Preliminary report on the Quaternary geology and palaeo-iceflow in the Bridge of Orchy – Glen Lyon area, SW Scottish Highlands – June 2003 Land and Resources Directorate Internal Report IR/03/105 BRITISH GEOLOGICAL SURVEY INTERNAL REPORT IR/03/105 Preliminary report on the Quaternary geology and palaeo-iceflow in the Bridge of Orchy – Glen Lyon area, SW Scottish Highlands – June 2003 N R Golledge The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty’s Stationery Office. Ordnance Survey licence number GD 272191/2003 Key words Quaternary geology, iceflow, Scottish Highlands, Loch Lomond Stadial. Front cover Cover photo shows Beinn Dorain and Beinn an Dothaidh from Beinn Achaladair ridge. Bibliographical reference GOLLEDGE, N R., 2003. Preliminary report on the Quaternary geology and palaeo- iceflow in the Bridge of Orchy – Glen Lyon area, SW Scottish Highlands. British Geological Survey Internal Report, IR/03/105. 39pp. © NERC 2003 Keyworth, Nottingham British Geological Survey 2003 IR/03/105; Final Version Last modified 2003/08/22 09:47 BRITISH GEOLOGICAL SURVEY The full range of Survey publications is available from the BGS Keyworth, Nottingham NG12 5GG Sales Desks at Nottingham and Edinburgh; see contact details 0115-936 3241 Fax 0115-936 3488 below or shop online at www.thebgs.co.uk e-mail: [email protected] The London Information Office maintains a reference collection www.bgs.ac.uk of BGS publications including maps for consultation. 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Forde House, Park Five Business Centre, Harrier Way, Sowton, Exeter, Devon EX2 7HU 01392-445271 Fax 01392-445371 Geological Survey of Northern Ireland, 20 College Gardens, Belfast BT9 6BS 028-9066 6595 Fax 028-9066 2835 Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB 01491-838800 Fax 01491-692345 Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU 01793-411500 Fax 01793-411501 www.nerc.ac.uk ii Foreword This report is the published product of a study by the British Geological Survey (BGS) concerning the Quaternary geology of an area of the south-west Scottish Highlands, including reconstructions of former iceflow of the Loch Lomond Stadial ice cap. The report summarises the results of four weeks field work in an area of 160 km2, and highlights areas where future research may prove useful. The work was undertaken as part of the Moine and Dalradian Basins project, a component of the Highlands and Islands Integrated Surveys (E1263S71). An element of the preparatory and fieldwork time was additionally funded by the SIGMA Toolkit project, (E1258S65). Acknowledgements Many thanks to Nikki Smith and Emma Bee for assistance in setting up the iPAQ and ArcPad software for use in the field, and to Martin Smith for loan of the Vaio laptop. Discussions in the field with Tom Bradwell provided the basis of many of the ideas described in this report, for which I am indebted. Thanks also to Wishart Mitchell for valuable input in the field. Angela Muir assisted greatly by formatting the report. The owners and keepers of both Auch and Glen Lyon Estates are gratefully acknowledged for allowing access to the field area and for 4WD use of their tracks. iii Contents Foreword ...................................................................................................................................... iii Acknowledgements ...................................................................................................................... iii Contents.........................................................................................................................................iv Summary ......................................................................................................................................vii 1 Introduction ............................................................................................................................1 1.1 Area.................................................................................................................................1 1.2 Legacy.............................................................................................................................1 1.3 Literature.........................................................................................................................2 1.4 Mapping techniques........................................................................................................2 2 Overview of the superficial geology ......................................................................................2 3 Description and occurrence of Quaternary deposits...........................................................3 3.1 Bedrock at or near surface ..............................................................................................3 3.2 Head / Regolith ...............................................................................................................4 3.3 Till...................................................................................................................................6 3.3.1 ‘Morainic’ diamicton...................................................................................................6 3.3.2 Olive-brown till ...........................................................................................................7 3.3.3 Grey till........................................................................................................................7 3.4 Hummocky Moundy Glacial deposits (moraine)............................................................8 3.5 Glaciofluvial and glaciolacustrine deposits ..................................................................10 3.5.1 Ice-contact deposits ...................................................................................................10 3.5.2 Fan deposits ...............................................................................................................10 3.5.3 Sheet deposits ............................................................................................................11 3.5.4 Glaciolacustrine deposits...........................................................................................11 3.5.5 Glacial Lake Tulla .....................................................................................................12 3.6 Alluvium .......................................................................................................................12 3.7 Peat................................................................................................................................14 4 Geomorphology.....................................................................................................................14 4.1 Corries...........................................................................................................................14 4.2 Nunataks / arêtes...........................................................................................................14 4.3 Benches.........................................................................................................................15 4.4 Meltwater channels .......................................................................................................15 4.5 Shorelines......................................................................................................................16 4.6 Landslips.......................................................................................................................16 4.7 Ice-moulding / striae / roche moutonnée / perched boulders........................................18 4.8 Moraines and streamlined mounds ...............................................................................19 iv 4.9 Eskers............................................................................................................................20 5 Quaternary history...............................................................................................................21 5.1 Previous research ..........................................................................................................21 5.1.1 Geological Survey .....................................................................................................21 5.1.2 K.S.R. Thompson ......................................................................................................22 5.1.3 B.R. Horsfield............................................................................................................22