New geological record for the late Pleistocene chronostratigraphy, paleoecology and correlations across northern eurasia: Tyiakha section, north-western Siberia

The vast northern region of the West Siberian Lowlands still has relatively few detailed geological archives for the Late Quaternary, most of which are distributed along the Arctic coast. An extensive section of the Tyiakha River terrace and several neighboring outcrops provide a rich record of sedimentary, cryogenic and soil forming processes located in the inland part of this region. Detailed description together with particle size analysis, morphoscopy of quartz grains and micromorphological observations reveal the set of surface processes responsible for section development, whereas palynological investigations provided a proxy for paleoenvironment. During MIS 3 and possibly beginning of MIS 2, medium-strong cryogenic alluvial sedimentation prevailed. Some eolian reworking is indicated by quartz grain surface microstructures. Signs of palustrine deposition and syn-sedimentary cryohydromorphic soil development were observed in the low-energy alluvial unit corresponding to the end of MIS 3, being consistent with the pollen spectra indicative of tundra-steppe ecosystems. At that, the revealed polygenetic MIS 5 paleosol fragment in the bottom of the section, with contrasting pollen assemblages, was incorporated into younger alluvium in a frozen state. During the coldest phase of MIS 2, alluvial deposition seized, and epigenetic ice wedges developed, which were converted into pseudomorphs filled with gleyic pedosediments at the terminal Pleistocene. The combination of cold alluvium, ice wedge casts, and cryohydromorphic pedosediments was used as a representative stratigraphic unit for MIS 2 in NW Siberia and for stratigraphic correlation of the Tyiakha section with the Late Pleistocene continental geological records of Northern Eurasia.