Computer Code: |
BBA |
Preferred Map Code: |
notEntered |
Status Code: |
Full |
Age range: |
Caradoc Series (O4)
— Caradoc Series (O4) |
Lithological Description: |
Sheets of massive, unbedded, poorly sorted, generally lithic-rich welded lapilli-tuff of andesitic and rhyolitic composition; interbedded volcaniclastic sandstone, siltstone, pumice lapilli-tuff and accretionary lapilli-tuff. Contains the rhyolitic welded lapilli-tuff (Seascale Hall Member) and, in BH RCF1, a rhyolitic lava flow or lava-like tuff. |
Definition of Lower Boundary: |
At the change from coarse, eutaxitic, fiamme-rich lapilli tuff at the top of the Bleawath Formation to generally lithic-rich sequence above. Various members of the Formation overlap on to the top of the Bleawath Formation. |
Definition of Upper Boundary: |
At the upward change from the generally lithic-rich sequence to homogeneous andesitic welded tuff of the Fleming Hall Formation. |
Thickness: |
255.55m in Type Section (355.5m in core because of andesite sill); 188m in Sellafield BH No.2; 127m in Sellafield BH No. 4; 45m in Sellafield BH No.5. |
Geographical Limits: |
Seen in Sellafield boreholes 2 (NY00/28), 4 (NY00SE/29), 5 (NY00SE/30), 10A (NY00SW/38), RCF1 (NY00SE/35), RCF3 (NY00SE/37), RCM1 (NY00SE/41) and RCM2 (NY00SE/40). |
Parent Unit: |
Borrowdale Volcanic Group (BVG)
|
Previous Name(s): |
Brown Bank Ignimbrite Formation [Obsolete Name and Code: Use BBA]
(-1967)
|
Alternative Name(s): |
none recorded or not applicable
|
Stratotypes: |
Type Section |
Nirex Sellafield borehole No 10A, BGS Registered No NY00SW/38, 1053.0-1408.5m below Rotary Table Elevation, 1012.5m - 1368.0m below OD. |
Reference Section |
Nirex Sellafield borehole No RCF1, BGS Registered No NY00SE/35, 908.71m - 1150m (section incomplete) belo Rotary Table Elevation. This is a deviated vertical borehole; true depths and thicknesses are as yet unknown. |
Reference(s): |
Millward, D, Beddoe-Stephens, B, Williamson, I T, Young, S R, and Petterson, M G. 1994. Lithostratigraphy of a concealed caldera-related ignimbrite sequence within the Borrowdale Volcanic Group of west Cumbria. Proceedings of the Yorkshire Geological Society, Vol.50, part 1, 25-36. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
none recorded or not applicable |