ИСТИНА

Base tills of Moscow (Late Saalian / Warthe / MIS 6) glaciation form an important component of landscapes in northern Europe, including the center of the Russian Plain. They are often covered only with a thin veneer of sands, sandy and silty loams - the cover layer, so that basal till and cover layer forms bipartite sediment. Such bipartite sediments are among the oldest soil parent materials subjected to pedogenesis starting from the time of their deposition (MIS 6) till now. This was confirmed by our numerous OSL datings of the cover layer and spatial field studies. Thus, an assemblage of bipartite sediments features was formed within several climatic cycles. We have subdivided them to a) pre-depositional, b) syn-depositional and c) post-depositional (cryogenic and pedogenic). Morphologically, the impact of a pedogenesis during the last interglacial (MIS5e) has resulted in the formation of pedogenic structural architecture (cracks, subangular blocky peds) with a superimposed well-developed set of cutans. These lead to the formation of a sequence of Bt horizons. Holocene pedogenesis being mostly of eluvial-illuvial character, probably strengthens initial lithological discontinuity of bipartite parent material: soil horizonation is clearly seen within the cover layer unit (a sequence of A and E or Bw horizons), while the boundary between the basal till, and the cover layer, especially in the frost fissures remains abrupt. Transformation degree of pre-depositional and syn-depositional features under the influence of pedogenesis have been studied in various regions of the Russian Plain (Moscow, Yaroslav, Tver and Archangelsk) using a set of morphological (X-ray high resolution microtomography on Skyscan 1172 (Bruker, Belgium) for visualization and morphometric analysis of the internal microstructure in non-disturbed natural samples of peds; micromorphology on polarizing microscope and photo scanner; submicromorphology on SEM) and analytical methods. Many depositional features show high stability under pedogenetic impact. They look similar for the lower soil horizons (BC and C) formed in the basal till at a depth approx. 2m and for those subjected to intensive pedogenesis (Bt1 and Bt2 horizons at a depth approx. 60 cm). These key features include: high weathering through the whole strata; bright reddish-brown color (up to 5YR 6/6 by Munsell soil color chart) inherited from sediments mobilized by the glacier; overconsolidated matrix supported fabric with low porosity as a result of big pressure under the glacier; till architecture including sand lenses, shearing features, folding, thrusting and rotational structures, tension fractures and other evidences of emplacement of matrix within the mobile sediment. The research was supported by the Russian Foundation for Basic Research, Project №17-04-01221 https://app.oxfordabstracts.com/events/574/program-app/submission/92497