南沙海区晚第四纪的碳酸盐旋回

根据水深200～2 800m范围内的17个沉积柱状样分析结果,讨论南沙海区晚第四纪沉积中碳酸钙相对含量的垂向和横向变化。南沙海区的碳酸盐旋回普遍属于"大西洋型",冰期时含量低、间冰期含量高,反映出陆源物输入量的控制作用。在平面上,南沙海区的碳酸钙含量与纬度几乎呈线性关系,由北向南递减,冰期时趋势不变而梯度加大。南海南部陆坡由于集水盆地处于热带湿热条件而且有大河注入海区,使碳酸钙含量相对北部陆坡为低。

LATE QUATERNARY CARBONATE CYCLES IN THE NANSHA ISLANDS AREA, SOUTH CNINA SEA

Stratigraphic and geographic variations of carbonate percentages in late Quaternary deposits of the Nansha Islands area, southern South China Sea, are discussed based on data from 17 sediment cores ranging from 200 to 2 800m in water depth. The revealed carbonate cycles of the Nansha Islands area all belong to so called "Atlantic type" with glacial lower and interglacial higher values, implying a controlling role played by the terrigenous input. Geographically, the carbonate percentage in Holocene sediment of the Nansha area displays a nearly linear relationship with the latitudes of the sites, decreasing gradually from north(60%～70%) to south (<20%). During the glacial time, the carbonate content was generally lower than that in the Holocene whereas the gradient of its southward decline was increased. This is explained by the different nature of the two parts of the Nansha area: the northern part is stubbed with coral reefs, whereas the southern part is adjacent to the Sunda Shelf yielding great amounts of terrigenous clasts from the Paleo-Sunda River at the glacial low sea-level stand. The carbonate content in sediments from the southern continental slope of the South China Sea is generally lower than that from the northern slope. This is caused by greater amounts of terrigenous input and the warm humid conditions of the tropical catchment basins of the southern slope, resulting in enhanced deep-water carbonate dissolution.