The BGS Lexicon of Named Rock Units — Result Details

GROVESEND FORMATION
Computer Code: GDB  Status Code: FORMAL, NATIONAL 
Preferred Map Code:  
Age or Age Range: [ CD ] WESTPHALIAN D  to [  ]  
Lithological Description:
Predominantly argillaceous, comprising mudstones and siltstones, with well developed coals; minor lithic ("Pennant") sandstones; locally developed red mudstones in the type area. 
Definition of Lower Boundary:
The base is placed at the base of the Swansea Four-Feet Coal of the Swansea district (equivalent of the Llantwit No.3 Seam in the Pontypridd district and the Mynyddislwyn Seam east of the Taff valley), where it overlies mudstone seatearth at the top of the predominantly arenaceous Swansea Member in the Swansea district and the similar Hughes Member in the east of the coalfield. It is a conformable boundary in the west, but is assumed to be an unconformable one in the east (Woodland et al., 1957; Squirrell and Downing, 1969; Barclay, 1989). Also taken at the base of the laterally correlatable Rudge Coal in the Radstack part of the Somerset Coalfield, the High Coal of the Bristol Coalfield and the Avonmouth No.1 Coal of the Severn Coal Basin. 
Definition of Upper Boundary:
The Grovesend Formation is the youngest unit found in the South Wales and Forest of Dean coalfields. It is overlain unconformably by sandstones of the Sherwood Sandstone Group in the Newent Coalfield, by mudstones of the of the Mercia Mudstone Group in the Oxfordshire Coalfield and either the Sherwood Sandstone or Mercia Mudstone groups in the Bristol/Somerset Coalfields. 
Thickness:
To 426m in the South Wales Coalfield; 700m in the Oxfordshire-Berkshire coalfields. 
Geographical Limits:
Small areas in the South Wales Coalfield, the Formation being preserved in the cores of synclines and fault troughs from Llanelli [SN 50 00] to Llanhilleth [SO 25 05]. Also in the Somerset, Bristol, Forest of Dean and Oxfordshire coalfields. 
Parent Unit: Parent Unit Code:
WARWICKSHIRE GROUP  WAWK
Previous Name(s): Previous Code(s):
GROVESEND BEDS  GDB 
SUPRA-PENNANT MEASURES   
SUPRA-PENNANT FORMATION  SP 
SUPRA-PENNANT GROUP   
GROVESEND MEMBER   
Alternative Name(s):
none recorded or not applicable
Stratotypes:
Type Area  Type area named after the village of Grovesend [SN 593 005], 10km northwest of Swansea, South Wales. 
Reference Section  Railway cutting at Penllergaer exposes 22m of mainly grey mudstones and siltstones with two coals (Loughor Seam, 0.5m and Penyscallen Seam, 0.4m). Fossiliferous mudstones with non-marine bivalves and estheriids lie in the roofs of the coals. 
Reference(s):
Owen, T R. 1971. Excursion 2: South Wales. Compte Rendu 6e Congres International de Stratigraphie et de Geologie Carbonifiere. (Sheffield, 1967), Vol.4, 1669-98. 
Welch, F B A and Trotter, F M, 1961. Geology of the country around Monmouth and Chepstow. Explanation of one-inch geological sheets 233 and 250. Memoir of the Geological Survey of Great Britain. 
Barclay, W J, 1989. Geology of the South Wales Coalfield, Part II, the country around Abergavenny. Memoir of the British Geological Survey, Sheet 232, (England and Wales). 
Kellaway, G A and Welch, F B A. 1993. Geology of the Bristol district. Memoir of the British Geological Survey Special Sheet [England and Wales]. 
Cleal, C J and Thomas, B A. 1996. Penllergaer Railway Cutting. 96-97 in Cleal, C J and Thomas, B A (editors), British Upper Carboniferous Stratigraphy. [London: Chapman and Hall.] 
Waters, C N, Barclay, W J, Davies, J R and Waters, R A. In press. Stratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
Woodland, A W, Evans, W B and Stephens, J V. 1957. Classification of the Coal Measures of South Wales with Special reference to the Upper Coal Measures. Bulletin of the Geological Survey of Great Britain, No. 13, 39-60. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
Map Code Sheet Name
E  232
E  230
E  247

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