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

The Taroucht sheet covers the extreme southwestern part of the Ougnat massif, in the western Anti-Atlas, which is part of the deformed northern margin of the western African craton. Here outcrop formations of upper to uppermost neoproterozoic, paleozoic and quaternary age. The substratum is composed of volcanic formations of upper neoproterozoic age (middle and upper NP3) in which two different complexes have been distinguished: the Ougnat rhyolitic complex, belonging to the middle NP3 and which has by far the largest one, and the Ougnat pyroclastic complex (upper NP3), much more limited. The first complex has been subdivided into three sequences : - The Bou Ibhla-Bou Tikidine sequence composed of rhyolites in flows and domes, some volcano-clastics and rhyolitic ignimbrites with local interbeds of andesitic lavas. - The Azlou sequence entirely constituted by andesitic flows and dykes. - The Bou Blouh charachterized by alternation of rhyodacitic and dacitic flows, of breccias, tuffs and levels of volcano-sedimentary rocks. The first and the last sequences, in particular, are made up by volcanic products with acidic predominance and associated pyroclastic products, with very few sedimentary rocks. They are the expression of predominant explosive rhyolitic volcanism. From the chemical point of view, the rocks forming the different complexes and sequences of the Taroucht Neoproterozoic are of the high potassic to shoshonitic calc-alkaline type. They were emplaced in a rifting context evolving after the continental collision between the west African craton and an undefined northern block, which took place in the Anti-Atlas at about 685 Ma (main phase of the panafrican orogeny) and ended at about 615 Ma. The volcanic activity is accompanied by important plutonic events, represented in the sheet by the intrusions of Imelouane and of Tilmlaline, that were intruded towards the end of the magmatic cycle. The Paleozoic is represented by a complete lower Cambrian to Carboniferous (Visean) sequence. The lowermost formation of the paleozoic cover (Igoudine Formation, or basal sandstones and conglomerates) indicates a clear disconformity over a rough paleomorphology made of the Proterozoic substratum of the Ougnat massif and locally of the Assif Toulla formation, which represents the top unit of a volcano-clastic sequence, inturn unconformable overlaying the basement units. The paleozoic sequence is several hundreds of meters thick and it is composed by terrigenous clastic deposits with subordinate carbonates, in an environment of deposition from continental to shallow marine. The Taroucht sheet is characterized by an important tectonic lineament (Tizi n'Boujou-Bou Tiouit shear zone), represented by a system of high angle faults which locally juxtapose the Proterozoic basement to the paleozoic sequence, and shows a complex polyphase kinematics. This shear zone is almost E-W striking and cuts the sheet into two nearly equal parts; in the southern sector are developed predominantly the two sedimentary cycles of the Cambrian, made up, respectively of the Groupe de Tata formations of lower Cambrian, and by the formations of the Groupe des Feijas internesof middle Cambrian age. To the North of the Tizi n'Boujou-Bou Tiouit shear zone outcrop the sequences of the Ordovician and Carboniferous. In particular, the sequence of the Ordovician, made of monotonous deposits of sandstones, petites and mudstones, cut by levels of oolitic iron, is very complex and has been subdivided into four groups: Groupe des Feijas externes (Arenigian-Llanvimian); Groupe du 1er Bani (Llandeilian); Groupe du Ktaoua (Caradocian-upper Ashgillian); Groupe du 2ème Bani (upper Ashgillian). The formations of the Silurian and Devonian are very limited, whereas the carboniferous sequence, composed by the sediments of the Groupe du Flysch du Jbel Tisdajine (Visean), prevails in the north-western sector of the Taroucht sheet (Jbel Tisdafine and Jbel Asdaf). From the tectonic point of view, the paleozoic sequence essentially records the traces of the hercynian orogeny. The deformational structures can be related to a fold and fault sys- tem. High angle faults show a complex polyphased kinematic evolution, whereas gentle folds develops along two main directions (N-S and E-W) and display sub-vertical axial planes. Systems of thrusts, associated with large scale folds, deform the carboniferous sequence of the jbels Tisdafine and Asdaf.