The BGS Lexicon of Named Rock Units — Result Details

Cregennen Formation

Computer Code: CREN Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Abereiddian Stage (O2) — Abereiddian Stage (O2)
Lithological Description: Dark grey or black graptolitic mudstones interbedded with felsic acid and mafic tuffs and tuffites in places; sandstones and conglomerates occur locally.
Definition of Lower Boundary: Conformably overlies the felsic tuffs and tuffites of the Offrwm Volcanic Formation.
Definition of Upper Boundary: Conformably overlain by the felsic tuffs and conglomerate of the Brithion Formation in the north of the Cadair Idris district, and by pillowed basaltic lavas and mafic tuffs of the Llyn y Gafr Volcanic Formation elsewhere within the district.
Thickness: To 350m
Geographical Limits: Cadair Idris, southern Snowdonia, North Wales.
Parent Unit: Aran Volcanic Group (AVG)
Previous Name(s): Moelyn Slates (-3325)
Crogenen Slates (-2721)
Bifidus Slates (-1346)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Crags extending from the west side of Llynnau Cregennen to north of Pared y Cefn Hir. Pratt, W T, Woodhall, D G and Howells, M F. 1995. 
Reference(s):
Jones, B, 1933. The geology of the Fairbourne-Llwyngwril district, Merioneth. Quarterly Journal of the Geological Society, Vol.89, 145-171. 
Cox, A H and Wells, A K, 1927. The geology of the Dolgelley district, Merionethshire. Proceedings of the Geologists' Association, Vol.38, 265-318. 
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 
Cox, A H, and Wells, A K, 1921. The Lower Palaeozoic rocks of the Arthog-Dolgellau district (Merionethshire). Quarterly Journal of the Geological Society, London, Vol.76, p. 254-324. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E136 E135