The BGS Lexicon of Named Rock Units — Result Details

Broad Vein Mudstone Formation

Computer Code: BRV Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Rawtheyan Stage (OW) — Rawtheyan Stage (OW)
Lithological Description: Pale-medium blue, silty-mudstone, intensely bioturbated in parts.
Definition of Lower Boundary: No lower boundary is exposed but the pale-medium blue mudstones of the Formation rest with sharp contrast upon the black mudstones of the Nod Glas Formation.
Definition of Upper Boundary: The upper boundary can be examined at Aberllefenni Quarry, where the contact is transitional, over 0.5m, from the pale-blue of the Broad Vein Mudstone Formation to a medium-blue, laminated silty mudstone of the Narrow Vein Mudstone Formation, accompanied by the development of lamination.
Thickness: 400 to 560m
Geographical Limits: Passes west into Cardigan Bay. The outcrop of the Broad Vein Formation crosses sheet 149 diagonally from southwest - northeast (Tywyn - Aberllefenni).
Parent Unit: Abercorris Group (ARO)
Previous Name(s): Red Vein [Obsolete Name and Code: Use BRV] (-1393)
Broad Vein [Obsolete Name and Code: Use BRV] (-3245)
Broad Vein Formation [Obsolete Name and Code: Use BRV] (-2025)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  The southwest facing slope of Foel Crochan, northeast of Aberllefenni Quarry. No reference sections need be cited as the type section is fully representative of the Formation. 
Reference(s):
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp 
Pratt, W T, Scott, M M, Leng, M J. 1990. Geological notes and local details for sheets SH71SE and SH71NE, Cadair Idris. British Geological Survey Technical Report WA/90/41. 
Pugh, W J. 1923. The geology of the district around Corris and Aberllefenni, (Merionethshire). Quarterly Journal of the Geological Society, London, Vol.79, 508-541. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E149