Cenozoic tectonic evolution of the eastern Liaodong Bay sub-basin, Bohai Bay basin, eastern China — Constraints from seismic data

The eastern Liaodong Bay sub-basin is located in the northeastern Bohai Bay basin, where Cenozoic fault patterns are thought to be largely affected by the movement of the Tan-Lu strike-slip fault zone. Based on three-dimensional seismic data, we identify the initial timing of faulting on normal faults with various orientations in the eastern Liaodong Bay sub-basin, document the structural features and evolution of the fault system and compare the fault patterns with analog models. The basin experienced phases of extensional, strike-slip and inversion-type deformation from the Paleogene syn-rift stage to the Neogene-Quaternary post-rift stage. During the Eocene, the eastern Liaodong Bay sub-basin was in a nearly NNW-SSE oriented extensional setting, with active faults predominantly trending NE-SW to ENE-WSW. During the Oligocene, the eastern Liaodong Bay sub-basin was in a predominantly dextral strike-slip setting. In the study area, the NE-SW trending boundary faults were reactivated, and the reactivated pre-existing internal faults rotated to a more E-W trend. Some of the newly formed extensional faults were orthogonal to the eastern boundary fault F1 and were oriented NW-SE, while others were predominantly oriented E-W. The renewed minor phase of N–S extension during the Miocene caused the reactivation of some pre-existing faults striking NE-SW (boundary faults) and E-W (internal faults); the faults exhibit a bidirectional character in the post-rift section, and the later inversion caused regional compressional deformation. These results suggest that the reactivation of pre-existing faults under phases of extension, strike-slip and inversion provides a more comprehensive explanation for the fault patterns and anticlines observed in the eastern Liaodong Bay sub-basin.