中文摘要：

分析了南海西北部198个表层沉积物的常量元素地球化学特征,研究了沉积物常量元素的含量分布特征、富集程度和粒度效应。结果显示,沉积物的常量元素以SiO2、Al2O3、CaO含量较高,平均值分别为45.9%、8.53%、16.7%,其中SiO2、Al2O3代表了陆源碎屑组分,CaO代表了生物碎屑组分。陆架区具有较高的SiO2含量,陆坡区具有较高的Al2O3、CaO含量,但是,Al2O3的高含量在深水下陆坡区,而CaO的高含量在上陆坡岛礁区。总体上,常量元素Fe2O3、K2O、MgO、Na2O、TiO2与Al2O3具有相似的含量分布特征,指示细粒组分的吸附作用;而SiO2、CaO与Al2O3呈相反的分布特征以及负相关关系,反映了沉积物的常量元素受到石英矿物和碳酸盐矿物的稀释作用。大部分元素的富集因子介于1~2之间,富集特征不明显,表明碎屑物质主要为地壳来源,仅CaO、MnO出现较高的富集因子,指示陆坡区生物富集作用和深水陆坡区化学沉积作用的贡献。

英文摘要：

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,Al2O3 and CaO,45.9%,8.53% and 16.7% respectively on average.The SiO2 and Al2O3 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 Al2O3 and CaO.The distribution patterns of Fe2O3,K2O,MgO,Na2O and TiO2 are similar to that of Al2O3,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.