The BGS Lexicon of Named Rock Units — Result Details

Yottenfews Tuff Formation

Computer Code: YOT Preferred Map Code: notEntered
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Welded tuffs and lapilli-tuffs with intercalations of volcaniclastic sandstone; interpreted as two sheets of rhyolitic ignimbrite and one of dacitic ignimbrite.
Definition of Lower Boundary: Taken at the base of the spherulitic, rhyolitic welded tuff that constitutes the Sella Park Member. This is a major change from dominantly volcaniclastic sandstones of the underlying Newton Manor Formation to the ignimbrite sequence of the Yottenfews Tuff Formation.
Definition of Upper Boundary: Not seen in its original form as the formation is unconformably overlain by Carboniferous strata.
Thickness: 194m+ (uncorrected for structural dip or borehole deviation from the vertical). Thickness includes a 49.3m-thick sill.
Geographical Limits: Sellafield borehole No.7A only.
Parent Unit: Borrowdale Volcanic Group (BVG)
Previous Name(s): Yottenfews Formation (-4990)
Alternative Name(s): none recorded or not applicable
Partial Type Section  Sellafield borehole No.7A, BGS Registered No. NY00SE/36, 577.83 - 718.15m below Rotary Table Elevation, 524.77 - 718.44m below OD. 
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