The BGS Lexicon of Named Rock Units — Result Details

Yellowford Formation

Computer Code: YEL Preferred Map Code: Yel
Status Code: Full
Age range: Permian Period (P) — Permian Period (P)
Lithological Description: Reddish brown silty and sandy mudstone; clayey sandy siltstone; and silty clayey fine-grained sandstone. Laterally equivalent to the Crediton Breccia.
Definition of Lower Boundary: Rests on Thorverton Sandstone, probably unconformably, around Dunsmore (SS 957 015). Basalt at the top of the Thorverton Sandstone is directly overlain by basal Yellowford Formation clay. East of Poundsland (SS 961 013) change from Thorverton Sandstone to Yellowford Formation less clear, due to greater proportion of sand in the Yellowford Formation.
Definition of Upper Boundary: Overlain by Shute Sandstone; gradational boundary.
Thickness: To 150m. Lower 75m penetrated in Yellowford Farm Borehole (SS9255 0089).
Geographical Limits: Crops out from near Berrysbridge (SS 917 010), about 1km south of Thorverton, eastwards through Yellowford, across the Exe Valley to near Ellerhayes (SS 980 020).
Parent Unit: Exeter Group (EXE)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  Borehole at Yellowford Farm, Thorverton. No curated material. Top of formation was not penetrated; lower contact with Thorverton Sandstone at 76.5m depth. 
Edwards, R A, 1984. Geological Notes and Local Details for 1:10,000 Sheets. Parts of Sheets SS80SE and SS90SW (Thorverton, Devon). British Geological Survey, Exeter. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable