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 re gion were studied by field observations in the onshore basin and offsh ore by seismic profiles and borehole data. During the Late Jurassic an d the Early Cretaceous, they were frequently disturbed by repeated syn sedimentary tectonic instability, extensively demonstrated by structur es such as slumps, breccias, faults, etc. Regionally, these movements led to the initiation of ridges, in some cases diapiric, as well as de pocentres. These are mainly N 70 degrees E to E-W trending. Contempora neously with a slight tectonic inversion of some of the offshore half grabens, the Late Jurassic-Cretaceous regional deformation converted t he synsedimentary ridges to anticlines, and the depocentres to synclin es, before the latest 'Atlasic' orogenic uplift, during the Cenozoic. This structural evolution distinguishes the Agadir-Essaouira segment f rom other parts of the Atlantic margin of Morocco. It results from an interference between the N20 degrees E-oriented passive margin of Moro cco and the N70 degrees E-oriented Atlasic zone. The latter acted as a transform zone during Late Jurassic-Early Cretaceous limes and then s uffered a N-S compression during the Atlasic orogeny.