Diagenetic processes in carbonate mound sediments at the south‐west Rockall Trough margin |
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| Authors: | CEES VAN der LAND FURU MIENIS HENK DE HAAS NORBERT FRANK RUDY SWENNEN TJEERD C E VAN WEERING |
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| Institution: | 1. Royal Netherlands Institute for Sea Research, Department of Marine Geology, P.O. Box 59, 1790 AB Den Burg, The Netherlands (E‐mail: cees.van.der.land@nioz.nl);2. LSCE, Laboratoire des Sciences du Climat et de L'Environnement‐IPSL/CEA‐CNRS‐UVSQ, Bat. 12, Avenue de la Terrasse, 91198 Gif‐sur‐Yvette, France;3. K.U. Leuven, Earth and Environmental Sciences, Celestijnenlaan 200E, Heverlee 3001, Belgium;4. VU University, Faculty of Earth and life Sciences, Department of Paleoclimatology and Geomorphology, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands |
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| Abstract: | Cold water coral covered carbonate mounds at the south‐west margin of the Rockall Trough form ridges several kilometres long and up to 380 m high. Piston cores obtained at three mound crests reveal the complex internal structure of the mound build up, with alternating unlithified coral‐dominated intervals and lithified intervals. The most recent lithified interval is covered by corals embedded in a fine‐grained matrix, comprising ca 11 000 years of continuous mound evolution. Before this time 230Th/U dating shows the presence of several hiatuses in mound build‐up. Aragonitic coral material is absent or only present as mouldic porosity in the lithified intervals and coccoliths display widespread overgrowth. Downcore X‐ray fluorescence scanning, computer tomography scan images and petrographic observations indicate different degrees of diagenetic alteration. The upper boundary of the most recent lithified interval shows some erosional features, but petrographic observations indicate that initial lithification of the sediments is not related to this erosive event or to long‐term non‐sedimentation, but to earlier sub‐surface diagenesis. Organic matter oxidation and the subsequent lowering of the saturation state of the carbonate system drives dissolution of the unstable aragonitic coral skeletons. Depending on the openness of the system, this can lead to precipitation of a more stable low‐magnesium carbonate. A model is presented describing the sedimentary and diagenetic processes leading to the formation of lithified intervals. |
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| Keywords: | Carbonate diagenesis carbonate mound cold watercorals lithification Rockall Trough |
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