Identification and age of submarine Girkanian sediment beds (Upper Pleistocene) in the Caspian Sea

Abstract

For the first time, the Upper Pleistocene Girkanian sediment subhorizon was recorded in the submarine boreholes of the northern Caspian Sea and its radiocarbon age was estimated. Girkanian beds lying at a depth of 25 m beneath the seafloor were studied by lithological, biostratigraphical, seismic and radiocarbon dating methods. They were distinguished based on the characteristic assemblage of Mollusca (Didacna subcatillus, D. cristata, Corbicula fluminalis, etc.). This assemblage is similar to its onshore analogue and differs from the fauna of the underlying Upper Khazarian (D. surahanica, D. nalivkini, etc.) and overlying Lower Khvalynian (D. ebersini, D. parallella, D. protracta, etc.) layers. Acoustic profiling indicates the ubiquity of the horizon in the northern Caspian Sea, as seen from the clear correlation between boreholes. AMS 14C dating has shown that the age of the Girkanian deposits exceeds 55 ka. Their real age haze to be about 80 ka. The obtained results on identification and age estimation of Girkanian beds are an important contribution to the verification of the Upper Pleistocene stratigraphy of the Caspian Sea region.