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Formation and Evolution of the Ancient "Lake Xiaozhongdian" in Diqing,Yunnan and Its Relationship with Development of the Ancient "Lake Shigu" and the Modern Valley of the Jinsha River

ZHAO Xitao1,3),ZHENG Mianping1,2),LI Daoming1)1)Key Laboratory of Saline Lake Resources and Environment,Ministry of Land and Resources,Beijing,1000372)Institute of Mineral Resources,CAGS,Beijing,1000373)Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing,100029  
In the Zhongdian—Xiaozhongdian Basin on the Diqing Plateau,the northwestern Yunnan Province,there are three sets of the Quaternary lacustrine deposits.The first set of the lacustrine and delta deposits are distributed in the southeast part of the zhongdian Basin.Because of discovery of rich mammalian fossils in it,their age was determined to the Early Pleistocene.The second one of lacustrine deposits over 100m thick is distributed in the Xiaozhongdian Basin and constitutes the bases of five terraces of the Xiaozhongdian River.The results of the OSL and U-series dating of six lacustrine deposits samples from two profiles,the Xiaozhongdian Forestry Bureau and Dangaodi Village,show that from the middle part to the top the dates of the lacustrine deposits are ranging from 147.2±13.9 to 67.57±5.30 ka BP,the late Mid-Pleistocene and the early-middle Late Pleistocene.The third one of lacustrine deposits are represented with the deposits of the Napahai Lake.Ostracode in each layer from the second lacustrine deposits in the two profiles are characteristics of Limnocythere-Leucocythere-Candona-Eucypris,showing that they have been deposited since the Middle or Late Pleistocene.The authors think that the Jinsha River had appeared in the today's place during the Early or Middle Pliocene.The crustal movements in the area iduring the Late Pliocene and Early Pleistocene were not block the flow of the Jinsha River in its channel.During the Middle Pleistocene the different parts of the Jinsha River were dammed into lakes due to accumulations of glacial,fluvioglacial,collapse,landslide or debris flow.The ancient "Lake Shigu" was overflowed owing to erosion of the modern Jinsha River until about 80 thousand years ago.The ancient "Lake Xiaozhongdian" was overflowed b the Xiaozhongdian River,the tributary of the Jinsha River at about 60 thousand years ago,too.
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