THE CORNBRASH FORMATION (CALLOVIAN) IN NORTH YORKSHIRE AND CLEVELAND

Abstract

SUMMARY The Cornbrash Formation comprises two main units together forming one marine cycle—the Cornbrash Limestone followed by the Shales of the Cornbrash. The formation is the expression in the Yorkshire Jurassic of the world-wide marine transgression which began in the Lower Callovian. This study concentrates on the petrographical aspects of the Cornbrash Limestone Member. Brief discussions of the palaeoecology of the Cornbrash Limestone and the sedimentology of the Shales of the Cornbrash are also given. Contrary to previously held opinion, the Cornbrash Limestone does not form one homogeneous unit. At the most complete sections on the coast, it is made up of four units differing markedly in petrology and thus in environment of deposition. Study of the relations of the four units along the coast and inland shows that the Callovian transgression was a gradual, step by step process, with frequent halts and periods of erosion.