SEDIMENTATION PATTERNS ON THE NORTH-EAST ATLANTIC MARGIN

The NE Atlantic margin shows distinct changes in sedimentation with latitude. Three sectors have been identified

North of 56°N: The margin is heavily influenced by glaciomarine processes which build sediment fans composed of stacked debris flows. These occur in front of the fast flowing ice streams that have cut cross-shelf troughs. During interglacials, this part of the margin is influenced by alongslope currents. Giant submarine landslides are a prominent feature, particularly off Norway and the Faeroe Islands. Some of these landslides have occurred during the Holocene, and are related to slope instability caused by high glacial sedimentation rates and melting gas hydrate layers.

From 30°N to 56°N: In this area there is quite high fluvial input and the margin is less prone to landsliding. On the Biscay margin, there is high sediment supply to the shelf edge as much sediment is transported by meltwater during late-glacial periods, and numerous canyons funnel turbidity currents down the steep slopes to the extensive abyssal plains. The lithospheric plate boundary off SW Iberia is associated with frequent earthquakes, and has led to high rates of sediment transport to the deep sea via canyon systems. The Mediterranean outflow has built a series of sediment drifts in the Gulf of Cadiz and off SW Portugal, although the alongslope transport is interrupted by a number of large canyons.

South of 30°N: High rates of upwelling produce high sediment accumulation rates along the upper slope, although there is little fluvial input and canyons are rare. The sediment is subject to landsliding involving dislocation of hundreds to thousands of km³ of sediment in single events, although these events may be separated by a few tens of thousands of years. The resultant debris flows are deposited across the continental slope and rise, and large-scale turbidity currents transport hundreds of km ³ of sediment to the abyssal plains.