Fault structure and evolution of Baiyun Sag in Zhujiang River Mouth Basin

Baiyun Sag(BYS) lies in the deep water area of the Zhujiang River Mouth Basin(PRMB).It is the largest,deepest and most potential sag in the north margin of the South China Sea.The faults in the BYS are mainly in normal type and may be divided into three groups by orientation,i.e.NWW,E-W and NE,with NWW predominant.On plane view these faults form parallel,fastigiated,and en echelon combinations.In vertical sections these faults form flower,horsetail,or ladder shaped combinations,while a single fault may be of planar,listric,or chair shape.The fault movement velocity varies in difference districts.Statistics indicates that the strongest fault activity occurred during the period of 50—30MaBP and controlled the sag formation and the syn-rifting sedimentation.The faulting rejuvenated in the Dongsha movement(13.8—10MaBP) with secondarily strong activity.