Types and genesis of the alluvial fans in the lower submember of the fourth member of the Shahejie Formation in the Huimin depression, Shandong

Two types of depositional systems are identified for the lower submember of the fourth member of the Shahejie Formation in the Huimin depression, Shandong, including the debris flow fan and braided stream fan. The braided stream fan deposits are well developed on the downthrown sides of the Ningnan fault and Wunan fault. In a planar view, they display the fan shape, and extend over a wide range of scale. The interchannel flood plain and crevasse splay deposits are less developed, and the sedimentary facies belts are less differentiated. The channel lag deposits and channel sandbar deposits are interpreted as the main sediment types. The debris flow fan deposits occur near the fault scarp of the Qiguang fault, and consist of the proximal fan, mid-fan and terminal fan subfacies. In comparison with the braided stream fan deposits, the debris flow fan deposits are characterized by the enrichment of conglomerate, smaller scales of fans, and sharp facies changes. The controlling factors for the formation of this type of depositional systems contain tectonism, palaeogeomorphology and palaeoclimates, especially active faulting.