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 Compared with the prolific success of the Triassic play in the East Irish Sea Basin (EISB) the lack of hydrocarbon discovery in neighbouring Permo-Triassic basins of the Irish Sea has been an enigma. However, recent exploration of the Peel, Solway and Central Irish Sea basins has provided new insights into the geology of these basins and the controls upon hydrocarbon prospectivity in the Irish Sea area. Regional seismic interpretation suggests that 12 of the 15 exploration wells drilled in the basins adjacent to the EISB tested valid structural closures at top Triassic reservoir level. Re-evaluation of the Irish Sea petroleum system reveals that, although effective reservoirs occur in the Lower–Middle Triassic Ormskirk Sandstone Formation, and evaporites in the Middle–Upper Triassic Mercia Mudstone Group provide a regional top seal, the major factor controlling hydrocarbon prospectivity is the limited presence of effective source rocks in the underlying Carboniferous section. A further control upon prospectivity is the timing of hydrocarbon migration, from those areas where Carboniferous source rocks were deposited and preserved. The Namurian basinal marine oil- and gas-prone shales, which form the principal source of hydrocarbons for the Triassic play in the EISB, are restricted to an east–west fairway extending from the EISB into the Kish Bank Basin. Rocks of this age are absent from the Peel and Solway basins as a result of Variscan uplift and erosion. However, palaeogeographical reconstructions based on well and outcrop data suggest that, even if preserved, the depositional environment was not conducive to the formation of marine oil-and gas-prone source rocks. Well and seismic data suggest that rocks of Namurian age were not deposited in the Central Irish Sea area, which remained high during much of Dinantian and Namurian time. Potential source rock development in the Central Irish Sea area is therefore limited to the Westphalian section, which is organically lean and dominated by inertinitic kerogens. Potential hydrocarbon traps in the Central Irish Sea, Peel and Solway basins formed largely as a result of Early Cretaceous tectonism and were subsequently modified by fault reactivation during Tertiary uplift phases. Trap formation appears to postdate the most likely timing of hydrocarbon charge, which this study suggests would have occurred in Late Triassic and Jurassic time. Hydrocarbon entrapment in the EISB may have been favoured by limited Early Cretaceous uplift, coupled with renewed hydrocarbon generation and re-migration during Early Tertiary time. It is concluded that the remaining prospectivity of the Triassic play in the Irish Sea area is likely to be restricted to the proven play fairway within the EISB.

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).