“Warm” stages in the West Siberian Late Pleistocene

The revised study of stratotypes and key sections of the Karginsky regiostage in the West Siberian Plain with the use of 230Th/U dating determinations and advanced 14C dating indicated that many 14C ages obtained in the 1960–1970s were incorrect, and revealed the pre-Karginsky age of the Karginsky regional substage stratotypes adopted in the modern Pleistocene stratigraphic schemes of West Siberia. The available 230Th/U and 14C data along with the new paleobotanical record provided substantial refinement of the Late Pleistocene succession of paleoclimatic events in the West Siberian Plain. The 5e5 and 5e1 optima corresponding to climatic events of the Greenland ice core and 5e2 and 5e4 pessima are revealed in boreal West Siberia. The obtained 230Th/U dating determinations, even with their wide tolerance interval, make it possible to recognize not only the major but certain minor climatic events within the Kazantsevsky interglacial in boreal West Siberia. Beds corresponding to MIS 5c are recorded in the middle reaches of the Ob River. The preceding cooling was comparable with that of the later stages of the Zyryansky glaciation and is correlated with MIS 5d, which suggests the beginning of the Zyryansky glaciation occurred in the second half of MIS 5. The obtained records do not require elimination or reducing of the range of the Karginsky regiostage. However, the stratotypes of its regional sub-stages, chosen mainly in the 1960–1970s, appear to be invalid.