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Diagenetic formation of gypsum and dolomite in a cold-water coral mound in the Porcupine Seabight, off Ireland
Pirlet, H.; Wehrmann, L.M.; Brunner, B.; Frank, N.; Dewanckele, J.; Van Rooij, D.; Foubert, A.; Swennen, R.; Naudts, L.; Boone, M.; Cnudde, V.; Henriet, J.-P. (2009). Diagenetic formation of gypsum and dolomite in a cold-water coral mound in the Porcupine Seabight, off Ireland. Eos, Trans. (Wash. D.C.) AGU Fall Meet. Suppl. 90(52): abstract PP23A-1358
In: Eos, Transactions, American Geophysical Union. American Geophysical Union: Washington. ISSN 0096-3941; e-ISSN 2324-9250, more

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Document type: Summary

    Lophelia Milne Edwards & Haime, 1849 [WoRMS]
Author keywords
    Cold-water coral; dolomite; early diagenesis; gypsum; Lophelia; Porcupine Seabight; sulphur isotopes

Authors  Top 
  • Pirlet, H., more
  • Wehrmann, L.M.
  • Brunner, B.
  • Frank, N.

    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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