Seismic-Reflection Imaging of a Pull-Apart Sag within Tan-Lu Strike-Slip Fault Zone: Cenozoic Structure and Evolution of the Weibei Sag, Southeastern Bohai Bay Basin, China

Early Paleogene strike‐slip transition of the Tan–Lu Fault Zone across the southeast Bohai Bay Basin: Constraints from fault characteristics in its adjacent basins

“…It is generally agreed that the Cenozoic deformation of the TLFZ plays an important role in the formation and evolution of these sags (e.g., Chen, ; Chen, , ; Jia et al, ; Zhang & Qi, ; Zheng et al, ; Zhou, ). The Weibei Sag located within the TLFZ is thought to be a typical pull‐apart basin (e.g., Cheng et al, ; Cheng et al, ; Zhang & Qi, ), while the Dongying and Qingdong sags situated to the west of the TLFZ are considered as transtensional faulted basins (e.g., Wang, Yang, & Zhang, ; Zhan, ; Zhan & Zhu, ; Zheng et al, ).…”

“…With different research purposes, some studies divided E s and E k further into E s 1 , E s 2 , E s 3 (E s 3 U , E s 3 M , and E s 3 L ), E s 4 (E s 4 U and E s 4 L ), E k 1 , E k 2 , and E k 3 , respectively (e.g., Zhang et al, ; Zheng, ; Zhan & Zhu, ; Zhang, ; Table ). Compared with the sequences in above two sags, those in the Weibei Sag miss the upper part of E s 4 ‐E d (e.g., Cheng et al, ; Li et al, 2009; Li et al, ; Zhang & Qi, ).…”

“…In its E k ‐E k 4 L , there are five orientations (WNW/NW, E‐W, ENE/NE, NNW, and NNE) of secondary faults. The former three are extensional faults, while the NNW‐ and NNE‐trending ones are strike‐slip faults (Cheng et al, ). The distribution characteristics of the extensional secondary faults is quite interesting with the WNW‐trending ones located in the west, E‐W‐trending ones in the middle, and ENE‐trending ones in the east and close to the east branch of the TLFZ, the CDF (Figure ).…”

“…However, the strike‐slip transition time of the TLFZ is still controversial. Some scholars held the opinion that this transition occurred between the Mesozoic and Cenozoic (e.g., Cai, Luo, & Yao, ; Cheng et al, ; Wan & Zhu, ; Zhang & Qi, ), but more and more authors considered that it happened in Early Paleogene, for example, in the depositional stage of (1) the second member of the Kongdian Formation (designated as E k 2 ; e.g., Sun et al, ; Zhou, ), (2) E k (Chen, ; Chen, ; Wang, ), (3) E k to the fourth member of the Shahejie Formation (E k ‐E s 4 ; e.g., Cao, ; Guo, ; Gao, ; Huang, Wang, Wu & Wang, ; Huang, Liu, Zhou & Wang, ; Jia et al, ; Wu et al, ; Zheng et al, ; Zhang, Wang, Ding, & Zhong, ; Zhao & Li, ), (4) E k to the lower sub‐member of E s 4 (E k ‐E k 4 L ; e.g., Jia et al, ; Jia et al, ; Wang et al, ; Wei et al, ; Wu et al, ; Yang, ; Zhang, ; Zheng et al, ), or (5) E s 4 (e.g., Chen, ) and in geological time (1) in the Palaeocene (e.g., Shi, ), (2) from the Palaeocene to the Early Eocene (e.g., Han et al, ; Hsiao et al, ; Huang, Yu, Zhang, Fu, Yuan, & Fan, ; Li et al, ; Teng, Zou, & Hao, ; Xia, Liu, & Chen, ; Xu et al, ; Zhang et al, ; Zhang, ; Zhang et al, ; Zhang, Xue, Wu, Nie, & Hu, ; Zheng, ; Zhou, ), or (3) in the Early Eocene (e.g., Gao, ; Wang, Zhang, & Li, ). Besides, they did not explain how exactly the TLFZ turned into dextral motion from sinistral motion during the above transition stage as well (e.g., Gao, ; Huang et al, ; Jia et al, ; Wu et al, ; Zhao & Li, ; Zheng et al, ; Zhou, ).…”

“…The Dongying (e.g., Gao, ; Jia et al, ; Jia et al, ; Li et al, 2012; Wu et al, ; Zhang et al, ; Zhang et al, ; Zhang, ; Zhang et al, ; Zheng, ; Zheng et al, ), Qingdong (e.g., Cheng et al, ; Guo, ; Han et al, ; Li et al, ; Wang et al, ; Wei et al, ; Yang, ; Zheng et al, ), and Weibei (e.g., Cheng, Li, Wang, & Tang, ; Huang et al, ; Li et al, ; Li et al, ; Ren, ; Xu et al, ; Zhang & Qi, ) sags are common research targets on the strike‐slip transition of the TLFZ in the Early Paleogene. They are close to each other and adjacent to the TLFZ (Figure ).…”