Biogeochemical processes controlling authigenic carbonate formation within the sediment column from the Okinawa Trough
Biogeochemical processes controlling authigenic carbonate formation within the sediment column from the Okinawa Trough
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DOI：
10.1016/j.gca.2017.10.029
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发表时间：
2018-02
影响因子：
5
通讯作者：
Jiwei Li;Xiaotong Peng;S. Bai;Zhiyan Chen;J. D. Nostrand
中科院分区：
文献类型：
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作者：
Jiwei Li;Xiaotong Peng;S. Bai;Zhiyan Chen;J. D. Nostrand
自生碳酸盐岩是渗漏环境中的一种重要表现形式，它可以提供过去渗漏活动和海洋甲烷循环的长期档案。然而，缺乏对微生物群落功能结构及其在碳酸盐形成过程中的作用的全面调查。本文对采自冲绳海槽北方段西斜坡的渗漏碳酸盐沉积物进行了矿物学、地球化学和微生物功能组成的研究。本文旨在探讨碳酸盐存款形成过程中矿物相与微生物代谢之间的对应关系。矿物学分析表明，这些碳酸盐岩样品中存在自生碳酸盐矿物（文石、富镁方解石、白云石、铁白云石和菱铁矿）和含铁矿物（褐铁矿、褐铁矿和黑云母）。碳酸盐岩样品的碳、氧同位素值分别在−51.1‰ ~ −4.7‰和−4.8‰ ~ 3.7‰之间变化。碳氧同位素组成呈负线性相关，表明古生界碳酸盐为甲烷成岩（低δ 13 C/高18 O）和碎屑成因（高δ 13 C/低18 O）的混合物。GeoChip分析表明，微生物的各种代谢活动，包括甲烷生成，甲烷氧化，亚硫酸盐氧化，硫酸盐还原和金属生物转化，都发生在形成过程中。在此基础上，提出了奥陶系沉积柱中甲烷循环和渗漏碳酸盐存款形成的模式：（1）在上氧化带，甲烷的好氧氧化是甲烷消耗的主要途径;（2）在硫酸盐-甲烷过渡区，硫酸盐依赖的AOM（甲烷的厌氧氧化）消耗甲烷，自生矿物如文石、镁方解石和硫化物矿物沉淀;（3）在下伏的硫酸盐贫化带中，热液和陆源输入的铁氧化物的存在，为Fe依赖的AOM消耗甲烷创造了有利的条件，并在该带中沉淀出白云石和菱铁矿/铁白云石。
Authigenic carbonates are one type of conspicuous manifestation in seep environments that can provide long-term archives of past seepage activity and methane cycling in the oceans. Comprehensive investigations of the microbial community functional structure and their roles in the process of carbonate formation are, however, lacking. In this study, the mineralogical, geochemical, and microbial functional composition were examined in seep carbonate deposits collected from the west slope of the northern section of the Okinawa Trough (OT). The aim of this work was to explore the correspondence between the mineralogical phases and microbial metabolism during carbonate deposit formation. The mineralogical analyses indicated that authigenic carbonate minerals (aragonite, magnesium-rich calcite, dolomite, ankerite and siderite) and iron-bearing minerals (limonite, chlorite, and biotite) were present in these carbonate samples. The carbon and oxygen isotopic values of the carbonate samples varied between −51.1‰ to −4.7‰ and −4.8‰ to 3.7‰, respectively. A negative linear correlation between carbon and oxygen isotopic compositions was found, indicating a mixture of methane-derived diagenetic (low δ13C/high18O) carbonates and detrital origin (high δ13C/low18O) carbonates at the OT. GeoChip analyses suggested that various metabolic activities of microorganisms, including methanogenesis, methane oxidation, sulfite oxidation, sulfate reduction, and metal biotransformations, all occurred during the formation process. On the basis of these findings, the following model for the methane cycle and seep carbonate deposit formation in the sediment column at the OT is proposed: (1) in the upper oxidizing zone, aerobic methane oxidation was the main way of methane consumption; (2) in the sulfate methane transition zone, sulfate-dependent AOM (anaerobic oxidation of methane) consumes methane, and authigenic minerals such as aragonite, magnesium–calcite, and sulfide minerals precipitate; (3) in the underlying sulfate depleted zone, the presence of iron-oxides supplied by hydrothermal fluids and terrestrial inputs created thermodynamically favorable conditions for Fe-dependent AOM to consume methane, and dolomite and siderite/ankerite precipitate in this zone.