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Late Silurian zircon U–Pb ages from the Ludlow and Downton bone beds, Welsh Basin, UK
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EPub Date
Issue Date
21/09/2020
Submitted Date
2020-11-12
Subject Terms
Welsh Basin
Cowie Harbour Fish Bed
Pr ídol Series
land arthropod-bearing sediments
UK
Po žáry Section
Cathodoluminescence images show
Ludlow Bone Bed marks
CA
Detrital zircon grains
Downton Bone Beds
SIMS
Ion Mass Spectrometry
Ludlow Bone Bed
Cowie Harbour Fish Bed
Pr ídol Series
land arthropod-bearing sediments
UK
Po žáry Section
Cathodoluminescence images show
Ludlow Bone Bed marks
CA
Detrital zircon grains
Downton Bone Beds
SIMS
Ion Mass Spectrometry
Ludlow Bone Bed
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Abstract
The Ludlow Bone Bed (Welsh Basin) is a critical stratigraphic horizon and contains a rich assemblage of fish scales. Units above provide insights into the early evolution of animal and plant life. The bed has not yet been radioisotopically dated. Here, we report 207 secondary ion mass spectrometry (SIMS) ages from 102 zircon (ZrSiO4) grains from the Ludlow (n = 2) and stratigraphically higher Downton (n = 1) bone beds. SIMS ages are middle Ordovician (471.6 ± 20.7 Ma) to late Devonian (375.7 ± 14.6 Ma, 238U–206Pb, ±1σ analytical uncertainty). Cathodoluminescence images show that the youngest ages appear affected by alteration. Chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) U–Pb geochronology was utilized to improve precision. Detrital zircon grains from Downton yield 424.91 ± 0.34/0.42/0.63 Ma and from Ludlow 424.85 ± 0.32/0.41/0.62 Ma (n = 5 each, 238U–206Pb, ±2σ analytical, tracer or systematic uncertainty). These ages provide a maximum deposition age. Results overlap the basal Přídolí age (423.0 ± 2.3 Ma) in its stratotype (Požáry Section, Reporyje, Prague, Czech Republic). The Ludlow Bone Bed marks the base of the local Downton Group, which has previously been correlated with the base of the Přídolí Series. The CA-ID-TIMS ages are older than those for other land arthropod-bearing sediments, such as the Cowie Harbour Fish Bed and Rhynie Chert.
Citation
Elizabeth J. Catlos, Darren F. Mark, Stephanie Suarez, Michael E. Brookfield, C. Giles Miller, Axel K. Schmitt, Vincent Gallagher, Anne Kelly; Late Silurian zircon U–Pb ages from the Ludlow and Downton bone beds, Welsh Basin, UK. Journal of the Geological Society doi: https://doi.org/10.1144/jgs2020-107
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Journal Article
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© 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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NHM Repository
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ISSN
0016-7649
EISSN
2041-479X