Origin of the high elevated Pyrenean peneplain

Peneplanation of mountain ranges is generally considered the result of long-term erosional processes that smooth relief and lower elevation near sea level. Therefore peneplain remnants at high elevation in mountain ranges are used to infer posttectonic surface uplift. Such an interpretation has been proposed for the Pyrenees where high-elevation, low-relief erosional surfaces rose up to more than 2000 m. Because the Pyrenean foreland basins are filled with very thick continental deposits, which have buried the early jagged landscape, we challenge this hypothesis by pointing out that relief applanation does not necessarily require elevation lowering. We propose an alternative interpretation in which piedmont aggradation of detrital sediment that comes from erosion of the high chain induces the rise of the base level of the range, therefore reducing strongly the erosive efficiency of the drainage system and resulting in the progressive smoothing of the relief. Such a process allows a high-elevation, low-relief erosional surface to develop at the scale of the range. In the Pyrenees, occurrence of high-elevation, low-relief erosional surface remnants does not imply a posttectonic uplift, but is instead due to the dissection of the initial Miocene high-elevation, low-relief surface by the recent drainage system, the erosive activity of which has been enhanced by global climate change from the late Pliocene onward