[en] Up to the present, the age of the Brioverian of Central and Western Brittany has been constrained by the Ordovician age attributed to Red Beds at the base of the Palaeozoic cover. Single crystal Pb/Pb zircon radiometric datings presented here provide the following results: 1) confirmation of an Ordovician age for the Central Brittany Red Beds on the basis of zircon dating of the intercalated volcanic rocks (Reminiac); 2) a new chronostratigraphic constraint on the Precambrian/Cambrian boundary based on dating of the Saint-Germain-le-Gaillard ignimbrites (Normandy); 3) a Cambrian age for at least a portion of the Brioverian sediments, judging from the dating of detrital zircons