Transtensive synsedimentary tectonics associated with ocean opening: the Essaouira–Agadir segment of the Moroccan Atlantic margin

The Mesozoic–Cenozoic sedimentary sequences of the Agadir–Essaouira region were studied by field observations in the onshore basin and offshore by seismic profiles and borehole data. During the Late Jurassic and the Early Cretaceous, they were frequently disturbed by repeated synsedimentary tectonic instability, extensively demonstrated by structures such as slumps, breccias, faults, etc. Regionally, these movements led to the initiation of ridges, in some cases diapiric, as well as depocentres. These are mainly N 70°E to E–W trending. Contemporaneously with a slight tectonic inversion of some of the offshore half grabens, the Late Jurassic–Cretaceous regional deformation converted the synsedimentary ridges to anticlines, and the depocentres to synclines, before the latest ‘Atlasic’ orogenic uplift, during the Cenozoic. This structural evolution distinguishes the Agadir–Essaouira segment from other parts of the Atlantic margin of Morocco. It results from an interference between the N20°E-oriented passive margin of Morocco and the N70°E-oriented Atlasic zone. The latter acted as a transform zone during Late Jurassic–Early Cretaceous times and then suffered a N–S compression during the Atlasic orogeny.