Geochemical records reveal protracted and differential marine redox change associated with Late Ordovician climate and mass extinctions

Kozik, Nevin P.; Gill, Benjamin C.; Owens, Jeremy D.; Lyons, Timothy W.; Young, Seth A.

doi:10.1002/essoar.10506877.1

Cited by 2 publications

(1 citation statement)

References 66 publications

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“…C org , organic carbon. δ 238 U is modified from Bartlett et al ( 18 ) (dark purple line) and reinterpretation presented by Kozik et al , ( 74 ) (light purple line) and Liu et al , ( 19 ) (red line).…”

Section: Discussionmentioning

confidence: 95%

Rapid marine oxygen variability: Driver of the Late Ordovician mass extinction

et al. 2022

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The timing and connections between global cooling, marine redox conditions, and biotic turnover are underconstrained for the Late Ordovician. The second most severe mass extinction occurred at the end of the Ordovician period, resulting in ~85% loss of marine species between two extinction pulses. As the only “Big 5” extinction that occurred during icehouse conditions, this interval is an important modern analog to constrain environmental feedbacks. We present a previously unexplored thallium isotope records from two paleobasins that record global marine redox conditions and document two distinct and rapid excursions suggesting vacillating (de)oxygenation. The strong temporal link between these perturbations and extinctions highlights the possibility that dynamic marine oxygen fluctuations, rather than persistent, stable global anoxia, played a major role in driving the extinction. This evidence for rapid oxygen changes leading to mass extinction has important implications for modern deoxygenation and biodiversity declines.

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Section: Discussionmentioning

confidence: 95%

Rapid marine oxygen variability: Driver of the Late Ordovician mass extinction

et al. 2022

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Geochemical Records Reveal Protracted and Differential Marine Redox Change Associated With Late Ordovician Climate and Mass Extinctions

et al. 2022

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The Ordovician (Hirnantian; 445 Ma) hosts the second most severe mass extinction in Earth history, coinciding with Gondwanan glaciation and increased geochemical evidence for marine anoxia. It remains unclear whether cooling, expanded oxygen deficiency, or a combination drove the Late Ordovician Mass Extinction (LOME). Here, we present combined iodine and sulfur isotope geochemical data from three globally distributed carbonate successions to constrain changes in local and global marine redox conditions. Iodine records suggest locally anoxic conditions were potentially pervasive on shallow carbonate shelves, while sulfur isotopes suggest a reduction in global euxinic (anoxic and sulfidic) conditions. Late Katian sulfate‐sulfur isotope data show a large negative excursion that initiated during elevated sea level and continued through peak Hirnantian glaciation. Geochemical box modeling suggests a combination of decreasing pyrite burial and increasing weathering are required to drive the observed negative excursion suggesting a ∼3% decrease of global seafloor euxinia during the Late Ordovician. The sulfur datasets provide further evidence that this trend was followed by increases in euxinia which coincided with eustatic sea‐level rise during subsequent deglaciation in the late Hirnantian. A persistence of shelf anoxia against a backdrop of waning then waxing global euxinia was linked to the two LOME pulses. These results place important constraints on local and global marine redox conditions throughout the Late Ordovician and suggest that non‐sulfidic shelfal anoxia—along with glacioeustatic sea level and climatic cooling—were important environmental stressors that worsened conditions for marine fauna, resulting in the second‐largest mass extinction in Earth history and the only example during an icehouse climate.

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Geochemical records reveal protracted and differential marine redox change associated with Late Ordovician climate and mass extinctions

Cited by 2 publications

References 66 publications

Rapid marine oxygen variability: Driver of the Late Ordovician mass extinction

Rapid marine oxygen variability: Driver of the Late Ordovician mass extinction

Geochemical Records Reveal Protracted and Differential Marine Redox Change Associated With Late Ordovician Climate and Mass Extinctions

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