Cenozoic sedimentary dynamics of the Ouarzazate foreland basin (Central High Atlas Mountains, Morocco)

Cenozoic continental sedimentary deposits of the Southern Atlas named "Imer hane Group" crop out (a) in the Ouarzazate foreland basin between the Preca mbrian basement of the Anti Atlas and the uplifted limestone dominated High Atlas, and (b) in the Ait Kandoula and Ait Seddrat nappes where Jurassic s trata detached from the basement have been thrust southwards over the Ouarz azate Basin. New biostratigraphic and geochronological data constraining th e final Eocene marine regression, the characterization of the new "Ait Ougl if Detrital Formation" presumed to be of Oligocene age, and the new stratig raphic division proposed for the Continental Imerhane Group clarify the maj or tectonogenetic alpidic movements of the Central High Atlas Range. Four c ontinental formations are identified at regional scale. Their emplacement w as governed principally by tectonic but also by eustatic controls. The Hadi da and Ait Arbi formations (Upper Eocene) record the major Paleogene regres sion. They are composed of marginolittoral facies (coastal sabkhas and fluv iatile systems) and reflect incipient erosion of the underlying strata and renewed fluvial drainage. The Ait Ouglif Formation (presumed Oligocene) had not been characterized before. It frequently overlies all earlier formatio ns with an angular unconformity. It includes siliciclastic alluvial deposit s and is composed predominantly of numerous thin fining-upward cycles. The Ait Kandoula Formation (Miocene-Pliocene) is discordant, extensive, and rep resents a thick coarsening-upward megasequence, It is composed of palustro- lacustrine deposits in a context of alluvial plain with localized sabkhas, giving way to alluvial fans and fluviatile environments. The Upper Conglome ratic Formation (Quaternary) is the trace of a vast conglomeratic pediment, forming an alluvial plain and terraces. The second and third formations co rrespond to two megasequences engendered by the uplift of the Central High Atlas in two major compressive phases during late Oligocene and Miocene-Pli ocene times. These two geodynamic events were separated by a tectonically c alm phase, materialized by palustro-lacustrine sedimentation (Gorler et al, 1988). Tectono-sedimentary analysis of the two megasequences shows that th e basin structure and depositional processes were controlled by the compres sive tectonic context generated by the collision of North Africa and Iberia in Tertiary times (Jacobshagen et al. 1988). The Quaternary Formation was apparently controlled by a tectonic continuum and by climatic variations.