New Data about the Section Stratigraphy near Kileshino (Tver Oblast, Russia)— the Key for Understanding Boundaries of Glaciations on the Valdai Hills in the Upper Pleistocene

The article presents the lithological and stratigraphic characteristics, the results of paleobotanical studies and radiocarbon dating of the one of the most important and insufficiently studied key sections of the Late Pleistocene in the Upper Volga basin. The Kileshino-2 section locates in the marginal part of the last glaciation in the Valdai Hills (Tver oblast, Selizharovo district). The studied section is a complex sequence of sediments which consists of limnoglacial, limnic, alluvial and fluvioglacial deposits. We identified four main stages of sedimentation on the base of complex investigations: the Late Moscow stage of the Middle Pleistocene, the Mikulino Interglacial of the Late Pleistocene, the Early Valdai stage and probably the Middle Valdai Interstadial of the Late Pleistocene. Local pollen zones distinguished in the lower part of the sequence correspond to initial phases of the Mikulino Interglacial. At that time broadleaf forests began to spread in the study area under conditions of progressive warming. The macroremains of temperate and thermophilic aquatic plants were determined by the carpological method. The deposits of the climatic optimum and the final phases of the Mikulino Interglacial are not represented in the studied section. According to pollen data, the middle part of the sequence consisting of loam and sandy loams with two paleosoils was formed at the beginning of the Early Valdai Glaciation. Against the background of a progressive cooling, two interstadial-type warmings probably corresponding to the Upper Volga (Brørup) Interstadial and Kruglitsky (Odderade) Interstadial were identified. The chronostratigraphic position of both interstadials in the Kileshino-2 section requires further clarification because of the complex structure of sequence and some interruptions in sedimentation. Analysis of the upper part of the section showed that the glacial deposits are absent in the studied section. This allows one to doubt the existence of not only Kalinin Glaciation (MIS 4), but also OstashkovGlaciation (MIS 2) in this region.

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