Correlation of the Late Pleistocene paleogeographical events of the Caspian Sea and Russian Plain

The present work shows the author's concept of paleogeographic development of the Caspian Sea in the Late Pleistocene, based on the comprehensive analysis of the Caspian deposits and their relation and synchronization with glacial–interglacial cycles on the Russian Plain, based on published materials. Global climate changes were fundamental for both the transgressive-regressive state of the Caspian basins, as well as for glacier formation and retreat on the Russian Plain. At the same time, glaciers influenced the Caspian basin development on a regional level. The long-term low Caspian Sea level, complicated by the double-stage “minor” Late Khazar transgression, corresponded to the Mikulino (Eemian) interglacial with two endothermals. This warm stage in the Caspian history encompassed the interval corresponding to Marine Isotope Stage (MIS) 5. This is in agreement with the point of view of researchers who correlate the Mikulino interglacial with the entire MIS 5. The “cold” vast Khvalynian transgression and preceding to it the Atel regression developed during the Valday glaciation (MIS 4–2). The Atel regression corresponds to cold MIS 2 and the beginning of MIS 3. Its lower boundary in the Lower Volga region is marked with ice wedges. A transgressive tendency began to show in the second half of the interstadial (second half of MIS 3) and continued into early stages of the Late Valdai cooling, but it was interrupted during the dry and cold Glacial Maximum (peak of MIS 2) by the regressive stage. Further transgression development occurred during the degradation of the glaciation. Its course was impacted by transgressive-regressive events of lower magnitude linked to oscillations of climatic parameters: i.e., cold dry conditions of the Middle Dryas by the Enotaevka regression, and the continentalization of the Boreal period of the Holocene by the Mangyshlak regression.