Le jurassique inférieur et moyen de la Tunisie septentrionale; corrélations avec l'axe Nord-Sud et paléogéographie

Abstract

Ammonites recently collected in Northern Tunisia specify precisely or modify the age of the Lower and Middle Jurassic formations, and allow correlations with Central Tunisia. The palaeogeographical reconstruction leads to distinguish from South to North: 1) two pelagic shoals (N-S Axis and Tunisian Dorsale) with reduced and incomplete sedimentation separated by a subsiding basin (El Haouareb Graben); 2) a slope zone situated towards the North of the Dorsale (Bou Garnine de Hammam Lif area) with pelagic sediments including tectogenetic brecias; 3) a trough filled up with pelagic sediments including radiolaritic beds since late Bajocian-? Bathonian time (Tunisian trough). Middle Jurassic sedimentary record of the N-S Axis and the Dorsale is characterized by major unconformities with important hiatuses. These later are related both to global eustatic changes and local tectonic movements associated to the Tethyan rifting.