Pre-existing thrust fault system influencing overlying pull-apart basin: New insights from the offshore Bohai Bay Basin of eastern China

Pre-existing faults play an important controlling role in the formation and later evolution of sedimentary basins. The oblique extension of strike-slip faults cause subsidence and lead to the formation of pull-apart basins, this foundational mechanism is verified by fault interpretations from seismic reflection data, laboratory experiments, and numerical models. While this mechanism is observed in contemporaneous faults, how pre-existing thrust faults affect the formation of an overlying rift basin is still being studied. Here we reveal a set of Indosinian thrust faults and their reactivation effects within the basement of the offshore Bohai Bay Basin (OBBB), eastern China. These faults provide insights into the influence of pre-existing faults on the overlying basin. Structural analysis of seismic profiles of the OBBB show that its basinal basement developed a series of NWW-trending pre-existing faults, most of which cease at the top of the basement, though some were profoundly reactivated, crossing the unconformity upward into Cenozoic strata, hence, influencing the morphology and structural evolution of the Cenozoic Bohai Bay Basin (BBB). The NWW-trending faults were in response to the collision between the South China and North China blocks. Zircon and apatite fission-tracks reveal the fault-controlled basement suffered three intervals of uplift-cooling processes during the Late Triassic−Early Jurassic, Late Cretaceous, and Oligocene, and three corresponding intervals of subsidence-heating stages during the Early Cretaceous, Paleogene, and Neogene. The reactivations during the Early Cretaceous and Paleogene induced NWW-trending half-grabens. The strike-slip activity of the NNE-trending Tanlu Fault zone formed a set of NNE-trending pull-apart sags in the eastern BBB and reactivated some NWW-trending pre-existing thrust faults reversely with slight rotation. The two orthogonal extensions on interconnected half-grabens and strike-slip faults drove the formation of the pull-apart BBB. Broadly, pre-existing faults could partially be reactivated by later orthogonal strike-slip faults and jointly form a pull-apart rhomboid basin characterized by multiple sags.