Late Miocene-Quaternary diapiric activity in the SW Iberian Margin: Interaction between salt and shale structures and deep-water sedimentation

The southwestern margin of Iberian (SWIM) underwent a complex tectonic evolution, related to its proximity to the plate boundary between Africa and Europe, and the Betic-Rif Orogeny. The Algarve, Doñana, Sanlucar and Cadiz Basins developed on the Betics’ foreland since the late Miocene, and their sedimentary infill is composed of deep-water turbiditic, hemipelagic and contourite deposits. This work aims to understand the influence of diapiric structures on the development and evolution of deep-water sedimentation associated with these sedimentary basins. It has been accomplished with the analysis of regional 2D and 3D seismic datasets and a chronological framework from well data.

Extensive diapiric activity was recorded throughout the Late Miocene-Quaternary basins. Salt and shale structures were identified characterized by their internal transparent to chaotic reflections with moderate to low amplitude. Three types of diapirs were observed: i) squeezed, vertical diapiric stocks, ii) vertical elongated diapirs related to compressive deformation, and iii) salt-cored normal faults. Eight diapiric pulses occurred during the late Miocene-Quaternary timeframe. Deep-water sedimentation is influenced by these diapiric pulses in two ways: i) diapiric-related reliefs on the seafloor control down- and along-slope current circulation, and consequently the turbidite and contourite sediment distribution and their deposits architecture, and by ii) changeable accommodation space: depocenter size and capacity for sediment accumulation are variable over time, being directly related to the intensity of the diapiric activity. Contourite deposits also respond to changes in depocenter characteristics by altering drifts geometry and size, from sheeted to mounded to confined, with the increasing intensity of diapiric activity.

This work demonstrates the influence of diapirism in shaping the seafloor paleo-morphology, with diapiric-related reliefs and depocentres, controlling the distribution of deep-water depositional systems. Thus, this study emphasizes the importance of an integrated basin analysis, considering sediment supply, regional tectonics, including diapiric activity, as well as climatic and sea-level variations in controlling deep-water sedimentation.

 

Acknowledgements: D.D. thanks the Portuguese Foundation for Science and Technology (FCT) for a PhD scholarship (reference SFRH/BD/115962/2016). This research has been conducted under the framework of ‘The Drifters Research Group’, Department of Earth Sciences, Royal Holloway University of London (UK). We thank DGEG (Direção-Geral de Energia e Geologia) and Dr. José Miguel Martins for the supply of the 3D seismic dataset. The bathymetric data used in this work is from the European Marine Observation and Data Network (EMODnet) Bathymetry Project (http://www.emodnet.eu/bathymetry).