Discovery of late Tortonian incised valleys in the Saouaf Formation (northeastern Tunisia) - Evidence of high-frequency sea-level variations in the central Mediterranean

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During the late Miocene, the connection between the Atlantic Ocean and the Mediterranean Sea was progressively restricted. Despite many discoveries of Messinian incised valleys and canyons in the peri-Mediterranean basins, the Tortonian incised valleys are poorly described. The Tortonian series exposed in the northeastern end of the Cap Bon peninsula (northeastern Tunisia, central Mediterranean) provide an excellent example of complex and extensive incised valleys system traceable for up to 5 km (entire length of the outcrop). Detailed facies and sedimentological analysis permitted the recognition of five distinct phases of incision. These valleys (approximately 300 m wide and 10 m to 30 m deep) were incised during sea-level fall and were filled during subsequent sea-level rise. These valleys are characterized by the lack of fluvial deposits at their bases. During sea-level rise, these valleys were filled mainly with cross-bedded estuarine sandstone forming multistorey channels and point-bar deposits. Tidal sand flat deposits are locally well developed at the margins of the valleys fills. These tide-dominated estuarine deposits, corresponding to the transgressive systems tracts, are arranged into fining-upward retrogradationnal parasequences. The highstand systems tracts correspond to wave-dominated deltaic deposits comprising offshore, offshore-transition and shoreface deposits. These successions are typically arranged in thickening and coarsening-upward parasequences. The upper surfaces of the highstand systems tracts are incised by later valleys. The formation and the filling of these valleys record the complex interplay of different allocyclic factors: (1) tectonic uplift due to the major compressive Atlassic phase, (2) high-frequency sea-level variations, (3) warm and humid climate, and (4) high river sediment input. The results of this study provide important data, such as incised valleys geometries, dimension, extension and connectivity. The results of this study emphasis the potential link between high-frequency sea-level variation and progressive restriction of the Mediterranean during the late Tortonian.