Rare earth elements of seep carbonates and using them to trace redox variation at seep sites
Rare earth elements of seep carbonates and using them to trace redox variation at seep sites
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发表时间：
2012
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通讯作者：
Bian Youyan;Lin Zhijia;Feng Dong;Chen Duo-fu
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作者：
Bian Youyan;Lin Zhijia;Feng Dong;Chen Duo-fu
在海洋渗漏中，甲烷被微生物氧化，导致碳酸盐沉淀到海底附近。甲烷氧化导致沉积物孔隙水中硫酸盐的消耗，并引起氧化还原条件的变化。从墨西哥湾和刚果扇现代渗漏以及两个古老的烃渗漏地点收集的石灰岩自生碳酸盐相的稀土元素（REE）模式，霍拉德丘冷泉碳酸盐岩的稀土总量变化范围为0.3× 106 ~ 43.7× 106，其共同趋势是微晶相的稀土总量高于亮晶胶结物中的稀土总量。这些Ce异常的变化表明，冷泉碳酸盐岩的氧化还原条件是多变的和复杂的。总的来说，我们的研究结果表明，在冷泉环境中，氧化条件至少是暂时普遍存在的。氧化还原条件的变化可能与冷泉流体通量的变化或与甲烷氧化产生氧气相关的反硝化作用有关。
At marine seeps,methane is microbially oxidized resulting in the precipitation of carbonate close to the seafloor.Methane oxidation leads to sulfate depletion in sediment pore water and induces change in redox conditions.Rare earth element(REE) patterns of authigenic carbonate phases from limestone collected from modern seeps of the Gulf of Mexico and the Congo Fan,as well as from two ancient hydrocarbon-seep localities,Hollard Mound(Middle Devonian) and Marmorito(Miocene),were investigated.The total REE content(ΣREE) of seep carbonates varies widely from 0.3×10 6 to 43.7×10 6,with a common trend that the ΣREE in microcrystalline phases is higher than that in sparite cement.The shale-normalized REE patterns of seep carbonates often show different Ce anomalies,even in the samples from the same site.These varied Ce anomalies suggested that the redox conditions of seep carbonates are variable and complex.Overall,our results show that oxic conditions are at least temporarily common in seep environment.The varied redox conditions might be related to the changes of flux of seep fluid or the denitrification associated with methane oxidation that produces oxygen.