Integrated Ocean Drilling Program, United States

During Integrated Ocean Drilling Program (IODP) Expedition 307, a downslope suite of three sites will be drilled on the eastern slope of Porcupine Seabight, west of Ireland. The sites are centered on Challenger mound (proposed Site PORC-03A), a 170 m high, partly buried carbonate mound in the Belgica mound province, topped by dead coldwater coral rubble. The Belgica mound province belongs to the best documented carbonate mound provinces worldwide. Very high resolution seismic profiling, multibeam bathymetry, and side-scan sonar imaging have shed light on the stratigraphic, structural, and morphological setting. The mounds are rooting on a strongly erosive unconformity and are seated partly on an enigmatic sequence of sigmoidal units and partly on a semitransparent layer. Proposed Site PORC-02A will identify the semitransparent basement layer, proposed off-mound Site PORC-04A and the basal sequence of on-mound proposed site PORC-03A will identify the nature of the sigmoidal units. Both Sites PORC-02A and PORC-04A will constrain the age of the unconformity and the importance of the hiatus. The on-mound Site PORC-03A will unveil the environmental record locked in a carbonate mound and shed light on the processes that may have controlled the genesis of the mound, in particular, testing the hypothesis of the possible role of fluid venting as trigger for mound growth and assessing the importance of environmental forcing factors. Particular attention will be paid to microbiological and biogeochemical processes in mound genesis and development.