Paleogeography of the Atelian regression in the Caspian Sea (based on drilling data)

Yanina, T.; Bolikhovskaya, N.; Sorokin, V.; Romanyuk, B.; Berdnikova, A.; Tkach, N.

Авторы: Yanina T., Bolikhovskaya N., Sorokin V., Romanyuk B., Berdnikova A., Tkach N.
Журнал: Quaternary International
Том: 590
Год издания: 2021
Издательство: Pergamon Press Ltd.
Местоположение издательства: United Kingdom
Первая страница: 73
Последняя страница: 84
DOI: 10.1016/j.quaint.2020.07.023
Аннотация: The Caspian Sea is the world's largest lake noted for a unique history of its evolution in the past. One of most important events in the Caspian history is the Atelian regression. The purpose of this work is to specify the extent, the time, and environments of the Atelian regression, as well as its correlation with events in the adjacent regions, on the basis of multidisciplinary studies of the Atelian deposits penetrated by engineering boreholes in the Northern Caspian. Processing of two-frequency seismoacoustic profiles permitted to stratify the sequence and to perform a spatial correlation between the determined boundaries of the sedimentary series. The laboratory studies included lithological and geotechnical analysis of the cores, floristic and faunal studies of the organic remains extracted from the cores, as well as analyses of pollen and spores, the isotope and radiocarbon (14C) analysis. In the seismic-acoustic profiles Atelian regression is represented by erosional landforms (incisions) under the reflecting horizon at the base of Khvalynian sediments. The regressive series is noted for inhomogeneous lithology. In depressions they are represented by interlayered clays and clay loams. The elevations between the depressions are composed of loamy sands in association with loams. Plant detritus occur as separate inclusions, or forms layered concentrations; there are also shells of freshwater and terrestrial mollusks. The paleontological material suggests aquatic or wetland environments with freshwater or freshened brackish-water shallow water bodies. The palynological materials provide evidence of diversified landscapes in the northern Caspian Lowland at the time of the Atelian regression – from forests dominated by conifers to periglacial forest-steppe and tundra-forest-steppe, mostly resulting from the climate fluctuations. The redeposited pollen is present in abundance, often well-preserved, indicative of highly active erosion at the time of regression. The Atelian regression maximum and the erosional processes on the northern Caspian Lowland correspond to the maximum cooling of the Kalinin (MIS 4) glacial time. The final stages of the regression fell on the initial phases of the MIS 3 interstadial. As follows from materials obtained by seismic-acoustic profiling and drilling, the Caspian level dropped to −100 m. We attribute the sea level lowering to the Caspian (Hyrcanian) water discharge through the Manych into the Pontian basin and to the specific glacial environment during the Valday (MIS 4) time. The Atelian regression maximum is correlatable with the maximum of the post-Karangatian regression of the Black Sea. It was at the same time that the lacustrine Burtass (Gudilo) series were deposited in the Manych depression. In the stratigraphic scheme of the Caspian Sea the Atelian regressive horizon (as a stratigraphic unit) is positioned between Hyrcanian and the base of Lower Khvalynian deposits. In the Northern Caspian the continental Atelian formation spans a greater chronological interval and should be considered as a suite (or formation) in the regional stratigraphic scheme. A comparison between the position of Atelian deposits in the Pleistocene sequence within the sea basin and on the dry land supports the assumption that the geological records exposed in the coastal zone are incomplete. Only a thorough analysis of the materials obtained from the offshore drilling and from the sequences studied in exposures on land can give a comprehensive picture of the history of regional environments and present them correctly in a stratigraphic scheme.
Добавил в систему: Сорокин Валентин Михайлович

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Paleogeography of the Atelian regression in the Caspian Sea (based on drilling data)статья

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