Mio-Pliocene

Eight stratigraphic sections, located in northeastern part of the Sahel area of Tunisia recorded evidences of " Lago-Mare " episode and events related to the Messinian-Late Pliocene interval. A comparison with previous studies carried on sections from neighboring areas and boreholes data drilled within the Gulf of Hammamet and the Gulf of Gab es, is conducted and gives useful information to characterize the Late Messinian to Late Pliocene events. The most notable feature distinguished in the studied area consists on the lack of gypsum, commonly recorded in relation with the crucial event of the Messinian Salinity Crisis. However, only lagoonal deposits, bearing messinian brackish fauna, are encountered. These sediments are usually attributed to the " Segui " formation or the so called " Mio-Pliocene continental ". Thin sections samples and field observations have recognized sands, marls, clays, lacustrine limestone, some gypsum lenses, mud-cracks, lignite and Messinian brackish fauna. Similar deposits were previously described in the Kechabta basin from the Northern Tunisia and in some wells from the Gulf of Gab es and the Gulf of Hammamet. We suggest that all these facies belong to the coeval of the " Lago-Mare " facies within Eastern and Western Mediterranean basins (e.g. Sicily, Mallorca, Libya and Cyprus). Finally, four major erosional surfaces have been recorded within the Late Messinian-Late Pliocene deposits, aged post-Tortonian, intra-Messinian, Late Messinian and intra-Pliocene times. They seem to be the result of local tectonic uplifts and eustatic fluctuations.

Six geological studied sections from the Ouled Maallah region (Dahra) allow the identification of lacustrine deposits, sandwiched between Messinian gypsum and Mio-Pliocene blue marls. The gypsum followed by white micritic limestones deposits is correlated with the "Terminal Carbonated Complex" subsequent to the coral platforms (Oran, Melilla, Sorbas). Correlated to the Lago Mare 1 episode, which is slightly older than 5.60 Ma, the lacustrine deposits tend to cover a large extension area, both on the southern margin of the Dahra and on the Beni Chougrane northern slopes. Subsequently, the early Messinian-Zanclean deposits fossilize the Messinian Erosional Surface and indicate the post-Messinian Crisis marine reflooding. They are characterized by two microfossiliferous successions: (i) the presence of Sphaeroidinellopsis subdehiscens, Globorotalia margaritae (foraminifers), Ceratolithus acutus, Reticulofenestra zancleana (calcareous nannofossils) indicating the latest Messinian to earliest Zanclean, followed by an association with (ii) G. puncticulata, G. bononiensis, G. aff. crassaformis and Helicosphaera sellii, Discoaster asymmetricus, and D. tamalis, indicating a late Zanclean age up to an early Piacenzian one. The regional correlations reveal large subsiding sedimentary depocentres built along the Chelif Valley. Likewise, the Mio-Pliocene sedimentation seals folded tectonics active during the latest Messinian, individualized by the tilted gypsum and Lago Mare deposits of Ouled Maallah. This deformation has resulted from gravity tectonics responsible for the "olistolite" made or reworked materials within the geological series located at the Chelif Valley and the Beni Chougrane Mounts. This testifies to a large-scale, compressive deformation that would correspond to a restructuring of paleogeographic spaces associated with the Tellian Massif uplifts.

The last overview of Cenozoic localities with records of freshwater gastropods was provided more than 80 years ago. Since then, a wealth of new information has been published: new localities have been discovered and fundamental changes occurred in regional stratigraphy. In addition, many localities are still attributed to erroneous or outdated stratigraphical concepts even in recent papers. Geopolitical evolution of Europe has, furthermore, led to name changes and confusion regarding the exact origin of samples in collections. Here we provide a fully georeferenced dataset for almost all published Miocene and Pliocene freshwater gastropod localities (2,930), including updated stratigraphic data where possible. This basic update will serve as an essential fundament for any future work related to the freshwater deposits and respective faunas in general.