南堡凹陷断裂发育特征及其演化机制

Development characteristics of fault and its evolution mechanism in Nanpu Sag

南堡凹陷受渤海湾盆地北东向断裂和北西向断裂的共同控制,凹陷北部是北西向的张家口—蓬莱断裂带,凹陷东部和西部分别是北东向且具有走滑性质的郯庐断裂带和沧东断裂带。因此,南堡凹陷的形成和构造变形既具有张性变形特征,又具有压扭或张扭变形特征。剖面上,断裂的组合样式较为复杂,大致可分为"y"形、"x"形、包心菜式、花状及阶梯状等;平面上,断裂的组合样式主要为帚状、梳状、平行式、雁列式、交织状和"入"字形。构造演化史表明,古近系沙河街组沉积时期为凹陷的伸展断陷阶段,主要受郯庐大断裂的右行扭动控制,断陷作用强烈、水体较深,是烃源岩发育的主要时期。东营组沉积时期,凹陷进入稳定的沉降阶段,为持续裂陷期,主要受近南北向区域张力的作用。新近系至今,凹陷进入坳陷阶段,主要受重力和热沉降的共同作用,次级断裂较为发育。

Because Nanpu Sag is controlled by northeast fault and northwest fault in Bohai Bay Basin, Zhangjiakou-Penglai fault zone with northwest trend is located in the northern part of the sag, and Tanlu fault zone and Cangdong fault zone with strike-slip nature are located separately in the eastern part and in the western part of the sag. Therefore the formation and tectonic deformation of Nanpu sag indicate both the characteristics of tensional deformation and the characteristics of compressional deformation or lensional defurmation. Faults of Nanpu sag can be classified into five styles in section： ＂y＂-shaped fault assemblage, ＂x＂-shaped fault assemblage, cahhage-shaped fault assemblage, flower-shaped fault assemblage and step-shaped fault assemblage. In plane, the fault assemblage type is mainly brush assemblage, comb assemblage, parallel assemblage, en echelon assemblage, interlaced assemblage and ＂λ＂-shaped fault assemblage. Analysis result of structural evolution history shows that the depositional period of Shahejie Formation in Paleogene is the extensional rift stage of the sag, and is the main period of hydrocarbon source rock development because of the eontrolling of right lateral wrench movement of Tanlu fault, with rift faulting strong and with water body deep. The sag enters the stahle subsidence stage during depositional of Dongying Formation by the strain near northern and southern region to keep the rift period. The sag has turned into depression stage from Paleogene to present. Subsidiary fauh develops well due to the combined effect of gravity and thermal subsidence.