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.

The East Greenland Caledonian orogen can be divided into distinct structurally bound geological domains composed of Archean to Lower Paleozoic lithostrati graphic and lithodemic components derived from the eastern margin of Laurentia. These domains originally evolved as major westward-displaced thrust units in the overriding plate during the collision with Baltica. The western border of the 1300-km-long and up to 300-km-wide segment of the orogen preserved onshore in East Greenland is thrust against the rocks of the Laurentian craton and is largely concealed beneath the Inland Ice. A foreland-propagating thrust pile is well-preserved in the extreme north of the orogen (79°N–82°N), and in the southern half (70°N–76°N), with less-well-preserved remnants in the western nunataks of the intervening region. Between 76°N and 81°N, the outer coastal region is dominated by high-grade Paleoproterozoic orthogneisses that were reworked during the Caledonian orogeny; most of this region is characterized by the presence of eclogitic mafic enclaves, which testify to exhumation from depths in excess of 50 km in late Caledonian time. Caledonian granites are confined to the southern orogen (70°N–76°N), where they intrude rock units now contained within the upper thrust sheet. Devonian continental basins are conspicuous in the southern part of the orogen and occur offshore farther north; their deposition can be linked to syn- to late-orogenic extension. Carboniferous and younger rocks are exposed onshore in the extreme north of the orogen (80°N–81°N) and are widespread in the south between 71°N and 75°N.

The Caledonian orogen of East Greenland contains remnants of Archean, Paleoproterozoic, late Mesoproterozoic, and early Neoproterozoic rocks that occur within far-traveled thrust sheets, and bear witness to a complex polyorogenic history of the region prior to Caledonian orogenesis. Archean and Paleoproterozoic complexes consist mainly of granitoid orthogneisses. A succession of Paleoproterozoic tholeiitic metabasalts is present in some of the foreland windows. A major unit of late Meso-proterozoic metasedimentary rocks (Krummedal supracrustal sequence) contains early Neoproterozoic (ca. 950 Ma) as well as Caledonian granites. There is evidence for Archean (ca. 2800–2600 Ma), Paleoproterozoic (2000–1750 Ma), and late Grenvillian (ca. 950 Ma) deformation and metamorphism, but Caledonian overprinting complicates the study of these events. This paper presents a broad overview of the various rock units with structural, geochemical, and geochronologic data. The Paleoproterozoic metabasaltic rocks from the foreland windows are described in more detail.

The 1300-km-long, up to 300-km-wide onshore segment of the East Greenland Caledonian orogen is divided into distinct structurally bound geological domains that originally evolved as major westward-displaced thrust units during collision with Baltica. The thrust systems accommodated contraction of an already complex Laurentian assembly of Archean to Neoproterozoic and Cambrian to Silurian lithostratigraphic units and are a consequence of the convergence, and final collision, of Baltica with Laurentia in the mid- to late Silurian Scandian orogeny. The transition from undisturbed foreland to orogen is perfectly preserved in the extreme north of the East Greenland Caledonides, where a younger lower (Vandredalen) thrust sheet carrying older thrust sheets (Western thrust belt) is displaced westward across a thin-skinned fold-and-thrust belt. In the southern half of the orogen, a pile of far-traveled thrust sheets (from youngest to oldest, Gemmedal, Niggli Spids, Hagar Bjerg thrust sheets) is displaced WNW across parautochthonous foreland windows, and the intact foreland is only intermittently exposed at the margin of the Inland Ice in the far west. These westward- and foreland-propagating systems are distinct from the Nørreland thrust sheet, the coastal region between 76°N and 79°N, in which Paleoproterozoic basement gneiss lithologies host enclaves of Devonian and Carboniferous eclogite-facies rocks. These rocks must have been exhumed from the roots of the collisional orogen, and their age suggests that the Nørreland thrust may be out of sequence relative to the main WNW foreland-propagating systems.

The orthotectonic Scottish Caledonides constitute only a small fragment of the Neoproterozoic to Paleozoic margin of Laurentia, albeit one which lies at a prominent bend in that margin. Sequences exposed in the Scottish outcrop include Mesoproterozoic, Neoproterozoic, and Cambrian-Ordovician strata that record sedimentation, volcanism, and deformation related to the latter stages of the amalgamation of Rodinia, the subsequent breakout of Laurentia, and growth of the Iapetus Ocean. Metamorphic and tectonic overprints then record the destruction of that ocean through Ordovician arc accretion and mid-to-late Silurian collision of Laurentia, Baltica, and Avalonia and the final closure of Iapetus by end-Silurian time. New isotopic data and recent advances in the understanding of the late Mesoproterozoic (Stenian) to Cambrian-Ordovician stratigraphic framework now better constrain the sequence and timing of events across the “Scottish Corner” and invite a dynamic comparison with the current research into the East Greenland Caledonides summarized in this volume. Although many broad similarities exist, the comparisons described here reveal for the first time a number of significant contrasts in the spatial arrangement of depocenters, location of rifting, and patterns and timing of magmatism, metamorphism, and contractional deformation. This expanded understanding of the late Neoproterozoic evolution of these adjacent sectors of Laurentia provides an important basis for reconstructions of the subsequent early Paleozoic Caledonian orogenic evolution of the present North Atlantic region.