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首页> 外文期刊>Oceanographic Literature Review >Non-evaporitic gypsum formed in marine sediments due to sulfate-methane transition zone fluctuations and mass transport deposits in the northern South China Sea
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Non-evaporitic gypsum formed in marine sediments due to sulfate-methane transition zone fluctuations and mass transport deposits in the northern South China Sea

机译：由于南海北部硫酸盐 - 甲烷过渡区波动和大规模运输沉积物，在海洋沉积物中形成的非蒸发石膏

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摘要

Gypsum (CaSO_4·2H_2O) 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.
机译：在过去十年中，在海洋沉积环境中观察到非蒸发起源的石膏（Caso_4·2H_2O）。我们通过分析石膏的硫和氧同位素组合物的硫和氧同位素组成来改善了我们对相关成岩过程的理解，但是，尚未进行富含甲烷的海洋环境中沉淀的Authigenic石膏的同位素组成的综合研究，以阐明其对硫循环的影响（例如，硫化物氧化）。此外，没有关于与潜艇大规模运输沉积物相关的关于潜艇的基因石膏，这是欧陆斜坡上的常见沉积特征。在这项研究中，我们分析了从甲烷水合物位点GMGS2-08，GMGS2-16和南海的GMGS4-W02B收集的钻孔中的石膏和硫同位素组合物的石膏和硫同位素组合物的硫磺和氧同位素组合物确定Authigenic石膏的形成机制。石膏和共同现有硫铁矿的稳定硫同位素分析显示，通过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‰的维也纳标准平均海水）表明厌氧条件下的金属氧化物氧化，掺入水氧，其同位素组合物通过气体水合物形成改性生产的硫酸盐。随着硫铁矿氧化还将质子（H〜+）释放到孔水中，可以通过碳酸盐矿物的溶解来升高钙浓度。在网站Gmgs2-08和Gmgs2-16中，AhereaInic石膏在古硫酸盐 - 甲烷过渡区内沉淀，表明石膏形成可能与硫酸盐 - 甲烷过渡区的向下迁移有关，这导致厌氧硫铁矿氧化在其原始网站上形成。然而，在SiteBMGS4-W02B，大多数石膏分布在大规模运输矿床中，其特征在于两种古硫酸盐 - 甲烷过渡区之间的高丰度的重新制备的Foraminiferas。鉴于海水硫酸盐比在现场Gmgs4-W02b的石膏硫酸盐上产生更多（> 85％），据信，Aheyigenic Gypsum形成与大规模运输沉积物有关，可以在孔隙空间内快速陷阱覆盖覆盖海水硫酸盐新沉积的沉积物，与硫酸盐和钙的硫酸盐氧化结合，导致局部石膏过饱和度。

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  • 来源
    《Oceanographic Literature Review》 |2021年第7期|1478-1478|共1页
  • 作者

    J.Zhao; J.Wang; S.C.Phillips;

  • 作者单位

    State Key Laboratory of Biogeology and Environmental Geology & Hubei Key Laboratory of Marine Geological Resources at College of Marine Science and Technology China University of Geosciences Wuhan Hubei 430074 China;

    State Key Laboratory of Biogeology and Environmental Geology & Hubei Key Laboratory of Marine Geological Resources at College of Marine Science and Technology China University of Geosciences Wuhan Hubei 430074 China;

    State Key Laboratory of Biogeology and Environmental Geology & Hubei Key Laboratory of Marine Geological Resources at College of Marine Science and Technology China University of Geosciences Wuhan Hubei 430074 China;

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