Sedimentary particle distribution and dynamics on the Nazare, canyon system and adjacent shelf (Portugal)

In the framework of the EUROSTRATAFORM project 108 bottom sediment samples (1 st cm) from the Nazare continental shelf have been analysed for grain-size, mineralogy (X-ray diffraction) organic carbon and carbonate contents. The particulate matter (PM) from intermediate (INL) and bottom nepheloid layers (BNL) was also analysed in 84 stations for grain-size and composition. The particle analysis was related to the present day sedimentary processes directly promoted (or intensified) by the presence of the Nazare submarine canyon. The Nazare canyon intersects the entire continental shelf and may act as a catchment area for material which is transported over the shelf, but its complex dynamics will extend to sediment distribution on the adjacent shelf. Major areas of erosion and resuspension and calmer areas where fine muddy sediments can settle on a temporary or permanent timescale were identified by their mineralogical and organic carbon (C-org) distribution pattern. According to this data the Victoria tributary and the Nazare canyon head (280-300m) seem to act as permanent depocenters. A conceptual model was proposed to delineate the mechanisms acting in this particular area, taking into account three different sources of material to the Nazare canyon: 1. during upwelling conditions, resuspension of middle shelf deposits by internal wave activity and transport to the canyon in the BNL; 2. erosion of northen/southern beach and sea cliff materials transported by littoral drift to the canyon head and 3. fine sediment input from the southern river and transport to the canyon, during downwelling conditions (winter). (c) 2007 Elsevier B.V. All rights reserved.