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南海神狐海域沉积物自生黄铁矿和石膏S同位素特征及对甲烷渗漏强度的示踪 总被引:1,自引:1,他引:0
The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments.Anaerobic oxidation of methane(AOM) coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment,including pyrite and gypsum.Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor(cmbsf) in the entire core sediment of HS328 from the northern South China Sea.Most pyrites are tubes consisting of framboidal cores and outer crusts.Gypsum aggregates occur as rosettes and spheroids consisting of plates.Some of them grow over pyrite,indicating that gypsum precipitation postdates pyrite formation.The sulfur isotopic values(δ~(34) S) of pyrite vary greatly(from –46.6‰ to –12.3‰ V-CDT) and increase with depth.Thus,the pyrite in the shallow sediments resulted from organoclastic sulfate reduction(OSR) and is influenced by AOM with depth.The relative high abundance and δ~(34) S values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone(SMTZ).The sulfur isotopic composition of gypsum(from–25‰ to –20.7‰) is much lower than that of the seawater sulfate,indicating the existence of a 34 S-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR.Pyrite oxidation is controlled by ambient electron acceptors such as MnO_2,iron(Ⅲ) and oxygen driven by the SMTZ location shift to great depths.The δ~(34) S values of gypsum at greater depth are lower than those of the associated pyrite,revealing downward diffusion of 34 S-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate.These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral,which will be favor to the formation of gypsum.Overall,the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities,and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage. 相似文献
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南海北部陆坡神狐海域晚中新世以来沉积物中生物组分变化及意义 总被引:5,自引:1,他引:4
对南海北部陆坡神狐海域4口钻孔(BY1、BY2、BY3、BY4)岩心沉积物中微体古生物的研究表明晚中新世以来该区沉积物中硅质和钙质生物组分丰度具有较大时间和空间变化。从时间上看,硅质生物在晚中新世—上新世几乎缺失,中更新世以来约40万年(0~24m)才较多出现,18万年以后繁盛,大于0.15mm粗粒级有孔虫在晚中新世期间丰度很低,而在更新世—上新世丰度很高;空间上的差异表现在不同的钻井岩心中生物丰度变化范围较大。根据硅质生物丰度变化可推测晚中新世—上新世—早更新世时海水表层古生产力极低,而中更新世以来古生产力相对较高。南海北部钙质生物丰度的变化主要受控于陆源物质的输入量,在钻探区可识别2个可能具有不同物质来源的小区块,如BY1、BY2孔晚中新世—上新世陆源物质的输入量高于更新世,BY3和BY4孔更新世陆源物质的输入量高于上新世。2007年本区钻探结果揭示的一个令人惊奇和十分独特的现象,水合物以高达20%~49%饱和度状态分散在细粒沉积物(黏土粉砂)孔隙中,本研究发现这些矿层富含钙质生物组分(钙质超微化石和有孔虫),而硅质组分贫乏。由此初步推测,大量钙质生物组分的存在可能增加了黏土粉砂沉积物的孔隙空间,从而为大... 相似文献
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东沙海区浅层沉积物中黄铁矿异常及其意义 总被引:1,自引:0,他引:1
东沙海区浅层沉积物的两个岩心出现大量的黄铁矿。GC10岩心中的黄铁矿在300cm以下含量增加,在700am的区段达到最高,主要为管状、棒状、莓球状;HD319岩心黄铁矿则相对较低,只在最底部730cm的区段突然增加,以莓球状为主。GC10岩心黄铁矿含量异常层位与甲烷含量增加层位一致,而在Corg-Ssulfide^2-含量变化图上,S^2-含量与有机碳含量线性关系不明显,显示了该岩心黄铁矿的形成主要受高甲烷流通量影响;而HD319岩心的有机碳高的层位,S^2-含量也高,表明HD319岩心黄铁矿的形成与沉积物中有机质降解密切相关。GC10岩心黄铁矿的δ^34S(‰)值在-17.149~-33.240CDT之间,显示了非常负的硫同位素比值和宽的区间;HD319的矿S(‰)值-36.363~-39.162CDT之间,相对比较稳定。GC10岩心黄铁矿的δ^34S(‰)值特征,可能与富甲烷环境有关,而HD319受其影响稍弱。 相似文献
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套管式加热器在维持孔壁稳定的同时还可实现对井周地层加热,以防止水合物开采过程中井周形成二次水合物。为分析水合物开采过程中日产水量、气水比和加热功率对井周地层温度分布的影响,采用COMSOL Multiphysics对加热过程进行模拟。模拟结果表明,日产水量对加热效果的影响明显大于加热功率,加热功率主要影响近井段的地层温度,气水比主要影响加热半径。通过数值模拟对套管加热器的加热效果进行了分析和评价,对天然气水合物的经济高效开采具有指导意义。 相似文献