Stratigraphie sequentielle et evolution geodnamique du Lias (Sinemurien terminal-Toarcien moyen) de l'Atlas de Beni-Mellal (Haut Atlas central, Maroc)

Universite Chouaib Doukkali, Departement de Geologie, El Jadida, Morocco

Biostratigraphical and sedimentological studies carried out in the Beni-Mellal Atlas lead to a sequence stratigraphy subdivision of the Liassic record (Uppermost Sinemurian-Mid Toarcian) into 9 third order sequences. These sequences are involved in two second order cycles which tectonically enhanced unconformities are located in the upper part of the lower Domerian boundary and the lower part of the mid Toarcian. The third order sequence organization shows similarities with the local or regional examples. Specific evolution seem to be related to autocyclic processes within the sedimentary supply or to correlation problems between the platform and basin formations. The second order cycles involve a real influence of local tectonic motions. So, the transgressive Uppermost Domerian-Lower Toarcian stage, far from indicating a northward extension of the sedimentary realm towards the Beni-Mellal platform, shows an "in situ" filling up of the southern Tilougguit trough, created during the preceeding transtension Mid-Upper Domerian structuration through transtension phase. The accommodation changes related to the associated eustatic and tectonic influences induce deep modifications in the trough faunic associations (ammonites), specially during the Pliensbachian period.

This record provided courtesy of AGI/GeoRef.