Vol 25, No 3 (2017)

It is demonstrated on the basis of the first monographic study of multiple and taxonomically variable organic-walled microfossils from the Ust’-Il’ya Formation of the Anabar Uplift that both prokaryotic and eukaryotic forms are present in the composition of this microbiota. They are divided into four formal groups on the basis of the specifics of the morphological indicators of the identified taxa. The review of the data on the isotopic age of hosting deposits showed that the Ust’-Il’ya Formation is of the Early Riphean in age which are currently evaluated as 1750 ± 10–1400 Ma. Relatively large and morphologically complex eukaryotic forms present in the Ust’-Il’ya Formation served in due time as the basis for an erroneous conclusion on the Late Riphean age of the specified formation and the overlying Lower Kotuikan Subformation of the Anabar Uplift. The paper provides a global comparative analysis of the Early Riphean microbiotas, demonstrates the position of the Ust’-Il’ya and Kotuikan microbiotas amidst the microbiotas of the same age, and shows that the relatively large acanthomorphic acritarchs Tappania, Valeria, Dictiosphaera, Satka, and Shuiyousphaeridium appeared in the geological history already during the Early Riphean Erathem. Moreover, the paper discusses the recently published data on the distribution of aerobic and anaerobic conditions in the Early Riphean paleobasins and provides the conclusion on the impact of the lateral change of these conditions on the taxonomic composition of the microbiota.

This paper presents the results of a palynological study of the natural outcrops of the Lower and Middle Jurassic on the Kelimyar River (Outcrops 5, 6, 7, 14, and 16) and two boreholes, Middle-Nakynskaya and Ygyata-Tyungskaya 1, in Eastern Siberia. The Ukugut, Tyung, Motorchuna, Suntar, Kyrin, and Kelimyar formations were studied. Six biostrata with dinocysts were established for the Upper Sinemurian–Toarcian. The analysis of the stratigraphic ranges of dinocysts in the sections allowed the identification of the stratigraphic ranges for important genera of dinocysts, which enabled the updating of the geochronology of some biostrata. Three main stages of the evolution of dinocysts in the Early Jurassic in the Siberian Paleobasin were characterized by the appearance, diversification, and disappearance of some orders of dinocysts at certain times. Seven biostrata (beds with characteristic palynoassemblages) were established for the upper Sinemurian–Toarcian on the basis of the study of the taxonomic composition of spores and pollen of land plants and successive changes in the composition of the palynospectra.

The stratigraphic subdivisions of the Paleogene included in the updated regional stratigraphic scheme of the Ulyanovsk-Syzran facial district with a wide development of biosiliceous deposits, are described and paleontologically characterized. The biostratigraphic subdivision of the reference sections using diatoms and dinocysts is discussed. The recently recognized stratigraphic units, Smyshlyaevka and Karanino within the Kamyshin (Upper Paleocene) and Proleyka (Lower Eocene) regional stages are described.

New micropaleontological and paleomagnetic data were obtained by studying core samples of Cenozoic continental deposits from two boreholes drilled in the south of Tyumen oblast (Western Siberia). Palynological assemblages in deposits of the Tavda (upper part), Novomikhailovka, Turtas, Abrosimovka, Tobolsk, Smirnovka, and Suzgun formations were described. Deposits of these formations are enriched in spore-pollen assemblages, which can be correlated with assemblages of regional palynozones of the West Siberian Plain. Ostracods were described in Quaternary deposits. On the basis of biostratigraphic and paleomagnetic data, the Late Eocene (Priabonian)–Holocene age of deposits was substantiated. For the first time, beds with dinocysts of genus Pseudokomewuia were identified in deposits of the Turtas Formation (Upper Oligocene) of the Ishim lithofacial area. In total, nine regional magnetozones were distinguished in the paleomagnetic section. On the basis of palynological and paleomagnetic data, sections of two boreholes were correlated, and hiatuses in sedimentation were revealed. A large hiatus is at the Eocene-Oligocene boundary (Western Siberia): the Lower Oligocene Atlym Horizon and Miocene–Pliocene and Eopleistocene sediments are missing. The Oligocene interval of the section is represented in a reduced volume.