Paleogeographical reconstruction of the western French Alps foreland during the last glacial maximum using cosmogenic exposure dating

International audienceAbstract The extent of glaciers in the western French Alps foreland during the last glacial maximum (LGM, 26.5–19 ka) has not yet been determined, so understanding glacial paleogeography during the LGM remains an open question. This study focuses on the glacial chronology in the western French Alps piedmont using 10 Be surface exposure ages on nine glacial boulders and 12 erratic boulders. Results indicate an LGM glacier advance between ca. 24 and 21 ka. During the late LGM, a smaller glacier readvance or stabilization phase occurred at ca. 19 ka, which was followed by a withdrawal phase between ca. 19 and 16.5 ka. Our outcomes show that the LGM extent in the western French Alps was similar or slightly less extensive than the pre-LGM ice extents during the last glacial. Such paleogeography has also been suggested in the western Italian Alps, which share the same accumulation zone with the western French Alps glaciers. The LGM dynamic of the western French Alps foreland glaciers highlighted by our exposure ages is consistent with the timing of the LGM glacier advances and deglaciation with the western Italian ice lobes