HR: 0800h
AN: PP21B-1374    [Abstracts]
TI: Seismic Investigation of El'gygytgyn Lake, Chukotka (NE Siberia)
AU: * Gebhardt, C
EM: cgebhardt@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstr., Bremerhaven, D-27515 Germany
AU: Niessen, F
EM: fniessen@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstr., Bremerhaven, D-27515 Germany
AU: Kopsch, C
EM: ckopsch@awi-potsdam.de
AF: Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, Potsdam, D-14473 Germany
AU: Wagner, B
EM: wagner@rz.uni-leipzig.de
AF: University Leipzig, Institute for Geophysics and Geology, Talstrasse 35, Leipzig, 04103 Germany
AB: Lake El'gygytgyn is a 3.6 Mio years old crater lake located in Central Chukotka, NE Russia, with a water depth of 170 m and a diameter of 12 km. Not having been glaciated ever since, it would reveal a paleoclimatic record unique in the Arctic realm. During the last years it has become a major focus of multi-disciplinary international research as a target for deep drilling in the near future. During expeditions in 2000 and 2003, reflection and refraction seismic combined with high resolution 3.5 kHz echosound profiling was carried out. Raytracing of the sonobuoy refraction data reveals a four-layer model of the lake that is interpreted as follows: (a) upper sedimentary unit, consisting of lacustrine muds with velocities of around 1500 m/s and a thickness of about 170 m, (b) lower sedimentary unit, consisting of lacustrine muds with velocities of around 1650 m/s and a thickness between 80 and 200 m, (c) fallback breccia with velocities of about 3000 m/s and a thickness between 50 and 300 m and (d) brecciated bedrock with velocities of > 3600 m/s. The brecciated bedrock forms a central uplift structure which is almost levelled by the overlying fallback breccia. The lower sedimentary unit drapes the smooth topography of the fallback breccia, whereas the upper sedimentary unit is almost flat. Small faults are associated with the central uplift structure and have been active until recently. Reflection seismic data indicate that the upper sedimentary unit is characterized by well stratified sediments, whereas the lower sedimentary unit is more massive. The upper sedimentary unit is locally intercalated with debris flows to a depth of at least 160 m subbottom. Debris flows are more common in the western part of the lake and along the slopes. The 3.5 kHz profiling allows a detailed mapping of the debris flow distribution. At the proposed drillsite near the centre of the lake, the sediments appear to be well stratified and largely unaffected by debris flows and promises a almost undisturbed paleoclimatic record reaching back one million years prior to the first major glaciation of the Northern Hemisphere. A second possible drillsite is located more proximal to the western shoreline and is, therefore, more intercalated with debris flows.
DE: 1630 Impact phenomena
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting