MODERN CARBONATE SEDIMENTS IN SANYA GULF, HAINAN ISLAND
Feng Zengzhao (East China Petroleum College) Wang Qi , Zhou Li , Zhang Jianhua ) , Zhang Xiaoyi and Ye Mengjie ( Shandong College of Oceanology )
Sanya Culf is situated at the southern tip of the Hainan Island and is connected with the South China Sea. The water of the Gulf is about 5-20 m in depth, and is deeper than 30 m at its southern margin. The bathymetric lines are generally parallel to its north shoreline. Forty samples have been gathered. The surface sediments of the Sanya Gulf consist of the terrigenous materials and carbonates, and the grain size of the sediment ranges from coarse sand to mud. The highest CaCO_3 content of the sediments is 83.7%, the lowest is 6.68%, and the mean is 19.12%. These carbonate sediments are distributed around the fringing reefs of Dongmaozhou, Ximaozhou and Luhuiton, and consist of the fragments of corals, mollusca, foraminifera, etc. The corals are maimly hexacorallia, such as Acropora, Porites, Goniastrea, Favia, Platygyra, Montipora, etc.; they are the chief reef-building corals. The Octocorallia is rare. The molluscas are mainly pelecypoda, such as Atactodea stri-ata,Cardium feavum,Quidnipagus palatam, etc. ,and gastropoda, such as Cerithium sp., Epitonium sp., Odostomia sp., etc. The foraminiferas are mainly benthonic, and the most common species are Nummulites venosa and Amphistegina sp. The planktonic foraminifera is rare. The components of non-skeletal CaCO_3 are mainly faecal pellets. The minerals of the hexacorallia, pelecypoda and gastropoda are aragonites; those of the octocorallia, echinodea, ostracoda and most of the foraminifera are Mg-calci-tes; and those of the ostrea and a few of foraminifera are calcites. The Sr content of coral is higher ( 6700-7400 ppm ) , but that of pelecypoda is lower ( 650-1200 ppm ) . The δO~(18) and δO~(13) contents of corals are lower. On the basis of the above data, the results of R-type factor analysis and correspondence analysis, the authors have classified the sediments of the Sanya Gulf into five sedimentary facies: Ⅰ. facies of calcarenitic-terrigenous delta sands, Ⅱ. facies of reef and reef-flank sands, Ⅲ. facies of terrigenous shore silts with calcarenites, Ⅳ. facies of Gulf top silts, and Ⅴ. facies of terrigenous off-shore silts with calcarenites.