Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea
Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea
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DOI：
10.3390/min9100624
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发表时间：
2019-10
期刊：
影响因子：
2.5
通讯作者：
Xi Xiao;Qian-Zhi Zhou;S. Fu;Q. Liang;Xiang-Po Xu;Yan Li;Jiang-Hai Wang
中科院分区：
文献类型：
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作者：
Xi Xiao;Qian-Zhi Zhou;S. Fu;Q. Liang;Xiang-Po Xu;Yan Li;Jiang-Hai Wang
铁锰氧化物和氢氧化物是海洋沉积物中最丰富的固相电子受体，铁锰异化还原通常与甲烷厌氧氧化（AOM）和有机质氧化（OMO）有关。在这项研究中，我们报告的结果，地下海洋沉积物在东沙水合物在南中国海地区。岩石学和地球化学特征表明，由AOM和OMO介导的Fe/Mn还原可能发生在硫酸盐-甲烷过渡带上方的沉积物中。沉积物的X射线衍射和扫描电镜分析表明，Fe（III）/Mn（IV）-氧化物和自生碳酸盐矿物共存的Fe/Mn还原带。溶解无机碳的δ 13 C值较低，无机碳总量明显增加，Ca 2+和Mg 2+浓度降低，表明该带发生了AOM，孔隙水中PO 43 −和NH 4+浓度变化较大，表明地下沉积物中的OMO速率较高。地球化学和矿物学分析表明，以前埋藏的Fe（III）/Mn（IV）氧化物可能被激活，并导致由AOM和OMO诱导的Fe/Mn还原的开始。这些发现可能会扩大我们的理解，在大陆架丰富的甲烷，有机质和陆源金属氧化物的铁/锰还原参与的地球化学过程。
Fe and Mn oxides and (oxy)-hydroxides are the most abundant solid-phase electron acceptors in marine sediments, and dissimilatory Fe/Mn reduction usually links with the anaerobic oxidation of methane (AOM) and organic matter oxidation (OMO) in sediments. In this study, we report the results from subsurface marine sediments in the Dongsha hydrate-bearing area in the South China Sea. The petrological and geochemical signatures show that the Fe/Mn reduction mediated by AOM and OMO might occur in sediments above the sulfate-methane transition zone. X-ray diffraction and scanning electron microscopy analyses of sediments indicate that Fe(III)/Mn(IV)-oxides and authigenic carbonate minerals coexisted in the Fe/Mn reduction zone. The lower δ13C values of dissolved inorganic carbon, coupled with an evident increase in total inorganic carbon contents and a decrease in Ca2+ and Mg2+ concentrations indicate the onset of AOM in this zone, and the greater variation of PO43− and NH4+ concentrations in pore water suggests the higher OMO rates in subsurface sediments. Geochemical and mineralogical analyses suggest that the previously buried Fe(III)/Mn(IV) oxides might be activated and lead to the onset of Fe/Mn reduction induced by AOM and OMO. These findings may extend our understanding of the biogeochemical processes involved in Fe/Mn reduction in continental shelves with abundant methane, organic matter, and terrigenous metal oxides.