西沙海槽表层沉积物地球化学特征及其地质意义

GEOCHEMICAL CHARACTERISTICS AND SEDIMENTARY ENVIRONMENT OF SURFACE SEDIMENTS FROM XISHA TROUGH

对西沙海槽区50个表层沉积物的常微量元素进行了地球化学及沉积环境特征研究。西沙海槽区表层沉积物具有SiO2、TiO2含量低和CaO含量高的特征;除了MnO外,各组分的变异系数均较小,元素的分布差异较小,元素分异不明显。常量组分对比表明研究区兼具浅海及深海沉积的特点,为由浅海向深海过渡的半深海沉积环境。富集因子分析表明,从槽坡至槽底富集因子变化不大,略呈增加趋势,Cu、Co、Ni、Pb、Zn、Ba、Mn的富集因子都大于1,表明这些元素除了陆源之外还有其他的来源。海槽区沉积物的化学组分及其来源是复杂多样的,其中包括陆源组分、生物源、火山碎屑等,但陆源碎屑和黏土组分以及碳酸盐型的生物碎屑组分是控制研究区沉积物化学成分的最主要因素。

Geochemical characteristics and sedimentary environments of surface sediments from the Xisha Trough, South China Sea are studied. Fifty sediment samples have been analyzed for their major and trace element contents. The surface sediments in the Xisha Trough show relatively low contents of SiO_2and TiO_2 and high content of CaO. The variation coefficients of each major chemical composition show rather limited variation, except for MnO that shows larger variation.The difference in element distribution is unconspicuous. By comparing with the major chemical compositions,we know that sediments from the study area share some similar characteristics both with the shallow-sea and deep-sea sediments, and our data suggest a transitional sedimentary environment from shallow sea to deep sea for the surface sediments in the Xisha Trough. The enrichment factors (EF) of some elements in the sediments, from trough slope to trough bottom,show little change but with a slightly increasing tendency. The EF values of Cu,Co,Ni,Pb,Zn,Ba and Mn are larger than one, suggesting that these elements not only came from terrestrial source, they also have some other sources. The results of factor analysis show that the sources for the surface sediments are complicated, including a combination of components from terrestrial,biological and volcanic materials. However, the components of terrestrial clastic and clay minerals and biological materials are primary factors that control the chemical compositions of sediments in the study area.