南海北部陆架区表层沉积物粒度特征与沉积环境

对南海北部陆架沉积区244个表层沉积物样品进行了粒度组分、多元统计及输运趋势分析,结果表明:南海北部陆架区共分布9种沉积物类型,粒度组成以砂和粉砂为主,砂含量占绝对优势,沉积物主要粒级为0~8 Φ,优势粒级为0~4 Φ。研究区东北部粒径较粗,以中砂为主,分选中等-好,负偏,峰态中等-平坦,西南部粒径较细,以粉砂为主,分选较差,正偏,峰态平坦,中间过渡及陆架外缘粒径中等,以细砂为主,分选中等,正偏,峰态尖锐。基于粒度多元统计及输运趋势分析,南海北部陆架划分为3个沉积区:珠江口及粤东近岸沉积区(I区):主要受控于沿岸流,水动力条件较弱,物质来源以珠江、韩江等河流输运物质及近岸基岩风化、岛屿剥蚀作用产物为主,少量东沙群岛海底冲刷剥蚀产物;混合过渡沉积区(Ⅱ区):受黑潮南海分支、南海暖流及沿岸流共同作用,水动力条件中等,物源复杂多样,为珠江携带陆源物质、台湾浅滩物质以及东沙群岛附近海底剥蚀产物的混合沉积区域;台湾浅滩及珠江古三角洲残留沉积区(Ⅲ区):受黑潮南海分支、南海暖流、北部九龙江、沿岸流等影响,海洋水动力条件较强,以晚更新世的残留沉积为主,同时可能接受了少量现代沉积物质。

CHARACTERISTICS OF GRAIN SIZE DISTRIBUTION OF SURFACE SEDIMENTS AND DEPOSITIONAL ENVIRONMENTS IN THE NORTHERN SHELF REGION OF THE SOUTH CHINA SEA

Grain size parameters and their distribution patterns are studied for 244 surface sediments collected from the northern shelf region of the South China Sea.Results show that there is a total of 9 types of sediments distributed in the region,dominated by sand and silt from 0~8Φ,with the deposits of 0-4Φ as the major.The northeastern part of the study area is dominated by coarse and medium sediments,finely sorted with negatively skewness and relatively flat kurtosis,and the southwest area by poorly sorted fine sediments with positively skewness and flat kurtosis.In the transitional zone,however,the sediments along the edge of the continental shelf are characterized by the fine sand moderately sorted with positively skewness and sharp kurtosis.The research area is then divided into three different depositional zones based on Q-type cluster analysis and grain-size trend analysis,i.e. 1) the deposition zone of the Pearl River estuary and the nearshore area of eastern Guangdong Province (Ⅰ district) dominated by the coastal current,and the sediments are mainly terrestrial from the Pearl River,the Hanjiang River and others,such as those from coastal bedrock weathering,denudation of islands,and a small amount of erosioal products from the Dongsha Island.The hydrodynamic conditions are weak in the region; 2) the transitional zone (Ⅱ district) controlled by the branch of the Kuroshio current,South China Sea warm current and coastal current.It is under moderate hydrodynamic conditions,having mixed provenance from the Pearl River,Taiwan bank and Dongsha Islands erosion products; 3) the residual deposits of Taiwan bank and ancient Pearl River delta (Ⅲ district). Under the joint affect of the branch of Kuroshio current,South China Sea warm current,Jiulong River and coastal current,the area is under a strong hydrodynamic conditions and dominated by Late Pleistocene residual deposits mixed with a small amount of modern sediments.