The BGS Lexicon of Named Rock Units — Result Details

Lower Bala Group

Computer Code: LBA Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Calcareous ashy mudstones, dark blue silty mudstones, siltstones with fine-grained sandstones, ash, dark blue mudstones and subordinate siltstones with limestone.
Definition of Lower Boundary: Drawn at the base of the Derfel Limestone Member of the Nant Hir Mudstones Formation. The oldest rocks exposed in the area.
Definition of Upper Boundary: Drawn at the conformable upward passage of calcareous ashes of the Gelligrin Calcareous Ashes Formation where it is unconformably overlain by the Moelfryn Mudstones Formation.
Thickness: 1505 metres approx.
Geographical Limits: The Arenig and Bala areas of 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  The area immediately surrounding Lake Bala. 
Reference(s):
Bassett, D A, Whittington, H B and Williams, A. 1966. The stratigraphy of the Bala district, Merionethshire. Quarterly Journal of the Geological Society of London, Vol.122, 219-271. 
Williams, A and others, 1972. A correlation of Ordivician rocks in the British Isles. Geological Society of London Special Report No.3. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable