Conrad Kopsch

High-Resolution Seismic Stratigraphy of Lake Sediments on the Taymyr Peninsula, Central Siberia

High-resolution seismic profiles (GeoChirp, 1.5-11.5 kHz) were recorded in two lakes on the Taymyr Peninsula during the Taymyr Expedition 1996 in order to reconstruct changes in the depositional environment and to test different hypotheses of glaciation in central Siberia. Four major seismic units of mostly well-stratified sediments are identified in both Lakes Taymyr (T1–T4) and Levinson-Lessing (L1–L4). The sequential stratigraphic approach is used to explain different unit geometry by lake level changes. The lowermost units L3, L4 and T4 cover hummocky topography and are interpreted as high-stand deposits. Overlying units L2 and T3 occur only in the deeper part of the basin and onlap against the slope. These deposits represent a lower lake level followed by a transgression during the Holocene (L1, T1 and T2). The chronology of the lower units is somewhat speculative. Correlation of our evidence with the results of other studies suggest that, in Lake Taymyr, the high-stand unit T4 was probably deposited during Mid to Late Weichselian, and the low-stand unit T3 during Latest Weichselian times. In Lake Levinson Lessing, high-stand units L4 and L3 are possibly older than Mid-Weichselian overlain by low-stand deposits (L2) of Mid to Late Weichselian age as indicated by a pollen-dated sediment core penetrating into unit L2. In total, the fills of the basins comprise unconsolidated muds and sands of more than 20 m in Taymyr and more than 60 m in Levinson Lessing. The units L4 to L1 are undisturbed, whereas T4 to T1 are partly erosive. None of the units were overconsolidated by glacier ice. This implies that the last major glaciation of the lake basins occurred earlier than the Mid-Weichselian, possibly during the Early Weichselian (Marine Isotope Stage 4).