Microvertebrates from the Rhaetian bone beds at Westbury Garden Cliff, near Gloucester, UK

Abstract

Westbury Garden Cliff has been a noted site for Rhaetian bone beds for over a century. It is known especially as a source of excellently preserved bones of the small marine reptile Pachystropheus as well as other reptiles, and fishes. Further it is the type locality of the Westbury Formation, the lower half of the British Rhaetian (Penarth Group). It was also featured in a debate over lateral equivalence of the basal Rhaetian bone bed, with supposedly 5–6 m of pre-basal bone bed deposition. However, the bone beds at different localities are unlikely to be of exactly the same age, and the succession at Westbury Garden Cliff lacks the erosive base of the Westbury Formation seen elsewhere and so presumably started later, perhaps reflecting progressive inundation of the Welsh High, the nearest land. However, the main bone bed occurs in lenses up to 20 cm wide, and may represent hummocky cross stratification, evidence of storm bed deposition. Trace fossils in several sandstones include Selenichnites and Crescentichnus, evidence of shallow-water limulids ploughing the sediment for food, Lockeia, the living burrows of bivalves, and Chondrites burrow systems, suggesting subsequent stability of the sandstone beds.