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Quaternary Environment of NE-Siberian Arctic inferred from permafrost sequences of Bol'shoy Lyakhovsky Island

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Citation:
Schirrmeister, L. , Andreev, A. , Grosse, G. , Meyer, M. , Derevyagin, A. Y. , Kunitsky, V. , Kuznetsova, T. and Ilyashuk, B. (2004): Quaternary Environment of NE-Siberian Arctic inferred from permafrost sequences of Bol'shoy Lyakhovsky Island , International Conference: Cryosphere of oil and gas bearing provinces; Tyumen Russia. .
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Abstract:

Permafrost sequences exposed at the coast of the southernmost New Siberian Island multidisciplinary studied by a Russian-German team present several stages of the Saalian to Holocene environmental and landscape history of Siberian Arctic. The deposits were studied using cryolithology, sedimentology, geochronology, stable isotope geochemistry of ground ice as well as investigations of biological remains (pollen, insects, rhizopods, chironomids). The oldest frozen deposits contains remains of a reworked tertiary weathering crust as proved by the yellowish colour and the occurrence of weathering products like kaolinite and montmorillonite. In addition it is characterized by separate epigenetic ice wedges and the absence of pollen. The Late Saalian climate variations are documented by two units dated between > 200 to c. 170 ky. The older unit is cryolithological similar to Late Pleistocene Ice Complex because of large ice wedges and ice rich deposits. The lower part of this unit contains pollen associations of sparse grass-sedge vegetation and reflects stadial climate conditions. The upper part of these ice-rich unit is characterized by pollen spectra of a dense grass dominated tundra probably of the Tasovsky Interstadial. The Saalian Ice Complex deposits were eroded and covered with a sharp boundary by a younger Saalian unit 170 to 130 ky old). This well-sorted fine-grained sand contains less ground ice and again pollen spectra of a sparse grass-sedge dominated vegetation assigned to the Kuchchugui Stadial. The most interesting unit was assigned to the Eemian (Kazantsevo/Krest Yuryakh) Interglacial because of the occurrence of large ice wedge casts as well as many paleo-ecological evidences of a warm stage. The Early Weichselian (Zyryan) Stadial is reflecting again of fine-grained, well-sorted sands with rare grass-sedge pollen. These deposits turn gradually into the about 20 m thick ice-rich Late Weichselian Ice Complex horizon, dated to about 50 to 30 ky and containing the pollen spectra of a typical mammoth tundra-steppe. Whereas peaty deposits of the Kargin Interstadial often occur within the studied Ice Complex sequences the Sartan Stadial sequences were not found. The Ice Complex deposits seem to be cut about 30 ky before and than covered by Late Glacial/Holocene deposits. The Late Pleistocene/Holocene transition including the Alleroed warming and Younger Dryas cooling events is preserved within lacustrine thermokarst deposits flanking the Late Weichselian Ice Complex sequences.

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