冷泉碳酸盐岩的稀土元素地球化学特征及氧化还原条件示踪*

doi:10.11978/j.issn.1009-5470.2012.05.006

Abstract

Abstract: 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 (?REE) of seep carbonates varies widely from 0.3×10^-6 to 43.7×10^-6, with a common trend that the ?REE 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.

Key words: seep carbonates, redox variation, rare earth elements

BIAN You-yan,LIN Zhi-jia,FENG Dong,CHEN Duo-fu,. Rare earth elements of seep carbonates and using them to trace redox variation at seep sites[J].Journal of Tropical Oceanography, 2012, 31(5): 37-44.

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Rare earth elements of seep carbonates and using them to trace redox variation at seep sites

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