Drilling to reveal permafrost history and dynamics of Elgygytgyn Meteorite Crater in the Russian Arctic

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Schwamborn, G. , Fedorov, G. B. , Schirrmeister, L. and Hubberten, H. W. (2010): Drilling to reveal permafrost history and dynamics of Elgygytgyn Meteorite Crater in the Russian Arctic , IPY (International Polar Year) Oslo Science Conference 8-12 Juni 2010 Oslo, Norway. .
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Elgygytgyn Meteorite Crater in Chukotka holds the unique chance to trace frozen ground conditions back to the Pliocene. The basin was not glaciated in Quaternary time and terrestrial deposits accumulate at piedmont settings and continuously in a lake basin.Recent drilling into the permafrost of the Elgygytgyn basin recovered a 141 m long core of coarse-grained slope deposits. Drilling the complete lake fill and into the underlying bedrock provides a core that stretches back to 3.6 Myr BP, the time of the meteor impact.Permafrost conditions through time are preserved in proxy data of cryogenic weathering. Mineralogic weathering features originate in the active layer and grains are transported into the neighbouring lake forming a sediment trap. Production of silt size debris, a peculiar quartz grain morphometry, and the enrichment of quartz in the silt fraction are indicators of frozen ground conditions. They reflect thaw and freeze dynamics in the catchment when using the lake core. By now the permafrost history expands to at least 220.000 years BP documenting persistent active layer dynamics.Environmental change and climate signals linked to permafrost formation can be traced in ground ice hydrochemistry (i.e. 18O, D) and ice wedge architecture. The stable isotope record highlights thermal periods during the Late Quaternary, and the vegetation history based on frozen ground pollen records improves the local resolution.Subaerial lake terrace remnants show a lake shrinking by about 80 m after an ancient highstand in the Pleistocene. A permafrost borehole temperature profile indicates a talik history of a formerly flooded area. This hypothesis is tested by a thermal modelling approach to back up the interpretation. The presentation sums up current results of studying Elgygytgyn permafrost and lake sediments and is devoted to elucidate permafrost history for Far East Russia, an area yet underexposed in understanding Siberian permafrost history.

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