| Computer Code: |
CHLM |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Arundian Substage (CJ)
— Arundian Substage (CJ) |
| Lithological Description: |
Thin- to medium-bedded, mainly fine-grained limestones with pale green clay interbeds; the limestones are commonly arranged in fining-upwards cycles and comprise grainstone, wackestone and lime mudstone (including algal laminites). |
| Definition of Lower Boundary: |
The base is placed at the base of the lowest bedded limestone, where it sharply overlies the topmost rubbly limestone or clay with limestone nodules that forms the topmost bed of the underlying Clydach Halt Member. |
| Definition of Upper Boundary: |
The top is placed at the sharp junction between the topmost fine-grained limestone of the Cheltenham Limestone Member and the base of the ooidal grainstone at the base of the overlying Penllwyn Oolite Member. A palaeosol horizon is commonly present at the top of the Member, its top marking the junction. |
| Thickness: |
1.7m at Cwar yr Hendre [SO 099 149] to 8m in the Clydach gorge [SO 224 125]. |
| Geographical Limits: |
Northeast crop of the South Wales Coalfield; the Cheltenham Limestone Member is the most widespread of the members of the Llanelly Formation, with the same geographic limits - from the Hepste Valley [SN 971 129] east to the Clydach gorge [SO 214 125] and southwards down the east crop on the west side of the Afon Lwyd valley to about 1km south of Blaenavon [SO 261 077]. |
| Parent Unit: |
Llanelly Formation (LLY)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Llanelly Quarry on the south side of the Clydach gorge, 2km east of Brynmawr, South Wales, provides a complete section of the Member, where it is at its thickest. It is 8m thick and comprises a succession of mainly thin-bedded limestones. Wright, 1981. |
| Reference(s): |
| Wright, V P. 1981. Llanelly Formation. 36-72 in Wright, V P, Raven, M and Burchette, T P (editors), A field guide to the Carboniferous Limestone around Abergavenny. [Cardiff: Department of Geology, University College of Wales.] |
| Wright, V P. 1986. Facies sequences on a carbonate ramp; the Carboniferous Limestone of South Wales. Sedimentology, Vol.33, 221-241. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
