Stratigraphic, paleomagnetic, and palynological data on the Paleogene-Neogene continental sediments of southwestern West Siberia

摘要

The paper presents magnetostratigraphic data on Paleogene-Neogene continental sediments stripped by borehole 8 at the southern periphery of the Om' basin, in the Ishim-Irtysh interfluve, on the border with northern Kazakhstan. Pollen assemblages and zones have been distinguished, and a paleomagnetic section of borehole 8 has been compiled. The section consists of 11 magnetozones, which are associated with pollen zones and paleocarpological data. The absence of some paleomagnetic and pollen zones from the section suggests that the geological record is incomplete, because the formations in the studied sediments are partly eroded. A dinoflagellate community was first recorded in Upper Oligocene-Lower Miocene sediments at the periphery of the Om' basin. The composition and ecologic characteristics of this community cannot give an unambiguous answer to the question whether seawater could penetrate southwestern Siberia through the Turgai Sea. The composition of pollen and spores from the Lower Oligocene sediments (Novomikhailovka Formation) and from the Chilikty Formation (northern Kazakhstan) is similar and reflects the development of Turgai flora in a huge territory. Later, in the second half of the Miocene, broad-leaved/coniferous forests were replaced by small-leaved ones. In the late Miocene, the latter were replaced by forest steppes with some arid flora.