神狐海域08CF7岩心沉积物的自生矿物特征及其对甲烷渗漏的指示

神狐海域是南海北部深水油气和天然气水合物的重点研究区域。为评价该区冷泉活动与天然气水合物分布情况,利用神狐海域08CF7岩心沉积物,对其自生矿物组成及其碳同位素进行测定,并观察自生矿物形貌特征,结合沉积物岩性特征及研究区地质构造背景,探讨了沉积物中的自生矿物及其碳同位素组成对该区泥火山构造背景下的甲烷渗漏活动及其甲烷厌氧氧化的指示意义。研究表明:在08CF7岩心埋深188cm以上和以下的沉积物中,自生矿物的组成、含量和碳同位素值均有明显差异,188cm以下的特殊沉积段可能反映了该区泥火山构造背景,自生碳酸盐矿物属于冷泉成因,其形成指示了海底甲烷渗漏及甲烷厌氧氧化(AOM)过程。进而提出了利用细粒组分的自生矿物及碳同位素组成识别AOM的方法,该方法有助于我国南海渗漏型天然气水合物的探查工作。

Characteristics of authigenic minerals in sediments of core 08CF7 in Shenhu area in northern South China Sea: Implications for methane seepage

The Shenhu area in northern South China Sea (SCS) is a focus for the study of deepwater hydrocarbon resources and gas hydrate exploration. A core of shallow sediment from Site 08CF7 was used to test compositions and carbon isotope of authigenic minerals and observe their morphologic characteristics. In combination with the lithologic characteristics of core sediments and the regional tectonic setting of this study area, this paper discussed the implications of the authigenic minerals and their carbon isotopes for methane seepage and anaerobic oxidation in the mud volcano structural background. The compositions, content and carbon isotopes of authigenic minerals in the sediments above and below 188 cm were obviously different. Sediments below 188 cm might be formed under the volcano structural background, and their authigenic minerals are of cold seep genesis and can indicate methane seepage and anaerobic oxidation of methane (AOM). A method is proposed to identify AOM according to the fine authigenic minerals and their carbon isotopes. It has great scientific value and application prospect in the exploration of seepage type gas hydrates in South China Sea.