THE EVOLUTION OF SMALL LAKE BASINS IN THE GOBI DESERT IN MONGOLIA

In order to investigate pluvial lakes in the Gobi two places were selected for field studies： Khongoryn Els in South- and Mongol Els in West-Mongolia. In the eastern and central parts of Khongoryn Els two small endorheie basins, Bayan Tukhem and Khongoryn Gol depressions were studied. Pluvial lake deposits and beach ridges both supposedly midHoloeene in age give evidence of a 9m and a 15m deep freshwater lake, respectively. Today both depressions are nearly dried out and exposed to wind deflation. A different situation was found at Uujin Sair river valley which cuts through the dune field at its lowest and narrowest （3km） part. Here, a 22.5m thick fossil accumulation of at least 20 layers of fine sand （dune sand）alternating with silt（fluvial playa sediment）was exposed and OSL dated. 12 dates ranging between 14ka and 17ka reveal the accumulation as Late Glacial which correlates well with the aridity at that time reported for Central Asia by several authors. Interpreting the dates it seems obvious that the whol