Impacts of Tectonic-Paleogeographic Transitions on Cenozoic Sedimentary Distribution in the Dangerous Grounds, South China Sea

       The Dangerous Grounds, located along the southern margin of the South China Sea, has undergone substantial tectonic and paleogeographic changes during the Cenozoic, spanning three distinct evolutionary stages: continental rifting, breakup from South China and southward drift, and collision with Borneo. This study utilized a robust dataset comprising 67 seismic reflection profiles, complemented by drilling and dredging data, to quantitatively reconstruct the sedimentary filling history of the Dangerous Grounds. By correlating sediment budget outcomes with the spatial distribution characteristics of sediment thickness, we have gained valuable insights into the region’ s geological evolution.

       Our findings reveal a progressive increase in sediment budgets across the three tectonic stages, despite relatively stable sediment budgets during the southward drift stage associated with seafloor spreading. Spatial analysis of sediment distribution, as revealed by sediment isopath maps, shows a continued decrease in the north and expansion in the south and west, suggesting the influence of regional tectonic transitions and variations in paleogeographic environment. By integrating the temporal and spatial distribution of depocenters with drilling results and sediment provenance geochemical analyses, we provides a comprehensive regional perspective on the factors controlling sediment budget trends, including regional tectonic transitions, variations in paleogeographic environment (such as climate, sea level, and sedimentary facies, and the evolution of local river systems).

       The sedimentary inputs to the Dangerous Grounds have shifted over time, with Paleocene-Eocene sediments primarily originating from the north. From the Oligocene to the Early Miocene, northern sediment supply progressively declined, while inputs from the southwest, transported through river systems originating in the Indochina and Malay Peninsulas, gradually increased. Since the Mid-Miocene, the collision with Borneo has led to enhanced sediment supply from the south, with sediments predominantly accumulating along slope edges, channel outlets, and within the Nansha Trough.