Xiazijie alluvial fan in Xiaoguai Oilfields could be divided into three subfacies and ten microfacies.Fanhead subfacies is composed of coarse sediments with high resistivity

and could be subdivided into main trough

side trough

trough beach

flood land and mudrock flow microfacies;the intrafan subfacies is composed mainly of fine grained sediments of high maturaty and could be subdivided into braided stream

sand island and difusion microfacies;the fan margin subfacies is composed of the finest grained sediments among the three subfacies with the lowest fluid energy

and could be further subdivided into radial water channel and laminar flow microfacies.The sedimentary model of the alluvial fan has been established based on its multisource

its evident volcanic activity and vitric tuff sediments.