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Palaeoecoligical reconstructions of predelta area of the North Caspian Sea were based on the multidisciplinary study of the core from the Rybachya borehole containing the Holocene deposits. Geochemical, grain size, mollusk fauna, diatom and ostracod analyses were performed, and the radiocarbon dating was carried out. The structure of deposits reflects palaeogeographic events of different scales including the inception of a palaeoincision in the Lower Khvalynian deposits, accompanied by erosion of the Upper Khvalynian deposits; its development during the Mangyshlak regression and gradual filling during the multistage Holocene Neocaspian transgression. The Holocene age of the deposits filling the palaeodepression is confirmed by radiocarbon dates - 8070 ± 110 and 7020 ± 140 cal. BP. The paleontological data indicate the interchange of tranquil and dynamic water regimes and the quasicyclical change in the conditions of the water basin, from brackish to freshwater and to marine during the stage of sedimentation, corresponding to the presentday conditions on the North Caspian shelf.
Лысенко et al. (Sat,) studied this question.