Along-strike depositional variability of syn-rift lacustrine systems along the Shinan Fault (Oligocene Dongying Formation, Bozhong Sag, eastern China)

Fault evolution controls proximal to distal architectures and facies distribution of rift deposits. Resulting wedge-shaped syn-rift strata show thinning or thickening towards the fault as a response to breached or unbreached monocline during the sedimentation. However, the integration of seismic data and cored material to understand along-strike fault-controlled depositional variation in overall geometries and detailed sedimentary characteristics remains little studied. In this study, we reconstructed the tectono-stratigraphic evolution along the Shinan Fault System at the northern margin of the Bozhong Sag (Bohai Bay Basin, eastern China) by integrating 3D seismic data (i.e., structures and seismic stratigraphy), wireline logs (i.e., GR-log shapes), and sedimentary logs of cored material. Our results indicate that in the northern part of the study area the fault has breached the surface since the early stage of its activity generating an asymmetric syncline characterised by the main deposition loci located close to the fault. Here, base-of-scarp deposits showing up to 100 m in thickness adjacent to the fault and extending up to 2.5 km away from the fault accumulated evolving upwards and laterally into fine-grained lacustrine deposits and large-scale clinoforms prograding for up to 25 km parallel to the main fault. Towards the tip, the fault doesn't breach the monocline producing a fault propagation fold. Here, strata onlapped towards the unbreached monocline where sediments form wave-influenced deltaic systems. Our results provide insight into variations in along-strike stratigraphic architectures, thickness, lateral juxtaposition, and facies changes.