The BGS Lexicon of Named Rock Units — Result Details

Thirlmere Tuff Member

Computer Code: TMR Preferred Map Code: Tmr
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: White to pink-weathered, parataxitic, garnetiferous rhyo-dacitic lapilli-tuff and vitric tuff, locally lithic-rich and with breccia.
Definition of Lower Boundary: Mostly faulted but locally rests conformably on bedded pyroclastic rocks at the base of the Lincomb Tarns Tuff Formation, or unconformably on sandstone (Seathwaite Fell Sandstone Formation) or andesite lavas (Birker Fell Andesite Formation).
Definition of Upper Boundary: Conformably overlain by tuff and volcaniclastic sandstones of the Raise Beck Member (Lincomb Tarns Tuff Formation), or by undivided parts of the Lincomb Tarns Tuff Formation.
Thickness: At least 300m
Geographical Limits: North Lake District, around Thirlmere Reservoir, including Watson's Dodd and Stybarrow Dodd.
Parent Unit: Lincomb Tarns Tuff Formation (LTA)
Previous Name(s): Thirlmere Rhyolite (-1868)
Thirlmere Member (-4372)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Crags along east side of Thirlmere, to Dunmail Raise. 
Type Area  Whelpside to Dunmail Raise. 
Reference Section  Crags on and around Steel Fell. 
Reference(s):
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:
E029