Three episodes of rifting once developed in Beibuwan basin during Paleogene. The first eposode was stronger in the activity of NE-trending faults and controlled the distribution of the Changliu Formation. During the second and third rifting episodes, the activity of NEE-trending faults and EW trending faults were stronger re spectively, and the distribution of Liushagang For marion and Weizhou Formation were controlled re spectively. The variations of these three rifting ep isodes in time and space have resulted in the differences in vertical superimposition of the three Formations in each sag and the areal migration of the sedimentation subsidence centers. From the fault activities and the formation distribution, the sags in Beibuwan basin can be divided into four types, i.e. the thicker-Changliu, thicker Liushagang, thicker-Weizhou and persistent-subsidence type, and these types of sags are quite different in resources potential, main occurence interval and ac cumulation model of hydrocarbon.
China Offshore Oil and Gas