Natalia K. Lebedeva

—Dinocyst assemblages are subjected to taxonomic typification based on a qualitative and quantitative assessment of their generic composition for the Northern Hemisphere during the Coniacian–Santonian time in order to identify correlation taxa. The typification is carried out using a cluster analysis according to the Jacquard calculation model (BioDiversity Professional, 1997). Three types of dinocyst assemblages have been identified in the Coniacian. As compared to the Turonian, the relatively cold-water West Siberian basin is characterized by a decrease in the number of cosmopolitan taxa and an increase in species endemism. The only taxa identified at present are those allowing for intrabasin correlations. Three types of dinocyst assemblages have also been established for the Santonian. Free interbasin connections in the Northern Hemisphere contribute to the equalization of the generic composition between the three identified types and to the identification of characteristic taxa that allow for interregional correlation.

The taxonomic typification of dinocyst assemblages was carried out on the basis of a qualitative and quantitative assessment of their generic composition for the Northern Hemisphere in the Cenomanian–Turonian time to identify correlation taxa. Three types of dinocyst assemblages were identified in the Cenomanian. Cenomanian dinocyst assemblages are poorly differentiated; a large number of cosmopolitan genera were identified, which is in good agreement with paleobotanical data indicating a very warm, humid climate. Three types of dinocyst assemblages were established for the Turonian. The number of cosmopolitan dinocyst genera decreases and species endemism sharply increases in some Turonian basins. The differentiation of assemblages increases and their correlation potential decreases. However, the identified common genera and species of dinocysts in different types of assemblages provide the possibility of interregional correlation of Upper Cretaceous deposits at the stage, substage, and, at some sections, even more detailed levels in different climatic zones.

Taxonomical Diversity of Cenomanian-Turonian Dinocyst in the Northern Hemisphere: Some Aspects of Paleobiogeography and Paleoclimatology Таксономическое разнообразие сеноман-туронских диноцист (Dinoflagellate cysts) Северного полушария: некоторые аспекты палеобиогеографии и палеоклиматологии

The results of a palynological study of the Upper Cretaceous and Paleogene sediments of three boreholes drilled in the South Transurals are presented. The Upper Cretaceous Kuznetsovo, Kamyshlov, Zaikovo, Fadyushino, and Gan’kino formations are exposed by Boreholes 3, 9, and 13, which contain four spore and pollen biostratons. Five dinocyst biostratons are identified for the first time: local zone with Chatangiella spectabilis, local zone with Spinidinium sverdrupianum, local zone with Chatangiella chetiensis, local zone with Chatangiella manumii–Dinogymnium spp., and local zone with Cerodinium diebelii. The comparison of the Late Cretaceous dinocyst assemblages of the southern and northern territories of Western Siberia shows that, in spite of significant provincialism of dinoflagellates, there is a series of stratigraphic intervals in the middle–upper Turonian, lower Coniacian, lower Santonian, Campanian, and lower Maastrichtian, which have interregional correlation potential. In the Talitsa, Serov, Irbit, and Chegan formations, intervals of six zones of the Thanetian–Bartonian age of the dinocyst scale of Western Siberia are identified in Borehole 9 (Alisocysta margarita, Apectodinium hyperacanthum, Deflandrea oebisfeldensis (acme), Dracodinium simile, Rhombodinium draco, and Rh. ornatum), as well as five local zones by spores and pollen. The Kurtamysh Formation is characterized by a Rupelian spore and pollen assemblage. Significant sedimentation hiatuses in the Cretaceous–Paleogene sequence corresponding to the upper part of the Maastrichtian, the most part of the Danian and Selandian, the lowermost parts of the Ypresian, middle–upper Ypresian, Lutetian, the upper parts of Bartonian, Priabonian, and the lower parts of the Rupelian are established.

The results of palynological and micropaleontological study of Upper CretaceousCenozoic strata exposed by boreholes (BH) 23 and 19 of the Aleisk Square (Altai Region) are presented. The obtained data allowed to substantiate the age of deposits, to make assumption about its depositional conditions and to clarify the division of the section into suites. Two palynological assemblages were established in the Cretaceous part of the BH 23 section: the first characterizes the Lenki Formation and dates by SenomanianTuronian, the second one is revealed in the Upper-Sym Subformation and dates by the Maastrichtian. The Paleogene Ostrovnoye Formation of continental genesis lies on the Upper Cretaceous sediments. In BH 23 and BH 19, this formation contains spore and pollen spectra of presumably Late PaleoceneEarly Eocene and Middle Eocene age respectively. According to palynological data, the Late Miocene age of the sediments at the upper part of BH 23 section and its affiliation to Pavlodar Formation have been substantiated. The structure of palynological assemblages, features of macerate and the absence of foraminifera indicate the continental genesis of the Upper CretaceousPaleogene sediments common in the southern part of the Kulunda Depression of the Altai Region.

— The results of palynological and micropaleontological studies of the Upper Cretaceous–Cenozoic strata penetrated by Boreholes 23 and 19 of the Aleiskaya area (Altai krai) are presented. The...

The Jurassic–Cretaceous terrigenous complex of the Laptev and East Siberian Seas is of considerable interest as a potential exploration target. However, the key Jurassic and Cretaceous sections of the New Siberian Islands have been poorly studied. The results of this study were used to provide a detailed micropaleontological description of these sections and substantiation of the previous lithostratigraphic subdivision. We first identified a series of Boreal standard zones in the Jurassic and Cretaceous sections, based on the foraminifers, ostracods, dinocysts, and terrestrial palynomorphs. Our results, along with the published data on ammonites, bivalves, and terrestrial palynomorphs and the results of radiometric dating, provide more precise constraints on the stratigraphic position of the identified lithostratigraphic units. The results of this study can be corroborated by seismic data to explore offshore areas of the Laptev and East Siberian Seas. We also present detailed data on the geochemistry of organic matter from the Pestsovaya Formation (Hettangian–lowermost Upper Pliensbachian).

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...

Mesozoic sections in the New Siberian Archipelago are important for understanding of the geology of underexplored shelf areas in the east of the Laptev Sea and in the west of the East Siberian Sea. They are reference sections for interpretation of seismic data in these regions. However, there are still many unresolved problems concerning the lithology, lateral extent, and age of Mesozoic deposits, as the sections have a complex structure and are heavily deformed. The performed research makes a basis for the first facies zoning of Jurassic and Cretaceous deposits in the New Siberian Islands and adjacent landmasses of continental Siberia at the junction of the Laptev and East Siberian Seas. The lithostratigraphic division of the Jurassic and Cretaceous is refined, being proposed for the first time for some stratigraphic intervals, and allows updating their lithostratigraphic division (or undertaking it for the first time for some stratigraphic intervals). Facies features of Jurassic and Cretaceous deposits allow the definition of three depositional series.