Characteristics and provenance of rare earth element in mud wedge in the sea area north of Shandong Peninsula since 2 ka

The mud wedge in the Shandong Peninsula serves as a pivotal sedimentary body, linking the Bohai Sea with the Yellow Sea. It plays a significant role in the sedimentation system of China seas as an essential component of "source-sink" system in the edge of the Chinese continental shelf. The controlling factors of rare earth elements (REEs) and the provenance of the wedge sediment in this area were studied based on the analysis of AMS ¹⁴C dating, grain size, and REEs content of the ZZ04 boxcore samples at the northern offshore of the Shandong Peninsula. Results indicate that the boxcore samples consist of mainly silty sand in relatively simple material composition with a trend of coarsening in grain size from deeper to shallower depths. Upon normalization with chondrites, the REEs exhibit a characteristic enrichment of light rare earth elements (LREEs) and relative stability of heavy rare earth elements (HREEs), forming a distinct right-leaning V-shaped pattern indicative of a clear terrigenous signature. Further comparative analysis on the REEs between the ZZ04 sample and surrounding rivers’ after continental crust normalization revealed that the distribution patterns of ZZ04 samples closely resemble those of the Yellow River. In contrast, they show significant differences from those of the rivers in South Korea and the Shandong Peninsula. Additionally, correlation analysis between REEs and grain size suggested that the distribution of REEs in the mud wedge is influenced by the "grain size effect" since approximately 2,000 years ago. The source of the mud wedge comes mainly from the Yellow River. After the establishment of the modern ocean circulation system, the fine-grained sediments carried by the Yellow River flowed eastward along the northern coast of the Shandong Peninsula through the Bohai Strait into the Yellow Sea, and then encountered by the northward Yellow Sea Warm Current, which decreased the flow velocity and resulted in the settlement of a large amount of fine-grained matter in the northern waters of the Shandong Peninsula, forming a uniqueΩ-shaped underwater delta.