歧口凹陷滑脱构造剖析及对油气地质意义

重力滑脱构造在盆地演化中较为常见,地层或岩体在重力作用下向下方滑动所产生的构造变动存在广泛。歧口凹陷为渤海湾新生代盆地内一个次级构造单元凹陷,其特点是新生代沉积巨厚且构造活动强烈,为重力滑脱和相关构造形成提供了发育条件。按照滑脱面性质的不同,将歧口凹陷的滑脱构造分为3类:地层-断裂复合滑脱、顺层滑脱和断裂滑脱。在该凹陷中选其各自具代表性的构造,如埕北滑脱构造、塘沽新港滑脱构造和大张坨滑脱构造进行结构特征和演化等方面剖析。研究认为,歧口凹陷滑脱构造形成的主控因素为新生代凹陷区快速沉积、凸起带强烈隆升、前第三纪地层的滑移层和热力作用。滑脱构造大多有褶皱和断裂相伴生,其组合方式不同可为油气成藏提供有利条件。

Analysis on decollement structure of Qikou Sag and the petroleum geological significance

Gravitational decollement structures are extremely common in the basin evolution,the structure changes by the downhill slide of rock mass or rock mass structure under the influence of gravity are extensive.Qikou Sag is Cenozoic sag in eastern China with the characteristics by thick Cenozoic sedimentary and tectonic activities,which provide good structural conditions to gravitational decollement structures.Based on the differences of the decollement surfaces,the decollement structures in Qikou Sag can be divided into three types:bedding-fault decollement,bedding decollement and fault decollement,choose the typical representatives of the three types to analyze,such as Chengbei decollement structure,Tanggu-Xingang decollement structure and Dazhangtuo decollement structure.Through the study on the structural characteristics and evolution of decollement structures,it is considered that the major reasons to decollement in Qikou Sag are Cenozoic rapid sedimentary,strong uplifting of convex belts,the distribution of pretertiary strata and thermal effects.Besides,the study found that there always be folds and faults accompany the decollement structure,different combinations of the folds and faults can provide favorable conditions for hydrocarbon accumulation.