Reophax sp., Ammodiscus aff. perlucidus Andreae, cies of three to four genera), is represented by smaller A. tenuiculus Subb., Haplophragmoides sp., H. aff. per- tests compared to earlier Eocene plankton, and iferoexcavatus Subb., Cyclammina turosa Ter-Grig., includes the index species Globigerina officinalis. C. aff. clivosa Subb., C. aff. kubanica Ter-Grig., Thus, the foraminiferal assemblage is strikingly differ- Ammomarginulina aff. lobsanense (Andr.), Baggina aff. ent from the typical Late Eocene Belaya Glina assem- iphigenia (Sam.), Pseudoparella caucasica Bogd., Cibi- blage with large tests, but is genetically connected with cidina amphisyliensis (Andreae), Globigerina officinalis the Pshekha assemblage of small plankton and diverse Subb., G. bulloides Orb., G. praebulloides Blow,

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 349

Lithology Species of foraminerfers nerfers Beds Series Samples Beds with Scale, m Scale, Formations, with forami- subformations foraminerfers Thickness, m Thickness,

230 220 17

Karadzhalga 210

300 18-1 magna Caucasina . terekensis 290 25

16 aff . . pertusa Bolivina Bolivina goudkoffi

280 sp Globigerina officinalis Globigerina Globigerina bulloides Globigerina

270 BA370 ex gr BA364

260 BA332 praebulloides Globigerina Chiloguembelina gracillima Bagina pseudoungerianus Cibicides almaensis Cibicides buliminoides Caucasina

BA328 complecta Trochammina 250 40 9/07 240 15 BA314 Uvigerinella californica Uvigerinella Virgulinella Virgulinella Bolivina goudkoffi caucasica goudkoffi Bolivina Septarian + Zelenchuk Septarian Spiroplectammina Spiroplectammina

BA309 terekensis 230

220 Spiroplectammina Caucasina schischinskajae Caucasina 210 14 40 200 . sp 190 13 0.7 BA256 180 . sp

170 12 perlucidus Ammodiscus Batalpashinsk Cibicides Cibicides Upper OligoceneUpper 36 L. Miocene 160

150 missippiensis Bolivina 5 140 11 Bolivina dilatata Bolivina Virgulinella neobuliminiformis Virgulinella Cibicidoides expertus Cibicidoides schreibersiana Fursenkoina Glomospirella Glomospirella californica Virgulina Virgulinella ex gr. pertusa gr. ex Virgulinella Globigerina officinalis Globigerina Trochammina complecta Trochammina caucasica Trochammina parva Trochammina concentricus Trochamminоides BA220 pseudoedita Globigerina 130 BA200 120 Globigerina parva Globigerina Globigerina praebulloides Globigerina Cyclammina turosa Cyclammina clivosa Cyclammina kubanica Cyclammina

35 tenuiculus Ammodiscus 10 bulloides Globigerina Haplophragmoides periferoexcavatus Haplophragmoides Virgulinella Subformation 110 Saccammina variabilis variabilis Saccammina Upper Morozkina Upper 100 BE347 Cyclammina turosaCyclammina 90 BE338 BE334 9 Lower 80 36 Baggina iphigenia

Morozkina BE295 Subformation Pseudoparella caucasica Pseudoparella caucasica

70 Pseudop. Polb. 8

7 5 Chiloguembelina gracillima 60 BE284 oligocenicus Cibicidoides BE279 amphisyliensis Cibicidina

50 micra Pseudohastigerina BE265 40 6 32 BE252 30 BE240 Haplophragmoides fidelis Haplophragmoides

Lower Oligocene Lower BE235 20 5 9 Pshekha BE220 H. stavropolensis 4 4.5 BE216 10 Asterigerina lucida 3 7 BE210 BE200 lucida Asterigerina 0 1–2 4 BE193 officinalis Globigerina Eocene BE191

Fig. 4. Stratigraphic distribution of foraminifers in the Belaya River Section and zonations of Oligocene–Lower Miocene depos- its. Polb.—Polbian Bed.

G. yeguaensis Wienz. et Applin, G. aff. ouachitaensis is characterized by a relatively diverse benthic assem- ouachitaensis Howe et Wallace, G. parva Bolli, blage dominated by representatives of Cibicidoides, G. pseudoedita Subb., and G. sp. Virgulinella, and Bolivina and low number of plank- The Upper Morozkina Subformation (Samples ВЕ347, tonic species. The foraminiferal assemblage contains ВА200, 209, 214, 220), composed of calcareous clay, Ammodiscus sp., Ammodiscus aff. perlucidus Andreae,

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 350 POPOV et al.

A. aff. tenuiculus Subb., Saccammina sp., Trochammi- ied samples from this outcrop collected by noides aff. concentricus Subb., Trochammina sp., N.Yu. Filippova (in 2004) and T.N. Pinchuk (in T. compressa Ter-Grig., T. caucasica Ter-Grig., 2016). This locality contained a foraminiferal assem- T. parva Cuhman et Laiming, T. aff. khadumica Ter- blage of a relatively deep-water normally saline basin Grig., Baggina iphigenia (Samoilova), Pseudoparella with calcareous benthic taxa: cf. Lenticulina, Cauca- aff. caucasica Bogd., Cibicidina amphisyliensis sina schischinskajae (Sam.), C. aff. magna Bugrova, (Andreae), Cibicidoides oligocenicus (Samoilova), C.aff. buliminoides Bogd., Buliminella aff. pulcha C. expertus (Schutzkaya), C. almaensis (Samoilova), Subb., Virgulinella ex gr. pertusa (Reuss), Uvigerinella C. aff. pseudoungerianus (Cushman), Fursenkoina sch- aff. hybridica Subb., U. californica Cushman, Bolivina reibersiana (Czjzek), Virgulinella ex gr. pertusa aenariensiformis Mjatl., B. carnata complanata Subb., (Reuss), V. aff. neobuliminiformis Kuznezova, Angulo- B. mississippiensis Cush., B. aff. goudkoffi caucasica gerina gracilis (Reuss) oligocenica Andreae, Bolivina sp., Bogd., B. dilatata Reuss, Asterigerina sp., and A. aff. B. dilatata Reuss, B. mississippiensis Cushman, B. aff. bracteata Cush. Plankton is represented by Globigerina anglica Cushman, Globigerina praebulloides Leroyi, aff. bulloides (Orb.), G. aff. officinalis Subb., etc. Blow et Banner, G. yeguaensis praedovenezuelana Blow In his early papers, Bogdanovich (1960) noted that et Banner, and G. officinalis Subb. The assemblage con- the co-occurring species Uvigerinella ex gr. californica tains the common Oligocene species Ammodiscus aff. and Spiroplectammina carinata are index species of the perlucidus Andreae and Cibicidoides pseudoungerianus second zone in the foraminiferal biostratigraphic (Cushman), indicating a normal marine basin. The scheme of the Maikop Group of the Kuban Lowland, assemblage contains index species of beds with fora- Stavropol Region, and Trans-Terek Plain and assigned minifers (Cyclammina turosa Ter-Grig. and Virguli- them to the Oligocene. The species Uvigerinella cali- nella ex gr. pertusa (Reuss)); the latter species first fornica Cushm. was described as a characteristic spe- appears at that level. Trochamminoides concentricus is cies of the foraminiferal assemblage of the Kalmyk an index species of the assemblage of the foraminiferal Formation of the Chattian Stage of the Volga-Don beds of the Stavropol Region, overlying the deposits region (Kurgalimova in Voronina et al., 1988). How- with abundant ostracodes (Ter-Grigoryants, 1964). In ever, in the section on the Fyuntv River, these taxa are the section of the Belaya River, deposits with T. con- found alongside nannoplankton of the NP25–NN1 centricus also lie above beds with ostracodes Disopon- zones and Miocene dinocyst species (Beluzhenko tocypris oligocenica, which allows their correlation with et al., 2014). Occurrences of index species Bolivina biostratigraphic units of the Stavropol Region. goudkoffi caucasica and Uvigerinella californica, char- The Batalpashinsk Formation is represented by acteristic of the Caucasus Regional Stage (Bog- non-calcareous clay without remains of foraminifers. danovich, 1965), in Bogdanovich’s opinion, indicated The latter are found in only one calcareous interbed the beginning of the Neogene and the transgressive (Fig. 4, Sample ВА256), which contains rare Ammo- depositional stage in a normally saline marine basin. discus aff. perlucidus Andreae and Cibicides sp. The Septarian + Zelenchuk Formation is mostly Mollusks represented by non-calcareous clay lacking foramini- fers. Only the presently covered sandstones of Lysaya Mollusks are rare in the deep-water Maikop sections Hill (Sample 9/07 of N.Yu. Filippova) contained of Ciscaucasia. They are associated with short-term sponge spicules, radiolarians, and small tests of fora- stages of restoration of the gas regime, favorable for minifers Spiroplectammina aff. terekensis Bogd., Tro- large benthic fauna. Mollusks (Propeamussium fallax, chammina depressa Subb., Baggina sp., Cibicides aff. Nucula sp., nautiloids Aturia ziczac) are found at the top pseudoungerianus Cushman, C. almaensis Samoilova, of the Belaya Glina Formation together with remains of Caucasina aff. buliminoides Bogd., Globigerina prae- echinoids and imprints of bryozoans. This benthic bulloides Leroyi, Blow et Bannet, G. yeguaensis assemblage is found far beyond Ciscaucasia: in Crimea, yeguaensis Winz., Globorotalia sp., and Guembelina in the Southern Aral Region, and in Kyzylkum (Korob- gracillima (Andreae). This assemblage suggests an kov, 1939; Merklin, 1974; Popov et al., 1993). environment of the outer shelf of a normally saline The lower part of the Pshekha Formation (Beds 2–4) marine basin. This assemblage is of Oligocene–Lower is characterized by planktonic pteropods of the genus Miocene (middle–upper Maikop). Limacina (= Planorbella, Spiratella). These mollusks Clay deposits in the lower reaches of the Fyuntv were very widely distributed in the outer shelf of Para- River contain carbonate interbeds with microfauna. tethys at the base of the Oligocene—from the Central Dmitrieva et al. (1959) characterize these interbeds as Carpathian Paleogene basin of Hungary to Transcau- Alkunian and trace them to Eastern Ciscaucasia. This casia and the Pre-Kopetdag Depression. Baldi (1986) is a stable, accepted regional marker level, the age of suggested that such a wide distribution of these mol- which is indicated by nannoplankton and dinocysts as lusks was connected with Boreal influence, i.e., the Early Miocene (Filippova et al., 2010, 2015). We stud- influx of North Sea waters. However, modern species

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 351 of Limacina are more widely distributed in warm- Up the section, mollusks are absent in the Maikop water basins, where they are buried at moderate depths deposits and appear only in the beds immediately in non-bioturbated sediment (Berger, 1978). Appar- overlying the Maikop group. ently, it would be more correct to explain the occur- rence of pteropod facies at the base of Oligocene by the Ichthyofauna favorable conditions of their burial: moderate depth prevented their dissolution, whereas a constrained gas In the Belaya Glina Formation, the ichthyofauna is regime limited the existence of benthic fauna. represented by rare full skeletal remains and large scales of Lyrolepis caucasica and also by accumulation In Bed 3, interbeds with Limacina alternate with of small bones and scales of other bony fishes. The rar- somewhat bioturbated beds with burials in the living ity of the full skeletal remains suggests unfavorable position of the bivalves Pterolucina batalpaschinica conditions for burial of bony fishes in the Priabonian (Korob.), Yoldiella chadumica (Korob.), and Thyasira basin owing to intensive bioturbation. nysti (Phil.); there are occurrences of the gastropod Pshekha Formation. The Pshekha Formation is Aporrhais speciosa Sch. and scaphopod Dentalium generally widely characterized by a diverse fauna of (Antalis) acutum parvum (Gonch.) (identified by I.A. Gontsharova), which is a typical member of the marine fishes, sharply dominated by bony fishes assemblage of the basal Oligocene, also traceable very (more than 70 species; Bannikov, 2010 and this widely from the Crimea, Volga-Don Interfluve, and paper), with rare skeletal imprints and isolated teeth of Georgia to Mangyshlak and the Pre-Kopetdag sharks Carcharias acutissima, C. cuspidata, Alopias cf. Depression, and characteristic of the outer shelf exigua, Echinorhinus sp., Isurolamna (Lethenia) van- (Korobkov, 1937, 1939; Merklin and Gontsharova, denbroeckani, and Physogaleus latus (identified by 1967; Popov et al., 1993). Up the section, in Bed 4, T.P, Malyshkina); the assemblage also contains gill benthic mollusks disappear, but Limacina continues to rakers of the whale shark Keasius parvus. be present. The disappearance of large benthos, The Pre-Planorbella Bed (Bed 1) contains pelagic including mollusks, was directly connected with rein- taxa: Clupeidae and fragments of Thunnini. statement of an unfavorable gas regime, indicated by The lower part of the Pshekha Formation (Planor- results of geochemical studies (Sachsenhofer et al., bella Bed according to Danilchenko, 1960; Beds 2–4 2017) and study of dinocysts (Zaporozhets and in this paper) characteristically contains numerous Akhmetiev, 2017). Up the section (Bed 5), Limacina “Sardinella” rata, Anenchelum angustum, Palimphyes also disappears, which could have been caused by con- chadumicus, Auxides cernegurae, Protobrotula sobijevi, tinuous deepening of the basin. In modern basins, the Eophycis pshekhiensis, and Palaeogadus (five species); depth of aragonitic compensation where pteropods are pelagic Pomolobus curtus, Palaeorhynchus zitteli, completely dissolved varies considerably, reaching Homorhynchus colei, Pavlovichthys mariae, and Oligo- 1.5 km in low latitudes. In the Aegean Sea, which in its balistes robustus; pelagic hatchings of Caprovesposus climatic and bathymetric characteristics could have parvus; and coastal Doryrhamphus squalidus, Pshek- been near the conditions of the early Maikop basin, hagnathus polypterus, Oliganodon comparabilis, Pria- samples from depths of 500–800 m contained ptero- canthus spinosus, Caranx daniltshenkoi, and Champ- pods, whereas at greater depths and in sapropel, their sodon grossheimi. abundance sharply decreased (Aksu et al., 1995). This Less common bathypelagic taxa lacking photo- suggests that the depth of the Maikop Basin in the phores (Proargentina inclinata, Glossanodon confusus, Adygea Region by the mid-Pshekha time could have and Gephyroberix robustus) are sporadically found in been close to critical values and later reached 1 km. the overlying beds (Beds 3–4 of the Planorbella level). Similar estimates are obtained using seismic profile With the disappearance of pteropods (Bed 5 of the methods (Antipov and Kurina in Popov et al., 2010) Pshekha Formation; the Amphisyle Bed according to and ichthyological studies. Danilchenko, 1960) in the second half of the Pshekha Rare imprints of benthic mollusks were found in time, assemblages of coastal marine and pelagic fishes the bed of Polba marl. These imprints are only identi- were replaced by subtropical ones as a result of a fiable to genus: Janschinella, Lenticorbula, and cardiid warming episode. At the same time, the deepening of costae. Despite their poor state of preservation, they the Paratethys in the area of the Caucasus resulted in clearly belong to the brackish-water endemic associa- the development of diverse very deep-water fish tion characteristic of the lower Solenovian Regional assemblages (including taxa with luminescent organs, Substage. A more diverse assemblage was collected on which included the genera Eovinciquerria, Scopeloides, the Fars River, right tributary of the Belaya River, in Argyropelecus, and Eomyctophum. The abundance of dark carbonate clay. These beds contain Urbnisia lata, deep-water taxa in the late Pshekha assemblage, which Janshinella vinogrodski, Korobkoviella sp., and Cer- was dominated by Myctophidae, suggests the presence astoderma cf. chersonense. This is a typical early Sole- of very deep zones in the basin, probably up to 1000 m. novian association. The entire generic range of the deep-water Caucasian

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 352 POPOV et al. ichthyofauna of the late Pshekha time was also repre- dae, Abadzekhia marinae, and Sarda remota; and sented in the Carpathian Basin, where the generic coastal Carangidae, Oliganodon budensis, Cooceolus diversity of a synchronous deep-water ichthyofauna artus, and Scorpaenidae (Sytchevskaya in Akhmetiev was twice the Caucasian one. The assemblage under et al., 1995 and this paper). consideration lacks some early Pshekha species; Aeo- Batalpashinsk and Septarian + Zelenchuk Forma- liscus heinrichi (subdominant) appears; and mesope- tions. In the deposits of these formations, fish occur- lagic taxa with photophores (Eovinciquerria obscura, rences are relatively rare and are mostly represented by Eomyctophum koraense, and Scopeloides glarisianus) are incomplete or fragmented specimens. A locality in the present. The assemblage contains Sparus priscus, Leiog- lower reaches of the Fyuntv River yielded Aeoliscus sp., nathoides altapinna, Rybapina caucasica, and rare Breg- Holosteus sp., Repropca sp., Capros longispinatus, and maceros filamentosus, Doryrhamphus squalidus, and Pseudotetrapturus luteus. Syngnathus incertus. This assemblage corresponds to the Aeoliscus assemblage with warm-water tropical and sub- tropical taxa (Bregmaceros, Aeoliscus, and Fistularia) PALEOMAGNETIC STUDY OF THE SECTION (Sytchevskaya in Akhmetiev et al., 1995; Prokofiev, The paleomagnetic study of the Belaya River sec- 2005, 2006a, 2006b, 2007; Bannikov, 2010, et al.). tion was conducted during the fieldwork in 2015, in Some fish species in common have been recorded collaboration with colleagues from the Paleomagnetic in various regions of the Paratethys at various geochro- Laboratory of Utrecht University, Netherlands. Sam- nological intervals. For instance, the Rauenberg local- ples were collected with an interval of 0.4–0.8 m; the ity in the Upper Rhine Graben dated as the NP23 cases where the interval exceeded 2 m are shown in Zone (Maxwell et al., 2016), most distant from the Fig. 1 as discontinuities in the outcrop. The sampling Maikop Basin, is characterized by several species method and preparation of samples for the analysis is found on the Belaya River in older and younger beds: described by van der Boon et al. (2017). For the Pinichthys pulcher (NP21), Aeoliscus heinrichi and Maikop part of the section, about 400 samples were Leiognathoides altapinna (NP22), and Abadzekhia analyzed from the Pshekha Formation, Polbian Bed, marinae (NP24). The ichthyofauna of the outer Car- and Morozkina Balka Formation. Up the section, pathian basins (Poland, Romania) is not recorded from samples were collected during the fieldwork of 2016– the basal Oligocene ichthyofauna (NP21 Zone) (Cio- 2017, but these results have not been completed. banu, 1977; Kotlarczyk and Jerzmańska, 1988; Changes in the polarity in the section are shown in Sytchevskaya in Akhmetiev et al., 1995; Kotlarczyk Fig. 1. The lower ~20 m of the Pshekha Formation et al., 2006), although the earliest of the Carpathian mainly show normal polarity, and up the section, ichthyofaunas (from the bituminous marl of Romania reversed polarity becomes dominant up to the Polbian and ichthyofaunal IPM1 Zone of Poland) includes spe- Bed. In this interval, radiometric argon dating of 33.20 ± cies occurring in the NP21 Zone on the Belaya River. 0.34 Ma was obtained from a tuffite interbed (Fig. 1). Morozkina Balka Formation. The lower part of the The Polbian Bed (61 m above the base of the Lower Morozkina Subformation contains a marine Maikop deposits) is characterized by normal polarity. fish assemblage (Sytchevskaya in Popov et al., 2009, The following brief intervals of normal polarity p. 69; Sytchevskaya and Prokofiev, 2013; Prokofiev, were recorded in the lower part of the Lower Moroz- 2013), indicating the restoration of normal salinity kina Subformation (62–64 and 68–70 m), an interval after the early Solenovian salinity decrease. Beds at of alternating polarity was recorded in its middle part this stratigraphic level on the right bank of the Belaya (75–80 m), and an interval of reversed polarity was River yielded imprints of sharks of the family recorded in its upper part (87–97 m). The Upper Charcharinidae: Physogaleus cf. latus (Storms, 1894); Morozkina Subformation, except for its uppermost part remains of the bony fishes of the families Clupeidae: for which no data have yet been obtained (97–135 m), “Sardinella” sp. nov., Osmeridae: Austromallotus mus- has mostly normal polarity, except for the interval celi (Paucă, 1929), Syngnathidae: Hypposyngnathus sp., 108–113 m, part of which is in a covered interval. Gadidae: Palaeogadus simionescui Daniltshenko, 1950; The interpretation of these data is discussed the Repropcidae: Repropca surcula Prok.; Priacanthidae: next section. Pristigenys geminus Prok.; Caproidae: Proantigonia radobojana (Kramberger, 1882); and Scombridae gen. indet. The assemblage is dominated by neritic-pelagic CHANGES IN BIOTIC ASSEMBLAGES, taxa of a moderately warm normally saline marine basin FACIES, AND PALEOMAGNETISM 100 to 600 m deep. OF THE SECTION AND THEIR POTENTIAL Deposits of the Upper Morozkina Subformation USE FOR CORRELATION AND RESTORATION (Bed 10) contain an ichthyofauna with mesopelagic OF DEPOSITIONAL SETTINGS Palaeogadus latebrosus and P. simionescui; numerous Despite an extreme impoverishment of the mala- normally marine pelagic Clupeidae, Palaeorhynchi- cofauna in deep water facies of the Ciscaucasian Oli-

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 353

Biotic data from the Belaya River Ciscaucasian Calcareous Series Foraminifers, formations

chrons nanno- Dinocysts chrons Age, Ma

Dinocysts ostracodes Calcareous Planktonic plankton foraminifers Paleomagnetic Paleomagnetic nannoplankton Aquitanian C6B Labyrinthodinium 23.03 N4 CN1 D16b Bolivina Karadzhalga C6C NN1 NP25–NN1 truncatum goudkoffi Septarian D16a Spiroplectam. + C7 Deflandrea terekensis Zelenchuk C7A NP25 spinulosa 25 P22 (non typica) Chattian NP25 C6B D15c ? Batalpashinsk CP19

C9 C9n 27.82 D15b Upper P21 NP24 NP24 Cyclammina

draco Morozkina C10 turosa C9r Subformation Chiropteridium partispinatum Chiropteridium Virgulinella

D15a Rhombodinium C10n CP18 C11 P20 Pseudoparella C10r 30 D14b Lower Rupelian caucasica Morozkina NP23 Wetzeliella CP17 NP23 Subformation P19 gochtii s.s. Disoponocypris ??C11nC11n D14a oligocaenica C12 C12nC12n Polbian Asterigerigerina NP22 NP22 W. symmetrica lucida C12r Pshekha P18 CP16 Globigerina D13 NP21 P. amoenum D13 C13n 33.9 NP21 Beds with officinalis C13 D12c C. subdist. Charlesdowniea Brotzenella P16/ clathrata 35 P17 taurica, Belaya Glina C15 D12b NP19–20 angulosa/ Bolivina NP Rh. perforatum 19–20CP19 antegressa Eocene Oligocene

Priabonian C16 P15 D12

Fig. 5. Correlation of the zonal division of the Belaya River section with the International Scale (after Gradstein et al., 2012; Inter- national…, 2017) using nannoplankton, dinocysts, and paleomagnetic data. gocene, this was the group from which the faunistic with Clausicoccus subdistichus are important for cor- dating of the Maikop deposits began in the 1930s relation (Fig. 5); a sharp increase in abundance of the (Korobkov, 1937, 1939; Liverovskaya, 1938). Using index species in these beds is within the Eocene–Oli- mollusks, I.A. Korobkov determined the position of gocene boundary beds, within the NP21 Zone or the “Lower/Middle Oligocene boundary” inter- CP16 Zone (Gradstein et al., 2012). Therefore, despite preted as the Latdorfian–Rupelian boundary: the presence of occasional specimens of Discoaster between molluscan assemblages with Propeamussium barbadiensis and D. saipanensis, the disappearance of fallax and association with Pterolucina batalpashi- which determines the upper boundary of the NP20 nica. Later, the same position of the boundary (but Zone (or CP15 Discoaster barbadiensis), we assign the interpreted as the Priabonian–Rupelian boundary or upper part of the Belaya Glina Formation to Zone the Eocene–Oligocene boundary) was supported by NP21 or CP16, considering the mass redeposition of planktonic groups (planktonic foraminifers and nan- microbiota at this level (Zaporozhets, 1999). The noplankton) (Krasheninnikov and Muzylev, 1975; paleomagnetic data (normal polarity in the deposits Krhovsky et al., 1995; Muzylev, 1980) and later by from the very base of the Maikop Group) suggest the dinocysts (Akhmetiev et al., 1995; Andreeva-Grigor- possible position of the Eocene–Oligocene boundary ieva, 1980; Zaporozhets, 1999; Zaporozhets and in the uppermost horizons of the Belaya Glina Forma- Akhmetiev, 2017). tion, because in the international scale it is drawn In the uppermost part of the Belaya Glina Forma- within the reversed Chron C13r (Berggren et al., 1995; tion and at the base of the Pshekha Formation, Beds International…, 2017).

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 354 POPOV et al.

Pshekha Formation. The assignment of the lower Bed and the Lower Morozkina Subformation, can be part of the Pshekha Formation to the nannoplankton confidently traced from the foothills of the Alps and NP21 (CP16) Zone and to the Phthanoperidinium Carpathians and intra-Carpathian depressions using amoenum (D13) Zone by dinocysts and the presence endemic brackish-water mollusks, ostracodes, spe- of a large zone of normal polarity characterizing the cific composition and morphs of dinocysts of the lower third of the Pshekha Formation and interpreted lower subzone of the Wetzeliella gochtii Zone, and as Chron C13r allow this formation to be confidently nannoplankton of the NP23 Zone (Popov and Stu- dated to the beginning of the Rupelian (Fig. 5). A dencka, 2015; Voronina and Popov, 1984; Zaporozhets change in lithology from light-colored marly biotur- and Akhmetiev, 2015), across southern Ukraine and bated facies to dark laminated weakly carbonate clay the Volga-Don interfluve, Ciscaucasia, and Transcau- with abundant pyrite, the change in the molluscan casia to Ustyurt and Kopetdag (Merklin, 1974; Popov assemblage of the Beds with Propeamussium fallax to et al., 1993). the assemblage with Pterolucina batalpaschinica, and It is possible to observe on the Belaya River dis- the appearance of assemblages of benthic foraminifers cernible unconformities at the base and top of the Pol- with Asterigerina lucida and Haplophragmoides fidelis bian Bed sharply changing in thickness from 0.2 to have a regional correlative value for the bathymetric 0.6 m. In the more complete sections (Kuban River, zone of the outer shelf of the entire Paratethys. In Keu River), it is known that the Polbian Bed has nor- addition, Beds with Limacina recognized from Hun- mal polarity, which is interpreted as the next positive gary to Kopetdag are well traceable in this sea zone. Chron C12n (Bogachkin, 2004), although in the even A number of shared species connect the Rupelian more complete sections of the Volga-Don interfluve ichthyofaunas of the Caucasus, Carpathians, Switzer- and Kalmykia, the transition to the Solenov Forma- land, and the Rhine Basin: Aeoliscus heinrichi, Pria- tion occurs at the top of the previous Chron C12r, canthus spinosus, Leiognathoides altapinna, and Capros whereas interval С12n of normal polarity is deter- rhenanus; Homorhynchus colei so far has not been mined 25–27 m above (Bogachkin, 2004; Zastrozh- recorded from the Rhine graben. Some other species of nov et al., in press). genera in common allopatrically replace one another in Morozkina Balka Formation, lower subformation. the Paratethys (Bannikov, 2010). For instance, These beds contain species of dinocysts indicating a Anenchelum glarisianum is recorded from the Rhine brackish water depositional environment for the lower basin, Switzerland, Carpathians, and Abkhazia, subzone of the Wetzeliella gochtii Zone (thin-shelled whereas A. angustum is recorded from the Northern Hystrichokolpoma, Batiacasphaera sphaerica). How- Caucasus and Azerbaijan; Palaeorhynchus zitteli is ever, the middle part of the member is dominated by known from the Caucasus and the Carpathians, and cysts of taxa inhabiting marine environments: P. glarisianus is recorded from the Rhine basin, Swit- Lejeunecysta spp., Wetzeliella gochtii, Selenopemphix zerland, and Slovenia. The genus Eophycis is repre- nephroides, and Operculodinium. This suggests the sented in the Rupelian of the Paratethys by three spe- influx of marine waters in the basin, which was sug- cies (E. pshekhiensis from the Caucasus, E. jamnensis gested earlier by E.K. Sytchevskaya (Popov et al., from the Carpathians and E. froidefontainensis from 2009, p. 69). The ichthyofauna of this interval includes the Rhine basin), and Trachinus is represented by two sharks of the family Charcharinidae and bony fishes of species (T. minutus from the Carpathians and Rhine the families Clupeidae, Osmeridae, Gadidae, Reprop- basin and T. rusticus from Ciscaucasia). The deep cidae, Priacanthidae, Caproidae, Scombridae gen. zones of the Rhine basin and some of the intra-Car- indet., and coastal Syngnathidae (Sytchevskaya and pathian basins were insufficiently deep for the meso- Prokofiev, 2013). Higher beds are again characterized pelagic luminescent fishes. In the sufficiently deep by dinocysts, which indicate decreased salinity and areas, Scopeloides glarisianus (Switzerland, Carpathi- restoration of brackish-water conditions. ans, and Caucasus), Eovinciguerria obscura, Oligophus A positive chron in the lower part of the subforma- moravicus, and Eomyctophum koraense (Carpathians tion we tentatively correlate with Chron С11n, and the and Caucasus) are recorded. An almost entire generic overlying part of the subformation with reversed polar- range of the deep-water Caucasian ichthyofauna is ity we correlate with Chron C10r. also represented in the Carpathian basin, deep-water Morozkina Balka Formation, upper subformation. ichthyofauna of which was twice as diverse in the The restoration of marine conditions in the Paratethys number of genera compared to the Caucasian fauna and the beginning of carbonate sedimentation is the (Prokofiev, 2006, 2007). next regional marker event. As in the deposits of the Polbian Bed. The accumulation of a carbonate bed Pshekha Formation, carbonate material accumulated corresponding to the beginning of the Solenovian mainly as light-colored pellets on the bedding planes decrease in salinity is the most important marker level of non-bioturbated sediment. These pellets are com- for the entire Paratethys. This level, corresponding in posed of nannoplankton and apparently represent the Western and Central Ciscaucasia to the Polbian feces of planktonic copepods. Such facies were also

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 LECTOSTRATOTYPE OF THE MAIKOPIAN GROUP 355 widespread in the Oligocene of the Carpathian basin Ciscaucasia and also in the upper part of the Batal- (Сiurej and Pilarz, 2016; Krhovsky’s unpublished pashinsk and Abadzekh formations (Ter-Grigoryants, data). According to nannoplankton data, the upper 1964), above the Solenovian level in Mangyshlak subformation belongs to the NP24 Zone (Nagymarosy (Stolyarov, 2001), in sections of the Salo-Manych and Voronina, 1993; Tabachnikova’s data in this interfluve and Ergenei (Bugrova, 2005; Stolyarov, paper), although Krhovsky et al. (1995) correlated the 2001), and in the Lower Miocene (Sakaraulian) of lower part of the subformation with the NP23 Zone. Abkhazia (Dzhanelidze, 1964). Virgulinella neobuli- The dinocyst assemblage with Wetzeliella gochtii–Chi- miniformis Kuznezova is also known from the Lower ropteridium partispinatum established for this subfor- Miocene deposits of Azerbaijan and Eastern Ciscau- mation is characteristic of the transitional beds from casia (Ter-Grigoryants, 1964). the Early to Late Oligocene. The ichthyofauna con- In the Belaya River Section, Virgulinella ex gr. рer- tains marine pelagic Clupeidae, Palaeorhynchidae, tusa and V. neobuliminiformis are found not only in the Gempylidae, Scombridae. Owing to detailed data on upper part of the Upper Morozkina Subformation but dinocysts and geochemistry, it has become possible to also considerably higher in the section, at the level of precisely reconstruct changes in the hydrology and gas the Upper Oligocene Septarian + Zelenchuk Forma- regime of this basin throughout time (Sachsenhofer tion (Fig. 4). Apparently, these taxa, like Fursenkoina et al., 2017; Zaporozhets and Akhmetiev, 2017). The (Virgulina) schreibersiana, are not confined to any fluctuations in the oceanic water influx during resto- narrow stratigraphic level, but rather reflect certain ration of marine conditions have been documented. conditions in a basin. According to Stolyarov’s data, Along with nannoplankton and dinocysts, benthic Virgulinella occurrences are restricted to anoxic facies, foraminifers of the families Fursenkoinidae Loeblich in the zone from a transition from deep-water to shal- et Tappan, 1961 and Virgulinellidae Loeblich et Tap- lower water sediments with rich benthos associations pan, 1984 have a significant correlative importance at and with no indications of anoxia. In deeper water this level in the Paratethys (Semenov and Stolyarov, facies, Virgulinella assemblages are replaced by purely 1970). Stolyarov considered “Virgulinellidae Beds” planktonic ones with Globigerina and nannoplankton. “as second (after the ostracode) marker horizon of the According to Krasheninnikov (pers. comm.), Virguli- Maikop Group” (Stolyarov, 2001, p. 164). In the sec- nella consume sulfate-reducing bacteria and are there- tion on the Belaya River, virgulinellids become fore assigned to the upper boundary of the sulfate numerous in the upper part of the Upper Morozkina reduction zone. Subformation, where they are represented by three The interval of normal polarity at the base of the species: Fursenkoina (Virgulina) schreibersiana (Czjzek), Upper Morozkina Subformation with the nanno- Virgulinella ex gr. Рertusa, and V. neobuliminiformis plankton NP24 Zone is interpreted here as Chron Kuznetzova. С10n, the overlying interval of the subformation with reversed polarity is interpreted as Chron C9r, and the According to the published data, these species are upper interval of normal polarity also with the nanno- not confined to any certain stratigraphic level. For plankton NP24 Zone is correlated to Chron С9n. instance, the species Fursenkoina (Virgulina) sch- reibersiana was recorded in the Upper Khadum of the Batalpashinsk Formation. The overlying deposits of southwestern regions of the Black Sea Region (Pech- the Batalpashinsk Formation correspond to the time enkina, 1964) and Northern Stavropol Region (Ter- of the maximum Late Oligocene anoxia in the basin Grigoryants, 1964), but at the same time, it is found in also characterizing the entire Paratethys. Therefore the upper part of the Lower Chegan Subformation of benthic fauna is absent here and above this level. The the Northern Aral Region (Chernyshev Bay; Bonda- lower third of the formation contains a thin bed of reva, 1964) currently dated as Barthonian, in the banded marl (0.7 m), also composed of pellets with the upper part of the Middle Maikop Group (Zeiva For- nannoplankton NP25 Zone. mation of Azerbajian) (Khalilov and Kuznetsova, The dinocyst assemblages below this marl con- 1964), and in the middle part of the Lower Maikop stantly contain Deflandrea spinulosa f. majkopica and series of the Akhaltsikh Depression in Georgia Rhombodinium draco and also Wetzeliella, Chiropterid- (Kacharava, 1964). This species was also found in the ium (Ch. partispinatum and Ch. mespilanun) and Bati- Lower and Middle Oligocene of the Khiva Depression acasphaera hirsuta (Zaporozhets and Akhmetiev, of the Central Karakum Dome (Balakhmatova, 1964); 2017). Up the section of the marl, cavate cysts of Wet- in the Upper Oligocene of the Salo-Manych interfluve zeliella and Rhombodinium completely disappear, and Ergenei (Bugrova, 2005); in the Lower Miocene, whereas the diversity of Chiropteridium is reduced in Beds with Bolivina goudkofi caucasica of the Cau- (only Ch. partispinatum remains). In the zonal scale of casian Stage; and higher up in the section, in the the Upper Oligocene, these changes are reflected as a Olginskaya Formation of Western Ciscaucasia (Bog- transition from the dinocyst Chiropteridium mespila- danovich, 1965). Virgulinella ex gr. рertusa is encoun- num–Ch. patrispinatum Subzone to the Deflandrea tered in the Upper Khadum of Western and Central spinulosa f. majkopica Subzone. The former subzone

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 27 No. 3 2019 356 POPOV et al. encompasses a significant interval of the section of the Pshekha Formation at the base of the Maikop Group first half of the Late Oligocene: Bed 11 of the Upper coincides with a replacement of the assemblage of the Morozkina Subformation and also Bed 12 of the lower dinocyst Charlesdowniea clathrata angulosa Zone part of the Batalpashinsk Formation. Ch. mespilanum (D12), characteristic of the Priabonian, by the assem- dominates in the Upper Morozkina Subformation, blage of the Phthanoperidinium amoenum Zone (D13) and Ch. partispinatum dominates in the Batalpashinsk of the lower Rupelian, and also with a change in the Formation. assemblage of mollusks of Beds with Propeamussium The clay sediments of the formation accumulated in fallax by the assemblage with Pterolucina batalpaschi- a basin with a slightly reduced salinity with a distinctly nica. However, according to the paleomagnetic data, pronounced anoxia of bottom waters, which is inferred the interval of normal polarity (Chron C13n) begins from the mass occurrences of acritarchs and prasino- from the very base of the Pshekha Formation. The phytes (Leiosphaeridia, small Pterospermella, and also Eocene–Oligocene boundary is probably in the Horologinella), with cyanobacterial accumulations. upper part of the Belaya Glina Formation, since in Septarian + Zelenchuk Formation. Anoxic condi- the international scale it is drawn within the previous tions were preserved later, when septarian concretions Chron C13r. were formed, followed by calcareous nodules. Inter- (2) A replacement of a diverse planktonic foramin- beds of fine-grained sand are characteristic of the iferal assemblage with Turborotalia centralis and Globi- Septarian and Zelenchuk formations. This is suggested gerinatheka tropicalis by an impoverished association by the presence of prasinophytes and acritarchs Ptero- with Globigerina officinalis and small tests characteristic spermella sp. and Leiosphaeridia in palynoassem- of the Oligocene occurs at the upper part of the Belaya blages, but their role was considerably less important. Glina Formation, in Beds with Propeamussium fallax. Up the section, in the main part of the Septarian + These beds are overlain by beds with a sudden increase Zelenchuk Formation, dinocyst species diversity con- in Clausicoccus subdistichus in the NP21 Zone, charac- siderably decreases; the considerable dominance of teristic of the Eocene–Oligocene boundary. the amount of spores and pollen over organic-walled (3) The Pshekha Formation corresponds to the phytoplankton indicates a lower coefficient of marine nannoplankton NP21 Zone, dinocyst Phthanoperi- conditions (less than 5%) and suggests the formation dinium amoenum (D13) Zone in its lower part and of sediments in the high-energy environment in a nor- nannoplankton NP22 Zone, dinocyst Wetzeliella mally marine basin (Zaporozhets and Akhmetiev, symmetrica Zone and Wetzeliella gochtii Zone in the 2017). Apparently, the impoverishment of marine middle terminal parts, and also several assemblages of phytoplankton resulted from a considerable influx of ichthyofauna and paleomagnetic Chrons С13n and fresh water of the Laba paleodelta. This is indicated by C12r (Fig. 5). The disappearance of first benthic mol- the composition of palynomorphs including redepos- lusks and later planktonic mollusks and the abundance ited taxa not only from Paleogene but also from Meso- of deep-water luminescent taxa in the late Pshekha zoic series. ichthyofauna suggest a considerable deepening (up to Importantly, this formation contains occasional about 1000 m). representatives of Labyrinthodinium trunсatum, zonal (4) The Polba marl, containing brackish-water species of the basal Miocene, together with Rhombod- Early Solenovian mollusks, ostracodes of the Disopon- inium, Chiropteridium, and Thalassiphora. Represen- tocipris oligocaenica association, nannoplankton of the tatives of these genera hardly continue to the Miocene; NP23 Zone, dinocysts of the Wetzeliella gochtii Zone, therefore, we date this formation, probably except for and incomplete fish remains, overlies the Pshekha the terminal beds, as Late Oligocene. Formation with a gap and unconformity overlain by Carbonate nodules and host clay in the upper part the Morozkina Balka Formation. of the Formation sometimes contain the nannoplank- (5) The lower subformation of the Morozkina ton NP25 Zone and the top horizons of the NP25– Balka Formation contains foraminifers, marine NN1 Zone, according to J. Krhovsky (Fig. 5). fishes, and dinocysts of the Wetzeliella gochtii Zone, Up the section, there is a transition to anoxic “fish indicating a considerably changing hydrology of the facies” of the Karadzhalga Formation, which has an basin from brackish water to normal marine. Chrons important correlative potential and is traced, apart C11n and C10r are recognized by paleomagnetic data. from Ciscaucasia, in Mangyshlak and depressions of (6) The upper carbonate subformation of the Ustyurt (Semenov and Stolyarov, 1970; Stolyarov and Morozkina Balka Formation at the base shows a fluc- Ivleva, 2004). tuating character of marine water influx during epi- sodes of salinity restoration, contains nannoplankton of the NP24 Zone, dinocysts of the Chiropteridium CONCLUSIONS partispinatum Zone, Rhombodinium draco Subzone, (1) The lithological transition from the light marl and is dated by paleomagnetic Chrons С10n, C9r and of the Belaya Glina Formation to the dark clay of the С9n (Fig. 5).

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(7) The Batalpashinsk Formation corresponds to Balakhmatova, V.T., Analogues of the Maikop in Northern the episode of the maximum anoxia in the Late Oligo- Turkmenistan, in Maikopskie otlozheniya i ikh vozrastnye cene and corresponds to the dinocyst Chiropteridium analogi na Ukraine i v Srednei Azii (Maikop Deposits and partispinatum Zone, Rhombodinium draco Subzone their Age Analogs in Ukraine and Middle Asia), Kiev: Nau- in the lower part and Deflandrea spinulosa (non typ- kova Dumka, 1964, pp. 223–231. ica) Subzone above the interbed of laminated marl of Baldi, T., Mid-Tertiary Stratigraphy and Paleogeographic the nannoplankton NP25 Zone. Evolution of Hungary, Budapest: Akad. Kiado, 1986. (8) The undivided Septarian + Zelenchuk Forma- Baldi-Beke, M., The nannoplankton of Transdanubian tion is composed of clay with concretions, septarian in Paleogene formations, Geol. Hung. Ser. Paleontol., 1984, the lower part, and in places subdominant sands. The no. 43. carbonate interbeds of the upper part of the formation Bannikov, A.F., Iskopaemye pozvonochnye Rossii i sopre- contain nannoplankton of the NP25 Zone and dino- del’nykh stran. Iskopaemye kolyucheperye ryby (Teleostei, cysts of the Deflandrea spinulosa Subzone, and the Acanthopterygii) (Fossil Vertebrates of Russia and Adjacent top part of the formation contains nannoplankton of Countries: Fossil Acanthopterygian Fishes (Teleostei, Acanthopterygii), Moscow: GEOS, 2010 [in Russian]. the NP25–NN1 Zone. Bannikov, A.F. and Parin, N.N., The list of marine fishes (9) The basal part of the overlying clayish-silty from Cenozoic (Upper Paleocene–Middle Miocene) local- non-carbonate Karadzhalga Formation, composed ities in southern European Russia and. adjacent countries, mainly of “fish lithofacies” characteristic of anoxic J. Ichthyol., 1997, vol. 37, no. 2, pp. 149–161. conditions, contains dinocysts of the Lower Miocene Beluzhenko, E.V., Stratigraphy of Oligocene-Lower Mio- Labyrinthodinium truncatum Zone. cene (Maykop) deposits of the northwestern Caucasus, Byull. Mosk. O-va Ispyt. Prir., Otd. Geol., 2010, vol. 85, ACKNOWLEDGMENTS no. 4, pp. 35–46. Beluzhenko, E.V. and Kovalenko, E.I., To the problem of We are sincerely grateful to the reviewers V.N. Ben- the Oligocene-Miocene boundary position in the northern yamovsky and Yu.B. Gladenkov for constructive criti- Caucasus (in support of the Caucasian regional stage), cal reviews. Stratigr. Geol. Correl., 2006, vol. 14, no. 2, pp. 211–218. Beluzhenko, E.V., Filippova, N.Yu., and Pis’mennaya, N.S., FUNDING Marker horizons of the Oligocene–Lower Miocene (Maikop) deposits of Northern Caucasus and Cis-Caucasus, Byull. The field and laboratory studies were supported by Mosk. O-va Ispyt. Prir., Otd. 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