At present, the Pyrenees do not have the characteristic relief of a chain whose orogenic paroxysm took place more than 40 Ma ago. The chain is characterized by deep rivers, showing a resumption of erosion with a topography that preserves in some places relics of low relief surfaces. This renewed incision is estimated at 15 Ma in the east of the chain (perched cave ages), while thermochronological data show a cooling around 10 Ma in the southeast and center of the chain. In the post-orogenic phase, flexural rebound should favor erosion of the foreland basin (e.g. Tucker and van der Beek, 2013), yet sedimentation in the northern Pyrenean basin has persisted for more than 20Ma. Some authors propose that the Pyrenees were flattened to near base level ~10Ma ago, while others propose that incision of the Ebro Basin to the south is responsible for this reactivation of relief. Some other models suggest that the present relief is a flexural response to erosion and normal faults, while others suggest that delamination of the eclogitic root of the chain caused this rebound. The recent evidence of deep dense bodies seems to contradict these mechanisms. The role of tectonics is also poorly constrained. In short, the dynamics of the relief of the Pyrenees and its basins after ~10Ma (+/5) remains a mystery: is it the result of climatic or tectonic change?
To answer this question, we will establish a state of the chain ~10Ma ago. To do so, we will 1- date the burial of the Mio-Pliocene sediments and reconstruct the denudation paleo-stones using cosmogenic isotopes, 2- analyze the weathering proxies (climate) of these sediments, 3- reconstruct the periods of sedimentation and by-pass from onshore data and compare them to existing reconstructions in the Gulf of Aquitaine, 4- compile and revisit the role of faults 5- reassess the tectonic role of the Mediterranean opening, 6- characterize the alteration profiles of perched surfaces and date them with secondary minerals, 7- model the joint evolution of the relief and the southern and northern basins to test different climatic and tectonic scenarios, and finally 8- integrate the evolution of the southern Massif Central as a northern boundary condition of the chain and its basin (pilot project of the Relief LOA GROUP).