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" sandstones) of southerly provenance, with thin mudstone/siltstone and seatearth interbeds and mainly thin coals; the lithologies are commonly arranged in fining-upwards channel-fill sequences.
Definition of Lower Boundary: The base of the Formation is placed at the base of the first thick (c. over 3m) "Pennant" sandstone bed. Generally sharp and non-gradational, the base overlies grey mudstones/siltstones of the South Wales Coal Measures Group.
Definition of Upper Boundary: The top is placed at the base of the Grovesend Formation (base of Swansea Four-Feet/Mynyddislwyn Coal), where the coal lies between massive "Pennant" sandstones of the underlying Swansea Member and the grey mudstones of the overlying Grovesend Formation. 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: c.275m in the east of the coalfield [c.SO 25 03] to c.1350m in the Swansea area [SS 73 94].
Geographical Limits: Crops out widely in the South Wales Coalfield, from near Llanelly [SN 40 00] in the west to Pontypool [SO 25 03] in the east. It is also present in the Forest of Dean and Bristol coalfields, and in the subsurface in the Oxfordshire and Berkshire coalfields.
Parent Unit: Warwickshire Group (WAWK)
Alternative Name(s): none recorded or not applicable
Type Area  Formation named after the predominant "Pennant" sandstone facies of the South Wales Coalfield, which provided a "type area". It crops out widely in the coalfield, from near Llanelly [SN 40 00] in the west to near Pontypool [ST 25 03] in the east. 
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 c.170m thickness of the Rhondda Member. 
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. 
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. 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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E250 E281 E246 E264