Upper Neopleistocene Peat Deposits in the Section near the Verkhnie Nemykari Village (Smolensk Region): Age and Conditions of Their Accumulation

Ideas about the age and climatic conditions of the Valdai interstadials on the Russian Plain are based on biostratigraphic and limited 14C dating data. The chronometric reference of the Valdai interstadial deposits is not always reliable, including due to the use of the 14C method at the limit of its accuracy. Their paleobotanical characterization is complicated due to the lower specificity of plant complexes in contrast to interglacial deposits. This makes it difficult to conduct spatiotemporal correlations of Upper Pleistocene warmings stages over a large territory. We applied a comprehensive approach to the study of Upper Pleistocene buried peat deposits in a well-known section near the Verkhnie Nemykari village in the Smolensk region based on their 230Th/U and 14C dating and paleobotanical study. It has been revealed that the lower peat in the section accumulated during the pre-optimal and optimal phases of the Mikulino Interglacial. The 230Th/U age of the peat layers corresponding to the interglacial optimum is ~112–106 ka, which is consistent with previously obtained 230Th/U dates for Mikulino organogenic deposits on the Russian Plain. The upper peat layer was dated using 230Th/U and 14C methods. The close age intervals were obtained in the range of ~50–40 ka. According to paleobotanical data, a successive change in forest vegetation took place during the accumulation of the upper peat horizon: birch forests, spruce-birch forests, spruce-pine forests with larch, and spruce-birch-pine forests. These new data suggest that the upper peat horizon was formed during the Middle Valdai period, in the initial phases of MIS 3, under relatively favorable interstadial conditions that were slightly cooler than interglacial conditions. Despite the tentative age estimate of the upper peat layer, we propose to extend this comprehensive approach to a new study of known sections containing Valdai interstadial deposits. In combination with OSL dating of minerogenic deposits, this approach is promising for clarifying issues of chronostratigraphy of Upper Neopleistocene interstadial deposits in the Russian Plain.