渤海湾盆地秦南凹陷构造发育特征与有利勘探方向

Tectonic development characteristics and favorable exploration direction of Qinnan sag in Bohai Bay Basin

渤海湾盆地秦南凹陷位于NE向郯庐断裂带和NW向张家口—蓬莱走滑断裂带交会形成的强烈转换拉张构造区,其断裂系统具有伸展与走滑双重动力作用机制。通过对秦南凹陷各个洼陷的结构和构造特征进行精细描述,统计对比了主要控洼断裂在新生代各时期的活动量,并运用平衡剖面技术对秦南凹陷的形成演化进行了恢复。研究认为,秦南凹陷的断裂发育特征存在时空差异性,断裂活动强度在区域上具有"东强西弱、南强北弱"的特点,活动性总体呈现出由西向东、由北向南迁移;秦南凹陷具有"南北分带、东西分块"的构造格局,其中,西洼和东南洼为伸展构造,东洼以走滑—伸展构造为主;秦南凹陷中生代晚期—新生代的构造演化可分为7个阶段。通过分析秦南凹陷伸展与走滑的双重动力作用机制及各个洼陷构造发育特征的差异性,揭示了秦南凹陷的构造特征对油气赋存和成藏的影响,为秦南凹陷东洼的有利油气勘探方向提供了依据和指导。

The Qinnan sag of Bohai Bay Basin is located in the strongly transtensional tectonic zones at the intersection of the NE-trending Tanlu fault zone and the NW-trending Zhangjiakou-Penglai strike-slip fault zone,of which the fault system has two dynamical mechanisms,i.e.,extension and strike-slip.Through finely describing the structure and tectonic characteristics of each subsag in Qinnan sag,a statistical comparison is made on the activity of the main subsag-controlling faults in each period of the Cenozoic;the formation and evolution of Qinnan sag is restored by using balanced section technology.The research indicates that the fault development in Qinnan sag shows spatiotemporal difference,and the strength of fault activity presents the characteristics of'strong in the east and the south but weak in the west and the north'on a regional scale.The activity generally shows the migration from west to east and from north to south.Qinnan sag has a tectonic pattern of'zonation in north-south direction and segmentation in east-west direction'.The west subsag and the southeast subsag are dominated by extensional structures,while the east subsag is dominated by strike-slip and extensional structure.The Late Mesozoic-Cenozoic tectonic evolution of Qinnan sag can be divided into seven stages.Through analyzing the dual dynamic mechanism of extension and strike-slip in Qinnan sag as well as the difference in the tectonic development characteristics of each subsag,the impacts from the tectonic characteristics of Qinnan sag on hydrocarbon occurrence and accumulation are revealed to provide the basis and guidance for determining favorable hydrocarbon exploration direction in the east subsag of Qinnan sag.