The BGS Lexicon of Named Rock Units — Result Details

Penllwyn Oolite Member

Computer Code: PENO Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Arundian Substage (CJ)
Lithological Description: Ooidal limestone and bioclastic limestone, bioturbated, locally ripple-marked and cross-bedded; oncoids are present at the base and stromatolites are present at the top. The limestone is a grainstone, with some local fining up to packstone and wackestone.
Definition of Lower Boundary: The base is placed where the bioclastic grainstone forming the base of the Member lies sharply on and truncates the underlying limestone or calcrete forming the topmost bed of the Cheltenham Limestone Member.
Definition of Upper Boundary: The top is placed at a palaeokarstic surface that truncates the Member and is overlain by the green clay forming the lowermost part of the overlying Gilwern Clay Member.
Thickness: 3 to 5m
Geographical Limits: Northeast crop of the South Wales Coalfield, from Cwar yr Ystrad [SO 081 142] to the Gilwern Hill area [SO 247 120].
Parent Unit: Llanelly Formation (LLY)
Previous Name(s): Linoproductus Oolite (-4836)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Clydach Halt Lime Works (Cwm) Quarry provides a good section of the Member where it is at its thickest (4m) and has a thin algal laminite in its middle. Wright, 1981. 
Type Section  Llanelly Quarry on the south side of the Clydach Gorge, 2km east of Brymawr, South Wales, provides a complete section of the Member, where it is 3m thick. Wright, 1981. 
Reference(s):
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. 
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.] 
Dickson, J A D and Wright, V P. 1993. Carboniferous Limestone of the north crop of the South Wales Coalfield. 331-349 in Woodcock, N H and Bassett, M G (editors), Geological excursions in Powys, central Wales. [Cardiff: University of Wales Press, National Museum of Wales.] 
George, T N. 1954. Pre-Seminulan Main Limestone of the Avonian Series in Breconshire. Quarterly Journal of the Geological Society of London, Vol.110, 282-322. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable