Using iron speciation in authigenic carbonates from hydrocarbon seeps to trace variable redox conditions |
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| Institution: | 1. Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Guangzhou Marine Geological Survey, China Geological Survey, Ministry of Natural Resources, Guangzhou 510075, China;1. Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA;2. Geological Survey of Norway, 7491 Trondheim, Norway;3. Department of Geology, Tallinn University of Technology, Ehitajate 5, 19086 Tallinn, Estonia;4. School of Earth and Environmental Sciences, University of St Andrews, Fife KY16 9AL, UK;5. Department of Earth Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, IN, USA;1. School of Geosciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK;2. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK |
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| Abstract: | Seepage of hydrocarbon-rich fluids out of the marine sedimentary column is characterized by temporal changes of flow intensity and resultant spatially variable redox conditions. Authigenic carbonates at marine hydrocarbon seeps provide excellent geological and geochemical archives that serve to explore seepage dynamics over time. In this study, we investigated the potential of Mössbuaer spectroscopy and Fe contents of seep-related authigenic carbonates from the Congo Fan, the Gulf of Mexico, and the Black Sea for reconstructing past redox conditions and fluid seepage activity at cold seeps. The Fe speciation observed by Mössbauer spectroscopy and Fe contents suggest that (1) the Congo Fan carbonates precipitated in a sulfidic environment, (2) the formation conditions of seep carbonates were variable at the Gulf of Mexico seep site, ranging from oxic to suboxic and anoxic and even spanning into the methanogenic zone, and (3) the stratified water column of the Black Sea or suboxic condition resulted in low Fe contents of Black Sea carbonates. The study reveals that Fe speciation can provide constraints on the wide range of redox conditions that imprinted seep carbonates during the life span of seepage. Similarly, Mössbauer spectroscopy – particularly when used in combination with the analysis of redox-sensitive elements – is a promising tool to trace variable redox conditions in marine paleoenvironments other than seeps. |
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| Keywords: | Hydrocarbon seep Authigenic carbonate Redox condition Iron Mössbauer spectroscopy |
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