Keywords: 
• valley remained accommodation /
• slumping turbidity fan /
• the first member of Qingshuihe Formation /
• Shinan Area /
• Junggar Basin

Abstract: The first member of Qingshuihe Formation is a major pay formation of the lithologic oil reservoir in Well Shinan 31 area, of the lowamplitude structural oil reservoir in Well 44 Shinan area, and of the whole hinterland region in Junggar Basin. Researching its sequence stratigraphic characteristics is significant for the prospecting on subtle reservoir in Shinan area, even in the whole hinterland region. Based on the comprehensive analysis of cores, logs and seismic data, this paper points out that the first member of Qingshuihe Formation corresponds with the sediments of the lowstand and transgressive systems tracts of the first third class sequence in Lower Cretaceous. The sequence stratigraphy is characterized by as follows: the lowstand systems tracts, distributing limited, is consisted of the remained accommodation sediments in trench and valley, which deposited mainly pebbly sandstone of braided channel; the transgressive systems tracts develops retrograding delta and delta front slumping turbidity fan. The paper sets up a model for the hydrocarbon reservoir forming in Well Shinan 31 area and concludes that the middlewestern part of Sannan depression is the favorable prospecting region for the type of stratigraphiclithologic reservoir. Regionally, the stratigraphic traps make up of the channel pebbly sandstone and the slumping turbidite fan occurred in deltafront, and, the lithologic traps make up of the retrograding delta; the mudstone on the top of the transgressive systems tracts can be regarded as the seal; The effective passage system is matched up with the slope palaeotopography, the discordogenic fault, middleshallow fault system, and the unconformity.