Triassic salt in the High Atlas of Morocco

Chellai El Hassane (Morocco), Ghanmi Mohamed (Tunisia) and Doblaas Miguel (Spain) The Triassic terrestrial deposits at the northern edge of the High Atlas near Marrakech are mainly represented by thick sequences of massively layered, red sandstone. These are topped by a formation of silt and pink-brown clay containing large deposits of evaporites consisting mainly of rock salt and gypsum. The silt and clay formations form domed structures characterised by intruded gypsum and irregular (disharmonic) folds capped by fine sandstone beds, as well as by small, isolated anticlines only a few metres in scale. The direction of folding shows no relationship to that of the major tectonic folding that gave rise to the Atlas Mountains. In contrast, the folding is closely linked to the deposition of rock salt and gypsum in the High Atlas near Marrakech during the Late Triassic. The same phenomenon is observed in the passive margins of the Atlantic of western Morocco. Lithostratigraphy These Triassic formations are the most prominent features of the landscape, with thicknesses that can reach up to 400m. They consist essentially of two formations: F5 (the Oukaïmeden sandstone) and F6 (the Superiors Silts), which correspond to the uppermost part of the Triassic, as defined in the Ourika valley by Biron (1982). The first formation consists of thick (400m) beds of detrital sandstones with fine to medium-sized, diamond-shaped sedimentary bodies, interbedded with layers (a few centimetres to several metres thick) composed of red clay as well as red and brown silts. These are overlain by … Read More

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