National Geological Screening: South-west England region Minerals and Waste Programme Commissioned Report CR/17/095 BRITISH GEOLOGICAL SURVEY MINERALS AND WASTE PROGRAMME COMMISSIONED REPORT CR/17/095 National Geological Screening: South-west England region K Westhead1, A Holden1, D Schofield1,2, R Haslam2, S Loveless3, J P Bloomfield3, J R Lee4, B Baptie4, R P Shaw5, T Bide5 and F M McEvoy 1Rock type, 2Rock structure, 3Groundwater, 4Natural processes, 5Resources Contributors/editors L P Field, R Terrington, P Williamson, I Mosca, N J P Smith, D E Evans, C Gent, M Barron, A Howard, G Baker, R M Lark, A Lacinska, S Thorpe. H Holbrook, I Longhurst and L Hannaford The National Grid and other Ordnance Survey data © Crown Copyright and database rights 7. Ordnance Survey Licence No. 100021290 EUL. Keywords National geological screening, GDF, South-west England, rock type, structure, groundwater, natural processes, resources Bibliographical reference WESTHEAD, K, HOLDEN, A, SCHOFIELD, D, HASLAM, R, LOVELESS, S, BLOOMFIELD, J P, LEE, J R, BAPTIE, B, SHAW, R P, BIDE, T, and F M MCEVOY. 2018. National geological screening: South-west England region. British Geological Survey Commissioned Report, CR/17/095. 100pp. BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops British Geological Survey offices at Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at www.geologyshop.com Environmental Science Centre, Keyworth, Nottingham The London Information Office also maintains a reference NG12 5GG collection of BGS publications, including maps, for Tel 0115 936 3100 consultation. We publish an annual catalogue of our maps and other BGS Central Enquiries Desk publications; this catalogue is available online or from any of Tel 0115 936 3143 the BGS shops. email [email protected] The British Geological Survey carries out the geological survey of Great Britain and Northern Ireland (the latter as an agency BGS Sales service for the government of Northern Ireland), and of the Tel 0115 936 3241 Fax number removed surrounding continental shelf, as well as basic research email [email protected] projects. It also undertakes programmes of technical aid in geology in developing countries. The Lyell Centre, Research Avenue South, Edinburgh EH14 4AP The British Geological Survey is a component body of UK Research and Innovation. Tel 0131 667 1000 email [email protected] Natural History Museum, Cromwell Road, London SW7 5BD Tel 020 7589 4090 Tel 020 7942 5344/45 email [email protected] Cardiff University, Main Building, Park Place, Cardiff CF10 3AT Tel 029 2167 4280 Maclean Building, Crowmarsh Gifford, Wallingford OX10 8BB Tel 01491 838800 Geological Survey of Northern Ireland, Department of Enterprise, Trade & Investment, Dundonald House, Upper Newtownards Road, Ballymiscaw, Belfast, BT4 3SB Tel 01232 666595 www.bgs.ac.uk/gsni/ Natural Environment Research Council, Polaris House, North Star Avenue, Swindon SN2 1EU Tel 01793 411500 Fax 01793 411501 www.nerc.ac.uk UK Research and Innovation, Polaris House, Swindon SN2 1FL Tel 01793 444000 www.ukri.org Website www.bgs.ac.uk Shop online at www.geologyshop.com Foreword This report is the published product of one of a series of studies covering England, Wales and Northern Ireland commissioned by Radioactive Waste Management (RWM) Ltd. The report provides geological information about the South-west England region to underpin the process of national geological screening set out in the UK Government’s White Paper Implementing geological disposal: a framework for the long-term management of higher activity radioactive waste (DECC, 2014). The report describes geological features relevant to the safety requirements of a geological disposal facility (GDF) for radioactive waste emplaced onshore and up to 20 km offshore at depths between 200 and 1000 m from surface. It is written for a technical audience but is intended to inform RWM in its discussions with communities interested in finding out about the potential for their area to host a GDF. i Contents Foreword ......................................................................................................................................... i Acronyms and abbreviations ....................................................................................................... v Glossary ........................................................................................................................................ vi 1 Introduction ............................................................................................................................ 1 2 Background ............................................................................................................................ 2 2.1 National geological screening guidance ......................................................................... 2 2.2 Detailed technical instructions ....................................................................................... 3 2.3 Technical information reports and maps ........................................................................ 4 3 The South-west England region ............................................................................................ 5 3.1 Overview of the geology of the region ........................................................................... 5 4 Screening topic 1: rock type .................................................................................................. 9 4.1 Overview of rock type approach .................................................................................... 9 4.2 Potential rock types of interest in the South-west England region ............................... 10 5 Screening topic 2: rock structure ....................................................................................... 52 5.1 Overview of approach .................................................................................................. 52 5.2 Regional tectonic setting .............................................................................................. 52 5.3 Major faults .................................................................................................................. 57 5.4 Folding.......................................................................................................................... 61 5.5 Uncertainty ................................................................................................................... 62 6 Screening topic 3: groundwater .......................................................................................... 63 6.1 Overview of approach .................................................................................................. 63 6.2 Groundwater systems in South-west England .............................................................. 63 6.3 Overview of regional-scale groundwater flow and hydrostratigraphy ......................... 63 6.4 Evidence for connections between groundwater systems ............................................ 69 7 Screening topic 4: natural processes .................................................................................. 71 7.1 Overview of approach .................................................................................................. 71 7.2 Glaciation ..................................................................................................................... 71 7.3 Permafrost .................................................................................................................... 73 7.4 Seismicity ..................................................................................................................... 74 8 Screening topic 5: resources ................................................................................................ 83 8.1 Overview of approach .................................................................................................. 83 8.2 Overview of resources in the region ............................................................................. 83 8.3 Coal and related commodities ...................................................................................... 84 8.4 Potash, halite, gypsum/anhydrite and polyhalite deposits ............................................ 84 8.5 Other bedded and miscellaneous commodities ............................................................ 84 8.6 Vein-type and related ore deposits ............................................................................... 84 8.7 Hydrocarbons (oil and gas) .......................................................................................... 85 ii 8.8 Underground gas storage .............................................................................................. 85 8.9 Geothermal energy ....................................................................................................... 85 8.10 High density of deep boreholes .................................................................................... 86 8.11 Supporting information ................................................................................................ 89 References .................................................................................................................................... 91 FIGURES Figure 1 The BGS region boundaries as defined by the Regional Guides series of reports ........................ 1 Figure 2 Schematic diagram