Geology of the Huntly and Turriff Districts Sheet Description for the 1:50 000 Geological Sheets 86W (Huntly) and 86E (Turriff) (Scotland)
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Geology of the Huntly and Turriff Districts Sheet description for the 1:50 000 geological sheets 86W (Huntly) and 86E (Turriff) (Scotland) Geology and Landscape Scotland Open Report OR/15/026 BRITISH GEOLOGICAL SURVEY GEOLOGY AND LANDSCAPE SCOTLAND OPEN REPORT OR/15/026 The National Grid and other Ordnance Survey data © Crown Geology of the Huntly and Turriff Copyright and database rights 2015. Ordnance Survey Licence No. 100021290. Districts Keywords Report; Geology, Huntly, Turriff. Sheet description for the 1:50 000 geological National Grid Reference sheets 86W (Huntly) and 86E (Turriff) SW corner 34338, 82923 Centre point 36309, 84315 (Scotland) NE corner 38281, 85705 Maps Sheet 86W, 1:50 000 scale, Huntly; Sheet 86E, 1:50 000 scale, Turriff A G Gunn, J R Mendum and C W Thomas Front cover Contributors Huntly Castle, Aberdeenshire, from the north-east, showing the magnificent 17th century heral- D Ball, D Gould, A M Hall, K E Rollin, D Stephenson dic doorway of Old Red Sand- stone (P001147) Bibliographical reference Gunn, A G, Mendum, J R and Thomas, C W. 2015. Geology of the Huntly and Turriff Districts. Sheet description for the 1:50 000 geological sheets 86W (Huntly) and 86E (Turriff) (Scot- land). British Geological Survey Open Report, OR/15/026. 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 Sur- vey, 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 Ord- nance Survey mapping. © 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 www.geologyshop.com BGS Central Enquiries Desk Tel 0115 936 3143 Fax 0115 936 3276 The London Information Office also maintains a reference collec- tion of BGS publications, including maps, for consultation. email [email protected] We publish an annual catalogue of our maps and other publica- tions; this catalogue is available online or from any of the BGS Environmental Science Centre, Keyworth, Nottingham shops. NG12 5GG Tel 0115 936 3241 Fax 0115 936 3488 The British Geological Survey carries out the geological survey of email [email protected] Great Britain and Northern Ireland (the latter as an agency ser- vice for the government of Northern Ireland), and of the surround- ing continental shelf, as well as basic research projects. It also Murchison House, West Mains Road, Edinburgh EH9 3LA undertakes programmes of technical aid in geology in developing Tel 0131 667 1000 Fax 0131 668 2683 countries. email [email protected] The British Geological Survey is a component body of the Natural Environment Research Council. Natural History Museum, Cromwell Road, London SW7 5BD Tel 020 7589 4090 Fax 020 7584 8270 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 Foreword This report summarises the results of detailed geological remapping and related studies under- taken by the Geological Survey in the Huntly and Turriff districts of North-east Scotland. It pro- vides an account of the geology to accompany the published 1:50 000 geological maps sheets 86W (Huntly) and 86E (Turriff). The districts occupy a tract of generally rolling country, which ranges from about 50 to 200 m above sea level in its eastern part, to more elevated hilly country, commonly reaching over 300 m and 400 m above OD, in its western and southern parts. The drainage is dominated by the sinuous incised valley of the River Deveron and its main tributar- ies, the rivers Isla and Bogie, except for the southern part of the Turriff district, which is drained by the headwaters of the River Ythan. Agriculture and forestry are the dominant economic ac- tivities, with tourism and whisky distilling also significant. The Huntly and Turriff districts are underlain mainly by Dalradian metasedimentary rocks of Neoproterozoic age that have been strongly deformed and metamorphosed during the Grampian event of the Caledonian Orogeny. The Dalradian rocks have been intruded by igneous intrusions that range from large plutons to small pods and dykes. Granite sheets and pods were emplaced at about 600 million years (Ma), followed later by small ultramafic and mafic bodies. However, the main intrusive igneous event occurred in the Early to Mid Ordovician at 474 to 470 Ma, coeval with the Grampian event. It resulted in the emplacement of mafic and ultramafic plutons, com- monly zoned; the Insch Pluton includes monzonites and syenites in its upper zone. Dioritic and granitic bodies are associated with the plutons. The major structural feature is the north-north-east-trending Portsoy Shear Zone, which traverses the Huntly district. This steeply easterly dipping zone is coincident with a major regional linea- ment, which separates stratigraphically discrete packages of Dalradian rocks with different tec- tonometamorphic histories. The shear zone has also facilitated and in part controlled the emplacement of the Huntly and Knock mafic-ultramafic plutons. The Dalradian metasedimen- tary rocks contain both Buchan and Barrovian metamorphic zonal assemblages. Folding and shearing have caused local repetition of lithological units, but overall the Dalradian sequence be- comes younger eastwards until the broad hinge of the regional Turriff Syncline is reached in the central part of that district. Here, the youngest Dalradian rocks are exposed and metamorphic grade is low (biotite grade). Farther east older Dalradian rocks again crop out and the Buchan metamorphic isograds are re-crossed such that the rocks contain andalusite and sillimanite. Following the Grampian orogenic event the area was uplifted, and during the Early Devonian fluvial and lacustrine Old Red Sandstone rocks were deposited in the northerly trending fault- bounded basins, namely the Turriff and Rhynie basins. In Strath Bogie a basaltic andesite lava unit linked to the Rhynie chert occurs within the Rhynie Basin succession. Subsequently, a Mid- dle Devonian conglomerate-dominated sequence, linked to the Orcadian Lake farther north, was deposited unconformably on the older succession in the Turriff Basin. In the Turriff district deep Tertiary weathering profiles and local fluvial sands and gravels are preserved, testifying to only limited erosion by the later Quaternary glaciations. The Devensian glacial and postglacial history of the districts was dominated by an ice sheet derived from the highland areas farther to the south-west. The related glacial and postglacial superficial deposits form a pervasive if generally thin cover over much of the bedrock. Till derived from the Moray Firth is present in the north-eastern part of the Turriff district. Eastward migration of glacial meltwater gave rise to channels that in places have significantly influenced development of the Holocene fluvial drainage pattern. British Geological Survey i OR/15/026 The Huntly district has been the focus of several periods of exploration since 1970 for platinum group elements, copper and nickel linked mainly to the mafic-ultramafic plutons and their meta- morphic aureoles. The limited drilling and more extensive ground magnetic surveys, in combina- tion with geochemical studies and gravity modelling, have provided detailed information as to the nature, distribution and origin of prospective areas. No economic deposits have been deline- ated to date. However, this BGS report and the geological maps provide a sound foundation for existing and any future commercial and/or conservation-related developments. Acknowledgements The original geological survey was carried out by mainly by J Horne between 1880 and 1884, with minor contributions from J S Grant Wilson and LW Hinxman. Detailed revision was under- taken by H H Read between 1917 and 1919 and the resultant 1:63,360 scale Sheet 86 (Huntly) and related memoir were published in 1923. The more recent mapping in the districts took place in the late 1980s and early 1990s, as part of the wider East Grampian Project. It has concentrated mainly in the Huntly district, where, the Department of Trade and Industry (DTI) funded detailed mapping and investigations by BGS in areas thought likely to be prospective for minerals, work complemented by the DTI Mineral Reconnaissance Programme. However, the bulk of the map- ping and related work in the Huntly andTurriff districts was funded by the Department of Edu- cation and Science as part of its remit to provide geological data, maps and reports to underpin the UK infrastructure and economy. The Forestry Commission and other landowners within the Huntly and Turriff districts are thanked for their cooperation and assistance. The mapping and related geological studies have resulted in significant revision of the geology, culminating in publication of the accompanying 1:50 000 Sheet 86E (Turriff) and 86W (Huntly) maps in 1995 and 2000 respectively. The solid geology was compiled from 1:10 000 maps pro- duced by A G Gunn, J R Mendum, S D Redwood, D Stephenson, C W Thomas and D Gould, and from other map and data sources held in the archives of the British Geological Survey.