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Outcrop-scale manifestations of reactivation during multiple superimposed rifting and basin inversion events : the Devonian Orcadian Basin, northern Scotland.

Dichiarante, A.M. and Holdsworth, R.E. and Dempsey, E.D. and McCaffrey, K.J.W. and Utley, T.A.G. (2020) 'Outcrop-scale manifestations of reactivation during multiple superimposed rifting and basin inversion events : the Devonian Orcadian Basin, northern Scotland.', Journal of the Geological Society., 178 (1).

Abstract

The Devonian Orcadian Basin in Scotland hosts extensional fault systems assumed to be related to the initial formation of the basin, with only limited post-Devonian inversion and reactivation. However, a recent detailed structural study across Caithness, underpinned by published Re–Os geochronology, shows that three phases of deformation are present. North–south- and NW–SE-trending Group 1 faults are related to Devonian ENE–WSW transtension associated with sinistral shear along the Great Glen Fault during the formation of the Orcadian Basin. Metre- to kilometre-scale north–south-trending Group 2 folds and thrusts are developed close to earlier sub-basin-bounding faults and reflect late Carboniferous–early Permian east–west inversion associated with dextral reactivation of the Great Glen Fault. The dominant Group 3 structures are dextral oblique NE–SW-trending and sinistral east–west-trending faults with widespread syndeformational carbonate mineralization (± pyrite and bitumen) and are dated using Re–Os geochronology as Permian (c. 267 Ma). Regional Permian NW–SE extension related to the development of the offshore West Orkney Basin was superimposed over pre-existing fault networks, leading to local oblique reactivation of Group 1 faults in complex localized zones of transtensional folding, faulting and inversion. The structural complexity in surface outcrops onshore therefore reflects both the local reactivation of pre-existing faults and the superimposition of obliquely oriented rifting episodes during basin development in the adjacent offshore areas.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1144/jgs2020-089
Publisher statement:© 2020 The Author(s). Published by The Geological Society of London. This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0/)
Date accepted:07 September 2020
Date deposited:27 November 2020
Date of first online publication:16 September 2020
Date first made open access:27 November 2020

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