The BGS Lexicon of Named Rock Units — Result Details

Lower Nantglyn Flags Group [Obsolete Name And Code: See NGF]

Computer Code: LNF Preferred Map Code: notEntered
Status Code: Index Level
Age range: Sheinwoodian Age (SS) — Homerian Age (SH)
Lithological Description: Alternations of bands of fossiliferous mudstone and laminated muddy siltstone with subordinate thin lenticular bands of calcareous siltstones.
Definition of Lower Boundary: Drawn at the base of the Lower Nantglyn Flags where massive dark blue/grey mudstones with siltstone bands rests conformably upon the fossiliferous beds of grey sandstone of the Llanddoged Formation.
Definition of Upper Boundary: Drawn at the conformable upward passage of the Bryn Sylldy Formation where part ribbon banded mudstones but more frequent silty mudstone is conformably overlain by graptolitic ribbon banded mudstones of the Upper Nantglyn Flags Group.
Thickness: 320-660 metres.
Geographical Limits: The Denbigh Moors, Denbigh, North Wales.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): Nantglyn Flags Formation
Stratotypes:
Type Area  From Tywyn through Eglwysbach to Llanrwst,through Oerfa across the Denbigh Moors as far as Llech Daniel. 
Type Area  Sheet (120) Corwen. Through Clocaenog Forest terminating against the Gwaynynog Fault. 
Type Area  From Llan Sannan through Moel Grugoer to Bylchau. 
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. 
Boswell, P G H, 1926. A contribution to the geology of the eastern part of the Denbighshire Moors. Quarterly Journal of the Geological Society, Vol.82, p.562. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable