The BGS Lexicon of Named Rock Units — Result Details
Castell Coch Limestone Formation
| Computer Code: | CCL | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Courceyan Substage (CF) — Courceyan Substage (CF) | ||
| Lithological Description: | Grey, locally reddened, medium- to thick-bedded, cross-bedded, oolitic and skeletal grainstones deposited as part of a barrier complex. Thin units of grey mudstone, calcite mudstone and calcisiltite are locally present in the uppermost part of the Formation and represent back barrier peritidal deposits. North of Risca, conglomerates, calcareous sandstones and sandy limestones are present in the lowermost part. | ||
| Definition of Lower Boundary: | Interbedded thin- to medium-bedded grey skeletal packstones and mudstones forming the upper part of the Tongwynlais Formation thicken upwards and pass up quickly, but gradationally, into the medium- to thick-bedded oolitic and skeletal grainstones of the Castell Coch Limestone Formation. The base of the Castell Coch Limestone Formation is taken at the incoming of a mudstone-free sequence. North of Risca, the Castell Coch Limestone Formation oversteps the Tongwynlais Formation to overlie the component formations of the Quartz Conglomerate Group. The base is taken at the sharp erosive contact between the green grey sandstones, quartz conglomerates and red and green mudstones of the Quartz Conglomerate Group and the overlying calcareous sandstones, sandy limestones, and skeletal and oolitic grainstones of the Castell Coch Limestone Formation. A persistent phosphatic, conglomeratic lag up to 0.7m thick is present at the base. | ||
| Definition of Upper Boundary: | Where barrier mudstones, calcite mudstones and calcisiltites occupy the uppermost part of the formation, the top is taken at the sharp base of the overlying marine interbedded grey mudstones and packstones of the Cwmyniscoy Mudstone. The contact is commonly erosional and overlain by a packstone or grainstone bed rich in interclasts of the underlying back barrier mudstones. Where the uppermost part of the formation comprises barrier grainstones, the top is taken at the sharp incoming of the overlying interbedded grey mudstones and packstones of the Cwmyniscoy Mudstone Formation. | ||
| Thickness: | 30m on the north crop of the South Wales Coalfield [Abergavenny], thinning southwards to 9m in the south of the Vale of Glamorgan. | ||
| Geographical Limits: | Vale of Glamorgan [ST 00 74] and South Wales Coalfield [SO 09 02], east of Swansea. Present but currently unmapped in the east crop of the South Wales Coalfield [ST 25 90], Gower [SS 50 90] and Monmouth and Chepstow areas [ST 53 93]. | ||
| Parent Unit: | Avon Group (AVO) | ||
| Previous Name(s): | Bastard Limestone [Obsolete Name and Code: Use CCL]
(-115)
Castell Coch Limestone [Obsolete Name and Code: Use CCL] (CTC) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Castell Coch Quarry, 50m west of Castell Coch, Tongwynlais, Cardiff. Entire formation seen, mainly in oolitic/skeletal kimestone; thin unit of peritidal deposits in upper part. Basal contact with Tongwynlais Formation not exposed due to 1m-thick exposure gap; upper contact with Cwmyniscoy Mudstone Formation exposed. (see Waters and Lawrence, 1987) | ||
| 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). | |||
| Strahan, A, and Cantrill, T C. 1902. The geology of the South Wales Coalfield, Part III. The country around Cardiff. First Edition. Memoir of the Geological Survey, Sheet 263 [England and Wales]. | |||
| Burchette, T P. 1987. Carbonate barrier shorelines during the basal Carboniferous transgression: The Lower Limestone Shale Group, South Wales and western England. 239-263 in European Dinantian Enviroments. Miller, J, Adams, A E, and Wright, V P (editors). (Chichester: John Wiley and Sons.) | |||
| Barclay, W J, Jackson, D I, Mitchell, M, Owen, B, Riley, N J, White, D E, Strong, G E, and Monkhouse, R A. 1989. Geology of the South Wales Coalfield, Part II, the country around Abergavenny. Memoir of the British Geological Survey. | |||
| 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: | |||
| E232 E263 E214 E262 | |||