Analysis of the Structural Characteristics in Eastern Nanwu Sag of South Yellow Sea Basin

Based on the fine structural interpretation of 2D seismic data,it is revealed that the architecture of the eastern Nanwu Sag is the asymmetric graben type,with large scale faulted anticline belt in the central part,and depression in the southern part and northern part.In plane,the anticline belt in the central part was dislocated in the western and eastern parts of eastern Nanwu Sag which might result from the oblique extension.It is indicated through analysis of the key geologic boundary and the back-stripping of the subsidence history that the eastern Nanwu sag underwent the tectonic evolution history of rifting stage,the uplifting stage and the depression stage.The rifting stage can be divided into two episodes through analysis of subsidence rate variation and the balanced cross-section.During the sedimentation time from late Cretaceous Taizhou Fm.to Palaeocene Funin Fm.(K₂t-E₁f),the eastern Nanwu sag was characterized by rifting-depression,and the faulting activity was weak,with no controlling role on sedimentation.The depocenter during this stage was in the middle of the sag.During the sedimentation time from Eocene Dainan Fm.to Sanduo Fm.(E₂d-E₂s),the eastern Nanwu sag was characterized by depression,the controlling role of boundary faults on sedimentation became strong,resulting in shift of depocenter southward,and the faulted-fold belt was formed gradually.During Oligocene,the whole South Yellow Sea Basin was uplifted and eroded widely.From Neogene,the South Yellow Sea Basin entered into regional depression stage,and the eastern Nanwu sag entered into stable thermal subsidence.