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The nature and significance of rift-related, near-surface fissure fill networks in fractured carbonates below regional unconformities

Hardman, Kit; Holdsworth, Robert E; Dempsey, Edward; McCaffrey, Ken

Authors

Kit Hardman

Robert E Holdsworth

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Dr Eddie Dempsey E.Dempsey@hull.ac.uk
Lecturer in Structural Geology, Programme Director (Geology and GPG)

Ken McCaffrey



Contributors

Abstract

Hosted in carbonate and crystalline basement rocks below regional unconformities, fissure-fill networks are a widely recognized, but relatively little described near-surface phenomenon (< 1-2km). Faults and fractures in otherwise tight Devonian carbonate basement rocks of the Tor Bay region, Devon, are associated with the development of millimetre- to decametre-wide fissures containing red early Permian sedimentary material, vuggy calcite mineralisation and wall-rock collapse breccias. These features preserve evidence concerning the style and history of fault deformation and reactivation in near surface settings, and on fluid-related processes such as elutriation and/or mineralization. Field observations, palaeostress analysis, and fracture topology analyses show that the rift-related faults and fractures created a network of long-lived open cavities during the early Permian development of the Portland-Wight Basin. Once formed, they were subjected to episodic, likely seismically-induced fluid fluxing events and local karstification. The large, well-connected networks of naturally propped fractures were - and possibly still are - important fluid migration pathways within otherwise low permeability host rocks. These structures are likely equivalent to those observed in many other rift-related, near-surface tectonic settings, and suggest that the Tor Bay outcrops can be used as a global analogue for sub-unconformity open fissure systems hosted in low permeability basement rocks.

Citation

Hardman, K., Holdsworth, R. E., Dempsey, E., & McCaffrey, K. (2020). The nature and significance of rift-related, near-surface fissure fill networks in fractured carbonates below regional unconformities. Journal of the Geological Society, https://doi.org/10.1144/jgs2020-074

Journal Article Type Article
Acceptance Date Jun 15, 2020
Online Publication Date Jun 18, 2020
Publication Date Jul 22, 2020
Deposit Date Jun 24, 2020
Publicly Available Date Jun 25, 2020
Journal Journal of the Geological Society
Print ISSN 0016-7649
Electronic ISSN 2041-479X
Publisher Geological Society
Peer Reviewed Peer Reviewed
DOI https://doi.org/10.1144/jgs2020-074
Keywords Geology
Public URL https://hull-repository.worktribe.com/output/3525658
Publisher URL https://pubs.geoscienceworld.org/jgs/article-lookup?doi=10.1144/jgs2020-074

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Accepted article (5.8 Mb)
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Publisher Licence URL
https://creativecommons.org/licenses/by/4.0/

Copyright Statement
© 2020 The Author(s). 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/). Published by The
Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics


Published article (17 Mb)
PDF

Publisher Licence URL
https://creativecommons.org/licenses/by/4.0/

Copyright Statement
© 2020 The Author(s). 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/). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics





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