CASPIAN MOLLUSKS IN THE BLACK SEA DURING THE LATE PLEISTOCENE

The presence of the Caspian mollusks in the Black Sea basins is of primary importance for the correlation of events in the basins; it proves undoubtedly the paleo-straits functioning between them. The Caspian mollusk fauna consists of species autochtonous for the Caspian Sea and endemic of the Pontian-Caspian basin.

As follows from the analysis of the Late Pleistocene malacofauna of the Pont brackishwater didacnas persisted in freshened water areas throughout the Karangatian epoch. Two groups of the mollusks are identified: 1) Euxinian-Uzunlarian species (Didacna pontocaspia, D. borisphenica) that survived the increased salinity interval in the freshened parts of the basin; 2) Caspian species (Didacna cristata, D. subprotracta, D. subcatillus) penetrated into the retreating Karangatian basin with the Hyrcanian water and settled on a few limited areas of the Tarkhankut basin. At the time of the New Euxinian regression, when the basin was noticeably freshened, all the didacnas became extinct. The New Euxinian transgressive basin was dominated by Caspian species (Monodacna, Adacna, Hypanis, Dreissena) with occasional Didacna ebersini which is an index species of the Early Khvalynian fauna of the Caspian Sea.

The presence of members of the Caspian assemblages in the Tarkhankut and New Euxinian basins strongly suggests the Caspian water inflow into the Black Sea at that time by the Manych Strait.

Some researchers are of opinion that the faunal elements of the Old Euxinian basin could survive during the marine Karangatian transgression in the freshened limans and then disperse over the New Euxinian basin. Others consider the brackish-water New Euxinian species to be migrants from the Caspian Sea to the Surozh basin; they could survive in the most freshened areas and then – at the New Euxinian time – expanded widely. The isolation presents a powerful factor of species formation. The species of the two isolated basins are similar, so the Caspian fauna existing now in the Azov-Black Sea basin persists seemingly since the end of the Pleistocene. The work is supported by RSF Project 21-44-04401