Depositional architecture and structural evolution of a region immediately inboard of the locus of continental breakup (Liwan Sub-basin, South China Sea)

New 3D seismic data and regional 2D seismic profiles from the northern South China Sea, the most extensive dataset imaging a distal rifted margin in the world, are used to characterize a region located immediately inboard of the locus of Cenozoic continental breakup. The interpreted dataset images a ~6 km thick continental crust in which the Moho and the base of syn-rift sediment are observed as clear, well-resolved seismic reflections. This extremely thinned continental crust was offset at its base by a complex detachment fault system from which oceanward-dipping listric faults propagated vertically to bound six separate tilted blocks, in a style akin to tectonic rafts. The seismic reflection data in this work allowed us to investigate the thickness of synand post-rift strata above tilt blocks to reveal that the early-middle Eocene syn-rift topography was gradually blanketed in the late Eocene (~38 Ma). After 33 Ma (earliest Oligocene), the main depocenter on the margin migrated to the south of the Liwan Sub-basin, i.e. oceanward, as recorded by the thickening of strata within a breakup sequence. This work is important as it demonstrates how closely structures and sedimentation within the Liwan Sub-basin were controlled by a basal, rift-related detachment system, which is imaged in detail by 3D seismic data for the first time on a rifted continental margin. Continental breakup was marked by a shift in the locus of subsidence (and crustal stretching) toward ocean crust, within a time period spanning ~16 m.y. We extrapolate our findings from the South China Sea to the development of asymmetric passive margins across the world.