A 3D seismic study of the morphology and spatial distribution of buried mounds in the Porcupine Seabight

In the Porcupine Seabight, along the North-Atlantic Continental Margin, a province of mostly buried mound structures was found (500 – 750 m water depth) by means of high-resolution 2D seismic profiles taken the last few years. Comparison with similar seabed structures in the area allows their identification as coral banks, associated with the growth of deepsea-coral species such as Lophelia sp. and Madrepora sp.. To allow a more detailed study of morphology and spatial patterns of the mounds, a unique opportunity was offered by Statoil Exploration (Ireland) Ltd., and its partners Arco, Conoco and Dana: the upper 400 ms of a 830 km2 industrial 3D seismic data block in the area were made available to the RCMG for scientific research.Morphological key horizons were interpreted and mapped, and several of these were entered in a GIS for integrated study and interpretation. Mound morphologies were mapped automatically, together with the associated moats, and possible spatial trends were derived. A large swarm of mounds was found, with densities of 1/km2, even up to 1.4/km2 and heights up to 100m. All mounds seem to originate from the same reflection, hence forming a mound ‘event’ in time and space. Morphologies range from round, conical single mounds to multiple, ridgelike and complex structures. The biggest structures are found on the western edge of the region under investigation; mounds here sometimes come up to the seabed. The smallest ones occur on the eastern side and seem to be buried much quicker by a much thicker sediment package. Most morphologies are elongated in the N/S direction, indicating a N/S (paleo)current activity. Hence both currents and sediment patterns clearly have influenced the mound growth dynamics and environment. The western edge of the mound swarm also coincides geographically with the upslope border of a slump feature deeper in the geological section. At the downslope – eastern – side however the coincidence is non-existent. Hence, the possible role of the deeper lying slope failure is not clear yet.3D seismics clearly forms an ideal tool to study morphologies and spatial patterns and relationships of local phenomena in the geological record, such as the mound structures in the Porcupine Seabight