Abstract: Through core analysis, well logging, borehole log and seismic data, the sedimentary facies feature and depositional system of Triassic in Wu-Xia fault belt of Junggar basin is systematically studied. The result shows that four types of sedimentary facies occur in this area, they are alluvial fan, fan delta, sublacustrine fan and lake facies. The Baikouquan formation to Baijiantan formation here experienced arid-wet changing climate in lake transgressive process. Baikouquan formation is characterized by alluvial fan groups of Xiazijie and Baikouquan areas; Upper and Lower Karamay formation by fan delta and shore-lake sediment; Baijiantan formation as a largest laketransgressional episode dominated by lacustrine fan sediment with small scale fan delta and sublacustrine fan sediments. It is concluded that the fan delta front of Karamay formation is the most favorable sedimentary facies with best reservoir property; the midfan of Baikouquan alluvial fan fitted with the faults and unconformities could also be good prospecting areas for hydrocarbon accumulation.

Key words: Junggar basin, Wuerhe-Xiazijie fault belt, Triassic, sedimentary facies, sand body