Compositional characteristics of sediment from Jiaozhou Bay in North China and the implication to the provenance

Rare earth elements (REEs) can be used to trace source materials and identify their provenances, because of significant conservation and immobility during chemical alteration processes after erosion of materials from the provenance. This study focused on the temporal variation of REEs for columnar sediments from the mouth of Jiaozhou Bay in North China to understand the potential controls for the geochemical variations of sediments. Through extraction experiments, we identified that the residual fraction is the main host for REEs compared with other fractions (i.e., exchangeable and carbonate fraction, easily reducible oxides fraction, reducible oxides fraction, magnetite fraction). REE ratios (e.g., La-N/Sm-N and La-N/Yb-N; N: normalized by chondrite) lack correlations with grain size or the chemical index of alteration (CIA), which is correlated with major elements. All these indicate that these REE variations reflect the varying contribution of source materials from different provenances instead of grain size or chemical weathering effects. REE ratios (e.g., La-N/Sm-N and La-N/Yb-N) remain relatively constant until the depth of roughly 40 cm (equivalent to the year 1995), and show obvious changes beyond this depth. Compared REE characteristics of Jiaozhou Bay with those of neighboring rivers and bedrocks, the relative contributions of Dagu River-Jiaolai River, and Licun River may have been increased during the sedimentary processes, which could be caused by the construction of reservoir and related change of aquaculture (e.g., rapid accumulation of organic materials).

Automated summary

Rare earth elements (REEs) are useful in tracing source materials and determining their origins due to their conservation and immobility during chemical alteration processes. This study investigated the temporal variation of REEs in columnar sediments from Jiaozhou Bay in North China to understand the factors influencing sediment geochemical variations. The results showed that the residual fraction was the main host for REEs compared to other fractions, and the REE variations were determined by contributions from different provenances rather than grain size or chemical weathering effects. The study also found changes in REE ratios after a certain depth, indicating increased contributions from certain rivers due to human activities like reservoir construction and aquaculture.