Cretaceous–Palaeogene sedimentation patterns and structural evolution of the Tunisian shelf, offshore the Pelagian Islands (Central Mediterranean)

Abstract

The Late Jurassic–Palaeogene structural evolution of the eastern Tunisian platform exerted a significant control on the depositional architecture of the 4.5-km-thick carbonate-marl succession, that was deposited on this African plate margin, throughout this period. Widespread Jurassic platform carbonates (Nara Fm.) underwent extension and subsidence throughout the Early Cretaceous. This extension resulted in the formation of a system of NW–SE-trending normal faults, coupled with minor antithetic structures, flanking half grabens up to 20 km wide. These subsiding basins hosted the deposition of shallow-water carbonates interfingered with marls and fine-grained siliciclastics. This succession, which is up to 2.5 km thick, is interpreted to have been deposited during a syn-rift episode which continued until the mid-Aptian. Overlying basinal marls and carbonates seal the NW–SE syn-rift extensional faults, thus marking a post-rift stage that extends up to the Eocene. Post-rift sedimentation ends in the Middle–Upper Eocene with the deposition of platform carbonates relating to the Halk el Menzel Formation, which lies unconformably above different stratigraphic levels of the underlying basinal carbonates. This is capped by an erosional surface of regional extent. From the latest Cretaceous onwards, compressional activity occurred on this part of the Pelagian Block partially reactivating Lower Cretaceous extensional structures. Thrusting and folding generated uplift and associated erosion, leading to the development of local unconformities and hiatuses at different levels in the stratigraphic column. This compressional event marks the onset of convergence between the African and European plates and thus the transition from a passive margin to a foreland in this area. The structural history of this part of the African plate margin displays similar evolutionary trends to other Tethyan passive margins which were established during the Jurassic and Early Cretaceous times when extensional events split pre-existing carbonate platforms.