Palaeoenvironmental change during the end-Guadalupian (Permian) mass extinction in Sichuan, China

Abstract

The end-Guadalupian mass extinction has been investigated in Sichuan province, SW China. In the south of the province the platform carbonates of the Maokou Formation are overlain by the Emeishan flood basalts, a possible factor in the extinction event, and in the north of the province the formation is succeeded by shallow-marine carbonates of the Wuchiaping Formation (Late Permian). The extinction event is primarily recorded by the loss of fusulinaceans and possibly by species-level turnover amongst calcareous algae. The high-diversity, Middle Permian microfossil assemblages are last seen beneath a surface recording widespread emergence and karstification. In northern Sichuan emergence occurred early in the Capitanian Stage and the succeeding strata record restricted hypersaline deposition that preceded the deposition of a thick ash horizon, the Wangpo Bed. These mid-Capitanian arid conditions are replaced by humid conditions towards the end of the stage as indicated by the development of a widespread coal seam. In southern Sichuan only a thin development of this humid, coaly facies is seen developed atop the Maokou karstic surface and below the oldest flood basalt. The Guadalupian interval saw the development of large C isotope excursions in the carbonate record. These include a positive-then-negative swing late in the Capitanian and a newly discovered negative spike superimposed on an early Capitanian heavy interval. This spike may be a global phenomenon but the magnitude (8‰) may have been exaggerated by an increased contribution from light, respired C derived from soils during relative sea-level fall. A plethora of environmental factors approximately coincide with the extinction event, including regression, acidic volcanism and flood basalt volcanism making it difficult to unravel the relative significance of each.