The effect of river dynamics induced by the Messinian Salinity Crisis on karst landscape and caves: Example of the Lower Ardeche river (mid Rhone valley) - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Geomorphology Année : 2009

The effect of river dynamics induced by the Messinian Salinity Crisis on karst landscape and caves: Example of the Lower Ardeche river (mid Rhone valley)

Ludovic Mocochain
  • Fonction : Auteur
Philippe Audra
  • Fonction : Auteur
Georges Clauzon
  • Fonction : Auteur
Jean-Yves Bigot
  • Fonction : Auteur
Olivier Parize
  • Fonction : Auteur
Philippe Monteil
  • Fonction : Auteur

Résumé

The karstic canyon of Lower Ardehe is located in the Middle Rhone valley, which is directly tributary to the Mediterranean Sea. The Rhone River is emblematic of the Messinian Salinity Crisis (MSC) impact on landscape morphology. Along the edge of the Saint-Remeze Plateau, the Rhone valley displays four benchmark levels generated by the MSC: the Pre-evaporitic abandonment surface (11), the Messinian erosional surface (2), the Marine/non-marine surface of the Pliocene ria (3) and the Pliocene abandonment surface (4) The study of these benchmark levels allows us to reconstruct the evolution of the regional base level over the last 6 Ma. We obtain a curve for base-level evolution that provides a geodynamic reference. Which is used to investigate the morphogenesis of the Sant-Remeze karstic plateau. The Ardeche River downcuts the Saint-Remeze Plateau in a deep canyon, from Vallon-Pont-d'Arc to the West, to its confluence with the Rhone to the East. Several abandoned valleys are present along the western edge of the Saint-Remeze Plateau at the inlet of the Ardeche canyon. In these abandoned valleys, the fluvial deposits are related to several periods, from the Pliocene onwards. They Provide important insights into the fluvial dynamics: a 160 m-thick aggradation sequence infilled the Ardeche canyon during the Pliocene. This aggrading river caused the first lateral shifting, as an aggradation epigenesis. This first infilling shows that the Ardeche canyon already existed before the Pliocene. Secondly, it has been demonstrated that the Ardeche Canyon is downcut into the Pre-evaporitic surface of the Saint-Remeze Plateau, dated to 5.45 Ma [Martini, J., 2005. Etude des paleokarsts des environs de Saint-Remeze (Ardeche, France): mise en evidence d'une riviere souterraine fossilisee durant la crise de salinity messinienne. Karstologia 45-46, 1-18]. Consequently, the canyon downcutting is entirely due to the MSC, and occurred during a time span of only 100 000 years. Based on these observations, it is possible to elucidate the curve of the regional base-level evolution. Hence, we are able to propose a new interpretation of the geomorphological evolution of the Saint-Remeze karstic plateau and its cave levels for the last 6 Ma. The cave levels Consist in underground short-cuts of the surface meanders. They mainly developed during the Pliocene aggradation cycle. The Chauvet Cave, famous for its Palaeolithic paintings, corresponds to one of these underground short-cuts. The aggradation period ends at the end of the Pliocene with long hi.-h-level riverbed stability. It favours the development of large low gradient surfaces as pediments. The complete Messinian-Pliocene eustatic cycle is responsible for the downcutting of the Ardeche canyon and its infilling during the Pliocene. Consequently, karst developed according to the base-level oscillations, as low gradient Surfaces and as cave levels. For the Study of the pen-Mediterranean caves and karst areas, we propose to apply the Lower Ardeche valley evolution model, based on the base-level oscillations during and after the MSC. (C) 2008 Elsevier B.V. All rights reserved.

Domaines

Tectonique

Dates et versions

hal-01882025 , version 1 (26-09-2018)

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Citer

Ludovic Mocochain, Philippe Audra, Georges Clauzon, Olivier Bellier, Jean-Yves Bigot, et al.. The effect of river dynamics induced by the Messinian Salinity Crisis on karst landscape and caves: Example of the Lower Ardeche river (mid Rhone valley). Geomorphology, 2009, 106 (1-2), pp.46-61. ⟨10.1016/j.geomorph.2008.09.021⟩. ⟨hal-01882025⟩
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