The imprint of methane seepage on the geochemical record and early diagenetic processes in cold-water coral mounds on Pen Duick Escarpment, Gulf of Cadiz

Exploring a link between Atlantic coral mounds and Phanerozoic carbonate mudmounds: Insights from pore water fluorescent dissolved organic matter (FDOM), Pen Duick mounds, offshore Morocco

“…These results suggest an important role of sedimentary organic matter and suboxic remineralization processes due to dissimilatory iron reduction and sulphate reduction coupled to oxidative sulphur cycling via iron reduction (Canfield et al, 1993;Weber et al, 2006;Wehrmann et al,2011). In contrast, Alpha and Beta mounds are influenced by ascending methane and the role of anaerobic oxidation of methane is significant (Foubert et al, 2008;Wehrmann et al,2011). However, at very shallow sediment depth down to a few tens of centimetres, the geochemical contrast between methanic and non-methanic mounds is minor or even absent .…”

“…Gamma mound is a non-methane influenced coral mound, and displays high reactive iron contents, an absence of hydrogen sulphides, relatively low pyrite concentrations, light to uniform δ 34 S-pyrite and very low rates of sulphate reduction (Wehrmann et al, this issue). These results suggest an important role of sedimentary organic matter and suboxic remineralization processes due to dissimilatory iron reduction and sulphate reduction coupled to oxidative sulphur cycling via iron reduction (Canfield et al, 1993;Weber et al, 2006;Wehrmann et al,2011). In contrast, Alpha and Beta mounds are influenced by ascending methane and the role of anaerobic oxidation of methane is significant (Foubert et al, 2008;Wehrmann et al,2011).…”

“…ISOM was used to explain a variety of carbonate sediments ranging from stromatolites and ooid growth (Ferguson et al, 1978;Dupraz et al, 2009 for review) to microcrystalline seafloor precipitates in ancient carbonate mounds (Neuweiler et al, 1999;Desrochers et al, 2007). Organomineralization does not apply to any kind of biologically-mediated mineralization process that occurs in connection with metabolic functions of microorganisms (see respective study of Wehrmann et al, 2011).…”

Formation of large carbonate concretions in black cherts in the Gufeng Formation (Guadalupian) at Enshi, South China

“…Sulfur isotope fractionation during sulfate reduction is negatively correlated with sulfate concentration, exhibiting a small fractionation when sulfate concentration is less than 1 mM (Canfield & Raiswell, ; Habicht, Gade, Thamdrup, Berg, & Canfield, ). In the AOM zone, deeper in the subsurface, pore water sulfate can be largely consumed by the methane flux (Kaplan & Rittenberg, ; Wehrmann et al, ), leading to 34 S enriched pyrites in this zone (Jørgensen, Böttcher, Lüschen, Neretin, & Volkov, ; Lash, , ; Wehrmann et al, ). The relatively light values at Tianfengping suggest that concretion growth occurred early, at a shallow depth, prior to the development of the closed‐system conditions that favor methanogenesis (Canfield et al, ; Pallud & van Cappellen, ; Thamdrup & Canfield, ).…”

Carbonate mounds: From paradox to World Heritage

“…water coral dissolution and carbonate precipitation Foubert and Henriet, 2009). The Alpha Mound on Pen Duick Escarpment, featuring a shallow zone of anoxic oxidation of methane (AOM) (Maignien et al, 2010), comprises up to 40% of microbial dolomite Wehrmann et al, 2011;Pirlet et al, 2012). …”