Coupling cosmogenic dating and magnetostratigraphy to constrain the chronological evolution of peri-Mediterranean karsts during the Messinian and the Pliocene: Example of Ardèche Valley, Southern France

The Ardèche River entrenches a deep canyon in the Saint Remèze plateau from Vallon-Pont-dʹArc to its confluence with the Rhône. This plateau is part of the Ardèche Cretaceous limestone plateau located at the edge of the Mid Rhône valley. It is characterized by dense multi-level cave systems, such as Saint-Marcel Cave (50 km of mapped passages) and Chauvet Cave, famous for its paleolithic paintings. Until now, and despite the absence of absolute dating, stepping of the Saint Remèze cave levels has been interpreted as the result of the Messinian salinity crisis. To clarify this interpretation, fluvial sediments of cave systems have been absolutely dated, while cave sediments have been demonstrated to be ideal for “burial dating” based on the different radioactive decay rates of the in situ-produced cosmogenic nuclides 10Be and 26Al. Combined with magnetostratigraphy and constrained by the Lower Ardèche base-level curve, this contribution provides an absolute dating for each cave level. The obtained results are consistent with the stepping per ascensum model of both surface landforms and caves for the Messinian–Pliocene eustatic cycle. Finally, this study provides evidence for a rise of the Ardèche river level to 40 m above the Pliocene abandonment surface. The second active period of the Chauvet Cave is evidenced between 2.96 and 2.18 Ma (cave filling). An absolute dating for the Pliocene abandonment surface between 1.94 and 1.77 Ma is also obtained, which brings new understandings to the geodynamic evolution of the area. The Lower Ardèche has been uplifted after the Pliocene, with a rate of 0.03 mm/year since 1.77 Ma.