THE-IMPACT PROJECT: SEDIMENTOLOGICAL STUDIES OF THE PALEOCLIMATE RECORD FROM EL’GYGYTGYN CRATER LAKE

Knowledge of the full range of climate variability across the Arctic during the past is important for understanding the sensitivity of the Arctic system to future change. El’gygytgyn Lake with over 300 m of sediment fill may offer the longest and most complete Late Cenozoic lucustrian paleoclimate records available from the entire Arctic. This lake located in central Chukotka, NE Russia, lies in an impact crater ~18 km in diameter dated to ~3.6 Ma. In 1998 a multinational team collected a series of overlapping cores yielding a total depth of 13.5 m extending nearly 400 ka. THE-IMPACT Project (Terrestrial History of El’gygytgyn Lake -International Multidisciplinary PaleoClimaTe project) includes collaborators from the Alfred Wegener Institute (AWI) Germany, Northeastern Interdisciplinary Science Research Institute (NEISRI), Magadan Russia, University of Alaska Fairbanks, and UMass, Amherst USA. The Sedimentological history of the cores is being carried out at the UMass for comparison with other paleoclimate proxies. A macro overview of the full core was investigated for grain-size and clay mineralogy, with a more focused study on the upper 2 m for clay mineralogy. Grain-size analyses of point samples indicates a more event-based biasing of clastic deposition and little correlation to other measured proxies. The principle clay mineral assemblage includes illite, inter-stratified illite-smectite (I-S) and chlorite with I-S the most dominant. The analyses show fluctuations in relative abundance and crystallinity of the clay minerals with depth. Correlations with other proxy data from the core indicate that the clays are responding to climatic fluctuations seen in: 1) an increase in the relative abundance of inter-stratified illite-smectite during warm periods and a decrease in crystallinity during cold periods, 2) an increase in both crystallinity and abundance seen in chlorite during cold periods, and 3) illite decreasing during warm periods at the expense of I-S development. The properties of clay minerals are dependent on climatic conditions, making them a useful tool in paleoclimate reconstructions.