Palynostratigraphy of the Upper Cretaceous and Paleogene Deposits ...

ISSN 0869-5938, Stratigraphy and Geological Correlation, 2018, Vol. 26, No. 1, pp. 80–108. © Pleiades Publishing, Ltd., 2018. Original Russian Text © N.K. Lebedeva, O.B. Kuz’mina, 2018, published in Stratigrafiya, Geologicheskaya Korrelyatsiya, 2018, Vol. 26, No. 1, pp. 85–114.

Palynostratigraphy of the Upper Cretaceous and Paleogene Deposits in the South of Western Siberia by Example of Russkaya Polyana Boreholes, Omsk Trough N. K. Lebedevaa, b, * and O. B. Kuz’minaa aTrofimuk

Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia b Novosibirsk State University, Novosibirsk, 630090 Russia *e-mail: [email protected] Received March 14, 2016; in final form, June 27, 2016

Abstract—The detailed study of Boreholes 8, 10, and 2 in the Russkaya Polyana district (Omsk Trough) made it possible to reveal the complex structure of the Upper Cretaceous sediments formed in unstable conditions of the marginal part of the Western Siberian basin. The Pokur, Kuznetsovo, Ipatovo, Slavgorod, and Gan’kino formations were subjected to palynological analysis and substantiation of their Late Cretaceous age. Eight biostratigraphic units with dinocysts and five units with spores and pollen from the Albian to the Maastrichtian were identified. The joint application of biostratigraphic and magnetostratigraphic methods made it possible to reveal the stratigraphic breaks in the studied sedimentary stratum and to estimate their scope. The age of the Lower Lyulinvor Subformation was specified in the marginal part of the Omsk Trough. The ingression traces of the Western Siberian basin in the Albian were found for the first time in the considered region. Keywords: biostratigraphy, Upper Cretaceous, Paleogene, Omsk Trough, south of Western Siberia, palynology, dinocysts DOI: 10.1134/S0869593818010069

tsovo, Ipatovo, Slavgorod, and Gan’kino formations using dinocysts, macrofauna, nannoplankton, spores, and pollen and to perform the paleomagnetic investigations (Gnibidenko et al., 2008, 2012; Lebedeva et al., 2013). The biostratigraphic data on the top of the section of Boreholes 8 and 10 (Maastrichtian–Lower Paleogene) were published in (Iakovleva et al., 2010, 2012; Aleksandrova et al., 2011). Recent years were marked by active studies of dinocysts in the Paleogene marine sediments developed in the considered part of the Omsk Trough, and paleomagnetic data were obtained (Akhmetiev et al., 2004, 2010; Iakovleva et al., 2010, 2011, 2012). Z.N. Gnibidenko et al. constructed the regional magnetostratigraphic section of the Upper Cretaceous deposits in the Omsk Trough on the basis of the comprehensive data (paleomagnetic, palynological, and paleontological) from the sections of Boreholes 8, 10, and 2 in the Russkaya Polyana district (Gnibidenko et al., 2013, 2015). The last two publications contained only brief palynological data making it possible to conduct the biostratigraphic correlation. The objective of this investigation is to study in detail the age of the Upper Cretaceous deposits in Boreholes 10 and 2 and Paleogene deposits in Bore-

INTRODUCTION The Upper Cretaceous sediments uncovered by three boreholes in the Russkaya Polyana district in Omsk oblast were studied for a number of years by paleontological (mostly palynological) and paleomagnetic methods. These areas were not previously subjected to drilling, and the obtained data made it possible to clarify for the first time the structure and biostratigraphy of the Upper Cretaceous sediments. The members of the Interdepartmental Stratigraphic Meeting (Novosibirsk, 2003) approved the improved regional stratigraphic schemes of the Mesozoic sediments in Western Siberia; however, no changes were made, relative to the previous versions, in the regional and correlative parts of the scheme of the Upper Cretaceous sediments in the southern area of Western Siberia (Reshenie…, 1991). The first palynological studies demonstrated the high potential for both the clarification of spore–pollen characteristics of this part of the Omsk-Lar’yak facies zone (Reshenie…, 1991) and the development of new scales based on dinocysts and paleomagnetic data. The most thoroughly studied Borehole 8 was involved to substantiate the age of the Pokur, Kuzne80

PALYNOSTRATIGRAPHY OF THE UPPER CRETACEOUS AND PALEOGENE DEPOSITS

hole 2 using the palynological data, to correlate the sections on the basis of dinoflagellate cysts (dinocysts), and to generalize the available data on biostratigraphy of the sections studied in the south of Western Siberia. MATERIALS AND METHODS Palynological and paleoalgological study of 47 samples in Borehole 10 and 46 samples in Borehole 2 was carried out. Microphytofossils were extracted from the rocks with the use of potassium pyrophosphate to remove clay particles and cadmium heavy liquid with a specific gravity of 2.25 in order to subdivide the sediment into mineral and organic parts. A glycerol-gelatinous medium was used as a basis for permanent preparations. Almost all samples contained a wide range of microphytofossils with satisfactory and good preservation. They included spores of mosses and ferns, pollen of gymnosperms and angiosperms, cysts of dinoflagellates (division Dinoflagellata), prasinophytes (division Chlorophyta, class Prasinophyceae), acritarchs (group with an unclear systematic position), and freshwater microscopic algae (division Chlorophyta, close to present-day Zygnemataceae). At least 200–300 specimens were used to calculate the quantitative participation of marine and terrestrial palynomorph taxa. The percentage of each taxon was calculated from the total amount of microphytofossils. The first occurrence, disappearance of taxa, and their percentage were taken into account in identification of biostratigraphic units based on dinocysts, spores, and pollen. The sections were compared on the basis of appearance or disappearance of the most stratigraphically important dinocyst genera and species. The collection of palynomorphs is stored in the Laboratory of Paleontology and Stratigraphy of the Mesozoic and Cenozoic, Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences (Novosibirsk). THE SECTION OF EARLY CRETACEOUS AND BASAL HORIZONS OF THE PALEOGENE SEDIMENTS UNCOVERED BY BOREHOLES 8, 10, AND 2 Boreholes 8, 10, and 2 are located in the Russkaya Polyana district in the southern wing of the Omsk Trough. In terms of geomorphology, they are drilled in the top of the gentle slope to Lake Kyzylkak (Fig. 1). Absolute marks: Borehole 8 is 128 m, Borehole 10 is 109.8 m, and Borehole 2 is 121 m. All three boreholes have uncovered terrigenous deposits of the sedimentary cover, reaching the Paleozoic basement, which is located at a depth of 593 m in Borehole 8, 524.6 m in Borehole 10, and 441.2 m in Borehole 2. The Upper Cretaceous deposits represented by the Pokur, Kuznetsovo, Ipatovo, Slavgorod, and Gan’kino formations are overlapped by Cenozoic sediments. STRATIGRAPHY AND GEOLOGICAL CORRELATION

81

Having compared the geophysical well logging (WL) data and the factual lithological description of the core in Borehole 10, we established a 13-m core shift in the boundary sediments of the Ipatovo and Slavgorod formations (Fig. 2). In this connection, the depth values will be indicated using the WL data. Such inconsistency was not noted in Boreholes 8 and 2. The detailed description of Borehole 8 was published earlier (Lebedeva et al., 2013); therefore, below we report the data on Boreholes 10 and 2 and the available specific structural features of the considered formations in all three boreholes. Pokur Formation. Borehole 8 (interval 593–408 m, apparent thickness 185 m); Borehole 10 (interval 522– 368.2 m, apparent thickness 153.8 m); and Borehole 2 (interval 441.2–349 m, apparent thickness 92.2 m). This formation is composed of alternating gray and brownish gray sands, from fine- to coarse-grained, occasionally with abundant coalified plant detritus; variably grained silty and clayey sandstones; gravelstones and conglomerates with clay cement, moderately and slightly cemented; gray, variegated, compact clays with plant remains; brown claystone, gray brickred siltstone, variably sandy. The content of clay, claystone, and siltstone is much higher in Borehole 8 (Pokur Formation), especially at the bottom, than in Boreholes 10 and 2, where the Pokur Formation consists of coarse-grained rocks. Kuznetsovo Formation. Borehole 8 (interval 408– 380 m, thickness 28 m); Borehole 10 (interval 368.2– 360.6 m, thickness 7.6 m); and borehole 2 (interval 348.6–330.4 m, thickness 18.2 m). The base of the formation in Borehole 10 consists of thin gravelstone interbed (0.1 m). Upward, clays are gray, dark gray, silty to sandy, compact, with plant remains, with a thickness of 6 m in Borehole 10 and 5 m in Borehole 2. Clays are overlapped by gray, greenish gray, variably grained sandstone with a thickness of 1.5 m in Borehole 10 and gray variably grained clayey sand with a thickness of 13.2 m in Borehole 2. Ipatovo Formation. Borehole 8 (interval 380–343 m, thickness 37 m); Borehole 10 (interval 360.6–336.2 m, thickness 24.4 m); and Borehole 2 (interval 330.4– 320.4 m, thickness 10 m). In Borehole 10, the base of the formation is composed of a member of gravelstones and coarse-grained gray sandstones with a thickness of 13.35 m. The upper layer is characterized by alternating variably grained sand and sandstone, quartz–glauconite sand, and gravelstone. The rocks are gray, dark gray, and greenish gray in color. In Borehole 2, the Ipatovo Formation is composed of gray sand, from fine- to coarse-grained, occasionally, clayey with gray sandy micaceous silt interbeds. In Borehole 8, the Ipatovo Formation is thicker and consists of thinner sediments represented by alternating sand, silt, and clay. Slavgorod Formation. Borehole 8 (interval 343– 311.2 m, thickness 31.8 m); Borehole 10 (interval Vol. 26

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LEBEDEVA, KUZ’MINA

Ket’

Tobolsk

Irt

lym

u Ch

ys h

55°

Ishim

Tomsk

Barabinsk

Novosibirsk

Omsk Ob Biya Pavlodar

50°

tu Ka

ysh

n

Irt

70°

75°

Boundary between Russia and Kazakhstan Location of studied sections 0

85°

80°

5

Russkaya Polyana

10 km

53°40′

Borehole 8 Borehole 10 Borehole 2 Ag y

nsa

73°31′

i Cr .

Lake Kyzylkak

74°00′

Fig. 1. Location of the Russkaya Polyana boreholes. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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336.2–276.2 m, thickness 60 m); and Borehole 2 (interval 320.4–266.9 m, thickness 53.5 m). It is composed of dark gray, sandy, opoka-like clay with gravel of different composition and size, and dark gray, clayey, indistinctly laminated silt. The Slavgorod Formation is the thinnest in the section of Borehole 8. Gan’kino Formation. Borehole 8 (interval 311.2– 273 m, thickness 38.2 m); Borehole 10 (interval 276.2–258.35 m, thickness 17.85 m); and Borehole 2 (interval 266.9–246 m, thickness 20.9 m). It is composed of alternating gray and greenish gray clayey siltstone and grayish green fine-grained quartz-glauconite sands. The Upper Cretaceous sediments in Boreholes 2, 8, and 10 are overlapped by the Paleogene deposits represented by the Talitsa Formation and Lower Lyulinvor Subformation. Talitsa Formation is uncovered only in Borehole 8. Its lithological and paleontological characteristics are published in (Iakovleva et al., 2011, 2012). Lyulinvor Formation, Lower Lyulinvor Subformation. In Boreholes 2 and 10, the Paleogene base consists of the Lower Lyulinvor Subformation of the Lyulinvor Formation. In Borehole 10, the subformation is dated to the early Thanetian (Akhmetiev et al., 2010; Aleksandrova et al., 2011; Iakovleva et al., 2011, 2012). The cited works also describe this lithostratigraphic unit and overlying Paleogene sediments in Boreholes 8 and 10. In Borehole 2, the Lower Lyulinvor Subformation is uncovered in the interval of 246–220.4 m and has a visible thickness of 25.6 m. It is composed of clayey glauconite sand (interval 246–243.75 m), interstratified sandy clay and glauconite sand (interval 243.75–237.7 m), gray uniform opoka (interval 237.7– 222.5 m), gray compact clay (interval 222.5–220.7 m), and gray uniform opoka (interval 220.7–220.4 m). PALYNOLOGICAL CHARACTERIZATION Layers with Dinocysts In Borehole 8, the marine microphytoplankton appears at a depth of 412 m; in Borehole 10, it appears at a depth of 369 m (Fig. 2). In Borehole 2, the dinocyst assemblage was found in the Pokur Formation in the interval of 367.6–362.65 m. Above, the mass appearance of microphytoplankton was recorded at a depth of 346.5 m (Fig. 3). Local zone Cepadinium subtile–Palaeoperidinium cretaceum. Borehole 2 (interval 367.6–362.65 m). Middle part of the Pokur Formation. The lower and upper boundaries are determined, respectively, by appearance and disappearance of the dinocyst assemblage of these layers. Present: Cepadinium subtile, Chlamydophorella nyei, Palaeoperidinium cretaceum, Pseudoceratium sp., Alterbidinium spp., Canningia sp., and Systematophora sp. Despite a small set of taxa, this assemblage is very representative. It is most similar to the dinocyst assemSTRATIGRAPHY AND GEOLOGICAL CORRELATION

83

blages found in the Khanty-Mansiysk Formation in Borehole Sogom 1 (Savchenkova, 2004) and dated to the early Albian on the basis of the foraminifera assemblage (Zakharov et al., 2000). Yu.I. Gogin identified the dinocyst assemblage in eleven boreholes in the EmYega and Tallin areas and compared it with the Sogom assemblage (Gogin, 2010). According to Gogin (2010), most identified taxa have a wide stratigraphic distribution range, complicating the correlation with the Albian assemblages described in the literature, but the general taxonomic composition is indicative of the Albian age of the considered sediments. The composition of dinocysts from the Pokur Formation in Borehole 2 is the most uniform, but the combination of key taxa coincides in all compared assemblages. The early Albian dating of the Sogom foraminifera assemblages is extremely important in this case; however, judging by the stratigraphic distribution of most dinocyst taxa, their age may be wider. Therefore, only the Albian age of the host sediments can be assumed in this case. Stratigraphic interval: Albian. Local zone Eurydinium saxonianse. Borehole 10 (depth 369 m); Borehole 2 (interval 346.5–344 m). Lower part of the Kuznetsovo Formation. The lower boundary is defined by appearance of the dinocyst assemblage in the section. Present: Eurydinium sp., E. saxoniense, Chlonoviella agapica, Pterodinium cingulatum, Rhiptocorys veligera, Trithyrodinium suspectum, Odontochitina operculata, Alterbidinium spp., Kallosphaeridium ?ringnesiorum, Alterbidinium “daveyi,” and Microdinium sp. All listed taxa, except for the index species, are characterized by a wide distribution range. Meanwhile, the joint presence of Eurydinium sp., E. saxoniense, Chlonoviella agapica, Pterodinium cingulatum, Alterbidinium “daveyi,” Rhiptocorys veligera, and Odontochitina operculata and the absence of dinocysts, pointing to a younger age, in Boreholes 10 and 2 can be indicative of age analogs of the layers with Chlamydophorella nyei–Chlonoviella agapica identified in the Ust’-Yenisei district (Lower Agapa River) at the top of the Inoceramus pictus Zone (upper Cenomanian), in the Inoceramus (Mytiloides) labiatus Zone (lower Turonian), and in the Inoceramus (Inoceramus) cf. cuvieri Zone (middle Turonian) (Lebedeva, 2006b, 2007). However, in the Lower Agapa section, the layers with Chlamydophorella nyei–Chlonoviella agapica are distinguished by a considerable thickness (about 50 m) and are dated largely to the lower and middle Turnoian. This very stratigraphic interval is likely observed in Boreholes 2 and 10. The indirect proof of this suggestion is the absence of the characteristic Cenomanian taxa in the layer assemblage with Eurydinium saxoniense. Anyway, at present, there are no compelling reasons for redating the base of the Kuznetsovo Formation with allowance for dinocysts, which was found in the Omsk-Lar’yak facies district in the lower Turonian (Reshenie…, 1991). Vol. 26

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400

402.5

410

Albian

Cenomanian Pokur 380 390 370

Turonian Kuznetsovo

Coniacian–Santonian Ipatovo 350 360 340

26–29

290

?

318.3

318.3

323.45 16 328.1 15 328.1 14 332.75 13 332.75 337.4 337.4 12 342.05 11 346.7 10

351.35 356 360.05 360.05 365.3 365.3 369.9 369.9 374.6

379.25

383.9

402.5 411.8 18–20

Core shift 13 m

320

Samples Kallosphaeridium ?ringnesiorum Chlonoviella agapica Rhiptocorys veligera Trithyrodinium suspectum Fromea amphora Odontochitina operculata Microdinium sp. Eurydinium saxoniense Alterbidinium “daveyi” Alterbidinium sp. Alterbidinium minus Dorocysta litotes Subtilisphaera sp. Geiselodinium cenomanicum Kallosphaeridium circulare Glyphanodinium facetum Cribroperidinium exilicristatum Fromea chytra Heterosphaeridium difficile Palaeohystrichophora infusorioides Dorocysta sp. A Microdinium ornatum Eisenackia sp. Surculosphaeridium longifurcatum Spiniferites ramosus Chatangiella spectabilis Laciniadinium sp. Isabelidinium cooksoniae Leberidocysta chlamydata Fromea laevigata Chatangiella sp. Chatangiella granulifera Chatangiella tripartita Chatangiella vnigrii Achomosphaera sp. Spinidinium sp. Exochosphaeridium sp. Fromea sp.A Isabelidinium thomasii Chatangiella bondarenkoi Chatangiella serratula Chatangiella chetiensis Chatangiella victoriensis Alterbidinium acutulum Oligosphaeridium complex Isabelidinium magnum Chlamydophorella nyei Cyclonephelium/Circulodinium Alisogymnium euclaense Dinogymnium nelsoniense Dinogymnium sp.

Interval, m

Lithological characteristic

Maastrichtian T Stage Gan’kino L Formation 280 270 260 Depth, m

263.0 263.0 267.65 267.65 272.3

7–9

330

Campanian Slavgorod 310 300

84 LEBEDEVA, KUZ’MINA

258.35

46 45 47

44 43

42 276.95 41 40 39 281.6 38 286.25 37 36

291.25

35 34 33 296.25 32 31 302.85 30 302.85 309.50 309.50 25 23 314.15 22

21

6

5

4 3

388.55 393.2

397.85

2

Fig. 2. Dinocyst distribution in the Borehole 10 section in the Russkaya Polyana district. (1) Clay; (2) silt; (3) sand; (4) sandstone; (5) gravelstone; (6) opoka; (7) break; (8) no data; (9) shell detritus. Abbreviations: (T) Thanetian; (L) Lyulinvor; (E.s.) Eurydinium saxoniense; and (H.d.–Ch.s.) Heterosphaeridium difficile–Chatangiella spectabilis.

STRATIGRAPHY AND GEOLOGICAL CORRELATION

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400

402.5

410

Albian


7–9

Turonian Kuznetsovo

Coniacian–Santonian Ipatovo 360 350 340

42 276.95 41 40 39 281.6 38 286.25 37 36 291.25 35 34 33 296.25 32 31 302.85 30 302.85 309.50 309.50 25 23 314.15 22

318.3

318.3

402.5 411.8

1 Chatangiella manumii–Dinogymnium spp.

26–29

290

?

323.45 16 15 328.1 328.1 14 332.75 13 332.75 337.4 337.4 12 342.05 11 346.7 10 18–20

Core shift 13 m

320

47

46 45 44 43

Cerodinium diebelii

351.35 356 360.05 360.05 365.3 365.3 369.9 6 369.9 374.6 5 379.25 4 383.9 3

2

3

4


5

Vol. 26

6

No. 1

7

Fig. 2. (Contd.)

2018

8

Dinocyst local zones

Samples Dinogymnium alberti Dinogymnium sibiricum Odontochitina costata Dinogymnium longicorne Dinogymnium heterocostatum Dinogymnium digitum Dinogymnium acuminatum Alisogymnium sphaerocephalum Laciniadinium arcticum Chatangiella manumii Dinogymnium digitum crassum Microdinium kustanaicum Senoniasphaera protrusa Gillinia hymenophora Cladopyxidium reticulatum Isabelidinium sp. Isabelidinium belfastense Senoniasphaera rotundata Laciniadinium rhombiforme Phellodinium sp. Rhiptocorys sp. Trithyrodinium quingueangulare Leberidocysta chlamydata Trigonopyxidia ginella Spongodinium delitiense Xenikoon sp. Pterodinium cingulatum Pulchrasphaera minuscula Cladopyxidium sp. Areoligera senonensis Membranilarnax liradiscoides Laciniadinium firmum Cerodinium diebelii Spinidinium uncinatum Isabelidinium rectangulatum Palaeotetradinium silicorum Fromea fragilis Hystrichosphaeridium tubiferum Leptodinium sp. Rottnestia borussica Pervosphaeridium monasteriense Isabelidinium bakerii Florentinia sp. Phanerodinium cf. squamosum Phanerodinium cayeuxi Achomosphaera ramulifera Chatangiella madura Phanerodinium sp. Coronifera oceanica

Interval, m


Maastrichtian T Stage L Formation Gan’kino 280 270 260 Depth, m

263.0 263.0 267.65 267.65 272.3

Chatangiella spp.

330

Campanian Slavgorod 310 300

PALYNOSTRATIGRAPHY OF THE UPPER CRETACEOUS AND PALEOGENE DEPOSITS 85

258.35

?

H. d.– Ch. s. E. s.

Palynomorph content: 0–5% 5–10% >10% ?

388.55 393.2

397.85

2

9

Albian

Pokur

370

Kuznetsovo

Turonian

310

290

Slavgorod

Campanian

270

250

Gan’kino

Maastrichtian

255.95

240 230

Lyulinvor

Thanetian

238.0 50 49

243.65

48 47 46 45 44 43 42 41

248.3 251.3

265.3

269.9

274.6

297.85

302.5

307.15

311.8

316.45

321.1

325.75

330.4

335.05

344.35

353.65

358.3 8–11

330

Ipatovo

Coniacian– Santonian

246

4–7

350

Cenomanian

220.4 53 52

225.05 51

362.95 367.6

3 2

380.0 384.65

1

Laciniadinium sp. Alterbidinium acutulum Isabelidinium magnum Dorocysta sp. A Chatangiella spectabilis Spiniferites ramosus Trithyrodinium suspectum Oligosphaeridium complex Leberidocysta chlamydata Spinidinium sp. ?Canningia macroreticulata Chatangiella vnigrii Chatangiella bondarenkoi Eisenackia sp. Dinogymnium sp. Chatangiella chetiensis Isabelidinium spp. Dinogymnium alberti Chatangiella manumii Alisogymnium sp.

Surculosphaeridium longifurcatum

Chlamydophorella nyei Cepadinium sp. Palaeoperidinium cretaceum Pseudoceratium sp. Alterbidinium sp. Canningia sp. Systematophora sp. Alterbidinium minus Kallosphaeridium ?ringnesiorum Chlonoviella agapica Alterbidinium “davey” Microdinium sp. Rhiptocorys veligera Kallosphaeridium ?circulare Pterodinium cingulatum Cyclonephelium/Circulodinium Dorocysta litotes Microdinium ornatum Eurydinium saxoniense Fromea chytra Odontochitina operculata Chatangiella sp. Heterosphaeridium difficile Glyphanodinium facetum

Samples

Interval, m


220 Depth, m

Formation

Stage


229.7

234.35

260.25 39

38 37 36 35 34 33 32 31

279.25

283.9 29

293.2

28

27 26 25 24 23

22 21 20 19 18

17 16 15

14

339.7 13

12

349.0

Fig. 3. Dinocyst distribution in the Borehole 2 section in the Russkaya Polyana district. For legend, see Fig. 2. Abbreviations: (C.s.–P.c.) Cepadinium subtile–Palaeoperidinium cretaceum, (C.s.) Cerodinium speciosum, and (Apect. hyp.) Apectodinium hyperacanthum.


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350

Cenomanian

353.65

358.3 4–7

Pokur

370

Albian Kuznetsovo

Turonian

310 290

Slavgorod

Campanian

270 250

Gan’kino

Maastrichtian

246

248.3 251.3

255.95

265.3

269.9

274.6

297.85

302.5

307.15

311.8

316.45

321.1

325.75

330.4

335.05

344.35

349.0 8–11

330

Ipatovo


240 230

Lyulinvor

Thanetian

220.4 53 52

225.05 51

238.0 50 49

243.65

48 47 46 45 44 43 42 41

362.95 367.6

3 2

Isabelidinium microarmum Isabelidinium belfastense Laciniadinium rhombiforme Fromea laevigata Palaeotetradinium silicorum Dinogymnium acuminatum Alisogymnium euclaense Biconidinium reductum Cladopyxidium reticulatum Rhiptocorys sp. Senoniasphaera rotundata Amphigymnium mitratum Palaeocystodinium sp. Microdinium kustanaicum Alterbidinium varium Xenikoon sp. Leberidocysta deflocata Pulchrasphaera minuscula Trithyrodinium quingueangulare Isabelidinium rectangulatum Triblastula utinensis Laciniadinium firmum Cerodinium diebellii Laciniadinium arcticum Membranilarnacia hapala Cerodinium sp. Cerodinium speciosum Areoligera senonensis Hystrichosphaeridium tubiferum Achomosphaera sp. Areoligera coronata Cribroperidinium sp. Deflandrea denticulata Deflandrea oebisfeldensis Dinogymnium sibiricum Kallosphaeridium sp. Polygonium sp. Spiniferites sp. Spiniferites ramosus granosus Palaeocystodinium golzovense Areoligera sp. Cerodinium markovae Alisocysta margarita. Senegalinium sp. Areoligera gippingensis

Samples

Interval, m


220 Depth, m

Formation

Stage


229.7

234.35

260.25 39

38 37 36 35 34 33 32 31

279.25

283.9 29

293.2

28

27 26 25 24 23

22 21 20 19 18

17 16 15

14

339.7 13

12

380.0 384.65 1

Fig. 3. (Contd.)


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87

Pokur

370

Albian 350

Cenomanian Kuznetsovo 270

250

Gan’kino 240

51

229.7

234.35

255.95

238.0 50 49

243.65

48 47 46 45 44 43 42 41

265.3

269.9

274.6

297.85

302.5

307.15

311.8

316.45

321.1

325.75

330.4

335.05

344.35

349.0

353.65

358.3

362.95 367.6

380.0 384.65

Alisocysta margarita

Formation

Stage

38 37 36 35 34 33 32 31

279.25

283.9 29

293.2

28

27 26 25 24 23

17 16 15

339.7 13

3 2


Dinocyst local zones

Prazinophyta Acritarchs Zygnemataceae Paralecaniella Microforaminifera Hydropteris indutus Tetraporina horologia Pterospermella sp. Paucilobimorpha sp. Botryococcus

Cerodinium leptodermum Cleistosphaeridium spp. Eocladopyxis sp. Cladopyxidium septum Apectodinium homomorphum Apectodinium hyperacanthum Achomosphaera ramulifera Tectatodinium pellitum Glaphyrocysta sp. Cordosphaeridium fibrospinosum Operculodinium eisenakii Adnatosphaeridium sp.

Melitasphaeridium pseudorecurvatum

Samples Caligodinium aceras Caligodinium spp. Cordosphaeridium gracile Cordosphaeridium inodes Deflandrea sp.

Interval, m


220 Depth, m

225.05

Cerodinium diebelii

230

Lyulinvor

Thanetian

53 52

Chatangiella manumii–Dinogymnium spp.

290

Slavgorod

Maastrichtian

220.4

Chatangiella spp.

310

Campanian

248.3 251.3

8–11

330

Ipatovo


246

E. s.

4–7

Turonian


Apect. hyp.

C. s.

260.25 39

?

Vol. 26

?

22 21 20 19 18

14

H. d.– Ch. s.

12

C. s.– P. c.

?

1

Fig. 3. (Contd.)

No. 1

2018


Owing to poor diversity of the dinocysts, more accurate dating of this part of the Kuznetsovo Formation is impossible. The dinocyst assemblage was not found in Borehole 8. Stratigraphic interval: lower–middle Turonian. Local zone Heterosphaeridium difficile–Chatangiella spectabilis. Borehole 8 (interval 407–380 m); Borehole 10 (interval 365.3–360 m); Borehole 2 (interval 342–331.2 m). Upper part of the Kuznetsovo Formation. The lower boundary is defined by the appearance of Chatangiella spp. (Plate I) and Heterosphaeridium difficile. The greatest diversity of dinocysts is characteristic of Borehole 8. Characteristic taxa: Chatangiella spp., Ch. spectabilis, Heterosphaeridium difficile, Alterbidinium spp., Dorocysta sp. А, Dorocysta litotes, Surculosphaeridium longifurcatum, Subtilisphaera sp. Sporadic occurrence: Eurydinium sp., E. saxoniense, Isabelidinium magnum, Odontochitina spp., Laciniadinium sp., Leberidocysta sp., Chatangiella serratula, etc. Species Heterosphaeridium difficile in the Northern Hemisphere is characteristic of the upper Turonian– lower Santonian (Williams et al., 1993). Occurrence of this species in the lower Turonian is traced thoroughly in the Northwestern Europe (Davey and Verdier, 1971; Foucher, 1981; Tocher and Jarvis, 1987; Costa and Davey, 1992; Olde et al., 2015; etc.). Acme of Heterosphaeridium difficile was recorded in the middle– upper Turonian in the Banterwick Barn Borehole in Berkshire, England (Pearce et al., 2003), and in the middle Turonian of the Bohemian Cretaceous basin, Czech Republic (Olde et al., 2015). The Heterosphaeridium difficile Zone was identified in the northeast of Greenland (Nøhr-Hansen, 2012), in the southwestern part of the Barents Sea shelf (Radmacher et al., 2014), and in a borehole drilled in the Norwegian Sea (Radmacher et al., 2015), in the Turonian– lower Coniacian, with the key taxa Heterosphaeridium difficile and Chatangiella sp. Numerous Heterosphaeridium difficile and Surculosphaeridium longifurcatum were found in the Coniacian layers with Canningia macroreticulata in the Seida River section, Polar Cis-Ural Region (Lebedeva, 2005, 2006а) and in the Santonian layers with Surculosphaeridium longifurcatum–Heterosphaeridium difficile in the boreholes of the Gremyach’e deposit in the south of the Volgograd Right Bank (Aleksandrova et al., 2012). Meanwhile, the specified species have been found with other taxa, relative to the abovedescribed assemblage: with different species belonging to genera Chatangiella, Spinidinium, Isabelidinium, etc. Hence, the mentioned biostratigraphic units can be justifiably dated to a younger age. The dinocyst assemblage including Heterosphaeridium difficile, Dorocysta sp. А, Dorocysta litotes, Surculosphaeridium longifurcatum, Subtilisphaera sp., Eurydinium sp., E. saxoniense, Isabelidinium magnum, STRATIGRAPHY AND GEOLOGICAL CORRELATION

89

and Odontochitina spp. is typical of the Kuznetsovo Formation of Western Siberia (Lebedeva, 2006b). This very dinocyst assemblage dated to the early Turonian on the basis of the foraminifera fauna was identified by G.N. Aleksandrova (Aleksandrova et al., 2010) in two boreholes drilled in the southern part of the Var’egan megaswell. However, it did not include the representatives of genus Chatangiella, characteristic of the layers with Chatangiella spectabilis–Heterosphaeridium difficile found in the Boreholes Yuzhno-Russkaya 113 and Berezovskaya 23k (Aleksandrova et al., 2010). The biostratigraphic unit Heterosphaeridium difficile–Chatangiella spectabilis is the most consistent with the local zone Chatangiella spectabilis–Oligosphaeridium pulcherrimum and the layers with Chatangiella bondarenkoi–Pierceites pentagonus in the Ust’Yenisei section (In. (In.) lamarckii and Volviceramus inaequalis zones, middle–upper Turonian) (Lebedeva et al., 2004, 2013; Lebedeva, 2006b). It should only be noted that dinocysts in the Omsk Trough boreholes are marked by a considerably less diverse composition. Stratigraphic interval: middle–upper Turonian. Local zone Chatangiella spp. Borehole 8 (interval 372.1–343 m); Borehole 10 (interval 346.7– 323.45 m); Borehole 2 (interval 328.4–322 m). Ipatovo Formation. The poorest dinocyst assemblage was found in the Ipatovo Formation in Borehole 8. In Boreholes 10 and 2, the more diverse microphytoplankton composition makes it possible to justify more reliably the age of uncovered deposits. The layer basement: Isabelidinium cooksoniae, I. thomasii, diverse Chatangiella: Ch. granulifera, Ch. tripartita, Ch. vnigrii, Ch. bondarenkoi, Ch. chetiensis, and Ch. victoriensis. Absent: Pterodinium cingulatum, Dorocysta sp. А, D. litotes, Eurydinium sp., E. saxoniense, and Surculosphaeridium longifurcatum. Despite the insignificant number and diversity of dinocysts, the considered section interval is distinguished by much higher content and number of species belonging to the genera Isabelidinium and Chatangiella, characteristic of Coniacian–Santonian sediments of Western Siberia (Lebedeva, 2001, 2006b). Rare Canningia macroreticulata has been identified for now only in the upper Coniacian–lower Santonian sediments (Lebedeva, 2005, 2006b; Aleksandrova et al., 2012). However, its real distribution range is still unclear. The poor taxonomic composition of the dinocysts suggests only the broad Coniacian–Santonian age range of the studied sediments. Stratigraphic interval: Coniacian–Santonian. Local zone Chatangiella manumii–Dinogymnium spp. Borehole 8 (interval 339.9–311.2 m); Borehole 10 (interval 323.45–281.6 m); and Borehole 2 (interval Vol. 26

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90


319–256.6 m). The Slavgorod Formation–lower part of the Gan’kino Formation. In order to unify the layer nomenclature, all biostratigraphic units corresponding to the Slavgorod Formation–lower part of the Gan’kino Formation in Boreholes 2, 8, 10 and having different names (Lebedeva et al., 2013; Gnibidenko et al., 2014) have been renamed to the layers with Chatangiella manumii– Dinogymnium spp. The lower boundary is found by occurrence of diverse Dinogymnium and Chatangiella manumii. This assemblage is characterized by permanent presence of numerous species of the genus Dinogymnium: D. albertii, D. nelsonense, D. sibiricum, D. longicorne, D. heterocostatum, D. digitus, etc. (Figs. 2, 4). Chatangiella manumii and Ch. vnigrii are present. The species of Chatangiella are diverse. At the top of the Slavgorod Formation in Boreholes 10 and 2, there are Gillinia hymenophora, Cladopyxidium reticulatum, Microdinium kustanaicum, Isabelidinium spp., I. belfastense, Trithyrodinium quingueangulare, etc. The geography and stratigraphic significance of the Dinogymnium representatives in the Late Cretaceous have not been studied in detail yet. Having appeared in the Turonian, this genus reached the greatest diversity in the Campanian. According to the analysis of the data on the Dinogymnium spatial distribution, a large number of species are observed in relatively warm water conditions in the southern part of the Western Siberian basin and the Atlantic coast of North America (Fig. 5). Meanwhile, the Dinogymnium representatives were not identified in the Campanian sediments uncovered by Borehole 15 in the Northern Kura area (Kuzmina et al., 2003). This genus is rare in the Arctic regions. Numerous findings of these algae are related by some authors to specific features of the habitat conditions. Dinogymnium is predominant at low diversity of phytoplankton at the top of the New Jersey Campanian sediments (May, 1980). May believes that the specific features of the genus morphology such as channels in the walls and corrugated structure can serve to prevent cell damage by change in its volume under extreme salinity fluctuations in the estuarine or coastal–marine environments. G.N. Aleksandrova

(Aleksandrova et al., 2012) suggests that the sediments uncovered by boreholes in the Gremyach’e district of the Lower Volga Region, dominated by Dinogymnium in combination with a large amount of amorphous organic matter and enrichment in Corg, are related to the middle Campanian OAE (Ocean Anoxic Event). These sediments are dated to the middle Campanian on the basis of foraminifera and radiolarians (Aleksandrova et al., 2012). The upper Campanian section in Saratov oblast (Middle Volga Region) contains the dinocyst assemblage with Chatangiella manumii, Chatangiella vnigrii, and numerous Dinogymnium (Pervushov et al., 2015), thus being similar to the Omsk Trough assemblage, but the latter is less diverse and is relatively depleted in chorate forms. The Saratov sediments of the Volga Region are dated on the basis of ammonites, belemnites, and benthic and planktonic foraminifers. The Kheta River section (Khatanga district) contains three biostratigraphic units with dinocysts, two of which correspond to the Sphenoceramus patootensiformis Zone defining the boundary Santonian–Campanian age of the sediments (Khomentovskii et al., 1999). The overlying layers with Chatangiella niiga with characteristic taxa such as Chatangiella manumii, Ch. spinata, Ch. madura, Ch. biapertura, Dinogymnium sibiricum, Spinidinium sp., and Laciniadinium sp. are compared to the layers with Chatangiella manumii– Dinogymnium spp. from Boreholes 2, 8, and 10, despite differences in the composition of the dinocysts related to their provincialism. This fact is indicative of possible interruption at the Santonian–Campanian boundary. The poor dinocyst composition and the leading role of the Dinogymnium representatives in the assemblage in the Slavgorod and lower part of the Gan’kino formations are likely caused by peculiarities of the coastal–marine habitats. Despite the evidence for the fact that, in the studied boreholes, the Campanian can be represented by the middle and, partially, by the upper divisions, the low diversity of dinocysts in this interval of the section impedes dating of the considered sediments. However, on the basis of the paleomagnetic data, a significant

Plate I. Palynomorphs from the Upper Cretaceous sediments of Borehole 10 in the Russkaya Polyana district. Magnification is shown in microns (μm). (1) Chatangiella granulifera, depth 271.3 m, Sample 43, prep. 2951.1; (2) Chatangiella tripartita, depth 262.3 m, Sample 47, prep. 2955.1; (3) Isabelidinium microarmum, depth 276.01 m, Sample 41, prep. 2949.3; (4) Isabelidinium belfastense, depth 276.01 m, Sample 41, prep. 22949.4; (5) Alterbidinium “daveyi,” depth 271.3 m, Sample 43, prep. 2951.3; (6) Senoniasphaera protrusa, depth 280.6 m, Sample 38, prep. 2940.1; (7) Senoniasphaera rotundata, depth 280.6 m, Sample 38, prep. 2940.2; (8, 9) Alterbidinium acutulum: (8) depth 276.01 m, Sample 41, prep. 2949.5; (9) depth 271.3 m, Sample 43, prep. 2951.2; (10) Laciniadinium rhombiforme, depth 271.3 m, Sample 43, prep. 2951.3; (11) Fromea amphora, depth 364.9 m, Sample 7, prep. 2911.2; (12) Fromea ?laevigata, depth 273.65 m, Sample 42, prep. 2950.3; (13) Fromea fragilis, depth 262.3 m, Sample 47, prep. 2955.1; (14) Fromea chytra, depth 276.01 m, Sample 41, prep. 2949.3; (15) Trithyrodinium quingueangulare, depth 266.65 m, Sample 45, prep. 2953.2; (16, 17) Trithyrodinium suspectum, depth 324 m, Sample 16, prep. 2922; (18, 19) Cribroperidinium exilicristatum, depth 266.65 m, Sample 45, prep. 2953.3; (20) Circulodinium distinctum, depth 262.3 m, Sample 47, prep. 2955.3; (21) Cordosphaeridium sp., depth 262.3 m, Sample 47, prep. 2955.3; (22, 23) Spiniferites ramosus, depth 273.65 m, Sample 42, prep. 2950.2. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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91

Plate I

20

20

1

20

6

50

2

20

3

20

20

7

20

4

8

20

9

5

20

10

14

20

20

20

11

20

16

20

20

20

12

20

20

13

20

17

21


20

18

20

Vol. 26

22

No. 1

2018

15

20

20

19

23

400


7–9

Turonian Kuzne tsovo

Coniacian–Santonian Ipatovo 350 340 360 330

26–29

290

280

Moss and fern spores

318.3

402.5

402.5 411.8

Samples Leiotriletes spp. Cyathidites spp. Cyathidites minor Gleicheniidites spp. Gleicheniidites senonicus Plicifera delicata Ornamentifera echinata Laevigatosporites ovatus Cicatricosisporites spp. Cicatricosisporites minutaestriatus Cicatricosisporites pacificus Cicatricosisporites cuneiformis Cicatricosisporites auritus Cicatricosisporites mtchedlishviliae Matonisporits sp. Todisporites minor Stereisporites spp. Lophotriletes babsae Taurocusporites reduncus Rouseisporites reticulatus Rouseisporites laevigatus Klukisporites spp. Foraminisporis dailyi Concavisporites jurienensis Dictyophyllidites sp. Trilobosporites spp. Undulatisporites sp. Concavissimisporites punctatus Eboraciasporites sp. Aequitriradites verrucosus Leptolepidites verrucatus Lygodiumsporites japoniciformis Kuylisporites lunaris Balmeisporites glenelgensis Camarozonosporites insignis Ruminatisporites delicatus Leptolepidites sp. Densoisporites microrugulatus Clavifera rudis Clavifera sp. Osmundacidites sp. Foveosporites sp. Lycopodiumsporites sp. Appendicisporites unicus Appendicisporites matesovae Cicatricosisporites minor Cicatricosisporites stoveri Distaltiangularisporites sp. Trilites hebetatus Foveosporites cenomanicus Ruffordia aralica

Interval, m


Stage Maastrichtian Gan’kino Formation 270 260 Depth, m

263.0 263.0 267.65 267.65 272.3

323.45 16 328.1 15 328.1 14 332.75 13 332.75 337.4 337.4 12 342.05 11 346.7 10 18–20

Core shift 13 m

320

Campanian Slavgorod 300 310 ?

410

Albian


258.35

46 45 47

44 43

42 276.95 41 40 39 281.6 38 286.25 37

291.25

35 34 33 296.25 32 31 302.85 30 302.85 309.50 309.50 25 23 314.15 22

318.3

351.35 356 360.05 360.05 365.3 365.3 369.9 6 369.9 374.6 5 379.25 4 383.9 3

388.55 393.2

397.85

2

Fig. 4. Distribution of characteristic taxa of spores and pollen of the terrestrial plants in borehole 10 in the Russkaya Polyana district. For legend, see Fig. 2.


Vol. 26

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400

Cenomanian Pokur 380 390

PA II

370 7–9

Kuzne tsovo

360

Ipatovo 350 18–20

16 15 14 13

12

PA III

330

340

Turonian Coniacian–Santonian

320 35 34 33 32 31 30

25 23 22

PA IV

26–29

Campanian Slavgorod 310 300 290 280

?

410

Albian

46 45

44 43

PA V

Gymnosperm pollen


Vol. 26

Cedripites spp. Cedripites parvisaccatus Alisporites spp. Alisporites grandis Pinuspollenites spp. Pinuspollenites minimus Podocarpidites spp. Taxodiaceaepollenites hiatus Ginkgocycadophytus spp. Eucommiidites sp. Cedrus cristata Phyllocladidites spp. Ephedripites costatus Rugubivesiculites spp. Classopollis sp. Gnetaceapollenites sp.

2

Fig. 4. (Contd.)

No. 1

2018

Layers with spores and pollen

Tricolpites spp. Retitricolpites spp. Tricolpites sagax Menispermum turonicum Trudopollis spp. Triporopollenites plicoides Kuprianopollis spp. Nyssapollenites sp. Pseudovacuopollis sp. Tricolpopollenites sp. Aquilapollenites spp. Triorites harrisii Vacuopollis spp. Oculopollis spp. Normapolles Trudopollis protrudens Tricolporopollenites sp. Aquilapollenites quadrilobus Mancicorpus spp. Plicapollis serta Myricaceae Liliacidites sp. Proteacidites spp. Beaupreadites elegansiformis Aquilapollenites dispositus Wodehousea sp. Cranwellia striata

Moss and fern spores

Polypodiaceae Velosporites sp. Appendicisporites sp. Neoraistrickia sp. Lophotriletes babsae Ornamentifera sp. Foraminisporis asymmetricus Hemitelia separata Matonia parva Cingulatisporites sp. Stenozonotriletes radiatus Reticulasporites sp. Clavifera triplex Baculatisporites comaumensis

Samples

Maastrichtian Stage Gan’kino Formation 270 260 Depth, m

PALYNOSTRATIGRAPHY OF THE UPPER CRETACEOUS AND PALEOGENE DEPOSITS 93

Angiosperm pollen

47

?

42 41 40 39 38 37

11 10

?

6

4 3 5

?

PA I

94


3 21

19 1

3

4

2 20

1 1

3 22

1

3 5 22

17

5 23 4

24 3 25

7 26 9

29 15

16

3

6

7 3

18

2 12 5 13 2 14

10 7

10 11

2 15

27 28 2

2 9

85 12 6

7 8

10

3

Land Sea Number of Dinogymnium species

1

30

3 31

Fig. 5. Location and number of species of genus Dinogymnium in the Upper Cretaceous deposits of the Northern Hemisphere. Paleogeographic setting is shown for the Campanian. Locations: (1) Ust’-Yenisei and Khatanga areas (author’s data); (2) Subpolar Urals (Chlonova, 1996); (3) Polar Cis-Ural Region (Lebedeva, 2006); (4) Kara Sea shelf, Borehole Leningradskaya 1 (Lebedeva, 2006); (5) South Kolpashevo area (Vozhennikova, 1967); (6) Omsk Depression, Boreholes 8, 10, 2 (author’s data); (7) Turgai Depression, north of Kazakhstan (Sharafutdinova, 1986; author’s data); (8) Northern Iran (Wheeler and Sarjeant, 1990); (9) Israel (Hoek et al., 1996); (10) Egypt (Schrank and Perch-Nielsen, 1985; Schrank, 1988); (11) Volgograd oblast (Aleksandrova et al., 2012); (12) Kaliningrad oblast, Borehole 1Р (Aleksandrova and Zaporozhets, 2008а, 2008b); (13) Germany (Kirsch, 1991, 2000; Smelror et al., 1995; Smelror and Riegraf, 1996); (14) Austria and Czech Republic (Mohamed et al., 2012; Olde et al., 2015); (15) Northern Apennines, Italy (Rocaglia and Corradini, 1997); (16) Belgium (Slimani, 2001); (17) England (Costa and Davey, 1992; Prince et al., 1999; Dodsworth, 2000); (18) France (Foucher, 1974, 1981; Robaszynski et al., 1982); (19) Eastern Greenland (Nøhr–Hansen, 2012); (20) Western Greenland (Dam et al., 2000; Nøhr–Hansen, 1996); (21) Arctic Archipelago, Canada (Ioannides, 1986; Núňez–Betelu and Hills, 1998); (22) Mackenzie River delta (McIntyre, 1974); (23) Internal Canadian areas (Harker et al., 1990; McIntyre, 1999); (24) Alberta, Canada (Harland, 1973; Wall and Singh, 1975); (25) Wyoming, United States of America (Harker et al., 1990); (26) Grand Banks of Newfoundland, Scotian Shelf (Williams and Brideaux, 1975; Jansa et al., 1977; Barss et al., 1979); (27) New Jersey, Atlantic Coast, United States (May, 1980; Tocher, 1985; Aurisano, 1989); (28) South Carolina, Georgia, Atlantic Coast, United States (Habib and Miller, 1989); (29) Texas, United States (Srivastava, 1995); (30) Western Venezuela (Helenes et al., 1998); (31) equatorial part of the Atlantic coast of Africa (Masure et al., 1998).

interruption is expected at the top of the Campanian (Gnibidenko et al., 2014). Stratigraphic interval: Campanian. Local zone Cerodinium diebelii. Borehole 8 (interval 309.9–288.4 m); Borehole 10 (interval 276.05–258 m);

Borehole 2 (interval 256.6–249.8 m). Gan’kino Formation. The lower boundary is characterized by occurrence of Cerodinium diebelii (Plate II), Pulchrasphaera minusculа, and Triblastula utinensis.

Plate II. Palynomorphs from the Upper Cretaceous sediments of Borehole 8 in the Russkaya Polyana district. Magnification is shown in microns (μm). (1) Cerodinium diebelii, depth 276.01 m, Sample 41, prep. 2949.3; (2) Phelodinium tricuspis, depth 282.75 m, Sample 38, prep. 2940.1; (3, 4) Florentinia buspina (Davey et Verdier) Duxbury, depth 271.3 m, Sample 43, prep. 2951.3; (5) Chlonoviella agapica, depth 273.65 m, Sample 42, prep. 2950.2; (6) Phanerodinium cayeuxii, depth 266.65 m, Sample 45, prep. 2953.3; (7) Rhiptocorys veligera, depth 364.9 m, Sample 7, prep. 2911.1; (8, 9) Microdinium carpentieriae, depth 264.65 m, Sample 46, prep. 2954.1; (10) Hystrichosphaeridium tubiferum, depth 262.3 m, Sample 47, prep. 2955.2; (11) Samlandia mayii, depth 276.01 m, Sample 41, prep. 2949.4; (12) Alisogymnium sphaerocephalum, depth 285.15 m, Sample 37, prep. 2939; (13, 14) Cladopyxidium reticulatum, depth 273.65 m, Sample 42, prep. 2950.1; (15–17) Microdinium ornatum, depth 278.6 m, Sample 40, prep. 2942.1; (18, 19) Microdinium sp., depth 278.6 m, Sample 40, prep. 2942.1; (20–22) Microdinium kustanaicum, depth 262.3 m, Sample 47, prep. 2955.2; (23, 24) Eisenackia brevivallata, depth 273.65 m, Sample 42, prep. 2950.2. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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Plate II 20

20

2

20

20

3

4

20

1

20

5

10

6

20

7

20

8

9

13 20

20

10

10

20

10

15

20

10

10

16

10

21

10

This dinocyst assemblage is the most diverse in Boreholes 8 and 10. In the layers with Cerodinium diebelii in Borehole 2, the dinocyst composition is much poorer, chorate forms are rare, Laciniadinium and IsaSTRATIGRAPHY AND GEOLOGICAL CORRELATION

20

11

17

22

10

20

14

12

18

23

10

19

20

24

belidinium representatives are sporadic. Meanwhile, the key taxa of the assemblage are present. Characteristic assemblage: Cerodinium diebelii, Laciniadinium sp., L. arcticum, L. rhombiforme sp., Vol. 26

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L. firmum, Membranosphaera maastrichtica, Trithyrodinium quingueangulare, Pulchrasphaera minusculа, Microdinium kustanaicum, Isabelidinium sp., I. belfastense, I. rectangulatum, Triblastula utinensis, Hystrichosphaeropsis quasicribrata, Phanerodinium cayeuxii, Rottnestia borussica, Membranilarnax liradiscoides, and Achomosphaera ramulifera. Cladopyxidium spp. and Fromea chytra are numerous. The number of Dinogymnium representatives decreases dramatically to rare specimens. In Boreholes 8 and 10, the bottom of layers contains species Samlandia mayii characteristic of the upper Campanian–lower Maastrichtian. In Borehole 8, at the top of the local zone Cerodinium diebelii (interval 288.5–288 m), there is the bivalve mollusk assemblage characteristic of the lower Maastrichtian, while the finding of ammonite Hoploscaphites cf. constrictus constrictus (Sowerby) makes it possible to assume that this interval contains the upper part of the lower Maastrichtian (Lebedeva et al., 2013). In the same work, M.N. Ovechkina, having studied the nanoplankton, assumes that the base of the Gan’kino Formation (interval 304–286.4) refers to the lower Maastrichtian; this assumption is consistent with the data on the studied dinocysts. In the stratotypic Campanian–Maastrichtian Tercis les Bains section (France), the first finding of species Cerodinium diebelii was recorded in the uppermost part of the Campanian, while its permanent occurrence was found out to be characteristic of the lower Maastrichtian (Schiøler and Wilson, 1993). The species Trithyrodinium quingueangulare was described in the lower Maastrichtian of Germany and France (Marheinecke, 1992; Schiøler and Wilson, 1993). The constant occurrence of the species Triblastula utinensis and genus Areoligera is typical of the middle Maastrichtian or, in the case of two-term division (Gradstein et al., 2012), of the upper part of the lower Maastrichtian (Nøhr-Hansen, 2012). Everything stated above is in agreement with the paleomagnetic data indicating the stratigraphic break that covers a part of the Campanian and the lower part of the Maastrichtian (Gnibidenko et al., 2014). Stratigraphic interval: lower Maastrichtian. Local zone Cerodinium speciosum. Borehole 8 (interval 288.4–278 m); Borehole 2 (depth 246.9 m). Gan’kino Formation. This assemblage was not found in Borehole 10. The lower boundary can be identified by the index species. Characteristic assemblage: Cerodinium speciosum, Spongodinium delitiense, Hystrichosphaeridium tubiferum, Microdinium kustanaicum, Areoligera coronata, A. volata, Glaphyrocysta spp., Pulchrasphaera minusculа, and Palynodinium helveticum. Cladopyxidium spp. and Fromea chytra are numerous. The number of the Chatangiella representatives is reduced and there is almost complete disappearance of Isabelidinium and Dinogymnium.

According to the data on nanoplankton in Borehole 8, the boundary of the СС24/UC18 and СС25а/UC19 zones (interval 284–274 m), corresponding to the boundary of the lower and upper Maastrichtian, passes inside the layers with Cerodinium speciosum. The analysis of the dinocyst composition in these layers and the comparison of assemblages from the Maastrichtian sediments (Lebedeva et al., 2013), dated on the basis of different fauna groups, indicate of the transitional early–late Maastrichtian age of the studied intervals. Stratigraphic interval: upper part of the lower Maastrichtian–lower part of the upper Maastrichtian. Local zone Palynodinium sp. A. was identified only in Borehole 8 in the interval of 278–270.5 m and dated to the first half of the late Maastrichtian (Lebedeva et al., 2013). The Upper Cretaceous deposits in all three boreholes are overlapped by the Paleogene sediments. The Paleogene basal horizons are represented by the Talitsa Formation dated to the middle Selandian in Borehole 8 and by the Lower Lyulinvor Formation of early Thanetian age in Borehole 10 (Aleksandrova et al., 2011; Iakovleva et al., 2012). Local zone Alisocysta margarita was identified in the Lower Lyulinvor Subformation in Borehole 2 (interval 246–222.5 m) (Fig. 3). The base of layers contains Deflandrea denticulata and Alisocysta margarita, and the upper boundary is outlined by occurrence of Apectodinium hyperacanthum. Stratigraphically important species are jointly present in the assemblage: Alisocysta margarita, Deflandrea denticulata, D. oebisfeldensis, and Areoligera gippingensis. In addition, the following taxa are noted: Achomosphaera sp., Areoligera coronata, A. senonensis, Hystrichosphaeridium tubiferum, Fromea chytra, F. laevigata, Caligodinium sp., C. aceras, Cerodinium speciosum, C. leptodermum, C. markovae, Cordosphaeridium gracile, C. inodes, Cladopyxidium septum, Cleistosphaeridium sp., Eocladopyxis sp., Eisenackia sp., Kallosphaeridium sp., Melitasphaeridium pseudorecurvatum, Microdinium sp., Palaeocystodinium golzowense, Pulchrasphaera minuscula, Senegalinium sp., Spiniferites sp., S. ramosus, S. ramosus granosus, and Spinidinium sp. The dinocyst assemblage including species Alisocysta margarita, Deflandrea denticulata, and D. oebisfeldensis was identified in the Lower Lyulinvor Subformation in Boreholes 8 and 10 and was assigned to the Alisocysta margarita Zone (Akhmetiev et al., 2010; Iakovleva et al., 2012; Iakovleva and Aleksandrova, 2013). Taking into account a reverse magnetization of the deposits in the interval of 246–222.5 m in Borehole 2 (Gnibidenko et al., 2014), they are partially dated to the early Thanetian (~56.5–58.5 Ma, part of chrone С25, nanoplankton-based zones NP7–NP8 (Unifitsirovannye…, 2001; Iakovleva et al., 2012; Iakovleva and Aleksandrova, 2013)).


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Local zone Apectodinium hyperacanthum was identified in Borehole 2 in the Lower Lyulinvor Subformation (interval 225.05–220.4 m) (Fig. 3). The lower boundary of layers is outlined by occurrence of species Apectodinium hyperacanthum. The dinocyst assemblage is dominated by species Areoligera senonensis. Spiniferites ramosus, S. ramosus granosus, Cleistosphaeridium spp., and Hystrichosphaeridium tubiferum are abundant. Almost all taxa from the complex of layers with Alisocysta margarita are sporadic, except for Alisocysta margarita and Deflandrea denticulata. The presence of the stratigraphically important species Apectodinium homomorphum and A. hyperacanthum in the assemblage allows us to compare the sediments of this interval with the Apectodinium hyperacanthum Zone identified in the Western Siberia in the Serovo Formation and Lower Lyulinvor Subformation (Unifitsirovannye…, 2001; Iakovleva and Aleksandrova, 2013). The Apectodinium hyperacanthum Zone is dated to the late Thanetian (~55.8–56.8 Ma) (Unifitsirovannye…, 2001; Iakovleva and Aleksandrova, 2013). Hence, the Lower Lyulinvor Subformation uncovered by Borehole 2 in the interval of 246–220.4 m is characterized by the most complete stratigraphic volume and corresponds mostly to the Thanetian (~55.8–58.5 Ma). Layers with Spores and Pollen Six biostratigraphic units in the rank of layers with spores and pollen were identified on the basis of changes in the spore and pollen composition of the terrestrial plants in the studied boreholes. The palynological assemblages (PAs) characterizing them are described below, while the age of the Late Cretaceous assemblages is substantiated in (Lebedeva et al., 2013). Layers with PA I. Borehole 8 (interval 590.5– 500.5 m); Borehole 10 (interval 411.8–402.5 m) (Fig. 4); Borehole 2 (interval 384.65–362.95 m). Pokur Formation (Plate III). The spore content is 52–65% at 14–31% of gymnosperm pollen, 7–28% of angiosperm pollen, and 3– 6% of microphytoplankton. The spores are dominated by Leiotriletes spp., Gleicheniidites spp., and Cyathidites sp. The representatives of family Schizaeaceae (Cicatricosisporites spp., Appendicisporites spp., Trilobosporites sp.) are numerous and diverse. There are also Laevigatosporites ovatus, Stereisporites spp., Ornamentifera echinata, Aequitriradites verrucosus, Matonisporites sp., Kuylisporites lunaris, Biretisporites sp., Rouseisporites reticulatus, R. laevigatus, Lobatia involucrata, Impardecispora apiverrucata, Lycopodiumsporites sp., Taurocusporites reduncus, Klukisporites sp., Concavissimisporites punctatus, Dictyophyllidites sp., Leptolepidites sp., Undulatisporites sp., Lophotrilets babsae, Foraminisporis dailyi, Camarozonosporites insignis, Eboraciasporites sp., etc. Ruminatisporites delicatus is sporadic. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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The gymnosperm pollen is represented by abundant bisaccate pollen of poorly preserved coniferous woods Coniferales gen. indet. and also Cedripites sp., Pinuspollenites spp., Alisporites spp., Phyllocladidites sp., Taxodiaceaepollenites hiatus, and Ginkgocycadophytus sp. The angiosperm pollen is permanent in occurrence: Tricolpites spp., Retitricolpites spp. (4–20%). Other palynomorphs include prasinophytes Leiosphaeridia sp., freshwater green algae (Zygnemataceae): Ovoidites and Schizosporis. Stratigraphic interval: Albian. Layers with PA II. Borehole 8 (interval 500.5– 382.0 m); Borehole 10 (interval 383.9–360 m). Upper part of the Pokur Formation, Kuznetsovo Formation. The spore content is 16–30% at 29–59% of gymnosperm pollen, 4–9% of angiosperm pollen, and 20– 46% of microphytoplankton. The spores are dominated by Leiotriletes spp. and Gleicheniaceae (Gleicheniidites senonicus, G. laetus, G. umbonatus, Plicifera delicata, and Clavifera spp.). The representatives of the family Schizaeaceae become less abundant, but they are still diverse: Cicatricosisporites minutaestriatus, C. pacificus, C. cuneiformis, C. mtchedlishviliae, Appendicisporites spp., and Trilobosporites sp. Rouseisporites laevigatus, R. reticulatus, Taurocusporites reduncus, Foveosporites cenomanicus, Polypodiaceae (bean-shaped, ornamented), and Stenozonotriletes radiatus are permanent in occurrence. Accompanying components: Cyathidites sp., Laevigatosporites ovatus, Stereisporites spp., Camarozonosporites insignis, Ornamentifera echinata, Todisporites minor Coup., Aequitriradites verrucosus, Baculatisporites comaumensis, Velosporites triquetrus, Foraminisporis asymmetricus, Matonisporites sp., etc. Kuylisporites lunaris is absent. Gymnosperm pollen is dominated by Coniferales gen. indet., Cedripites sp., and Taxodiaceaepollenites hiatus. Pinuspollenites spp., Alisporites spp., Rugubivesiculites sp., Phyllocladidites sp., Ginkgocycadophytus sp., Ephedripites costatus, Eucommiidites sp., etc., are present. Angiosperm pollen is 4–9% on average: only Tricolpites sp. and Retitricolpites sp. are observed in Borehole 10, while borehole 8 also contains Fraxinoipollenites constrictus, Menispermum turonicum, and Vacuopollis sp. Other microfossils include Leiosphaeridia, Ovoidites, and Schizosporis. The lower boundary is determined by changes in the assemblage described above. Stratigraphic interval: Senomanian–Turonian. Layers with PA III. Borehole 8 (interval 372.1– 343 m); Borehole 10 (interval 346.7–323.45 m). Ipatovo Formation. The spore content is 13–42% at 21–46% of gymnosperm pollen, 14–34% of angiosperm pollen, and 17–45% of microphytoplankton. Vol. 26

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The taxonomic composition is significantly reduced. The number and variety of spores decreases. The permanent components include Gleicheniidites spp., Leiotriletes spp., Stereisporites spp., Matonisporites spp., and Laevigatosporites ovatus. Accompanying components: Cyathidites sp., Ornamentifera echinata, Cicatricosisporites spp., Foveosporites cenomanicus, Appendicisporites spp., Polypodiaceae (bean-shaped, ornamented), etc. No significant changes are observed in the gymnosperm pollen composition. The content of Taxodiaceaepollenites hiatus decreases. The angiosperm pollen composition is more diverse. Borehole 10 contains Trudopollis sp., Triporopollenites plicoides, Kuprianipolls sp., Pseudovacuopollis sp., Aquilapollenites sp., Triorites harrisii, Vacuopollis sp., Oculopollis sp., etc. (Fig. 3). In addition to the above-mentioned taxa, Plicapollis retusus, P. serta, Causarinidites cainozoicus, and Triporopollenites plicoides are noted in Borehole 8 for the first time. The lower boundary is identified by higher content and greater diversity of the angiosperm plants. Stratigraphic interval: Coniacian–Santonian. Layers with PA IV. Borehole 8 (interval 343.1– 311.2 m); Borehole 10 (interval 323.45–281.6 m). Slavgorod Formation–lower part of the Gan’kino Formation. The spore content is 18–28% at 12–26% of gymnosperm pollen, 29–45% of angiosperm pollen, and 16–28% of microphytoplankton. The spore composition is quantitatively dominated by Leiotriletes spp. Permanent components include Gleicheniaceae, Cyathidites spp., Laevigatosporites ovatus, Cicatricosisporites spp., Matonisporites sp., Stereisporites spp., Camarozonosporites insignis, Lycopodiumsporites sp., Leptolepidites sp., and Polypodia-

ceae (bean-shaped, ornamented), while other taxa are sporadic (Fig. 3). The gymnosperm pollen is dominated by Taxodiaceaepollenites hiatus and Ginkgocycadophytus sp. The saccate pollen content of coniferous plants decreases. The angiosperm pollen becomes more abundant. Tricolpites spp., Retitricolpites spp., Trudopollis spp. (6–8% on average), and Oculopollis spp. are predominant. Permanent components: Kuprianipolls spp., Aquilapollenites sp., Plicapollis serta, Triorites harrisii, and betoloid–miricoid pollen. Mancicorpus sp., Proteacidites sp., Nudopollis sp., etc., are observed. The lower boundary is defined by occurrence of Mancicorpus sp., Proteacidites sp., and Nudopollis sp. Stratigraphic interval: Campanian. Layers with PA V. Borehole 8 (interval 309.9– 274.2 m); Borehole 10 (interval 281.6–258.35 m). Gan’kino Formation. The spore content is 5–9% at 8–20% of gymnosperm pollen, 9–19% of angiosperm pollen, and 52– 74% of microphytoplankton. The content and diversity of spores and pollen of terrestrial plants dramatically decrease at an increase in the marine microphytoplankton content. The spores constantly include Gleicheniidites spp., Leiotriletes spp., Cyathidites sp., Laevigatosporites ovatus, Stereisporites spp., Camarozonosporites insignis, Polypodiaceae (bean-shaped, ornamented), and Lycopodiumsporites sp., while other taxa are sporadic. The gymnosperm pollen is represented by Coniferales gen. indet., Cedripites sp., Taxodiaceaepollenites hiatus, Ginkgocycadophytus sp., Pinuspollenites spp., Rugubivesiculites sp., and Ephedripites costatus. The angiosperm representatives include Tricolpites sp., Retitricolpites sp., Trudopollis spp., Tricolpopollenites spp., Tricolporopollenites spp., Aquilapollenites sp.,

Plate III. Palynomorphs from the Upper Cretaceous sediments of Borehole 10 in the Russkaya Polyana district. Magnification is shown in microns (μm). (1) Gleicheniidites senonicus, depth 376.85 m, Sample 5, prep. 2909.1; (2) Clavifera sp., depth 266.65 m, Sample 45, prep. 2953.2; (3) Ornamentifera echinata, depth 271.3 m, Sample 43, prep. 2951.1; (4) Lycopodiumsporites sp., depth 276.01 m, Sample 41, prep. 2949.4; (5) Velosporites triquetrus, depth 369 m, Sample 6, prep. 2910.1; (6) Osmundacidites sp., depth 280.6 m, Sample 39, prep. 2941.2; (7) Todisporites minor, depth 364.9 m, Sample 7, prep. 2911.2; (8) Biretisporites sp., depth 376.85 m, Sample 5, prep. 2909.1; (9) Concavissimisporites punctatus, depth 401.5 m, Sample 2, prep. 2906.1; (10) Rouseisporites laevigatus, depth 401.5 m, Sample 2, prep. 2906.1; (11) Rouseisporites reticulatus, depth 401.5 m, Sample 2, prep. 2906.2; (12) Dictyotosporites sp., depth 401.5 m, Sample 2, prep. 2906.2; (13) Cicatricosisporites pacificus, depth 401.5 m, Sample 2, prep. 2906.1; (14) Cicatricosisporites cuneiformis, depth 401.5 m, Sample 2, prep. 2906.3; (15) Cicatricosisporites stoveri, depth 401.5 m, Sample 2, prep. 2906.1; (16) Anemia exilioides, depth 369 m, Sample 6, prep. 2910.2; (17) Appendicisporites macrorhyzus, depth 364.9 m, Sample 7, prep. 2911.1; (18) Balmeisporites glenelgensis, depth 401.5 m, Sample 2, prep. 2906.3; (19) Foveosporites cenomanicus, depth 401.5 m, Sample 2, prep. 2906.2; (20) Foraminisporis asymmetricus, depth 401.5 m, Sample 2, prep. 2906.1; (21) Cicatricosisporites minutaestriatus, depth 401.5 m, Sample 2, prep. 2906.1; (22) Kornilovites sp., depth 383.2 m, Sample 3, prep. 2907.1; (23) Ginkgocycadophytus sp., depth 276.01 m, Sample 41, prep. 2949.2; (24) Eucommiidites sp., depth 401.5 m, Sample 2, prep. 2906.2; (25) Tricolpites albiensis, depth 275.6 m, Sample 41, prep. 2949.4; (26) Tricolpites sp., depth 320.85 m, Sample 19, prep. 2924; (27) Rugubivesiculites sp., depth 262.3 m, Sample 47, prep. 2955.3; (28) Cedrus cristata, depth 369 m, Sample 6, prep. 2910.1; (29) Cedripites parvisaccatus, depth 401.5 m, Sample 2, prep. 2906.1; (30) Podocarpidites multesimus, depth 401.5 m, Sample 2, prep. 2906.1; (31) Podocarpidites sp., depth 401.5 m, Sample 2, prep. 2906.1; (32, 33) Retitricolpites sp., depth 376.85 m, Sample 5, prep. 2909.1; (34) Nyssapollenites sp., depth 364.6 m, Sample 8, prep. 2912.1; (35) Triorites harrisii, depth 276.01 m, Sample 41, prep. 2949.3; (36) Aquilapollenites unicus, depth 264.65 m, Sample 46, prep. 2954.2; (37) Trudopollis protrudens, depth 264.65 m, Sample 46, prep. 2954.2; (38) Ocullopollis sp., depth 273.65 m, Sample 42, prep. 2950.1; (39) Trudopollis nonperfectus, depth 276.01 m, Sample 41, prep. 2949.4; (40) Trudopollis ordinatus, depth 276.01 m, Sample 41, prep. 2949.1; (41) Trudopollis bulbosus, depth 280.6 m, Sample 39, prep. 2941.1; (42) Trudopollis baculotrudens, depth 321.75 m, Sample 18, prep. 2923; (43) Ocullopollis sp., depth 332.25 m, Sample 13, prep. 2917; (44) Lancetopsis sp., depth 269.30 m, Sample 44, prep. 2952.2. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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Plate III

20

20

1

20

2

20

3

20

4

20

5

6

20

7

20

12

20

20

20

8

20

13

20

9

20

14

10 11

20

20

15

16

20

17

20

20 20

50

18

20

32

10

20

33

10

20

24 10

20

35

20

25

20

29

34

39

20

40

20

41


20

42

Vol. 26

20

No. 1

36

43

2018

20

22

27

20

30

20

26

31

20

20 20

20

20

23

20

28

10

19

21

37

20

38

44

1

2 Ch. spectabilis, Dorocysta spp. H. difficile

E. saxoniense

?

STRATIGRAPHY AND GEOLOGICAL CORRELATION 350

E. saxoniense Dorocysta sp. A

?

310

290

270

Maastrichtian

250

Cerodinium diebelii

Gan’kino

C. s.

330

Chatangiella manumii–Dinogymnium spp.

Dinogymnium spp. Chatangiella manumii

Chatangiella spp.

Campanian Slavgorod

Cerodinium Cerodinium speciosum diebelii

Ipatovo

240

230


Tanetian Lyulinvor


H. d.–Ch. s.

?


Core shift 13 m

Maastrichtian T L Gan’kino Cerodinium diebelii 280 270 260

?

370

E.s.

Albian Cenomanian Pokur

E. saxoniense Dorocysta sp. A 330

Dinogymnium spp. Chatangiella manumii

370

Chatangiella spp.

380

Campanian Slavgorod Chatangiella manumii–Dinogymnium spp. 290 320 310 300

?

390

Lower Maastrichtian Upper Maastrichtian Sel. Gan’kino Tal. Cerodinium Cerodinium Palynospeciosum dinium diebelii sp. A 310 290 270

Cerodinium diebelii

Coniacian–Santonian Ipatovo Chatangiella spp. 350 340 360

350

Chatangiella spp.

Campanian Slavgorod Chatangiella manumii– Dinogymnium spp. 330

Cerodinium speciosum

Kuznetsovo H.d.– Ch.s.

370

Coniacian–Santonian Ipatovo

Apect. hyp.

Vol. 26


Stage/Substage Formation Layers with dinocysts 220 Depth, m


Stage/Substage Formation Layers with dinocysts Depth, m


Stage/Substage Formation Layers with dinocysts Depth, m

Borehole Russkaya Polyana 8

Turonian Kuznetsovo

Ch. spectabilis, Dorocysta spp. H. difficile

Cenomanian Pokur

?

Turonian

Middle, upper Turonian Kuznetsovo Heterosphaeridium difficile– Chatangiella spectabilis 410 390

?

400

Pokur

Senomanian–Turonian

100 LEBEDEVA, KUZ’MINA Borehole Russkaya Polyana 10 Borehole Russkaya Polyana 2

246

Chatangiella spp.

E. s.

?

C. s.– P. c.

3

Fig. 6. Dinocyst correlation of borehole sections in the Russkaya Polyana district. (1) Appearance of a taxon, (2) disappearance of a taxon, (3) characteristic taxon. Abbreviations: (Sel.) Selandian, (Tal) Talitsa, (E. saxoniense) Eurydinium saxoniense, (H. difficile) Heterosphaeridium difficile, and (Ch. spectabilis) Chatangiella spectabilis. Other legend and abbreviations are shown in Figs. 2 and 3.

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Plicapollis serta, Myricaceae, Oculopollis spp., Liliacidites sp., Proteacidites sp., and Wodehousea sp. The lower boundary is defined by drastic changes in quantitative ratios of the basic spore and pollen groups. Stratigraphic interval: Maastrichtian. Layers with Triatriopollenites myricoides, Triporopollenites robustus, and Interpollis supplingensis. Borehole 2 (interval 246–220.4 m). Lower Lyulinvor Subformation. Plant spores and pollen make up 8–16%, rarely, up to 40% (sample from a depth of 243.75 m), of total palynomorphs identified in the sediments of this interval. Their composition is dominated by angiosperm pollen such as Triatriopollenites myricoides, T. roboratus, Momipites sp., Tricolporopollenites spp., T. cingulum, Triporopollenites sp., T. plicoides, T. robustus, Interpollis sp., I. supplingensis, Pompeckjoidaepollenites subhercynicus, Trudopollis sp., T. menneri, Exstratriporopollenites sp., Nyssa sp., Juglans sp., Quercus sp., Loranthus sp., Caryapollenites sp., Platycaryapollis sp., and Palmae. Gymnosperm pollen belongs to the family Pinaceae: Pinus sp., Pinus s/g Haploxylon, and P. s/g Diploxylon. Picea sp., Glyptostrobus, Podocarpus sp., Cedrus sp., and Taxodiaceae/Cupressaceae are rare. Spores of Cyathidites sp., Sphagnum sp., and Schizosporites sp. are sporadic. Taking into account the presence of index species Triporopollenites robustus, Triatriopollenites myricoides, and Interpollis supplingensis, the found palynological assemblage can be compared to that of the cognominal regional palynozone SPZ-3 characterizing the Thanetian sediments in Western Siberia (Unifitsirovannye…, 2001). Stratigraphic interval: Thanetian. DISCUSSION The studied sections of three closely spaced boreholes in the Russkaya Polyana district have revealed a complex structure of the Upper Cretaceous sediments formed in the unstable environments of the marginal part of the West Siberian basin (Fig. 6). The biostratigraphic, mostly palynological, data have made it possible to substantiate the age of the studied sediments and to reveal numerous interruptions in the sedimentation process. The Pokur Formation composed mainly of continental sediments is Albian–Cenomanian and, likely, partially Turonian in age, according to the palynological data, because the palynological assemblage of the undivided Cenomanian–Turonian was identified in Borehole 8 (Lebedeva et al., 2013), which is typical of the southern areas of Western Siberia and the Southern Trans-Urals. The Turonian palynological assemblages were not identified in Boreholes 2 and 10 likely STRATIGRAPHY AND GEOLOGICAL CORRELATION

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because of the stratigraphic break at the top of the formation. The dinocyst assemblage with Cepadinium subtile–Palaeoperidinium cretaceum indicating the ingress of the West Siberian Sea in the Albian time was found for the first time in this part of Western Siberia in Borehole 2, in the middle part of the Pokur Formation. The available paleogeographic maps show a lowland accumulative plain (sediments of channels, floodplains, lakes, etc.) in this area (Atlas…, 1976; Kontorovich et al., 2014). The Kuznetsovo Formation, composed of both clayey and sandy rocks, is the thinnest in Borehole 10. Despite a very reduced volume of the formation, Boreholes 10 and 2 contain two dinocyst assemblages characterizing both the lower Turonian (local zone Eurydinium saxoniense) and the middle–upper Turonian (local zone Heterosphaeridium difficile–Chatangiella spectabilis). The lower Turonian assemblage was not identified in Borehole 8 likely because of the break in sedimentation. The most unfavorable conditions for the fossilization (and, perhaps, the habitat) of microphytoplankton existed during deposition of the Ipatovo Formation. Coarse-grained and coarse-clastic rocks composing its groundmass in Borehole 8 do not contain dinocysts. The sand–siltstone varieties of all studied boreholes are depleted in taxa. The thick Ipatovo Formation composed of thinner sediments in Borehole 8 is still characterized by the least diverse dinocyst assemblage. Because of insufficient factual material for analysis, we failed to estimate the age of the studied sediments more accurately than the Coniacian–Santonian. The dinocyst content increases and the diversity becomes greater in the Slavgorod Formation. Meanwhile, the dinocyst assemblages characterizing the Campanian substages have yet to be identified in Western Siberia. G.N. Aleksandrova found four dinocyst assemblages dated to the late Santonian–early Campanian, end of the early–beginning of the middle Campanian, and middle and late Campanian in the Upper Cretaceous deposits uncovered by boreholes within the Gremyach’e deposit (Lower Volga Region). The age was justified on the basis of dinocysts and also foraminifers and radiolarians. The Campanian dinocyst assemblage identified in the Russkaya Polyana district is much less diverse, but is confidently compared with the middle Campanian assemblage with the Dinogymnium acme in the Lower Volga Region. The paleomagnetic studies of Boreholes 8, 10, and 2 showed a significant break in the upper part of the Campanian (Gnibidenko et al., 2014). Meanwhile, the low dinocyst diversity in this interval does not make it possible to estimate more accurately the scope of breaks in the Campanian member. According to the paleomagnetic data, a stratigraphic break is also recorded at the boundary of the Slavgorod and Gan’kino formations. However, the presence of the lower Maastrichtian biostratigraphic Vol. 26

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unit of Cerodinium diebelii in all three studied boreholes is indicative of the fact that this break can cover only a part of the lower Maastrichtian. The Maastrichtian dinocyst sequence is represented the most fully in the Borehole 8 section, where the lower Maastrichtian and a part of the upper Maastrichtian have been revealed. In Boreholes 10 and 2, the Maastrichtian is likely represented by the lower substage only. A break in sedimentation is observed at the boundary between the Cretaceous and the Paleogene in the studied region. In Borehole 8, the Gan’kino Formation is overlapped by the Talitsa, the break interval is estimated from the upper part of the Maastrichtian to the middle part of the Selandian (Iakovleva et al., 2012; Lebedeva et al., 2013). In Boreholes 2 and 10, at the Cretaceous–Paleogene boundary, the longer break corresponds to a significant part of the Maastrichtain–Selandian (Iakovleva et al., 2012). In the sections of these boreholes, the Gan’kino Formation is overlapped with washout by the Lower Lyulinvor Subformation. It is established that Borehole 10 uncovered only the lower part of this subformation containing the dinocyst assemblage of the early Thanetian Alisocysta margarita Zone (Iakovleva et al., 2012). In Borehole 2, the Lower Lyulinvor Subformation consists of both the early Thanetian dinocyst assemblage of the Alisocysta margarita Zone and the late Thanetian assemblage of Apectodinium hyperacanthum absent in Boreholes 8 and 10 (Iakovleva et al., 2012). The Lower Lyulinvor Subformation uncovered in Borehole 2, according to our data, corresponds to a major part of the Thanetian layer. The dinocyst assemblage of the Apectodinium hyperacanthum Zone was previously identified in the Lower Lyulinvor Subformation in Borehole 9 (Novosibirsk oblast) (Akhmetiev et al., 2004). According to Iakovleva et al. (2012), the total range of the studied subformation in the south of Western Siberia, indeed, corresponds to a greater part of the Thanetian Stage. Hence, on the basis of a comparison with the data on dinocysts published earlier (Iakovleva et al., 2012), we have specified the age of the Lower Lyulinvor Subformation in the Russkaya Polyana district. CONCLUSIONS Generalization of the biostratigraphic and magnetostratigraphic data on three boreholes in the Russkaya Polyana district (Omsk Trough) has made it possible to establish specific structural features of the Upper Cretaceous and boundary Paleogene sediments. The age of the Upper Cretaceous member has been substantiated from the Albian to the Maastrichtian on the basis of dinocysts, spores, and pollen. The Pokur, Kuznetsovo, Ipatovo, Slavgorod, and Gan’kino formations have been subjected to the palynological analyses. Eight biostratigraphic units with dinocysts and five units with palynological assemblages have been identified.

The joint application of biostratigraphic and magnetostratigraphic methods has made it possible to reveal stratigraphic interruptions in the studied sedimentary member and to estimate their scope. In the Pokur Formation, a break is possible in the upper part of the section in Boreholes 10 and 2 and in the Albian sediments in Boreholes 8 and 10. The lower Turonian is not observed in the Kuznetsovo Formation in the Borehole 8 section, as follows from the absence of the Eurydinium saxoniense local zone. The found stratigraphic break at the boundary between the Slavgorod and Gan’kino formations covers the Campanian and partially the lower Maastrichtian (Gnibidenko et al., 2014). In the boundary Cretaceous–Paleogene deposits in Borehole 8, the interval of the break is estimated from the upper Maastrichtian to the middle Selandian. In Boreholes 2 and 10, the longer break corresponds to a large part of the Maastrichtian–Selandian. Thanetian age of the Lower Lyulinvor Subformation in the Russkaya Polyana district has been substantiated by comparison of the dinocyst assemblages from the Paleogene sediments in the Borehole 2 section with the data on dinocysts published earlier (Iakovleva et al., 2012). The ingression traces of the Western Siberian basin in the Albian have been found for the first time in the studied area. These data make it possible to specify the paleogeographic reconstructions. The results obtained in the course of investigation of three boreholes in the Omsk Trough make it possible to complete and detail the regional stratigraphic scheme of the Mesozoic deposits in the south of the Omsk-Lar’yak facies zone of Western Siberia, to clarify the position of the basal horizons of the Paleogene sediments, and also to specify the paleogeographic reconstructions. TAXA LIST Dinoflagellate cysts: Achomosphaera ramulifera (Deflandre) Evitt Alisocysta margarita Harland Alisogymnium euclaense (Cookson et Eisenack) Lentin et Vozhennikova Alisogymnium sphaerocephalum (Vozhennikova) Lentin et Vozhennikova Alterbidinium acutulum (Wilson) Lentin et Williams Alterbidinium “daveyi” (Stover et Evitt) Lentin et Williams Alterbidinium minus (Alberti) Lentin et Williams Alterbidinium varium Kirsch Amphigymnium mitratum (Vozzhennikova) Lentin et Williams Apectodinium homomorphum (Deflandre et Cookson) Lentin et Williams


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Apectodinium hyperacanthum (Cookson et Eisenack) Lentin et Williams Areoligera coronata (O. Wetzel) Lejeune-Carpentier Areoligera gippingensis Jolley Areoligera senonensis Lejeune-Carpentier Areoligera volata Drugg Biconidinium reductum (May) Kirsch Caligodinium aceras (Manum et Cookson) Lentin et Williams Canningia macroreticulata Lebedeva Cepadinium subtile Savchenkova Cerodinium diebelii (Alberti) Lentin et Williams Cerodinium leptodermum (Vozzhennikova) Lentin et Williams Cerodinium markovae (Vozzhennikova) Lentin et Williams Cerodinium speciosum (Alberti) Lentin et Williams Chatangiella bondarenkoi (Vozzhennikova) Lentin et Williams Chatangiella chetiensis (Vozzhennikova) Lentin et Williams Chatangiella granulifera (Manum) Lentin et Williams Chatangiella madura Lentin et Williams Chatangiella manumii (Vozzhennikova) Lentin et Williams Chatangiella serratula (Cookson et Eisenack) Lentin et Williams Chatangiella spectabilis (Alberti) Lentin et Williams Chatangiella vnigrii (Vozzhennikova) Lentin et Williams Chatangiella tripartita (Cookson et Eisenack) Lentin et Williams Chatangiella victoriensis (Cookson et Manum) Lentin et Williams Chlamydophorella nyei Cookson et Eisenack Chlonoviella agapica Lebedeva Cladopyxidium reticulatum (Deflandre) Marheinecke Cladopyxidium septum (Morgenroth) Stover et Evitt Cordosphaeridium fibrospinosum Davey et Williams Cordosphaeridium inodes (Klumpp) Eisenack Coronifera oceanica Cookson et Eisenack Cribroperidinium exilicristatum (Davey) Stover et Evitt Deflandrea denticulata Alberti Deflandrea oebisfeldensis Alberti Dinogymnium acuminatum Evitt et al. Dinogymnium albertii Clarke et Verdier Dinogymnium digitus (Deflandre) Evitt et al. Dinogymnium heterocostatum (Deflandre) Evitt et al. Dinogymnium longicorne (Vozzhennikova) Harland STRATIGRAPHY AND GEOLOGICAL CORRELATION

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Dinogymnium nelsonense (Cookson) Evitt et al. Dinogymnium sibiricum (Vozzhennikova) Lentin et Williams Dorocysta litotes Davey Eisenackia brevivallata (Harker et Sarjeant) Quattrocchio et Sarjeant Eurydinium saxoniense Marshall et Batten Florentinia buspina (Davey et Verdier) Duxbury Fromea amphora Cookson et Eisenack Fromea chytra (Drugg) Stover et Evitt Fromea fragilis (Cookson et Eisenack) Stover et Davey Fromea laevigata (Drugg) Stover et Evitt Geiselodinium cenomanicum Lebedeva Gillinia hymenophora Cookson et Eisenack Glyphanodinium facetum Drugg Heterosphaeridium difficile (Manum et Cookson) Ioannides Hystrichosphaeridium tubiferum (Ehrenberg) Davey et Williams Hystrichosphaeropsis quasicribrata (Wetzel) Gocht Isabelidinium bakeri (Deflandre et Cookson) Lentin et Williams Isabelidinium belfastense (Cookson et Eisenack) Lentin et Williams Isabelidinium cooksoniae (Alberti) Lentin et Williams Isabelidinium magnum (Davey) Stover et Evitt Isabelidinium microarmum (McIntyre) Lentin et Williams Isabelidinium rectangulatum Lebedeva Isabelidinium thomasii (Cookson et Eisenack) Lentin et Williams Kallosphaeridium ?circulare (Cookson et Eisenack) Helby Kallosphaeridium ?ringnesiorum (Manum et Cookson) Helby Laciniadinium arcticum (Manum et Cookson) Lentin et Williams Laciniadinium firmum (Harland) Morgan Laciniadinium rhombiforme (Vozzhennikova) Lentin et Williams Leberidocysta chlamydata (Cookson et Eisenack) Stover et Evitt Leberidocysta defloccata (Davey et Verdier) Stover et Evitt Melitasphaeridium pseudorecurvatum ((Morgenroth) Bujak et al. Membranilarnacia hapala (Schiøler et Wilson) Fensome et Williams Membranilarnax liradiscoides Wetzel Membranosphaera maastrichtica Samoilovitch Microdinium kustanaicum Vozzhennikova Vol. 26

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Microdinium ornatum Cookson et Eisenack Odontochitina costata Alberti Odontochitina operculata (Wetzel) Deflandre et Cookson Oligosphaeridium complex (White) Davey et Williams Palaeocystodinium golzowense Alberti Palaeohystrichophora infusorioides Deflandre Palaeoperidinium cretaceum (Pocock) Lentin et Williams Palaeotetradinium silicorum Deflandre Palynodinium helveticum Kirsch Pervosphaeridium monasteriense Yun Hyesu Phanerodinium cayeuxii Deflandre Pterodininium cingulatum (Wetzel) Below Pulchrasphaera minuscula Schiøler, Brinkhuis, Roncaglia et Wilson Rhiptocorys veligera (Deflandre) Lejeune-Carpentier et Sarjeant Rottnestia borussica (Eisenack) Cookson et Eisenack Senoniasphaera protrusa Clarke et Verdier Senoniasphaera rotundata Clarke et Verdier Spinidinium uncinatum May Spiniferites ramosus (Ehrenberg) Mantell Spiniferites ramosus granosus (Davey et Williams) Lentin et Williams Spongodinium delitiense (Ehrenberg) Deflandre Surculosphaeridium longifurcatum (Firtion) Davey et al. Tectatodinium pellitum Wall Triblastula utinensis Wetzel Trigonopyxidia ginella (Cookson et Eisenack) Downie et Sarjeant Trithyrodinium quingueangulare Marheinecke Trithyrodinium suspectum (Manum et Cookson) Davey Moss and fern spores: Aequitriradites verrucosus (Cookson et Dettmann) Cookson et Dettmann Anemia exilioides (Maljavkina) Bolchovitina Appendicisporites macrorhyzus (Maljavkina) Bondarenko Appendicisporites matesovae (Bolchovitina) Norris Appendicisporites unicus (Markova) Singh Baculatisporites comaumensis (Cookson) Potonie Balmeisporites glenelgensis Cookson et Dettmann Densoisporites microrugulatus Brenner Camarozonosporites insignis Norris Cicatricosisporites auritus Singh Cicatricosisporites cuneiformis Pocock Cicatricosisporites minor (Bolchovitina) Pocock

Cicatricosisporites minutaestriatus (Bolchovitina) Pocock Cicatricosisporites mtchedlishviliae Griazeva Cicatricisporites pacificus (Bolchovitina) Chlonova Cicatricosisporites stoveri Pocock Clavifera triplex (Bolchovitina) Bolchovitina Concavisporites jurienensis Balme Concavissimisporites punctatus (Delcourt et Sprumont) Brenner Cyathidites minor Couper Foraminisporis asymmetricus (Cookson et Dettman) Dettman Foraminisporis dailyi (Cookson et Dettman) Cookson et Dettman Foveosporites cenomanicus (Chlonova) Schvetzova Gleicheniidites laetus (Bolchovitina) Bolchovitina Gleicheniidites senonicus Ross Gleicheniidites umbonatus (Bolchovitina) Bolchovitina Hemitelia separata Chlonova Hydropteris indutus Kondinskaja Impardecispora apiverrucata (Couper) Venkatachala, Kar et Raza Kuylisporites lunaris (Cookson et Dettmann) Laevigatosporites ovatus Wilson et Webster Leptolepedites verrucatus Couper Lobatia involucrata (Chlonova) Chlonova Lophotrilets babsae (Brenner) Singh Lygodiumsporites japoniciformis (E. Ivanova) Bondarenko Matonia parva Agranovskaya Ornamentifera echinata (Bolchovitina) Bolchovitina Plicifera delicata (Bolchovitina) Bolchovitina Rouseisporites laevigatus Pocock Rouseisporites reticulatus Pocock Ruffordia aralica (Bolchovitina) Ruminatisporites delicatus Strepetilova Stenozonotriletes radiatus Chlonova Taurocusporites redunctus (Bolchovitina) Stover Todisporites minor Couper Trilites hebetatus Chlonova Velosporites triquetrus (Lantz) Dettmann Gymnosperm pollen: Cedripites parvisaccatus (Sauer) Chlonova Cedrus cristata Sauer Ephedripites costatus Bolchovitina Pinuspollenites minimus (Couper) Kemp Podocarpidites multesimus (Bochovitina) Pocock Taxodiaceaepollenites hiatus (Potonie) Kremp


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Angiosperm pollen: Aquilapollenites dispositus (N. Mtchedlishvili) Srivastava et Rouse Aquilapollenites quadrilobus Rouse Aquilapollenites unicus Chlonova Beaupreaidites elegansiformis Cookson Causarinidites cainozoicus Cookson et Pike Cranwellia striata (Couper) Srivastava Fraxinoipollenites constrictus (Chlonova) Chlonova Interpollis supplingensis (Pflug) W. Krutzsch Menispermum turonicum N. Mtchedlishvili Nudopollis terminalis Pflug Plicapollis retusus Tschudy Plicapollis serta Pflug Pompeckjoidaepollenites subhercynicus (W. Krutzsch) W. Krutzsch Triatriopollenites myricoides Kremp Triatriopollenites roboratus Pflug Tricolpites albiensis Kemp Tricolpites sagax Norris Triorites harrisii Couper Triporopollenites plicoides Zaklinskaja Triporopollenites robustus Pflug Tricolporopollenites cingulum (Potonie) Thomson et Pflug Trudopollis menneri (Martynova) Zaklinskaja Trudopollis nonperfectus Pflug Trudopollis baculotrudens (Pflug) Zaklinskaja Trudopollis bulbosus Zaklinskaja Trudopollis ordinatus Zaklinskaja Trudopollis protrudens Pflug ACKNOWLEDGMENTS We are grateful to the reviewer G.N. Aleksandrova for valuable comments and critical remarks that enabled us to improve the paper. This work was supported by the Comprehensive Program of the Siberian Branch of the Russian Academy of Sciences II. 2P “Integration and Development” and by the IGCP 608 Project. Reviewers G.N. Aleksandrova and V.A. Zakharov REFERENCES Akhmetiev, M.A., Aleksandrova, G.N., Beniamovsky, V.N., et al., New data on the marine Paleogene of the Southern West Siberian Plate, Paper 2, Stratigr. Geol. Correl., 2004, vol. 12, no. 5, pp. 495–513. Akhmetiev, M.A., Zaporozhets, N.I., Iakovleva, A.I., et al., Comparative analysis of marine Paleogene sections and biota from West Siberia and the Arctic Region, Stratigr. Geol. Correl., 2010, vol. 18, no. 6, pp. 635–569. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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Translated by E. Maslennikova


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