Cumbria and the northern Pennines

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. 12.1). 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 High, 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

Lithostratigraphy and biostratigraphy of the Lower Carboniferous (Mississippian) carbonates of the southern Askrigg Block, North Yorkshire, UK

A rationalized lithostratigraphy for the Great Scar Limestone Group of the southeast Askrigg Block is established. The basal Chapel House Limestone Formation, assessed from boreholes, comprises shallow-marine to supratidal carbonates that thin rapidly northwards across the Craven Fault System, onlapping a palaeotopographical high of Lower Palaeozoic strata. The formation is of late Arundian age in the Silverdale Borehole, its northernmost development. The overlying Kilnsey Formation represents a southward-thickening and upward-shoaling carbonate development on a south-facing carbonate ramp. Foraminiferal/algal assemblages suggest a late Holkerian and early Asbian age, respectively, for the uppermost parts of the lower Scaleber Force Limestone and upper Scaleber Quarry Limestone members, significantly younger than previously interpreted. The succeeding Malham Formation comprises the lower Cove Limestone and upper Gordale Limestone members. Foraminiferal/ algal assemblages indicate a late Asbian age for the formation, contrasting with the Holkerian age previously attributed to the Cove Limestone. The members reflect a change from a partially shallow-water lagoon (Cove Limestone) to more open-marine shelf (Gordale Limestone), coincident with the onset of marked sea-level fluctuations and formation of palaeokarstic surfaces with palaeosoils in the latter. Facies variations along the southern flank of the Askrigg Block, including an absence of fenestral lime-mudstone in the upper part of the Cove Limestone and presence of dark grey cherty grainstone/packstone in the upper part the Gordale Limestone are related to enhanced subsidence during late Asbian movement on the Craven Fault System. This accounts for the marked thickening of both members towards the Greenhow Inlier

Mississippian reef development in the Cracoe Limestone Formation of the southern Askrigg Block, North Yorkshire, UK

The southern margin of the Askrigg Block around Cracoe, North Yorkshire, shows a transition from carbonate ramp to reef-rimmed shelf margin, which, based on new foraminiferal/algal data, is now constrained to have initiated during the late Asbian. A late Holkerian to early Asbian ramp facies that included small mudmounds developed in comparatively deeper waters, in a transition zone between the proximal ramp, mudmound-free carbonates of the Scaleber Quarry Limestone Member (Kilnsey Formation) and the distal Hodderense Limestone and lower Pendleside Limestone formations of the adjacent Craven Basin. The ramp is envisaged as structurally fragmented, associated with sudden thickness and facies changes. The late Asbian to early Brigantian apron reefs and isolated reef knolls of the Cracoe Limestone Formation include massive reef core and marginal reef flank facies, the latter also including development of small mudmounds on the deeper water toes of back-reef flanks. The position of the apron/knoll reefs is constrained to the south (hangingwall) of the North Craven Fault, but it is syn-depositional displacement on the Middle Craven Fault that accounts for the thick reefal development. Subsequent inversion of this structure during the early Brigantian caused uplift and abandonment of the reefs and consequent burial by the Bowland Shale Formation

Western Ireland

The Carboniferous rocks of western Ireland extend from the Ox Mountains in south Co. Mayo, south to Galway Bay, east to the western margin of the Dublin Basin Co. Roscommon (Chapter 21) and west to Clew Bay and Clare Island (Figure 19.1). Tournaisian rocks of mostly continental or marginal marine facies, Visean rocks of mostly marine limestone, and Namurian predominantly marine and fluviodeltaic siliciclastic rocks crop out in the region, the entire succession belonging to the Mississippian Subsystem. In western Ireland, late Tournaisian and Visean (Chadian- Asbian) aged shelf limestones occur within structurally controlled basins, many of which are extensions of structures in the adjacent northwest region (see Chapter 19). In the Castlebar area of south Co. Mayo, the Castlebar Syncline represents a southwest extension of the Ballymote Syncline, bounded to the north by the Ox Mountains Inlier and to the south by the Belhavel Fault (Long et al. 2004)

Northern Ireland

During the Carboniferous, Northern Ireland straddled a zone of dextral strike-slip, 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 (E2b1 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 southeast 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. 18.1). 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. 18.1

International correlation

Globally, the Carboniferous System can be subdivided into two time intervals, associated with a climatic change which produced quite distinct floral and faunal distribution and characteristics of sedimentation (Wagner & Winkler Prins 1991). The early Carboniferous, equivalent to the Mississippian of the U.S.A. and Lower Carboniferous of Russia, was a time of equitable climate in which sea levels were generally high and successions within low latitudes are typically marine. Unobstructed marine communication between the Palaeo-Tethys and Panthalassan shelves (Davydov et al. 2004) allowed marine fauna to have a world-wide distribution, in which latitudinal variations were stronger than longitudinal differences (Ross & Ross 1988). The late Carboniferous, equivalent to the Pennsylvanian of the U.S.A., and Middle and Upper Carboniferous of Russia, is typified by coal-bearing successions that displayed marked latitudinal climatic differentiation associated with the Gondwanan Ice Age. The mid-Carboniferous boundary, which separates the two climatic periods, is associated with widespread regression and on many cratonic areas by the presence of a nonsequence or unconformity. The comparable transition is seen in Western Europe between the Visean and Namurian stages, though this is not a direct time equivalent of the Mississippian – Pennsylvanian boundary (Fig. 2.1). The carbonate-dominated succession of the Visean and terrestrial clastic-dominated succession of the Namurian are interpreted as a facies change with no world-wide significance (Wagner & Winkler Prins 1991)

South Central Ireland

The South Central Ireland region extends from the South Munster Basin north to the southern margin of the Dublin Basin and from Wexford in the southeast to the Burren in the northwest (Fig. 22.1). The region is dominated by strata of Mississippian age, with Pennsylvanian strata preserved in boreholes in south Co. Wexford and in the upper part of the Leinster and Kanturk Coalfields. Throughout the South Central region, the Tournaisian strata present below the Waulsortian mud-bank limestones, which form a continuous thick unit of massive pale grey limestone across most of the region, is represented by the Lower Limestone Shale and Ballysteen Limestone groups (Brück 1985) of the Limerick Province (see Philcox 1984; Sevastopulo & Wyse Jackson 2001). The Lower Limestone Shale Group is related to a northward-directed marine transgressive event across the North Munster shelf. The deepening trend, which started during the deposition of the Ballysteen Limestone Group, continued with the Waulsortian facies on the distal part of a ramp. From the latest Tournaisian time and throughout the Visean there is widespread development of shallow-water marine carbonate platform sediments with only localised deeper water ramp and basinal facies (mostly in the Shannon Basin) (Somerville et al. 1992b; Strogen et al. 1996; Sevastopulo & Wyse Jackson 2001). The greatest areal extent and stratigraphic thickness (c. 2 km) of Namurian rocks occurs in the Shannon Basin, centred on counties Clare and Limerick. This basin developed as a result of extension and collapse above the position of the former Iapetus Suture and was the locus of a thick Lower Carboniferous succession in the Shannon Basin (Strogen et al. 1996). The Namurian succession was assigned to a lower Shannon Group followed by the Central Clare Group (Rider 1974), and its palaeogeographic development was summarised in Collinson et al. (1991). Westphalian strata are restricted to outliers of the Leinster, Slieve Ardagh and Kanturk coalfields (Fig. 22.1)

Midland Valley of Scotland

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 northwest and the Southern Upland Fault to the southeast. Onshore, the graben is about 90 km wide and extends some 150 km from the Ayrshire coast and Glasgow in the west to the east Fife and East Lothian coasts in the east (Fig. 14.1). The basins within the graben are associated with Carboniferous rocks more than 6 km thick. The Highland Boundary and Southern Upland faults were active and helped 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 Island 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. The Scottish Highlands to the north, of Lower Palaeozoic and Precambrian rocks, were similarly a positive, mainly emergent area with outcrops of Carboniferous (Johnstone 1966) limited to the west coast around Inninmore (Sound of Mull), Bridge of Awe (Pass of Brander) and Glas Eilean (Sound of Islay)

Northumberland Trough and Solway Basin

Carboniferous rocks within this region occupy a broadly east–west 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. 13.1). 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

A potential global chronostratigraphic boundary for the base of the middle Viséan

High-resolution foraminiferal biostratigraphy of carbonates immediately below and near the base of the Holkerian Substage in three sections of the South Cumbria Shelf allows the recognition of the Cf5α and Cf5β subzones. The most complete section at Grubbins Wood is almost free of dolomitisation. At the White Scar Quarry and Barker Scar sections, minor faunal gaps are inferred at the base of one or both subzones, respectively. The Grubbins Wood section has the most limited exposure, whereas White Scar Quarry has extensive exposure of this interval, especially the basal horizons of the subzones, compared to Barker Scar. The Grubbins Wood section, because of its exceptional foraminiferal record is more suitable for the establishment of a coincident boundary stratotype for the mid Viséan and Holkerian boundary at the base of the Ο’5β subzone. However, the Barker Scar section should be retained as the Holkerian unit stratotype for Britain, with the base of the Holkerian repositioned lower in the section, at the base of the Ο’5β subzone. White Scar is a suitable unit-parastratotype, filling data gaps due to possible faunal gaps and dolomitisation at Barker Scar. The rich foraminiferal assemblages allow good global correlation with other regional zonations, which if refined in other countries, would allow a more affirmative global chronostratigraphic basal boundary for the middle Viséan.Natural England, Cumbria Wildlife Trust, Holker Hall Estate, the Arnside Silverdale AONB, and the Landowners of Crosthwaite and Lyth, allowed access, permission and permits to collect samples from these sections. MWH was part funded by NERC (grant NE/P00170X/1). We thank John Murray and two other anonymous reviewers for their many helpful comments and suggestions which have significantly improved the paper