The assemblage feature of clay minerals in the South China Sea and its environmental significance

Based on XRD analysis,the clay mineral components and their assemblage feature of the surface sediments(12 samples) as well as the suspended particles(20 samples) in the South China Sea were studied.The surface sediments were collected by box sampler and the suspended particles were collected from 3 different water depth layers in NE2 station by sediment trapper during July 8,1998 and April 30,1999.The results show that the surface sediments are dominated by illite,followed by chlorite,kaolinite,illite/smectite,and smectite;suspended particles collected in NE2 station are dominated by chlorite,followed by kaolinite,smectite,illite and illite/smectite.The composition and distribution of clay minerals are mainly controlled by climate,sediment sources,hydrodynamic condition,and dilution effect.Illite content increases with the water depth,kaolinite mainly occurres in the coastal area,particularly in estuaries.The eastern arc area has more chlorite than the western coast.Smectite which has close relationship with volcanism mainly occurred in eastern arc area.The clay minerals mainly transported by river,some were authigenic and some were carried by wind.The variation of different clay mineral phases is a good indicator of the change of climate and environment,particularly,the crystallinity of illite is climate and environment sensitive,with the increase of the water depth,the crystallinity of illite gets lower.