Nd isotopic variations and its implications in the recent sediments from the northern South China Sea

Abstract

The chondrite-normalized REE distribution patterns in recent sediments from the northern South China Sea and surrounding areas are similar, with the HREE values being almost equal to or slightly higher, and the LaN/LuN ratio being lower, than PAAS standards. However, samples from the Xijiang River, a major branch of the Pearl River system, show opposite trends, i.e., with slightly lower HREE values and higher LaN/LuN ratio than PAAS. The distribution of Nd isotopes in sediments from the northern South China Sea was controlled by the Pearl River and the inshore area of South China, respectively. The volume of eNd(0) from inshore areas of southern China is apparently higher than that from the Pearl River, and eNd(0) values in offshore sediments and Taiwan Island are between these values. The results clearly show that eNd(0) volume in the northeastern South China Sea is higher than in the southwest part of the northern South China Sea, indicating different source rock types. The main source rock of the Pearl River sediment is carbonate types and affects sediment deposition in the southwest of the northern South China Sea, while the source rock in the inshore area of southern China, mainly Mesozoic and Cenozoic granites, contributes to sediments in the northeastern area of the northern South China Sea. Due to different source rock types, the HREE values and the volume of eNd(0) in recent sediments supplied by the inshore area of southern China are higher than those from the Pearl River. Over 80% of the rapidly accumulated sediments on the northern slope of the South China Sea in the southeast of Dongsha Islands area were derived from Taiwan Island and from inshore areas of South China, with only less than 20% from the Pearl River.