Recent sediment transport and deposition in the Lisbon–Setúbal and Cascais submarine canyons, Portuguese continental margin

Recent sediment transport and deposition in the Lisbon–Setúbal and Cascais submarine canyons, Portuguese continental margin, were investigated on the basis of water column profiles of suspended particulate matter, records of near-bottom currents and settling fluxes of particulate matter obtained with benthic landers, and analysis of surface sediments. The results show that fine-grained predominantly lithogenic sediment derived from adjacent shelf areas accumulates in the upper reaches of the canyons. Sediment deposited further down in the middle and lower reaches of the canyons is essentially similar to the hemipelagic sediment found on the adjacent continental slope, indicating that down-canyon transport of sediment from the upper to the lower canyon is limited. Tidal currents measured at various depths in the Lisbon–Setúbal Canyon appear sufficiently strong to resuspend and transport sediment, but net up-canyon flow of the bottom water may retain shelf-derived lithogenic sediment in the upper canyon. Sediment gravity flows, which in the nearby Nazaré Canyon are an effective mechanism for down-canyon sediment transport, appear rare in the Lisbon–Setúbal Canyon and probably also in the Cascais Canyon. Turbidity current events recorded in the sedimentary record of the canyons may correspond to seismic events of 1969 and 1755 AD.