Darren Mark along with Vincent Gallagher and Anne Kelly have published the first high-precision zircon U-Pb age data collected at SUERC in our new geochronology suite. The CA-ID-TIMS measurements were made using our 205Pb-235U inhouse spike and provide age constraints for key fossil-bearing sequences within Wales.

Catlos et al., 2020, Late Silurian U-Pb ages from the Ludlow and Downton Bone Beds, Welsh Basin, UK

View paper in the Journal of the Geological Society

photo of signpost marking Ludford Corner.Ludlow Bone Bed

Abstract

The Ludlow Bone Bed (Welsh Basin) is a critical stratigraphic horizon and contains a rich assemblage of fish scales. Units above shed 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 spectrometer U-Pb geochronology was utilized to improve precision. Detrital zircon grains from Downton yield 424.91 ± 0.34/0.42/0.63 Ma and Ludlow are 424.85 ± 0.32/0.41/0.62 Ma (n=5 each, 238U-206Pb, ± 2σ analytical/tracer/systematic uncertainty). These ages provide a maximum deposition age. Results overlap the basal Prídolí 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 correlated with the base of the Prídolí Series. The CA-ID-TIMS ages are older than other land arthropod-bearing sediments, such as the Cowie Harbour Fish Bed and Rhynie Chert.

 

First published: 25 August 2020

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