Carboniferous stratigraphy and depositional environments in the Ahnet Mouydir area (Algerian Sahara)

An up to 3,000-m-thick pile of Carboniferous rocks covers the northern fringe of the Precambrian Hoggar Massif (Touareg Shield) in southern Algeria, thus terminating the depositional history of the Palaeozoic in this sector of the North African Craton. The previous Devonian (Eifelian to Frasnian) palaeogeographic configuration of the area, characterized by ridges and shallow basins, is leveled by a widespread Famennian playa and lower Tournaisian delta sedimentation on a largely undifferentiated shelf. Tournaisian to Moscovian strata were deposited under open-marine, deltaic, shallow-subtidal, fluvial, and continental environments. The Carboniferous sequence can be subdivided into 12, largely interfingering, lithostratigraphic formations, which were dated by conodonts, ammonoids, foraminifers, and brachiopods, yielding a modified biostratigraphic framework of the area. The formations are stacked in four transgressive-regressive cycles, which include two major gaps, one during the middle Tournaisian, the other during the middle Visean to Serpukhovian. The oscillations of sea level can be traced into neighboring areas and seem coeval to early pulses of the Late Carboniferous/Early Permian glaciation of Gondwana. To a lesser degree they may reflect more local tectonic effects of the Variscan orogeny.