DISTRIBUTION CHARACTERISTICS AND CONTROLLING FACTORS OF CLAY MINERALS IN SURFACE SEDIMENTS FROM THE CENTRAL AND SOUTHERN SOUTH CHINA SEA

Based on clay mineral analysis data obtained from 151 surface sampling sites in the central and southern South China Sea, the average percent contents of four clay minerals have been accounted and the clay minerals percent content distribution have been illustrated on maps in this paper. And then, the distribution characteristics and their controlling factors have been interpreted.Clay minerals in the surface sediments of the central and southern South China Sea are illite, smectite, kaolinite and chlorite and their average percent contents are in tune 47%,19%,17% and 16%. Kaolinite percent content is low in the north and high in the south, and to the opposite, smectite, hige in the north and low in the south. Illite and chlorite percent content distributions have no obvious regularity. The distribution of the former goes a little higher in the north than in the south with large percent content undulation,and that of the latter is almost the same and only the difference is that the content is lower in the northwest. In addition, the ratio of illite/kaolinite percent content shows a negative interrelation with kaolinite percent content. The main factors that control the average percent content distributions of clay minerals are transportation of continental material, the variation of hydrodynamic condition, seabed volcano activities and geochemical environment.