U-Pb zircon-rutile dating of the Llangynog Inlier, Wales: constraints on an Ediacaran shallow-marine fossil assemblage from East Avalonia

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dc.contributor.authorClarke, A.
dc.contributor.authorKirkland, C.
dc.contributor.authorMenon, L.
dc.contributor.authorCondon, D.
dc.contributor.authorCope, J.
dc.contributor.authorBevins, R.
dc.contributor.authorGlorie, S.
dc.date.issued2024
dc.descriptionPublished online: 15 January 2024
dc.description.abstractThe Llangynog Inlier of south Wales contains an assemblage of Ediacaran macrofossils from a shallow-marine environment, including discoidal morphs of Aspidella and rare examples of Hiemalora, Palaeopascichnus and Yelovichnus. These are taxa found at other sites in the Avalonian microcontinent (e.g. Charnwood Forest and eastern Newfoundland) and in the younger White Sea Ediacaran assemblages. As the Charnwood fossils reflect a deep-water environment, and no macrofossils have been found in the Ediacaran rocks of the Long Mynd, the fossils of the Llangynog Inlier represent a unique glimpse of shallow-marine life in southern Britain (East Avalonia). However, the lack of absolute age constraints has hampered direct comparison with other assemblages. Here, we report in situ zircon and rutile U–Pb dates from a rhyolitic ash-flow layer of the Coed Cochion Volcaniclastic Member, Llangynog Inlier, which constrains the age of the fossiliferous strata. A weighted mean single grain zircon isotope dilution thermal ionization mass spectrometry U–Pb age of 564.09 ± 0.70 Ma is interpreted as the rhyolite's crystallization age. This age is consistent with in situ laser ablation inductively coupled plasma mass spectrometry zircon and rutile U–Pb dating. The Llangynog age temporally correlates these fossils to dated horizons within East Avalonia at the Beacon Hill Formation, Charnwood (565.22 ± 0.89 Ma) and the Stretton Shale Formation, Long Mynd (566.6 ± 2.9 Ma). Correlations to West Avalonia include the time-equivalent Fermeuse Formation, St John's Group, eastern Newfoundland (564.13 ± 0.65 Ma). The data presented here establish the biota of the Llangynog Inlier as a lateral equivalent to the similarly shallow-marine, tidally influenced ecosystem of the upper Fermeuse Formation. Intra-terrane depositional environmental variability also affects what is preserved in Avalonian fossil sites. Further, time-constrained geochemical data reinforce the Llangynog Inlier's classification within the Wrekin Terrane.
dc.description.statementofresponsibilityAnthony J. I. Clarke, Christopher L. Kirkland, Latha R. Menon, Daniel J. Condon, John C. W. Cope, Richard E. Bevins and Stijn Glorie
dc.identifier.citationJournal of the Geological Society, 2024; 181(1):jgs2023-081.-1-jgs2023-081-12
dc.identifier.doi10.1144/jgs2023-081
dc.identifier.issn0016-7649
dc.identifier.issn2041-479X
dc.identifier.orcidGlorie, S. [0000-0002-3107-9028]
dc.identifier.urihttps://hdl.handle.net/2440/140580
dc.language.isoen
dc.publisherGeological Society
dc.relation.granthttp://purl.org/au-research/grants/arc/DP200101881
dc.relation.granthttp://purl.org/au-research/grants/arc/FT210100906
dc.rights© 2024 The Author(s). Published by The Geological Society of London. All rights reserved.
dc.source.urihttps://doi.org/10.1144/jgs2023-081
dc.titleU-Pb zircon-rutile dating of the Llangynog Inlier, Wales: constraints on an Ediacaran shallow-marine fossil assemblage from East Avalonia
dc.typeJournal article
pubs.publication-statusPublished

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