We based an integrated petrological and petrophysical model for the Ediacaran crust of southern Britain on a review of the c. 570–550 Ma Charnian volcano-sedimentary complex. The latter was emplaced in a magmatic rift wedge within the juvenile continental crust of the c. 720–600 Ma Marches Terrane, a subduction magmatic domain formed at the margin of the Gondwana palaeocontinent. The Charnian magmatic arc is characterized by primitive island arc tholeiite to more evolved calc-alkaline compositions. The inversion of aeromagnetic potential field data and petrophysical modelling reveals details of the internal structure of the Charnian Domain, including a median rift, superimposed annular structures and partitioning lineaments. The modelling suggests that the arc foundation could incorporate magnetite-rich cumulates, which may explain the anomalous geophysical properties, including crustal thickness, rigidity and buoyancy. There is no evidence for significant tectonic displacement between the Charnian Domain and its Marches Terrane host. Instead, the domain likely occupies a wedge-shaped arc/marginal rift basin complex, propagated from a neighbouring ocean into the Gondwana margin. Contemporaneous volcanic rift successions in the Welsh Borderland and Wales of the 570–550 Ma Charnian magmatic phase developed in coeval ensialic rifts within less strongly extended Marches Terrane lithosphere. A comparable diversity of subduction-related magmatism is found in the Neogene–recent Hikurangi destructive margin of New Zealand, providing a plausible analogue for Charnian magmatism. Supplementary material: Supplementary Publication 1 (borehole geophysical log correlation; petrophysical data table; unannotated geophysical maps and sections) and Supplementary Publication 2 (geochemistry analytical conditions and data table) are available at https://doi.org/10.6084/m9.figshare.c.6805248

In Britain, thick limestones of early Carboniferous (Mississippian: 359-323 Ma) age are present in two provinces, respectively south and north of the Wales-Anglo-Brabant landmass. In the southern province, early Carboniferous lime-stones were deposited upon a southward-deepening shelf, laterally continuous from Ireland to the Rhineland. They now occupy a number of discrete minibasins as a consequence of Variscan orogenic thrusting and significant post-Carboniferous erosion. In the northern province, local tectonic controls led to the development of a mosaic of deepwater basins, ramps and platforms in response to Mississippian extensional stress. The interaction with glacioeustatic sea-level change led to the development of complex carbonate system tracts on these ramps and platforms. Given favourable conditions of palaeokarst development and fracturing, hydraulic transmissivity could be sufficient to allow development as a geothermal resource. Deep geothermal prospectivity is controlled by a hierarchy of factors, operat-ing on scales ranging from provincial (1000-100 km) down to outcrop (1000-100 m), reflecting processes operating on the lithospheric down to sub-basinal scale respectively. On the scale of the individual prospect, these factors include the mode of carbonate deposition, particularly depth of water and angle of depositional slope, which are tectonically controlled; the history of synsedimentary exposure, erosion and karstification, strongly influenced by sea-level change; by the diagenetic history and subsequent basin evolution; by deformation and fracturing during Variscan basin inversion; and by the post-Carboniferous history of subsidence, uplift and karstification. The contrasting impact of these various processes upon hydraulic transmissivity in the two provinces is reviewed, and a preliminary assessment of the geothermal prospectivity of each is presented. The most prospective areas for deep geothermal exploitation are considered to be basins, shelves and platforms lying at depths of 2 to 5 km below sea level. Deepwater ba-sins are considered less prospective because of the lack of thick limestones, except in the hanging wall at fault-bounded margins, where Waulsortian mud-mounds with good residual porosity and fault-zones with polyphase history are likely present. Granite underpinned highs in N England, where Carboniferous limestones are typically at crop, and shallow basins of Carboniferous age lying on the Wales-Anglo-Brabant Massif, are considered less prospective in the deep geothermal context.

We present updated seismic hazard maps for the United Kingdom (UK) intended for use with the National Annex for the revised edition of Eurocode 8. The last national maps for the UK were produced by Musson and Sargeant (Eurocode 8 seismic hazard zoning maps for the UK. British Geological Survey Report CR/07/125, United Kingdom, 2007). The updated model uses an up-to-date earthquake catalogue for the British Isles, for which the completeness periods have been reassessed, and a modified source model. The hazard model also incorporates some advances in ground motion modelling since 2007, including host-to-target adjustments for the ground motion models selected in the logic tree. For the first time, the new maps are provided for not only peak ground acceleration (PGA) but also spectral acceleration at 0.2 s (SA 0.2s ) and 1.0 s for 5% damping on rock (time-averaged shear wave velocity for the top 30 m Vs30 ≥ 800 m/s) and four return periods, including 475 and 2475 years. The hazard in most of the UK is generally low and increases slightly in North Wales, the England–Wales border region, and western Scotland. A similar spatial variation is observed for PGA and SA 0.2s but the effects are more pronounced for SA 0.2s . Hazard curves, uniform hazard spectra, and disaggregation analysis are calculated for selected sites. The new hazard maps are compared with the previous 2007 national maps and the 2013 European hazard maps (Woessner et al. in Bull Earthq Eng 13:3553–3596, 2015). There is a slight increase in PGA from the 2007 maps to this work; whereas the hazard in the updated maps is lower than indicated by the European maps.

The national baseline aeromagnetic survey of Britain allows a uniform assessment of the shallow and deep magnetic properties of the British tectonic terranes. The most significant is that associated with destruction of early Palaeozoic oceanic lithosphere across the Iapetus Suture separating Baltica and Avalonia from the Laurentian terranes. Here a formal 3D inversion of a continuous swathe of the data is considered. The study provides a uniform volumetric whole crust assessment extending for over 1000 km. Normally a 3D inversion of magnetic data is controlled using a variety of constraints however this is not appropriate at the crustal scale due to our increasingly imprecise knowledge of lithology at increasingly greater depths. The main crustal interface encountered occurs at the Curie isotherm depth. We demonstrate the behaviour of introducing different magnetic crustal depths and suggest the crustal 'magnetic depth' of our models can be independently constrained using global or regional studies of the deep geotherm. Static magnetic data have no inherent depth resolution. Here an empirical '1D depth' weighting and a more formal '3D distance' weighting are assessed. The inversion procedure is regularised to provide stable models appropriate to the data and their errors. To gain confidence when using such a 'geologically-unconstrained' inversion, we compare our 3D inversion results with an existing geologically-constrained 2.5D profile inversion across northern Britain. A surprising agreement in the 3D susceptibility magnitudes is observed. The chosen study area traverses 10 British terranes and images their tectonic fabric by way of non-magnetic zones (i.e. susceptibilities <0.0001 to 0.001 SI) and magnetic zones displaying geological relevance and tectonic significance at deeper crustal levels. Here we discuss the more significant 3D model features which, by virtue of a continuous crustal-scale assessment and fitting the data with a high degree of fidelity, provide additional structural insights.

The Southern North Sea Basin area, stretching from the UK to the Netherlands, has a rich hydrocarbon exploration and production history. The past, present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals, ranging from the Lower Carboniferous to Cenozoic. In the period between 2007 and 2017, a total of 95 new hydrocarbon fields were discovered, particularly in Upper Carboniferous, Rotliegend and Triassic reservoirs. Nineteen geothermal systems were discovered in the Netherlands onshore, mainly targeting aquifers in the Rotliegend and Upper Jurassic/Lower Cretaceous formations. Although the Southern North Sea Basin area is mature in terms of hydrocarbon exploration, it is shown that with existing and new geological insights, additional energy resources are still being proven in new plays such as the basal Upper Rotliegend (Ruby discovery) for natural gas and a new Chalk play for oil. It is predicted that hydrocarbon exploration in the Southern North Sea Basin area will probably experience a slight growth in the coming decade before slowing down, as the energy transition further matures. Geothermal exploration is expected to continue growing in the Netherlands onshore as well as gain more momentum in the UK.

Abstract Seismic mapping of key Paleozoic surfaces in the East Irish Sea–North Channel region has been incorporated into a review of hydrocarbon prospectivity. The major Carboniferous basinal and inversion elements are identified, allowing an assessment of the principal kitchens for hydrocarbon generation and possible migration paths. A Carboniferous tilt-block is identified beneath the central part of the (Permian–Mesozoic) East Irish Sea Basin (EISB), bounded by carbonate platforms to the south and north. The importance of the Bowland Shale Formation as the key source rock is reaffirmed, the Pennine Coal Measures having been extensively excised following Variscan inversion and pre-Permian erosion. Peak generation from the Bowland source coincided with maximum burial of the system in late Jurassic–early Cretaceous time. Multiphase Variscan inversion generated numerous structural traps whose potential remains underexplored. Leakage of hydrocarbons from these into the overlying Triassic Ormskirk Sandstone reservoirs is likely to have occurred on a number of occasions, but currently unknown is how much resource remains in place below the Base Permian Unconformity. Poor permeability in the Pennsylvanian strata beneath the Triassic fields is a significant risk; the same may not be true in the less deeply buried marginal areas of the EISB, where additional potential plays are present in Mississippian carbonate platforms and latest Pennsylvanian clastic sedimentary rocks. Outside the EISB, the North Channel, Solway and Peel basins also contain Devonian and/or Carboniferous rocks. There have, however, been no discoveries, largely a consequence of the absence of a high-quality source rock and a regional seal comparable to the Mercia Mudstone Group and Permian evaporites of the Cumbrian Coast Group in the EISB.

The surface geology of central England and Belgium obscures a large ‘basement’ massif with a complex history and stronger crust and lithosphere than surrounding regions. The nucleus was forged by subduction-related magmatism at the Gondwana margin in Ediacaran time. Partitioning into a platform, in the English Midlands, and a basin stretching to Belgium, in the east, was already evident in Cambrian/earliest Ordovician time. The accretion of the Monian Composite Terrane during the Penobscotian deformation phase preceded late Tremadocian rifting, and Floian separation, of the Avalonia Terrane from the Gondwana margin. Late Ordovician magmatism in a belt from the Lake District to Belgium records subduction beneath Avalonia of part of the Tornquist Sea. This ‘Western Pacific-style’ oceanic basin closed in latest Ordovician time, uniting Avalonia and Baltica. Closure of the Iapetus Ocean in early Silurian time was soon followed by closure of the Rheic Ocean, recorded by subduction along the southern margin of the massif. The causes of late Caledonian deformation are poorly understood and controversial. Partitioned behaviour of the massif persisted into late Palaeozoic time. Late Devonian and Carboniferous sequences show strong onlap onto the massif, which was little affected by crustal extension. Compressional deformation during the Variscan Orogeny also appears slight, and was focussed in the west where a wedge-shaped mountain foreland uplift was driven by orogenic indentation, splitting the massif from the Welsh Massif along the reactivated Malvern Line. Permian to Mesozoic sequences exhibit persistent but variable degrees of onlap onto the massif.

This second and completely revised edition of Special Report No. 6 provides a comprehensive review and report of work earned out since 1975. It emphasizes the relationship between, and the correlation of, the units in to which the Precambrian rocks of England, Ireland, Scotland, Wales and the Channel Islands have been divided The chapters also provide a comprehensive bibliography of the work on which the correlations have been based.

The deep crustal magnetic structure of Britain has not previously been described in a uniform manner. We provide a new assessment of the deep crustal magnetic bodies responsible for the long wavelength magnetic features. The study area contains deep crustal relics of the destruction of early Palaeozoic oceanic lithosphere along the Thor-Tornquist Suture and primarily the Iapetus Suture separating Baltica and Avalonia from the Laurentian terranes. Spectral decomposition is applied to a merged onshore and offshore magnetic anomaly data set. Thirty idealised basement bodies are compared with a representation of the subsurface obtained by a coarse 3D inversion of the data. The central area separating Laurentia and Avalonia, is largely characterised by an absence of high susceptibilities throughout the whole crustal volume. We find that the idealised basement bodies are largely consistent with relatively high susceptibility zones at depths in excess of 10km. The zones of higher relative susceptibility are referenced to the tectonic-terrane framework of the area and possible geological explanations for the contrasts are reviewed. In the north, the Laurentian terranes are diverse, comprising crust first created in the Archaean (Hebridean Terrane), Palaeoproterozoic (Rhinns Terrane), Mesoproterozoic? (Midland Valley Terrane), Neoproterozoic (sub-Southern Upland rocks) and Ordovician. Magnetic anomalies further record the assembly of the Gondwanan (Eastern Avalonian) part of the country through Neoproterozoic and Ordovician (Tornquist) arc magmatism and accretion. The convergence zones between Laurentia, Avalonia and Baltica have all left a magnetic imprint, as has Variscan convergence to the south.

This report synthesises the results of the 21CXRM Palaeozoic project in the Irish Sea to describe the Palaeozoic petroleum systems of that area. One hydrocarbon play system dominates the basin system: Namurian organic-rich marine shales (Bowland Shale Formation) generated oil and gas with a peak during maximum burial of the system in late Jurassic/early Cretaceous time. These hydrocarbons passed to reservoirs in the Triassic Ormskirk Sandstone (Sherwood Sandstone Group) by way of structures generated during the Variscan Orogeny and Cenozoic inversion, resulting in the Morecambe, Hamilton and other gas and oil fields The Palaeozoic study of the wider Irish Sea area has assessed the potential for more widespread petroleum systems situated outside the well-known play, particularly within the Carboniferous. Within the Main Graben system of the East Irish Sea Basin, Coal Measures strata were partially removed following Variscan inversion and early Permian uplift. They are not rich in coals, and not inferred to be a significant source rock. There is some potential in the Millstone Grit and Yoredale sequences, as some shales (particularly those associated with marine bands) are known to have high Total Organic Contents. The source rock potential of shales within the Carboniferous Limestone sequence is poorly constrained by data. A Devonian source rock is unproven and considered unlikely. Potential Namurian source rocks, such as the Yoredale Group, have been largely eroded in the Peel and North Channel basins, considerably reducing their prospectivity, although terrestrial sequences of equivalent age in the Solway Basin may offer better potential. The variable seismic data quality at Carboniferous levels and sparsity of deep well control have led to challenges in interpretation, particularly of the deeper picks. The interpretation of the surfaces contains a strong model-driven element, evidenced by the onshore relationships and areas where seismic picks can be made with the greatest confidence. Based upon the integration of regional seismic mapping with a limited well, source rock and reservoir property dataset, the most prospective parts of the region, outside the Ormskirk conventional gas play, are considered to be:  The thick Westphalian sequences preserved in the Eubonia Tilt-Block in Quadrant 109, outside the main Permian-Mesozoic graben system and unaffected by Cenozoic inversion. The presence and quality of seals form a major risk as the Cumbrian Coast Group seal is thin or absent and Carboniferous intraformational seals are required but untested. Based on the limited dataset available in adjacent basins, reservoir quality is also a significant risk.  A belt of Variscan inversion structures correlated with structures on the Formby Platform, and Ribbledale Foldbelt onshore, from which hydrocarbons have leaked into the overlying, Ormskirk-hosted Hamilton fields. The biggest risk here is whether reservoirs remain unbreached at the Pre-Permian level, and retain good poroperm characteristics at depths of about 2500 m.  A more speculative play lies in the extensive carbonate platform in Quadrant 109 and surrounding the Isle of Man, in reefal facies with enhanced secondary porosity. Here, source rock presence and migration pathways, reservoir properties and seal quality are major risks.

This report is designed simply to provide a summary tectonic outline and contextual setting against which offshore seismic and well data relating to the Devono-Carboniferous evolution of the Central North Sea, Forth Approaches, and adjacent UK onshore region can be considered. This summary is intended to help better frame the questions that will arise during interrogation of that data; the findings that result from that analysis are presented elsewhere in the report series (Arsenikos et al., 2015; Kimbell & Williamson, 2015; Monaghan et al., 2015). Apparently contradictory, wrench- or extension-dominated patterns of Lower Carboniferous basin development are recorded in the Forth Approaches, Quadrant 29, North Dogger and Silverpit basins of the Central North Sea, as well as the Midland Valley of Scotland (MVS) and Northumberland and Solway basins onshore. Partitioning Carboniferous deformation across inherited pre-existing Caledonian or Tornquist structures is likely to be an important control on the tectonic architecture developed in these regions during intervals of the geological record in the Carboniferous. Onshore, spatially separate but contemporaneous domains of extension-dominated tectonics versus wrench-dominated tectonics explain the contrasting tectonic framework of the MVS/Forth Approaches region (wrench-dominated) compared with Northumberland Basin (classic ‘stags head’ structure). NE-SW trending Caledonian inheritance strongly controls the domain boundaries and the patterns of deformation created in each of these domains. Offshore, in the Devono-Carboniferous basins of the Central North Sea, the likelihood that strain is partitioned in a similar way across features inherited from the NW-SE Tornquist trend is proposed and examined. The data currently under consideration suggests that a NW-SE trending wrench-dominated domain is spatially associated with the region underlain by the Dogger Granite pluton; domains affected by extension-dominated tectonics appear to be arranged on either side of that feature, namely the Quadrant 29 and North Dogger basins to the NE, and the Silverpit Basin to the SW. Extension is expressed as a NE-SW directed stretch in both of these domains. Patterns of broadly N-S trending fold axes need to be carefully assessed in terms of their structural setting, as folding cannot implicitly be linked with inversion/compression when partitioned strains are developed. Superficially similar features can develop in the MVS in dextral transpression, in north Northumberland buttressed around the Cheviot Granite in overall dextral wrench, and as superimposed late compressional folds in end-Variscan convergence, for example in the Boldon syncline of County Durham. Offshore, similar inversion effects can be seen in the patterns of transpressive faulting associated with features such as the Murdoch Ridge, and with examples of superimposed NE-SW trending extensional faults active in the latest Carboniferous to early Permian.

U-Pb (zircon) ages for key stratigraphic volcanic horizons within the ~3200-m-thick Ediacaran-age Charnian Supergroup provide an improved age model for the included Avalonian assemblage macrofossils and, hence, temporal constraints essential for intercomparisons of the Charnian fossils with other Ediacaran fossil assemblages globally. The Ives Head Formation (Blackbrook Group), the oldest exposed part of the volcaniclastic Charnian Supergroup of the late Neoproterozoic Avalonian volcanic arc system of southern Britain, contains a bedding plane with an impoverished assemblage of ivesheadiomorphs that is constrained to between ca. 611 Ma and 569.1 ± 0.9 Ma (total uncertainty). Higher-diversity biotas, including the holotypes of Charnia, Charniodiscus, and Bradgatia, occupy the upper part of the volcaniclastic succession (Maplewell Group) and are dated at 561.9 ± 0.9 Ma (total uncertainty) and younger by zircons interpreted as coeval with eruption and deposition of the Park Breccia, Bradgate Formation. An ashy volcanic-pebble conglomerate in the Hanging Rocks Formation at the very top of the supergroup yielded two U-Pb zircon populations: an older detrital one at ca. 604 Ma, and a younger population at ca. 557 Ma, which is interpreted as the approximate depositional age. The temporal association of the fossiliferous Charnian Supergroup with comparable fossiliferous deep-water successions in Newfoundland, and the probable temporal overlap of the youngest Charnwood macrofossils with those from different paleoenvironmental settings, such as the Ediacaran White Sea macrofossils, indicate a primary role for ecological sensitivity in determining the composition of these late Neoproterozoic communities.

Summary Subsurface 3D geological models of aquifer and seal rock systems from two contrasting analogue sites have been created as the first step in an investigation into methodologies for geological storage of carbon dioxide in saline aquifers. Development of the models illustrates the utility of an integrated approach using digital techniques and expert geological knowledge to further geological understanding. The models visualize a faulted, gently dipping Permo-Triassic succession in Lincolnshire and a complex faulted and folded Devono-Carboniferous succession in eastern Scotland. The Permo-Triassic is present in the Lincolnshire model to depths of −2 km OD, and includes the aquifers of the Sherwood Sandstone and Rotliegendes groups. Model-derived thickness maps test and refine Permian palaeogeography, such as the location of a carbonate reef and its associated seaward slope, and the identification of aeolian dunes. Analysis of borehole core samples established average 2D porosity values for the Rotliegendes (16%) and Sherwood Sandstone (20%) groups, and the Zechstein (5%) and Mercia Mudstone (<10%) groups, which are favourable for aquifer and seal units respectively. Core sample analysis has revealed a complex but well understood diagenetic history. Re-interpretation of newly reprocessed seismic data in eastern Scotland has significantly reduced interpretative uncertainty of aquifer and seal units at depths of up to −6 km OD in a complex faulted and folded Devono-Carboniferous succession. Synthesis of diverse data in the 3D geological model defines a set of growth folds and faults indicative of active Viséan to Westphalian dextral-strike slip, with no major changes in structural style throughout the Carboniferous, in contrast to some published tectonic models. Average 2D porosity values are 14–17% in aquifer units and <2% in the seal unit, with a ferroan dolomite cement occluding porosity at depth.

This volume forms part of the product of a multidisciplinary study by the British Geological Survey (BGS), commissioned by the UAE Federal Government, Ministry of Energy, to produce 1:100 000 scale geological maps of the bedrock and superficial geology of the central and western part of the UAE. 1:50 000 scale maps were produced of selected areas near Abu Dhabi and for seven emergent salt domes (mainly on offshore islands). This document therefore follows on from the previous volume (Styles et al., 2006) on the geology of the northern Emirates. The present volume similarly contains information about the findings of the geological mapping and associated specialist research. Much of the central and western part of the UAE is blanketed by Quaternary and recent dune sands, fluvial sediments and sabkhas. The only significant areas of exposed older rocks occur along the coast between Abu Dhabi and As Sila and on the various salt islands. Previous geological maps were made more than 20 years ago and were based largely on air photo interpretation with limited ground-truthing. The rapid economic development in the intervening period has seen a tremendous expansion of the national infrastructure and this has greatly increased the demand for high quality, field-based geological maps. The area was mapped at a scale of 1:50 000 and maps produced at 1:100 000, with the exception of the salt dome islands which were mapped at 1:25 000 scale. An area of the coast around Abu Dhabi is illustrated in two additional maps produced at 1:50 000 scale. Each 1:100 000 scale map is accompanied by a Sheet Explanation that describes the rock sequences in the area covered by that particular map. This report describes the broader features of the main rock groups on a regional basis and includes the results of the specialist laboratory studies that were used to define and interpret the geology of the project area. The field mapping was undertaken in the winter months between October 2008 and March 2011. The mapping was carried out by A R Farrant, R A Ellison, R J Thomas, J W Merritt, S J Price, A J Newell, J Merritt, J R Lee, A B Leslie, H F Burke, R A Smith, K M Goodenough, A Finlayson, C J Jordan and S L B Arkley. The laboratory studies were mostly carried out at the BGS. The petrographic study of the Miocene and Quaternary rocks and sediments was carried out by E R Phillips, whilst the igneous petrology of the Hormuz Complex rocks was undertaken by members of the mapping team. I P Wilkinson undertook micropalaeontologial determinations of both Miocene and recent sediments. The macropalaeontology of the basal Baynunah Formation is based largely on published information provided by Dr Mark Beech, Professor Andrew Hill and Dr Faisal Bibi. Some additional data on the Fars Group was provided by M A Woods. R Knox did the heavy mineral analyses, whilst D Wagner and S Kemp worked on the XRD analysis. The U-Pb zircon and carbonate geochronology was undertaken by M Horstwood, N Roberts and R Parrish at the NERC Isotope Geoscience Laboratories at the BGS, Keyworth. The Optically Stimulated Luminescence (OSL) dating was carried out by Professor G Duller and Dr H Roberts in the Aberystwyth Luminescence Research Laboratory at the Institute of Geography and Earth Sciences, Aberystwyth University. P Turner and C Simpson were responsible for the GIS systems and map layouts. H Holbrook and S Ward drew the majority of the illustrations. W Masterson and A Hill formatted this Memoir and the Sheet Explanations. This volume was compiled by A R Farrant and edited by R J Thomas.

The northwestern part of the Scandinavian Caledonides, formed by SE- to ESE-directed thrusting through the Neoproterozoic W. Baltica continental shelf, contains numerous small and often isolated outcrops of diamictite and associated strata. No precise bio-stratigraphic or isotopic data are available to constrain the age of these sediments, but, on the basis of their stratigraphic position, most are correlated with the Mortensnes Formation (Fm.) in E. Finnmark and also presumed to be of glaciogenic origin. The Mortensnes Fm. has been correlated with the 580 Ma Gaskiers glacial event on the basis of delta C-13 isotope studies. Structurally, the deposits occur in the Autochthon (below the Tornetrask Fm.), within an external imbricate zone (Lower Allochthon), within cover successions lying unconformably on allochthonous basement (Window Allochthon) palaeogeographically derived from below or outboard of the Lower Allochthon and, more rarely, within the Middle Allochthon, derived from outboard of the Window Allochthon. Evidence for a glaciogenic origin is typically poor or lacking. Only in the Komagfjord Antiformal Stack (Window Allochthon), where an up to 40-m-thick succession of three fining upwards cycles has been mapped, are the deposits comparable in thickness and complexity to the Mortensnes Fm. Other sequences are sometimes <1m thick and unconformably overlain by post-'glacial' deposits. The Vakkejokk Breccia, a submarine slump in the Tornetrask area of the Autochthon closely underlies the correlative Precambrian-Cambrian lithostratigraphic boundary in E. Finnmark but overlies the first appearance of the boundary marker fossil Treptichnus pedum. Although sometimes interpreted as peri-glacial, this seems unlikely in view of the 30-50 degrees palaeolatitude during deposition. Calcite nodules (<1cm size) in the Vakkejokk Breccia have previously been interpreted as glendonite, but the microstructure and palaeolatitude makes this unlikely; they are likely a replacement of gypsum. Diamictites of uncertain origin have also been found in the Ediacaran Lower Siltstone Member of the Tornetrask Fm. and unconformably under the ?Lower Cambrian Lomvatn Fm. in the Komagfjord Antiformal Stack.

Abstract The northwestern part of the Scandinavian Caledonides, formed by SE- to ESE-directed thrusting through the Neoproterozoic W. Baltica continental shelf, contains numerous small and often isolated outcrops of diamictite and associated strata. No precise biostratigraphic or isotopic data are available to constrain the age of these sediments, but, on the basis of their stratigraphic position, most are correlated with the Mortensnes Formation (Fm.) in E. Finnmark and also presumed to be of glaciogenic origin. The Mortensnes Fm. has been correlated with the 580 Ma Gaskiers glacial event on the basis of δ13C isotope studies. Structurally, the deposits occur in the Autochthon (below the Torneträsk Fm.), within an external imbricate zone (Lower Allochthon), within cover successions lying unconformably on allochthonous basement (Window Allochthon) palaeogeographically derived from below or outboard of the Lower Allochthon and, more rarely, within the Middle Allochthon, derived from outboard of the Window Allochthon. Evidence for a glaciogenic origin is typically poor or lacking. Only in the Komagfjord Antiformal Stack (Window Allochthon), where an up to 40-m-thick succession of three fining upwards cycles has been mapped, are the deposits comparable in thickness and complexity to the Mortensnes Fm. Other sequences are sometimes <1 m thick and unconformably overlain by post-‘glacial’ deposits. The Vakkejokk Breccia, a submarine slump in the Torneträsk area of the Autochthon closely underlies the correlative Precambrian–Cambrian lithostratigraphic boundary in E. Finnmark but overlies the first appearance of the boundary marker fossil Treptichnus pedum. Although sometimes interpreted as periglacial, this seems unlikely in view of the 30–50° palaeolatitude during deposition. Calcite nodules (<1 cm size) in the Vakkejokk Breccia have previously been interpreted as glendonite, but the microstructure and palaeolatitude makes this unlikely; they are likely a replacement of gypsum. Diamictites of uncertain origin have also been found in the Ediacaran Lower Siltstone Member of the Torneträsk Fm. and unconformably under the ?Lower Cambrian Lomvatn Fm. in the Komagfjord Antiformal Stack.

sedimentary history of the eastern part of the English Midlands (hereafter referred to as the region) emphasising the structure and evolution of the Carboniferous basins. It is the fourth in the Subsurface Memoir series of the British Geological Survey, following the Northumberland– Solway Basin (Chadwick et al., 1995), the Craven Basin (Kirby et al., 2000) and south-west Pennine Basin (Smith et al., 2005), and forms a sequel to a previously published subsurface study of the Mesozoic basins of England and Wales (British Geological Survey, 1985a). The region includes areas of high urban population density, contrasting with pastoral countryside and fenland (Figure 1). The cities of Nottingham, Leicester, Lincoln and Peterborough are the principal conurbations, but much of north Nottinghamshire and South Yorkshire bear the legacy of industrialisation following development of the concealed Yorkshire–Nottinghamshire coalfield. The geology of the region (Figure 2) is superficially simple. Carboniferous strata of the southeastern part of the Pennine Basin dip eastward beneath a cover of Permian and Mesozoic strata. This description belies the complex structure and stratigraphy of the Carboniferous basins however; rapid stratigraphical variation occurs where the Carboniferous strata onlap onto the Anglo–Brabant Massif in the south of the region. Early Palaeozoic strata have very limited outcrop, and are mainly known from deep boreholes. Deformation of the rocks occurred during a number of tectonic episodes, producing structures that control their nature and distribution. The surface and near-surface geology have been described in the British Geological Survey 1:50 000 Series maps and memoirs (Appendix 1). This account examines the deeper parts of the Permian– Mesozoic and, in particular, the Carboniferous successions, in greater detail than in earlier publications. Over 2000 seismic reflection profiles have been interpreted, and some 500 deep boreholes studied during the course of this work, and the results are synthesised in the accompanying 1:625 000 scale structure contour and isopach maps (Appendix 3) and associated text figures. This account provides both a regional review and an explanation of these maps and figures. The Carboniferous rocks of the region have long been of economic significance. Coal has been worked for centuries. Prior to the 1960s, only limited investigation of the concealed geology was possible, mainly through coal exploration and extraction, and oil exploration. The National Coal Board (NCB) established a sophisticated system for coal seam identification and correlation using geochemical methods. This was combined with biostratigraphical information from marine bands to yield a very detailed lithostratigraphical correlation of the Coal Measures. The region has experienced several phases of hydrocarbon exploration: immediately following the First World War; just before and after the Second World War, when drilling was mainly on the edges of structural highs recognised from gravity anomalies; in the 1950s and 1960s, with the widespread application of seismic techniques; in the 1970s and 1980s, using 2D reflection seismic data of increasingly high fold; and since 1995, using 3D reflection seismic. The 2D data are variable in fold of stack (12 to 60) and data quality (poor to good). The acquisition of the hydrocarbon exploration seismic data, in combination with Coal Authority high resolution seismic data over more localised areas, has resulted in an extensive network of seismic reflection profiles (Figure 3), except across the Anglo–Brabant Massif (Figure 4) and in the main conurbations. This account relies heavily on these data. The 3D data are now becoming available through release, but were not extensively used during the mapping programme. A few examples of these data are however included as figures. All phases of exploration have involved the drilling of deep boreholes which, together with surface exposures, provide stratigraphical calibration. Depth conversion of interpreted seismic data to produce the structural maps was complicated by a number of factors, including the variable age of the data and the quantity and quality of the data. Horizons mapped from the seismic data in two-way-travel-time (TWTT) were converted to depth using velocity functions based on depths and times in key boreholes. Particular attention was paid to the depth conversion of the early Carboniferous interval, due to the known variation of Tournaisian and Visean lithologies (and thus interval velocities) at crop and in boreholes in surrounding basins (i.e. platform carbonates and basinal mudstone facies)