LATE CENOZOIC SEDIMENT DRIFT COMPLEX, NORTHEAST ROCKALL TROUGH, NORTH-ATLANTIC

Seismic reflection profiles and two shallow cores have revealed a sediment drift complex in the northeastern Rockall Trough. The drift complex consists of an elongate drift with associated sediment waves, a broad sheeted drift with a larger field of sediment waves, and smaller, moat-related isolated drifts. The internal reflection configuration of these features indicates consistent upslope migration throughout the late Cenozoic. The larger field of sediment waves has been described previously with a southerly migration; a reevalution of these waves suggests a migration direction to the east, conforming with the other drift complex features. The most vigorous current activity probably occurred during the Miocene, with a more reduced current now prevailing during the Pliocene to Holocene interval. Core evidence from the elongate drift and the moat has revealed upper Pleistocene and lower Holocene glaciomarine sediments reworked to produce muddy-silty and sandy contourites. Sedimentation rates for the early Holocene (pre-7.5 ka) are up to 4-times greater on the drift compared to the moat. It is suggested that the sediment drift complex has formed through the interaction of a northward flowing slope current, of North Atlantic Deep Water origin, with an area of complex bathymetry at the northeastern end of the Rockall Trough, where the Wyville-Thomson Ridge intersects the Hebridean Margin.