Upper Neogene climate change in northern Africa based on chemical weathering indices and clay mineralogy: a case study of southeastern Tunisia (Gulf of Gabès)

The Upper Neogene period is considered one of the most significant episodes of environmental shift in Mediterranean history, which has been recorded and documented in every region bordering this basin. In southeastern Tunisia, the Gulf of Gabes witnessed a wide span of climate change during this period. The main objective of the present study is to assess climatic variations, during the Neogene, in the form of a geochemical signature preserved in the siliciclastic facies of the lower part of the Segui formation and Ouedhref sands. Calculations of weathering proxies from chemical composition and detailed mineralogical study of these sediments revealed that the lower part of the Segui formation had been deposited in contrasted climatic conditions with a tendency to aridity which is proved by the low values of the Chemical Index of Alteration (CIA), the low degree of elements depletion calculated for each element separately and the abundance of smectites and illites. However, weathering proxies and kaolinite abundance in clay samples from Ouedhref deposits indicate high weathering intensity within a warm and humid climatic condition. The evidence of moisture during the deposition of Ouedhref sediments is also proven by sedimentary structures and the fossils collected from the field. The source area of these sediments could be from low Cretaceous siliciclastic sediments (Bouhedma and Sidi Aich formations), which outcrop largely in southwest Tunisia.