Near Le Kef, Tunisia, Triassic gypsum and supratidal carbonates with subordinate terrigenous clastic rocks and metabasites (so-called ophites) form the highly deformed core of a northeast-southwest anticlinal structure. The competent enveloping strata, chiefly massive limestone and marlstone, range in age from Aptian-Albian to early Tertiary. The Triassic rocks are multiply deformed and so dismembered as to be best described as tectonic breccia. The Kef anticline, as well as numerous analogous features in the northern Tunisian Atlas, commonly has been interpreted as a diapiric structure emplaced into the younger cover rocks during the early deformation phases of the Alpine orogeny (i.e., Late Cretaceous to Paleogene) and partly reactivated during the Neogene (late Alpine) Our detailed mapping and structural analysis of the Kef structure suggest modifications of this model involving the following major elements: (1) local or regional unconformity between Triassic and Cretaceous strata, (2) regional decollement gliding in part localized within the Triassic evaporite-rich sequence, and (3) late-phase box folding of both the highly deformed Triassic assemblage and the more competent cover rocks.

The unconformity between Triassic and Cretaceous rocks is preserved only locally, for late brittle faulting along the margins of the anticline and local bedding-plane thrusts between the competent cover and the incompetent core are common. However, where well-preserved, a distinctive bedded sedimentary carbonate breccia overlies the Triassic assemblage. This sedimentary breccia is in turn conformably overlain by Aptian-age rocks and, thereby, indicates major pre-Aptian uplift and erosion prior to the main phase of deformation in the Tunisian Atlas. The nature of this uplift is problematic, but pre-Aptian diapirism is a viable hypothesis. According to this model, diapirism was restricted to pre-Aptian time, whereas compressive buckling and associated lateral shortening are Neogene defo mation mechanisms superimposed on earlier halokinesis.

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