HR: 0800h
AN: PP21B-1387    [Abstracts]
TI: The Significance of Late Quaternary Mass Movement Events for the Paleoenvironmental Interpretation of Sediment Records from Lake El'gygytgyn, NE Siberia
AU: * Juschus, O
EM: juschus@uni-leipzig.de
AF: University Leipzig, Inst. Geoph. Geol. Talstr. 35, Leipzig, D-04103 Germany
AU: Melles, M
AF: University Leipzig, Inst. Geoph. Geol. Talstr. 35, Leipzig, D-04103 Germany
AU: Brigham-Grette, J
AF: University, of Massachusetts, Amherst, 01003 United States
AU: Dehnert, A
AF: University Leipzig, Inst. Geoph. Geol. Talstr. 35, Leipzig, D-04103 Germany
AU: Gebhardt, C
AF: Alfred Wegener, Institute, Bremerhaven, D-27515 Germany
AU: Minyuk, P S
AF: North-East Interdiscipl., Sci. Res. Inst., Magadan, 685010 Russian Federation
AU: Niessen, F
AF: Alfred Wegener, Institute, Bremerhaven, D-27515 Germany
AU: Wennrich, V
AF: University Leipzig, Inst. Geoph. Geol. Talstr. 35, Leipzig, D-04103 Germany
AB: The paleoclimatic and paleoenvironmental significance of sediment records from Lake El'gygytgyn, NE Siberia, may depend on the impact of mass movement deposits. In order to investigate their genesis, composition, and distribution, a subrecent debris flow at the western lake slope was identified by 3.5 kHz echo sounding and penetrated by two sediment cores. The composition of these cores was compared to that of a 16.7 m long core from the central lake part, where both shallow seismic data and the core composition exclude the existence debris flows. The lower part of the debris flow is stratified, probably reflecting an initial stage with sediment sliding and limited sediment mixture. Massive sediments above and in front of the stratified deposits indicate a second stage with turbulent transport. The debris flow led to basal erosion of ca. 1 m thick unconsolidated sediments along parts of his flow path. It produced a suspension cloud in the lake water, whose deposition caused the formation of a graded subrecent turbidite in the entire lake, i.e. not only in front but also on top of the debris flow. Hence, the turbidite was not a product of a density-driven turbidity current, but of 'pelagic rain' following Stokes' Law. In consequence, it was not erosive. According to the results from the long core, these conclusions are valid for the majority if not for all of the mass movement events that have taken place in Lake El`gygytgyn during the past 300 kyr. Given that one debris flow has produced one turbidite all over the lake, the total number of turbidites in this core (24) reflects the number of debris flows during the last 300 kyr. Altogether 19 turbidites were found in sediments deposited during warm periods. Only five turbidites were settled under cold climatic conditions. The composite thickness of all turbidites within the long core is 2.1 m (13 % of the sequence).
DE: 9604 Cenozoic
DE: 1815 Erosion and sedimentation
DE: 1845 Limnology
DE: 1620 Climate dynamics (3309)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting