Chronology and Development of Cryogenesis in Loess-Paleosol Sequence in the Lower Volga Region1

The article presents the results of studying four sediment sections in the Lower Volga region that containing numerous traces of cryogenesis in Late Pleistocene subaerial deposits, represented by thin vertical wedges in loess and soils, involutions and wedges in alluvial deposits. In order to establish the stages of development and the boundaries of permafrost in the southeast of the East European Plain, morphology of cryogenic structures, morphoscopy and micromorphology of quartz grains were established, the coefficient of cryogenic contrast were calculated, and also absolute dating of deposits was performed. Five stages of cryogenesis development in the Late Pleistocene, which differed in type, scale of distribution, and conditions for the formation of cryogenic structures were established on the studied territory. The processes of cryogenic transformation of sediments occurred due to both seasonal freezing and the long-term development of a perennial permafrost zone. This determined the composition, structure and properties of loess-paleosol sequences and alluvial layers. The results obtained significantly refine the current understanding of the conditions for the formation of the Atelian deposits in the Lower Volga Region and the distribution of permafrost zone in the south of the East European Plain in the Late Pleistocene.