The Late Cenozoic sedimentary succession of the Taza-Guercif Basin, South Rifian Corridor, Morocco

The Taza-Guercif Basin is located in the area between the eastern terminati on of the Rifian front and the Middle Atlas System. It was part of the Sout h Rifian Corridor, the Miocene foredeep of the Rif. Stratigraphic analyses enabled us to distinguish two areas with a different evolution. A north-western area, on the left side of the Melloulou River, presents a Tortonian succession up to 500-600 m thick. The south-eastern ar ea is characterised by a succession at least 1500 in thick, which develops from Tortonian to Pliocene. The examined successions locally begin with continental deposits, followed by transitional and shallow marine deposits and by thick, open marine sedim ents, developing up again to marginal and continental facies. The stratigraphic analysis, together with a structural study, enabled to po int out the most significant steps in the evolution of the basin. The onset of sedimentation in the Taza-Guercif Basin, induced by the advanc ement of the Rifian front during the Tortonian, is marked by fluviatile dep osits of the Draa Sidi Saada Unit. The following transgressive trend, outlined by the deposition of the Ras el Ksar Unit, develops upwards with a deposition of open marine deposits of t he Blue Marl Subunit, in the late Tortonian. The intercalation of two turbi ditic units, late Tortonian-Messinian in age, may represent the expression of a tectonic uplift of the internal Middle Atlas area. During the early Messinian, thick deposits of the Gypsiferous Marl Subunit indicate that strong subsidence still continued in the south-eastern part o f the basin. A final regressive trend during the Messinian-Pliocene is pointed out by th e development of transitional to continental sedimentation of the Kef ed De ba and Bou Irhardaiene Units. (C) 2000 Elsevier Science Ltd. All rights res erved.