Abstract: Numerous studies on sediment drifts have demonstrated a close interaction between sea-bed morphology, palaeoceanography, sediment supply and climate. Contourites have been reported in areas along continental margins directly influenced by the effect of intensive deep-water currents from the global conveyor belt. In this paper, we report the occurrence of a small-scale confined contourite drift from Porcupine Seabight, SW of Ireland, and its association with a province of coral banks. The Porcupine Basin is a relatively shallow, semi-enclosed basin characterized by the presence of cold-water coral bank provinces. These coral banks are often associated to a strong northward-flowing bottom current, created and steered by a complex interaction of the water mass characteristics, tidal influences and sea-bed morphology. Very high-resolution seismic stratigraphy allowed the identification of a small mounded drift, located between a depression created by (1) an irregular palaeotopography caused by a vigorous Late Pliocene erosion event and (2) a north-south alignment of coral banks. Core MD99-2327, taken on the flank of this drift mound, shows the variability of the bottom currents. Sortable silt data show several periods of bottom-current enhancement, which may be linked with warmer periods and an inferred influx of Mediterranean Outflow Water. The glacial part of the core has been interpreted as a muddy contourite with a high content of ice-rafted debris. The lower part of the core is a deep-water massive contourite sand resembling the present-day sea-floor sediments.

Abstract High-resolution reflection seismic investigations carried out in the Porcupine Basin, SW of Ireland, have shed light on the presence of several provinces of giant carbonate mounds. An intriguing setting is found on the northern slope of the basin. A cluster of surface mounds appears to be flanked by a large upslope, crescent-shaped province of buried mounds. Below the transitional zone, large imbricated slide scars suggest repeated failures. The buried mounds rise from an undisturbed basal horizon and seem to represent a single event, confined in time and space. Both high-resolution and industrial seismic data reveal a close vertical match of the mound cluster with a lower, buried sea-bed failure, where hydrate build-up may have played a role. The latter association may not be entirely fortuitous. It is suggested that gas venting may have triggered the formation of the mound clusters, and that the underlying sea-bed failure forms a previous but different expression of gas venting, on a common, episodic fluid migration pathway but under strongly contrasting bottom water temperature conditions.