Wave-form sheeted contourite drift on the Barra Fan, NW UK continental margin

Abstract

Abstract The lithology of a 30 m long piston core (MD95-2006) and high-resolution, seismic profiles from the lower Barra Fan, Rockall Trough, reveal a sheeted drift form with internal sediment waves deposited over the last glacial-interglacial cycle. Deposition of these mainly fine-grained deposits was controlled by a combination of downslope and alongslope transport mechanisms that interacted with the positive topography created by debrite lobes on the lower fan. The core penetrates a small field of sediment waves (wavelength approx. 1 km, height 3-6 m), which onlap a debrite lobe dated to the last glacial maximum. The sedimentary sequence shows: (1) silty-muddy contourites deposited during the mid-Devensian (Marine Isotope Stage 3), (2) glacimarine hemipelagites and sandy turbidites deposited between 26 and 18 C14 ka BP, followed by a short phase of erosion and redeposition by bottom currents, and (3) glacimarine hemipelagites and silty-muddy contourites representing the glacial to Holocene transition. On the distal fan edge, a drift sequence with upslope-migrating sediment waves (wavelengths approx. 3 km, height 15-30 m) onlaps the tongue of a previous slide event (pre-Devensian?). These bedforms were probably generated by decelerating, low-density glacigenic turbidity currents, but pirated by contour-following bottom currents on the distal part of the drift.