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1. Calibrating the zenith of dinosaur diversity in the Campanian of the Western Interior Basin by CA-ID-TIMS U–Pb geochronology

   https://doi.org/10.1038/s41598-022-19896-w  

   Ramezani, Jahandar; Beveridge, Tegan_L; Rogers, Raymond_R; Eberth, David_A; Roberts, Eric_M (September 2022, Scientific Reports)

   Abstract The spectacular fossil fauna and flora preserved in the Upper Cretaceous terrestrial strata of North America’s Western Interior Basin record an exceptional peak in the diversification of fossil vertebrates in the Campanian, which has been termed the ‘zenith of dinosaur diversity’. The wide latitudinal distribution of rocks and fossils that represent this episode, spanning from northern Mexico to the northern slopes of Alaska, provides a unique opportunity to gain insights into dinosaur paleoecology and to address outstanding questions regarding faunal provinciality in connection to paleogeography and climate. Whereas reliable basin-wide correlations are fundamental to investigations of this sort, three decades of radioisotope geochronology of various vintages and limited compatibility has complicated correlation of distant fossil-bearing successions and given rise to contradictory paleobiogeographic and evolutionary hypotheses. Here we present new U–Pb geochronology by the CA-ID-TIMS method for 16 stratigraphically well constrained bentonite beds, ranging in age from 82.419 ± 0.074 Ma to 73.496 ± 0.039 Ma (2σ internal uncertainties), and the resulting Bayesian age models for six key fossil-bearing formations over a 1600 km latitudinal distance from northwest New Mexico, USA to southern Alberta, Canada. Our high-resolution chronostratigraphic framework for the upper Campanian of the Western Interior Basin reveals that despite their contrasting depositional settings and basin evolution histories, significant age overlap exists between the main fossil-bearing intervals of the Kaiparowits Formation (southern Utah), Judith River Formation (central Montana), Two Medicine Formation (western Montana) and Dinosaur Park Formation (southern Alberta). Pending more extensive paleontologic collecting that would allow more rigorous faunal analyses, our results support a first-order connection between paleoecologic and fossil diversities and help overcome the chronostratigraphic ambiguities that have impeded the testing of proposed models of latitudinal provinciality of dinosaur taxa during the Campanian. 

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2. Spatiotemporal variability of the late Paleozoic glacial-to-postglacial transition across eastern Paraná Basin, Brazil

   https://doi.org/10.1016/j.sedgeo.2023.106420  

   Mottin, T.E.; Vesely, F.F.; Iannuzzi, R.; Griffis, N.P.; Montañez, I.P. (July 2023, Sedimentary Geology)

   The late Paleozoic glacial-to-postglacial turnover evolved complexly across Gondwana. Successions bearing volcaniclastic material that can be radiometrically dated provide crucial information about the timing of those climate events. The southernmost part of the Paraná Basin, for instance, has a high-precision geochronological framework. The eastern sector of this basin (Paraná State and north of Santa Catarina State), however, lacks radiometric ages, but conversely, has a more complete stratigraphic record, and paleontological information still poorly explored for the purpose of biostratigraphic correlation. This work examines the glacial-to-postglacial interval in the Paraná State, represented by the upper Itararé Group (Taciba Formation; glacial) and lower–middle Rio Bonito Formation (postglacial). Sedimentological, paleontological and geochemical data from outcrops, cores and well logs were used to decipher the timing, paleoclimatic and paleogeographic scenarios of this transition. The examined succession comprises four stacked units (U1 to U4, from older to younger). Diamictite-dominated units (U1 and U3), here interpreted as consecutive glaciation–deglaciation events, are separated by non-glacial, continental to shallow marine deposits, commonly bearing fossil plants and coal seams (U2). An important transgression followed the first deglaciation,which is equivalent to the “Eurydesma transgression”, basedonthepresence of marine invertebrates of the homonymous fauna in the Passinho Shale. U2 holds elements of two different floras, i.e., Phyllotheca–Gangamopteris (P–G), predating the “Eurydesma transgression”, and Glossopteris Brasilodendron (G–B), above the transgression. Therefore, U2 is interpreted as an interglacial interval, once it records a climate improving before the last glacial episode of U3, which is further supported by relatively high values of the Chemical Index of Alteration (CIA). Deposits of U3, associated with a decrease in the value of the CIA, are unconformably overlain by U4. The occurrence of coal-bearing postglacial facies (U4) associated with the G–B Flora, coincides with an increase in the CIA values. Sediment transport was toward the SWin all units and in the same direction it is observed an overall thinning of U1 and U3 and thickening of U2. The interglacial P–G Flora of the study area correlates with postglacial southernmost floras, based on U–Pb CA-TIMS Asselian ages of tonsteins. Correlation of the Eurydesma fauna-containing Passinho Shale with equivalent successions with high-precision age control in southern Africa, allowed us to position both deglaciations of the Taciba Formation (U1 and U3) in the Asselian. These findings suggest that U1 and U3 record two early Permian glacial episodes, with the younger one (U3) disappearing southward. Accordingly, our results indicate that the glacial-to-postglacial turnoverwas diachronous along the eastern belt of the Paraná Basin, being progressively older southward, considering that interglacial fossil plant assemblages in the eastern margin correspond in time to postglacial assemblages farther south. 

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3. Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana

   https://doi.org/10.1130/G46740.1  

   Griffis, Neil Patrick; Montañez, Isabel Patricia; Mundil, Roland; Richey, Jon; Isbell, John; Fedorchuk, Nick; Linol, Bastien; Iannuzzi, Roberto; Vesely, Fernando; Mottin, Thammy; et al (October 2019, Geology)

   The demise of the Late Paleozoic Ice Age has been hypothesized as diachronous, occurring first in western South America and progressing eastward across Africa and culminating in Australia over an ~60 m.y. period, suggesting tectonic forcing mechanisms that operate on time scales of 106 yr or longer. We test this diachronous deglaciation hypothesis for southwestern and south-central Gondwana with new single crystal U-Pb zircon chemical abrasion thermal ionizing mass spectrometry (CA-TIMS) ages from volcaniclastic deposits in the Paraná (Brazil) and Karoo (South Africa) Basins that span the terminal deglaciation through the early postglacial period. Intrabasinal stratigraphic correlations permitted by the new high-resolution radioisotope ages indicate that deglaciation across the south to southeast Paraná Basin was synchronous, with glaciation constrained to the Carboniferous. Cross-basin correlation reveals two additional glacial-deglacial cycles in the Karoo Basin after the terminal deglaciation in the Paraná Basin. South African glaciations were penecontemporaneous (within U-Pb age uncertainties) with third-order sequence boundaries (i.e., inferred base-level falls) in the Paraná Basin. Synchroneity between early Permian glacial-deglacial events in southwestern to south-central Gondwana and pCO2 fluctuations suggest a primary CO2 control on ice thresholds. The occurrence of renewed glaciation in the Karoo Basin, after terminal deglaciation in the Paraná Basin, reflects the secondary influences of regional paleogeography, topography, and moisture sources. 

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4. Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information

   https://doi.org/10.1130/B37321.1  

   Condon, Dan; Schoene, Blair; Schmitz, Mark; Schaltegger, Urs; Ickert, Ryan B; Amelin, Yuri; Augland, Lars E; Chamberlain, Kevin R; Coleman, Drew S; Connelly, James N; et al (April 2024, Geological Society of America Bulletin)

   Abstract U-Pb geochronology by isotope dilution–thermal ionization mass spectrometry (ID-TIMS) has the potential to be the most precise and accurate of the deep time chronometers, especially when applied to high-U minerals such as zircon. Continued analytical improvements have made this technique capable of regularly achieving better than 0.1% precision and accuracy of dates from commonly occurring high-U minerals across a wide range of geological ages and settings. To help maximize the long-term utility of published results, we present and discuss some recommendations for reporting ID-TIMS U-Pb geochronological data and associated metadata in accordance with accepted principles of data management. Further, given that the accuracy of reported ages typically depends on the interpretation applied to a set of individual dates, we discuss strategies for data interpretation. We anticipate that this paper will serve as an instructive guide for geologists who are publishing ID-TIMS U-Pb data, for laboratories generating the data, the wider geoscience community who use such data, and also editors of journals who wish to be informed about community standards. Combined, our recommendations should increase the utility, veracity, versatility, and “half-life” of ID-TIMS U-Pb geochronological data. 

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5. U–Pb ID-TIMS geochronology using ATONA amplifiers

   https://doi.org/10.1039/d0ja00135j  

   Szymanowski, Dawid; Schoene, Blair (June 2020, Journal of Analytical Atomic Spectrometry)

   We document the performance of new ATONA (‘aA to nA’) amplifiers installed on an Isotopx Phoenix thermal ionisation mass spectrometer (TIMS) at Princeton University and evaluate their suitability for high-precision analyses of Pb and U isotopes in pg- to ng-size samples characteristic for U–Pb geochronology. The new amplifiers are characterised by low and stable noise levels comparable to 10 12 to 10 13 ohm resistors, response time <0.5 s, exceptional gain stability <1 ppm and a vast dynamic range theoretically allowing to quantify signals from aA (10 −18 A) to nA (10 −9 A) level. We measured a set of Pb standards, synthetic U–Pb solutions and natural zircons at currents of 2 × 10 −16 to 2 × 10 −12 A (corresponding to intensities of 20 μV to 200 mV relative to a 10 11 ohm amplifier) to assess the utility of ATONA in replacing ion counting for the smallest samples. The results show a clear precision benefit of using ATONA-Faraday detection over Daly ion counting for ion currents of >10 −14 A (1 mV relative to a 10 11 ohm amplifier or ca. 60 kcps). As such currents are routinely achievable for major Pb peaks of interest ( 205–208 Pb) in natural samples containing more than ca. 10 pg Pb* (radiogenic Pb), we expect ATONA-Faraday detection to find broad applications in U–Pb geochronology. Its practical use for low-blank, radiogenic samples continues to require ion counting for 204 Pb, either with a fixed Faraday–ion counter gain or using a dynamic two-step ( e.g. FaraDaly) method. Routine adoption of ATONA-Faraday collection in place of ion counting for most major Pb and U isotopes has the potential to increase sample throughput and precision, both improving the accessibility of isotope dilution (ID)-TIMS geochronology and pushing this technique towards better reproducibility. 

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