1 Mississippian reef development in the Cracoe Limestone Formation of the southern 2 Askrigg Block, North Yorkshire, UK 3 4 C. N. Waters1*, R. B. Haslam1, P. Cózar2, I. D. Somerville3, D. Millward4 & M. Woods1 5 1 British Geological Survey, Environmental Science Centre, Keyworth, Nottingham NG12 6 5GG, UK 7 2 Instituto de Geociencias CSIC-UCM, Madrid, Spain 8 3 UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland 9 4 British Geological Survey, The Lyell Centre, Research Avenue South, Riccarton, Edinburgh 10 EH14 4AS, UK 11 * Correspondence:
[email protected] 12 13 Abstract: The southern margin of the Askrigg Block around Cracoe, North Yorkshire, shows 14 a transition from carbonate ramp to reef-rimmed shelf margin, which, based on new 15 foraminiferal/algal data, is now constrained to have initiated during the late Asbian. A late 16 Holkerian to early Asbian ramp facies that included small mudmounds developed in 17 comparatively deeper waters, in a transition zone between the proximal ramp, mudmound- 18 free carbonates of the Scaleber Quarry Limestone Member (Kilnsey Formation) and the distal 19 Hodderense Limestone and lower Pendleside Limestone formations of the adjacent Craven 20 Basin. The ramp is envisaged as structurally fragmented, associated with sudden thickness 21 and facies changes. The late Asbian to early Brigantian apron reefs and isolated reef knolls of 22 the Cracoe Limestone Formation include massive reef core and marginal reef flank facies, the 23 latter also including development of small mudmounds on the deeper water toes of back-reef 24 flanks. The position of the apron/knoll reefs is constrained to the south (hangingwall) of the 25 North Craven Fault, but it is syn-depositional displacement on the Middle Craven Fault that 1 26 accounts for the thick reefal development.