The BGS Lexicon of Named Rock Units — Result Details

Fleming Hall Tuff Formation

Computer Code: FLH Preferred Map Code: FlH
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Andesitic tuff and lapilli-tuff (eutaxitic to parataxitic). At least three welded ignimbrite sheets, locally separated by thin beds of sandstone. Side Farm Member comprises poorly sorted beds of lapilli-tuff and pyroclastic breccia.
Definition of Lower Boundary: Taken at the base of the sequence of homogeneous, thick, generally lithic - poorly welded tuffs, above the Brown Bank Ignimbrite Formation, which is composed of thinner sheets of lithic-rich andesite and rhyolitic lapilli tuff. Locally a coarse lithic-rich lag-breccia occurs at the base of the lowest member.
Definition of Upper Boundary: Not seen, but mapped at the change from densely welded tuff to a mixed sequence of lithic-rich tuff and parataxitic tuff of the Loweray Formation.
Thickness: 403m in type section; 506m in Sellafield BH No.4 (NY00SE/29). Thicknesses are incomplete and uncorrected for dip, as boreholes deviated from vertical.
Geographical Limits: Crops out east of Gosforth, Cumbria, as far as the Thistleton Fault (Lake District Boundary Fault). Also proved in Sellafield boreholes 2 (NY 00SE/28), 4 (NY00SE/29), 5 (NY00SE/30), 10A (NY00SW/38), 11A (NY00SE/34), 12A (NY00SW/39); RCF1 (NY00SE/35), RCF2 (NY00SE/36), RCF3 (NY00SE/37), RCM3 (NY00SE/39), PRZ1 (NY00SE/45), PRZ2 (NY00SE/44) and PRZ3 (NY00SE/42).
Parent Unit: Borrowdale Volcanic Group (BVG)
Previous Name(s): Fleming Hall Formation (-3406)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Sellafield Borehole No. 5, (BGS No. NY00SE/30), 489.83-892.42m beneath Rotary Table, 404.20m-806.79m below OD. 
Type Area  Type area on Table Rock, 1.8km east of Gosforth, Cumbria. 
Reference(s):
Beddoe-Stephens, B and Millward, D, 2000. Very densely welded, rheomorphic ignimbrites of homogeneous intermediate calc-alkaline composition from the English Lake District. Geological Magazine, Vol.137, 155-173. 
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:
E037