The geology of Tunisia is defined by the tectonics of North Africa, with large highlands like the Atlas Mountains as well as basins such as the Tunisian Trough.
Southwest of Jebel Zaghouan, Jurassic strata are for the most part limestones, while to the north and south dolomite sequences shift into Late Cretaceous argillites.
Several thousand meters of clay from the Cretaceous fill the Tunisian Trough, laden with ammonite fossils and calpionellids, an extinct species of single celled organisms, as well as sand and calcareous deposits.
The Boudinar Formation comprises fluvial sandstones with poor sorting and the Gafsa Group contains clay, sand and carbonation sequences.
As in other places in Africa, southern Tunisia's Early Cretaceous rocks are part of the Continental Intercalation—which sometimes hold dinosaur bones.
The Fortuna Formation in the Cap Bon area records the Oligocene with sandy limestone and marls, overlain by coarse sandstones and quartz pebbles, although it fades out in southern Tunisia.