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
Stratotypes:
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 
Reference(s):
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