The BGS Lexicon of Named Rock Units — Result Details
Ashgill Formation
Computer Code: | AHL | Preferred Map Code: | Ahl |
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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 Shale Formation [Obsolete Name and Code: Use AHL]
(-3793)
Swindale Shale Formation [Obsolete Name and Code: Use AHL] (SWSH) Ashgill Shales [Obsolete Name and Code: Use AHL] (-4422) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
Reference Section | Rebecca Hill and Rebecca Quarry (SD 2292 7830) | ||
Type Area | Ashgill Beck and Ashgill Quarry, Sheet 38 (Ambleside). | ||
Reference(s): | |||
Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) | |||
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. | |||
Millward, D, and Stone, P. 2012. Stratigraphical framework for the Ordovician and Silurian sedimentary strata of northern England and the Isle of Man. British Geological Survey Research Report, RR/12/04. 119pp. | |||
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 |