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A carbonate molybdenum isotope and cerium anomaly record across the end-GOE: Local records of global oxygenation

Abstract : Earth's Great Oxidation Event (GOE), ca. 2.5-2.0 Ga, was one of the most extreme environmental perturbations in the history of the planet. In addition to the first sustained accumulation of O2 in the atmosphere, the latter half of the GOE is associated with a very large positive carbon isotope excursion, both in terms of magnitude and inferred duration. The end of the GOE may have been associated with a decrease in atmospheric oxygen levels, although this transition remains poorly understood. We test if this suggested decline in atmospheric O2 is reflected in the molybdenum stable isotope compositions (δ98Mo) and Ce anomalies of a large number (N = 299) of carbonate sedimentary rocks collected from Finnish Lapland and the Canadian Labrador Trough and Belcher Group, which collectively span ca. 2.1-1.88 Ga. Clear evidence for a shift in redox conditions across the end-GOE is obscured by coupled stratigraphic variations in δ98Mo values, Ce anomalies, and Mn concentrations, suggesting local controls on these redox proxies as a function of depositional environment, likely as a result of particulate shuttling of Mo and Ce associated with Mn redox cycling across a chemocline. The most negative Ce anomalies recorded in the Belcher Group (<0.6) are among the lowest reported in literature from the mid-late Paleoproterozoic to early Neoproterozoic; however, the strong local controls on these proxies hinder direct evaluation of secular trends. These findings highlight the critical role of stratigraphic and paleobasinal context for the robust interpretation of δ98Mo values and Ce anomalies for the evolution of marine redox conditions.
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Submitted on : Wednesday, June 1, 2022 - 3:08:51 PM
Last modification on : Thursday, June 2, 2022 - 3:39:45 AM

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Malcolm S. W. Hodgskiss, Stefan V. Lalonde, Peter W. Crockford, Alec M. Hutchings. A carbonate molybdenum isotope and cerium anomaly record across the end-GOE: Local records of global oxygenation. Geochimica et Cosmochimica Acta, Elsevier, 2021, 313, pp.313-339. ⟨10.1016/j.gca.2021.08.013⟩. ⟨insu-03684635⟩

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