Depositional features of the fan delta from lower Cretaceous Kezilesu Group in Yecheng sag, southwestern Tarim Basin

Abstract：Based on field outcrop and core observation, combined with mud logging, logging and grain size analysis, the authors found that there are prograded fan delta sediments in lower Cretaceous Kezilesu Group of Yecheng sag, which can be divided into fan delta plain, fan delta frontier underwater distributary channel, mouth bar and interdistributary bay. Fan delta plain was obviously affected by gravity flow, whereas fan delta frontier was mainly affected by traction current. The latter extended limitedly in the direction of the short axis, and extended a considerable distance in superimposition association with adjacent fan delta frontier leaves in the direction of the long axis. Fan delta experienced progradation from the piedmont area to the faulted lake basin, forming mono-faulted fault basin filling model in the direction of the short axis, which was steep slope on one side, and wide and gentle slope on the other side. This sedimentary model controlled not only characteristics of each unit of the fan delta but also microfacies types and sand distribution.