Sr/Ca and Mg/Ca ratios in Niger Delta sediments: Implications for authigenic carbonate genesis in cold seep environments
|Author(s)||Bayon Germain1, Pierre C2, Etoubleau Joel1, Voisset Michel1, Cauquil E3, Marsset Tania1, Sultan Nabil1, Le Drezen Eliane1, Fouquet Yves1|
|Affiliation(s)||1 : IFREMER, Dept Geosci Marines, Brest, France.
2 : Univ Paris 06, LOCEAN, Paris, France.
3 : TOTAL, Paris, France.
|Source||Marine Geology (0025-3227) (Elsevier), 2007-06 , Vol. 241 , N. 1-4 , P. 93-109|
|WOS© Times Cited||92|
|Keyword(s)||Niger Delta, Gas hydrates, Cold seeps, Mg/Ca, Sr/Ca, Authigenic carbonates|
|Abstract||We report on a reconnaissance analysis of the geochemical composition of authigenic carbonates and sediment samples collected from various seepage sites on the Niger deep-sea fan. Our aim has been to investigate whether evidence for the presence of authigenic carbonates and gas hydrates within sediments is discernible from solid-phase sediment geochemistry. We show that sedimentary Sr/Ca and Mg/Ca ratios can be used to infer the presence of authigenic aragonite (Sr-rich) and Mg-rich carbonate phases (high-Mg calcite, dolomite) in cold seep settings. Using Sr/Ca and Mg/Ca ratios, the proportion (wt.%) of authigenic carbonates in Niger Fan sediments can be calculated from a mixing model between sediment fractions of terrigenous material, biogenic calcite, aragonite and high-Mg calcite. This approach was applied to high-resolution geochemical profiles along sediment cores recovered from various cold seep settings (mud volcano, diapirs, pockmarks, gas-hydrate bearing sediments). Our data reveal that authigenic carbonates occur as discrete phases in sediments from gas-hydrate-bearing areas, suggesting that such carbonate-rich sediment layers may represent paleo-indicators for ancient methane seepage in marine sediments, possibly associated to gas-hydrate reservoirs. (C) 2007 Elsevier B.V. All rights reserved.|