Last glacial fluctuations in the southwestern Massif Central, Aubrac (France): first direct chronology from cosmogenic 10 Be and 26 Al exposure dating

International audienceThe chronology of the late Pleistocene glaciation in the Massif Central, France, is not well documented and there are divergent hypotheses regarding the timing of glacial events in this area. This study aims at reconstructing the chronology of late Pleistocene glacier fluctuations in the Aubrac massif. We present a new set of Be-10 and Al-26 exposure ages from twenty erratic boulders embedded in six glacial landforms. Glacial landforms were sampled to determine the timing of three glacial stades and the deglaciation of the Aubrac Mountains. These new data allowed us to constrain the timing of: (i) the Local Last Glacial Maximum, which is coeval to the early part of Marine Isotopic Stage 2 (MIS 2) (28-24 ka), and (ii) the Grandvals and Bouquincan stades, which are both coeval with the later part of MIS 2 (24-16 ka). Deglaciation occurred during Heinrich Stadial 1 (18-15.6 ka). This new direct glacial chronology is supported by regional paleoenvironmental proxies and it updates the chronostratigraphic framework available for the southwestern Massif Central. Western European atmospheric circulation changes (i.e., a southward shift in North Atlantic storm tracks and Mediterranean influences) during MIS 2 were identified as significant factors controlling glacier growth in the Aubrac Mountains as well as other glaciated mountains within the southwestern Massif Central, such as the Cantal, Margeride and Lozère mountains.