NEW DATA ON THE GENESIS AND TIMING OF FORMATION OF THE GRIVA SEQUENCE AND GRIVA RELIEF OF THE UPPER PLEISTOCENE BARABA PLAIN IN THE SOUTH OF WESTERN SIBERIA

This article examines the structure, composition, and textural features of the Griva Sequence in the Volchya Griva section and the paragenetically associated relief. Additional data supporting the aeolian origin of the Griva Sequence and the Griva relief are presented. Optically stimulated luminescence and infrared stimulated luminescence dating of the Volchya Griva section indicate that the Griva Sequence formed during the last glaciation and fully corresponds to Marine Isotope Stage (MIS) 2. The findings confirm that aeolian relief formation and the intensification of aeolian processes occurred during cold glacial periods of the Late Pleistocene, when southwesterly winds prevailed. The textural and structural characteristics of the Griva Sequence are similar to those of Upper Pleistocene niveo-aeolian sands that formed in cold, periglacial, arid regions of the world and are distributed along the southern margin of the last glacial ice sheets from Northwestern Europe to Western Siberia and Alaska. The formation of a deflationary truncation and a system of mega-yardangs in the northern part of the Lake Chany basin indicates a significant intensification of aeolian processes at the transition between the deposition of the lower and upper members of the Griva Sequence. The orientation of the Griva relief, which coincides with the prevailing direction of modern winds, suggests that wind directions during the cold and warm epochs of the Quaternary in southern Western Siberia were similar. The complete stratigraphy of the Volchya Griva section, its correspondence to the last glaciation and MIS 2, the presence of the largest Eurasian mammoth faunal locality, its distinct lithological characteristics, and the relatively high degree of its study allow this section to be considered one of the reference sections for the Upper Pleistocene of Siberia. It should be regarded as the stratotype of the widely distributed Griva Sequence in this area, which is proposed as a separate Baraba horizon (formation) for the south of Western Siberia, comprising the Eltsovka and Bagan loesses and the Suma soil that separates them.