Capecastle
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Geology & landscape
Mining / Industrial: Quarry · Geological Period: Cretaceous, Triassic · Rock Type: Basalt, Chalk, Limestone, Sandstone
Landscape processes: Volcanic / Igneous
Description
Capecastle Cretaceous Stratigraphy Capecastle is of importance because of its geology. Specifically the site contains excellent exposures of the Ulster White Limestone Formation. In particular the influence of the positive Dalradian ridge during chalk sedimentation can be demonstrated. The rock relationships reflect the importance of the Dalradian ridge as a more positive feature during chalk sedimentation. The sequence is much thinner and less complete than those in the flanking Rathlin Basin and Lame-Lough Neagh Basin. Capecastle is the best exposure of the Ulster White Limestone on the Dalradian ridge. It enables the influence of this more positive area during deposition of the Ulster White Limestone to be demonstrated. The lowest and oldest rocks seen at Capecastle are the glauconitic Creggan Chalk Member that form the quarry floor. This rock unit is capped by a stromatolitic biostrome. The prominent bedding planes of the Larry Bane Chalk Member can be seen near the base of the face. The intervening Boheeshane Chalk Member is only approximately 3 m thick here compared with a thickness of over 24m in the type section in Boheeshane Bay in the adjoining Rathlin Basin. The overlying 20 metres of chalk comprises the Ballintoy Chalk and Glenarm Chalk Members. Fossils recorded from the site include Porosphaera globularis, Echinocorys scutata, Carneithyris sp., Cretirhynchia sp., Orbirhynchia sp., Inoceramus sp., Ostrea sp., Belemnitella langei, and Belemnitella mucronata minor. No Santonian chalk is found in the Capecastle Quarry area where the basal Campanian Creggan Chalk Member overlies the Triassic Sherwood Sandstone Group. The Creggan Chalk is overlain disconformably by the Boheeshane Group Member. Sedimentation continued through the Larry Bane Chalk, Ballintoy Chalk and Glenarm Chalk members with the younger members of the Ulster White Limestone Formation removed by pre-basalt erosion. https://www.daera-ni.gov.uk/publications/capecastle-assi