The BGS Lexicon of Named Rock Units — Result Details

Clydach Halt Member

Computer Code: CLDH Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Arundian Substage (CJ)
Lithological Description: A heterolithic, lenticular unit of conglomerates, limestone layers and nodules, green clays and sandstones with some dolostones.
Definition of Lower Boundary: The base is placed at the base of green claystone and rubbly limestones (calcretes), where they overlie and infill an irregular palaeokarstic surface at the top of the underlying Gilwern Oolite Formation.
Definition of Upper Boundary: The top is placed at the incoming of well-bedded, thinly bedded, cyclic limestones (the Chelternham Limestone Member), where the basal bed of limestone sharply overlies the topmost green clay or rubbly limestone of the Clydach Halt Member.
Thickness: Generally up to 1 to 2m, 6m locally; 4m at the type locality [SO 235 127].
Geographical Limits: Northeast crop of the South Wales Coalfield, with sporadic development or preservation from Pontsticill, as seen in Baltic Quarry [SO 0659 1184] and Odynau Tyler Bont Quarry [SO 0635 1125], east to the Gilwern Hill area [c.SO 250 117].
Parent Unit: Llanelly Formation (LLY)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Quarry face of the abandoned Clydach Lime Works (Cwm) Quarry, where the member is 4m thick and comprises two calcrete palaeosols separated by conglomerate. Wright, 1981. 
Reference(s):
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.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable