The BGS Lexicon of Named Rock Units — Result Details

Pembroke Limestone Group
Computer Code: PEMB Preferred Map Code: notEntered
Status Code: Full
Age range: Courceyan Age (CF) — Brigantian Age (CX)
Lithological Description: Skeletal and ooidal limestones with some calcite- and dolomite-mudstones, sandstones and mudstones, and a few coals and cherts. Waulsortian reef limestones occur in the south. Extensively dolomitised on the east crop of the South Wales Coalfield. Interfingers with fluvial sandstones in the Monmouth, Chepstow and Bristol areas. Deposited in a ramp setting that, with time, became a platform.
Definition of Lower Boundary: Conformable and taken in southern settings at the incoming of dark grey fine to coarse skeletal packstones with scattered mudstone partings of the Black Rock Limestone Subgroup above the interbedded mudstones and skeletal packstones of the Avon Group. Along the north crop of the South Wales Coalfield, taken at the gradational incoming of the dolomitised skeletal packstones [Sychnant Dolomite Formation] of the Clydach Valley Subgroup above the interbedded mudstones and skeletal packstones of the Avon Group.
Definition of Upper Boundary: Conformable and gradational in south Pembrokeshire, Swansea and Bristol/Mendip areas and taken at the incoming of banded cherts, silaceous mudstones and mudstones [Aberkenfig Formation] of the Marros Group above the interbedded limestones and mudstones and cherts [Oystermouth Formation] of the Group. Elsewhere, overlain unconformably by the Marros Group.
Thickness: To 1025m
Geographical Limits: South Wales [SN 99 02], Bristol and the Mendip Hills area [ST 50 65].
Parent Unit: Carboniferous Limestone Supergroup (CL)
Previous Name(s): Main Limestone Group (-4177)
Clifton Down Group (-4834)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  South Pembrokeshire, where it is well exposed along the coast from Tenby to Frainslake Sands. 
Reference(s):
Waters, C N, Brown, M A E, Dean, M T and Powell, J H. In press. Lithostratigraphical framework for Carboniferous successions of Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
Dixey, F and Sibly, T F. 1918. The Carboniferous Limestone Series on the southeastern margin of the South Wales Coalfield. Quarterly Journal of the Geological Society of London, Vol.73, 111-164. 
Dixon, E.E.L.. Geological Survey of Great Britain. 1921. The geology of the south Wales coalfield. Part XIII, The country around Pembroke and Tenby, being an account of the region comprised in sheets 244 and 245. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E244 E245
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