Observations and speculations on the northeast Towy ‘axis’, mid-Wales

Late Ashgill and Llandovery sedimentation across the Towy ‘axis’ southeast of Rhayader is interpreted within the context of the rapid southeasterly thickening of the upper portion of the Ashgill best demonstrable in the Chwefru valley. This thickening sequence overlies deep-water middle-fan arenites and is interpreted as a northwest prograding shelf/slope association. The slope eventually became non-depositional and was onlapped by the basinal facies of the Llandovery during relative sea-level rise. The non-depositional slope and associated major slump-scars at the shelf-edge explain many of the non-sequences- in the region previously ascribed to erosion related to episodes of tectonism. The regional strain history is thus simplified.