The BGS Lexicon of Named Rock Units — Result Details

Moelfryn Mudstones Formation

Computer Code: MFN Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Ashgill Series (OA) — Ashgill Series (OA)
Lithological Description: Pale grey, brown-weathering burrow-mottled mudstones with thin siltstone and locally, sandstone beds. A thin, muddy, bioclastic limestone member [Rhiwlas Limestone] occurs at the base of the Formation in places.
Definition of Lower Boundary: Unconformable on various Caradoc formations.
Definition of Upper Boundary: Conformably overlain by the Foel y ddinas Mudstone Formation, but in the Corwen District is unconformably overlain by the the sandstones and siltstones of the Bron-y-graig Formation.
Thickness: To 900m
Geographical Limits: none recorded or not applicable
Parent Unit: Not Applicable (-)
Previous Name(s): Moelfryn Mudstone (-4791)
Maerdy Mudstone Formation [Obsolete Name And Code: Use MFN] (MAE)
Rhiwlas Mudstones (-1690)
Alternative Name(s): Maerdy Mudstone Formation
Stratotypes:
none recorded or not applicable
Reference(s):
Elles, G L. 1922. The Bala country: its structure and rock succession. Quarterly Journal of the Geological Society of London, Vol.78, 132-175. 
Alder, K E, 1976. The geology of an area around Bettws Gwerfil Goch and Melin-y-Wig. Unpublished PhD Thesis, University of Cambridge. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E136 E120