Growth and Linkage of a Basin-Bounding Normal Fault System: Insights from the Pinghu Fault, Xihu Sag, East China Sea Basin

   The growth and linkage of basin-bounding normal faults play a pivotal role in controlling the structural architecture and tectono-stratigraphic evolution of rift basins. High quality, well-constrained 3D seismic data from the Xihu sag, East China Sea Basin document the growth history and transtensional reactivation of the basin-bounding fault system along the Western Slope Zone. The Pinghu fault system in the Xihu Sag is characterized by pronounced segmentation and progressive segment linkage, comprising six major fault segments that together define an overall “X”-shaped fault zone. 
   Our analysis identifies three distinct evolutionary stages: (1) isolated segment growth, characterized by independently evolving NNE-striking segments; (2) soft linkage, during which interactions between overlapping segments led to the formation of relay ramps; and (3) hard linkage, when continued displacement accumulation resulted in the breaching of relay ramps and the development of a through-going basin-bounding fault zone. This multi-stage fault evolution was jointly controlled by segmented fault growth during Eocene rifting and subsequent rotation of the regional stress field.
   The spatiotemporal evolution of the Pinghu fault exerted a first-order control on syn-rift sedimentation within the Pinghu Formation. During the fault linkage stage, intact relay ramps functioned as a key sediment entry pathways, channeling sediment supply into the basin and controlling the distribution of deltaic sandbodies. Progressive fault growth and linkage strongly influenced syn-depositional architectures: variations in thickness and facies within the Pinghu Formation record shifting depocenters and sedimentary responses to evolving fault activity.
   This study demonstrates the critical importance of basin-bounding fault segmentation and linkage histories in controlling sand-body distribution and understanding the tectono-sedimentary coupling processes in continental marginal rift basins.