First results from the Late Pleistocene paleosols in northern Western Siberia: Implications for pedogenesis and landscape evolution at the end of MIS3

摘要

Recent revision of the extent of Late Pleistocene glaciations in Northern Eurasia the justified search for the new paleopedological records in the center-north West Siberian Plain. We encountered paleosols in several exposures of the high alluvial terrace of the river Vakh (Middle Ob' basin), buried in the sequence of alluvial and lacustrine sediments. A paleosol dated to the end of Marine Isotope Stage (MIS) 3, Karga thermochron, was studied in detail in the key section "Zeleniy Ostrov". The paleosol demonstrates strong morphological evidence of gleysation and accumulation of plant residues, both processes indicating water logging and a reduced environment. The modern soil on top of the exposure is a typical Podzol, formed in under conditions of perfect soil drainage and no water excess, in agreement with current geological and geomorphological conditions. We suppose that permafrost was the main factor hampering percolation and switching redoximorphic processes in the paleosol, which thus was classified as a Reductaquic Cryosol. Presence of permafrost implies colder climate than the present one. Furthermore, neutral reaction, presence of neoformed calcium carbonate and abundance of silt fraction, which points to eolian sedimentation, suggest drier conditions. However, the studied paleosols differ considerably from the synchronous Chernozems found in the loess sequences of Southern Siberia. Paleobiological proxies such as pollen, plant macroremains, phytoliths and fossil insects indicate a tundra or tundra-steppe ecosystem (possibly with some forest stands), in good agreement with the paleopedological and sedimentary records. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.