Diagenetically formed magnetic minerals at marine methane seep sites are potential archive of past fluid flow and could provide important constraints on the evolution of past methane seepage dynamics and gas hydrate formation over geologic time. In this study, we carried out integrated rock magnetic, and mineralogical analyses, supported by electron microscope observations, on a seep impacted sediment core to unravel the linkage between greigite magnetism, methane seepage dynamics, and evolution of shallow gas hydrate system in the K-G basin. Three sediment magnetic zones (MZ-1, MZ-2, and MZ-3) have been identified based on the down-core variations in rock magnetic properties. Two events of intense methane seepage are identified. Repeated occurences of authigenic carbonates throughout the core indicate the episodic intensification of anaerobic oxidation of methane (AOM) at the studied site. Marked depletion in magnetic susceptibility manifested by the presence of chemosynthetic shells (Calyptogena Sp.), methane-derived authigenic carbonates, and abundant pyrite grains provide evidences on intense methane seepage events at this site. Fracture-controlled fluid transport supported the formation of gas hydrates (distributed and massive) at this site. Three greigite bearing sediment intervals (G1, G2, G3) within the magnetically depleted zone (MZ-2) are probably the paleo-gas hydrate (distributed-type vein filling) intervals. A strong linkage among clay content, formation of veined hydrate deposits, precipitation of authigenic carbonates and greigite preservation is evident. Hydrate crystallizes within faults/fractures formed as the methane gas migrates through the gas hydrate stability zone (GHSZ). Formation of authigenic carbonate layers coupled with clay deposits restricted the upward migrating methane, which led to the formation of distributed-type vein filling hydrate deposits. A closed system created by veined hydrates trapped the sulfide and limited its availability thereby, causing arrestation of pyritization and favored the formation and preservation of greigite in G1, G2, G3.

在海洋甲烷渗漏点上双渗碳形成的磁性矿物是过去流体流动的潜在档案，并可能对过去甲烷渗流动力学和天然气水合物在地质时间内的演化提供重要的限制。在这项研究中，我们在电子显微镜观察的支持下，对受渗流影响的沉积物核心进行了综合的岩石磁学和矿物学分析，以揭示KG盆地中的钙铁矿磁性，甲烷渗透动力学和浅层天然气水合物系统演化之间的联系。 。根据岩石磁特性的下核变化，确定了三个沉积物磁性带（MZ-1，MZ-2和MZ-3）。确定了两个强烈的甲烷渗透事件。在整个岩心中反复出现自生碳酸盐，表明研究地点的甲烷厌氧氧化（AOM）呈间歇性加剧。化学合成壳的存在表明磁化率显着降低（lySp。），源自甲烷的自生碳酸盐和丰富的黄铁矿晶粒提供了该地点甲烷强烈渗漏事件的证据。裂缝控制的流体输送支持了该地点天然气水合物（分散的和大量的）的形成。磁贫化区（MZ-2）中三个带钙铁矿的沉积物层段（G1，G2，G3）可能是古天然气水合物（分布型脉状充填）层段。粘土含量，脉状水合物沉积物的形成，自生碳酸盐的沉淀和钙镁石的保存之间存在很强的联系。在甲烷气体通过天然气水合物稳定区（GHSZ）迁移时，水合物在所形成的断层/断裂中结晶。自生碳酸盐层的形成加上粘土沉积物限制了甲烷向上迁移，这导致了分布型静脉充填水合物沉积物的形成。由脉状水合物形成的封闭系统捕获了硫化物，并限制了硫化物的可用性，从而导致黄铁矿的捕集，并有利于G1，G2，G3中钙铁矿的形成和保存。