Abstract: The data from reservoir of Lower Karamay formation of District 4-(2) in northwestern margin of Junggar basin are applied to elaborate the lithology, the depositional structure and the type of sedimentary facies. The flood plain-like alluvial fan, a type of alluvial fan different from other districts in Karamay oilfield, is then discovered. This alluvial fan is characterized by thin, narrow and straight sand bodies as well as developed gully microfacies (hydrocarbon-bearing facies). Also, this paper presents the measures and suggestions for effective exploration and development of such oil-gas fields.

Key words: alluvial fan, flood plain, mudflow microfacies, gully microfacies