Gravity Flow Deposits in the Deep Rockall Trough, Northeast Atlantic

Abstract

The north-western margin of the Irish Rockall Trough in the Northeast Atlantic is dominated by the scarps of the Rockall Bank Mass Flow (RBMF) which extends towards the centre of the Rockall Trough, whereas the eastern margin is incised by numerous canyons that have no obvious associated fans at the foot of the slope. Terminal lobes associated with the glaciogenic Donegal-Barra Fan extend into the Rockall Trough from the northeast, whereas in the southwest the seafloor is dominated by the Feni Drift, a giant contourite drift formed by ocean bottom currents which was truncated by the sidewalls and depositional lobes of the RBMF. In June 2010 the RV Celtic Explorer cruise CE10008 collected the first comprehensive set of piston cores from the Irish sector of the deep Rockall Trough. Here we report on a sub-set of those cores recovered from across and beyond the bathymetric expression of the RBMF eastern outer limit in order to determine whether gravity flows were released during this event and whether they have traversed across the basin. The cores, taken in water depths of nearly 3,000 m, reveal that significant coarse sediment (up to coarse sand) was emplaced on the deep basin floor by both turbidity currents and bottom currents. We identify several discrete turbidite sand and silt deposits with geochemical signatures that point to different source areas. The youngest two appear to have been generated from the area occupied by the RBMF to the west during the Holocene. The remaining turbidite beds came from an easterly or northeasterly source and tie back to the Donegal-Barra Fan and are probably glacially related. Between the two periods we find a thick (>1.5 m) contouritic sand, possibly formed by bottom current reworking of the Feni Drift.