Multiphase growth and basin control of main faults on Northern sub-basin, Beibuwan basin, Northwestern South China sea

Abstract

The basement-involved faults and multiphase extension control the three-dimensional (3-D) fault geometries and kinematics, producing different fault growth models in continental rift basins. In this paper, we apply qualitative and quantitative fault analysis techniques to 3D high-resolution seismic data from the Northern sub-basin of Beibuwan basin, building the tectonic-stratigraphic framework and proposing the evolutionary meachanisms of main normal faults. The results suggest that extensional stress changed from NW-SE direction during Paleocene-Middle Eocene to N-S direction in Late Eocene-Oligocene, leading to the ENE or E-W directed propagation of fault networks together with lateral and vertical linkage of fault segments. This includes three conceptual models: (1) F1 originated from propagation, interaction, linkage and failure of initial seven ENE-directed isolated faults, and grows following isolated fault growth model; (2) F2 nucleated as a normal fault before buried in Late Eocene, and reactivated as dextral strike-slip fault in Oligocene, therefore experienced vertical segmentation and linkage; (3) F3 activated as a long-term constant-length fault with generally increased displacement in Paleogene. Our study proposes that the T83 interface (the top of the second member of the Liushagang Formation) is a tectonic stress transition interface, while the T60 interface is both a tectonic inversion interface and a post-rift unconformity interface. Furthermore, the growth of extensional faults commonly accompanied single breached, transfer-fault breached or double breached relay ramps and fault-related folds, thereby exerting a significant influence on the basin architecture and sediment distribution.