The Chester Formation (Early Triassic, southern Britain): sedimentary response to extreme greenhouse climate?

Abstract

The Early Triassic of onshore southern Britain is dominated by the Chester Formation; a red-bed succession of braidplain origin, sourced mainly from the Armorican Massif over what is now north-west France. At outcrop in south-west England and the English Midlands the Chester Formation comprises an abrupt conglomeratic outbreak that fines further northwards into arenaceous strata. Previous interpretations have invoked tectonic or climatic causes for the Early Triassic development of the Budleighensis river system and emplacement of the Chester Formation. Climatic models variously invoke a shift to a wetter climate, high erosion rates associated with the end-Permian mass extinction (EPME), and an Early Triassic (Olenekian) arid phase. We support the concept of a fundamental climatic control, and suggest that the Chester Formation reflects an extreme Early Triassic greenhouse climate characterised by high temperatures, aridification, de-vegetation, heavy floods and high erosion rates.