Radioisotopic ages used in GTS2020

Schmitz, Mark D.

doi:10.1016/b978-0-12-824360-2.00046-2

Cited by 7 publications

(11 citation statements)

References 165 publications

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“…However, the use of correlating these early organisms has been problematic due to local evolutionary provincialism and convoluted age interpretations with the correlation of fluvial and marine deposits with a standard geologic timescale (Berry, 1987; Finney & Chen, 1990; Pogson, 2009; Brookfield et al 2021). Additionally, the Ordovician–Silurian boundary age at Dob’s Linn has been estimated by several radioisotopic dates with varying precisions, calculated by spline fitting interpolation from units stratigraphically above and below the boundary (Tucker et al 1990; Hu et al 2008; Schmitz & Ogg, 2020).…”

Section: Geological Backgroundmentioning

confidence: 99%

“…Elsewhere, hornblende from the Coronagraptus cyphus zone in the Descon Formation in Esquibel Island, Alaska, produced a 40 Ar- 39 Ar date of 442.6 ± 5.0 Ma (Lanphere et al 1977; Ross et al 1982; Kunk et al 1985; Schmitz & Ogg, 2012). Utilizing mechanically (air) abraded zircon 238 U- 206 Pb ID-TIMS dates, Tucker et al (1990) produced a biozone age of 439.57 ± 1.33 Ma from the weighted mean of six multigrain zircon fractions from Dob’s Linn, Scotland (Table 2) (Schmitz & Ogg, 2020).…”

Section: Biozone Agesmentioning

confidence: 99%

“…However, the current age interpretations of 443.8 ± 1.5 Ma or 443.1 ± 0.9 Ma are calculated by spline fitting interpolation from U-Pb multigrain zircon fractions stratigraphically above ( Coronograptus cyphus zone) and below ( Dicellograptus anceps zone) the Akidograptus ascensus zone. Gradstein et al (2020) interpolated the Ordovician–Silurian boundary age to 443.1 ± 0.9 Ma from Katian and Rhuddanian ID-TIMS 238 U- 206 Pb zircon dates from Dob’s Linn and a Hirnantian SHRIMP 238 U- 206 Pb date from South China (Tucker et al 1990; Hu et al 2008; Ogg et al 2016; Schmitz & Ogg, 2020). The International Commission of Stratigraphy interpolated the age of the boundary to 443.8 ± 1.5 Ma only using Dob’s Linn’s Katian and Rhuddanian ID-TIMS 238 U- 206 Pb zircon dates (Table 2) (Tucker et al 1990; Cohen et al 2022).…”

Section: Biozone Agesmentioning

confidence: 99%

“…Subsequently, three (of four) multigrain zircon fractions ( n = 58 of 73 grains analyzed) zircons fractions from the Dicellograptus anceps zone, located 4.5 metres below the Ordovician–Silurian boundary, yielded a mechanically (air) abraded zircon 238 U- 206 Pb ID-TIMS date of 445.7 ± 2.4 Ma (Tucker et al 1990). Using Tucker et al (1990) zircon multigrain fractions and via spline fitting modelling, Schmitz & Ogg (2020) recalculated the age of the biozone to 444.88 ± 1.17 Ma (Schmitz & Ogg, 2020). Elsewhere, the Metabolograptus extraordinarius zone in Wanhe, SW China, the equivalent of the Dicellograptus anceps zone at Dob’s Linn, produced two CA-ID-TIMS 238 U- 206 Pb dates of 443.81 ± 0.24 Ma and 444.06 ± 0.20 Ma (Table 2) (Ling et al 2019).…”

Section: Biozone Agesmentioning

confidence: 99%

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How old is the Ordovician–Silurian boundary at Dob’s Linn, Scotland? Integrating LA-ICP-MS and CA-ID-TIMS U-Pb zircon dates

Garza,

Catlos,

Chamberlain

et al. 2023

Geol. Mag.

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Sedimentary rocks exposed at Dob’s Linn, Scotland, have significantly influenced our understanding of how life evolved over the Ordovician to Early Silurian. The current interpreted chronostratigraphic boundary between the Ordovician and Silurian periods is a Global Boundary Stratotype Section and Point (GSSP), calibrated to 443.8 ± 1.5 Ma (Hirnatian–Rhuddanian age), based on biostratigraphic markers, radioisotopic dates and statistical modelling. However, challenges arise due to tectonic disturbances, complex correlation issues and the lack of systematic dating in Ordovician–Silurian stratigraphic sections. Here, hundreds of zircon grains from three metabentonite ash horizons were dated using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). A subset of the grains were re-analyzed using Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS). We present a high-precision CA-ID-TIMS 238U-206Pb weighted mean date of 440.44 ± 0.55/0.56/0.72 Ma (±analytical/with tracer/with U-decay constant) for the Coronagraptus cyphus biozone. However, the study reports younger, and in certain cases, older LA-ICP-MS zircon dates within the Coronagraptus cyphus, Akidograptus ascensus and Dicellograptus anceps zones, suspected as being influenced by Pb loss and LA-ICP-MS matrix mismatch. The study reports concerns about the suitability of Dob’s Linn as a GSSP section and examines various LA-ICP-MS maximum depositional age (MDA) approaches, suggesting the use of the TuffZirc date and the youngest mode weighted mean (YMWM) as suitable MDA calculations consistent with CA-ID-TIMS results.

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Section: Geological Backgroundmentioning

confidence: 99%

Section: Biozone Agesmentioning

confidence: 99%

Section: Biozone Agesmentioning

confidence: 99%

Section: Biozone Agesmentioning

confidence: 99%

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How old is the Ordovician–Silurian boundary at Dob’s Linn, Scotland? Integrating LA-ICP-MS and CA-ID-TIMS U-Pb zircon dates

Garza,

Catlos,

Chamberlain

et al. 2023

Geol. Mag.

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“…For the Indian-Callovian we used a bio-chronostratigraphic stratigraphic scale estimated from the zonal range assignments and biostratigraphy listed in the Appendix 2 by Schmitz (2020) on the radioisotopic ages used in GTS2020. Again, each data set with modified chronostratigraphic scale x n has two anchor points set at the beginning and end of each period.…”

Section: Superspline Fittingmentioning

confidence: 99%

Application of Supersplining to the Mesozoic and Paleozoic Geologic Time Scales

Gradstein

Agterberg

2022

Math Geosci

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Methods to determine the ages of period and stage boundaries of the geologic time scale (GTS) have a long history and continue to be steadily improved. Stage boundary age estimates are now accompanied by error bars showing stratigraphic uncertainty. Most GTS2004, GTS2012 and GTS2020 results involved cubic spline-curve fitting, and in this study, Ordovician through Cretaceous smoothing splines of GTS2020 are spliced together to construct a Paleozoic–Mesozoic superspline. This methodology, its advantages and its results are outlined.

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U-Pb zircon dates from North American and British Avalonia bracket the Lower–Middle Cambrian boundary interval, with evaluation of the Miaolingian Series as a global unit

Landing,

Schmitz,

Westrop

et al. 2023

Geol. Mag.

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High-precision U-Pb zircon ages on SE Newfoundland tuffs now bracket the Avalonian Lower–Middle Cambrian boundary. Upper Lower Cambrian Brigus Formation tuffs yield depositional ages of 507.91 ± 0.07 Ma (Callavia broeggeriZone) and 507.67 ± 0.08 Ma and 507.21 ± 0.13 Ma (Morocconus-Condylopyge eliAssemblage interval). Lower Middle Cambrian Chamberlain’s Brook Formation tuffs have depositional ages of 506.34 ± 0.21 Ma (Kiskinella cristataZone) and 506.25 ± 0.07 Ma (Eccaparadoxides bennettiZone). The composite unconformity separating the Brigus and Chamberlain’s Brook formations is constrained between these ages. An Avalonian Lower–Middle Cambrian boundary between 507.2 ± 0.1 and 506.3 ± 0.2 Ma is consistent with maximum depositional age constraints from southwest Laurentia, which indicate an age for the base of the Miaolingian Series, as locally interpreted, of ≤ 506.6 ± 0.3 Ma. The Miaolingian Series’ base is interpreted as correlative within ≤ 0.3 ± 0.3 Ma between Cambrian palaeocontinents, although its exact synchrony is questionable due to taxonomic problems with a possibleOryctocephalus indicus-plexus, invariable dysoxic lithofacies control ofO. indicusand diachronous occurrence ofO. indicusin temporally distinct δ13C chemozones in South China and SW Laurentia. The lowest occurrence ofO. indicusassemblages is linked to onlap (epeirogenic or eustatic) of dysoxic facies. A united Avalonia is shown by late Early Cambrian volcanics in SW New Brunswick; Cape Breton Island; SE Newfoundland; and the Wrekin area, England. The new U-Pb ages revise Avalonian geological evolution as they show rapid epeirogenic changes through depositional sequences 4a–6.

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Radioisotopic ages used in GTS2020

Cited by 7 publications

References 165 publications

How old is the Ordovician–Silurian boundary at Dob’s Linn, Scotland? Integrating LA-ICP-MS and CA-ID-TIMS U-Pb zircon dates

How old is the Ordovician–Silurian boundary at Dob’s Linn, Scotland? Integrating LA-ICP-MS and CA-ID-TIMS U-Pb zircon dates

Application of Supersplining to the Mesozoic and Paleozoic Geologic Time Scales

U-Pb zircon dates from North American and British Avalonia bracket the Lower–Middle Cambrian boundary interval, with evaluation of the Miaolingian Series as a global unit

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