The role of late Quaternary tectonic activity and sea-level changes on sedimentary processes interaction in the Gulf of Cadiz upper and middle continental slope (SW Iberia)

Spanish; Castilian. Versión del editor

English. A morphological and seismic-stratigraphic analysis of the Gulf of Cadiz area near the Strait of Gibraltar is presentedin this work, focused on the sedimentary evolution of the upper and proximal middle-continental slopesince the Mid-Pleistocene. Based on the analysis of seismic reflection profiles and swath bathymetry data, thiswork analyses the close influence of the activity of buried and outcropping diapiric ridges and late Quaternarysea-level changes on the evolution of contouritic features related to the Mediterranean Outflow Water (MOW)and Eastern North Atlantic Central Water (ENACW), gravitational features and fluid-escape structures. Thestratigraphic architecture reveals that, under active diapiric deformation, the upper slope plastered drift grewduring low sea-level stages, when sediment supply was high and the ENACW swept the upper slope, contrastingwith the present-day highstand situation dominated by northwest-trending MOW flow. The south-estwardENACW flow forced asymmetry and lateral migration of gullies incised in the plastered drift. Two evolutionarystages have been established: 1) After the Mid Pleistocene, activity of diapirs with a NE trend determinedthe location of the deepest depressions which were infilled by plastered contouritic drifts; 2) Between LateQuaternary and present, a drastic change of buried diapirs growth pattern and orientation to a NW trendenhanced slope-derived gravitational processes affecting the bottom current dynamics. Adjustments to tectonicchanges led to a phase of plastered drift growth on the upper slope during which depocenters varied their distributionand orientation. In a long-term the structural control on sedimentation shows a northwestwarddisplacement of deformation, resulting in an overall extension of the contourite depositional system to the NW.In a short-term, sea-level changes favored drift deposition, gullies incision and the strengthening of water masses.This work evidences the importance of tectonic deformation in sedimentation at recent time scales, and the twodirectionalinterplay between recent tectonic activity and bottom current dynamics.