Z.N. Gnibidenko

Comparative analysis of marine paleogene sections and biota from West Siberia and the Arctic Region

The analysis of the main biospheric events that took place in West Siberia and the Arctic region during the Early Paleogene revealed the paleogeographic and paleobiogeographic unity of marine sedimentation basins and close biogeographic relations between their separate parts. Most biotic and abiotic events of the first half of the Paleogene in the Arctic region and West Siberia were synchronous, unidirectional, and interrelated. Shelf settings, sedimentation breaks, and microfaunal assemblages characteristic of these basins during the Paleogene are compared. The comparative analysis primarily concerned events of the Paleocene-Eocene thermal maximum (PETM) and beds with Azolla (aquatic fern). The formation of the Eocene Azolla Beds in the Arctic region and West Siberia was asynchronous, although it proceeded in line with a common scenario related to the development of a system of estuarine-type currents in a sea basin partly isolated from the World Ocean.

Paleontological and magnetostratigraphic data on Upper Cretaceous deposits from borehole no. 8 (Russkaya Polyana District, Southwestern Siberia)

This work presents results of complex research (palynological, macro- and microfaunistic, and paleomagnetic) of Upper Cretaceous deposits, opened by borehole no. 8 in the Russkaya Polyana District (the southern margin of the Omsk Depression, Southwestern Siberia). The paleontological data obtained allowed us to establish the age of deposits. Based on dinocysts, nannoplankton and spore-pollen complexes, the section of borehole no. 8 has been divided into Pokur, Kuznetsovo, Ipatovo, Slavgorod, and Gan’kino Formations. This work gives data on the composition of zonal palynomorphs, nannoplankton, and microfaunistic complexes. Based on the complex data obtained, the magnetostratigraphic section of Upper Cretaceous deposits has been developed. The section consists of three magnetozones: normal and two reversed polarity magnetozones. The Pokur, Kuznetsovo and Ipatovo Formation (Cenomanian-Santonian) belong to the long normal polarity magnetozone; the Slavgorod and Gan’kino Formations (Campanian-Maastrichtian), separated by a stratigraphic break, belong to reversed polarity magnetozones. The magnetostratigraphic section has been correlated with the general magnetostratigraphic and magnetochronological time scales.

A Regional Upper Cretaceous Magnetostratigraphic Section of Southern West Siberia (Omsk Depression)

1107 Construction of regional magnetostratigraphic sections and scales for different geological provinces of continents is an important element of investigations aimed at development of the standard geomagnetic scale, which is widely used in geochronological, strati� graphic, and geodynamic studies, as well as in theoret� ical and applied geophysics. Recent investigations have yielded extensive data on the paleomagnetic properties of Cretaceous sections in the former Soviet Union and around the world. At the same time, the progress in development of the Cretaceous paleomag� netic scale has been determined by the results of pale� omagnetic investigations in the most important geo� logical provinces of continents, such as, for example, the West Siberian Basin (WSB). Paleomagnetic data on Cretaceous sections are practically missing from this region, which represents one of the largest petroliferous basins in the world, except for some information in [1–3]. We have studied and analyzed paleomagnetic and paleontological data on Upper Cretaceous sections of the Omsk depression located in the southwestern mar� ginal part of West Siberia. The geological section of the region in question (Russkaya Polyana area) is represented by Mesozoic– Cenozoic marine and terrestrial sediments that form the platformal cover resting upon the eroded surface of

New data on stratigraphy (palynomorphs, ostracods, paleomagnetism) of Cenozoic continental deposits of the Ishim plain, Western Siberia

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.