| Computer Code: |
AFL |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Holkerian Substage (CQ)
— Holkerian Substage (CQ) |
| Lithological Description: |
The distinctive Ashfell Limestone Formation is characteristically dark grey to dark blue-grey and mainly a packstone, shelly grainstone or lime mudstone. Strongly cross-bedded units, with thin interlaminae of siltstone and fine-grained sandstone occur at the base of the formation. Convolute beds and nodules of dark grey chert occur locally, and partial dolomitisation is common. The top of the formation is marked by the presence of dark grey, cross-bedded, coarse-grained crinoidal grainstone, grey mudstone with bivalves, and vuggy porcellanous limestone (the Bryozoa Band of Garwood, 1913).
Shallow marine, perhaps slightly restricted carbonate environment. Holkerian. |
| Definition of Lower Boundary: |
The mainly packstone, shelly grainstone or lime mudstone of the Ashfell Limestone Formation conformably overlies the sandstones, mudstones and thin limestones of the Ashfell Sandstone Formation. |
| Definition of Upper Boundary: |
On the northern margin of the Stainmore Trough, the Bryozoa Band (BZB) at the top of the Ashfell Limestone Formation is overlain either conformably by the mainly sparry packstone of the Potts Beck Limestone Formation, or disconformably by the rhythmically bedded limestone (mainly wackestone and packstone) of the Knipe Scar Limestone Formation. |
| Thickness: |
Thickness The formation is 40-50 m thick at Penrith and Brough, but thickens to 100 m in the Stainmore Trough. |
| Geographical Limits: |
Penrith, Brough and the Stainmore Trough. |
| Parent Unit: |
Great Scar Limestone Group (GSCL)
|
| Previous Name(s): |
Hillbeck Limestone [Obsolete Name and Code: Use AFL]
(HLBL)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Partial Type Section |
Potts Valley [NY 6988 0827], [NY 6981 0820] and [NY 6972 0805 to 6969 0813] where more than 48 m of limestones in the upper and middle parts of the formation are exposed. |
| Partial Type Section |
Ewe Fell [NY 6971 0702 to 6999 0711] where 60 m of the lowest part of the formation, comprising limestone and 7 m of sandstone, are exposed (see Pattison, 1990). |
| Reference(s): |
| Dean, M T, Browne, M A E, Waters, C N and Powell, J H. 2011. A lithostratigraphical framework for the Carboniferous successions of northern Great Britain (onshore). British Geological Survey Research Report, RR/10/007. 165pp. |
| 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.) |
| Dunham, K C, and Wilson, A A. 1985. Geology of the Northern Pennine Orefield. Volume 2 Stainmore to Craven. Economic Memoir of the British Geological Survey, Sheets 40, 41 and 50, and parts of Sheets 31, 32, 51, 60 and 61(England and Wales). |
| Garwood, E J. 1913. The Lower Carboniferous succession in the north-west of England. Journal of the Geological Society, London, Vol.68 (for 1912), 449-586. |
| George, T N, Johnson, G A L, Mitchell, M, Prentice, J E, Ramsbottam, W H C, Sevastopulo, G D and Wilson, R B. 1976. A correlation of the Dinantian rocks of the British Isles. Special Report of the Geological Society of London, No 7. |
| Mitchell, M, Taylor, B J and Ramsbottom, W H C, 1978. Carboniferous, 168-188 in The geology of the Lake District. Moseley, F (editor). Yorkshire Geological Society Special Publication. No.3. |
| Pattison, J. 1990. Geology of the Orton and Sunbiggin Tarn districts. Geological notes and local details for 1:10,000 Sheets NY60NW and NY60NE and part of 1:50,000 Sheets 30 (Appleby), 31 (Brough), 39 (Kendal) and 40 (Kirkby Stephen). British Geological Survey Onshore Geology Series, Technical Report, WA/90/12. |
| Ramsbottom, W H C. 1973. Transgressions and regressions in the Dinantian: A new synthesis of British Dinantian stratigraphy. Proceedings of the Yorkshire Geological Society, Vol.41, 261-291. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
