Coupling in the evolution between shelf break belt and deep-water sedimentation of the Zhuhai Formation in the Southern Subsag of the Baiyun Sag

In the deposition of the Zhuhai Formation in the Southern Subsag of the Baiyun Sag, Pearl River Mouth Basin, South China Sea, the basin was in the transitional stage from a graben to a sag, and the morphology and location of the shelf slope break underwent significant changes, resulting in distinct differences in the types and characteristics of deep-water sedimentation. We investigated the influence of slope break morphology on deep-water sedimentation types. By interpreting the 3D seismic profiles of the Zhuhai Formation, the shelf slope break zones of various intervals were identified. The characteristics and evolutionary patterns of the slope break were quantitatively analyzed, and the coupling between the slope break evolution and deep-water sedimentation was discussed. Results shows that the shelf slope break migration and evolution types were classified into four categories: descending, straight, low-angle ascending, and high-angle ascending. Based on the integration of well and seismic data, and according to the seismic facies assemblages and distribution characteristics of sedimentary systems, four major deep-water sedimentation types were identified: slope fans, mass transport deposits, deep-water channel complexes, and basin floor fans. A distinct coupling relationship was recognized between the slope break evolution type and deep-water sedimentation type: the straight, high-angle ascending, low-angle ascending, and descending migration trajectories of the shelf margin correspond to the preferential development of slope fans, mass transport deposits, deep-water channel complexes, and basin floor fans, respectively. From the fourth member to the third member of the Zhuhai Formation, the overall shelf slope break zone transitioned from a descending type to a low-angle ascending type, and the deep-water sedimentation system was dominated by the development of slope fans and deep-water channel complexes. From the third member to the early stage of the first member of the Zhuhai Formation, the overall trend transitioned from a low-angle ascending type to a descending type, and the deep-water sedimentation system was dominated by the deep-water channel-basin floor fan depositional system. During the late stage of the first member of the Zhuhai Formation, the overall trend evolved from a descending type to a high-angle ascending type, and the deep-water sedimentation system was almost undeveloped. This study revealed the control effect of shelf slope break migration on the types and distribution of deep-water sedimentation systems, which is of great significance for a deeper understanding of deep-water sedimentation processes and hydrocarbon exploration.