LATE PLEISTOCENE GLACIATION HISTORY OF THE SOUTHWESTERN KARA SEA

The Kara Sea is a critical area for establishing the patterns of Quaternary glaciations in northern Eurasia. It is now generally accepted that the eastern limit of the LGM Eurasian ice sheet is to be sought in the Kara Sea, but little actual data on the structure and stratigraphy of its Quaternary deposits have been presented. Based on a large number of seismic records and sediment cores obtained from the southwestern Kara Sea by the former Soviet Union programs and our expeditions in 2000-2001, we present data on the geometry and stratigraphy of Quaternary deposits together with an improved sea-floor morphology for this area. The overall Quaternary sedimentary cover is subdivided into six major seismo-lithostratigraphic units, SSU VI to I (bottom to top). Despite the remaining uncertainties with chronostratigraphy and with the distribution of some portions of the identified units, the overall picture allows us to characterize major fetaures of the glacial history and related events in the study area. Two units, SSU V and III, are composed of stiff diamictons interpreted as subglacial tills. The older SSU V is mostly confined to the southernmost area and is correlated to the Kara Till of the Yamal Peninsula interpreted to have been emplaced during the Middle Weichselian glaciation (OIS 4). The younger till, SSU III, is correlated to the Kolguev Till of the southeastern Barents Sea and is believed to indicate the distribution of the LGM ice sheet. We map its margin east of Novaya Zemlya Trough where SSU III forms a series of morainic constructions up to 100 m thick. Two distinct morainic belts more proximal to Novaya Zemlya were probably formed during the ice-sheet retreat. Our data also elucidate the patterns of riverine drainage on the Kara Sea shelf during the Late Pleistocene and Holocene. Notably, we identify thick deposits formed by extension of the Ob' river into the southwestern Kara Sea prior to the Middle Weichselian glaciation, but do not see traces of a similar extension in this area during the last sea-level fall. Possibly, this difference is related to erosional and/or glacioisostatic effects of Middle to Late Pleistocene Eurasian glaciations that were progressively diminishing in size.