Heterogeneous volcanism across the Permian–Triassic Boundary in South China and implications for the Latest Permian Mass Extinction: New evidence from volcanic ash layers in the Lower Yangtze Region

Abstract

Volcanism has been suggested to have occurred widely in South China across the Permian–Triassic boundary (PTB); this has important implications for understanding the cause of the Latest Permian Mass Extinction (LMPE). However, few volcanic deposits have been reported in the Lower Yangtze Region and the extent of volcanism is uncertain. Herein we report new discoveries of intensive volcanism in this region for the first time, as evidenced by multiple (n>20) and thick (3–5cm) claystones (volcanic ash layers, K-bentonite) found in three deep-water outcrops in Xuancheng city, southern Anhui Province. Detailed petrographic and geochemical analyses of the ash layers were conducted to understand their origin and implications for the cause of the LPME, including X-ray diffraction, scanning electronic microscopy, energy dispersive spectroscopy, and whole-rock geochemistry. The petrological and mineralogical results show that the claystones contain clastic minerals indicative of a volcanic origin, such as zircon, analcites, pentagonal dodecahedral pyrite, and micro-spherules. The whole-rock geochemical data of the claystones suggest that the source rock of the ash layers was intermediate–acidic rhyodacite. The claystones are different from previously known claystones in the Middle–Upper Yangtze regions, indicating the occurrence of chemically heterogeneous volcanism in South China at the PTB.