Main geomorphologic features in the Canary Current Large Marine Ecosystem

This work describes the main geomorphological features of the seabed on the Atlantic continental shelf of Northwest Africa (NWA) (region encompassing the Canary Current Large Marine Ecosystem – CCLME). Knowledge of these geological shapes and the existing materials are fundamental for studying the biological habitats they comprise, particularly the benthonic and demersal ecosystems. In general, geomorphological data on this region collected by universities and research centres is limited and sometimes inaccessible. This report is therefore based on research carried out by the Instituto Español de Oceanografía (IEO) in various oceanographic campaigns conducted in recent years together with scientific publications dealing with particular zones in this region. For this purpose, a review has been made of the geological data obtained in the seven multidisciplinary campaigns undertaken by the IEO throughout the continental margin of Morocco, Western Sahara and Mauritania between 2004 and 2010. In these oceanographic campaigns, exploration of the seabed was carried out using multibeam echo sounders, high-profile seismic profiling and the direct collection of sediment samples and sedimentary rocks. The passive continental margin of NWA marks the transition between the lithosphere of the African continent and the oceanic lithosphere generated in the Atlantic Ridge. Continental rift and ocean crust formation in this part of the East Atlantic took place over the course of 225 Ma. The substrate of this continental margin is therefore composed of Palaeozoic metamorphic rocks, the oldest sedimentary rocks are Triassic and the ancient oceanic crust is Jurassic. As for the sedimentary rocks, the oldest are of continental origin while the later ones are of marine origin from various depositional environments (coastal, shelf, slope and seabed). In slope and continental shelf zones, these sedimentary materials can all reach thickness of up to 10 km, while in seabed zones they are below 5 km. In this zone of NWA, various surveys have also been carried out in recent decades under the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP), which have described the main geological features of the materials and morphologies of the continental margin. In addition, distensive tectonic structures have been cited throughout the region, most consisting of normal faults on an axis more or less parallel to the continental edge and structures perpendicular to the latter. On the Morocco-Western Sahara-Canaries margin, and on the Mauritania-Senegal-Guinea margin, descriptions exist of numerous salt domes, pockmarks and faults associated with diapiric processes related to Triassic saline deposits that have fluidified and intruded into the stratigraphic column of the continental margin Finally, two volcanic archipelagos associated with hotspots and consisting of islands and numerous seamounts exist in ocean interplate areas of the CCLME. The main geomorphological features of the CCLME region are described below in a survey of four geographical areas selected on a north-south basis, namely Morocco-Western Sahara, Canary Islands, Mauritania, and Senegal–Guinea-Bissau–Guinea–Cape Verde Islands.
MAVA (Contract 12087 Coastal West Africa C4/2012)