The Lower and Middle Jurassic of Northern Tunisia; correlations with the North-South axis and palaeogeography

Ammonites recently collected in Northern Tunisia specify precisely or modif y the age of the Lower and Middle Jurassic formations, and allow correlatio ns with Central Tunisia. The palaeogeographical reconstruction leads to dis tinguish 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 includi ng tectogenetic breccias; 3) a trough filled up with pelagic sediments incl uding radiolaritic beds since late Bajocian-? Bathonian time (Tunisian trou gh). 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 as sociated to the Tethyan rifting.