The BGS Lexicon of Named Rock Units — Result Details

Fron-fawr Formation

Computer Code: FRFA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: Red, purple and variegated silty mudstones, siltstones and sandstones with lenticular conglomerates and basal breccias. The silty mudstones locally display glaebular calcrete profiles including abundant calcareous nodules and thin units of nodular limestone. Records the accumulation of terrestrial scree and alluvial deposits in a fault controlled embayment prior to the establishment of the Clwyd Limestone Group carbonate platform.
Definition of Lower Boundary: Rests unconformably on Silurian rocks (Elwy Formation and Dinas Bran Beds).
Definition of Upper Boundary: Conformable contact with limestones of the Leete Limestone Formation.
Thickness: To 90m
Geographical Limits: West of Eglwyseg Rocks escarpment (SJ 22 45), north of Llangollen, North Wales.
Parent Unit: Not Applicable (-)
Previous Name(s): Basement Beds (-3812)
Basement Beds Formation [Obsolete Name And Code: See Supplementary Information] (BED)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Eastern slope of Fron-fawr Hill provides intermittent exposures in red sandstone and conglomerate within the lower part of the formation. Wedd et al., 1927. 
Reference(s):
Wedd, C B, Smith, B and Wills, L J. 1927. The geology of the country around Wrexham, Part 1. Lower Palaeozoic and Lower Carboniferous rocks. Memoir of the Geological Survey of Great Britain. [London: HMSO.] 179pp. 
Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. 
Morton, G H 1876-8. The Carboniferous Limestone and Millstone Grit of North Wales. Proceedings of the Liverpool Geological Society. Vol.3, 190-201. 
Waters, C N, Barclay, W J, Davies, J R and Waters, R A. In press. Stratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable