The Carboniferous coal basins, Bristol and Gloucester region

Green, G W. 1992. British regional geology: Bristol and Gloucester region (Third edition). (London: HMSO for the British Geological Survey.)

Distribution of Coal Measures (outcrop and subsurface) in Avon and Somerset, showing coal 'basins'. (P948967)

The coal ‘basins’

The Coal Measures are associated with a number of discrete structural areas, all but the Kingswood Anticline being informally described as coal ‘basins’ (P948967).

Other Coal Measures occurrences

A small outcrop of Lower Coal Measures, including the Subcrenatum Marine Band, is present at Ebbor beneath the Ebbor Thrust, north-west of Wells. Other slices of Coal Measures are probably present beneath the Mesozoic cover within the Cheddar-Wells Thrust Belt on the south side of, and adjacent to the Mendips. In the absence of deep boreholes penetrating to the Palaeozoic basement, it is not known whether any appreciable areas of Coal Measures are present beneath the Mesozoic rocks of the Central Somerset Basin, though the geophysical evidence is thought to make this unlikely (Green and Welch, 1965).

Farther south and east, steeply dipping Coal Measures were proved in the Westbury Boring (Wiltshire), apparently on the southern side of the buried continuation of the Beacon Hill Pericline or an associated en échelon fold. The lithology and flora suggest that the strata are Lower or lower Middle Coal Measures.

Boreholes in the Moreton-in-Marsh to Burford area indicate that the western limit of the Oxfordshire Coalfield extends to the line of the Moreton 'Axis'. The coalfield succession comprises a thick coal-bearing grey sandstone sequence of Pennant Measure type in the lower part. There are two coal-bearing groups above, separated by barren and red measures, and a thick barren red measure sequence at the top. The total thickness is of the order of 1350 m. The fauna and flora show that the measures lie entirely in the tenuis Biozone of Westphalian D age. They unconformably overlie Upper Devonian but without any apparent angular discordance.