The BGS Lexicon of Named Rock Units — Result Details

Birkby Fell Andesite Member

Computer Code: BKB Preferred Map Code: Bkb
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Dark grey to greenish grey basaltic and basaltic andesite lava flows; generally thin, porphyritic, simple aa-flows and intercalated bedded tuffs and volcaniclastic sandstones.
Definition of Lower Boundary: Base of lowest basaltic andesite/basalt flow. Rests on Devoke Water Member in type area; farther east on undivided feldspar-phyric andesites of the Birker Fell Andesite Formation.
Definition of Upper Boundary: Overlain by blocky, porphyritic andesite flows of Birker Fell Andesite Formation (undivided).
Thickness: 430 - >500m (upper boundary faulted in part). Absent to east of Devoke Water.
Geographical Limits: Birkby Fell, Eskdale, Cumbria (SD 14 95) also Whincop, Eskdale (SD 180 993), Cumbria.
Parent Unit: Birker Fell Andesite Formation (BFA)
Previous Name(s): Birkby Fell Member [Obsolete Name and Code: Use BKB] (-3219)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Crags of Birkby Fell and Woodend Height, southwest and south of Devoke Water, Cumbria. 
Reference(s):
Millward, D, Johnson, E W, Beddoe-Stephens, B, Young, B, Kneller, B C, Lee, M K, Fortey, N J, Allen, P M, Branney, M J, Cooper, D C, Hirons, S, Kokelaar, B P, Marks, R J, McConnell, B J, Merritt, J W, Molyneux, S G, Petterson, M G, Roberts, B, Rundle, C C, Rushton, A W A, Scott, R W, Soper, N J, and Stone, P. 2000. Geology of the Ambleside district. Memoir of the British Geological Survey, England and Wales, Sheet 38. 
Petterson, M G, Beddoe-Stephens, B, Millward, D and Johnson, E W, 1992. A pre-caldera plateau-andesite field in the Borrowdale Volcanic Group of the English Lake District. Journal of the Geological Society, London, Vol. 149, 889-906. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E038