Keywords: 
• geochemical characteristics /
• implications to provenance and environment /
• surface sediments /
• southern Okinaw a Trough

Abstract: Chemical compositions of 33 surface sediment samples were measured.The samples were collected from the continental shelf, slope and the south Okinaw a Trough, respectively.The major chemical compositionsare dominantly composed of SiO₂, CaO and Al₂O₃, w hich account for about 68 percent weig ht of the sediments.Most of the elements change w ith a w ide range in the shelf and slope sediments, but keep stable in the trough sediments.From shelf to trough, the g rain size of the sediment becomes finer, at the same time, the content of SiO₂ and CaO decrease, and the content of Al₂O₃ and most of other elements increase.Based on the dist ributions of the major elements/ Al₂O₃ ratio, it can be concluded that the sediments are transported from the provenance area to the trough.The sediments mainly composed of terrigenous, biogenic and autogenetic deposits in the study area.Comparing the enrichment factors (EF )of some element s of the shelf sediment swith the Yang tse River and Yellow River sediment s, It can be concluded that the sediments in the study area are similar to the Yang tse River sediments.The high enrichment factors of Cu, Zn, Pb, Co, Ni and Cr in the slope are caused by the biogenic enrichment.The enrichment of Mn is caused by autogenetic deposit.Based on the R -mode factor analy sis of the chemical compositions, combined w ith analysis of the distributions of the elements, four major facto rs indicate four sedimentary environments respectively.Every sedimentary area has its own typical elements group.They are, 1)Shelf-type elements group :SiO₂, TiO₂, Zr,CaO and Sr;2)Slope-type elements group :Fe₂O₃,MgO and P₂O₅;3)Trough-type elements group :Al₂O₃, K₂O, Cu, Zn, Co, Ni, Cr and Ba, and 4)Redox elements group :MnO and FeO respectively.