SEDIMENTOLOGY OF THE LAST INTERGLACIAL FROM EL’GYGYTGYN LAKE, NORTHEAST SIBERIA, RUSSIA

Located in northeast Siberia, El’gygytgyn Lake (67*30’N, 172*05’E) contains a sediment record with the best resolved information of the last interglacial (marine isotope stage 5), and may also hold the most comprehensive record of millennium scale environmental change in the Arctic. The lake, roughly circular in shape and having a diameter of 15 km, was formed by a 3.6 million year old meteorite impact. The location of the lake within an unglaciated region of the Arctic allows for a complete record of climate change. During May of 1998, a 13.0 m sediment core was retrieved from the lake, and a return field excursion during the summer of 2000 yielded the recovery of strictly Holocene-age sediments at distinct lake-bottom depths. The magnetic susceptibility record from the sediment recovered in 1998, shows a strong pattern in the upper 6.0 m, where significant geochronologic control exists. These fluctuations reflect the continuous seasonal injection of sediment into the catchment basin with major shifts between glacial and interglacial modes. Current cumulative grain size distribution demonstrates that the sediment is 10-42% clay and 30-75% silt, with a tiny portion of sand. Clay mineralogical analyses have identified the major clay components as illite-smectite (I-S), illite, and chlorite, with I-S the most abundant. Work by Cosby (in progress) has revealed that the abundance of chlorite increases during colder periods within the upper 200 cm of the core, representing roughly the last 40ka. This work has been expanded to examine the relationship within the last interglacial (marine isotope stage 5). Microscopic slides have been utilized to further investigate the orientation and diagenesis of clay formation within the last interglacial. The location of the lake and in the Arctic, and the subsequent overlying circumpolar air circulation pattern, has led to preliminary research involving volcanic tephra classification as part of the geochronology program.