中文摘要：

黏土矿物研究在示踪物源、源区风化历史乃至洋流变迁能力等方面具有重要的作用,尽管目前对南海表层沉积物黏土矿物宏观分布特征已获得了较系统的认识,但在受珠江和海南岛物源共同影响的南海西北部其高分辨率的黏土矿物学工作还未开展。本文对南海西北部表层沉积物中的黏土矿物组成、结晶学特征进行了分析,讨论了研究区黏土矿物的物质来源。结果表明,南海西北部表层沉积物的黏土矿物组成以伊利石为主（平均45%）,蒙脱石（平均27%）与高岭石（平均21%）次之,绿泥石含量最少（平均6%）。在区域空间分布上,蒙脱石含量呈现西南高东北低的特征,伊利石含量则与之相反;高岭石含量表现为近岸高离岸低,而绿泥石含量呈现离岸高近岸低的特征。总体上,研究区表层沉积物黏土矿物组成与现代珠江沉积物组成差异较大,而与珠江口2.5ka前的沉积物黏土矿物组成比较接近,并且结合研究区岩心揭露的全新世以来极低的沉积速率（4cm/ka）以及上部很薄（小于0.6m）的泥质沉积,推测该区表层沉积物可能并非是现代沉积的结果,更可能主要来自全新世末期古珠江输送的沉积物。除古珠江作为研究区表层沉积物中蒙脱石的一个主要来源外,海南岛北部河流也贡献了少量蒙脱石到其邻近的东南海域。运用高岭石/伊利石比值和伊利石化学指数等进一步对比分析表明,珠江是研究区沉积物中伊利石、高岭石和绿泥石的主要物源,其次台湾和海南岛也可能分别提供了少量富含伊利石/绿泥石和高岭石的沉积物。本工作对于南海西北部沉积物源-汇过程和相应的古环境研究有重要的参考意义。

英文摘要：

As an effective tracer of sediment provenance, continental weathering and oceanic currents evolution, clay mineral has been widely used in palaeoenvironmental research of the South China Sea in the recent years. The gen- eral character of spatial distribution of clay minerals in the surface sediments of the South China Sea basin has been established. However, there remains no detailed knowledge about the distribution and sources of clay minerals in the northwestern South China Sea, which is possibly influenced by terrigenous materials input from both of the Zhujiang River and Hainan Island. Here we analyze assemblages and crystallinity of the clay minerals in the surface sediments of this area, and further investigate the sediment provenance of clay minerals. The clay mineral assem- blage in sediments of the northwestern South China Sea mainly consists of illite （average -45%）, with associated smectite （-27%） and kaolinite （N 21%）. Chlorite （- 6%） is present in lesser amounts. On the spatial scale of this area, smectite is characterized by higher contents in the southwest South China Sea and lower in the northeast of the study area. On the contrary, illite contents are higher in the northeast and lower in the southwest. The per- centage of kaolinite shows a decreasing trend from the coast to the shelf, while the contents of chlorite shows an increasing trend. Generally, clay mineral assemblage in the surface sediments of the study area is distinct from the modern Zhujiang River sediments, but it is more similar to the old Zhujiang River mouth sediments deposited a- bout 2.5 ka ago. Moreover, the seismic and sediment core studies revealed a very low sedimentation rate （4 cm/ ka） and thin muddy sediments （〈0.6 m） on the surface of the continental shelf of the northwestern South China Sea since the Holocene. Therefore, we suggest that the surface sediment in this area is possibly resulted from re- worked old materials which were mainly transported from the old Zhujiang River in the late Hol