南黄海盆地南五凹东洼构造特征分析

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

地震资料的精细刻画揭示,南五凹东洼在结构上表现为南北两侧成洼、中部为大型断裂褶皱带的不对称地堑式。在平面上,中部背斜带在东洼的东、西部发生错位,可能是受斜向拉伸作用的影响。关键地质界面分析和盆地沉降史回剥恢复表明该区经历了断陷-隆升-坳陷的构造演化过程。结合沉降速率的变化规律和平衡剖面分析,盆地的断陷期可进一步划分为两个阶段。在上白垩统泰州组-古新统阜宁组(K_2t-E_1f)沉积时期,断层活动较弱,对沉积作用控制小,沉积中心位于洼陷的中部,整体表现为断拗的特征;在始新统戴南组-三垛组(E_2d-E_2s)沉积时期,边界断层对沉积的控制作用增强,沉积中心向南迁移,洼陷中部的断裂褶皱带逐渐定型,整体表现为断陷的特征。渐新世时期,南黄海盆地区域性隆升剥蚀。新近纪以后,南黄海盆地进入区域性拗陷期,东洼表现为稳定的热沉降过程。

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 north- ern 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-Ejf）, the eastern Nanwu sag was characterized by rifting-depression, and the faulting activity was weak, with no controlling role on sedimentation. The depo- center during this stage was in the middle of the sag. During the sedimentation time from Eocene Dainan Fro. to Sanduo Fro. （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.