Diagenetic formation of gypsum and dolomite in a cold‐water coral mound in the Porcupine Seabight,off Ireland |
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| Authors: | HANS PIRLET LAURA M WEHRMANN BENJAMIN BRUNNER NORBERT FRANK JAN DEWANCKELE DAVID VAN ROOIJ ANNELEEN FOUBERT RUDY SWENNEN LIEVEN NAUDTS MATTHIEU BOONE VEERLE CNUDDE JEAN‐PIERRE HENRIET |
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| Institution: | 1. Renard Centre of Marine Geology, Department of Geology and Soil Science, Ghent University, Krijgslaan 281 s8, B‐9000 Gent, Belgium (E‐mail: hans.pirlet@ugent.be);2. Biogeochemistry Research Group, Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D‐28359 Bremen, Germany;3. Coral Reef Ecology Work Group, GeoBio‐Center, Ludwig‐Maximilians Universit?t, Richard‐Wagner‐Strasse 10, D‐80333 München, Germany;4. Laboratoire des Sciences du Climat et de L’Environnement (LSCE), Unité Mixte CEA/CNRS/UVSQ, Bat 12, Avenue de la Terrasse, F‐91190 Gif‐sur‐Yvette, France;5. Department of Geology and Soil Science, Ghent University, Krijgslaan 281 s8, B‐9000 Gent, Belgium;6. Department of Subatomic and Radiation Physics, Ghent University, B‐9000 Gent, Belgium;7. Department of Earth and Environmental Sciences, Geology, K.U. Leuven, Celestijnenlaan 200E, 3001 Heverlee, Belgium |
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| Abstract: | Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold‐water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore‐water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment‐water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate‐rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds. |
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| Keywords: | Cold‐water coral dolomite early diagenesis gypsum Lophelia Porcupine Seabight sulphur isotopes |
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