Carte Geologique du Maroc au 1/50 000, feuille Boumalne - Notice explicative

The Boumalne sheet cover the northern margin of the Anti-Atlas, which is made up of precambrian Saghro massif and its paleozoic cover, the western part of the Ouarzazate Basin and the southern margin of the central High Atlas. The oldest Saghro basement outcrops in the Boumalne window and is characterized by two units referable to the middle Neoproterozoic and Cryogenian (NP2-PII):i) arenaceous-pelitic metasediments with few flows and dikes of tholeitic basalts, metamorphosed and folded at a regional scale during the panafrican orogeny; ii) some intrusive calc-alkaline bodies, slightly metamorphosed (Imider: 675 Ma; Tiboulkhirine:645 Ma). This middle proterozoic is discordantly covered by thiks volcano and volcano-clastic sequences (Group of Ouarzazate) and truncated by sub-volcanic and intrusive bodies (Tiounouine and Aguensou) which can be referred to the upper Neoproterozoic or Ediacaran (NP3-PIII). The Paleozoic correspond to a reduced cambro-ordovician sequence outcropping only in the eastern part of the sheet. It indicates a bathynetry varying between intertidal and open marine. Its base is unconformable on the proterozoic basement and the Ordovician is separated from the middle Cambrian by the clastic upper cambrian/termadocian hiatus. Towards the top, the Ordovician and the upper Paleozoic are cut by the unconformity following the hercynian orogeny. The Paleozoic rapidly disappear towards the west at the so called "Imider Threshold" where the mesozoic-cenozoic sequence directly lie on the precambrian rocks of the Saghro basement. The mesozoic-cenozoic sequence is made of marine and continental sediments covering about three quarters of the map. The lower part of the sequence, Jurassic in age, is carbonatic and represents the filling of basins formed in the "Atlasic" rifting phase, while the upper part, Cretaceous to Pliocene in age, represents both the cover of the High Atlas and the filling of the Ouarzazate basin. A hiatus separates the jurassic from the cretaceous deposition , which starts in the Cemnomanian with a continental sequence. In the upper Cretaceous the sequence indicates syntectonic characters and corresponds to an alternation of continental and marine platform formations. The upper paleocene to middle eocene sediments, which unconformably lie on the middle-upper cretaceous sequence, are characterized by coastal sediments. In the upper Eocene the sediments become predominantly continental. At Present the northern sector of the Ouarzazate basin is partly overthrusted by the front of the High Atlas belt.