The BGS Lexicon of Named Rock Units — Result Details

Careg Onen Formation

Computer Code: OCO Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Ediacaran Period (AD) — Comley Series (EC)
Lithological Description: Fine- to coarse-grained, locally micaceous greywacke ["high-matrix"] sandstones, conglomeratic in places, with igneous and metamorphic clasts, interbedded with sandy mudstones, locally ferruginous.
Definition of Lower Boundary: Unknown, but Greenly [1919] supposed that it overlay the Gwna Melange (now the Gwna Group)] of Anglesey. There is some doubt about this, given current uncertainties on the age of these divisions.
Definition of Upper Boundary: Unknown, but probably overlain unconformably by Ordovician strata.
Thickness: Unknown.
Geographical Limits: Anglesey. The formation represents part of the Arfon Group of the mainland that extends onto Sheet 105 Caernarfon.
Parent Unit: Arfon Group (ARN)
Previous Name(s): Careg-Onen Beds (A) [Obsolete Name And Code: Use OCO] (CON)
Careg-Onen Beds (B) [Obsolete Name And Code: Use OCO] (CGO)
Careg-Onen-Beds (-1737)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  North slope of Mynydd Llwydiarth. Greenly, 1919. 
Type Section  Sea cliff at Careg-onen Cove. 
Reference(s):
Greenly, E. 1944. The Arvonian rocks of Arvon. Quarterly Journal of the Geological Society, London, 100, 269-287. 
Greenly, E. 1919. The Geology of Anglesey, Vol 2. Memoir of the Geological Survey of Great Britain [England and Wales]. [London: H.M.S.O.]. 
Reedman, A J, Leveridge, B E and Evans, R B. 1984. The Arfon Group (Arvonian?) of North Wales. Proceedings of the Geologists' Association, Vol.95, 313-321. 
Greenly, E. 1946. The Monio-Cambrian interval. Geological Magazine, Vol. 83, 237-240. 
Carney J N et al. 2000. Precambrian rocks of England and Wales. Geological Conservation Review Series. No 20. [Peterborough: Joint Nature Conservation Committee]. 252pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E093 E105