南海西沙海槽S14站位的地球化学异常特征及其意义

西沙海槽具备良好的天然气水合物的形成条件, 并已发现与其有关的地球物理标志———模拟海底反射层(BSR)。通过对西沙海槽S14大型活塞站位的孔隙水和沉积物样品进行化学组分、酸解烃和热释光等方面的分析测试,结果发现在海底之下 4~5m区间存在着较明显的高盐高烃异常, 其中酸解烃中的甲烷、乙烷、丙烷含量及其热释光值均有所增高, 孔隙水中的绝大部分离子及其盐度也存在着明显的升高, 这一高盐高烃异常可能是下部与天然气水合物有关的孔隙流体沿着断层向上迁移所致。这些地球化学异常以及模拟海底反射层等地球物理标志显示该站位之下可能存在天然气水合物。

Geochemical Anomalies and Their Implication from Site 14, the Xisha Trough, the South China Sea

Piston Site 14 is located in the central part of the Xisha Trough, northern slope of the South China Sea, whose geological background, gas source, temperature and pressure are preferential for gas hydrate, and some bottom simulation reflectors (BSRs) have been found. The thickness of sulfate reduction zone is about 25 meters, which indicates that gas hydrate perhaps occurs in the deeper part. A series of geochemical anomalies, including higher salinity from interstitial water, higher hydrocarbon gas concentrations and higher thermoluminescence values from sediments, have been detected at interval of 4-5 meters below sea floor at Site 14. The pore fluids with higher salinity and higher hydrocarbon, which related to gas hydrate, probably migrated into Site 14 along faults.