Gypsum (CaSO₄·2H₂O) of non-evaporitic origins has been observed in marine sedimentary environments over the past decade. Our understanding of related diagenetic processes has improved by analyzing the sulfur and oxygen isotopic compositions of gypsum, but, a comprehensive study of the isotopic composition of authigenic gypsum precipitated in methane-rich marine environments has not been performed to elucidate their implications for the sulfur cycle (e.g., sulfide oxidation). Furthermore, there are no studies of authigenic gypsum associated with submarine mass transport deposits, which are common sedimentary features on continental slopes. In this study, we analyzed the sulfur and oxygen isotopic compositions of gypsum and the sulfur isotopic composition of pyrite in drill cores collected from methane hydrate-bearing sites GMGS2–08, GMGS2–16, and GMGS4-W02B in the northern South China Sea to determine the formation mechanisms of authigenic gypsum. The stable sulfur isotopic analyses of gypsum and co-existing pyrite revealed that sulfate produced by pyrite oxidation contributed to gypsum precipitation. The low oxygen isotopic composition values of gypsum (−2.6 to 4.5‰ Vienna Standard Mean Ocean Water) suggest that pyrite is oxidized by metal oxides under anaerobic conditions, incorporating water oxygen, whose isotopic composition was modified by gas hydrate formation, into the produced sulfate. As pyrite oxidation also releases protons (H⁺) into the porewater, calcium concentrations may be elevated by the dissolution of carbonate minerals. At sites GMGS2–08 and GMGS2–16, authigenic gypsum was precipitated within paleo sulfate-methane transition zones, indicating that gypsum formation is probably associated with the downward migration of the sulfate-methane transition zone, which causes anaerobic pyrite oxidation at its original site of formation. However, at site GMGS4-W02B, most of the gypsum was distributed in a mass transport deposit characterized by a high abundance of reworked foraminiferas between the two paleo sulfate-methane transition zones. Given that seawater sulfate contributes more (>85%) than pyrite oxidation to the gypsum sulfate at site GMGS4-W02B, it is believed that authigenic gypsum formation is associated with mass transport deposits, which can rapidly trap overlying seawater sulfate within the pore space of the newly deposited sediments, combined with the sulfate and calcium from pyrite oxidation, leading to a local gypsum supersaturation.

在过去的十年中，在海洋沉积环境中发现了非蒸发性石膏（CaSO ₄ ·2H ₂ O）。通过分析石膏的硫和氧同位素组成，我们对相关的成岩过程的理解得到了提高，但是，尚未进行对富含甲烷的海洋环境中沉淀的自生石膏的同位素组成的综合研究，无法阐明其对硫循环的影响。 （例如硫化物氧化）。此外，还没有关于与海底大量运输沉积物有关的自生石膏的研究，这些沉积物是海底常见的沉积特征。大陆坡。在这项研究中，我们分析了从南海北部至北部的甲烷水合物位点GMGS2-08，GMGS2-16和GMGS4-W02B收集的钻芯中石膏的硫和氧同位素组成以及黄铁矿的硫同位素组成。确定自生石膏的形成机理。石膏和共存的黄铁矿的稳定硫同位素分析表明，黄铁矿氧化产生的硫酸盐有助于石膏沉淀。石膏的低氧同位素组成值（-2.6至4.5‰维也纳标准平均海水）表明，黄铁矿在厌氧条件下被金属氧化物氧化将水的氧结合到生成的硫酸盐中，水的氧的同位素组成因气体水合物的形成而改变。由于黄铁矿的氧化还将质子（H ⁺）释放到孔隙水中，因此碳酸盐矿物的溶解可能会增加钙的浓度。。在地点GMGS2-08和GMGS2-16上，自生石膏沉淀在古硫酸盐-甲烷过渡带内，这表明石膏的形成可能与硫酸盐-甲烷过渡带的向下迁移有关，这会在其原始位置造成厌氧性黄铁矿氧化。的形成。然而，在站点GMGS4-W02B处，大多数石膏分布在一个大规模运输矿床中，其特征是两个古硫酸盐-甲烷过渡带之间有大量返工的有孔虫。鉴于海水硫酸盐对位点GMGS4-W02B处的硫酸石膏的氧化作用比黄铁矿氧化作用更多（> 85％），据信自生石膏的形成与大量运移沉积物有关，该沉积物可以迅速将上覆的海水硫酸盐捕集到新沉积的孔隙空间内沉积物，再加上黄铁矿氧化产生的硫酸盐和钙，导致局部石膏过饱和。