Late Silurian zircon U–Pb ages from the Ludlow and Downton bone beds, Welsh Basin, UK

Catlos, E. J., Mark, D. F. , Suarez, S., Brookfield, M. E., Miller, C. G., Schmitt, A. K., Gallagher, V. and Kelly, A. (2021) Late Silurian zircon U–Pb ages from the Ludlow and Downton bone beds, Welsh Basin, UK. Journal of the Geological Society, 178(1), jgs2020-107. (doi: 10.1144/jgs2020-107)

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.Supplementary material: An Excel file containing detailed information on the SIMS analyses, a figure showing calibration curves for AS3 standards sputtered over sessions 1 and 2, and a figure showing CA-ID-TIMS U–Pb age data (concordia and weighted mean plots) are available at https://doi.org/10.6084/m9.figshare.c.5087031

• Item Type: Articles
• Additional Information: Support for obtaining the geochemical data in this paper was provided by funds to E.J.C. provided by the Jackson School of Geosciences at The University of Texas at Austin. Age data were collected by E.J.C. with the assistance of the Max Kade Foundation. This work was also funded by the Scottish Universities Environmental Research Centre. SIMS facilities at Heidelberg University acknowledge support through DFG Scientific Instrumentation and Information Technology programme.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Mark, Professor Darren

Creator Roles

Mark, D. F.: Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Validation, Visualization, Writing – review and editing

• Authors: Catlos, E. J., Mark, D. F., Suarez, S., Brookfield, M. E., Miller, C. G., Schmitt, A. K., Gallagher, V., and Kelly, A.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Journal of the Geological Society
• Publisher: Geological Society
• ISSN: 0016-7649
• ISSN (Online): 2041-479X
• Published Online: 14 August 2020
• Copyright Holders: Copyright © 2020 The Authors
• First Published: First published in Journal of the Geological Society 178(1): jgs2020-107
• Publisher Policy: Reproduced under a Creative Commons License