Lebedeva Marina Pavlovna

The lithological matrix of surface soil profiles in the northern Mologo-Sheksna Lowland, within the wide valley of the lower Sheksna River and the foothills of the Andoga Ridge, reveals the final stage of Late Pleistocene aeolian sedimentation, reflected in the composition of the surface soils. Morphological and genetic analysis of soil profiles at the macro- and microlevels, supported by analytical characteristics and particle size distribution data, allowed us to identify and substantiate at the regional level a series of four contiguous layers of different ages and lithologically contrasting features. The base of the studied soil profiles is the Moscow glacial basal till (layer I, which displays consistent features of Mikulino pedogenesis (Bt horizons). The final stage of loess sedimentation in the upper part of the soil profiles during the Late Glacial (layer III) has been dated using the OSL method and falls within the range of 17,000–22,000 years ago. Layer II, represented by gravelly-sandy sediments in the middle part of the profiles of several of the studied soils, reflects a local stage of active sedimentation after the Mikulino period, during which the upper part of the glacial till may have been truncated (eroded). Thus, the studied soils represent a pedocomplex formed in the Late Pleistocene (a 150,000-year macrocycle). Identifying the final stage of loess sedimentation in the Late Glacial will allow us to assess the contribution of soil and lithological processes to the formation of the profile of loamy soddy-podzolic soils. Establishing the final stage of eolian sedimentation in the Late Glacial is also of great importance for paleogeography, as it reflects the impact of the global climatic rhythm at the Late Pleistocene-Holocene boundary on the modern landscape. The mantling of the Sheksna River valley by glacial basal till confirms V.V. Dokuchaev's (1877) concept of the role of glaciations in the structure of river valleys on the Russian Plain. The terrace levels in the studied areas represent ancient basement steps and do not belong to the modern river valley.