| The Huahai Basin lies in west Hexi corridor of the northwest China, at an average altitude of 1195—1250m a.s.l. Being one of the aridest regions in China, Huahai Lake basin receives precipitation of only 56mm annually according to a 30-year meteorological records with annual mean temperature of 8℃, and annual mean evaporation adds up to 3000mm. It belongs to arid climate of Temperate Zone, dry and windy in the region and prevailing wind of NW. There are more than 300 days with wind and 3300 hours with sunlight in the region annual mean year. The region is sensitive to environment changes owing to its location at the boundary between the Inner Mongolia, Xinjiang arid and Tibetan Plateau. Therefore the sediments in such an enclosed basin can provide high-resolution archives for paleoclimate or paleoenvironmental changes since Holocene or last deglaciaton. But till now, there are still many questions unsolved and some aspects need to be improved.In the drainage basin, precipitation is very limited and the variation of river runoff depends on water of melting glacier of mountain distinctively. The runoff fluxes correlate with variations of temperature in drainage basin, and the same relation between temperature and melted glacier of mountain. In the terminal Huahai Lake of river, evaporation is many times to precipitation, and lake level fluxes reckon on runoff of river mainly. In the same time, we know that runoff correlates to temperature positively. So, in the drainage basin, if climate becomes warmer, melting glacier and runoff will increase respectively, and geochemical elements in the sediments will increase also, at the same time lake level also higher;on the contrary, lake level will fall. Consequently lake level fluxes register temperature variation of drainage basin in fact. We have analyzed geochemical and granularity indexes for climate and environment evolution, and found that geochemical elements Fe ,Mn et.al. redox-sensitive metals in sediments from Huahai Lake recorded oxic conditionsmainly and reducing conditions of sedimentary sequence existed seldom. Content of geochemical elements in sediments registered variations of runoff and temperature.The section which was analyzed in the dissertation is located in 40°26'05" N, 98 0 04'47" E? altitude of 1195m a.s.l. In order to retrieve the history of huahai drainage basin since 11000 aB.P., we have done much work in the drainage basin: spot investigation, profile sample collection, section strata analysis, geophysical analysis, geochemical analysis and dependable 14C dating. The main conclusions are as follows:During 10600—10200aBP, the mount of lake water decreased. Lake was in the phase of sulfate, and climate of area was dry.In 10200—9500aBP, lake level was higher, salinity of lake water was falling, and climate was becoming wanner gradually.9500—9000aBP, the mount of lake water cut down abruptly, activity of wind was violent, climate was dry and cold, and environment of drainage basin deteriorated.9000—3500aBP, it was in Holocene climate optimum, lake level was higher and more stable. But during 9000—8600aBP lake level fluctuated obviously, climate was unstable. About 8300aBP^ 6200aBP, 4500aBP, there were three times runoff reduced and lake shrunk events. During 4000—3500aBP, and the lakeshore age is 4000 aBP when altitude is 1225m a.s.l. which the lake level was highest, climate was wetness, and lake proportion was expanded.During 3500—290aBP, it was a cold stage. Lake level decreased and it was in the phase of sulfate again. But amount of water in the lake increased in 1600aBP and environment meliorated relatively.As to the whole basin, the Holocene climate and environment experienced three stages: the early cold relatively stage and transformation wet gradually, the mid wetter and warmer stage and the late cold stage.
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