Migration controls extinction and survival patterns of foraminifers during the Permian-Triassic crisis in South China

The Permian-Triassic mass extinction, the greatest biotic crisis in Earth history, triggered the complete replacement of ecosystems with the 5–10% surviving species giving rise to the Mesozoic fauna. Despite a long history of systematic studies on Permian-Triassic foraminifera, there have been few investigations into spatial and temporal patterns of survivorship and evolution during this critical interval. We interrogate a high-resolution data set comprising newly obtained and previously published foraminiferal data (including 173 species in 62 genera from 13,422 specimens) from seven well-studied Permian-Triassic successions that record a transect of platform to basin facies in South China. Shallow-water settings seen at the Cili and Dajiang sections suffered a single-pulse, sudden extinction with high extinction rates at the end of the Palaeofusulina sinensis Zone; deeper-water and slope environments seen at Liangfengya and Meishan experienced a two-pulse extinction in the Clarkina yini and Isarcicella staeschei zones; basinal settings, seen at Shangsi, Gujiao and Sidazhai, record a single, less devastating extinction pulse in and slightly above the C. yini Zone. In the Late Permian, foraminiferal diversity was greatest on the shallow platforms, where 76.4% of species recorded in our study lived. The two pulses of the Permian-Triassic extinction prompted this foraminiferal diversity hotspot to move to deeper slope settings (comprising 75.6% of contemporary species) and finally basinal settings (comprising 88.8% of species). We propose that foraminifera migrated to deeper water to avoid overheating and toxicity in shallow waters that were driven by the emplacement of the Siberian Traps and coeval volcanic activities around the Paleotethys Ocean. This study provides a methodological framework for investigating survival mechanisms for foraminifers and other taxonomic groups during mass extinction events