The BGS Lexicon of Named Rock Units — Result Details

Afon Gam Formation [Obsolete Name And Code: See DYN]

Computer Code: AFO Preferred Map Code: AFO
Status Code: Index Level
Age range: Tremadoc Series (O1) — Tremadoc Series (O1)
Lithological Description: Grey, blocky to slightly fissile mudstones and sporadic thin, discontinuous silty laminae. Bioturbated. Fossiliferous. Includes a siltstone member - the Tai-herion Member.
Definition of Lower Boundary: Succeeds black pyritous mudstones.
Definition of Upper Boundary: Marked by base of massive grits although this boundary may be gradational locally and where the grit is absent by incoming of streaky mudstones and siltstones.
Thickness: 500 metres. 20-500 metres.
Geographical Limits: Not defined.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): Dol-Cyn-Afon Formation
Stratotypes:
Type Area  Snowdon, Sheet 119. 
Reference(s):
Lynas, B D T, 1973. The Cambrian and Ordovician rocks of the Migneint area, North Wales. Journal of the Geological Society, London, Vol.129, 481-503. 
Rushton, A W A and Howells, M F. 1998. Stratigraphical framework for the Ordovician of Snowdonia and the Lleyn Peninsula. British Geological Survey Research Report, RR/99/08. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E120