On the age and expression of extreme Sarmatian hydrological changes of the Eastern Paratethys in the Caspian Basin (Late Miocene, Kazakhstan).

The Eastern Paratethys is a former epicontinental sea that in the Late Miocene was spread over the vast areas of Eastern Europe and Central Asia. Combining three major subbasins – The Dacian (Carpathian foreland), the Euxinian (Black Sea) and the Caspian basins, the Eastern Paratethys played a vital role in the regional climate, paleobiogeography and ecosystem sustainability. At around 11.6 Ma the Eastern Paratethys became hydrologically isolated from the global ocean due to the tectonic closure of its gateways. For the next 5.5 Ma (up until 6.1 Ma), the Eastern Paratethys turned into a megalake that was trapped in the Eurasian interior. Warming and drying of the climate during so-called Sarmatian Stage (12.65-7.65 Ma) disbalanced precipitation/evaporation ratio in the megalake and thus provoking extreme water-level fluctuation of several hundred meters. Subsequent changes in the water chemistry and temperatures drove the regional ecosystems to the edge of extinction.

The paleoenvironmental evolution of the Eastern Paratethys has been mainly inferred from geological record of the Black Sea and partly Dacian Basin. At the same time, reconstruction and dating of Sarmatian hydrological and faunal changes for the Caspian region remains uncomprehended.

Here, we present our new magnetostratigraphic data on Sarmatian record from the Caspian region (Karagiya Depression, Kazakhstan) and compare it with the data from the other Eastern Paratethys subbasins (the Dacian and Euxinian Basins). Sedimentological observations together with magnetostratigraphic constraints indicate incompleteness of the lower (Volynian) and upper Sarmatian (Khersonian) deposits in the studied section. The middle (Bessarabian) and upper Sarmatian (Khersonian) s.l. begin as transgression events within reversed zones preliminary correlated to C5r.2r (11.188 – 11.592 Ma) and to C4Ar.2r (9.426 - 9.647 Ma) respectively. Sarmatian deposits are transgressively overlain by Maeotian deposits with the boundary occurring within a small reversed chron preliminary correlated to C3Br.3r (7.499 – 7.537 Ma).

The newly acquired polarity patterns suggest that the major Sarmatian paleohydrological events in the Caspian segment were coherent with the other parts of the Eastern Paratethys. However, the complexity of polarity patterns and highly condensed character of the section require further refinement of magnetostratigraphic age constraints.