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FLUVIAL HISTORY OF AN ICE SHEET PROXIMAL CONTINENTAL SHELF: THE SOUTHERN KARA SEA, WEST SIBERIA DURING LATE QUATERNARY

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Dittmers, K. , Niesen, F. and Stein, R. (2004): FLUVIAL HISTORY OF AN ICE SHEET PROXIMAL CONTINENTAL SHELF: THE SOUTHERN KARA SEA, WEST SIBERIA DURING LATE QUATERNARY , European Geosciences Union First General Assembly, Nice (F)April 2004. .
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Abstract:

The history and extent of the Quaternary glaciations in Eurasia isstill discussed controversly. Within this context, the largestremaining uncertainty is how far the Kara Sea ice sheet extendedtowards the east during the Last Glacial Maximum (=LGM) (Svendsen etal., 1999; Polyak et al., 2000, 2002; Stein et al. 2002). The keyquestion related to this problem is: how did the discharge of thesiberian rivers interact with a proximal ice sheet?Detailed high frequency seismic reflection profiles provide data for amodel of shelf evolution based on the principles of sequencestratigraphy. Both rivers incised into the recent shelf, leaving filledand unfilled river channels and river canyons/valleys connecting to acomplex paleo drainage network.The lowstand (or regressive) system tract sediments are absent but arerepresented by an unconformity atop of Pleistocene sediments on theshelf. The subsequent transgressive and highstand system tracts arebest preserved in the incised channels and only minor sedimentaccumulation on the adjacent shelf areas are documented.Major factors governing the stratigraphic architecture area) sea level fluctuationsb) LGM ice sheet influenceAsymmetrical channel levee complexes with incision depths of 60 metersand more developed, in some places bordering to glacial dominatedmorphology, implying fluvial deflection by the LGM ice masses. Thisfinding denotes the non-existence of an ice sheet on large areas of theKara Sea shelf. Furthermore mapping of sediment thickness andreflection character reveals no evidence for an ice dammed lake, aspostulated by some workers.Sidorchuk et al. (2001) found "macromeanders" formed during the LGMuntil 14000 years BP, fluvial features an order of magnitude largerthan recent fluvial dimensions. Therefore it seems reasonable to relatefluvial features on the Kara Sea shelf, developed during sea levellowstand, to a pronounced riverine discharge as proposed by Sidorchuket al. (2001).Literature:Polyak, L., V. Gataullin, et al. (2000). New constraints on the limitsof he Barents-Kara ice sheet during the Last Glacial Maximum based onborehole stratigraphy from Pechora Sea. Geology 28 (7): 611-614.Polyak, L., V. (2002).Kara Sea expedition yields insight into extent ofLGM ice sheet. EOS, Tansactions, American Geophysical Union 83 No. 46.Sidorchuk et al. (2001) Fluvial response to the Late Valdai/Holoceneenvironmental change on the East European Plain. Global and PlanetaryChange Vol. 28, no. 1-4, pp. 303-318.Stein, R., (2002). ability of Siberian climate and Arctic riverdischarge, Geology.2002). Siberian River Run-Off and Late Quaternary Glaciation in theSouthern Kara Sea, Arctic Ocean: Preliminary Results, Polar Research,21, 315-322.Svendsen, J. I., V. I. Astakhov, et al. (1999). Maximum extent of theEurasian ice sheets in the Barents and Kara Sea region during theWeichselian. Boreas 28(1): 234-242.

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