Neogene–Quaternary postrift tectonic reactivation of the Bohai Bay Basin, eastern China

Abstract

The Bohai Bay Basin, located in the eastern China, is considered to be a Cenozoic rifted basin.The basin is atypical in terms of its Neogene-Quaternary post-rift subsidence history in that it experienced intensive tectonic reactivation, rather than the relative tectonic quiescence experienced during this stage by most rift basins.This Neogene-Quaternary tectonic reactivation arose principally in response to two tectonic events: (1) activity on a dense array of shallow faults and (2) accelerated tectonic subsidence that occurred during the post-rift stage; these two events were neither strictly temporally nor spatially equivalent.The dense array of shallow faults form a NW-SE trending belt in the central part of the basin, with displacement on them having been induced by the reactivation of older northeast-and northwest-trending basement faults and an associated substantial component of strike-slip displacement occurring after 5.3 Ma.The intense reactivation of these faults contributed to the atypical accelerated rate of post-rift tectonic subsidence of the basin, which commenced ~12 Ma.However, this was not the sole cause of this accelerated tectonic subsidence: a combination of geological activity at a deep level within the crust led to the build-up of intraplate stresses and this, combined with on-going thermal subsidence, acted as additional contributory factors that drove unusually high rates of subsidence for this basin.This episode of accelerated post-rift tectonic reactivation resulted in conditions favorable for hydrocarbon accumulation.