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Lithostratigraphy of the Old Red Sandstone successions of the Anglo-Welsh Basin Research Report RR/14/02 BRITISH GEOLOGICAL SURVEY RESEARCH REPORT RR/14/02 Lithostratigraphy of the Old Red Sandstone successions of the Anglo-Welsh Basin The National Grid and other Ordnance Survey data © Crown Copyright and database rights 2014. Ordnance Survey Licence W J Barclay, J R Davies, R D Hillier* and R A Waters* No. 100021290. * Geology Department, National Museum and Galleries of Wales, Cathays Park, Cardiff, CF10 3NP, UK Keywords Old Red Sandstone, lithostratigraphy, Devonian. Front cover Sandstones and mudrocks of the Freshwater West Formation, Daugleddau Group. Cobbler’s Hole, St Anne’s head, Pembrokeshire. P006692. Bibliographical reference BARCLAY, W J, DAVIES, J R, HILLIER, R D, AND WATERS, R A. 2015. Lithostratigraphy of the Old Red Sandstone successions of the Anglo-Welsh Basin. British Geological Survey Research Report, RR/14/02. 96pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. ISBN 978 0 85272 773 7 © NERC 2015. All rights reserved Keyworth, Nottingham British Geological Survey 2015 BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops at British Geological Survey offices Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at BGS Central Enquiries Desk www.geologyshop.com Tel 0115 936 3143 Fax 0115 936 3276 The London Information Office also maintains a reference email [email protected] collection of BGS publications, including maps, for consultation. Environmental Science Centre, Keyworth, Nottingham We publish an annual catalogue of our maps and other NG12 5GG publications; this catalogue is available online or from any of the BGS shops. Tel 0115 936 3241 Fax 0115 936 3488 email [email protected] The British Geological Survey carries out the geological survey of Great Britain and Northern Ireland (the latter as an agency Murchison House, West Mains Road, Edinburgh EH9 3LA service for the government of Northern Ireland), and of the surrounding continental shelf, as well as basic research projects. Tel 0131 667 1000 Fax 0131 668 2683 It also undertakes programmes of technical aid in geology in email [email protected] developing countries. Natural History Museum, Cromwell Road, London SW7 5BD The British Geological Survey is a component body of the Natural Tel 020 7589 4090 Fax 020 7584 8270 Environment Research Council. Tel 020 7942 5344/45 email [email protected] Columbus House, Greenmeadow Springs, Tongwynlais, Cardiff CF15 7NE Tel 029 2052 1962 Fax 029 2052 1963 Maclean Building, Crowmarsh Gifford, Wallingford OX10 8BB Tel 01491 838800 Fax 01491 692345 Geological Survey of Northern Ireland, Colby House, Stranmillis Court, Belfast BT9 5BF Tel 028 9038 8462 Fax 028 9038 8461 www.bgs.ac.uk/gsni/ Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon SN2 1EU Tel 01793 411500 Fax 01793 411501 www.nerc.ac.uk Website www.bgs.ac.uk Shop online at www.geologyshop.com British Geological Survey, Research Report RR/14/02 Foreword This report presents a revised lithostratigraphy of the Old Red Sandstone of the Anglo-Welsh Basin, prepared under the auspices of the British Geological Survey (BGS) Stratigraphical Framework Committee (SFC). The report provides a correlation of the successions in different parts of the basin and rationalises group and formation nomenclature for the outcrops of Old Red Sandstone in England and Wales. It is based on a previous discussion document (Barclay, unpublished MS, 2007) which presented options in a three-step approach towards rationalisation to a proposed single, standard scheme that can be applied to most of the Pridoli–Lochkovian succession (lower part of the Lower Old Red Sandstone) of the Anglo-Welsh Basin. The earlier discussion document was circulated among geologists with expertise in the Old Red Sandstone of the Anglo-Welsh Basin in and outside the British Geological Survey. This version takes account of the suggestions for improvement and comments made during the consultation process. One significant change from previous classifications concerns the base of the Old Red Sandstone. There is a consensus that this should be placed at the base of the first major incoming of red- or green-bed (‘Old Red Sandstone’) terrestrial facies, thereby excluding the shallow marine Downton Castle Sandstone and Tilestones formations that have traditionally been included in the Old Red Sandstone. The report proposes the introduction of two new names and group status for the successions traditionally referred to as the Lower Old Red Sandstone and Upper Old Red Sandstone. The two successions are separated by the major, regional, cleavage-forming Acadian unconformity, and because of this, the authors have made a case for giving them supergroup status. However, they are here accorded group status in accordance with practice in the other Old Red Sandstone basins of the United Kingdom, both onshore and offshore. In nationwide standardisation, all the groups are informally referred to the as-yet undefined parent ‘Old Red Sandstone Supergroup’, although the authors propose that the term ‘Old Red Sandstone’ is best retained as a facies (or magnafacies) term. The Lower Old Red Sandstone is termed the Daugleddau Group and the Upper Old Red Sandstone is termed the Brecon Beacons Group. Acknowledgements The authors are grateful to D Lowe, A Smith and C N Waters and the other members of the BGS Stratigraphy Committee for their work on the initial draft of this report and to J B Richardson (Natural History Museum, London) and B P J Williams (University of Aberdeen) for their criticisms and comments on an early version of the report. We are also grateful to members of the BGS Stratigraphy Committee (J Powell, C N Waters, A Smith, I Wilkinson, P Hopson, G Kirby, R Bowie, M Gillespie, H Johnson and J Merritt) for their valuable comments on a more recent version of the report. We also acknowledge the work of a large number of Geological Survey officers whose mapping of the Old Red Sandstone of the Anglo-Welsh Basin in south central, south-east and south Wales and the Welsh Borderland and West Midlands has contributed to our understanding of its lithostratigraphy. In areas of south-west Wales not recently mapped in detail by the British Geological Survey, the work of academic geologists, particularly that of J R L Allen and B P J Williams, requires special mention. i British Geological Survey, Research Report RR/14/02 ii British Geological Survey, Research Report RR/14/02 Contents Foreword ......................................................................................................................................... i Acknowledgements ......................................................................................................................... i Contents ......................................................................................................................................... iii Summary ........................................................................................................................................ v 1 Introduction ............................................................................................................................ 1 2 The base of the Old Red Sandstone .................................................................................... 10 3 The top of the Old Red Sandstone ...................................................................................... 13 4 Daugleddau Group ............................................................................................................... 17 4.1 Milford Haven Subgroup .............................................................................................. 18 4.2 Cosheston Subgroup ..................................................................................................... 43 4.3 Dulas Bay Subgroup ..................................................................................................... 52 5 Brecon Beacons Group ........................................................................................................ 57 5.1 Skrinkle Sandstones Subgroup ..................................................................................... 60 5.2 Portishead Subgroup ..................................................................................................... 64 References .................................................................................................................................... 78 Appendix 1 List of Old Red Sandstone lithostratigraphical units .................................... 91 Appendix 2 List of redundant Old Red Sandstone lithostratigraphical names .............. 95 Figures 1 Sketch map showing the amalgamation of the ORS continent ................................................ 2 2 Old Red Sandstone outcrops in England and Wales ...............................................................