The Cambrian of SW Wales: Towards a United Avalonian Stratigraphy

This Memoir reviews, revises and interprets the biostratigraphy, lithostratigraphy, process sedimentology, palaeoenvironments and sequence stratigraphy of the classic Cambrian succession of SW Wales. This 1250 m thick clastic sedimentary succession, of Terreneuvian to Furongian age, was deposited in environments ranging from alluvial fan to mid–outer shelf. Two lithostratigraphical groups are distinguished, each comprising six formations; where possible and appropriate, original and well-known names are retained in harmony with current usage. High-resolution sequence-stratigraphical techniques, constrained by biostratigraphical data whenever possible, allow the revised lithostratigraphy to be integrated with the western Avalonian chronostratigraphy developed in maritime Canada. A twofold subdivision is recognized. Megasequence 1 (sequences 3–7) spans the Terreneuvian, C2 and much of C3, with deposition occurring in an extensional rift-like regime on an epeirogenically active platform. Sequence 8 lies at the base of Megasequence 2, which extends from late C3 into the early Ordovician, and represents passive margin sedimentation.