南海北缘古近纪断裂活动规律及控盆特征:以阳江东凹为例

The Cenozoic continental marginal basins in the northern South China Sea margin can be divided into the Beibu Gulf Basin, the Qiongdongnan Basin, the Pearl River Mouth Basin, and the Taixinan Basin from west to east. These basins recorded the Cenozoic evolution of the northern South China Sea margin. To deepen the understanding of the fault activity and the Cenozoic tectonic evolution in the northern South China Sea margin, a case study of the eastern Yangjiang Sag in the ZhuⅢ Depression was carried out on the bases of high-resolution 3D seismic data. The 2D move software was used to restore the structural evolution of representative seismic profiles. The results showed that the structures in the eastern Yangjiang Sag during depositional period of the Wenchang Formation were dominated by the intensive NE-NEE- striking faults. By the depositional period of the Enping Formation, the NWW-striking faults became prevalent while a few NE-NEE-trending faults remainded active. The estimated activity rates showed that from early to late, the strikes of syn-sedimentary main faults changed from NE-NEE to near EW and NWW, while the corresponding depocenter migrated westward and southward. However, the activity intensity of individual main faults varied both temporally and spatially. The distribution and balanced cross sections of the fault system showed that the Mesozoic basement in the eastern Yangjiang Sag underwent multiple deformation and formed NE- and NWW-trending conjugate basement-involved faults. In the Early-Middle Eocene, the NE-striking pre-existing fault was preferentially re-activated under NW-SE- directed stress field, and its fault activity reached its climax during this period. During the Middle-Late Eocene, under the influence of the dextral slipping, the NE-trending faults evolved into NEE-striking and formed the NE-striking dextral faults which are characterized by right-step strike-slip and controlled the sedimentation and fault pattern. In the Oligocene, the NE-trending faults were mostly ceased, and the near-EW- and NWW-trending strike-slip faults were predominant. Therefore, the syn-rift eastern Yangjiang Sag experienced three-phase evolution: the NW-SE- directed extension in the depositional period of the Wen-3 Member, the NE-striking dextral, right-step pull-apart basin in the depositional period of the Wen-2 Member, and the NWW-trending sinistral, left-step pull-apart basin in the depositional period of the Wen-1 Member-Enping Formation. Based on previous results on the northern South China Sea continental margin, it is believed that the Cenozoic basins in the northern South China Sea margin are dextral, right-step pull-apart basins, and the NEE-trending secondary faults triggered by the dextral, right-step strike slipping of the main faults controlled the formation of the sags, in addition, the basins experienced a late stage superimposition related to the NWW-trending slipping. © 2021, Science Press. All right reserved.

Paleogene Fault Activity and Basin Controlling Characteristics in the Northern South China Sea Margin - A Case Study of the Eastern Yangjiang Sag

The Cenozoic continental marginal basins in the northern South China Sea margin can be divided into the Beibu Gulf Basin,the Qiongdongnan Basin,the Pearl River Mouth Basin,and the Taixinan Basin from west to east.These basins recorded the Cenozoic evolution of the northern South China Sea margin.To deepen the understanding of the fault activity and the Cenozoic tectonic evolution in the northern South China Sea margin,a case study of the eastern Yangjiang Sag in the ZhuⅢDepression was carried out on the bases of high-resolution 3D seismic data.The 2D move software was used to restore the structural evolution of representative seismic profiles.The results showed that the structures in the eastern Yangjiang Sag during depositional period of the Wenchang Formation were dominated by the intensive NE-NEE-striking faults.By the depositional period of the Enping Formation,the NWW-striking faults became prevalent while a few NE-NEE-trending faults remainded active.The estimated activity rates showed that from early to late,the strikes of syn-sedimentary main faults changed from NE-NEE to near EW and NWW,while the corresponding depocenter migrated westward and southward.However,the activity intensity of individual main faults varied both temporally and spatially.The distribution and balanced cross sections of the fault system showed that the Mesozoic basement in the eastern Yangjiang Sag underwent multiple deformation and formed NE-and NWW-trending conjugate basement-involved faults.In the Early-Middle Eocene,the NE-striking pre-existing fault was preferentially re-activated under NW-SE-directed stress field,and its fault activity reached its climax during this period.During the Middle-Late Eocene,under the influence of the dextral slipping,the NE-trending faults evolved into NEE-striking and formed the NE-striking dextral faults which are characterized by right-step strike-slip and controlled the sedimentation and fault pattern.In the Oligocene,the NE-trending faults were mostly ceased,and the near-EW-and NWW-trending strike-slip faults were predominant.Therefore,the syn-rift eastern Yangjiang Sag experienced three-phase evolution:the NW-SEdirected extension in the depositional period of the Wen-3 Member,the NE-striking dextral,right-step pull-apart basin in the depositional period of the Wen-2 Member,and the NWW-trending sinistral,left-step pull-apart basin in the depositional period of the Wen-1 Member-Enping Formation.Based on previous results on the northern South China Sea continental margin,it is believed that the Cenozoic basins in the northern South China Sea margin are dextral,right-step pull-apart basins,and the NEE-trending secondary faults triggered by the dextral,right-step strike slipping of the main faults controlled the formation of the sags,in addition,the basins experienced a late stage superimposition related to the NWW-trending slipping.