Gorstian sediments in south-central Wales preserve an asymmetric, compound mixed-process delta system north of the Carreg Cennen Disturbance and east of the Golden Grove Axis. The 30 km SW-NE outcrop, extending from the Cennen Valley to Y Pigwn, is oblique to the NNE delta progradation direction. The Hafod Fawr Formation comprises subaqueous delta slope deposits. Sandstone bed amalgamation indicates shoaling and wave/storm influence within the overlying subaqueous delta platform deposits of the Cwar Glas Member. The succeeding Mynydd Myddfai Sandstone Formation contains shoreline delta lithofacies within three geographical tracts. An embryonic Golden Grove Axis shed shoal water shoreline fan-delta and alluvial fan lithofacies (of the Trichrug Formation) in the Cennen Valley Tract. The SW Tract (Cilmaenllwyd to Banc Celynog) was deposited on the updrift flank of the asymmetric delta, with longshore drift to the NE. Amalgamated sandstone bedsets dominate in the mouth bar and terminal distributary channel lithofacies. Pen y Bicws preserves the axial gravel bed distributary channel lithofacies, which created a headland and palaeogeographic divide between the SW and NE tracts. The latter (Sawdde Gorge to Y Pigwn) records deposition in a low-energy bay that hosted cycles of heterolithic lithofacies. Collectively, these tracts occupied part of a sediment supply route to deeper facies of the subsidence-prone Clun Forest Sub-Basin. Emergent delta plain deposits become dominant within the overlying Trichrug Formation. Thin, locally preserved deposits of the Cribyn Du Member record delta abandonment and transgression during the Ludfordian associated with basin reconfiguration and expansion of the Caer’r mynach Seaway.

Lithofacies and biostratigraphical analysis has enabled the establishment of a stratigraphic event framework for Ludfordian and Pridoli strata in south Wales and the Welsh Borderland. In SW Wales, the Golden Grove Axis acted as a structural hinge separating the shallow marine storm-influenced Cae’r mynach Seaway from a pediment surface above which Ludfordian colluvium (Abercyfor Formation) was deposited. The Axis seeded four NW-derived river-influenced delta progrades of Leintwardinian to early Pridoli age (Tilestones Formation). A NE-sourced early Pridoli wave-influenced delta deposited the Downton Castle Sandstone Formation (DCSF), coeval to the youngest Tilestones prograde, with a lateral interface existing between Mynydd Epynt and the Clun Forest area. Except for the Malverns area, the DCSF is no longer recognized south of the Neath Disturbance. Early Pridoli forced regression promoted widespread subaerial exposure north of the Neath Disturbance, with incision into tracts close to the Welsh Borderland Fault System. The basinward-shift in facies belts resulted in marine erosion and deposition of a phosphatic ravinement pebble lag. The wave-influenced Clifford’s Mesne Sandstone Formation delta subsequently seeded on the Gorsley Axis with tidally influenced Rushall Formation accumulating in a back-barrier setting. The Pwll-Mawr Formation records the easterly advance of coeval coastal deposits on the western side of the remnant Cae’r mynach Seaway. Behind migrating delta coastlines, green muds accumulated on coastal plains (Temeside Mudstone Formation) with better drained red dryland alluvium (Moor Cliffs Formation) charting expansion of Old Red Sandstone lithofacies. Mid-Pridoli incision preserves the Pont ar Llechau Formation estuarine valley fill.