The BGS Lexicon of Named Rock Units — Result Details

Brofiscin Oolite Formation

Computer Code: BFO Preferred Map Code: notEntered
Status Code: Full
Age range: Courceyan Substage (CF) — Courceyan Substage (CF)
Lithological Description: Pale to purplish grey, thick-bedded to massive, cross-bedded, ooidal grainstone. On the southeast and east crop of the South Wales Coalfield the formation is dolomitized. Deposited as an ooid shoal.
Definition of Lower Boundary: The base of the Formation is taken at the sharp contact between the thin- to medium-bedded packstones of the underlying Barry Harbour Limestone Formation and the thick-bedded ooidal grainstones of the Brofiscin Oolite Formation. Along the southeast and east crop of the South Wales Coalfield the base is taken at the sharp junction between the dolomitized packstones of the Barry Harbour Limestone Formation and the overlying dolomitized oolite of the Brofiscin Oolite Formation.
Definition of Upper Boundary: The top of the Formation is taken at the sharp junction of the ooidal grainstones of the Formation and the overlying thin- to medium-bedded skeletal packstones of the Friars Point Limestone Formation. Along the south and east crop of the South Wales Coalfield the top is taken at the sharp junction between the dolomitized oolite of the Formation and the very fine- to fine-grained dolomitized packstones of the Friars Point Limestone Formation.
Thickness: 17m in the north of the Vale of Glamorgan, thinning southwards to a feather edge in the south of the Vale of Glamorgan.
Geographical Limits: Vale of Glamorgan [ST 00 74] and the south and east crops [ST 25 90] of the South Wales Coalfield, east of Swansea. Present in Gower [SS 50 90] but not mapped. Passes into the Clydach Valley Subgroup to the north.
Parent Unit: Black Rock Limestone Subgroup (BRL)
Previous Name(s): Candleston Oolite [Obsolete Name And Code: Use BFO] (CDO)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Brofiscin Quarry, 300m southsoutheast of Brofiscin Farm, Groesfaen, Vale of Glamorgan. Entire Formation exposed as oolitic grainstone. Contacts with the dolomitised underlying Barry Harbour Limestone and overlying dolomitised Friars Point Limestone formations exposed. 
Reference(s):
Waters, R A and Lawrence, D J D. 1987. Geology of the South Wales Coalfield - Part III: the country around Cardiff. Memoir of the British Geological Survey, Sheet 263. (England and Wales). 
George, T N, 1933. The Carboniferous Limestone Series in the west of the Vale of Glamorgan. Quarterly Journal of the Geological Society of London, Vol.89, 221-271. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E263 E262