Authigenic carbonates from the eastern Black Sea as an archive for shallow gas hydrate dynamics - Results from the combination of CT imaging with mineralogical and stable isotope analyses

A. Bahr, T. Pape, F. Abegg, G. Bohrmann, T.C.E. van Weering, M.K. Ivanov

    Research output: Contribution to JournalArticleAcademicpeer-review

    Abstract

    Authigenic carbonates associated with cold seeps provide valuable archives of changes in the long-term seepage activity. To investigate the role of shallow-buried hydrates on the seepage strength and fluid composition we analysed methane-derived carbonate precipitates from a high-flux hydrocarbon seepage area (" Batumi seep area" ) located on the south-eastern Black Sea slope in ca. 850 m. In a novel approach, we combined computerized X-ray tomography (CT) with mineralogical and isotope geochemical methods to get additional insights into the three-dimensional internal structure of the carbonate build-ups. X-ray diffractometry revealed the presence of two different authigenic carbonate phases, i.e. pure aragonitic rims associated with vital microbial mats and high-Mg calcite cementing the hemipelagic sediment. As indicated by the CT images, the initial sediment has been strongly deformed, first plastic then brittle, leading to brecciation of the progressively cemented sediment. The aragonitic rims on the other hand, represent a presumably recent carbonate growth phase since they cover the already deformed sediment. The stable oxygen isotope signature indicates that the high-Mg calcite cement incorporated pore water mixed with substantial hydrate water amounts. This points at a dominant role of high gas/fluid flux from decomposing gas hydrates leading to the deformation and cementation of the overlying sediment. In contrast, the aragonitic rims do not show an influence of
    Original languageEnglish
    Pages (from-to)1819-1829
    JournalMarine and Petroleum Geology
    Volume27
    Issue number9
    DOIs
    Publication statusPublished - 2010

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