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 next to campsite at Ashness Farm. |
Reference Section |
Crags adjacent to lookout car park at top of Lodore Wood Crags. |
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
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