Modelling of the erosion in the Rhone valley during the Messinian crisis (France)

摘要

A geometric reconstruction of the present day Messinian Rhone valley shows two slope breaks. After taking into account the post-Messinian tectonics and Messinian isostatic compensation due to deep valley incision and Mediterranean Sea unloading, these two slope breaks were still visible on the reconstructed original Messinian Rhone profile. One is located on the Cevennes fault system and the other one is downstream of St-Marie. The slope of the ante-Messinian profile was approximately 0.05%. The Messinian Rhone profile was simulated using a numerical erosional model based on mass conservation. The Messinian profile cannot be explained only by variations of erosional processes such as lithology or changes in discharge, and one has to consider that the Messinian crisis happened in two phases. The profile of the Rhone was in steady state just after the first Messinian phase of lowering. The amplitude of the sea level lowering is around 600 m for the first phase, whereas the amplitude of the second one is 1300-1700 m. The isostatic deformation during the Messinian crisis due to bedrock erosion and sea unloading produced important changes in the Mediterranean dynamic.