The BGS Lexicon of Named Rock Units — Result Details

Ashness Tuff Member

Computer Code: AHT Preferred Map Code: AhT
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Lithic-rich lapilli-tuff, very poorly sorted and massive to weakly eutaxitic.
Definition of Lower Boundary: Taken at base of lapilli-tuff resting on Grange Crags Andesite (lava); contact sharp but conformable or, at its eastern extent resting unconformably on Skiddaw Group rocks.
Definition of Upper Boundary: Overlain by bedded to massive volcaniclastic sandstones contact is abruptly gradational, or by andesite of the undivided Birker Fell Andesite Formation.
Thickness: 10 - 15m
Geographical Limits: North Lake District near Borrowdale (Ashness Wood to Dale Head).
Parent Unit: Birker Fell Andesite Formation (BFA)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Crags adjacent to lookout car park at top of Lodore Wood Crags. 
Reference Section  Crags next to campsite at Ashness Farm. 
Reference(s):
Beddoe-Stephens, B, 1997. The initiation of Borrowdale Volcanism in the Ordovician Lake District as indicated by basal volcaniclastic deposits. British Geological Survey Technical Report WG/97/14. 
Beddoe-Stephens, B, 1996. Mapping; petrology and geochemistry of the Borrowdale Volcanic Group on 1:10k sheets NY21NE and NY21NW. Part of the 1:50k Sheet 29 (Keswick). British Geological Survey Technical Report MPSR/96/16. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E029