西沙群岛永兴岛地貌与现代沉积特征

THE CHARACTERS OF GEOMORPHOLOGY AND MODERN SEDIMENTS OF YONGXING ISLAND, XISHA ISLANDS

通过对永兴灰沙岛的地貌考察和沉积物采样分析，认为永兴岛砂屑沉积物为现代环境的产物，指出了灰沙岛不同地貌单元沉积物的粒度和生物组分的特征；生物组分的分布还与其粒径大小有十分紧密的关系；同一粒级同一类型的生物屑的颗粒百分含量与重量百分含量之间存在比较密切的线性正相关关系；永兴岛西北部的沉积动力条件较东南部的强，并陆续向东南方扩大。

ccording to the lime-sand islet investigation on Yongxing Island of Xisha Islands,sediment analyses, mineral dyeing experiments and microscopic observations, this paper concludes that the sediments are deposited from modern environment. In different geomorphological zones of the lime-sand islet, there are different characters in biodetritus compositions and grain sizes. The contents of organic compositions are closely related to the grain grade of the sediments. The interrelated degree between the percentages of the granules and the percentages of the weights of the biodetritus at both the same grade and the same kind is notable. With the analyses of the geomorphology and the modern sediments, the fact that the depositing dynamics in northwest are stronger than that in southeast becomes very obvious. And Yongxing Island is extending towards southest in succession. In addition, because the sediments come from the neighbouring reef flat that is composed of biodetritus, the depositing dynamics is wave, alternate monsoon and tropical cyclone, Yongxing island has its characters in granulometric parameters.