The BGS Lexicon of Named Rock Units — Result Details

Helvellyn Tuff Formation

Computer Code: HLV Preferred Map Code: Hlv
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Dacitic lapilli-tuff, with eutaxitic foliation at the base and with intercalations of tuff.
Definition of Lower Boundary: Base of lapilli-tuff, or locally that of a very thin basal tuff layer, rests with slight unconformity on sandstone of the Esk Pike Formation.
Definition of Upper Boundary: Highest lapilli-tuff or (locally) tuff is overlain unconformably by volcaniclastic rocks of the Deepdale Sandstone Formation.
Thickness: 400m maximum known.
Geographical Limits: Helvellyn, Fairfield, Striding Edge eastwards to Glenridding, northeastern Lake District, Cumbria.
Parent Unit: Borrowdale Volcanic Group (BVG)
Previous Name(s): Helwellyn Tuff Member (-319)
Hellvellyn Formation (-4709)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Nethermost, Ruthwaite and Cock Coves, adjacent to Helvellyn. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E029