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, Hector K.; Catlos, Elizabeth J.; Chamberlain, Kevin R.; Suarez, Stephanie E.; Brookfield, Michael E.; Stockli, Daniel F.; Batchelor, Richard A.

doi:10.1017/s0016756823000717

Cited by 3 publications

(2 citation statements)

References 91 publications

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“…LA-ICP-MS U-Pb zircon geochronology allows in situ grain spatial resolution [29] and high single grain resolution throughput (usually >100 grains per sample analysis), which is required for (a) dating complex zircons, (b) detrital studies, and (c) accurately dating bentonites with a potential detrital or xenolith component. Determining crystallization/eruption or maximum deposition age "calls" from LA-ICP-MS U-Pb zircon data are complicated by potential undetermined Pb loss for young zircons (<~400 Ma), matrix mismatch, and large N analysis resulting in apparently robust populations of younger grains that are just an artifact of instrumental statistical spread [30][31][32].…”

Section: Radiometric Data From Study Areamentioning

confidence: 99%

“…Furthermore, these dual-technique studies have demonstrated that selecting the LA-ICP-MS U-Pb zircon youngest statistical population (YSP), which is the weighted mean of the youngest statistical population (2 or more grains) that produces a mean square weighted deviation (MSWD) close to 1, approximates CA-ID-TIMS U-Pb zircon results from the same sample [35,36]. A variation of this approach is the youngest mode weighted mean (YMWM), which uses the LA-ICP-MS zircon dates that define the youngest age mode from a kernel density estimate peak that consists of at least three grains that overlap at 2 sigma uncertainty with an MSWD that approximates 1 [32,34]. We use a modified version of the YSP and YMWM age determinations by utilizing an iterative approach that captures the largest population of young grains that overlap at 2 sigma uncertainty with an MSWD that approximates 1.…”

Section: Radiometric Data From Study Areamentioning

confidence: 99%

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New Dinosaur Ichnological, Sedimentological, and Geochemical Data from a Cretaceous High-Latitude Terrestrial Greenhouse Ecosystem, Nanushuk Formation, North Slope, Alaska

Fiorillo,

McCarthy,

Shimer

et al. 2024

Geosciences

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The Nanushuk Formation (Albian–Cenomanian) crops out over much of the central and western North Slope of Alaska, varying from ≈1500 to ≈250 m thick from west to northeast. The Nanushuk Formation records an inter-tonguing succession of marine and nonmarine conglomerate, sandstone, mudstone, and coal. These rock units comprise the Kukpowruk and Corwin formations of the former Nanushuk Group, respectively. Work presented here is centered in the foothills of the DeLong Mountains along the Kukpowruk River, from an area west of Igloo Mountain in the Coke Basin to the Barabara Syncline, approximately 80 km to the north. A radiometric date recovered from a tuff in our study area suggests a Cenomanian age for at least some of these rocks. Outcrops along the Kukpowruk River contain a well-preserved fossil flora previously recovered from marine, marginal marine, and terrestrial sediments. Our own work focuses on detailed measured sections of terrestrial rocks, interpretation of sedimentary facies and facies associations, and documentation of fossil vertebrates. Eight facies associations are identified in the study area that together are interpreted to represent meandering fluvial and upper delta plain environments. Plant fossils are common and include standing tree trunks up to 58 cm in diameter at some locations. Approximately 75 newly discovered tracksites, and a heretofore unknown, rich fossil vertebrate ichnofauna, are present. The ichnofaunal assemblage includes evidence of small and large theropod dinosaurs (including birds) and bipedal and quadrupedal ornithischian dinosaurs. Approximately 15% of the dinosaur ichnofauna record is represented by fossil bird tracks. Wood fragments from the Nanushuk Formation were analyzed for their carbon isotopic composition to relate δ13C to mean annual precipitation. Samples averaged −26.4‰ VPDB, suggesting an average MAP of 1412 mm/year. This record of increased precipitation in the Nanushuk Fm. during the mid-Cretaceous provides new data that supports global precipitation patterns associated with the Cretaceous Thermal Maximum. This work provides an important framework for much-needed further paleoecological and paleoclimatic analyses into greenhouse conditions in the terrestrial Cretaceous Arctic during this important window in time.

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Section: Radiometric Data From Study Areamentioning

confidence: 99%

Section: Radiometric Data From Study Areamentioning

confidence: 99%

New Dinosaur Ichnological, Sedimentological, and Geochemical Data from a Cretaceous High-Latitude Terrestrial Greenhouse Ecosystem, Nanushuk Formation, North Slope, Alaska

Fiorillo,

McCarthy,

Shimer

et al. 2024

Geosciences

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Detrital U-Pb ages for the first well-preserved vascular plant Cooksonia from the UK and Irish macrofossil record.

Garza,

Catlos,

Brookfield

et al. 2024

Geol. Mag.

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The emergence of vascular plants, such as Cooksonia, had a profound impact on Earth’s Early Paleozoic biogeochemical cycles (e.g. atmospheric oxygen, nitrogen and CO2), potentially triggering global environmental and biological changes. However, the timing of Cooksonia’s terrestrial emergence remains elusive as phylogenetic models, microfossils and macrofossils provide different timings for land colonization by vascular plants. Here, hundreds of zircon grains from three siltstones were dated using Laser Ablation-Inductively Couple Plasma-Mass Spectrometry (LA-ICP-MS). The study presents detrital zircon U-Pb dates, which refine the current biostratigraphy ages assigned to Cooksonia macrofossils from the three oldest sites globally. Specifically, siltstones hosting Cooksonia macrofossils from Borrisnoe Mountain (Ireland) and Capel Horeb (Wales) yield Gorstian–Homerian maximum depositional ages (MDAs) of 426 ± 2 Ma and 427 ± 2 Ma, respectively. Additionally, Cwm Graig Ddu (Wales) yields a (Pridoli-Ludlow) maximum age of 423 ± 3 Ma. The findings provide the first detrital zircon U-Pb dates for the oldest Cooksonia macrofossils globally and contribute crucial maximum ages. These maximum ages are instrumental in refining future calibrations of molecular clocks and improving phylogenetic models, thus contributing significantly to a better understanding of Cooksonia’s evolutionary history, including its environmental and ecological impacts.

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The leaky chronometer: Evidence for systematic cryptic Pb loss in laser ablation U‐Pb dating of zircon relative to CA‐TIMS

Howard,

Sharman,

Crowley

et al. 2024

Terra Nova

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U–Pb dating of zircon via laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) has become a primary method for determining the age of crystalline rocks and the provenance and maximum depositional age of (meta)sedimentary rocks. Although chemical abrasion has become a standard approach for mitigating Pb loss in zircon dated via high‐resolution thermal ionization mass spectrometry (CA‐TIMS), laser ablation dating is rarely accompanied by chemical abrasion. We evaluate the accuracy of U–Pb dates acquired via LA‐ICP‐MS relative to CA‐TIMS through analysis of a large database of paired analyses from the same zircon crystals. We show that laser ablation 206Pb/238U dates are systematically younger than their CA‐TIMS counterparts, with a greater shift in detrital zircon (−2.0%) versus igneous or metamorphic zircon (−0.9%). Although systematic biases related to “matrix effects” may be a contributing factor, our analysis suggests that unmitigated cryptic Pb loss is likely widespread in laser ablation U–Pb datasets.

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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

Cited by 3 publications

References 91 publications

New Dinosaur Ichnological, Sedimentological, and Geochemical Data from a Cretaceous High-Latitude Terrestrial Greenhouse Ecosystem, Nanushuk Formation, North Slope, Alaska

New Dinosaur Ichnological, Sedimentological, and Geochemical Data from a Cretaceous High-Latitude Terrestrial Greenhouse Ecosystem, Nanushuk Formation, North Slope, Alaska

Detrital U-Pb ages for the first well-preserved vascular plant Cooksonia from the UK and Irish macrofossil record.

The leaky chronometer: Evidence for systematic cryptic Pb loss in laser ablation U‐Pb dating of zircon relative to CA‐TIMS

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