The Jurassic Of The Jebel Ressas (Tunisia). Identification Of The Upper Sinemurian In The Zaghouan Formation. Stratigraphic Et Paleobiogeographic Precisions On The Tunisian Sinemurian

The revision of the Jurassic lithostratigraphic succession of Jebel Ressas Jurassic (Tunisian Dorsal, Tunisia) allows us to identify all the formations already defined in the Tunisian Dorsal. The Zaghouan Formation is newly dated by Upper Sinemurian ammonites belonging to the Obtusum (Stellare subchronozone) and Raricostatum (Raricostatum Subchronozone) chronozones. Six Ammonitina taxa belonging to the genera Asteroceras (A. gr. saltriense (Parona, 1896), A. cf. meridionalis Dommergues, Meister & Mettraux, 1990), Arnioceras (A. gr. ceratitoides (Quenstedt, 1849) - rejectum Fucini, 1902), Epophioceras (E. cf. landrioti (d'Orbigny, 1850)) et Paltechioceras (P. bavaricum (Bose, 1894), P. cf. charpentieri (Schafhault, 1847)) are described and illustrated. These ammonites make it possible to correlate the "Zaghouan Formation" with the "Condensed levels of the top of the Oust Formation", already well known for their rich sinemurian ammonitofauna and whose ages are here reevaluated. The palaeobiogeographic affinities of the Sinemurian ammonites of Tunisia are discussed.