Source-to-Sink Dynamics of Deep-Water Sediments in the Qiongdongnan Basin, South China Sea: Insights from Multi-Proxy Geochemistry

The South China Sea serves as a premier location for investigating sediment provenance and source-to-sink processes within marginal seas. However, the sediment composition and transport mechanisms within the deep-water areas of the Qiongdongnan Basin remain poorly understood. This study analyzed the grain-size distribution, bulk geochemistry, and clay mineralogy of surface sediments to identify their origins and transport controls. Results indicate that the sediments are predominantly silt-sized with a high smectite content. Major element geochemistry suggests derivation from stable ancient terranes, while trace element patterns—characterized by LREE enrichment and negative Eu anomalies—point toward a multi-source contribution. Our analysis suggests that the Red River is the primary sediment source, supplemented by inputs from the Pearl River, the Vietnamese coast, and Hainan Island. We propose that monsoon-driven surface circulation is the primary transport driver, while deep-water currents and a branch of the Kuroshio Current facilitate the influx of Taiwan-derived materials. Our study clarifies the source–sink relationship and transport mechanism in a semi-quantitative manner, offering new insights into sediment dynamics in monsoon-influenced marginal seas.