New timing and geochemical constraints on the Capitanian (Middle Permian) extinction and environmental changes in deep-water settings: evidence from the Lower Yangtze region of South China

The Capitanian (Guadalupian) witnessed one of the major crises of the Phanerozoic and, like many other extinctions, it coincided with the eruption of a large igneous province, in this case the Emeishan Traps of SW China. However, the timing and causal relationships of this event are in dispute. This study concentrates on the deep-water chert-mudstone strata of the Gufeng Formation and its transition to the Yinping Formation at Chaohu. Zircons from tuffs in the uppermost Gufeng Formation yield a U-Pb age of 261.6 +/- 1.6 Ma, and comparison with sections around Emeishan suggests that the tuffs appeared in the Jinogondolella altudaensis conodont zone and persisted to the Jinogondolella xuanhanensis zone. This coincides with the Emeishan eruptions, and suggests that the tuffs probably derived from this province. Mineralogical and geochemical characteristics also show the tuffs are of acid volcanogenic origin and have a geochemical fingerprint of the Emeishan large igneous province. Our dating shows that a crisis amongst radiolarian and a subsequent productivity decline occurred during the middle Capitanian, prior to the Guadalupian-Lopingian boundary. The Emeishan eruptions began immediately before this, indicating a likely causal relationship between these events. Major regression and marine anoxia/euxinia are two other important extinction-relevant environmental changes that occurred during this critical interval.