The BGS Lexicon of Named Rock Units — Result Details

Llanengan Formation

Computer Code: LGAN Preferred Map Code: Lgn
Status Code: Full
Age range: Arenig Series (OR) — Arenig Series (OR)
Lithological Description: Dark grey mudstone with thin laminae of sandstone and siltstone.
Definition of Lower Boundary: Sharply overlies well-bedded muddy sandstones of the St Tudwal's Formation. Boundary is marked by a thin phosphatic conglomerate horizon at the top of St Tudwals Formation, possibly representing a non-sequence or minor disconformity.
Definition of Upper Boundary: Sharply overlain by oolitic ironstones of the Hen-dy-Capel Ironstone which are succeeded by undivided mudstones of the Nant ffrancon Subgroup.
Thickness: 80m
Geographical Limits: Pwllheli area, northwest Wales.
Parent Unit: Nant Ffrancon Subgroup (NFR)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  South of Borth Fawr, near Pwllheli. 
Nicholas, T C. 1915. Geology of the St Tudwal's Peninsula. Quarterly Journal of the Gelogical Society of London, Vol.71, 83-143. 
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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used: