Product has been added to the basket

Upper Carboniferous (Pennsylvanian)

Chronostratigraphy Britain has some of the best exposed sequences of non-marine Upper Carboniferous strata anywhere in Europe, and the Upper Carboniferous ranks as one of the most significant parts of the geological column in Britain for its historical economic importance.

The Upper Carboniferous (Pennsylvanian) is distributed in 5 separate main regions. 1) The Culm Trough in SW England was a shallow marine to lacustrine basin that was progressively filled during the Namurian and Westphalian, in part coincidental with basin inversion and tectonic deformation. 2) The Kent Coalfield, known only through boreholes and underground mine workings. (3) South Wales, the Forest of Dean and the Bristol–Somerset coalfields where there is progressive infill of a shallow marine basin by deltaic sediments during the Namurian to Mid Westphalian, with the Westphalian successioncharacterised by development of extensive peat deposits. In the late Westphalian, the influx of arenaceous fluvial channel deposits formed the Pennant Sandstone Formation and the overlying mudstone-dominated fluvial floodplain deposits of the Grovesend Formation. (4) The northern English Midlands, North Wales, the Pennines, and northern England, where, the Namurian is formed from mainly northerly-derived deltaic deposits and the lower and middle Westphalian by fluvio-deltaic deposition, sourced variably from the north, west and southeast. The formation of primary red beds (e.g. Etruria and Salop formations) lacking significant coal development characterize the youngest deposits. (5) The Midland Valley of Scotland includes Namurian arenaceous fluvial and deltaic deposits and marine limestones. Coal-bearing deposits occur both in the Namurian and lower Westphalian successions and red beds in the upper Westphalian. Here volcanicity had a large influence on basin configuration and sedimentation (e.g. the Ayrshire Bauxitic Clay Formation).

Biostratigraphical sub-division of the British Upper Carboniferous is based mainly on ammonoids (goniatites), with non-marine bivalves, miospores and plant macrofossils also of importance. Marine bands (defined lithostratigraphically as a particular rock body, but also biostratigraphically) have then been used as the basis for defining the British chronozones and stages, often named with reference to particular ammonoid taxa (e.g. Subcrenatum Marine Band, Bilinguites bilinguis Marine Band. Cineritic tonsteins, (result of volcanic ash-falls) have also been extensively used for sub-division particularly in Europe (important for establishing correlations between the paralic coalfields and intra-montane basins).

There is considerable variation in the lithostratigraphical development of the Upper Carboniferous and different areas generally have their own formations. However, there is an underlying pattern of lithofacies broadly recognizable as eight groups/supergroups. A) Holsworthy Group: predominantly marine or marginal non-marine turbidite and deltaic deposits found in the Culm Trough (Component formations: Bealsmill Sandstone, Crackington, Bideford and Bude). B) Millstone Grit Group: mainly marine to non-marine shales and deltaic to fluvial sandstones found in the Namurian and locally basal Westphalian of central and northern England and North Wales (component subdivisions:,Pendleton, Silsden, Samlesbury, Hebden, Marsden and Rossendale in the Pennines; Cefn-y-fedw Sandstone in North Wales; Morridge in the English Midlands; and First Grit and Second Grit in northern England). In South Wales and southern England, the equivalent succession is represented by the Marros Group (component formations: Twrch Sandstone, Bishopston Mudstone and Telpyn Sandstone in South Wales and Quartzitic Sandstone in the Bristol area. C) Coal Measures Supergroup: grey coloured of fluvio-lacustrine origin, often including coal deposits, and thin marine beds (component groups: South Wales, Pennine and Scottish Coal Measures). D) Warwickshire Group: mainly primary alluvial red beds (component formations: Etruria, Halesowen, Salop in central England and North Wales; Whitehaven Sandstone in northern England, Pennant Sandstone and Grovesend in South Wales and southern England). The final closure of the Rheic Ocean led to the Variscan or Hercynian Orogeny during late Westphalian to Permian times. The sediments of the Warwickshire Group are in part the product of this deformation event (extracts modified from Cleal and Thomas, 1996).

Further Information

Cleal, C.J. & Thomas, B.A., (1996). British Upper Carboniferous Stratigraphy, Geological Conservation Review Series, No. 11, Chapman and Hall , London, 339pp.

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.

Dean, M T, Browne, M A E, Waters, C N, and Powell, J H. (2011). A lithostratigraphical framework for the Carboniferous successions of northern Great Britain (onshore). British Geological Survey Research Report, RR/10/07.

Waters, C N, Somerville, I D, Jones, N S, Cleal, C J, Collinson, J D, Waters, R A, Besly, B M, Dean, M T, Stephenson, M H, Davies, J R, Freshney, E C, Jackson, D I, Mitchell, W I, Powell, J H, Barclay, W J, Browne, M A E, Leveridge, B E, Long, S L, And Mclean, D. (2011). A Revised Correlation of Carboniferous Rocks in the British Isles. Special Report No. 26. (London: The Geological Society).