南海北部陆缘盆地半地堑类型及沉积充填模式

Research on half-graben types and sedimentary filling modes of northern continental margin basin of the South China Sea

对中国南海北部陆缘珠江口盆地与琼东南盆地的区域不整合进行研究,结果表明:该区域受控于幕式岩石圈整体拉张作用,主要经历了3个沉降阶段:初始裂陷、主裂陷、及裂陷衰减阶段,控制盆地内断裂系统发育及阶段性活动,形成了以半地堑为主的构造样式.依据主控断裂与次级断裂的位置关系,将半地堑分为3大类:简单型,缓坡断阶型及陡坡断阶型;同时,根据地震相的外部形状与内部反射特征,对盆地内地震相进行划分,识别出5种地震相类型:平行-亚平行席状地震相、前积楔状地震相、充填状地震相、丘状地震相及乱岗形滩状地震相.通过分析各种地震相的垂向分布规律和指相意义,结合研究区沉积背景及单井资料,将地震相转变为沉积相,建立了南海北部陆缘盆地各类半地堑充填模式,划分出三角洲、扇三角洲、深水扇等沉积相,明确了不同类型半地堑沉积充填模式的区别,为生储组合分析及勘探前景研究提供依据.

Regional unconformities of Pearl River Mouth basin and Qiongdongnan basin were studied. The results indicate that, controlled by the episodic lithospheric extension, there are three subsidence episodes in the study area, which are the initial rifting episode, the main rifting episode and the rifting ending, respectively. They controlled the development and episodic movement of fault system, and then the main half-graben structural styles formed. Based on the position relation of main faults and secondary faults, three types of half-grabens can be classified, which are the simple type, the fault terrace type in gentle slope and the fault terrace type in steep slope. Based on internal reflection tex- ture and external shape of the seismic sequence unit, the seismic facies of study area can be divided into five seismic facies, which are the parallel-subparallel sheet seismic facies, foreset wedge seismic facies, filling seismic facies, mound seismic facies and hummocky bank seismic facies. By the analysis of the vertical distribution rules and facies significance of seismic facies, and bounded by deposition back- ground and single well information in the reaserch area, converse the seismic facies to sedimentary fa- cies. The facies include delta, fan delta and deep-water fan. The differences among the various types of the half grabens are pointed. And evidences are provided for the source-reservior patterns analysis and exploration prospect.