The timing and sedimentary facies of the early Khvalynian stage in the Lower Volga Region (Northern Caspian Lowland)

The sedimentary record from the Lower Volga Region, located in the Northern Caspian Lowland, could provide detailed insights into the effects of global and regional changes on the world's largest endorheic basin over the last 35 ka. In this paper, we present the comparison results of sedimentological analysis and radiocarbon dating of the Khvalynian deposits obtained from key sections in the Lower Volga Region. Seven lithofacies (LF1–LF7) are recognized. According to the radiocarbon dates, the age of the Early Khvalynian stage in the Lower Volga Region ranges between 27.0 and 12.5 cal ka BP. The deposition of the chocolate clay corresponds to an interval between 20.0 and 12.5 cal ka BP. The density of radiocarbon ages peaks during the 14.1–13.4 cal ka BP period. The analysis of radiocarbon data from mollusc shells and the lithofacies characteristics of Khvalynian sediments reveal a distinct pattern corresponding to major Late Pleistocene climatic events. This information enables us to reconstruct the depositional history of the Lower Volga Region from the end of MIS 3 to the Younger Dryas. • The development of the Early Khvalynian Basin in the Lower Volga region corresponds to the interval between 27.0 and 12.5 cal ka BP. • The first phase of chocolate clay deposition in the Lower Volga region corresponds to post-LGM, Oldest Dryas. • Massive chocolate clay deposition in the north-west part of the Early Khvalynian Basin, occurred during the Bølling stage and could be used as an index strata in the Lower Volga Region. • The deposition of sand corresponds to the cold stages (LGM, post-LGM, Oldest Dryas, Older Dryas and Younger Dryas). The expansion of mollusc species in the Lower Volga Region prevailed during cold stages.