The BGS Lexicon of Named Rock Units — Result Details

Ashgill Formation

Computer Code: AHL Preferred Map Code: Ahl
Status Code: Full
Age range: Rawtheyan Stage (OW) — Hirnantian Age (OH)
Lithological Description: Dark blue-grey shales, distinguished from underlying formations of the Coniston Limestone Group by its lower calcareous content and the near absence of limestone nodules. Dark silty mudstones are commonly pervasively bioturbated.
Definition of Lower Boundary: Lower boundary taken at the junction of the shales with underlying calcareous mudstones with limestone nodules; the boundary is unconformable in places. Locally base taken at junction with rhyolitic tuff of the underlying High Haume Volcanic Formation.
Definition of Upper Boundary: Base of overlying Skelgill Formation - black graptolitic mudstone.
Thickness: c.20m at type section, thins eastwards to less than 2m in Longsleddale. 125 to 215m in Ulverston District, generally <25m elsewhere.
Geographical Limits: Northern England throughout the outcrop of the Windermere Supergroup.
Parent Unit: Dent Group (DNT)
Previous Name(s): Ashgill Shales (-4422)
Ashgill Shale Formation (-3793)
Alternative Name(s): none recorded or not applicable
Type Area  Ashgill Beck and Ashgill Quarry, Sheet 38 (Ambleside). 
Reference Section  Rebecca Hill and Rebecca Quarry (SD 2292 7830) 
Soper, N J, 1994. The Lower Palaeozoic rocks of 1:10,000 sheets SD28SW, SD27NW and SD27NE, Low Furness, Cumbria, British Geological Survey Technical Report WA/94/61. 
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. 
Rose, W C C. 1977. Geology and Hematite deposits of South Cumbria. Economic Memoir for 1:50,000 Sheet 58 and southern part of Sheet 48. Memoir of the geological Survey of Great Britain. 
McNamara, K J. 1979. The age, stratigraphy and genesis of the Coniston Limestone Group in the southern Lake District. Geological Journal, 14, 41-69. 
Johnson, E W, Soper, N J, Burgess, I C, Ball, D F, Beddoe-Stephens, B, Carruthers, R M, Fortey, N J, Hirons, S, Merritt, J W, Millward, D, Roberts, B, Walker, A B and Young, B. 2001. Geology of the country around Ulverston. Memoir of the British Geological Survey, England and Wales, Sheet 48. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E039 E038 E048