Evolution of the Cenozoic Sedimentary Environment in West Qaidam and the Revelation Altun Uplift Process

The western Qaidam Basin is located in the Piedmont of the southern foot of the middle Altun Mountain,where the Cenozoic stratigraphy was deposited continuously and recorded completely the deposition process of the basin since the Cenozoic.According to the lithology,the sedimentary facies,and the time and space variation law of Cenozoic stratigraphy of western Qaidam Basin,the sedimentary facies were identified as alluvial fan facies,proluvial fan facies and fan delta facies in the lower part,but it gradually change into rift lacustrine facies when it goes to the upper stratigraphy,then it changes from fan delta facies into shallow lake facies in the upper Youshashan Formation,and finally it becomes alluvial fan facies and fan delta facies in the Qigequan Formation of the Early Pleistocene.The particle size of the sediment changes alternately from coarse-fine-coarse-fine-coarse-fine,reflects the alternately evolutionary process of a faulted lake basin.Then according to the analysis of sedimentary facies and sand composition,we can conclude that the Altun Mountain had a multi-stage phase uplift history.There are three rapid uplift stages: the Late Eocene-the Early Oligocene,the Late Miocene and the Late Pliocene-the Early Pleistocene.