Fault system and basin prototype of the Great Qikou sag, Bohai Bay Basin
Xu Liqing1,2, Li Sanzhong1,2, Suo Yanhui1,2, Guo Lingli1,2, Cao Xianzhi1,2, Wang Pengcheng1,2, Zhou Lihong3, Lou Da3
1. Key Lab of Submarine Geosciences and Exploration Techniques, Ministry of Education, Qingdao, Shandong 266100;
2. College of Marine Geosciences, Ocean University of China, Qingdao, Shandong 266100;
3. Dagang Oilfield Company, CNPC, Tianjin 300280
The Great Qikou sag is located in north-central area of the Huanghua depression, Bohai Bay Basin which is oil-gas-bearing faulted basin. Although previous studies has revealed the structures, fault systems and dynamic mechanisms of the Great Qikou sag, the segmentation, development and migration, activity of faults, the relationship between the basement-involved slipping fault systems and Cenozoic extensional fault systems in the Cenozoic sedimentary cover remain still unclear. It is vital for undstanding of the structural patterns of Cenozoic sedimentary cover. Based on interpretation and analysis of a large number of seismic profiles, we find the coastal transfer zone is south-north-striking, which means that the master faults are west-east-striking. Cenozoic fault system of the Great Qikou sag is mainly controlled by basement-involved strike-slip and extensional fault system in the sedimentary cover and developed three steps fault systems in the deep-profile. The coupling between basement-involved strike-slip and extensional fault systems has two cases: One is accommodated by forced folds related to strike-slip faulting, another is tranferred by a series of left-step NE-striking en echelon normal faults. The main faults, fault activity have a trend of southward migrating. Tectonic evolution and mechanism of the Great Qikou sag is the result of the Pacific plate eastward retrogressive subduction and the Indian plate progressive subduction, resulting in intensive fault activity of the migration from the southwest to northeast in the Great Qikou sag.