Rifting and late extension of a cratonic margin during the Paleozoic: Tectono-stratigraphic evolution from the Anti-Atlas belt (Morocco)

Abstract

During the Early to Late Paleozoic time, several extensional tectonic events occurred in the eastern Anti-Atlas Belt along the northern margin of the West African Craton. In this paper, and based on lithostratigraphic and structural analysis, we evaluate the effect of the Variscan pre-orogenic events on the Paleozoic tectono-stratigraphic pattern in the Saghro-Ougnat junction zone (Eastern Anti-Atlas belt). The first Paleozoic event that occurred in the region corresponds to the regionally known Cambrian, rifting which involved a system of NE-to ESE normal faults mostly inherited from the Pan-African/Cadomian orogenic phases. The fragmentation of the metacratonic basement in a system of tilted blocks controlled the deposition of the Cambrian epicontinental sedimentary formations associated with alkaline volcanism (e.g., Taiert and J. Smile Ahbari). Criteria such as normal paleo-faults, slump folds, and synsedimentary breccias provide evidence for syn-rift sedimentation. The opening regime remained active until the Devonian period with a dual NW-SE and NE-SW direction. By this time, synsedimentary tectonics and SSE-block tilting had largely controlled abrupt thickness variations associated with a series of progressive unconformities. Detrital deltaic sediments characterize the observed Carboniferous outcrops, together with normal and strike-slip faults, indicating NW-SE extensional tectonic instability.

Thus, Paleozoic structural evolution prior to the Variscan orogeny played an important role in the lateral thickness and facies variation documented here at the Saghro-Ougnat junction along the northern fringe of the West African Craton.