CHANGES IN HYDROLOGICAL CONDITIONS IN THE CENTRAL QING-ZANG (TIBETAN) PLATEAU INFERRED FROM LAKE BOTTOM SEDIMENTS

Grain particle and chemical analyses of core samples obtained from Siling-co, a lake on the central Tibetan Plateau, and a sedimentation model for the lake with C-14 dating show fluctuations in the hydrological environment of the area during the past 15,000 yr. The area of the lake was small and the water level low in the late part of the last glacial period. Thereafter, the lake became larger and the water level high because of meltwater and rainfall. This hydrological environment continued until 4000 yr B.P., at about which time the level of the lake fell sharply and the lake area shrank. After a short period of low level and aridity, the water level increased markedly but did not reach the previous high level. After the large water inflow for a short period, the climate became again arid at about 3500 yr B.P. The change in this interval is closely related to global change. Statistical analyses of the datasets of the grain particle components of bottom sediments preserved in an aquatic condition over the past 13,000 yr show that most datasets for grain size and chemical parameters had a common period of 2000-2200 yr during this interval.