Stratigraphy, sedimentology and structure of the Jurassic (Callovian to Lower Oxfordian) succession at Castle Hill, Scarborough, North Yorkshire, UK

Site investigation borehole cores and temporary shaft exposures at the Toll House Pumping Station shaft site, Castle Hill, Scarborough, North Yorkshire, have revealed new data on the Callovian to Lower Oxfordian (Jurassic) succession. The condensed transgressive marine unit, the Lower Callovian Cornbrash Formation, rich in berthierine ooids and abundant shelly fossils, and the attenuated Cayton Clay Formation represent the Early Callovian marine transgression that flooded the low gradient alluvial plain, which is represented by the underlying Scalby Formation. The Callovian Osgodby Formation (Red Cliff Rock and Langdale members) is an extensively bioturbated, silty sandstone with abundant berthierine-pyrite ooids in the lower part. It was deposited in lower- to upper-shoreface settings. Slow sedimentation rates, with long sediment residence time, resulted in a diverse ichnofauna and a high bioturbation index. Framboidal pyrite ooids in the lower Osgodby Formation sandstones are interpreted as being formed in anoxic lagoons in the nearshore zone; ooids were subsequently swept offshore during storm surge-ebb events. Cold water dinoflagellate cysts of Boreal affinity such as Gonyaulacysta dentata in the lower part of the Oxford Clay Formation indicate an Early Oxfordian age. This is confirmed by the presence of the zonal ammonite species Quenstedoceras mariae and is consistent with a relatively cold, but warming, palaeoclimate at this time. Shaft excavations revealed a new major fault, the Toll House Fault, which is interpreted to be a splay fault bifurcating off the main Castle Hill Fault. Together, the Toll House and Castle Hill faults form the western bounding faults of the Peak Trough, a grabenlike structure that extends northwards, offshore.