198 samples of surface sediments collected from the northwestern South China Sea were analyzed for major elements, in order to investigate their distribution pattern, enrichment mechanism and grain size effect. The sediments in the study area have relatively high contents of SiO2
and CaO, 45.9%,8.53% and 16.7% respectively on average. The SiO2
abundance represents detrital materials, and CaO abundance is an indicator of the bioclast component. The samples taken from the continental slope are usually high in SiO2
compared to those from continental shelf, but low in Al2
and CaO. The distribution patterns of Fe2
O and TiO2
are similar to that of Al2
, indicating that they are absorbed by fine-grained clay minerals. The correlation indicates that the dilution effect caused by quartze and carbonate also can be founded. The enrichment index for most of the major elements ranges from 1 to 2, suggesting that they mainly derived from the continental crust. However, the relatively high abundance of CaO、MnO may indicate the significant contribution of biogenesis and chemical process on the continental slope.