The BGS Lexicon of Named Rock Units — Result Details

Devoke Water Tuff Member

Computer Code: DKT Preferred Map Code: DkT
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Weakly bedded and cross-bedded lapilli-tuff and tuff of basaltic/basaltic andesite composition; locally intruded by penecontemporaneous sills; pyroclasts include abundant Skiddaw Group mudstone and sandstone.
Definition of Lower Boundary: Overlies Skiddaw Group in type area where it is the lowest Member of the Birker Fell Andesite Formation (and of the BVG). On Latterbarrow overlies the Latterbarrow Sandstone, where the base of the Devoke Water Tuff Member is taken at the bed of lapilli-tuff overlying sandstone.
Definition of Upper Boundary: At change to basaltic/basaltic andesite flows of Birkby Fell Member, or to overlying andesite sheets of Birker Fell Andesite Formation (undivided).
Thickness: 550 - 620m; complete thickness unknown because of faulting.
Geographical Limits: Devoke Water, Cumbria (SD 14 96); Whincop, Eskdale (SD 18 99) and Stony Tarn (NY 20 02); roof pendants above Eskdale Granite (around NY 185 016), Cumbria; also on Latterbarrow-Town Bank, north of Gosforth, Cumbria (NY07 10).
Parent Unit: Birker Fell Andesite Formation (BFA)
Previous Name(s): Devoke Water Member (-3362)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Birkby Fell and Stord's Hill, south and south-west of Devoke Water, Eskdale, Cumbria. 
Reference(s):
Akhurst, M C, Chadwick, R A, Holliday, D W, McCormac, M, McMillan, A A, Millward, D, Young, B, Ambrose, K, Auton, C A, Barclay, W J, Barnes, R P, Beddoe-Stephens, B, James, J C W, Johnson, H, Jones, N S, Glover, B W, Hawkins, M P, Kimbell, G S, MacPherson, K A T, Merritt, J W, Milodowski, A E, Riley, N J, Robins, N S, Stone, P and Wingfield, R T R. 1997. The geology of the west Cumbria district. Memoir of the British Geological Survey, Sheets 28, 37 and 47 (England and Wales). 138pp. 
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. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E038 E037 E028