南海中部沉积物颗粒组分特征

Characters of grain-size populations of sediments in central South China Sea

为研究南海中部沉积物的粒度特征及其蕴含的古海洋信息,对南海中部中沙以南的陆坡和海盆区表层沉积物及分别位于陆坡和海盆的2根柱样进行了粒度、扫描电镜、CaCO3和生物硅含量的分析.结果显示,南海中部沉积物由三类颗粒组分构成,其中,第一类颗粒组分的峰值粒径在5～10μm之间,主要由陆源矿物碎屑组成;第二类组分的峰值粒径在40～70μm之间,主要由有孔虫和硅藻组成;第三类颗粒组分的峰值粒径>400μm,由生物骨骼碎屑组成.这三类颗粒组分中第一类在研究区表层沉积物中均存在,第三类则随机分布,第二类颗粒组分多以有孔虫为主,其含量受水深控制.在南海中部碳酸钙临界补偿深度[Dc(CaCO3)]以浅的陆坡区,因有孔虫含量较多,沉积物粒度曲线多为双峰形态,而在Dc(CaCO3)值以下的海盆区,因大部分有孔虫被溶解,沉积物中第二类颗粒组分为含量相对较低的硅藻,沉积物粒度曲线呈单峰或双峰形态.无论是陆坡区还是海盆区的柱样沉积,其平均粒径、第二类颗粒组分含量的变化均反映了有孔虫或硅藻含量的变化,因此,可以作为研究南海中部古生产力的替代性指标.

The grain size, contents of carbonate and biogenetic silica, along with scanning electron microscope anal- ysis were conducted to the surface and core sediments from continental slope and abyssal basin south of Zhongsha （Maccelesfield） Bank, with an attempt to reveal the sediment characteristics of grain size distribution and its impli- cations of paleo-climate change. The results show that there are 3 types of grain-size populations in sediments. The first population is almost composed of terrestrial minerals with a mode of 5 - 10txm. The second population is com- posed of foraminifera and diatom, and the mode of the population is 40 - 70 ~m. The third population is bio-clastic sand with mode larger than 4001~m. The first population occurs in all sediments and the third population exists in sediments randomly. The second population is mainly composed of foraminifera and the content of the population is controlled by water depth. The grain-size frequency curves are bimodal resulted from the higher content of foramini- fera in the continental slop where sea bottom is above the carbonate critical depth Do （ CaCO3 ） 1, whereas the grain-size frequency curves are both single-modal or bimodal and the second population is composed of diatoms with lower content in the abyssal basin, which is the result of dissolution of the foraminifera below the D （ CaCO3 ）. The mean values of grain size or the contents of the second population of core sediments slope or abyssal basin are responded well to the contents of foraminifera or diatom. proxies of paleo-productivity in central South China Sea. whether it from the Therefore, they can continental be used as