Petrographic and Geochemical Particularities of the NE Algerian Salt Domes and Associated “Cap-Rocks”

Salt domes are diapiric structures associated with various hydrocarbon and mineral resources (i.e., oil and gas, Pb–Zn deposits, halite and native sulphur). Surface and subsurface (boreholes and geophysical) data on the salt structures of the Tebessa region in the Northeast of Algeria allowed us to approach the anatomy of these structures and study the petrographic and geochemical characteristics of these evaporitic rocks. The salt stock consists of grey or red halite containing anhydrite, magnesite, and dolomicrite constituting an insoluble residue and up to 20% of the volume of the rock. It is often surmounted by a “cap-rock” made up of a brecciated anhydritic zone of about twenty metres thick and a gypsiferous zone also brecciated with a thickness of up to a hundred metres. The calcitic zone, often present in the American cap-rocks of the Gul-Coast, has not been observed in this region of north-eastern Algeria. The geochemical data made it possible to highlight the particularities of these Triassic evaporite rocks and underline the similarities and the differences with the Tunisian and American domes. The calcite zone as well as the Pb–Zn mineralization, generally linked to the American cap-rocks, were not observed. This difference could be due to the absence of hydrocarbons necessary for their genesis.