ИСТИНА

Since Dokuchaev Russian plain is known as a classic model of bioclimatic zonal soil sequence. However, soil geographic pattern correlates also to glacial history where earlier glaciations were more extensive than most recent one. The pattern of glacial and periglacial sediments and corresponding paleocryogenic and relic soil features follow three conspicuous belts. 1. Extensive loess mantles characterize the area south of Moscow (Late Saalian) glacial limits. Polygenetic features in Faeozems and Chernozems are determined by loess stratification, marked by paleocryogenesis, paleohydromorphism and relic soil features. These features are mostly pronounced in the soils of high interfluves (Opolie). Periglacial environment resulted in a network of thermokarst depressions. Constitution of loess strata depends on its position in a paleocryogenic complex. A clear evidence of sequential loess sedimentation, accompanied by slope processes and pedogenesis is presented in soil profiles within depressions. Sequential sedimentation here is confirmed by cryomorphic features (ice wedges, frost cracks, pseudomorphs) at different levels of loess strata. Slope processes resulted in micro striping of loess sediments. Buried humus horizons here are present at different depth. 2. An area within Moscow (Late Saalian) glacial limits is characterized by a diverse set of sediments (separate bodies of loess, glacial till, fluvioglacial sand, etc.) as a result of complex glacio-dynamic structure of cover glacier and high dissection of relief. The key to understanding relic soil features is the fact that day surfaces on different types of relief are heterochronous. Surface sediments of glacial and periglacial origin here exhibit clear vertical zonality. On the highest positions (200 -250 m a.s.l.), thick cover (3 to 5 m) of mantle loams (northern variety of loess) overlay glacial till. In the intermediate positions (170-200 m a.s.l.), only a thin veneer of sand, sandy loam, sometimes loess, covers glacial till. Fluvioglacial and fluvial sediments cover the surfaces below 170 m. The sediments in the intermediate position (glacial till) were subjected to pedogenesis since Late Saalian time till now. Such surfaces cover extensive terrain within Late Saalian limits (State Soil Map of the Soviet Union, 1:1000000). Soil profiles include two-layered sedimentary sequence: sandy loam or sandy clay loam covered by 30-70 cm of sand or sandy loam (glacial cover beds). Upper horizons have been formed in the cover bed and lower – in glacial till. So the E/Bt horizonation of Glossisols and Luvisols on glacial till is largely inherited from stratified sediments. An initial lithological discontinuity within the profile of surface soils provides an opportunity to assess the depth and cumulative effect of pedogenesis since Late Saalian time. 3. Within Valdai (Weichselian) glacial limits high flooding prevented extensive loess accumulation. Soils inherited specific layering of sediments (laminated clays, fluvioglacial sands and glacial till with veneer of fluvial sand; on higher levels glacial till with thin veneer of cover sand, sometimes of loess). Relic soil features need to be further investigated in relation to glacial history. On glacial and periglacial plains, they allow re-evaluating not only soil genetic models but also zonal soil pattern, with bioclimatic grade superimposed on zonal sequence of sediments and zonal pattern of paleocryogenic features.