Deglaciation and neotectonics in South East Raasay, Scottish Inner Hebrides

David E. Smith; Callum R. Firth; Tim M. Mighall; Phill A. Teasdale

doi:10.1144/sjg2021-006

Deglaciation and neotectonics in South East Raasay, Scottish Inner Hebrides

David E. Smith^* (Corresponding Author), Callum R. Firth, Tim M. Mighall, Phill A. Teasdale

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

3 Citations (Scopus)

Abstract

Changes in the physical landscape of SE Raasay at the end of the last Quaternary glaciation are examined. The area is marked by a major fault system defining the Beinn na Leac Fault Block, and field survey shows this to comprise a rollover anticline in the SW, with extensional movement towards the NE along an oblique transfer fault, the Main Beinn na Leac Fault. The fault system was reactivated after the Last Glacial Maximum (the LGM). Survey of a distinctive ridge of detached scree along the Main Beinn na Leac fault shows it to have involved a single movement of at least 7.12m vertical displacement, arguably the greatest fault movement since before the Younger Dryas in Scotland. The present work confirms that the scree became detached during the Younger Dryas, but finds that it overlies a lacustrine deposit of at least 5.6m of laminated sediments from a lake which had begun to accumulate earlier. Radiocarbon dating of peat overlying the lake sediments gave 10,176 – 10,315 cal. BP, but morphological and stratigraphical evidence indicates that drainage of the lake occurred earlier and only shortly before movement of the scree. Possible causes of displacement at the fault system are briefly discussed.Scientific editing by Martin Kirkbride

Original language	English
Article number	sjg2021-006
Number of pages	11
Journal	Scottish Journal of Geology
Volume	57
Issue number	2
Early online date	18 May 2021
DOIs	https://doi.org/10.1144/sjg2021-006
Publication status	Published - 29 Jun 2021

Bibliographical note

The authors greatly appreciate the help and advice which they have received from: Dr Nicol Morton, who read an early version of the manuscript and provided advice and permission to reproduce the geological map in Figure 3; Dr Iain Stewart for earlier discussions on the geology of Raasay; Dr Alison Macleod for her advice on the magnetic susceptibility of sediments; Dr Adrian Hall, for his advice on the Quaternary geology of the area; Mrs Rebecca Mackay for her advice on the correct Gaelic spelling for place names and Dr Stephan Harrison and Professor Michael Tooley for their help in the field. We are grateful for the comments of the two referees, whose evidently complementary knowledge of the area was most illuminating.

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title = "Deglaciation and neotectonics in South East Raasay, Scottish Inner Hebrides",

abstract = "Changes in the physical landscape of SE Raasay at the end of the last Quaternary glaciation are examined. The area is marked by a major fault system defining the Beinn na Leac Fault Block, and field survey shows this to comprise a rollover anticline in the SW, with extensional movement towards the NE along an oblique transfer fault, the Main Beinn na Leac Fault. The fault system was reactivated after the Last Glacial Maximum (the LGM). Survey of a distinctive ridge of detached scree along the Main Beinn na Leac fault shows it to have involved a single movement of at least 7.12m vertical displacement, arguably the greatest fault movement since before the Younger Dryas in Scotland. The present work confirms that the scree became detached during the Younger Dryas, but finds that it overlies a lacustrine deposit of at least 5.6m of laminated sediments from a lake which had begun to accumulate earlier. Radiocarbon dating of peat overlying the lake sediments gave 10,176 – 10,315 cal. BP, but morphological and stratigraphical evidence indicates that drainage of the lake occurred earlier and only shortly before movement of the scree. Possible causes of displacement at the fault system are briefly discussed.Scientific editing by Martin Kirkbride",

author = "Smith, {David E.} and Firth, {Callum R.} and Mighall, {Tim M.} and Teasdale, {Phill A.}",

note = "The authors greatly appreciate the help and advice which they have received from: Dr Nicol Morton, who read an early version of the manuscript and provided advice and permission to reproduce the geological map in Figure 3; Dr Iain Stewart for earlier discussions on the geology of Raasay; Dr Alison Macleod for her advice on the magnetic susceptibility of sediments; Dr Adrian Hall, for his advice on the Quaternary geology of the area; Mrs Rebecca Mackay for her advice on the correct Gaelic spelling for place names and Dr Stephan Harrison and Professor Michael Tooley for their help in the field. We are grateful for the comments of the two referees, whose evidently complementary knowledge of the area was most illuminating. ",

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N1 - The authors greatly appreciate the help and advice which they have received from: Dr Nicol Morton, who read an early version of the manuscript and provided advice and permission to reproduce the geological map in Figure 3; Dr Iain Stewart for earlier discussions on the geology of Raasay; Dr Alison Macleod for her advice on the magnetic susceptibility of sediments; Dr Adrian Hall, for his advice on the Quaternary geology of the area; Mrs Rebecca Mackay for her advice on the correct Gaelic spelling for place names and Dr Stephan Harrison and Professor Michael Tooley for their help in the field. We are grateful for the comments of the two referees, whose evidently complementary knowledge of the area was most illuminating.

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N2 - Changes in the physical landscape of SE Raasay at the end of the last Quaternary glaciation are examined. The area is marked by a major fault system defining the Beinn na Leac Fault Block, and field survey shows this to comprise a rollover anticline in the SW, with extensional movement towards the NE along an oblique transfer fault, the Main Beinn na Leac Fault. The fault system was reactivated after the Last Glacial Maximum (the LGM). Survey of a distinctive ridge of detached scree along the Main Beinn na Leac fault shows it to have involved a single movement of at least 7.12m vertical displacement, arguably the greatest fault movement since before the Younger Dryas in Scotland. The present work confirms that the scree became detached during the Younger Dryas, but finds that it overlies a lacustrine deposit of at least 5.6m of laminated sediments from a lake which had begun to accumulate earlier. Radiocarbon dating of peat overlying the lake sediments gave 10,176 – 10,315 cal. BP, but morphological and stratigraphical evidence indicates that drainage of the lake occurred earlier and only shortly before movement of the scree. Possible causes of displacement at the fault system are briefly discussed.Scientific editing by Martin Kirkbride

AB - Changes in the physical landscape of SE Raasay at the end of the last Quaternary glaciation are examined. The area is marked by a major fault system defining the Beinn na Leac Fault Block, and field survey shows this to comprise a rollover anticline in the SW, with extensional movement towards the NE along an oblique transfer fault, the Main Beinn na Leac Fault. The fault system was reactivated after the Last Glacial Maximum (the LGM). Survey of a distinctive ridge of detached scree along the Main Beinn na Leac fault shows it to have involved a single movement of at least 7.12m vertical displacement, arguably the greatest fault movement since before the Younger Dryas in Scotland. The present work confirms that the scree became detached during the Younger Dryas, but finds that it overlies a lacustrine deposit of at least 5.6m of laminated sediments from a lake which had begun to accumulate earlier. Radiocarbon dating of peat overlying the lake sediments gave 10,176 – 10,315 cal. BP, but morphological and stratigraphical evidence indicates that drainage of the lake occurred earlier and only shortly before movement of the scree. Possible causes of displacement at the fault system are briefly discussed.Scientific editing by Martin Kirkbride

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ER -

Deglaciation and neotectonics in South East Raasay, Scottish Inner Hebrides

Abstract

Bibliographical note

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