Pliocene and Quaternary depositional model of the Algarve margin contourite drifts (Gulf of Cadiz, SW Iberia): Seismic architecture, tectonic control and paleoceanographic insights

The contourite drifts off southwest Iberia that formed as a result of the interaction of the Mediterranean Outflow Water (MOW) with the continental middle slope were studied in the Algarve margin using multichannel reflection seismic lines, oil-wells, piston cores, and a bathymetric compilation of four datasets. The seismostratigraphic interpretation of a dense array of oil industry seismic and stratigraphic correlation allowed the identification of five seismic units of Early Pliocene through Holocene in the Faro and Albufeira drifts and four correlative seismic units in the Lagos and Sagres drifts and three in the Portimao drift. A three-phased evolutionary model for the contourite formation is proposed. Firstly, a precursory phase of Pliocene age made up of sheeted drifts represents an initial phase of deposition under bottom-current activity that is correlated with the first stages of an enhanced MOW at about 3.5 Ma. Secondly, the building up phase of Early Pleistocene age is related to a strengthening of the MOW close to the onset of the Northern Hemisphere glaciations at about 2.6 Ma during which were deposited low-mounded drifts. Thirdly, the growing phase from Middle-Pleistocene through Holocene suggests the presence of a stronger MOW since the beginning of the Middle-Pleistocene Transition at about 1.3–1.0 Ma, accounting for the deposition of mounded drifts and formation of the Alvares Cabral moat. Seismostratigraphic interpretation and isochron maps allowed for the establishment of the main oceanographic, climatic, morphologic and tectonic factors that controlled the drifts deposition: i) the Pliocene and Quaternary MOW circulation forced by climate changes; ii) the sea bottom topography inherited from the Late Miocene, mainly shaped by the Portimao, Lagos and Bartolomeu Dias canyons system; iii) the interaction between along-slope and down-slope processes since the Pliocene; and iv) Pliocene–Quaternary fault-activity and diapirism.