Provenance Evolution Since the Middle Pleistocene in the Western Bohai Sea, North China: Integrated Rare Earth Element Geochemistry and Sedimentological Records

Despite extensive research on sediment provenance in the Bohai Sea (BS), a significant knowledge gap persists concerning long-term provenance evolution, particularly in the western BS since the Middle Pleistocene. This shortcoming limits reconstructions of paleoenvironmental evolution and its interplay with climatic variability and sea-level fluctuations. This study presents integrated Rare Earth Element (REE) geochemical and sedimentological analyses of sediments from core DZQ01 in the western BS. The mean ΣREE concentration of 178.78 μg/g is characterized by pronounced light REE (LREE) enrichment relative to heavy REE (HREE). Chondrite- and upper continental crust (UCC)-normalized patterns exhibit distinct negative Eu anomalies, variable Ce anomalies, marked LREE enrichment, and pronounced LREE/HREE fractionation. Grain size exerts the dominant control on REE distribution, whereas the weak correlation between HREE fractionation parameter indices (e.g., Gd/Yb) and redox-sensitive proxies (e.g., δEu_UCC and δCe_UCC) confirms their fidelity as provenance indicators. When integrated with the δEu_UCC-δCe_UCC diagram, discriminant functions, and paleoenvironmental proxies (Rb/Sr and Mg/Ca ratios), the data indicate that, during interglacial highstands, the Yellow River (YR) was the principal source, delivering fine-grained terrigenous material from the Loess Plateau and thereby elevating REE concentrations. Conversely, glacial lowstands shifted the depositional environment to subaerial conditions, with the YR, Hai River, and Luan River supplying a coarse-fine admixture. Multi-river provenance and dilution by coarse detritus collectively lowered REE concentrations during these intervals.