The Appalachian-Caledonide orogen records protracted Paleozoic convergence during Iapetus Ocean closure. Grampian-Taconian arc-continent collision at the Laurentian margin and subduction polarity reversal were followed by Ordovician to Silurian subduction-accretion beneath the Laurentian margin, culminating in continental collision in the Scandinavian Caledonides, and soft collision along the Solway-Navan-Silvermines line in Britain and Ireland. Laurentiaderived detrital zircon crossed this boundary, commonly regarded as the main Iapetus suture, upon collision at ca. 430 Ma. Calc-alkaline magmatism continued into the Devonian on both sides of the supposed suture, producing the "trans-suture suite" of magmatic rocks that extend south as far as a boundary, here termed the Ynys M & ocirc;n line, separating the Lakesman terrane from the Monian belt of North Wales. South of this line, Laurentia-derived detritus is absent from Silurian samples, but appears in Emsian Old Red Sandstone. Laurentia-derived detritus was held up at the Ynys M & ocirc;n line for at least 12 Myr. This boundary is interpreted as a previously unrecognized suture, recording obliquely sinistral north-dipping subduction of a remaining tract of Iapetus, leading to magmatism north of the boundary and eventual Acadian collision.

Pyrite oxidation drives iron and sulfur availability across Earth's subsurface and is partly microbially mediated. Subsurface microbial communities accelerate this process at circumneutral pH directly by weathering pyritic surfaces and indirectly by causing changes to the surrounding microenvironment, thereby further accelerating pyrite weathering. However, our understanding of community structure dynamics and associated biogeochemistry in Fe- and S-rich lithologies, e.g. pyritic coal, is limited. Here, we present the first comprehensive regional and seasonal genus-level survey of bacterial groundwater communities in a pyritic coal-based aquifer in the South Wales Coalfield (SWC), using 16S rRNA gene amplicon sequencing. Seasonal changes in community structure were limited, suggesting limited influence of surface processes on subsurface communities. Instead, hydrogeologically distinct mine water blocks (MWB) and coal rank largely explained bacterial community structure variation across sites. Fe(II)-oxidizing Betaproteobacteriales genera Gallionella and Sideroxydans dominated the bacterial communities across nine sites and seven MWBs, while three sites within a single MWB, were dominated by S-oxidizing Epsilonbacteraeota genera Sulfuricurvum and Sulfurovum. The cooccurrence of pairs of Fe(II)- and S-oxidizing bacterial genera suggests functional redundancy, which coupled with genus-specific morphologies and life strategies, indicates the importance of distinct environmental and ecological niches within the SWC groundwater at seasonal and regional scales.

The Meelpaeg structure in southwestern Newfoundland comprises allochthonous tectonites formed during the Salinic (D 1-2 ) and Acadian (D 3 ) orogenies. D 1-2 occurred between 451 and 417 Ma and culminated in Barrovian metamorphism during terminal collision of the Gander margin with composite Laurentia. Collision was followed by tectonic escape of the deeply buried rocks between 417 and 412 Ma. Rocks of the Victoria arc and Exploits backarc preserved in the Port aux Basques and Grand Bay complexes were emplaced during D 1 by the Grandys River shear zone, which is outlined by a narrow band of the ca. 451 Ma Port aux Basques granite, towards the southeast above the Harbour le Cou Group. The contrasting histories displayed across the Grandys River shear zone are typical of the Dog Bay Line further northeast. Salinic structures were overprinted by faults and folds formed during Acadian D 3 transpression (≤412 Ma), which produced the bi-vergent Meelpaeg structure and emplacement of amphibolite facies tectonites above greenschist facies rocks along its bounding shear zones. F 3 folding progressively steepened the faults, which in turn led to progressive localization of dextral strike–slip in narrow fault zones. The high grade of metamorphism in the Meelpaeg structure is attributed to protracted underthrusting of the Cabot promontory of the Gander margin beneath composite Laurentia. Salinic convergence was sinistral but became dextral during the Early Devonian, diachronous Acadian orogeny. The kinematic switch is proposed as a tool to separate Salinic from Acadian structures in the central part of the northern Appalachians.

The Iapetus Ocean was the first ancient ocean to be identified following the development of plate tectonics; its history has been fundamental in relating orogenesis and plate motion. The ocean probably formed following 3-way rifting between Laurentia, Baltica, and Amazonia - West Africa (a block that became incorporated in Gondwana). Closure of the ocean trapped numerous terranes during the development of the Appalachian-Caledonide Orogen. Subsequent deformation, including late Paleozoic strike slip, transpression, and transtension, and Mesozoic stretching during Pangea breakup, must be taken into account in models for orogen development. Traditional analyses of Iapetan terranes have focussed on Cambrian sedimentary successions, and on isotopic criteria, to classify terranes into larger domains: Ganderia, Avalonia and Megumia. Detrital zircon data show that these domains did not cross the Iapetus as single entities, while paleomagnetic data reveal significant verticalaxis terrane rotations. We here review and interpret 17 paleomagnetic poles and >350 published detrital zircon data sets from the northern Appalachians and western Caledonides, using consistent and rigorous criteria for the selection and presentation of data. We place these data on an integrated stratigraphic chart to show timing relations and to seek constraints on the provenance and travel of terranes in the Iapetus Ocean. We distinguish groups of terranes that likely travelled together as terrane assemblages. In the Taconian/Grampian Orogeny, Furongian to Katian continent-arc collision involved off-margin blocks along the hyperextended Laurentian margin. In New England, early Taconian collision by 475 Ma involved the Gondwana-derived Moretown assemblage. An assemblage of the Bronson and Popelogan arc terranes probably arrived at the main Laurentian margin 25-30 Myr later. Subduction polarity reversal then led to the progressive accretion of additional terrane assemblages (Salinian Orogeny). The Miramichi-Victoria assemblage arrived close to the Ordovician-Silurian boundary. The Miramichi terrane underwent partial subduction in the Quebec re-entrant, whereas the Victoria terrane was juxtaposed with the Newfoundland promontory without major metamorphism. In mid-Silurian time, an assemblage including the Gander terrane of Newfoundland and related portions of Britain and Ireland was accreted to Laurentia, along with Baltica (Scandian Orogeny). The St. Croix - La Poile assemblage may have been accreted slightly later, but is distinguished by the development of a Silurian arc-backarc system (coastal igneous belt) above a northwest-dipping subduction zone. The Avalon-Brookville assemblage encountered this system in Pridoli to Middle Devonian time (Acadian Orogeny), leading to the collapse of the backarc basin and northwest-vergent thrust emplacement onto Laurentia during sinistral transpression in the Appalachian Orogen. Acadian deformation involved mainly sinistral strike slip in Britain and Ireland. Several of the terranes that were accreted to the Laurentian margin carried internal records of earlier deformation that took place near Amazonia - West Africa in Early Ordovician time and earlier (Monian/Penobscottian Orogeny). The Iapetus Ocean thus contained a complex array of terranes, small ocean basins, arcs, and previously emplaced ophiolites analogous to modern southeast Asia. It closed to form a complex array of sutures in an orogen within which no single Iapetus suture can be clearly identified.

The Appalachian-Caledonian Orogen preserves a complex record of piecemeal trans-oceanic terrane transfer and accretion during the early Paleozoic collision between West Gondwana and Laurentia, whilst the intervening Iapetus oceanic tracts were largely destroyed. The now preserved terranes include arc fragments of Laurentian and Gondwanan affinity, oceanic fragments incorporated into the Gondwanan continental margin, and remnants of the Gondwanan continental slope apron and adjacent platform (both Ganderia and Megumia). A new tectonostratigraphic synthesis for the island of Anglesey (and adjacent NW Wales) reveals a comprehensive record of the Appalachian orogenic cycle in the UK segment of the orogen of the peri-Gondwanan margin prior to amalgamation into the Laurentian margin. We identify elements of Late Neoproterozoic accretion forming the pre-Appalachian basement; Cambrian extension, deposition and continental margin growth; Early Ordovician accretion and renewed extension; and, finally, terminal Caledonian collision and continental foreland-basin development.

West and East Ganderia in the northern Appalachians and Caledonides, respectively, represent a Gondwanan superterrane situated along the Tornquist margin of Amazonia prior to Furongian drift into the Iapetus Ocean, which opened the Rheic Ocean from west to east. The ocean-facing Penobscot arcbackarc system was established by 515 Ma in West Ganderia. A correlative arc formed at ca. 480 Ma in East Ganderia. In West Ganderia, the Tremadocian Penobscottian orogeny involved closure of the Penobscot backarc basin. Tremadocian Monian tectonism in East Ganderia was mainly related to oblique accretion to East Avalonia and the Megumian Cymru terrane. Penobscottian and late Floian Monian orogenesis led to termination of Early Ordovician arc magmatism, probably due to shallow subduction of buoyant oceanic lithosphere. Early to Middle Ordovician arc-backarc systems were erected on Penobscottian-Monian modified West and East Ganderia. The active edge of West Ganderia accreted diachronously to peri-Laurentia between 475 Ma and 455 Ma, followed by Wenlock to Ludlow Salinic accretion of the inboard Gander margin through closure of the intervening backarc basin. In the Caledonides, East Ganderia and East Avalonia accreted to Laurentia during the correlative Wenlock Scandian orogeny. The Ordovician to Silurian tectonic evolution of Ganderia was markedly non-cylindrical with pronounced partitioning of SalinicScandian convergence. Pridoli to Lochkovian closure of the Acadian seaway in the northern Appalachians led to Acadian accretion of West Avalonia to composite Laurentia. Shallow Early Devonian underthrusting of West and East Avalonia beneath Laurentia produced widespread Acadian tectonism and voluminous Early Devonian Acadian magmatism. The Appalachian Meguma terrane formed part of Megumia, which probably formed originally adjacent to East Avalonia and West Africa. The Meguma terrane accreted dextrally to Laurentia during and after the late Emsian to Famennian Neoacadian orogeny, mainly driven by outboard subduction of the Rheic Ocean. No correlative terrane docking took place in the Caledonides. Crown Copyright (c) 2021 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. All rights reserved.

The Annual Technical Meeting was held virtually on February 22 and 23, 2021 from various home offices, dens, and bedrooms across St. John’s, Newfoundland and Labrador and beyond.This year the meeting kicked off on Monday with a Special Session to pay tribute to R. Frank Blackwood who passed away in the summer of 2020. Frank was a strong supporter of bedrock mapping, mineral exploration, and the mining industry in Newfoundland and Labrador which is reflected in the following abstracts. Tuesday featured a General Session with presentations on a wide range of geoscience topics.As always, this meeting was brought to participants by volunteer efforts and would not have been possible without the time and energy of the executive and other members of the section such as Anne Westhues, Jared Butler, James Conliffe, Shawn Duquet, Sarah Hashmi, Zsuzsanna Magyarosi, Annie Parrell, and Karen Waterman. The organizers are also indebted to their sponsors, particularly the Geological Association of Canada, Department of Earth Sciences (Memorial University of Newfoundland), and the Geological Survey of Newfoundland and Labrador, Department of Energy, Industry, and Technology.Although the abstracts are modified and edited as necessary for clarity and to conform to Atlantic Geology format and standards, the journal editors do not take responsibility for their content or quality.

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.

Low-temperature heat recovery, cooling and storage schemes, using abandoned flooded mine workings, are a viable option for low-carbon heating solutions within many abandoned British coalfields. The temperature of mine water is a useful parameter, coupled with depth to water, sustainable yield and recharge potential, to identify suitable locations and calculate the likely performance of heat recovery schemes. This paper aims to provide the first mapping and synthesis of the temperature of Britain's coalfields to support this emerging technology. Using the best available evidence, a median geothermal gradient of 24.1 degrees C km(-1) was calculated for the British coalfields. However, geothermal gradients between separate coalfields can vary from 17.3 to 34.3 degrees C km(-1). The North East, Cumbria and Yorkshire coalfields all have mean geothermal gradients generally >30 degrees C km(-1), whereas geothermal gradients of generally <23 degrees C km(-1) are measured in the Warwickshire, South Wales, Staffordshire, Douglas and Fife coalfields. Active dewatering schemes are shown to locally increase the apparent measured geothermal gradient by ingress and mixing of deeper water into the pumping shafts. This baseline spatial mapping and synthesis of coalfield temperatures offers significant benefit to those planning, designing and regulating heat recovery and storage in Britain's abandoned coalfields.

This study examines the long‐term neotectonic evolution of the Crag Basin of eastern England during the Plio‐Pleistocene (c. 4.0–0.48 Ma) and the influence of neotectonics on coastal and drainage development. The Crag Basin was situated within the western margins of the southern North Sea with palaeogeography influenced by changes in global sea‐level and longer‐term regional‐scale neotectonic uplift and subsidence. This study identifies an additional local‐scale neotectonic control on basin development with localized crustal displacement occurring along normal faults. Plio‐Pleistocene movement along these faults was accommodated by partial dip‐slip (normal) reactivation of an Oligocene‐age (Pyrenean) dextral strike‐slip shear zone, which in turn was inherited from much older Caledonian orogenic crustal structure. Fault displacement was driven by sediment‐loading reflecting enhanced landscape denudation under progressively deteriorating climates and increased rates of erosion/sedimentation. Faulting acted to regulate accommodation space, controlling sedimentation patterns and the courses of major preglacial drainage systems including the Kesgrave Thames and Bytham rivers. The lower reaches of both river systems are considered to have been confluent in the Crag Basin during much of the Early Pleistocene with their lower reaches structurally controlled. Divergence occurred at c. 0.9 Ma with the lower reaches of the Bytham utilizing the former Bytham‐Thames valley and the Kesgrave Thames adopting progressively more southern routes, aligned to the axis of subsidence within the London Basin. The study highlights the significance of tectonic inheritance in driving recent neotectonic crustal deformation and its influence on sedimentation patterns and drainage development within an intraplate setting.

Heat from the earth, or geothermal heat, arises from the heat dissipated from the centre of the earth and, at shallow depth, from heating by the sun. High-enthalpy (deep) geothermal heat is found within some granitic rocks due to slightly raised levels of the radiogenic isotopes of potassium, uranium and thorium. This resource in the UK is estimated to be able to provide the equivalent of around 2280 MWe of electrical power from a depth of around 4.5 km (Busby and Terrington 2017), sufficient to cover 85% of Scotland’s or 9% of England’s current (2016, BEIS 2018) electricity consumption. Another geothermal heat resource is low-enthalpy (shallow) geothermal heat, which is found in sedimentary basins and more widely available throughout the UK as ‘ground heat’ where heat from sunlight and from building foundations, tunnels and sewers is stored in the shallow subsurface. This heat resource is typically distributed by natural groundwater systems and through man-made structures such as the abandoned coal-mines that underlie many of the UK’s cities and towns and can be exploited through Ground Source Heat Pump (GSHP) systems that could provide sufficient heat for around 650 000 homes nationally (Adams and Gluyas 2017).

At the 2015 United Nations International Climate Change Conference in Paris (COP21), 197 national parties committed to limit global warming to well below 2°C.But current plans and pace of progress are still far from sufficient to achieve this objective.Here we review the role that geoscience and the subsurface could play in decarbonizing electricity production, industry, transport and heating to meet UK and international climate change targets, based on contributions to the 2019 Bryan Lovell meeting held at the Geological Society of London.Technologies discussed at the meeting involved decarbonization of electricity production via renewable sources of power generation, substitution of domestic heating using geothermal energy, use of carbon capture and storage (CCS), and more ambitious technologies such as bioenergy and carbon capture and storage (BECCS) that target negative emissions.It was noted also that growth in renewable energy supply will lead to increased demand for geological materials to sustain the electrification of the vehicle fleet and other low-carbon technologies.The overall conclusion reached at the 2019 Bryan Lovell meeting was that geoscience is critical to decarbonization, but that the geoscience community must influence decision-makers so that the value of the subsurface to decarbonization is understood.

Abstract In the original Wilson cycle, the northern Appalachian–Caledonide orogen resulted from the collision of two continental masses separated by a single ocean. One of these corresponds to the modern concept of Laurentia, but the colliding continent to the east has been variously subdivided into many smaller terranes and domains, including Ganderia, Avalonia and Megumia. Using published stratigraphic evidence and detrital zircon provenance data from units of known depositional age, the timing of arrival of these units at the Laurentian margin between the Early Ordovician and Early Devonian can be constrained. Several of the accreted terranes do not extend over the entire length of the orogen, with the result that the lines separating them change character along strike from terrane-bounding sutures to simple accretionary faults. The Ganderia domain consists of at least four separate terranes that share a common origin on the continental margin of Gondwana, but were separated by back-arc oceanic crust as they crossed the Iapetus Ocean and collided diachronously with the Laurentian margin.