40Ar/39Ar detrital white mica ages from a Westphalian C/D sediment in the Varisan foreland Forest of Dean Basin (SW England) range from 309±12 to 371±2 Ma. Combining these ages with chemical data from the detrital white micas constrain their provenance to two sources: reworked Westphalian A to C, and, more controversially, the central European Variscides. Taking into account the palaeogeography of the Late Devonian to Late Carboniferous, the sediment derived from the central European Variscides must have resided in a holding basin proximal to their source for 30–40 Ma. During the Mid- to Late Carboniferous sediment was transported longitudinally from east to west along the Variscan front. Deposition and mixing of the two source components took place in the Forest of Dean Basin at approximately 307 Ma.