The BGS Lexicon of Named Rock Units — Result Details

Tarn Crags Tuff Member

Computer Code: TNCR Preferred Map Code: TCr
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Bedded coarse-grained dacitic tuff and lapilli-tuff, sparsely garnetiferous.
Definition of Lower Boundary: Taken at the base of pyroclastic sequence unconformably overlying bedded sandstone of the Seathwaite Fell Sandstone Formation or andesite of the Birker Fell Andesite Formation.
Definition of Upper Boundary: Conformable contact with welded lapilli-tuff of the Thirlmere Member, or with that of the Lincomb Tarns Formation (undivided).
Thickness: Up to about 8m, except on Great Howe and Castle Rock, Thirlmere, where up to 280m
Geographical Limits: North Lake District around Thirlmere Reservoir.
Parent Unit: Lincomb Tarns Tuff Formation (LTA)
Previous Name(s): Tarn Crags Member (-4931)
Alternative Name(s): none recorded or not applicable
Reference Section  Crags near Black Crag Gill (Steel Fell). 
Reference Section  Tarn Crags. 
Woodhall, D G, 1998. The geology of the Wythburn, Thirlmere and Fairfield areas of the north-east Lake District. British Geological Survey Technical Report WA/98/07. 
Millward, D, 1998. Summary of the geology east of Thirlmere, part of 1:10000 Sheet NY31NW. British Geological Survey Technical REport WA/98/17. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: