Recent overdeepening of the middle Ouvèze riverbed (SE France) provides new data about the Pliocene infilling of the middle Rhône valley ria network

Abstract

Over 3.5 km south of Roaix village, the middle Ouvèze riverbed has undergone an incision of 5-9 m into its substratum since 1995. The local nesting of the river and erosion of its banks reveals a more complex geometry of exposed Pliocene deposits than previously recognised. The Pliocene stratigraphic succession includes, at the base of the classical Blue Marls, a prograding-aggrading stack of more or less nested, sigmoidal sandstone-marlstone cycles, each comprising an erosive sandstone wedge followed by a draping aggrading marlstone. Sedimentary features suggest that the main depositional mechanism for sandstone was high-velocity hyperpycnal bottom currents linked to river floods updip. These findings are presented in the context of the ria network of the Middle Rhône valley, including mostly unpublished data from the Andra (French Agency for Nuclear Waste Disposal) exploratory works in the lower Cèze valley in the 1990s. The combined data fail to support the idea of a so-called ”Zanclean Deluge” during the reflooding of the Mediterranean basin after the Messinian salinity crisis.