Abstract The Ribblesdale fold belt, representing the Variscan inversion of the Bowland Basin, is a well-known geological feature of northern England. It represents a crustal strain discontinuity between the granite-underpinned basement highs of the northern Pennines and Lake District in the north, and the Central Lancashire High/southern Pennines, in the south. Recent seismic interpretation and mapping have demonstrated that the Ribblesdale fold belt continues offshore towards Anglesey via the Deemster Platform, beneath the Permo-Triassic sedimentary cover of the southern part of the East Irish Sea Basin. The Môn–Deemster fold–thrust belt (FTB) affects strata of Mississippian to late Pennsylvanian age. Variscan thrusts extend down into the pre-Carboniferous basement but apparently terminate at a low-angle detachment deeper in the crust, here correlated with the strongly sheared Penmynydd Zone exposed in the adjacent onshore. Up to 15% shortening is observed on seismic sections across the FTB offshore, but is greater in the strongly inverted onshore segment. Pre-Carboniferous thrusting post-dates formation of the Penmynydd Zone, and is probably of Acadian age, when basement structures such as the southward-vergent Carmel Head Thrust formed. Extensional reactivation of the Acadian structures in early Mississippian time defined the northern edge of the offshore Bowland Basin. The relatively late brittle structures of the Menai Strait fault system locally exhume the Penmynydd Zone and define the southern edge of the basin. The longer seismic records from the offshore provide insights to the tectonic evolution of the more poorly imaged FTB onshore.

Abstract Decades of oil and gas exploration across the North Sea have led to a detailed understanding of its Cenozoic–Mesozoic structure. However, the deeper basin architecture of Paleozoic petroleum systems has been less well defined by seismic data. This regional structural overview of the Devono-Carboniferous petroleum systems incorporates interpretations from more than 85 000 line-kilometres of 2D seismic data and 50 3D seismic volumes, plus a gravity, density and magnetic study, from the Central Silverpit Basin to the East Orkney Basin. A complex picture of previously unmapped or poorly known basins emerges on an inherited basement fabric, with numerous granite-cored blocks. These basins are controlled by Devono-Carboniferous normal, strike-slip and reverse faults. The main basins across Quadrants 29–44 trend NW–SE, influenced by the Tornquist trend inherited from the Caledonian basement. North of Quadrants 27 and 28, and the presumed Iapetus suture, the major depocentres are NE–SW (e.g. the Forth Approaches and Inner Moray Firth basins) to east–west (e.g. the Caithness Graben), and WNW–ESE trending (e.g. the East Orkney Basin), reflecting the basement structural inheritance. From seismic interpretation, there are indications of an older north–south fault trend in the Inner Moray Firth that is difficult to image, since it has been dissected by subsequent Permo-Carboniferous and Mesozoic faulting and rifting.