| Computer Code: |
CBM |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Arundian Substage (CJ)
— Arundian Substage (CJ) |
| Lithological Description: |
Thinly interbedded grey and green grey peloidal and bioclastic micrites, wackestones and packstones, and cryptalgal laminites. Dolomitisation is locally common; on the southeast and east crop of the South Wales Coalfield and in the Chepstow area, the formation is predominantly dolomitised. |
| Definition of Lower Boundary: |
The base of the formation is taken at the sharp erosional contact between the mudstone/clay palaeosol at the top of the Gully Oolite Formation and the overlying thinly bedded calcite mudstones and mudstones of the formation. A conglomeratic lag is locally present at the base of the Caswell Bay Mudstone Formation. |
| Definition of Upper Boundary: |
The top of the formation is taken at the sharp erosional contact between the thinly bedded calcite mudstones and mudstones of the formation and the overlying coarse peloidal and skeletal packstones/grainstones forming the lower part of the overlying High Tor Limestone Formation. |
| Thickness: |
15m on the south crop of the South Wales Coalfield, thinning southwards to a feather edge in the central Vale of Glamorgan, southwest Gower and southwest Pembrokeshire. |
| Geographical Limits: |
The Gower [SS 50 90], Vale of Glamorgan [ST 00 74], southeast crop of the South Wales Coalfield [ST 17 85] and Weston-super-Mare [ST 32 60] areas. Present in Pembroke [SM 97 03] and Tenby [SN 13 01] areas but not currently mapped. Passes northwards into the Llanelly Formation in Wales and Clifton Down Mudstone in the Bristol area [ST 60 73]. |
| Parent Unit: |
Pembroke Limestone Group (PEMB)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Cliffs and foreshore reefs on west and east sides of Caswell Bay, Gower. The sequence, comprising thinly bedded peritidal limestones and mudstones, is mainly completely exposed in three separate crops repeated by folding. The contacts with the underlying Gully Oolite Formation and overlying High Tor Limestone Formation are exposed. (see Ramsay, 1987). |
| Reference(s): |
| 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). |
| Ramsey, A T S, 1987. Depositional enviroments of Dinantian limestones in Gower, South Wales. 265-308 in European Dinantian Environments. Millar, J, Adams, A E and Wright, V P (editors). [Chichester: John Wiley and Sons.] |
| 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). |
| Institute of Geological Sciences. 1973. Swansea, England and Wales sheet 247. Solid Geology, 1:63,360. [Southampton: Ordnance Survey]. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E263
E262
E247
E246
E279
|
