Sedimentation patterns in the Cornbrash Limestone Formation of the Cotswold Hills

Abstract

Fades and isopachyte maps are constructed for the Upper and Lower Cornbrash in the Cotswolds, and the formal name Cornbrash Limestone Formation is proposed. Three localities were selected for detailed field and laboratory analysis of temporal patterns. The formation is divided into members, corresponding to facies types examined in the field. Sedimentary patterns are interpreted and the depositional history is reconstructed. The facies and isopachyte patterns suggest that synsedimentary extensional faulting in the pre-Permian basement, which had strongly influenced earlier Permian to Jurassic sedimentation, had almost ceased. Progress of the initial Callovian transgression across England is suggested to have been only locally successful, in view of variable tectonic movement in the block faulted basement; the Upper Cornbrash was transgressive in North Yorkshire and Humberside, but simultaneous uplift in the south Midlands led to erosion or non-deposition, and in the Cotswolds a regressive phase is evident.