Some features of rare-earth element distribution in surface sediments of Tonkin Bay (South China Sea)

Abstract

The peculiarities of the rare-earth elements distribution in the surface bottom sediments in the Gulf of Tonkin (South China Sea) are considered. According to the results of granulometric analysis, the sediments are mainly represented by pelitic silt, silty pelite, and miktites. The REE contents normalized to the chondrite composition show the absence of cerium anomaly, the presence of negative europium anomaly and significant fractionation of light and heavy REE. The values of indicator ratios LaN/YbN), Cr/Th, Th/Co, La/Sc, Th/Sc indicate the predominance of rocks of intermediate and acidic composition in the erosion areas, due to which sediments were formed. The values of the Ce/La ratio and Strakhov lithochemical modulus (Fe+Mn)/Ti characterize the surface sediments as typical terrigenous without the admixture of endogenous exhalative material. The Eu/Sm ratio values indicate low permeability of the sediments for upward fluid flows, which is consistent with the measured methane concentrations. The analysis of correlations indicates the dominance of the terrigenous source of REE and a significant role of clay minerals and iron hydroxides in the migration and accumulation of REE.

Keywords

• ree
• sediment granulometry
• gulf of tonkin
• south china sea