The BGS Lexicon of Named Rock Units — Result Details

Brithion Formation

Computer Code: BRT Preferred Map Code: notEntered
Status Code: Full
Age range: Llanvirn Series (OE) — Llanvirn Series (OE)
Lithological Description: Volcanic breccias and felsic, welded ash-flow tuffs.
Definition of Lower Boundary: Sharp but conformable contact with underlying mudstones of the Aran Volcanic Group.
Definition of Upper Boundary: Conformably overlain by undivided siltstones of the Aran Volcanic Group.
Thickness: To 75m, but the formation wedges out southwestwards and northwards.
Geographical Limits: Harlech district.
Parent Unit: Aran Volcanic Group (AVG)
Previous Name(s): Brithion Tuff [Obsolete Name and Code: Use BRT] (-4502)
Creigiau Brithion Formation [Obsolete Name and Code: Use BRT] (-2641)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Crags to the northwest side of Craigiau Brithion. Dunkley, P N. 1978. 
Reference(s):
Dunkley, P N. 1978. The geology of the southwestern part of the Aran Range, Merioneth, with particular reference to the igneous history. Unpublished Ph.D. Thesis. University of Wales, Aberystwyth. 
Allen, P M, and Jackson, A A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 with part of Sheet 149 [England and Wales]. [London: HMSO.] 112pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E136 E149 E135