Late Cenozoic evolution of the Ariege River valley (Pyrenees) constrained by cosmogenic 26Al/10Be and 10Be/21Ne dating of cave sediments

Despite increasing knowledge on the orogenic phases of the Pyrenees, the Neogene evolution of the range re-mains poorly constrained. The central Pyrenees, particularly the Ariege River valley and its terrace systems and glacial extensions, are key to reconstructing Pyrenean evolution during the Neogene. However, few terrace relics remain on the piedmont edges. To overcome this limitation and temporally extend the dataset obtained from terraces, we focus on alluvium-filled horizontal epiphreatic passages developed in limestone karstic networks. These landforms record the transient position of former local base levels during the process of valley deepening, similar to fluvial terraces. The alluvium fills of the studied caves in the Tarascon-sur-Ariege area, in the transition zone between the upper range and the piedmont, therefore enable the reconstruction of the geodynamic evolution of the Ariege River valley. All studied caves are developed on at least eight levels. Based on burial durations determined by Al-26/Be-10 and Be-10/Ne-21 terrestrial cosmogenic nuclide dating of samples from epiphreatic levels, our results indicate Langhian to Messinian (similar to 13-5 Ma) incision rates averaging 48 m Myr(-1). However, the obtained record does not allow us to accurately retrace the Pliocene evolution of the area due to the lack of known caves at corresponding levels. Moreover, raised local base levels during glacial phases both make the re-cord more complex and call into question the methodological approach in terms of potential internal sediment remobilization and mixing related to implied re-flooding periods. (c) 2020 Elsevier B.V. All rights reserved.