Post-Salt Evolution of the Offshore Essaouira Basin (Morocco)

Abstract

Salt-bearing passive margins represent some of the most structurally complex and economically significant hydrocarbon provinces worldwide. However, these margins are often characterised by substantial uncertainties related to crustal and syn-rift basin architecture and suprasalt tectonic evolution. The Essaouira Basin, a salt-bearing passive margin and a promising hydrocarbon province encompassing all essential elements of a petroleum system, remains geologically complex, with unresolved questions regarding its post-salt gravity-driven deformation and overall tectonic evolution. This study presents an integrated analysis of the post-salt evolution of the Essaouira Basin, utilising 2D and 3D seismic reflection and well data combined with structural restoration. Our results indicate that salt deposition was strongly controlled by basement structural inheritance, evidenced by abrupt lateral variations in salt thickness across the basin. The evolution of the basin proceeded through three distinct phases: (1) An initial phase dominated by gravity-driven deformation, strongly influenced by the Cap Ghir Graben, which functioned as a localised depocenter and disrupted downdip salt flow, resulting in the development of two linked kinematic systems. This early configuration led to a distribution of structures and domains that differs from conventional salt-bearing passive margins; (2) A second phase characterised by halokinesis, primarily manifested through passive diapirism, driven by differential sedimentary loading during the Early Cretaceous; and (3) A final phase, commencing in the Late Cretaceous, marked by contractional deformation related to far-field compressional stresses associated with the Atlas orogeny. Additionally, Late Cenozoic shelf uplift is attributed to plume-related mantle upwelling. This study highlights the role of pre-existing rift architecture and subsequent tectonic events in shaping the Essaouira Basin's complex salt tectonics, providing new insights into the evolution of salt-bearing passive margins.