Upper Cretaceous (Coniacian-Campanian) lithostratigraphy on the Saharan platform, Dahar Plateau, southern Tunisia

Abstract

Four measured sections along the northern escarpment of the Dahar Plateau in southern Tunisia provide details of Cretaceous (Coniacian-Campanian) stratigraphy in this region of North Africa. These sections reveal various units of limestone with cross-stratification, limestone with in situ rudists, mud-supported limestone (carbonate mudstone, wackestone), argillaceous limestone, and limestone with stromatolites. These units are arranged vertically into several sequences of finer-grained limestone (mud-supported limestone, argillaceous limestone) overlain by coarser-grained limestone (limestone with cross-stratification, rudists, and/or stromatolites). Each sequence is interpreted as a shallowing upwards progression on a carbonate platform. Furthermore, cross-strqtified carbonate and beds with in situ rudists are more common in the lower parts of the measured sections, whereas units with stromatolites, argillaceous limestone, and finer-grained limestone are more common in the upper parts of the measured sections. The overall transition from the coarser-grained (higher energy) strata to the overlying finer-grained (lower energy) argillaceous strata is interpreted as having been caused by a relative fall in sea level that brought argillaceous sediment into the area. It is possible that the arrival of argillaceous sediments and the relative fall in sea level may have caused the demise of the rudist reefs. The lower interval (in which cross-stratified carbonates and in situ rudists are more common) is assigned to the Berressef Formation, whereas the upper interval (in which stromatolites, argillaceous limestone, and other fine-grained strata are more common) is assigned to the Toual Formation. Previous work suggests that the Berressef Formation is of Coniacian? to Santonian age, whereas the Toual Formation is of Campanian age. A regional cross section correlates these Cretaceous units on the Dahar Plateau with (1) rudist-bearing strata that are mapped in north–central Tunisia as the Merfeg Formation, and (2) argillaceous and marly limestone that is mapped in central Tunisia as the middle and lower Berda Formation and the middle Abiod Formation.