Sedimentology of sandwaves in an oolite shoal complex in the Cadeby (Magnesian Limestone) Formation (Upper Permian) of eastern England

Abstract

Summary Four depositional facies are recognizable in the Sprotbrough Member of the Cadeby Formation (formerly the Lower Magnesian Limestone) in eastern England; they are sabkha, semi-restricted lagoon, oolite shoal complex and open marine shelf. Of these, the oolite shoal complex occupies most of the present outcrop in the Yorkshire Province, i.e. south of the Cleveland High. It comprises large-scale cross-stratified oolite bedforms that are interpreted as sandwaves from their size, type of sediment and internal features. The sandwaves probably originated from the concentration of wave energy by eminences on the floor of the Zechstein Sea. Biogenic structures in the sandwaves show that they were inhabited by marine organisms. A complex pattern of palaeocurrent styles and azimuths is present within the sandwaves. At many exposures, the long axes of the sandwaves trend NW-SE, suggesting predominant currents normal to this direction. A predominant current from the NE is further indicated by the preferential abutment of SW-dipping beds on the NE flanks of bedforms; this was caused by sandwaves that climbed the backs of others. Occasional storms from the SE produced spillover lobes oriented towards the NW. Storms were also probably responsible for the formation of internal structures such as hummocky cross-stratification, fan-shaped bedding and contemporaneous erosion surfaces.