PROCESSES OF SEDIMENTATION IN GOLLUM CHANNEL, PORCUPINE SEABIGHT - SUBMERSIBLE OBSERVATIONS AND SEDIMENT ANALYSES

Manned submersible dives were conducted in the submarine canyon/channe l system of Porcupine Seabight, NE Atlantic Ocean. Visual observations were made, and sediment samples collected and analysed to elucidate t he nature of the sedimentary regime. In the upper part of the canyon ( 480-940 m water depth) sediments consisted of a mixture of terrigenous quartz rich silts and sands, skeletal carbonate of benthonic and plan ktonic origin and minor clay minerals and authigenic dolomite. There w ere localised Lophelia pertusa coral thickets on both the flanks and f loor of the canyon. Sedimentary structures and physical measurements r evealed there to be active transport of sediments in the canyon down t o a depth of at least 940 m, effected by (?tidal) reversing currents a nd bioturbation. In these parts of the canyon, deposits around glacial dropstones and coral thickets indicate that there has been a maximum of 0.1 m of net sediment accumulation since the last glacial period. A t 3000 m water depth, in the channel system, the sediments were fine c alcareous ooze with a drape (up to 0.3 m thick) of flocculant phytopla nkton detritus. At these depths, there was no evidence for present-day sediment resuspension by currents.