A MINERALOGICAL ANALYSIS OF KARST SEDIMENTS AND ITS IMPLICATIONS TO THE MIDDLE-LATE PLEISTOCENE CLIMATIC CHANGES ON THE TIBETAN PLATEAU

The minerals in various categories of Tibetan karst sediments were div ided into three groups: carbonate, iron and silicate. The carbonate mi nerals, including calcite, aragonite and dolomite, consist mainly of s peleothem, tufa and sinter. Most of the speleothems indicates wetter a nd warmer periods in early and middle Pleistocene, the youngest being 194,000 years old. The second formation of carbonate mineral, tufa, im plies an arid period starting 91,000 years BP. The iron minerals, goet hite and hematite, are often mixed up with cave alluvial sediments tha t are interbedded with flowstones, and the depression sediments. They indicate strong oxidizing environments during their deposition, which is absent at present. The clay minerals, specially kaolinite, were con tained in cave alluvial, flowstone and the depression sediments as wel l. Combined with stratigraphic study and U-series dating, the mineral analysis shows that warmer and wetter climates, which were suitable fo r speleothem development, probably disappeared 200 ka ago, and drier a nd colder climates dominated this plateau since then.