Volcanism in South China during the Late Permian and its relationship to marine ecosystem and environmental changes

A deep-shelf section at Xinmin (Guizhou Province, South China) records numerous volcanic ashfall events both preceding and following the latest Permian mass extinction. Each ash layer was associated with ecosystem and environmental changes, including significant declines in biogenic silica and carbonate production and shifts toward somewhat more reducing conditions within a generally suboxic facies. The extinction horizon itself, which coincided with an ashfall event, shows evidence of much larger changes, including a sharp and sustained reduction in radiolarian productivity, a shift from suboxic to mostly oxic conditions (although punctuated by episodic euxinic events), and an increase in weathering intensity due to increased climatic humidity. Ash layers of Late Permian–Early Triassic age at Xinmin and elsewhere in South China are thought to have had a regional volcanic source, perhaps in subduction-zone magmatic arcs along the margins of the South China Craton. The Xinmin section provides evidence that volcanically generated stresses were repeatedly imposed on marine systems of the South China Craton during the Late Permian, possibly weakening their resilience in advance of the Permian–Triassic boundary crisis.