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The Sines Contourite Depositional System, located in the Southwest Portuguese Margin, is a central segment of the Iberian Contourite Depositional Complex, built under the influence of the Mediterranean Outflow Water (MOW). This work presents the onset and evolution of this system using multibeam bathymetry, multichannel seismic reflection lines, sediment cores and well data. Six seismic units of Late Miocene through Holocene age have been identified, which defined three evolutionary stages for drift construction: a) an onset and initial stage, from the Latest Miocene to the Late Pliocene (5.33–2.5 Ma), where a sheeted drift was built under a weak flowing MOW; b) a growing stage from the Early to Middle Quaternary (2.5–0.7 Ma), characterized by the deposition of a mounded drift in the south and a sheeted drift in the north, which is correlated with a strengthening of the MOW; and c) a maintenance stage between the Middle Pleistocene and Holocene (0.7 Ma – present), where the modern depositional and erosional contourite features developed associated with three intensification periods of the MOW at 0.7 Ma, 0.4 Ma and 20 ka. The development of the Sines Contourite Depositional System was constrained in the long-term by seafloor paleomorphologies inherited from the Mesozoic rifting phases of the Southwest Portuguese Margin. The NNW-SSE horsts and grabens built during the Mesozoic rifting provided accommodation for drift growth, with limited lateral migration, and locally enhanced the alongslope bottom-current. In short-term, environmental (climate and sea-level) fluctuations modulated changes in bottom-current density and intensity, determining sedimentary cycles in the depositional record, especially during the Quaternary. Our findings emphasize the occurrence of three main plastered morphologies throughout the seismic record, which were compared with other plastered drifts in different continental margins to establish a conceptual model.
•Late Miocene to Present evolution of the Sines Contourite System, SW Portugal•Mesozoic paleomorphologies constrained drift growth and lateral migration•Climatic-eustatic fluctuations modulated bottom-current fluctuations•Three major events on the Mediterranean Outflow Water circulation•A refined conceptual model for plastered drifts