The BGS Lexicon of Named Rock Units — Result Details

Crummack Formation

Computer Code: CMK Preferred Map Code: Cmk
Status Code: Full
Age range: Rhuddanian Age (SR) — Telychian Age (ST)
Lithological Description: Mudstone and siltstone, black, graptolitic. Mudstones at the base of the formation are calcareous and contain a shelly fauna. Towards the top of the formation calcareous siltstones contain nodules and thin beds of limestone.
Definition of Lower Boundary: Taken at the base of calcareous mudstone and black graptolitic mudstone that contains a Rhuddanian and Aeronian fauna, overlying mudstone and siltstone of the Sowerthwaite Formation.
Definition of Upper Boundary: Defined by the base of the overlying Austwick Formation.
Thickness: Up to 35m
Geographical Limits: Restricted to the Craven inliers, North Yorkshire.
Parent Unit: Stockdale Group (STK)
Previous Name(s): Stockdale Shales (-4556)
Alternative Name(s): none recorded or not applicable
Partial Type Section  Capple Bank, about 1.5km NNE of Austwick Arthurton et al, 1988 
Partial Type Section  Hunterstye, on the east side of Crummack Dale Arthurton et al, 1988 
King, W B R and Wilcockson, W H, 1934. The Lower Palaeozoic rocks of Austwick and Horton-in-Ribblesdale, Yorkshire. Quarterly Journal of the Geological Society of London, Vol.90, 7-31. 
Kneller, B C, Scott R W, Soper N J, Johnson E W and Allen P M, 1994. Lithostratigraphy of the Windermere Supergroup, Northern England. Geological Journal, Vol. 29, 219-240. 
Arthurton, R S, Johnson, E W and Mundy, D J C. 1988. Geology of the country around Settle. Memoir of the British Geological Survey, Sheet 60 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E050 E060