Abstract In this paper, the QS-1 sediments (3.64 m long; at 1500 m water depth) collected from the Qiongdongnan Basin were used to analyze the relationship between sedimentary geochemical anomalies and methane seepage. Mo-U covariation, Ce anomaly, and Mg/Ca-Sr/Ca end-member model were analyzed to identify the variations of redox environment and authigenic carbonate precipitation, finally constructing the methane release events in this study area. These observations suggest that: 1) Significant Mo/U enrichments and Ba front indicate the presence of high-flux active methane seepage with SMI of 260 cmbsf in this study area. The depositional environment evolved as oxic-anoxic-reducing-sulfide environment from bottom to top, as evidenced by Mo-U covariation and Ce anomaly; 2) Based on Sr/Ca and Mg/Ca end-member model proposed by Bayon et al. (2007), the high-Mg calcite was the dominant authigenic carbonate currently which usually precipitated behind the methane seep events; and 3) The active cold seep can be divided into three methane release events (MREs): MRE I, the most intense methane seepage occurred at 22.1 ka BP; MRE II, three low-intensity methane seepage occurred at 19.3, 16.5, and 11.3 ka BP, respectively; and MRE III, the continuous methane seep began at 9.3 ka BP until now. The synthesis of geochemical indicators has significant implications for tracing methane seepage of varying intensity and duration.

中文翻译：

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南海琼东南盆地沉积物中甲烷渗流的地球化学证据

摘要 本文利用琼东南盆地QS-1沉积物（长3.64 m，水深1 500 m）分析沉积地球化学异常与甲烷渗流的关系。分析Mo-U协变、Ce异常和Mg/Ca-Sr/Ca端元模型，识别氧化还原环境和自生碳酸盐沉淀的变化，最终构建该研究区的甲烷释放事件。这些观察结果表明：1) 显着的 Mo/U 富集和 Ba 前沿表明该研究区域存在高通量活性甲烷渗流，SMI 为 260 cmbsf。沉积环境自下而上演化为好氧-缺氧-还原-硫化物环境，Mo-U共变和Ce异常证明；2) 基于 Bayon 等人提出的 Sr/Ca 和 Mg/Ca 端元模型。(2007), 高镁方解石是目前主要的自生碳酸盐，通常在甲烷渗漏事件之后沉淀；3）活动冷渗流可分为三个甲烷释放事件（MRE）：MRE I，最强烈的甲烷渗流发生在22.1 ka BP；MRE II，3次低强度甲烷渗流分别发生在19.3、16.5和11.3 ka BP；和 MRE III，直到现在，连续的甲烷渗漏始于 9.3 ka BP。地球化学指标的合成对于追踪不同强度和持续时间的甲烷渗流具有重要意义。19.3、16.5、11.3 ka BP分别发生3次低强度甲烷渗流；和 MRE III，直到现在，连续的甲烷渗漏始于 9.3 ka BP。地球化学指标的合成对于追踪不同强度和持续时间的甲烷渗流具有重要意义。19.3、16.5、11.3 ka BP分别发生3次低强度甲烷渗流；和 MRE III，直到现在，连续的甲烷渗漏始于 9.3 ka BP。地球化学指标的合成对于追踪不同强度和持续时间的甲烷渗流具有重要意义。