Hydrogen usage and storage may contribute to reducing greenhouse gas emissions by decarbonising heating and transport and by offering significant energy storage to balance variable renewable energy supply. Underground storage of hydrogen is established in underground salt caverns, but these have restricted geographical locations within the UK and cannot deliver the required capacity. Hydrogen storage in porous geological formations has significant potential to deliver both the capacity and local positioning. This study investigates the potential for storage of hydrogen in porous subsurface media in Scotland. We introduce for the first time the concept of the hydrogen storage play. A geological combination including reservoir, seal and trap that provides the optimum hydrogen storage reservoir conditions that will be potential targets for future pilot, and commercial, hydrogen storage projects. We investigate three conceptual hydrogen storage plays in the Midland Valley of Scotland, an area chosen primarily because it contains the most extensive onshore sedimentary deposits in Scotland, with the added benefit of being close to potential consumers in the cities of Glasgow and Edinburgh. The formations assessed are of Devonian and Carboniferous age. The Devonian storage play offers vast storage capacity but its validity is uncertain due to due to a lack of geological data. The two Carboniferous plays have less capacity but the abundant data produced by the hydrocarbon industry makes our suitability assessment of these plays relatively certain. We conclude that the Carboniferous age sedimentary deposits of the D'Arcy-Cousland Anticline and the Balgonie Anticline close to Edinburgh will make suitable hydrogen storage sites and are ideal for an early hydrogen storage research project.

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The Darende Basin is an excellent example of an important, but little known, type of sedimentary basin that can form on the top of emplaced ophiolites prior to and during continental collision. The basin formation was preceded by southward emplacement of accretionary mélange and ophiolites onto the Tauride carbonate platform during latest Cretaceous. Sedimentation began during the Maastrichtian with non-marine clastic sediments accumulating in palaeovalleys. This was followed by a Maastrichtian marine transgression, triggered by extension along the basin margins. Rudist-rich patch reefs and a carbonate shelf developed in different areas. A second transgression during the Mid-Eocene was preceded by emergence, a hiatus (Paleocene), localized faulting and low-angle (<5–10°) tilting. Middle Eocene hemipelagic marls, shallow-marine Nummulites-rich carbonates, calciturbidites and sparse alkaline volcanism culminated in Late Eocene shallowing, emergence and then deformation. The first phase of basin development (Maastrichtian) is seen as extensional, related to slab-pull that resulted from northward subduction of remnant oceanic lithosphere beneath Eurasia in the Pontides to the north. The second phase of basin development (Mid–Late Eocene) is explained by crustal downflexure to form an under-filled foreland basin during the final collision of the Tauride continent with Eurasia. Basin uplift was delayed until after a Mid-Miocene marine incursion.Supplementary material:Full results of the palaeontological determination of collected samples from the Eocene aged sedimentary rocks of the Darende Basin are available at www.geolsoc.org.uk/SUP18544

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The Zoophycos group of trace fossils is common in Carboniferous to recent marine strata and sediments, and is a common component of ichnofaunas in the Visean and Namurian stages of England and Wales. A review of new and published records indicates that it is often present in limestones and sandstones of Chadian to Arnsbergian age. Thereafter it is less common, and restricted to clastic rocks. There are no known records within Carboniferous strata above the lowest Westphalian. The form is most common and often abundant in limestones of the Yoredale facies in the upper Visean and lower Namurian stages of northern England, particularly so in northern Northumberland. Where detailed sedimentological data exist, they indicate that the organisms responsible for the Zoophycos group burrowed into unconsolidated carbonate substrate that was deposited under low accumulation rates, often affected by storm wave action and where seawater flow provided a nutrient supply. However, in mixed carbonate–clastic settings, the deep-tier nature of Zoophycos may indicate that the organism lived in overlying shallow-marine, clastic-dominated depositional environments and burrowed down into the carbonate substrate. The same may be true of siliciclastic depositional settings where the presence of Zoophycos in some sandstones may reflect the palaeoenvironment of the overlying, finer-grained transgressive marine (prodelta and distal mouth bar) deposits.Supplementary material: A spreadsheet with details of Carboniferous records of Zoophycos group fossils from England, Wales, the Isle of Man and the North Sea is available at https://doi.org/10.6084/m9.figshare.c.4994636

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