琼东南盆地甲烷微渗漏活动地球化学示踪研究

为了深入认识南海北部琼东南盆地的甲烷微渗漏活动，通过测试位于该盆地某似海底放射（BSR）发育区内柱状样HQ-6PC和HQ-38PC的孔隙水阴阳离子浓度及δ¹³C_DIC等指标，对甲烷微渗漏活动特征进行了研究。结果显示，在柱状样HQ-6P和HQ-38PC的5.2 m以上部分，硫酸盐消耗由有机质硫酸盐还原作用（OSR）和甲烷缺氧氧化作用（AOM）共同主导，而在柱状样HQ-38PC的5.2 m以下部分主要受AOM的影响。柱状样HQ-38PC的硫酸根甲烷转换界面（SMTZ）埋深为9.9 m，甲烷向上扩散的通量约为32 mmol·m^-2·a^-1。两个柱状样孔隙水的Mg/Ca和Sr/Ca质量比随深度的变化指示其中形成的自生碳酸盐矿物主要为高镁方解石。HQ-6PC的Cl^-浓度在3.5 m以下明显降低，可能有天然气水合物分解时排放的低盐度流体加入，而HQ-38PC在4.0~5.5 m处存在较高的盐度异常，暗示其中可能混入了来自水合物形成时排放的高盐度流体。因此，两个站位浅表层发育显著的甲烷微渗漏活动，其下方可能发育水合物。

Geochemical Tracers for Methane Microleakage Activity in the Qiongdongnan Basin

To understand methane microleakage activity in the Qiongdongnan Basin of the northern South China Sea, the concentrations of pore water anions and cations, δ¹³C_DIC, and other indices of the core samples HQ-6PC and HQ-38PC were measured using bottom stimulating reflectors (BSR) in the development zone to study the characteristics of methane microleakage. The results showed that sulfate consumption was dominated by organic sulfate reduction (OSR) and anaerobic oxidation of methane (AOM) in the HQ-6PC and HQ-38PC core samples above 5.2 m, whereas the effects of AOM were predominant in the HQ-38PC core sample below 5.2 m. The sulfate-methane transition zone (SMTZ) of the HQ-38PC core sample had a depth of 9.9 m and an upward methane flux of 32 mmol·m^-2·a^-1. The change in Mg/Ca and Sr/Ca depth in the pore water of the two core samples indicated that the authigenic carbonate minerals formed within were primarily high-magnesium calcites. The Cl^- concentration of HQ-6PC was significantly decreased below 3.5 m. Inclusions of low-salinity fluid released from hydrate decomposition are likely present. There is a relatively large salinity anomaly in HQ-38PC between 4.0~5.5 m, suggesting that there might be mixing with high-salinity fluid released during hydrate formation. Thus, there is significant methane microleakage activity in the shallow surface of the two stations and possible hydrate development underneath.