冲绳海槽南部表层沉积物地球化学特征及其物源和环境指示意义

Geochemical Characteristics and Their Implications to Provenance and Environment of Surface Sediments from the South Okinawa Trough

对冲绳海槽南部陆架、陆坡和海槽 33个表层沉积物进行了元素地球化学分析 ,结果表明研究区沉积物的主要化学组成为SiO2 、Al2 O3 和CaO ,这三种组分占沉积物总量的 6 8%左右。多数元素在陆架和陆坡的变化范围较大 ,在海槽区相对稳定。向海槽方向随沉积物粒径变细 ,SiO2 和CaO减少、Al2 O3 和其它多数元素含量增加。常量元素和Al2 O3 的比值分布特征表明 ,本区沉积物由物源区经由陆架向海槽输送 ,沉积物主要由陆源碎屑沉积组成 ,此外还有生物碎屑沉积和自生沉积。陆架区部分微量元素富集因子 (EF)与长江和黄河沉积物的富集因子对比结果表明 ,本区的沉积物与长江沉积物的关系更为密切。陆坡区Cu、Pb、Zn、Co、Ni和Cr的富集因子较高是由于生物的富集作用造成的 ,Mn的富集主要是自生沉积的结果。用R型因子分析方法对沉积物的化学组成进行了分析 ,结合元素的分布特征 ,给出了四个主因子所对应的沉积环境和特征元素组合 ,分别为 1)陆架型的元素组合 :SiO2 、TiO2 、Zr、CaO和Sr,2 )陆坡型的元素组合Fe2 O3 、MgO和P2 O5,3)海槽型的元素组合 :Al2 O3 、K2 O、Cu、Zn、Co、Ni、Cr和Ba ,4 )反映沉积环境氧化—还原属性的元素组合 :MnO和FeO。

Chemical compositions of 33 surface sediment samples were measured. The samples were collected from the continental shelf, slope and the south Okinawa Trough, respectively. The major chemical compositions are dominantly composed of SiO 2, CaO and Al 2O 3,which account for about 68 percent weight of the sediments. Most of the elements change with a wide range in the shelf and slope sediments, but keep stable in the trough sediments. From shelf to trough, the grain size of the sediment becomes finer, at the same time, the content of SiO 2 and CaO decrease, and the content of Al 2O 3 and most of other elements increase. Based on the distributions of the major elements/ Al 2O 3 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 elements of the shelf sediments with the Yangtse River and Yellow River sediments, It can be concluded that the sediments in the study area are similar to the Yangtse 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 analysis of the chemical compositions, combined with analysis of the distributions of the elements, four major factors indicate four sedimentary environments respectively. Every sedimentary area has its own typical elements group. They are, 1)Shelf type elements group:SiO 2,TiO 2,Zr,CaO and Sr; 2)Slope type elements group: Fe 2O 3,MgO and P 2O 5; 3)Trough type elements group:Al 2O 3, K 2O, Cu, Zn, Co, Ni, Cr and Ba, and 4)Redox elements group:MnO and FeO respectively.