The BGS Lexicon of Named Rock Units — Result Details

Pennant Sandstone Formation

Computer Code: PES Preferred Map Code: notEntered
Status Code: Full
Age range: Bolsovian Substage (CC) — Asturian Substage (CAS)
Lithological Description: Green-grey and blue-grey, feldspathic, micaceous, lithic arenites (Pennant-type sandstones) of southerly provenance and minor conglomerates, with thin mudstone/siltstone and seatearth interbeds and mainly thin coals. The lithologies are commonly arranged in fining-upwards channel-fill sequences. The sandstones formed in channels and floodplains within a broad alluvial tract, with low- to moderate-sinuousity rivers flowing northward from a rising Hercynian mountain belt to the south (Kelling and Collinson, 1992). Late Bolsovian to early Asturian age.
Definition of Lower Boundary: The base of the formation is markedly diachronous, placed at the base of the first thick (over approximately 3 m) sandstone of Pennant type (lithic arenite), occurring at younger levels towards the north. Generally sharp and nongradational, the base overlies grey mudstones/siltstones of the South Wales Coal Measures Group. In the Swansea area of the south-west of the coalfield, in practice the base can be taken at, or just above, the top of the Cambriense Marine Band. In the eastern part of the South Wales Coalfield the base of the formation rises to the level of the Brithdir Coal (base of Brithdir Member). The base of the formation ranges from up to 180 m below the Cambriense Marine Band in the Somerset Coalfield, to 180 m above the same marine band in the Bristol Coalfield.
Definition of Upper Boundary: The top is taken at the base of the grey mudstone-dominated succession of the Grovesend Formation. This is taken at the base of Swansea Four-Feet/Mynyddislwyn seam above the massive 'Pennant' sandstones of the underlying Swansea Member. In the eastern part of the coalfield, the coal appears to lie at an unconformity, with the Swansea Member apparently absent and the coal resting on 'Pennant' sandstones of the Hughes Member.
Thickness: The formation is thickest, up to 1335 m, in the Swansea area [SS 73 94] of the south-west of the South Wales Coalfield, thinning both to the north and east. In the east of the South Wales Coalfield [SO 25 03] the formation is c. 275 m thick. In the Somerset Coalfield the formation is in excess of 1000 m, thinning northwards to about 700 m in the Bristol Coalfield.
Geographical Limits: The formation extends across the South Wales, Bristol and Forest of Dean coalfields at outcrop and the subsurface Oxfordshire-Berkshire Coalfield. A distinct sandstone-dominated formation cannot be recognised within the subsurface Kent Coalfield.
Parent Unit: Warwickshire Group (WAWK)
Previous Name(s): Pennant Formation (Forest Of Dean) [Obsolete Name and Code: Use PES] (PNNT)
Arenaceous Coal Formation [Obsolete Name and Code: Use PES] (ACF)
Pennant Group (South Wales) [Obsolete Name and Code: Use PES] (PTS)
Pennant Group [South Wales Coalfield] [Obsolete Name and Code: Use PES] (*913)
Lower Pennant Sandstones [Obsolete Name and Code: Use PES] (-2300)
Pennant "Series" [Obsolete Name and Code: Use PES] (-2381)
Upper Pennant Sandstones [Obsolete Name and Code: Use PES] (-1896)
Lower Pennant Measures [Obsolete Name and Code: Use PES] (LPEM)
Pennant Sandstone Group [Obsolete Name and Code: Use PES] (-448)
Pennant Measures [Obsolete Name and Code: Use PES] (-1757)
Pennant Sandstones [Obsolete Name and Code: Use PES] (-2974)
Upper Pennant Measures [Obsolete Name and Code: Use PES] (UPEM)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The formation crops out widely in the South Wales Coalfield, from near Llanelly [SN 40 00] in the west to near Pontypool [ST 25 03] in the east (Woodland et al., 1957). 
Reference Section  The Earlswood road cutting [SS 730 944 to 730 946] and nearby Ferryboat Inn Quarry [SS 731 940] provide a well documented reference section of the Pennant Sandstone Formation, with more recent cuttings at the adjacent M4 interchange [SS 728 942 to 728 948] adding to the exposures. Records about 170 m thickness of the Rhondda Member (Kelling, 1971; Cleal and Thomas, 1996). 
Reference(s):
Kelling, G. 1971. Upper Carboniferous sedimentation in the central part of the South Wales Coalfield. 85-95 in Bassett, D A and Bassett, M G (editors), Geological excursions in South Wales and the Forest of Dean. [Cardiff: Geologists' Association, South Wales Group.] 
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. 
Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. 
Cleal, C J and Thomas, B A. 1996. Earlswood Road Cutting and Ferryboat Inn Quarry. 92-94 in Cleal, C J and Thomas, B A (editors), British Upper Carboniferous stratigraphy. [Chapman and Hall.] 
Kelling,G., and Collinson,J.D. 1992. Silesian. 239-273 in Duff,P.McL.D. and Smith,A.J. (editors). Geology of England and Wales. (London: The Geological Society.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E250 E281 E246 E264