The BGS Lexicon of Named Rock Units — Result Details

Ogwen Group

Computer Code: OGW Preferred Map Code: OG
Status Code: Full
Age range: Arenig Series (OR) — Caradoc Series (O4)
Lithological Description: Mudstones and siltstones, but including basal sandstone units and other sandstones, tuffs and oolitic ironstones.
Definition of Lower Boundary: Base of the Allt Lwyd Formation, at unconformable boundary overlying the Mawddach Group and Rhobell Volcanic Group.
Definition of Upper Boundary: Top of the Nod Glas Formation .
Thickness: c.1000m Pwllheli District.
Geographical Limits: Gwynedd, North Wales
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Extends from Cwm Graianog in Nant Ffrancon, along the Ogwen and Llugwy valleys towards the syncline south-west of Grinllwm. 
Reference(s):
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:
E135 E118