Canyons and late Quaternary sedimentation on the north Norwegian margin

The presence of erosive canyons on high latitude passive margins is unusual. Such margins are more normally dominated by subsidence and glacially influenced deposition. However, ten canyons are identified at the edge of the narrow shelf on the North Norwegian margin off the Lofoten Islands, between the Trænadjupet and Andøya slides, on the basis of GLORIA long-range side-scan sonar and contemporaneous 3.5 kHz profiler data, combined with a detailed bathymetry. The canyons are located down-stream of sediments transported through the Lofoten Drift, and the margin is characterized by an absence of cross-shelf troughs. Canyons are up to 420 m deep, U-shaped, display steep gradients in their upper parts, and sediments derived from them have short runout distances onto the continental rise. The canyons are estimated to be 20–30 Ma old, being incised into only thinly covered, lithified, pre-Miocene sediments as a response to Cenozoic uplift. Late Quaternary sedimentation processes associated with the canyons are inferred to occur during both glacials and interglacials. Glacial sedimentation is probably in the form of direct subglacial-debris input, in addition to turbid subglacial meltwater plumes. Interglacial sedimentation processes are probably dominated by the along-shelf transport of sediments by strong ocean currents; canyon heads ‘capture’ sediment from the shelf. The remobilization of this coarse material and erosion of the canyons occurs through debris flows and turbidity currents. Canyon preservation and continued development can be attributed directly to the comparatively low sedimentation rates during full-glacial conditions, as ice streams, located to the north and south, produce regional depocentres away from this area of relatively slow-flowing ice.