Abstract:A large number of coarse clastic rock deposits were developed in Lower Cretaceous Xiguayuan Formation in the Luanping Basin. Based on 3D digital model as well as manual photography of typical outcrops, combing with fluid transportation mechanism, micro-facies identification and debris deposits in fault depressed lacustrine basin were studied in detail. The results show that the northern part of Luanping Basin in Xiguayuan Formation is affected by the boundary fault activity, and the nearshore subaqueous fan deposition system of the typical fault basin is developed. According to outcrop observation and research, three sub-facies including root fan, mid fan and fan end can be divided. Among them, the root fan sub-facies are characterized by the fact that the detrital clasts directly enters the lake, the lithology is coarse, the sorting is extremely poor, and there is no rounding. The mid fan adopt the division method of “subaqueous channel micro-facies” and “marginal micro-facies”. The micro-facies of the subaqueous channel sediments were controlled by two different fluid properties of debris flow and turbidity flow which are developed simultaneously. The boundary is clear and slightly scoured, the lateral continuity is relatively stable, the gravel has a certain orientation, the rounding is poor, and it is most developed in the mid fan; the marginal facies are relatively mixed, the boulder is more common, and the obvious plate is visible. Interlaced bedding, poor lateral continuity, indicating diversion or marginal deposition of rivers, and no development of erosion-filling structures. The fan end sub-facies are characterized by thin-interbedded sandstone or thick layer of fine sandstone, showing bioturbation structures and fine gravel layers. The micro facies division method is more of a causal basis. The research results provide a new idea for the identification of nearshore subaqueous fans in similar basins and underground research and will be conducive with the oil and gas exploration and development.