Sequence stratigraphy of the subsurface cambro-ordovician siliciclastic deposits in the Chotts basin, Southern Tunisia: Petroleum implications

Subsurface study of the Palaeozoic deposits in the Chotts basin, part of the southern Tunisian Atlassic foreland, revealed an incomplete Pre-Hercynian deformed sequence. The remaining truncated Cambro-Ordovician siliciclastic deposits appear to be unconformably overlain by transgressive Late Silurian – Early Devonian shales. Early Ordovician El Atchane sandstones and Hamra quartzite constitute currently the most oil and gas productive levels in the Chotts basin. The main issues encountered in the exploration of these reservoirs are related to their spatial distribution along with their thickness and facies variations. Sequence stratigraphic analysis and correlation of the entire Cambro-Ordovician section using sequence stratigraphic surfaces seems necessary to locate both proven and prospective reservoirs in order to predict their spatial distribution and trend directions in the region. Seismostratigraphic facies analysis of these deposits in subsurface highlights their sequence organizations. The integration of well data revealed in detail the sequence hierarchy of the Cambro-Ordovician deposits throughout the Chotts basin. •The Palaeozoic section in the Chotts basin reveals five depositional sequences.•Cambro-Ordovician progradational sandstones constitute good hydrocarbon reservoirs.•Syn & post-sedimentary tectonic activities control reservoir spatial distribution.•Shaling out of clean sands affect reservoir quality by prevalence of clayey deposits.•Remaining hydrocarbon potential would be found in deeply buried reservoirs, stratigraphic closures & pinchouts.