Sedimentologic Studies in Jurassic of Tunisia: ABSTRACT

Abstract

Modern sedimentologic interpretation of the Tunisian Jurassic is based on excellent field studies by Tunisian and French geologists from 1955 to 1972. Jurassic facies north to south across Tunisia were formed where the African craton sloped into the southern edge of the Tethyan Sea and to the south in a restricted marine and evaporitic basin on the African shield itself. Thickness of the system varies abruptly off banks and into starved basins between 300 and 1,000 m. The Lias of central Tunisia forms a broad and typical carbonate platform separating the pelagic facies of the north from the major interior evaporite basin. A great north-south escarpment through southern Tunisia beautifully exposes these evenly bedded, restricted marine carbonate rocks and gypsum. Through the Middle and Late Jurassic the northern starved basin and slope facies (respectively radiolarian shales and Ammonitico Rosso) expanded into central Tunisia. Carbonate banks and patch reefs developed along the north-south axis west of the Sahel and its extension in the Jurassic ranges from Zaghouan to Bou Kornine uplifts. These probably rimmed the western margin of an ancestral Pelagian block. Bathonian slope deposits here consist of debris flows near Tunis, and the Kimmeridgian of Jebel Zaghouan shows a local reefy facies grading abruptly into turbidites and pelagic limestones to the north and west. These abruptly changing facies indicate a moderately unstable (rifting?) margin with intermittent reef growth. The Bathonian debris flows record a tectonic pulse which can be correlated with marked changes in thickening and elimination of strata along the Tebaga-Djeffara lineament, an important structural feature separating the southern evaporite basin from the northern unstable platform and basinal area. End_of_Article - Last_Page 553------------