Outburst floods of the Maly Yenisei. Part II - new age constraints from Darhad basin

摘要

Some of the largest cataclysmic floods of the Quaternary followed multiple breaches of glaciers damming the headwaters of the Maly Yenisei river in southern Siberia. The shorelines of the impounded lake in Darhad basin suggest at least four depths of 290, 175, 145, and 65m. Fossil evidence, together with previous C-14 and luminescence dating, indicates the existence of a deep lake during MIS 3; the eroded character of the highest shoreline suggests that the deepest lake was older. Be-10 dating of moraines in the surrounding mountains has documented major glacial advances during MIS 2, although no published direct dating has confirmed a highstand of the lake then. To address this problem, we extracted lake sediments from a 92.6m deep borehole, sampled beach sands from the nearby basin edge, and dated them both using luminescence methods. We also dated, with Be-10, the eroded remnants of the end moraine deposited by the last glacier that dammed Darhad basin, as well as other moraines in the mountains surrounding the basin. These numerical ages confirm that a deep lake existed in Darhad basin at similar to 20ka and that a large glacier crossed the Maly Yenisei and dammed Darhad basin at similar to 21ka. The deep lake persisted episodically until similar to 14ka. The Be-10 dating in the surrounding mountains shows that the MIS 2 glaciers subsequently retreated but stalled or re-advanced at similar to 12, 10, and 1.5ka. Be-10 dating from the central massif of Mongolia is consistent with this chronology and confirms that MIS 3 equilibrium-line altitudes were slightly (similar to 75m) lower or approximately the same as those of the MIS 2. The temporal and spatial patterns of glacial advances in southern Siberia and central Mongolia coincided with those of glacial advances in similar climate conditions of the Altai mountains.