TWO EPISODES OF CAPITANIAN (MIDDLE PERMIAN) MASS EXTINCTION LINKED TO OCEANIC ANOXIA

The Capitanian (late Middle Permian) mass extinction was a major Phanerozoic biocrisis yet its timing and causation remain poorly understood. Here, we generated a high-resolution U-isotopic (δ²³⁸U) profile for the mid-Capitanian to lower Wuchiapingian of the Penglaitan section (Middle/Upper Permian GSSP) to explore the causal relationship between the mass extinction and contemporaneous oceanic anoxic events (OAEs). This profile documents two distinct negative δ²³⁸U excursions, the first recording the mid-Capitanian OAE-C1 and the second the end-Capitanian OAE-C2. Box modeling indicates that the anoxic/euxinic sink for seawater U increased from <40 % to >80 % of the total U flux during these OAEs. Each of these OAEs coincided with a mass extinction pulse and a positive δ¹³C excursion and volcanic eruptions of the Emeishan LIP. We propose that volcanic eruptions enhanced nutrient availability and primary productivity, resulting in positive δ¹³C excursions and oceanic anoxic events. Furthermore, each OAE coincided with a phase of biotic extinction, providing the first evidence of a causal relationship between oceanic anoxia and mass extinction during the Capitanian. Our finding challenges hypotheses based on cooling or volcanic winter scenarios for this biotic crisis.