Structural Comparison Between Xijiang Sag And Baiyun Sag In Pearl River Mouth Basin

The Pearl River Mouth Basin is located on the northern continental margin of the South China Sea.The research area spans a wide area from the continental shelf to the continental slope to the deep sea basin,and different tectonic units have different tectonic features due to their different locations and tectonic evolution.By studying the structural differences in the Xijiang and Baiyun sags,the reasons for the differences are further explored,which is beneficial to the exploration and development of the Pearl River Mouth Basin.We use three-dimensional seismic data and oil-gas exploration data to analyze the structural features,fault system and tectonic evolution of the Xijiang and Baiyun sags in the central part of the Pearl River Mouth Basin.Several conclusions are as follows.?1?Differences of structural features:The Cenozoic sequences can be divided into three layers:the rifting structural layer,the depression structural layer,and the block faulting structural layer.The rifting structural layer of the Xijiang Sag includes the Wenchang and the Enping formations.The Wenchang Formation is shown as a shovel-type half-graben structure,while the Enping Formation displays a horst-graben shape.The rifting tectonic layer of the Baiyun Sag includes the Wenchang,Enping and Zhuhai formations,which are chacterized as the compound graben structures.The depression tectonic layer of the Xijiang Sag include the Zhuhai and Zhujiang formations,while the Baiyun Sag only includes the Zhujiang Formation,with sub-parallel or parallel reflection layers inside.The block faulting tectonic layer is strongly affected by the continental shelf and the continental slope.The layer of the Xijiang Sag is a thin layer with the sub-parallel seismic reflection inside,and the layer of the Baiyun Sag displays a thickened flexural structure at the foot of the continental slope.?2?Differences of fault system:The faults in the Xijiang Sag were mainly developed during the period of the Wenchang and Enping formations;the former mainly developed NE/NEE-striking faults,while the latter mainly developed nearly E-W-striking and NEE-striking faults.During the period of the Zhuhai Formation,the E-W-striking,NEE-striking,and NWW-striking faults were developed.After the Zhujiang Formation period,the faults mainly striked NWW.The faults in the Baiyun Sag have been relatively developed.The Wenchang and Enping formations mainly developed NEE-striking fault,while the Zhuhai Formation and the above formations mainly developed the nearly E-W-striking fault.The activity major faults in the Xijiang Sag is concentrated in the Wenchang and Enping formations.During the E₂w period,the NE/NEE-striking faults had the strongest activity.During the E₃e period,the NEE-striking and nearly E-W-striking faults were the most active.During the E₃zh period,the NEE-striking,NWW-striking and nearly E-W-striking faults were the most active.After that,the NWW-striking faults were the most active.The activity of the main faults in the Baiyun Sag is constantly strong during E₂w to E₃zh time.The activity of the NEE-striking faults was strong during E₂w and E₂e time,while the nearly E-W-striking faults became the strongest faults after E₂e time.?3?Differences in tectonic evolution:The tectonic evolution can be divided into three stages:rifting stage,depression stage,and block faulting stage.The rifting stage began from the Eocene:the Xijiang Sag deposited the Wenchang and Enping formations,while the Baiyun Sag deposited the extra Zhuhai Formation.The depression stage in the Xijiang Sag began from the Late Oligocene,with Zhuhai and Zhujiang formations deposited,while the Baiyun Sag began from Early Miocene,with the Zhujiang Formation deposited.The third stage began from the Middle Miocene,and the Hanjiang Formation and the above sequences were developed.