甲烷渗漏背景下硫酸盐还原对含铁自生矿物生成的影响

Effects of sulfate reduction on the formation of iron-bearing authigenic minerals in a methane seepage setting

海底甲烷渗漏现象广泛分布于天然气水合物潜在区,甲烷渗漏区发生的甲烷厌氧氧化和硫酸盐还原作用,不仅控制着甲烷的渗漏,还会促进自生矿物的形成,在铁含量较多的沉积层则呈现为含铁自生矿物的富集。利用低温高压反应釜模拟海底沉积层环境,对环境中甲烷-水-岩-微生物的相互作用进行了实验研究,探讨了甲烷渗漏环境中硫酸盐还原对含铁自生矿物生成的影响。实验结果显示:反应溶液中pH、ORP下降,HS^-和HCO_3^-离子浓度上升,指示反应釜内发生了硫酸盐还原和甲烷厌氧氧化作用。溶液中总铁含量实验前后减少了约7.5 mg/L,说明存在与铁有关的沉淀作用。扫描电镜观测到较多的铁硫化物及少量铁白云石和菱铁矿沉淀。自生矿物的生成和微生物作用密切相关,硫酸盐还原和甲烷厌氧氧化作用相互影响耦合,可以促进含铁自生矿物的生成。实验结果有助于深入认识海底甲烷渗漏区含铁自生矿物的形成以及其水合物指示意义。

Seabed methane seepage is common in areas with gas hydrate potential. Methane anaerobic oxidation and sulfate reduction occurring in these areas not only control the leakage of methane,but also facilitate the formation of authigenic minerals,which presenting itself as the enrichment of iron-bearing authigenic minerals in sediments rich in iron. This paper discussed the effect of sulfate reduction on the formation of iron-bearing authigenic minerals in a marine methane seepage environment through lab tests of methane-water-rock-bacteria reactions in a low-temperature and highpressure reactor that simulated seabed sediment environment. The results showed decrease of pH,ORP and increase of HS^- and HCO_3^- concentration,indicating sulfate reduction and anaerobic oxidation of methane in the reactor. The total iron content in the solution decreased by about 7. 5 mg/L before and after the tests,indicating iron-related precipitation.SEM images also showed precipitation of mostly iron sulfide with some ankerite and siderite. The paper suggested that a close relationship exist between the formation of authigentic minerals and microbial effect and that the interaction between sulfate reduction and anaerobic oxidation of methane play a positive role in the formation of iron-bearing authigenic minerals. This study may help in understanding further the forming mechanism of iron-bearing authigenic minerals in methane-seepage areas and its significance for gas hydrate prospecting.