The BGS Lexicon of Named Rock Units — Result Details

Wig Bach Formation

Computer Code: WGB Preferred Map Code: WgB
Status Code: Full
Age range: Moridunian Stage (OB) — Fennian Stage (OF)
Lithological Description: Dark grey mudstones, laminated siltstones and fine-grained bioturbated sandstones, with a ferruginous pisolitic sandstone and conglomerate at the base.
Definition of Lower Boundary: Unconformable on rocks of the Gwna Melange, Sarn Complex and Dol-cyn-afon Formation.
Definition of Upper Boundary: Conformably overlain by the Porth Meudwy, Llanengan and Trygarn formations as well as by undivided mudstones of the Nant Ffrancon Subgroup.
Thickness: To 550m
Geographical Limits: Not yet recorded.
Parent Unit: Nant Ffrancon Subgroup (NFR)
Previous Name(s): none recorded or not applicable
Alternative Name(s): Aberdaron Formation
Stratotypes:
Type Section  Composite section along 700m of cliffs between Aberdaron Beach and the islet of Ebolion. Young, T P, Gibbons, W and McCarroll, D. 2002. 
Reference Section  Parwyd (for base of Formation). Gibbons and McCarroll, 2003. 
Reference Section  Between Porth Simdde and Trwyn Cam. Gibbons and McCarroll, 2003 
Reference Section  Ogof Lleuddad. Gibbons and McCarroll, 2003. 
Reference Section  Wig (for base of Formation]. Gibbons and McCarroll, 2003. Note that the quoted NGR should be SH 1863 2570, but this has been modified by 10m to avoid constraint conflicts with the NGR of the Type Section. 
Reference Section  Porth Meudwy. Young, T P, Gibbons, W and McCarroll, D. 2002. 
Reference(s):
Matley C A. 1928. The Pre-Cambrian complex and assocciated rocks of south-western Lleyn (Carnarvonshire). Quarterly Journal of the Geological Society of London, Vol. 84, 440-501. 
Beckly, A J, 1988. The Stratigraphy of the Arenig Series in the Aberdaron to Sarn Area, Western Llyn, North Wales. Geological Journal, Vol.23, 321-337. 
Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). 
Shackleton, R M. 1956. Notes on the structure and relations of the Precambrian and Ordovician rocks of southwestern Lleyn (Carnarvonshire). Geological Journal, Vol.1. 400-409. 
Gibbons W and McCarroll D. 1993. Geology of the country around Aberdaron, including Bardsey Island. Memoir of the British Geological Survey, Sheet 133 (England and Wales). (London: H.M.S.O.). 88pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E133 E134