The BGS Lexicon of Named Rock Units — Result Details

Penwyllt Limestone [Obsolete Name And Code: Use OHL]

Computer Code: PNWL Preferred Map Code: notEntered
Status Code: Index Level
Age range: Brigantian Substage (CX) — Brigantian Substage (CX)
Lithological Description: 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: Pembroke Limestone Group (PEMB)
Previous Name(s): Middle Dibunophyllum Limestones (-462)
Alternative Name(s): none recorded or not applicable
Type Section  Penwyllt Quarry, near the hamlet of Penwyllt in the upper Tawe Valley, Powys. Barclay et al., 1988. 
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: