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Mound settings in provinces of fluid flow: status of research

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The EU FP5 projects GEOMOUND and ECOMOUND have endeavoured to increase our understanding of modern mound provinces, and to elucidate possible controls on mound genesis, development and decay, possibly driven by both external (oceanic) and internal (geological) controls. Mound provinces are a global phenomenon, increasingly reported on various margins. Exciting new observations along the West-European margin reflect both an enormous step forward in the elucidation of the setting and environment of modern carbonate mounds, and the puzzling or sometimes contradictory results when we try to lift the veil on their genesis. Spectacular cold-water coral communities have colonized such mounds, but convincing arguments for recognizing them as prime builders are still lacking. In other parts of the world, such as off British Columbia, sponges seem to play first fiddle. The geological record provides ample evidence of microbial mediation in mound build-up and stabilisation, but as long as mound drilling is lacking, we have no opportunity to verify the role of such processes and identify the key actors in the earliest stage of onset and development of modern mounds. Some evidence from the past record and from present very-high resolution observations in the shallow seabed suggest an initial control by fluid venting, and fluid migration pathways have been imaged or are tentatively reconstructed by modelling in the concerned basins. GEOMOUND has brought new evidence on this topic, but the ultimate link in the shallow subsurface seems still to elude a large part of our efforts. On the other hand, applying rigorously the interpretational keys derived from e.g. Porcupine Seabight settings on brand new prospective settings, e.g. on the Moroccan margin, have resulted in the discovery of totally new mound settings, in the middle of a field of giant, active mud volcanoes. Keys are apparently working, but we still do not understand how or why. We are no doubt facing complex systems, owing their genesis and growth to a complex woven of internal and external controls, feedback and process relay processes. Anyhow, what emerges from the increasing discoveries of mound provinces is that carbonate mounds are prime components of ocean margin systems. They also form a hitherto overlooked component of the global carbon cycle. Initial estimates of the total amount of carbon locked in the mound provinces of Porcupine Seabight are in the order of magnitude of ton C.

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