ZHANG Nan1,2, WANG Shu-hong1, CHEN-Han1,2,3, LI-Liang1,2, YAN Wen1
(1. Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China;
3. Island Research Center, SOA, Pingtan 350400, China)
Abstract: In this paper, grain size as well as some major and trace elements, including rare-earth elements (REE), were systematically analysed for the 273 surface samples collected from the shelf of the northern South China Sea. The sediments were classified based on grain-size according to Folk’s classification system. It showed that the main types of sediments in the study are mainly sandy silt and silt, which make up 60% of the whole sample, followed by mud, sandy mud, muddy sand and silty sand, which make up 27%. The analytical results of REEs showed that the total content of rare-earth elements (ΣREE) in this study range from 21.34 to 244.15 μg/g with an average of 155.26 μg/g. This is similar to the average ΣREE content in the Chinese loess, but different from that in deep-sea clay. It is evident that the REE has an “inherited” or “philo-continental” property. The distribution and enrichment of REE is generally controlled by sediment types and hydrodynamic characteristics. REE content in different sediment types vary greatly, mainly enriched in silt, sandy silt, mud and sandy mud. The contours of REE distribution parallel the coast, like strips, and the content of REE declines gradually with increasing distance from the coast. The highest content is found in the western part of the Pearl River estuary, the Shang/Xiachuan islands and Hailing Bay. These may be related to the coastal current that goes from east to west along to the Pearl River estuary in the northern part of the South China Sea. But chondrite-normalized REE patterns in various sediment types show no significant difference and are basically the same as those of coastal rivers and the upper continental crust. They all show relative enrichment in light REEs, a noticeable negative Eu anomaly and no Ce anomaly, indicating that these sediments are terrigenous sediments and are from the same source region. Further analysis shows that the sedimentary environment in the study area is relatively stable, and that granite widely distributed throughout the southern Chinese mainland is the main source of REE, which are mainly transported by the Pearl River.
Key words: rare-earth element; REE; sediment types ; provenance analyses; northern South China Sea shelf
E-mail: wyan@scsio.ac.cn
ACTA MINERALOGICA SINICA Vol. 34, No. 4, 2014, Page 503-511
