Multiphase cryogenesis and incipient paleosol development during MIS 2 in North-Western Siberia: Detailed chronostratigraphy, paleoenvironmental significance, and comparison with the global and European records

Abstract

New widely accepted scenario of glacier-free landscape evolution in the north of West Siberia during MIS 2 (Sartanian cryochron) raises a challenge to find new regional stratigraphic markers in the absence of reliable continuous sedimentary units. The cryogenic and pedogenic structures have been long applied for the European Late Pleistocene stratigraphy in the extra-glacial regions. We argue that such structures might also provide important markers for the detailed stratigraphic scheme in the north of West Siberia. Two types of indicators were suggested. Firstly, morphological features and ranges of radiocarbon dates in epigenetic ice wedge pseudomorphs of higher terraces are sensitive to events of abrupt climate amelioration. Regional analysis of radiocarbon dates of ice wedge pseudomorphs indicated four warmer climatic events in the Late Pleistocene – the Early Holocene (ca. 18000–16500 cal BP, ca. 13800–12500 cal BP, ca. 11700–11100 cal BP, and ca. 10400–9000 cal BP). They correlate to climatic events of the Greenland ice core record with minor temporal lag. Secondly, more detailed cryogenic-paleosol-sedimentary sequences formed at lower terraces where sedimentation continued during MIS 2 are another type of suggested indicator. Their morphological and paleobotanical analyses and radiocarbon dating provided a reconstruction of local paleolandscape evolution with events of cryohydromorphic soil development (ca. 15700–15300 cal BP, ca. 11200–9000 cal BP). Similar late-glacial paleosols are encountered in the European loess sequences. We propose that the cryopedogenic horizons, including ice wedge pseudomorphs, cryoturbation structures, and cryohydromorphic paleosols, are reliable regional stratigraphic markers in the north of West Siberia for the Sartanian cryochron.