南海琼东南盆地沉积物地球化学特征及其反映的甲烷微渗漏作用

Geochemical Characteristics of Sediments from Southeast Hainan Basin,South China Sea and Micro-Methane-Seep Activity

研究所用样品由"海洋四号"船于2005年8月在三亚市SEE方向约150 km处采取。XRD和扫描电镜观察表明样品普遍存在自生碳酸盐、硫酸盐和草莓状(framboidal)黄铁矿。自生矿物组合和显微结构特征与冷泉沉积物类似,属微生物成因。孔隙水中Mg^(2+)、Ca^(2+)和硫酸根的浓度均有随深度增加而降低的趋势,说明这些组分在成因过程中被消耗。成岩反应过程中的溶解二氧化碳可能来自甲烷的厌氧氧化。样品中硫酸根的消耗主要和硫酸盐矿物沉淀有关,而非硫酸根还原。这意味着造成沉积物中黄铁矿大量沉淀的还原态硫并非来自采样深度,它和甲烷及Ba^(2+)一样,均来自地层更深处。

The researched samples were taken from Qiongdongnan Basin, some 150 km in the SEE of Sanya. Complicated authigenic minerals were identified by XRD and SEM, such as miscellaneous carbonates, sulphates and frambiodal pyrite. The assemblage and fabric characters are similar to what being found in cold-seep sediments, which is thought to be related with microorganisms fueled by dissolved methane. There is a tendency that Mg^2＋, Ca^2＋ and SO4^2- content in pore water decreased with depth. The cations are consumed in diagenesis as carbonates, with the dissolved CO2 be supplied by anaerobic methane oxidation. The anion was precipitated as sulphate, instead of being reduced. This means that H2S to form frambiodal pyrite is from depth, the same as methane and Ba^2＋.