GSA Connects 2021 in Portland, Oregon

Paper No. 17-7
Presentation Time: 9:45 AM


LOBACHEVA, Daria, Faculty of Geography, Laboratory of the Pleistocene Paleogeography, MSU, Moscow, 119296, Russian Federation, BADYUKOVA, Ekaterina, Faculty of Geography, Laboratory of the Pleistocene Paleogeography, MSU, Moscow, Russian Federation and MAKSHAEV, Radik, Faculty of Geography, Moscow State University, Moscow, 199991, Russian Federation

Baer knolls are elongated ridges widespread in the Northern Caspian lowland. These ridges are not found in this region anywhere above 0 m a.s.l. Several hypotheses on the origin of knolls still exist. Studying these landforms is very important for restoring the history of the Caspian Sea and environments that existed on its shores during the Late Pleistocene - onset of Holocene. The results of radiocarbon dating of the mollusks shells from four samples showed an age from 16.4 to 13.8 thousand years cal. One radiocarbon date 15296 ± 298 thousand years cal. (LU-8739) was obtained from whole shells Didacna praetrigonoides, D. parallella sampled from a sandy interlayer in the underlying 'Chocolate clays' (CC) at the base of the Yaksatovo knoll (Volga delta). The radiocarbon date 14221 ± 427 ka cal was obtained in the same knoll at the contact between the knoll stratum and CC from the Didacna protracta shells. (LU-9200). In the sediments of the Sarai-Batu knoll (111 km to the northwest of Astrakhan), from the sandy interlayer in CC containing abundant shells of the mollusks Didacna ebersini, D.protracta, and Dreissena rostriformis, the date 16365 ± 700 ka cal was obtained. (LU-8740). One date 13865 ± 271 thousand years cal. (LU-9201) was received from the in-situ Didacna protracta and Dreissena polymorpha shells sampled from the sandy interlayer at the contact between the knoll stratum and CC in the Dolgiy knoll (Volga delta). Radiocarbon analysis of shells of mollusks from the underlying СС showed an age interval of 16.3-15.2 ka cal, which falls into the cold stage of the Early Dryas (Steffensen, 2008). Two radiocarbon dates obtained at the contact between the knoll stratum refers to the interval of 14.2-13.8 ka, which is correlated with the warm stage of belling-allered. This stage was characterized by the species reduction of the mollusk fauna due to the increased content of clay particles brought in by the Volga. The analyzed literature and field material allows us to conclude that the BB as landforms were most likely formed at the end of the Khvalynian time (end of the Pleistocene - beginning of the Holocene) while the flow of water through the Manych Strait into the Black Sea occured.

The research was carried out with the support of the Russian Science Foundation project No. 20-77-00068 (laboratory research).