The Caspian Sea shelf during the pleistocene regressive epochs

Abstract

During the Pleistocene regressive epochs, the Caspian Sea shelf became entirely (the Atel and Mangyshlak regressions) or partly (the Cheleken and Enotaevka regressions) exposed, which was accompanied by a change in the relief formation and sedimentation settings in the drained areas. The adjacent offshore areas were subjected to the transformation of the seawater salt composition, the temperature regime, and the biotic communities. The sea level falls during the Caspian Sea regressions were accompanied by large-scale environmental changes: the desiccation of spacious sea bottom areas, transformations of the landscapes and the relief formation and sedimentation settings, alterations of the seawater’s salt composition in the offshore areas, and the transformation of the biotic communities. The largest regressions were characteristic of the Tyurkyan, Bakuan-Khazarian, Khazarian-Khvalynian (Atel), and post-Khvalynian epochs. The shelf became entirely exposed (234 000 km2) during the maximal Atel and Mangyshlak regressions. During the Cheleken and Enotaevka regressions, the shelf was half drained. The epochs when the Caspian shelf was entirely exposed were marked by different climatic events in the Caspian Sea region and the adjacent glacier-affected areas of the Russian Plain. In general, the main regressive epochs correspond to interglacials on the Russian Plain, although this correlation was much more complex.