Abstract Carboniferous rocks within this region occur in a series of inliers, many occurring in the cores of periclines and anticlines. The Tournaisian and Visean strata comprise ramp carbonate successions (Avon and Pembroke Limestone groups), which show similarities with equivalent strata to the west in South Wales (Chapter 5). The main outcrops, broadly from south to north, are the Cannington Park inlier and Mendips, Weston-super-Mare, Broadfield Down, Bristol and Avon, Cromhall and Chepstow to Monmouth (Fig. 19). Namurian strata are present only in the south of the region, in the Bristol and Somerset coalfields. Little information is available on the nature of these strata, though they show some similarities to the fluvial and deltaic successions of the Marros Group of South Wales (Chapter 5). Westphalian strata are present in all the coalfields, broadly from south to north, the Somerset, Bristol, Severn, Forest of Dean and Newent coalfields (Fig. 19). Fluvio-lacustrine deposits (South Wales Coal Measures Group) are present only in the Somerset, Bristol and the south-eastern part of the Nailsea coalfields. These coalfields are laterally contiguous beneath Mesozoic strata. Deposition was also probably laterally contiguous with the concealed Berkshire Coalfield (Chapter 7). It has not been possible to demonstrate lateral continuity with the South Wales Coalfield (Chapter 5). Strata of this facies are absent from the Newent, Forest of Dean and Severn coalfields and the Cannington Park inlier along the axis of the syn-Westphalian Usk Anticline.

Abstract Carboniferous rocks within this area extend south from the exposed Warwickshire Coalfield (see Chapter 9) and are limited to the laterally contiguous concealed coalfields of Oxfordshire and Berkshire and the isolated Kent Coalfield. The oldest Tournaisian and Visean strata occur at subcrop within the Berkshire and Kent coalfields and include condensed ramp carbonate successions (Avon and Pembroke Limestone groups). Little is known of the stratigraphical and geographical extent of these deposits outside of these coalfields. Namurian strata have not been proved in any of the boreholes within the region. Westphalian strata are proved in all three coalfields, with progressively younger successions onlapping north-westwards onto the southern flank of the Wales-Brabant High. Pre-Asturian fluvio-lacustrine deposits (South Wales Coal Measures Group) are present in the Berkshire and Kent coalfields, but are restricted to isolated inliers beneath Asturian strata in the Oxfordshire Coalfield. A Westphalian to Stephanian succession of grey, alluvial Pennant facies (Warwickshire Group) characterized by feldspathic, micaceous and lithic sandstones occurs within all three coalfields (Fig. 22). The lithostratigraphical nomenclature is that of Waters et al. (2009).

Abstract Carboniferous rocks in this region occur in a broadly east-west trending syncline, the core of which includes the South Wales and Pembrokeshire coalfields (Fig. 16). Tournaisian and Visean strata (Avon and Pembroke Limestone groups) represent deposition on a southward prograding carbonate ramp evolving into a carbonate shelf (Wright 1987), in a succession which shows similarities to that of the Bristol and Mendips areas (Chapter 6). The main outcrops, in south Pembrokeshire, Gower and the Vale of Glamorgan, occur along the southern periphery of the coalfields and are commonly affected by Variscan thrusting and folding. Thinner successions occur along what are termed the East Crop and North Crop of the South Wales Coalfield, where much of the Visean succession is absent due to sub-Namurian and intra-Visean unconformities. Namurian fluvio-deltaic deposits (Marros Group) flank the South Wales and Pembrokeshire coalflelds. Much of the lower and middle Namurian succession is absent across the region, except in the west of the South Wales Coalfleld where only small parts are absent beneath an intra-Namurian unconformity. Westphalian fluvio-lacustrine deposits (South Wales Coal Measures Group) form the South Wales and Pembrokeshire coalfields, located to the east and west of Carmarthen Bay, respectively. Westphalian to Stephanian Pennant alluvial facies (Warwickshire Group) occur in the core of the South Wales Coalfield syncline.