The Oligocene-Miocene Ghomaride cover: A petro-sedimentary record of an early subsident stage related to the Alboran Sea rifting (Northern Internal Rif, Morocco)

New sedimentological, petrographic and structural data have been collected from the Oligocene-Miocene terrigenous deposits unconformably overlying the highest tectonic units of the Internal Rifian Chain (Ghomaride Units). These new data show (i) the abundance of coarse-grained facies (disorganized and organized conglomerates and pebbly sandstones), (ii) a sedimentary supply from very slightly metamorphic Paleozoic sources and from Mesozoic carbonate cover and (iii) the dominance of a mainly extensional syn-sedimentary tectonic activity. Stratigraphic and petrographic characters point out a paleogeographical scenario where the Ghomaride Units, believed to be the sources of the analysed successions, fed small "satellite basins" located above the fold-thrust belt by means of gravity and debris flow processes. Moreover, the low textural maturity of the analysed sandstones seems to suggest conditions of short transports linked to a rugged topography and to a very unstable tectonic setting. Structural data acquired, in good agreement with that of literature, confirm the existence of a mainly extensional tectonic activity which lasted from the Late Oligocene up to Middle Burdigalian times during the deposition of the analysed successions. So, within a mainly extensional geodynamic context, a continuous rapid erosion of the highly elevated parts (mainly Ghomaride Units) of the folded thrust belt, progressively uplifted, produced the sedimentary supply. During this Late Oligocene-Lower Miocene rifting stage, some of these "satellite basins" evolved, in the rear of the Rifian fold-thrust belt, to more subsiding areas as "continental trenchs" and triggered the opening of the Alboran Sea.