Age of the Khvalynian Strait in the Late Pleistocene History of the Manych Depression

Introduction. At the end of the Late Pleistocene, the early Khvalynian basin developed in the Caspian Basin. As soon as its waters exceeded the height of the watershed (about ۴۵-۵۰ m) with the Black Sea basin, the Early Khvalynian strait was opened (Yanina, ۲۰۰۵), the main link of which was the Manych Depression, a vast depression in the south of the East European Plain. Despite the long history of study of the region, researchers' opinions regarding the age of the Early Khvalynian strait deposits differ, and the time of the Strait's functioning has not yet been unequivocally correlated with the global chronostratigraphic scheme.The Levy Island section (N۴۶°۰۱′۳۸.۰, E۴۳°۲۳′۰۵.۹; altitude - ۲۲.۴ m) is located at the western end of Lake Manych. Levy Island is a sublatitudinally elongated positive relief form - a ridge with a gently sloping or sometimes subhorizontal slightly undulating surface, its length is ۱۶ km and average width is ۲۵۰ m. The relative height above the shoreline of Lake Manych is ۶-۷ m. The ridge is composed of clayey sediments of the ancient Burtasian lake, overlain by dealluvial and eluvial cover with leaning sediments of the Khvalynian transgression. The section has been described in detail, and malacofaunal and geochronological analyses have been carried out. The inclusions of mollusc fauna were studied in the Research Laboratory of Modern Deposits and Pleistocene Paleogeography of the Lomonosov MSU Faculty of Geography in order to provide biostratigraphic justification of the geological age of sediments and reconstruction of the paleoecological conditions of their accumulation. Malacofaunal analysis is traditionally the basis for the stratigraphy of Pleistocene sediments of the southern seas of Russia. Absolute chronology is obtained by optically stimulated luminescence (OSL) method. Dating of different-age sediments of the Levy Island section was carried out at the Nordic Luminescence Dating Laboratory of Aarhus University. We will present presents the results of optically-stimulated luminescence (OSL) dating of the Early Khvalynian deposits uncovered in the coastal outcrop of the western end of the island. The data were obtained for nine dates, six of which characterize the aqual stages of the territory's development, three - subaerial. Biostratigraphic analysis of the malacofauna confirmed that the marine sediments uncovered in the section belong to the Early Khvalynian transgression of the Caspian Sea. By the results of dating the time of early Khvalynian water intrusion into the Manych depression was determined to be late MIS ۲, which corresponds to the age of the Late Valdai glaciation degradation (Ostashkov stage, MIS ۲). This research was supported by Russian Science Foundation, project № ۲۱-۱۸-۰۰۵۵۲

Keywords:

Manych depression , stratigraphy , Atelian regression of the Caspian Sea , Late Quaternary