The Lower Ardèche River Karst Landscapes and Caves (Lower Rhône Valley): Unique Morphologies Induced by the Messinian Salinity Crisis
Résumé
The lower Ardèche and Cèze valleys are famous for their touristic sites. Besides their dramatic karstic landscapes such as the natural arch of the Pont d'Arc or the deep canyon of the Ardèche River, they conceal prehistoric caves among which the famous Chauvet Cave discovered in 1994. These landscapes of high plateaus, canyons, and caves were formed by a catastrophic geologic event, the Messinian Salinity Crisis (MSC), which affected the entire Mediterranean Basin and the morphological evolution of the surrounding mountains and plateaus. More specifically, the Saint-Remèze Plateau displays some good evidences to demonstrate that the Mediterranean Sea was completely desiccated. The MSC was also responsible for the downcutting of the Ardèche and Rhône canyons in less than 100,000 years. This evolution was followed by the formation of deep karst drainages. The MSC ended by a sudden reflooding of the basin, characterized by a rapid rise of the Mediterranean base level responsible for large river aggradations. It also provoked the development of a per ascensum karst adaptation characterized by (1) large galleries in the Saint-Marcel and Chauvet caves and (2) huge chambers in the Aven d'Orgnac Cave. Nowadays, more than one million tourists visit the area every year, attracted by its natural biotopes and sites, by its caves like Saint-Marcel and Aven d'Orgnac. In the future, the Chauvet Cave, where the oldest paintings in the World were found, will hopefully be nominated as a UNESCO World Heritage.