The rare earth element content in surface sediments of coastal areas in eastern China's sea areas and an analysis of material sources

The geochemical characteristics of rare earth elements in the surface sediments of the Bohai Sea, the Yellow Sea and the East China Sea have been studied systematically and macroscopically through the investigation, sampling, testing and analysis of eastern China's sea areas by China Geological Survey in the past 20 years. The results show that there are four REE enriched areas in the surface sediments of the eastern coast of China with the REE content generally higher than 180 μg/g. The distribution of highvalue areas is consistent with mud areas in eastern coast of China, such as mud area of western Bohai Sea, middle of south Yellow Sea, southeast of Jeju Island and inner shelf of the East China Sea. Chondrite- normalized REE patterns and UCC- normalized patterns in the surface sediments of the three seas are relatively homogeneous, with the distribution characteristics similar to features of China's mainland. It is found that δEu is most strongly negatively correlated with the content of rare earth elements in eastern China's sea areas, followed by the average grain size of sediments with significant positive correlation, as shown by the correlation analysis of the characteristic parameters of rare earth elements. The δEu- (La/Yb)n map was used to identify the material sources for the REE high-value areas, and the result indicates that the sediments in the mud area of west Bohai Sea and the middle of south Yellow Sea are mainly from the same source. It is generally considered that sediments from the mud area of the southwest of Jeju Island are mainly from Yangtze River and Yellow River, but the river input from the southeast of the Korean Peninsula can't be ignored, that the sediments from the north end of the mud area of the inner shelf of the East China Sea are basically from the Yangtze River, while the south end shows different REE fractionation characteristics which are related to the input of small and mediumsized rivers along the coast of Fujian, Zhejiang and Taiwan Island. The material source, sediment grain size brought by large and middle-small rivers and the flow system patterns of the sea areas jointly determine the geochemical characteristics of REE in the surface sediments of eastern China's sea areas.