Sedimentary Characteristics and Controlling Factors of Lower Cretaceous Nearshore Subaqueous Fans in Jiuxi Depression

The Shida sag is a half-graben fault depression lake basin which has fault in the east and onlap in the west.In Early Cretaceous,lots of transtensional faults of NE and NNE trend were formed under right lateral forces,they controlled the Lower Cretaceous sedimentation and led to nearshore subaqueous fans in the steep slope.The strong movement of the fault boundary in the Early Cretaceous epoch resulted in the formation of inshore subsea aprons.The sand bodies of the nearshore subaqueous fans cut down into the dark colored mudstones of deep lake and half-deep lake.It makes the sand bodies of the nearshore subaqueous fans have excellent conditions of petroleum accumulation.