Late Miocene continental slope evolution in the Gulf of Cádiz: decoding the importance of bottom currents in sedimentation and morphology

The Gulf of Cádiz is home to the well-studied modern contourite depositional system, which was deposited through the influence of bottom currents sourced from the Mediterranean Outflow Water exiting the Straits of Gibraltar since Pliocene to present. However, the Late Miocene sedimentary evolution and Mediterranean-Atlantic water-mass exchange prior and during the Messinian salinity crisis are poorly understood. Some progress on the characterisation of an ancient Late Miocene contourite depositional system were established from field studies onshore in the Betic and Rifian corridors albeit limited due to outcrop availability, but their downstream continuation in the Gulf of Cádiz has yet to be identified. This is partially due to the complexity of the area resulting from tectonic deformation, whose effect on contourite deposition are ambiguous. Consequently, identification and characterisation of the Tortonian to Messinian interval in the Gulf of Cádiz could answer questions related to the relationship between the Mediterranean and Atlantic during that period, as well as increase our knowledge of contourite deposition in tectonically active settings. This thesis presents a regional-scale study on the Late Miocene evolution of the Gulf of Cádiz, focusing on the role of bottom currents in sedimentation. A detailed seismic stratigraphic analysis was carried out for the available seismic and borehole data acquired from scientific and industry sources, to characterise the sedimentary and paleoceanographic evolution during the later parts of the Late Miocene, assisted by chronostratigraphic correlation. An ancient contourite depositional system is identified consisting of three evolutionary stages: initial-drift, growth-drift, and maintenance-drift, prior to its burial in the latest Miocene. The formation of the Late Miocene contourite depositional system occurred following the main emplacement of the regional Gulf of Cádiz allochthonous unit and can be traced towards southern West Iberian margin. The results allowed us to reconstruct the evolution of the paleo-Mediterranean Outflow Water responsible for the bottom current activity depositing the ancient contourite depositional system until its severe weakening or cessation during the latest Miocene, which led to the Messinian salinity crisis, as well as to suggest its impact on North Atlantic paleoceanographic and climate. This is mainly controlled by continuous uplifting and subsequent closure of the Mediterranean-Atlantic paleo-gateways. These findings also allowed us to understand the influence of tectonic and orbital control on gateway evolution and gravitational processes, and thus on contourite deposition. By unravelling these control factors, they enable us to propose diagnostic criteria of contourite depositional system in tectonically active margins.