Timing and geomorphological impact of Quaternary glaciations in the Eastern Pyrenees

This work aims to quantify the impact of glacial erosion on mountain landscapes in the mid latitudes. How reliably can the often high glacier erosion rates measured in the present be extrapolated to the entire Quaternary period, typically leading to the conclusion that glacial erosion has been the main driver of landscape evolution? How much evidence is there to support the alternative view that many Cenozoic landforms have survived Quaternary glaciation, thus pointing instead to the relative modesty of the glacial imprint? Because of sharp contrasts in the spatial distribution of glacial landforms across the Eastern Pyrenees, this region was chosen as the main study area for testing the two perceptions of glaciated landscape evolution outlined above.The approach begins by addressing the chronology and palaeogeography of Quaternary glaciation across the study area. Detailed geomorphological mapping first allowed to establish the extent of former ice fields. The production and interpretation of 81 in situ-produced 10Be ages has further assisted in capturing the chronology of the Würmian cycle in the Pyrenees. These results nourish an extensive discussion on ice recession chronologies within and between mid-latitude mountain ranges, and hence on the response of mountain glaciation to global change. This discussion leads on to the second major topic of the study, which involves quantifying the spatial variability of glacial erosion during successive stages of the Würmian cycle. Results based on cosmogenic nuclides and on systematic estimates of mapped glacial and paraglacial deposit thicknesses indicate that mean Würmian erosion depths on the southern part of the Carlit ice field did not exceed 5 m. A systematic attempt is also made to analyse the spatial variability of Quaternary glacial erosion in terms of cirque morphometry across the entire study area.