Conodont colour alteration pattern in the Carboniferous of the Craven Basin and adjacent areas, Northern England

Conodont Colour Alteration Indices (CAI) values in the Craven area show a general range of 2.5–3.5, the majority being a value of 3. The higher values generally occur in the south and south-west and low values are found on the Ashnott High (Ashnott Anticline and eastern closure of the Whitewell Anticline) and in Waulsortian limestones. These values are consistent with the limited vitrinite reflectance data and are a result of the Carboniferous sedimentary and tectonic history of the region. There is no evidence of significant modification by subsequent burial, igneous events, reheating or mineralization. Low values of CAI 2–2.5 on the Ashnott High are interpreted to be due to the thinner sedimentary cover in that area and possible insulation derived from underlying Waulsortian limestones. Relatively high values of CAI 4 for Dinantian strata in the Holme Chapel Borehole and 3.5 in the Silesian sediments to the south of the Craven Basin probably reflect a thicker Westphalian cover than further north.