Abstract: This paper presents the in-depth sedimentary facies characteristics of upper and lower Youshashan formation in Altun slope area, Qaidam basin based on the sequence stratigraphic study, and includes the alluvial fan facies, the fluvial-floodplain facies, the delta facies, the fan-delta facies and the lacustrine facies, etc. Using four second-order sequences identified, plane distribution of each sedimentary facies is discussed, and the Neogene lake basin evolution and eastward movement caused by tectonic uplift are speculated. In terms of pale ostructure, paleoclimate and sedimentary source recharge, the dominant factors for Youshashau sedimentary facies evolution are analyzed.

Key words: Qaidam basin, Altun slope, Youshushan fommtion, sedimentary facies, evolution