REE DISTRIBUTION PATTERN IN THE XIAODONGHAI FRINGING REEF-FLAT SEDIMENTS OFF SANYA, HAINAN ISLAND AND ITS ENVIRONMENTAL IMPLICATIONS

REE in the sediments of the northeast Xiaodonghai fringing reef-flat off Sanya City, Hainan Island were systematically analyzed using Inductively coupled palsma mass spectrometry(ICP-MS). A high resolution record of rare earth elements (REEs) were obtained. The REE content averages 80.22 mg/kg, and the Chondrite-normalized REE pattern of the reef-flat sediments is characterized by the enrichment of light REE(LREE) and deficiency of heavy REE(HREE),significantly negative Eu, normal Ce and low Y/Ho ratio (27.80). It indicates that the terrigenous influx is the major source of the reef-flat surface sediments. In addition, the sediments show a geomorphologic and ecological zonations from large massive corals zone, to inner reef flat zone to outer reef flat zone seaward, indicating the influence of marine and biological effects. However, the REEs content and distribution pattern show little change in the zones.It is believed that the REE pattern mentioned above represents a specific tropical fringing reef-flat REEs distribution pattern.It is probably related to the sediments from the bedrock around the reef-flat, and the joint affect of tropical marine climate.