Lithofacial structure and conditions of accumulation of Baer knoll deposits in the Northern Caspian region

Baer knolls are usually elongated ridges of predominately sub-latitudinal orientation, which are widespread in the Northern Caspian region from the Kuma River mouth in the Kizlyar Bay at the western coast to the Emba River mouth at the eastern coast of the Caspian Sea. These ridges are not found anywhere above 0…+2 m a.s.l. beyond the limits of the Late Khvalynian transgression of the sea. The objective of the paper is to interpret the genesis of relief forms under study basing on detailed structure and lithology descriptions and dating of their material. Sediments of the Baer knolls usually consist of three lithological formations (LF1, LF2 and LF3) referring to the time interval of 21 to 11 cal. ka BP. Chocolate clays, as well as underlying marine sediments of a regression terrace and alluvium of rivers flowing to the Khvalynian basin were principal sources of material for knoll formation. The mollusk complexes of predominately brackish-water Didacna protracta, D. ebersini, D. parallella, D. parallella borealis, D. praetrigonoides, Dreissena rostriformis and Dr. polymorpha were identified in the deposits. Baer knolls were formed during the Late Khvalynian – Early Holocene transition. The knolls’ material cannot be attributed to the aeolian deposits because of their lithological, faunistic and geochemical features. The Baer knolls were formed at the lagoon bottom by the currents resulting from the Late Khvalynian basin water outflow through the Manych Strait. The landforms are analogues of river ripples and dunes appearing at the bottom of a turbulent flow, where the accumulation of sandy material and shell detritus took place simultaneously with the deposition of clay particles at the geochemical barrier as a result of coagulation under the mixing of lagoon brackish water and river fresh water.

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