Computer Code: |
PNWL |
Preferred Map Code: |
notEntered |
Status Code: |
Index Level |
Age range: |
Brigantian Substage (CX)
— Brigantian Substage (CX) |
Lithological Description: |
[Obsolete: use OHL] Stacked cyclic sequence of dark grey limestones in which shelly and crinoidal grainstones are the major components; beds are locally sandy, and chert layers and nodules are abundant. Many cycles are truncated by subaerial surfaces underlain by nodular limestones and overlain by seatearths and thin coals. |
Definition of Lower Boundary: |
Taken at the point where dark limestones of the Penwyllt Limestone overlie pale grey oolite of the Penderyn Formation. |
Definition of Upper Boundary: |
Taken at the point where the dark grey limestones of the Penwyllt Limestone are overlain by thinly bedded impure limestones of the Oystermouth Formation. |
Thickness: |
20m |
Geographical Limits: |
The North Crop of the South Wales Coalfield. |
Parent Unit: |
none recorded or not applicable
|
Previous Name(s): |
Middle Dibunophyllum Limestones [Obsolete Name and Code: Use PNWL]
(-462)
|
Alternative Name(s): |
none recorded or not applicable
|
Stratotypes: |
Type Section |
Penwyllt Quarry, near the hamlet of Penwyllt in the upper Tawe Valley, Powys. Barclay et al., 1988. |
Reference(s): |
Robertson, T. 1932. Geology of the South Wales Coalfield, Part V, the country around Merthyr Tydfil, 2nd edition. Memoir of the Geological Survey of Great Britain, Sheet 231. |
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. |
Barclay, W J, Taylor, K and Thomas, L P, 1988. Geology of the South Wales Coalfield, Part V, the country around Merthyr Tydfil. Third Edition. Memoir of the British Geological Survey, Sheet 231 (England and Wales). |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
E231
|