Anatomy of a Late Triassic Bristol fissure: Tytherington fissure 2

Abstract

The Late Triassic and Early Jurassic fissures around Bristol and South Wales are famous as sources of excellent fossils of early mammals, dinosaurs, sphenodontians, and other tetrapods. However, the ways in which these fissures filled with sediment have not often been documented. Moreover, systematic faunal sampling up a working face exposure has rarely been attempted for the UK Triassic fissures. Here we show in detail how a complex fissure in Tytherington Quarry, north-east of Bristol, filled in multiple steps, and document both sedimentary facies and faunas. Tytherington Quarry is a key Late Triassic Bristol sauropsid fissure site, having previously yielded abundant Thecodontosaurus remains and a new genus of sphenodontian, Diphydontosaurus. Our findings comprise specimens of terrestrial reptiles, including sphenodontians and archosaurs. However, abundant remains of fishes and marine invertebrates were also recovered, indicating a significant marine influence during parts of the fissure-filling process. Comparisons of our results with those of previous studies on Tytherington and other Late Triassic SW UK fissure sites indicate some consistent patterns of faunal association and provide further evidence of a Rhaetian age for the Late Triassic palaeo-island fissures north of Bristol. Our analysis supports a model of fissure formation and filling entailing punctuated episodes of sedimentation through a relatively short time.