At Kef Touareg, one can observe the most complete and representative Triassic series at the foot of the Jebel Rehach cliff (type section). It features three main facies:
The Sandy Triassic, at the base, is represented by a thick 900-meter series, essentially consisting of sandstones with fossil wood and red clays with some Myophoria-bearing carbonate levels. These indicate a coastal depositional environment and allow for a Lower to Middle Triassic age (Scythian to Ladinian) for this series. Of these 900 meters, only the uppermost part, known as the Kirchaou formation, outcrops. This formation begins the Mesozoic outcrops of the Saharan platform and constitutes the substrate for the Erg el Makhzen sebkha and the Smar plain as far as the right bank of Wadi Fessi.
Paleogeography and Paleo-environment:
At the end of the Permian and in the Lower Triassic, the retreat of the sea left vast emerged lands bordering the rift which, thanks to favorable humid climatic conditions, were covered by significant fluvio-deltaic plains. The deposits of these marginal-littoral environments materialize the "Sandy Triassic" and correspond to the red sandstones and clays that begin the Mesozoic series of the Saharan platform. They mark the base of geological outcrops from the Paleozoic range near Medenine in the north to the reliefs of Jebel Sidi Toui in the El Ouara plain in the south.
The Carbonate Triassic, in the middle, includes two fossiliferous carbonate bars containing the first ammonites of the Tethys (Ceratites), nautili, Myophoria (Triassic fossil bivalves), and numerous other bivalve and gastropod mollusks. Alongside this rich invertebrate fauna, vertebrate remains of Nothosaurs and Placodonts—giant marine reptiles of the Triassic Tethys—have been discovered. Thanks to this marine fauna, the backbone of the Jebel Rehach plateau is attributed to Carnian carbonates (base of the Upper Triassic).
Paleogeography and Paleo-environments: The two carbonate bars overlying the red sandstones and clays and forming the backbone of the vast Jebel Rehach plateau materialize the first marine transgression of the Mesozoic. The bone debris of giant marine reptiles, the primitive Ceratite-type ammonites, nautili, and other mollusks indicate the establishment of a sufficiently large and deep sea to produce this biodiversity and give rise to an important carbonate platform.
The Evaporitic Triassic, at the top, represents the Upper Triassic (Norian to Rhaetian) and constitutes the base of a very thick gypsiferous series covering a wide plain extending about twenty kilometers between the Jebel Rehach and Jebel Grimissa plateaus. This materializes the establishment of vast sebkha systems occupying the coastal strip between Tethys waters and the arid lands of the Saharan platform.
Paleogeography and Paleo-environment:
The second major biodiversity crisis in Earth's history occurred at the Triassic-Jurassic boundary (205 Ma), leading to the formation of immense coastal sebkhas. This was likely due to extreme climatic conditions. This hypothesis is supported by the presence in the El Ouara plain of a powerful evaporitic series marking the Upper Triassic and the beginning of Jurassic times, covering about 50 million years. During this period, the northern edge of the Saharan platform became a gigantic salt-making machine. These are thick layers of gypsum outcropping in the Bhir and Mestaoua plains, deposited in immense coastal sebkhas covering hundreds of thousands of square kilometers. These gypsum layers show several carbonate intercalations testifying to brief marine transgressions that fed water to the sebkhas. The Messaoudi Formation dolomites (Norian), the Zarzour dolomites (Rhaetian), and the Zmitet Haber limestones (Pliensbachian) are sedimentary records of these transgressions.
