The Numidian flysch complex of Oligocene-Miocene age forms the highest structural unit in the Mahgreb orogenic belt of north Africa. In the western Mogod Mountains the Numidian complex lies on limestone and calcareous shale of the Tellian shelf sequence. Structural evidence clearly indicates a detachment zone between the Numidian complex and Tellian sequence that commonly is marked by the presence of Triassic cargneule. Paleontologically established age ranges for the two sequences do not overlap, and the superposition of the two sequences is younger over older thus making the significance of the contact controversial.

New evidence suggests that the Numidian complex is allochthonous and has been thrust to the southeast a minimum of 15 km. Paleodepth data indicate shallowing in the Tellian sequence from depths greater than 1 km in Cretaceous rocks to less than 200 m in middle and upper Eocene rocks. The Numidian complex is interpreted as a deep-sea-fan complex deposited in water more than 2 km deep as indicated by the presence of the isobathyal foram Melonis pompilioidies. Additionally, a newly discovered sequence of glauconitic sandstone and conglomerate depositionally overlies upper Eocene rocks of the Tellian sequence, and may be a time equivalent of the older part of the Numidian complex. These data suggest that the Numidian complex was detached from its substratum in a continental-rise setting, nd was thrust southeastward over the Tellian shelf sequence. Thrusting of continental-rise sequences over continental-shelf sequences is a common but difficult to explain feature within orogenic belts. In the Mogod Mountains, timing and mechanism of emplacement of the Numidian allochthon can be explained by the collision of the Sardinian continental fragment with the North African continental margin during middle Miocene time.

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