海洋天然气水合物成藏海区沉积物中自生矿物对古硫酸盐-甲烷转换带的指示

Authigenic mineral is one of the important results precipitated in the early diagenesis of marine sediments during their deposition, and it could record the multiple information of the exchanging materials between the downward seawater and the upward deep fluids & gases amonge the seafloor and sediments under the complex biogeological processes. Based on the comprehensive understanding of the coupling relationship between the authigenic mineral precipitation and the bacterial sulfate reduction -induced anaerobic oxidation of the sedimentary organic matters (SOM) and methane (AOM) in modern marine sedimentation, this proposal is focussed on the authigenic minerals as the solid geological records in the early diagenesis of marine sedimentation such as the carbonates, sulfides and sulfates. We want to analyze the types, distributions and isotopes of C, O, S of the authigenic minerals to probe the sulfate-methane transition zone (SMTZ). All researching sediment samples are from the Cascadia margin in northeastern Pacific Ocean and from the northern continental margin in South China Sea recovered by the drilling or piston core, which represents the typical areas reported having the marine gas hydrate depostions in the world. Our proposal hence could establish a new approach to discuss the evolution of paleo sulfate-methane transition zone (paleo SMTZ) in condition of unavailable paleo interstitial fluids. The final researching conclusions will be enable to uncover the unusual methane seepages in the ancient marine sedimentation and to better understand the evolution of marine gas hydrate accumulation.

海洋沉积物中自生矿物是沉积物在沉淀埋藏过程中早期成岩作用的重要产物，记录了海水-沉积物界面附近复杂的流体交换信息和地球生物学过程。申请书依据现代海洋水-岩界面附近硫酸盐还原细菌（BSR）参与下的沉积有机质（SOM）厌氧氧化作用、甲烷厌氧氧化作用（AOM）与自生矿物形成的成因关系，聚焦固态形式保存下来的地质载体（自生矿物），通过研究国内外海洋天然气水合物藏的典型海区（Cascadia大陆边缘和南海北部陆坡）的钻探和重力岩心沉积物中碳酸盐类、硫化物类和硫酸盐类等自生矿物的分布、丰度和碳-硫等稳定同位素组成，探索动态稳定的硫酸盐-甲烷转换带（SMTZ）变化特征，避免了无法直接获得古孔隙流体的缺陷，开创了利用自生矿物指示古硫酸盐-甲烷转换带（paleo-SMTZ）的研究新途径。研究结果将有助于揭开古海洋甲烷异常渗漏事件的沉积记录，也有助于深入探索古海洋沉积环境变化和海洋天然气水合物的成藏演化。

本项目的研究背景是围绕海洋天然气水合物藏的形成、演化、勘探和开发等基础理论及国民经济战略目标，试图通过研究国内外报道的海洋天然气水合物赋存海区岩芯沉积物中自生矿物发育特征等探讨研究区水合物藏的发育和演化史，进而服务于水合物勘探和开发的基础地学背景保障。主要研究内容包括对南海北部陆坡重力柱或钻探岩芯，以及大洋钻探航次（IODP）获得的钻探岩芯沉积物中自生矿物的类型、相对含量、分布、形貌和碳、氧、硫稳定同位素组成等，揭示研究海域沉积物中硫酸盐-甲烷转换带的发育特征和变迁规律，进而探讨研究区水合物的成藏演化特征。同时，运用“将今论古”原理，积极探讨地史重大转折期古海洋甲烷异常渗漏事件的地质记录及其古环境意义。经过全体参研师生的努力工作，本项目已圆满完成了预期研究目标，获得了大量国内外海洋天然气水合物赋存海区沉积物中自生矿物发育特征等资料，基本弄清了富甲烷流体渗漏引起的甲烷厌氧氧化作用和硫酸盐还原作用的生物地球化学机理，比较精确理解了硫酸盐-甲烷转换带（SMTZ）的含义及其位置变迁的控制因素等。项目在研期间共发表标注本项目资助的学术论文15篇（其中SCI论文10篇，EI论文1篇，核心期刊论文4篇），取得的研究成果将有助于加强我国南海水合物试采工程的基础地学背景，也对于深入探讨“深时地球”古海洋的甲烷事件及其古海洋、古环境和古生态的效应具有重要的理论意义。