PALEOGEOGRAPHIC ANALYSIS OFTHE RESULTS OF OPTICALLY STIMULATED LUMINESCENCE DATING OF PLEISTOCENE DEPOSITS OFTHE LOWER VOLGAAREA

Upper Pleistocene deposits of the Srednyaya Akhtuba section (basic for the Lower Volga area) were studied by the method of optically stimulated luminescence (OSL). Eleven dates corresponding to different paleogeographic stages of development of the region were received. It allowed constructing the geochronological scheme of development of the studied region of the Lower Volga area and correlating it with paleogeographic events in the Caspian Sea, as well as with the glacial and interglacial rhythmics of the late Pleistocene on the East European Plain. The beginning of the late Pleistocene (MIS 5e, Mikulino interglacial epoch) is characterized by formation of a soil horizon outside the zone of influence of the Late Khazarian transgression of the Caspian Sea. The transitional stage to the Valdai glacial era is reflected in the section by the horizons of fossil soils (MIS 5c, dating 102 500±5160 years ago and 5a, dating 68 280±4170 years ago) divided by loess subaeral sediments (MIS 5d, dating 112 630±5400 years ago; and MIS 5b, dating 87 620±4100 years ago). The first glacial stage (Kalinin) of the Valdai glaciation (MIS 4) is characterized by formation of loess strata. The final phase of its sedimentation dating 48 680±3100 years ago corresponds to the beginning of the interstadial warming (MIS 3) when the Caspian Sea was in a regressive state. The second half of the interstadial warming (MIS 3) in the Lower Volga area is represented by alluvial strata dating 36 780±3000, 35 500±2800 and 27 000±1580 years ago. Soil formation traces reflecting the heterogeneity of climatic conditions of the era are recorded in its structure. The early stage of Khvalynian transgression developed in the Caspian Sea at the time. The era of degradation of the late Valdai (Ostashkovo) glaciation (MIS 2, dating 15000±1000 and 13000±500 years ago) is characterized in the Lower Volga area by accumulation of chocolate clay strata of Khvalynian transgression of the Caspian Sea. The end of the Holocene stage of sedimentation is dated («control date») back to 720±70 years ago. The first experience of dating of the upper Pleistocene deposits of the Lower Volga area by OSL method showed its prospects both for creation of the geochronological scheme of deposits and events of the region, and for their correlation with global climate changes, paleogeographic events in the Caspian Sea and on the East European Plain. 

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