Journal ArticleDOI
Uranium isotope evidence for an expansion of marine anoxia during the end-Triassic extinction
A. B. Jost,Aviv Bachan,Bas van de Schootbrugge,Kimberly V. Lau,K. L. Weaver,Kate Maher,Jonathan L. Payne +6 more
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In this article, the authors measured δ238U in shallow-marine limestones from two stratigraphic sections in the Lombardy Basin, northern Italy, spanning over 400 m.Abstract:
The end-Triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia, suggesting that anoxia played a role in suppressing marine biodiversity. However, global changes in ocean anoxia are difficult to quantify using proxies for local anoxia. Uranium isotopes (δ238U) in CaCO3 sediments deposited under locally well-oxygenated bottom waters can passively track seawater δ238U, which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238U(VI) relative to 235U(VI) in anoxic marine sediments. We measured δ238U in shallow-marine limestones from two stratigraphic sections in the Lombardy Basin, northern Italy, spanning over 400 m. We observe a ∼0.7‰ negative excursion in δ238U beginning in the lowermost Jurassic, coeval with the onset of the initial negative δ13C excursion and persisting for the duration of subsequent high δ13C values in the lower-middle Hettangian stage. The δ238U excursion cannot be realistically explained by local mixing of uranium in primary marine carbonate and reduced authigenic uranium. Based on output from a forward model of the uranium cycle, the excursion is consistent with a 40–100-fold increase in the extent of anoxic deposition occurring worldwide. Additionally, relatively constant uranium concentrations point toward increased uranium delivery to the oceans from continental weathering, which is consistent with weathering-induced eutrophication following the rapid increase in pCO2 during emplacement of the Central Atlantic Magmatic Province. The relative timing and duration of the excursion in δ238U implies that anoxia could have delayed biotic recovery well into the Hettangian stage.read more
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Journal ArticleDOI
Abrupt global-ocean anoxia during the Late Ordovician-early Silurian detected using uranium isotopes of marine carbonates
Rick Bartlett,Rick Bartlett,Maya Elrick,James R. Wheeley,Victor J. Polyak,André Desrochers,Yemane Asmerom +6 more
TL;DR: The Hirnantian ocean anoxic event (HOAE) onset is coincident with the extinction pulse indicating its importance in triggering it, and it is interpreted that anoxia was driven by global cooling, which reorganized thermohaline circulation, decreased deep-ocean ventilation, enhanced nutrient fluxes, stimulated productivity, which lead to expanded oxygen minimum zones.
Journal ArticleDOI
The effects of diagenesis on geochemical paleoredox proxies in sedimentary carbonates
Ashleigh von S Hood,Ashleigh von S Hood,Noah J. Planavsky,Malcolm W. Wallace,Xiangli Wang,Xiangli Wang +5 more
TL;DR: In this paper, the variability in uranium isotopes, trace metal and rare earth element (REY) concentrations in carbonate successions that have undergone several common types of diagenetic alteration was explored.
Journal ArticleDOI
Diagenetic effects on uranium isotope fractionation in carbonate sediments from the Bahamas
Xinming Chen,Stephen J. Romaniello,Achim D. Herrmann,Dalton S. Hardisty,Benjamin C. Gill,Ariel D. Anbar +5 more
TL;DR: The authors examined the effects of diagenetic alteration on the U isotope composition in carbonate sediments, which are crucial to understand the accurate reconstruction of marine δ238U, are currently poorly constrained.
Journal ArticleDOI
Atmosphere-ocean oxygen and productivity dynamics during early animal radiations.
Tais W. Dahl,James N. Connelly,Da Li,Artem Kouchinsky,Benjamin C. Gill,Susannah M. Porter,Adam C. Maloof,Martin Bizzarro +7 more
TL;DR: 2 major oceanic anoxic events in the early Cambrian at the time when animals markedly diversified could have been driven by declining atmospheric O2 levels, plausibly set off by the appearance of bioturbating animals.
Journal ArticleDOI
Controls of eustasy and diagenesis on the 238U/235U of carbonates and evolution of the seawater (234U/238U) during the last 1.4 Myr
François L. H. Tissot,François L. H. Tissot,Cindy Chen,Benjamin M. Go,Magdalena Naziemiec,Garrett Healy,Andrey Bekker,Peter K. Swart,Nicolas Dauphas +8 more
TL;DR: This paper measured the U isotope composition of modern and ancient corals, a limestone and a dolostone, as well as 43 shallow-water carbonate sediments from the ODP Leg 166 Site 1009 drill core, on the slope of the Bahamas platform.
References
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