The BGS Lexicon of Named Rock Units — Result Details

Barry Harbour Limestone Formation

Computer Code: BHL Preferred Map Code: BHL
Status Code: Full
Age range: Courceyan Substage (CF) — Courceyan Substage (CF)
Lithological Description: Thin- to medium-bedded, dark grey, coarse- to fine-grained, commonly graded, skeletal [predominantly crinoidal, with subordinate brachiopods] packstones, either stacked or separated by thin beds and partings of calcareous mudstone. Planar, low angle and hummocky cross stratification, and cross lamination are common. Scattered bioturbation. Silicification of fossils and replacive elongate chert nodules common. In the Barry area, a unit [3 to 5m] of cross-bedded crinoidal grainstone, the Yorke Rock Bed, occurs at the top of the Formation. In the northwest of the Vale of Glamorgan, thin beds of ooid grainstone are present in the uppermost part of the Formation. Along the southeast and east crop of the South Wales Coalfield, the Formation is predominantly dolomitized; the upper part comprising very fine- to fine-grained, pale to dark grey, partly laminated and cross laminated dolomitised packstones with sparse fossiliferous lenses that are locally silicified.
Definition of Lower Boundary: The contact of the Cwmyniscoy Mudstone Formation with the overlying Barry Harbour Formation is gradational. In the uppermost part of the Cwmyniscoy Mudstone Formation, the proportion of packstone beds increases to exceed that of mudstone. The base of the Barry Harbour Limestone Formation is taken at the top of the last significant mudstone bed in the Cwmyniscoy Mudstone Formation, above which the succession becomes dominated by stacked fine- to coarse-grained skeletal packstones with scattered thin beds and partings of calcareous mudstone.
Definition of Upper Boundary: In the Barry area, the top of the Formation is taken at the sharp contact between the crinoidal grainstones of the Yorke Rock Bed, and the thin- to medium-bedded, fine- to coarse-grained, skeletal packstones with scattered thin beds and partings of mudstone of the overlying Friars Point Limestone Formation. To the north of Barry, the top of the Formation is taken at the sharp contact between the thin- to medium-bedded packstones of the 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 top is taken at the sharp junction between the dolomitized packstones of the Formation and the overlying dolomitized ooidal limestone of the Brofiscin Oolite Formation.
Thickness: 80m in the south of the Vale of Glamorgan, thinning northwards to 32m on the south crop of the South Wales Coalfield.
Geographical Limits: Vale of Glamorgan [ST 00 74]. Present in Gower [SS 50 90], Pembrokshire [SM 99 01], east crop of South Wales Coalfield [ST 25 90], Monmouth/Chepstow [ST 53 93] and Bristol/Mendip [ST50 65] areas but not mapped. Passes northwards in Wales into the Clydach Valley Subgroup.
Parent Unit: Black Rock Limestone Subgroup (BRL)
Previous Name(s): Black Rock Limestone (-3850)
Penmaen Burrows Limestone Formation [Obsolete Name And Code: See FPL And BHL] (PBL)
Shipway Limestone [Obsolete Name And Code: See BHL] (SPWL)
Lower Dolomite Formation [Obsolete Name And Code: See FPL And BHL] (LD)
Lower Dolomite (-1985)
Penmaen Burrows Limestone (-3213)
Rudry Formation [Obsolete Name And Code: See FPL] (RDY)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  The low cliffs and reefs on the western side of the old Barry Harbour. Entire Formation [80m] exposed, apart from a few minor exposure gaps. Unit mainly comprises thin to medium bedded, locally laminated and cross laminated skeletal limestones, capped by the Yorke Rock Bed. Junction with underlying Cwmyniscoy Mudstone Formation and Overlying Friars Point Limestone Formation exposed. 
Type Area  Sheet 263, Cardiff. 
Reference(s):
George, T N, Johnson, G A L, Mitchell, M, Prentice, J E, Ramsbottam, W H C, Sevastopulo, G D and Wilson, R B. 1976. A correlation of the Dinantian rocks of the British Isles. Special Report of the Geological Society of London, No 7. 
Kellaway, G A and Welch, F B A, 1955. The Upper Old Red Sandstone and Lower Carboniferous rocks of the Bristol and the Mendips compared with those of Chepstow and the Forest of Dean. Bulletin of the Geological Survey of Great Britain, No.9, p.1-21. 
Institute of Geological Sciences. 1973. Swansea, England and Wales sheet 247. Solid Geology, 1:63,360. [Southampton: Ordnance Survey]. 
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). 
Wilson, D, Davies, J R, Fletcher, C J N, and Smith, M. 1990. The Geology of the South Wales Coalfield, part VI the Country around Bridgend. Memoir of the British Geological Survey, 1:50 000 Geological Sheets 261 and 262 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E263 E262