THE PERCHED PALEOSURFACES OF THE PYRENEES -CANTABRIAN BELT

Perched paleosurfaces of the Central and Eastern Pyrenees have beenfirst described by geomorphologists for a long time (Birot, 1937; Lagasquie, 1982; Calvet, 1996) and more recently by geologists (Bosch et al., 2015; Monod et al., 2015; Bosch, in progress). These studies areof peculiar interestsince they provide robust constraints forthe timing and mechanisms of relief creation in a collision belt. Pyrenean paleosurfaces have been recognized over large areas in the Axial Zone between the Aure valley to the West and the Cerdagne and Capcirgrabens to the East. The actual elevation of theses surfaces varies between 1000 and 2500 m above sea level. In Cerdagne, the graben filling has been dated ofVallesian age (Middle to Late Miocene). Based on thisconstraint,the entire Pyrenean perched paleosurfaceshave been considered of Miocene age.Since the palynofacies of the Vallesian sediments is interpreted as a near-sea level deposit, the present elevation of the paleosurfaces should have been acquired after the Vallesian assuming that all paleosurfaces have nearly a Miocene age. In the vicinity of Cerdagne and Capcirgrabens, the central Pyrenees paleosurface appears connected to the uppermost terraced paleosurface, suggesting an age prior to the Vallesian times. A common feature of the Pyrenean paleosurfaces is the preservation of thick lateritic weathering profiles. In the Eastern Pyrenees, the paleosurfacesdisplay a terraced pattern with three or more levels, the highest being likely the oldest. In the Central Pyrenees (from the Aston Massif to the East to the Neouvielle Massif to the West), Thesinglepaleosurfaceis apparently offset along numerous faults. Field work will be conducted in order to collect structural data allowing a detailed tectonic evolution to be reconstructed.