南海中沙群岛海域表层沉积物粒度特征及其输运趋势

Grain size distribution pattern of surface sediments and its implications for transportation trend:A case from the waters off Zhongsha Islands,the South China Sea

对南海中沙群岛海域232个表层沉积物样品进行了粒度分析,以探讨研究区沉积物来源、沉积环境和输运趋势。根据Folk沉积物命名法,将研究区沉积物划分为砂、粉砂质砂、砂质粉砂、砂质泥、粉砂和泥等6种类型,以砂质泥和泥为主,粒径较粗、分选较好的沉积物主要分布在中沙台地海域。通过对组分含量、粒度参数和水深进行聚类分析和主成分分析,综合考虑沉积物来源和海底地形地貌的影响,将研究区划分为5类沉积区:台地区、台地阶地区、台地周缘斜坡区、海槽海岭区和深海盆地区。结合沉积环境分区进行了粒径趋势分析,研究显示,沉积物主要以中沙台地和西沙隆起海域为中心向周缘输运,在中沙海槽海域形成汇聚区。研究区沉积物输运格局主要受季风、海流、潮汐和波浪等因素的共同控制,与沉积物来源、海底地形地貌和实测水动力条件相吻合。

232 surface sediment samples taken from offshore Zhongsha Islands were analyzed so as to better understand the sources,depositional environment and transporting patterns of the sediments.6 types of sediments are recognized.i.e.sand,silty sand,sandy silt,silt,sandy mud and mud,dominated by sandy mud and mud.The coarser sediments,which usually have higher sorting,are mainly distributed in the water areas surrounding the Islands.Cluster analysis and principal component analysis are used for the study of component contents,grain size parameters and water depth.In consideration of the influences of sediment sources and seabed topography,the study area is divided into five depositional subareas:platform,platform terrace,slope around platform,trough and ridge,and deep-sea basin subareas.In combination with the depositional environment classification,grain size trend analysis is conducted.The results suggest that the sediments are mainly provided by the Zhongsha platform and the Xisha uplift,dispersed in surrounding waters,and finally deposited in the Zhongsha Trough.The sediment transportation is jointly influenced by sediment sources,seabed topography and water hydrodynamic conditions,under the control of monsoon,tide,wave and ocean current.