A New Biostratigraphic Level of Pliocene in West Siberia and the Age of the Lower-Middle Miocene Stratotype of the Beshcheul Horizon

摘要

Stratigraphic substantiation of the age of local and regional units defined in the Oligocene, Lower Miocene, and Middle Miocene continental units of West Siberia, as well as their correlation, are mainly based on palynological and paleocarpological data. In this respect, the Lower-Middle Miocene Beshcheul Horizon is one of the best-substantiated Stratigraphic units. At an Interdepartmental Stratigraphic Meeting in 1967, the exposure described by M.G. Gorbunov and V.P. Nikitin in [2] on the right scarp of the Irtysh River near the Isakovka Settlement was proposed as its stratotype. It encloses seed flora of the Isakovka level and Isakovka palynoflora that characterize, in opinion of paleobotanists, the Middle Miocene stage in Neo-gene flora development. Some researchers suggest that the Neogene section of West Siberia begins with the Beshcheul Horizon containing the Isakovka palynoflora.