Sedimentary processes shaping the eastern slope of the Faeroe–Shetland Channel

Abstract

Sidescan sonar images, high-resolution seismic profiles, sediment samples and seabed photographs have been used to characterize the seabed sedimentary environment of the continental slope west the Shetland. The seabed morphology and sedimentary regime in this area result primarily from sediment deposition during the last glacial, modified by erosion and re-distribution of surficial sediments during the Holocene. Examples of glacial age features which have a significant effect on present day seafloor morphology include iceberg ploughmarks, glacigenic debris flows and channels cut into glacigenic sediment sequences. Holocene modification of the late glacial seafloor by bottom currents has given rise to large areas of gravel lag deposits and sand bedforms at scales ranging from tens of centimetres to kilometres. However, evidence for strong currents, directed towards the NE, is largely restricted to the upper slope. Much of the gravel covered seafloor on the lower slope shows little evidence for strong currents, suggesting that low sediment input during the Holocene is the main reason why gravel of glacial age remains at the seabed. A localised contourite sand deposit on the lower slope suggests peak current speeds of a few tens of cm s −1, with derivation of the sand from a relict sandwave field which occurs immediately up current and upslope from the contourite body.