Abstract The report revises and expands upon the 1976 and 1978 publications for the Dinantian and Silesian, respectively, combining them into a single account of British and Irish Carboniferous stratigraphy. The need to update the two Special Reports reflects the considerable advances in Carboniferous geology over the last 30 years. The report covers developments in international chronostratigraphy and incorporates wholesale reassessments of British lithostratigraphy. A huge volume of biostratigraphical information has been published over recent decades and the report summarizes the key information. Carboniferous rocks have long been of economic importance, but it is the search for hydrocarbons, in its infancy at the time of the previous reports, which has greatly increased our understanding of Carboniferous successions offshore and at depth, particularly in southern and eastern England.

Abstract The succession of the Carboniferous System is questionably the most intensively studied part of the geological column in Britain and Ireland, and developments in this region continue to have implications on international correlation. The system is also probably the most geographically widespread, present at outcrop over much of the Midland Valley of Scotland, northern and central England, North and South Wales, SW England and much of Ireland. Significant areas of Carboniferous strata have also been identified at depth in eastern and southern England and in offshore areas of the North Sea and Irish Sea. The initial driver for investigations was the economic importance of Carboniferous strata, with the presence of large volumes of coal, sandstone, limestone, brick clay and ironstone helping to fuel the Industrial Revolution. Much of this early work occurred long before guidance was available for best-practice in naming lithostratigraphical units. Consequently, a haphazard approach to the establishment of the hierarchy of units resulted, with numerous local nomenclatures ensuing. To a certain extent, this complexity in nomenclature hindered the regional understanding of the Carboniferous successions in Great Britain. However, during the early part of the 20th century significant developments in biostratigraphy started to allow the widespread correlation of units, not previously possible. By the time of the publication of the two Geological Society Special Reports, for the Dinantian ( George et al. 1976) and Silesian (Ramsbottom et al. 1978) the biostratigraphical framework was well established and both publications were instrumental in establishing and promoting a new chronostratigraphical nomenclature upon which the current system is based.

Abstract The term Carboniferous was created as a stratigraphical term by Conybeare & Phillips (1822) for strata present in England and Wales and was first referred to as a system by Phillips (1835). The original definition of the Carboniferous included the Old Red Sandstone. With the establishment of the Devonian system in 1839 the Old Red Sandstone was removed from the Carboniferous and placed in the Devonian. Broad similarities within the successions of Britain and Ireland with the rest of Western Europe have allowed development of a regionally applicable chronostratigraphy. Munier-Chalmas & de Lapparent (1893) originally divided the Carboniferous of Western Europe into the Dinantian, Westphalian and Stephanian. Later, the lower part of the Westphalian was redefined as the Namurian and both were identified as stages (Jongmans 1928). The Namurian, Westphalian and Stephanian stages do not represent global faunal or fioral events, but were chosen to represent prominent facies variations and palaeogeographic separations in Western Europe. The Dinantian subsequently became a subsystem, with two component series, the Tournaisian and Visean (George & Wagner 1972), whereas the Namurian, Westphalian and Stephanian became series of a Silesian Subsystem. However, George et al. (1976) were not prepared to use the terms Tournaisian and Visean in their review of British chronostratigraphy.

Abstract The correlation of Tournaisian and Visean platform carbonate successions of Britain and Ireland initially relied upon the development of coral and brachiopod zonations. However, such zones are strongly facies-controlled and are only of local to regional significance. Over recent years, emphasis has been placed upon the use of foraminifers, and notably conodonts, to define international stages. They have been studied increasingly within the Tournaisian and Visean successions of Britain and Ireland, but are of limited stratigraphical value in younger Carboniferous strata. Ammonoids (goniatites) provide the greatest biostratigraphical resolution for the late Visean, Namurian and early Westphalian stages. Some ammonoid biozones can be recognized across Western Europe and some biozones are applicable globally. However, the marine bands that contain these ammonoids may be absent towards basin margins and marine influence is lost entirely throughout late Westphalian and Stephanian times. Within strata lacking ammonoids, biostratigraphical correlation initially relied upon the recognition of non-marine bivalve zonation, but over recent decades palynomorphs (miospores) and plant macrofioras have assumed greater importance.

Abstract To the south of the Mississippian platform carbonate successions of South Wales (Chapter 5) and Bristol, Mendips and Somerset (Chapter 6), Carboniferous rocks predominantly occur within the strongly deformed Culm crop of SW England. The Culm Basin has a broad graben architecture, with an inner graben (Central Devon Sub-basin) fianked by half-grabens (Bideford and Launceston sub-basins) (Fig. 14; Leveridge & Hartley 2006; Waters et al. 2009). The Bideford Sub-basin is bounded to the north by the Brushford Fault, the Central Devon Sub-basin by the Greencliff Fault and the Launceston Sub-basin by the Rusey Fault. To the north of the Brush-ford Fault is the northern margin of the Culm Basin. The Tavy Basin has limited development of Famennian-Tournaisian strata. The Laneast High separating the Tavy Basin and Launceston Sub-basin includes a Tournaisian to ?Visean succession (Yeolmbridge and Laneast Quartzite formations). Remnants of Carboniferous strata also occur in the South Devon Basin. In many areas there is no clear lithological break between the Tournaisian and the underlying Upper Devonian rocks, both of which are dominated by shallow-marine and deeper-water mudstones. The succession, commonly referred to as the Transition Series or Group (Dearman & Butcher 1959; Freshney et al. 1972), are assigned to the Exmoor Group in north Devon, the Hyner Mudstone and Trusham Mudstone formations of the eastern part of the Central Devon Sub-basin and the Tamar Group in south Devon.

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.

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 strata within this region occur in the broad eastern flank of the north-south axis of the Clwydian Range from Prestatyn to Oswestry, sections within the Vale of Clwyd and the outlying districts around Llandudno, Menai Straits and Anglesey (Fig. 25). In NE Wales and the Welsh Borderlands the gently tilted Visean limestones are succeeded to the east by Namurian to Westphalian strata forming the Flint and Denbigh coalfields. This region includes intermittent development of Tournaisian to Visean alluvial deposits (‘Basement Beds’). These are overlain by Visean ramp-to-shelf carbonates, present along the northern margin of the Wales-Brabant High, extending across North Wales (Clwyd Limestone Group). Visean to Namurian basinal deposits (Craven Group) occur on the north coast of North Wales (Fig. 25), deposited on the southern margin of the Irish Sea Basin (see Chapter 16). During the Namurian and Westphalian this region is represented by thick fluvio-deltaic successions, including the Millstone Grit and Pennine Coal Measures groups, in turn overlain by alluvial deposits of the Warwickshire Group.

Abstract The disparate coalfields and Carboniferous rocks in this area (Figs 28 & 29), mostly comprise Coal Measures lithofacies (Pennine Coal Measures Group) and red-bed sediments (Warwickshire Group) deposited at the southern margin of the Pennine Basin, which was initiated in Westphalian times. These strata generally rest unconformably on Lower Palaeozoic rocks in the west of the region, with local development of platform carbonates in Shropshire. The more extensive carbonate platform of the Hathern Shelf and coeval basinal mudstones (associated with the SE-trending Widmerpool Gulf) were deposited in the east of the region during late Tournaisian and Visean time. The basinal hemi-pelagic sedimentation continued in the SE throughout the early Namurian with an influx of southerly-derived quartzitic sandstone followed, in the Marsdenian, by northerly-derived feldspathic sandstone (Millstone Grit Group) (Fraser & Gawthorpe 2003). The oldest Carboniferous strata of late Tournaisian to Visean age do not crop out widely in the region, but are known from boreholes and geophysical records in South Derbyshire and the Vale of Belvoir, and from small inliers in Shropshire and the Clee Hills. Platform carbonates with thin beds of basic tuffite and subordinate sandstone (Peak Limestone Group) were deposited on the Hathern Shelf at the southern margin of the Widmerpool Gulf (half-graben) (Falcon & Kent 1960), but deepening of the basin through synsedimentary rift faulting and a rise in sea-level resulted in the deposition of deeper-water calcareous mud (Widmerpool Formation) (Fraser & Gawthorpe 2003).

Abstract Carboniferous rocks within this area occupy the region to the south of, and contiguous with, the Southern Pennines (see Chapter 11). The oldest Tournaisian and Visean strata occur at outcrop within the Peak District, represented by ramp-to-shelf carbonates (Peak Limestone Group) deposited on the Derbyshire High, a promontory of the East Midlands Shelf, and the laterally extensive Staffordshire and Hathern shelves. The platform carbonates of the East Midlands Shelf extend in the subsurface below Nottinghamshire and Lincolnshire, where the nature of the succession is based largely upon well records and geophysical information (Strank 1987). A 23 m thick succession of platform carbonates is recorded in the base of the Saltfleet by No. 3 Borehole [TF 4246 9135] (Hodge 2003) and at least 100 m is present in the Welton Oil-field (Fig. 31). The Derbyshire High platform carbonate rocks pass into more basinal successions in the Edale Basin to the north, the Widmerpool Gulf to the south and the Staffordshire Basin to the west, dominated by hemi-pelagic mudstone and carbonate turbidites (Craven Group). The lithostratigraphical nomenclature for the Tournaisian and Visean strata is that of Waters et al. (2009), adapted from Aitkenhead & Chisholm (1982).

Abstract Carboniferous rocks within this area occupy the region contiguous with the northern Pennines to the north (Chapter 12) and the Peak District to the south (Chapter 10). All of the stages of the Carboniferous are present at outcrop, with the exception of Stephanian strata, which are absent. The oldest Tournaisian strata crop out within the Craven Basin, and are represented by ramp carbonate rocks (Bowland High Group) deposited on the Bowland High and adjacent Lancaster Fells and Bowland sub-basins. These carbonate rocks are overlain by mainly Visean hemi-pelagic mudstone and carbonate turbidites (lower part of Craven Group). To the south of the Pendle Fault System (Fig. 34), further platform carbonate rocks are proved in the subsurface above the Central Lancashire High (Trawden Limestone Group) and the Holme High and Heywood High (Holme High Limestone Group). These carbonate rocks, which developed during the Tournaisian to late Visean, are known only from well records and geophysical information and are not divided into formations. During the Visean, the platform carbonate rocks pass laterally into more basinal successions in the Harrogate, Rossendale and Huddersfield sub-basins (Craven Group). The lithostratigraphical nomenclature for the Tournaisian and Visean strata is that of Waters et al. (2009), adapted from Riley (1990).

Abstract Carboniferous rocks within the Cumbria and northern Pennines region are bound by the Maryport-Stublick-Ninety Fathom Fault System, which forms the northern boundary of the Lake District and Alston blocks (Fig. 37). In the Pennines, the succession occupies the Alston and Askrigg blocks and the intervening Stainmore Trough, a broadly east-west trending graben. Carboniferous strata also flank the Lake District Block, occurring at outcrop in north Cumbria, Furness and Cartmel (south Cumbria) and the Vale of Eden, and in the subsurface in west Cumbria. The Askrigg Block succession is separated from that of the Craven Basin (Chapter 11), to the south, by the Craven Fault System. All of the stages of the Carboniferous, with the exception of the Stephanian, are present at outcrop. The oldest Tournaisian strata occur at outcrop along the flanks of the Lake District Block and within the Stainmore Trough. They are represented by continental and peritidal deposits (Ravenstonedale Group), and locally associated with volcanic rocks (Cockermouth Volcanic Formation of north Cumbria). The Ravenstonedale Group is diachronous, occurring later on the structural highs, with deposition during Chadian times on the Askrigg Block and Holkerian times on the Alston Block. The Ravenstonedale Group is overlain by upper Tournaisian to upper Visean platform carbonate rocks (Great Scar Limestone Group), which initially developed on the flanks of the Lake District Block, but by late Asbian times extended across the entire region (Mitchell 1978).

Abstract Carboniferous rocks within this region occupy a broadly east-west trending graben, referred to as the Northumberland Trough within Northumberland (Bewcastle to the North Sea coast) and the Solway Basin in the vicinity of the Solway Firth, where much of the succession is obscured by Permo-Triassic strata (Fig. 40). The graben is bounded to the south by the Maryport-Stublick-Ninety Fathom Fault System, which forms the northern boundary of the Lake District and Alston blocks (see Chapter 12). The Carboniferous rocks are broadly separated from the Midland Valley of Scotland (Chapter 14), to the north, by the Lower Palaeozoic rocks of the Southern Uplands, which formed an emergent upland area throughout much of the Carboniferous, with local deposition within small basins. At the eastern onshore extent of the Southern Uplands a relatively condensed Carboniferous succession was deposited upon the Cheviot Block. All of the regional stages of the Carboniferous are present at outcrop, though strata of Stephanian age have not been proved biostratigraphically. The oldest Tournaisian strata occur at outcrop along the northern margins of the Northumberland Trough-Solway Basin, represented by continental and peritidal deposits, typically separated by volcanic rocks (Inverclyde Group). These strata extend offshore in the North Sea (Chapter 15), linking directly with the outcrop of Inverclyde Group present within the Midland Valley of Scotland. In the Northumberland Trough-Solway Basin, the Inverclyde Group passes southwards into, and is overlain by, a lower to middle Visean heterolithic clastic and non-marine carbonate and fluvio-deltaic succession (Border Group).

Abstract Carboniferous rocks occupy much of the Midland Valley of Scotland, but are commonly obscured at surface by Quaternary deposits. The succession occupies an ENE-trending graben bounded by the complexes of the Highland Boundary Fault to the NW and the Southern Upland Fault to the SE. Onshore, the graben is about 90 km wide and extends some 150 km from the Ayrshire coast and Glasgow in the west to the Fife and East Lothian coasts in the east (Fig. 43). The basins within the graben are associated with a succession of Carboniferous rocks more than 6 km thick. The Highland Boundary and Southern Upland faults were active and helped to control sedimentation, initially during the Tournaisian as sinistral strike-oblique slip faults and subsequently in the Visean to Westphalian a regime of dextral strike-oblique slip deformation (Browne & Monro 1989; Ritchie et al. 2003; Underhill et al. 2008). Isolated exposures also occur on the Isle of Arran and at Machrihanish in Kintyre. The Midland Valley of Scotland was separated from basins to the south (Tweed and Solway Firth basins and the Northumberland Trough; see Chapter 13) by the Lower Palaeozoic rocks of the Southern Uplands Block, which formed a positive, mainly emergent area throughout the Carboniferous. However, this was breached during the Carboniferous by narrow NW-SE-trending basins, for example Stranraer and Sanquhar to Thornhill.

Abstract The Carboniferous strata of the Central and Northern North Sea occupy a depositional basin that is laterally contiguous with, and located to the east of, the Midland Valley of Scotland (Chapter 14). The Carboniferous strata of the Southern North Sea occupy a depositional basin located between the Mid North Sea High to the north and the Wales-Brabant High to the south (Fig. 46). It is laterally contiguous with the Pennine Basin complex. An isolated area of Carboniferous strata has also been proved in the Clair Basin of the NW Approaches, west of the Shetland Isles. The Tournaisian and oldest Visean strata have been proved beneath Permian and younger cover in the Central and Northern North Sea, within the Outer Moray Firth, Western Platform and Central Graben, eastwards from the coast of SE Scotland along the crest and southern flanks of the Mid North Sea High and in the Clair Basin, west of Shetland (Fig. 46). The strata are dominated by red, fluvial and playa-lake deposits (Upper Old Red Group). Younger Visean strata include the grey, fluvio-lacustrine deposits within the Forth Approaches Basin and Outer Moray Firth Basin of the Central and Northern North Sea (Firth Coal Formation). Visean to lower Namurian lacustrine, marine, fluvial and fluvio-deltaic sediments are proved in the Southern North Sea eastwards from the Northumberland coast along the western crest and southern flanks of the Mid North Sea High (Farne Group).

Abstract A thick and relatively complete succession of Carboniferous rocks of Tournaisian to Westphalian age, together with a probable Stephanian section (Floodpage et al. 2001) was deposited throughout the two main areas in the Irish Sea region. The larger Central Province Trough in the south includes the East Irish Sea Basin (EISB)-Quadrant 109 Syncline-Kish Bank Basin, linking the onshore successions of the Craven Basin (Chapter 11) and Dublin Basin (Chapter 21). The smaller Peel Basin-Solway Basin (Fig. 48) represents the extension of the onshore Solway Basin (Chapter 13) and continues westwards between the Drogheda Shelf and the Balbriggan Block (Chadwick et al. 2001; Sevastopulo & Wyse Jackson 2009). Seismic data suggest that Carboniferous strata some 4000–5000 m thick occur in the Solway Basin and EISB (Chadwick et al. 2001). The present day distribution of Carboniferous strata is controlled by the effects of uplift and erosion associated with Variscan basin inversion (Chadwick et al. 2001). Separating the Solway Basin and EISB is the Manx-Lakeland Ridge, which is believed to extend westward to form the Balbriggan Block (Chapter 21). The lithostratigraphical nomenclature of Jackson & Johnson (1996) is retained. In this scheme the Tournaisian and Visean successions are referred to as the Garwood Group, the Namurian succession as the Bisat Group and the Westphalian to Stephanian succession as the Kidston Group. There is insufficient information to subdivide these groups into component formations (Jackson & Johnson 1996).

Abstract This offshore area broadly comprises two ENE-trending Mesozoic and Tertiary grabens. The northern graben comprises the Fastnet, North Celtic Sea and St George’s Channel basins, separated from the South Celtic Sea and Bristol Channel basins by the Pembrokeshire Ridge-Labadie Bank (Fig. 50). The graben appears to represent the reactivation of Caledonian structures, for example, the southern margin of the St George’s Channel Basin was controlled by reactivation of the onshore Bala Fault System (Naylor 2001). The North Celtic Sea Basin locally developed in the hanging wall of a low-angle southerly dipping fault, which may represent the reactivation of the Variscan Front during Mesozoic extension (Gibbs 1987). However, traditionally, the Variscan Front has been taken as a poorly delineated feature extending across southern Ireland, north of the Munster Basin. Hydrocarbon exploration has revealed intermittent presence of Carboniferous strata of Tournaisian to Westphalian age, although the distribution of these strata is still poorly constrained. The Devono-Carboniferous South Munster Basin, evident onshore in southern Ireland (Chapter 23), extends at least 50 km south of the coastline (Higgs 1983). The platform developed to the south of the South Munster Basin has been proved within the Fastnet Basin and Goban Spur (Fig. 50; Sevastopulo & Wyse Jackson 2009). The presence of limestone within St George’s Channel suggests that this part of the Leinster-Wales Massif was drowned by Visean times (Sevastopulo & Wyse Jackson 2009).

Abstract During the Carboniferous, Northern Ireland straddled a zone of dextral strike-slip faulting, comparable to the Midland Valley of Scotland (see Chapter 14). The earliest Mississippian marine transgression reached Northern Ireland in the late Tournaisian (CM Miospore Biozone) and from then until the mid-Arnsbergian Substage (E 2b 1 Subzone) the sediment fill was deposited in close proximity to the northern margin of the basin. Metamorphic rocks of the Central Highlands (Grampian) Terrane to the north were repeatedly exposed during episodes of marine regression. In the SE of the region it appears that the Southern Uplands-Down-Longford Terrane was finally submerged in the late Asbian or early Brigantian. The cumulative thickness of 7000 m is represented mainly by Tournaisian, Visean and lower Namurian rocks in Co. Fermanagh, the Fintona Block, peripheral sections at Coalisland and isolated basins such as Newtownstewart, all in Co. Tyrone (Fig. 51). The most continuous outcrop and succession extend from Co. Fermanagh and south Co. Tyrone into north Co. Armagh. The Carboniferous outcrop in the eastern part of Northern Ireland is reduced to outliers at Ballycastle in Co. Antrim, and in Co. Down at Cultra, Castle Espie and Carlingford Lough. During the Pennsylvanian, much of Northern Ireland was land, and strata of this age are limited in extent to the Fintona Block and east Co. Tyrone (Fig. 51).