NEW DATA ON BIOSTRATIGRAPHY OF THE TAVDA HORIZON (RYUPELIAN STAGE) IN WESTERN SIBERIA (BASED ON THE RESULTS OF THE STUDY OF FORAMINIFERA)

The problematic point in the Paleogene biostratigraphy of Western Siberia is the age of the Tavda Horizon as well as the position of Oligocene Stages. In the regional stratigraphic chart for the Paleogene of Western Siberia, unicellular algae and some other data were used as the basis for conclusions on the age of the Tavda Formation (Horizon). As a result, the age of the Tavda Horizon is dated back to the Late Bartonian (Middle Eocene). According to the foraminifera data using geological information, as well as publiсations, the age of the Tavda Horizon is defined as the Ryupelian (Middle Oligocene). The Latdorfian Stage of the Lower Oligocene, as it turned out, falls out of the stratigraphic section of Western Siberia due to manifestation of positive tectonic movements, the rise of this and other northern regions. In the southern regions of Europe, the USA, and the Atlantic, the Latdorfian Stage is present as the Lower Oligocene or as planktonic foraminiferous zones.