Slope instability and sediment redistribution in the Rockall Trough: constraints from GLORIA

Abstract

AbstractA recent GLORIA (Geological LOng Range Inclined Asdic) sidescan survey covered 200 000 km2 of the sea bed in the Irish Rockall Trough. It revealed a range of sedimentary features on the trough floor and its steep (>6°) margins. The western margin is characterized by large-scale (of the order of hundreds of kilometres in length) downslope mass movement. Smaller-scale slides and slumps (tens of kilometres across) occur on the eastern margin, but they are subordinate to canyon, channel and fan systems. The western and central parts of the trough floor contain the Feni Sediment Ridge, a 600 km long contourite sediment build-up covered by large sediment waves trending sub-parallel to the dominant modern current pattern. Strong, northward-flowing bottom currents are thought to have eroded the base of the slope in the east and redeposited the sediments on the western margin and the trough floor. Mass wasting and terrigenous sediment input through canyons is regarded as the primary source of sediment in the region. The increase in the degree and frequency of canyon incision along the NE margin of the trough reflects increased terrigenous input from the Irish mainland and a possible glacial influence on the basin margin. The GLORIA images reflect a broad interplay of alongslope and downslope sediment transport processes in the Rockall Trough with sediments sourced from the NE margin and redistributed by currents along the western margin. Although alongslope and downslope processes are the major controlling factors, basin subsidence, Quaternary glaciations and glacio-eustatic sea-level fluctuations have also influenced the pattern of sedimentation in the Rockall Trough.