中文摘要：

在甲烷渗漏海域,沉积物磁化率通常表现出异常的低值特征,这与硫酸盐—甲烷转换带（SMTZ）内甲烷厌氧氧化反应（AOM）的发育而导致的自生矿物的形成作用有关。通过测定南海东北部Site DH-CL11、Site 973-2、Site 973-4三个站位400个岩芯沉积物样品的磁化率,并结合三个站位自生黄铁矿丰度和硫同位素等数据探讨了南海北部天然气水合物潜在区沉积物磁化率的变化特征及其对甲烷渗漏事件的指示意义。结果表明：在甲烷异常渗漏海域,上涌甲烷与下渗硫酸盐在SMTZ内发生AOM反应生成了大量的HS-,造成亚铁磁性矿物大量溶解,同时生成大量顺磁性自生黄铁矿,导致沉积物磁化率的异常降低;但是,在HS-不足时,铁硫化物黄铁矿化不充分,会优先生成胶黄铁矿,进而出现二次磁信号。在天然气水合物潜在海域,沉积物磁化率的异常特征可以反映下部甲烷通量的变化,从而指示下伏天然气水合物藏演化,因此能够成为探测天然气水合物藏的一种间接有效的手段,将有助于我国南海北部海域天然气水合物的勘探。

英文摘要：

In marine methane seepage areas,sedimentary magnetic susceptibility was characterized by abnormally low values,which was related to the formation of authigenic minerals resulted from the anaerobic methane oxidation（ AOM） within the sulfate-methane transition zone（ SMTZ）. In this study,400 sedimentary core samples from Site DH-CL11,Site973-2 and Site973-4 drilled in the northern South China Sea were measured. In connection with the relative content and the sulfur isotopic values of the authigenic pyrites handpicked from the aforementioned 3 sites,the variation characteristics of sedimentary magnetic susceptibility and its indication for methane seep events at the potential gas hydrate areas in the northern South China Sea were discussed. At Site DH-CL11,sedimentary magnetic susceptibility first significantly decreased and then abnormally increased within the paleo-SMTZ（ 705.5 ~ 765.5 cmbsf）,which is probably related to the depth change of the SMTZ. At Site 973-2,sedimentary magnetic susceptibility showed a decreasing trend within the paleo-SMTZ（ 453 ~ 492. 5 cmbsf）. Greigites were discovered under the SMTZ,which may be related to frequent changes of the SMTZ or the anaerobic oxidation of authigenic pyrites. At Site 973-4,sedimentary magnetic susceptibility significantly decreased within the paleo-SMTZ（ 584.5 ~ 878 cmbsf）,which was considered to be resulted from methane seep events. In general,these results show that under the methane seepage environments,HS-produced by AOM reacts with magnetic minerals in sediments,resulting in the dissolution of magnetic minerals coupled with precipitation of paramagnetic pyrite,both of which will make an anomalously low MS value in the SMTZ; However,with low HS-concentration,insufficient supply of HS-will lead to partial pyritization,which will result in the preferential formation of greigites followed by secondary magnetic susceptibility signals. Therefore,in gas hydrate prospecting areas,abnormal characteristics of the sedimentary magnetic susceptibility ar