The production of (1) silt size debris, a peculiar (2) single grain morphometry, and (3) the enrichment of quartz grains in the silt fraction with respect to feldspar occurrence serve as indicators of Siberian frozen ground conditions. The proxy data reflect thaw and freeze dynamics in the active layer resulting in a selective grain break-up. We use the Elgygytgyn Impact Crater, central Chukotka, to trace back frozen ground conditions beyond the Quaternary glacial cycles, since the basin is archiving sediments back to 3.6 Myr BP, the time of the meteor impact. In Elgygytgyn Crater deposits accumulate at piedmont settings and in a lake basin that partially fills the crater. A set of surface samples and two five-meter-sections extracted from slope deposits serve as a reference for the modern and the Holocene situation. Sediments cored in the neighbouring Crater Lake allow extending the geologic time. Recent deep drilling into the permafrost margin of Elgygytgyn recovered a core 140 m in length and ongoing lake sediment drilling will provide a core that covers the full sediment fill. The presentation sums up current results of both permafrost and lake sediment records when displaying the sediment-mineralogical properties. They illustrate the persistence of cryogenic weathering at least back to about 220,000 yrs BP, the time our study covers up to now.
Helmholtz Research Programs > PACES I (2009-2013) > TOPIC 3: Lessons from the Past > WP 3.1: Past Polar Climate and inter-hemispheric Coupling