Braided delta system and sublacustrine fan system constitute the primary Eogene coarse elastic sediments which are characterized mainly by short axial direction transportation depositlon.The asymmetrical bilateral fractures whthin the graben resulted in the drift of subsidence center and depocfnter towards the main fracture;the braided delta system then developed on the gentle slope.As the main reservoirs in the graben

the development of the braided delta system was closely related to its transverse structtyres such as cross faults

fault benches

borderland slopes and basement uplifts.Thus these structures should be im portant targets for oil and gas exploration.