The BGS Lexicon of Named Rock Units — Result Details

Foel Formation

Computer Code: FOF Preferred Map Code: notEntered
Status Code: Full
Age range: Chadian Substage (CI) — Chadian Substage (CI)
Lithological Description: Heterolith of dark-grey, peloidal limestones, shelly, oncolitic and locally oolitic limestones, porecllanous limestones, and fossil plant-bearing calcareous siltstones and calcareous sandstones. Limestones locally dolomitised. The oldest exposed parts of the Clwyd Limestone Group, the Foel Formation records peritidal deposition during the onset of the Dinantian transgression of North Wales.
Definition of Lower Boundary: Locally conformably overlies reddened "Basement Beds" (Ffernant Formation or Penbedw Formation); but elsewhere rests unconformably on Silurian rocks of the Clwydian Range (Nantglyn Flags Formation and Elwy Formation.
Definition of Upper Boundary: Conformable contact with thicker-bedded limestones of the Llanarmon Limestone Formation.
Thickness: To 88m
Geographical Limits: Confined to the north and east of the Clwydian Range in northeast Wales, between Moel Hiraddug [SJ0778] and Gelli Gynan. [SJ1854].
Parent Unit: Clwyd Limestone Group (CLWYD)
Previous Name(s): Lower Brown Limestone [Obsolete Name And Code: See FOF, LEEL, LNML, TNL] (LBRL)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  The northernmost of two quarries on the west side of Moel Hiraddog at Tan-y-Foel, which provides a section through the upper 12.9m of the Formation. Warren, P T et al, 1984 
Reference(s):
Warren, P T, Price, D, Nutt, M J C and Smith, E G. 1984. Geology of the country around Rhyl and Denbigh. Memoir for 1:50 000 geological sheets 95 and 107 and parts of sheets 94 and 106. 
Davies, J R, Wilson, D and Williamson, I T. 2004. Geology of the country around Flint. Memoir for 1:50 000 Geological Sheet 108. 
Somerville, I D, Strank, A R E and Welsh, A, 1989. Chadian faunas and floras from Dyserth: depositional environment and palaeogeographic setting of Visean strata in Northeast Wales. Geological Journal, Vol.24, 49-66. 
Strahan, A, 1890. The Geology of the Neighbourhoods of Flint, Mold and Ruthin. Memoir of the Geological Survey, Sheet 79SE (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E108 E096 E121