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The strike-slip influenced stratigraphic and structural development of the Foula Sandstone Group, Shetland: implications for offshore Devonian basin development in the northern UKCS

Utley, T.A.G.; Holdsworth, R.E.; Blackbourn, G.A.; Dempsey, E.; Strachan, R.A.; McCaffrey, K.J.W.; Morton, A.C.; Bird, A.F.; Jones, R.R.; Saßnowski, A.; Walker, R.J.

Authors

T.A.G. Utley

R.E. Holdsworth

G.A. Blackbourn

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Dr Eddie Dempsey E.Dempsey@hull.ac.uk
Senior Lecturer in Structural Geology and Geohazards

R.A. Strachan

K.J.W. McCaffrey

A.C. Morton

R.R. Jones

A. Saßnowski

R.J. Walker



Abstract

The island of Foula located 25 km SW of Shetland preserves a gently folded, 1.6 km thick sequence of Middle Devonian sandstones spectacularly exposed in kilometre-long cliff sections over 350 m high. These rocks unconformably overlie likely Precambrian-age amphibolite facies basement rocks, intruded by sheeted granites. The onshore succession is similar in age to the nearby Lower Clair Group offshore to the west. New mapping which incorporates use of drone imagery in inaccessible cliff sections uses down-plunge projections to show that growth folding and faulting on Foula were contemporaneous with sedimentation during basin filling. The large-scale structural geometry is consistent with regional constrictional strain due to sinistral transtension associated with movements along the Walls Boundary - Great Glen Fault Zone system during the Middle Devonian. Detrital zircon provenance studies indicate that the Devonian sequences of Foula - and nearby Melby in western Shetland - show similarities with the Clair Group and Orkney successions. We suggest that NE-SW transtensional fold development contemporaneous with regional subsidence may be more widespread than previously realised in the Devonian basins of Scotland. Large, kilometre-scale folds previously interpreted to be related to Permo-Carboniferous inversion may therefore have initiated earlier in the basin evolution than previously realised.

Citation

Utley, T., Holdsworth, R., Blackbourn, G., Dempsey, E., Strachan, R., McCaffrey, K., …Walker, R. (2023). The strike-slip influenced stratigraphic and structural development of the Foula Sandstone Group, Shetland: implications for offshore Devonian basin development in the northern UKCS. Journal of the Geological Society, 180(3), Article jgs2022-148. https://doi.org/10.1144/jgs2022-148

Journal Article Type Article
Acceptance Date Feb 17, 2023
Online Publication Date Feb 28, 2023
Publication Date Apr 27, 2023
Deposit Date Jul 18, 2023
Publicly Available Date Jul 21, 2023
Journal Journal of the Geological Society
Print ISSN 0016-7649
Electronic ISSN 2041-479X
Publisher Geological Society
Peer Reviewed Peer Reviewed
Volume 180
Issue 3
Article Number jgs2022-148
DOI https://doi.org/10.1144/jgs2022-148
Keywords Geology
Public URL https://hull-repository.worktribe.com/output/4270546

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