Ashfell Sandstone Formation
Ashfell Sandstone Formation is part of the Great Scar Limestone Group
The Ashfell Sandstone Formation comprises thick-bedded, fine-grained sandstone with current ripple laminations, rare cross-bedding, and convolute bedding. Interdigitating are beds of marine mudstone and thin limestone with shelly faunas.
The fluviodeltaic, marine-regressive, Ashfell Sandstone Formation represents an incursion of siliciclastic deposits into the Stainmore Trough encroaching from the north-east. It may be a southern and western, distal extension of the Fell Sandstone Formation, Border Group.
The longest and most complete section through the formation is along the Scandal Beck in the Ravenstonedale area, where up to 160 m of sandstone with four limestone interbeds occurs (see Pattison, 1990; Dunham and Wilson, 1985).
Lower and upper boundaries
The base of the formation overlying the Breakyneck Scar Limestone Formation cannot be defined precisely due to poor exposure.
The top of the formation conformably underlies the mainly packstone, shelly grainstone or lime mudstone of the Ashfell Limestone Formation in the Stainmore Trough (Figure 9, Column 16) and Shap, east Cumbria (Figure 14, Column 3), and the mainly biomicrosparites and biomicrites of the Fawes Wood Limestone Formation on the Askrigg Block (Figure 9, Column 17; Figure 15, Column 3).
The formation is 152 m thick in the Ravenstonedale area, thinning northwards. In the Raydale Borehole (BGS Registration Number SD98SW/1) (SD 9026 8474) it is 38.40 m thick. In the Appleby district it is 20–40 m thick.
Distribution and regional correlation
The formation extends from the edge of the Lake District to the Alston Block, including the Eden Valley and northern margin of the Stainmore Trough.
Age and biostratigraphical characterisation
Late Arundian. Fossils of the thin limestone beds include the corals Diphyphyllum smithi and Siphonodendron martini
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- Turner, J S.1959.Pinskey Gill Beds in the Lune Valley, Westmorland and Ashfell Sandstone in Garsdale, Yorkshire.Transactions of the Geological Association, Vol. 7, 78–87
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- Millward, D, McCormac, M, Hughes, R A, Entwistle, D C, Butcher, A, and Raines, M G.2003.Geology of the Appleby district.Sheet explantion of the British Geological Survey,Sheet 30 (England and Wales)
- Pattison, J.1990.Geology of the Orton and Sunbiggin Tarn districts: 1:10 000 sheets NY60NW and NE.British Geological Survey Technical Report, WA/90/12