Polygenetic features in Retisols, formed in Moscow (Late Saalian) glacial till

Abstract

Retisols are the most spread soil in the boreal forests of the Russian Plain. Their features are usually linked to the Holocene pedogenesis. However, Retisols formed in the bipartite sediments of Moscow age (sandy cover layer on top of the glacial till) could have experienced pedogenic and cryogenic impact much earlier, starting from the last Interglacial. The subdivision of relic and modern features is still incomplete. In our work, OSL datings together with micromorphological studies indicate that the cover layer was formed by local rewashing of the glacial till during the deglaciation of the Moscow glacier. GPR investigation shows the mantle bedding of the cover layer and proves the stability of uplands and slopes since deposition, which confirms their exposure to long time pedogenesis. Detailed morphology, micromorphology, microtomography, clay mineralogy and AMS dating confirm the presence of polygenetic modern and relic features in the profile of Retisols. Within the cover layer, pedogenesis resulted in a set of embedded soil profiles that have been formed in balance with the modern environment. In the glacial till pedogenesis is mostly exhibited on the ped faces as a set of multi-layered clay and clay-humus coatings. Based on AMS dating of the inner layer of the clay infilling, it was argued that clay illuviation had started during the last interglacial (MIS5e) and continued through the Holocene. The studied soils should be considered as surface paleosols (polygenetic soils) with the palimpsest type of soil memory, reflecting environmental evolution during the last interglacial-glacial cycle and the Holocene.