The depositional history of the Hackness Coral-Sponge Bed and its associated sediments within the Passage Beds Member of the Coralline Oolite Formation (Corallian Group; Oxfordian) of North Yorkshire

Abstract

SUMMARY The Passage Beds contain a varied assortment of terrigenous and carbonate sedimentary rocks in which there is the gradual upwards transition from predominantly terrigenous into predominantly carbonate sediment. From an initial widespread quartz-sand sheet covering most of the Cleveland Basin, terrigenous sedimentation later became confined to the southern margin of the basin while in the centre, shallow seas, minimal clastic clay input and substantial nutrient-transporting tidal currents enabled a coral reef to become established. Large amounts of reef-derived sediment were transported eastwards, forming a long ‘tail’ of coral–shell sand. Uplift and erosion of the reef in late Passage Beds times was followed by renewed subsidence. This produced a hardground which was colonised by thickets of a crinoid having pentalobate stem ossicles commonly referred to as ‘ Pentacrinus ’. The ‘ Pentacrinus ’ ossicles, along with further coral debris, were subsequently incorporated into a widespread sheet of ‘ Pentacrinus ’ biosparite.