Based on the drilling and seismic data comprehensive interpretation, at the end of the Ordovician, a sea level fall happened and resulted in the erosion and incise the top surface, forming a large east—west incised valley. At the incised valley base, there is around 30m of basalt and tuff branching northwestward. The incised valley is filled up nearly completely after deposition of the Lower Member of the Kepingtage Formation, Silurian. The Lower Member of the Kepingtage Formation, whose maximum thickness is about 800m, mainly distributes between the Tazhong Ⅰ fauls and North—Tarim Uplifted region. In the light of their thickness and the overlapping gradient of valley, three ancient tectonic units can be divided： the northern gentle slope zone, the central depocenter zone and the southern steep zone. The clastic masses of the Lower Member of the Kepingtage Formation mainly came from the eastern margin of the basin, and secondly northern margin. The Tazhong Uplifted region did not supply sediments to the Shun9 well area. The Lower Member of the Kepingtage Formation expired depositional evaluation from semi deep sea mud to deltaic deposit, having deltaic reservoir and low amplitude structure, forming a better hydrocarbon accumulation area.