Coupled carbonate-shale thallium isotopes reveal the evolution of deep-marine anoxia during the end-Permian mass extinction.

Coupled carbonate–shale thallium isotope records across four regions show deep-marine anoxia beginning 1 million years before the end-Permian extinction.

• Why it matters: Ocean anoxia is linked to the end-Permian crisis, but prior reconstructions lacked a deep-water oxygen-loss focus and were limited by siliciclastic-only Tl isotope applications.
• What they did: The study builds a near-continuous, combined carbonate–shale Tl isotope record from four geographically distant regions to track deep-ocean oxygenation via manganese oxide burial.
• The result: Both lithologies preserve consistent deep-marine redox signals, implying Late Permian oxygen depletion stayed largely in the deep ocean and differed from Early Triassic euxinia.