南海北部东沙海域沉积物地球化学特征及其反映的冷泉活动  

CHARACTERISTICS OF SEDIMENTARY GEOCHEMISTRY AND THEIR RESPONSES TO COLD-SEEP ACTIVITIES IN DONGSHA,THE NORTHERN SOUTH CHINA SEA

作　　者：张必东[1,2] 邬黛黛[1] 吴能友[3] 

机构地区：[1]中国科学院天然气水合物重点实验室中国科学院广州能源研究所,广州510640 [2]中国科学院大学,北京100049 [3]中国地质调查局青岛海洋地质研究所,青岛266071

出　　处：《海洋地质前沿》2015年第9期14-27,共14页Marine Geology Frontiers

基　　金：国家自然科学基金(41273022);中国科学院重点部署项目(KGZD-EW-301);国家海洋地质专项(GHZ2012006003;GZH201400309);中国科学院广州能源研究所所长创新基金培育专项(y307p51001)

摘　　要：南海北部东沙海域是典型的水合物成藏区,冷泉活动对其沉积物地球化学特征有显著影响。分析了东沙海域冷泉区973-4站位1 375cm(水深1 666m)和973-5站位935cm(水深2 998m)长的柱状样的总有机碳(TOC)、总硫(TS)含量,并挑选其中的底栖有孔虫进行了碳氧同位素测试。通过沉积物总硫含量分析和临近站位孔隙水数据分析表明,2个站位沉积物均有较浅的硫酸盐甲烷还原界面(SMI)深度和较大的甲烷通量,其中973-4站位硫酸盐甲烷界面深度为海水―沉积物界面以下约900cm,973-5站位硫酸盐甲烷界面深度为海水―沉积物界面以下约750cm。总碳/总硫比值表明冷泉流体活动对沉积物硫埋藏起主导作用。Uvigerina spp.的δ13 C表明末次盛冰期(LGM)之前东沙海域有持续的冷泉活动,而自末次盛冰期以来Uvigerina spp.的δ13 C其偏负程度逐渐变小、冷泉活动逐渐减弱,这可能是海平面上升扩大了天然气水合物稳定区范围,从而抑制了冷泉流体上涌的结果。The northern South China Sea is a typical active cold methane seeping area and the seeping fluids certainly have critical impact on the geochemistry of the sediments. Two gravity cores, 1375- cm-long at Site 973-4 （with water depth of 1,666 m） and 935-cmqong at Site 973-5 （with water depth of 2,998 m） respectively, were recovered from cold methane seeps in the Dongsha area. Total carbon and total sulfur analysis, foraminiferal oxygen and carbon isotope tests of the sediment samples at both sites are studied. According to the total sulfur and their porewater data from adjacent sites, it is deduced that the two sites have shallow sulfur methane interface and high methane fluxes. The depth of sulfur methane interface is 900 cm under the sea bottom at Site 973-4 and 750 cm under the sea bot- tom at Site 973-5. TOC and TS data demonstrate that cold-seep fluids and their AOMs are the con- trolling factors of the precipitations of pyrites. Oxygen and carbon isotopes compositions of Uvigerina spp. indicate that the activities of cold seeps in Dongsha area has been attenuated since the last glacier maximum and this might be the results of rising global sea level.

关 键 词：冷泉 有孔虫 碳氧同位素 沉积物地球化学 天然气水合物 

分 类 号：P736.21[天文地球—海洋地质] P591[天文地球—海洋科学]