Pyrite framboids in the Permian–Triassic boundary section at Meishan, China: Evidence for dysoxic deposition

Abstract

Pyrite framboid evidence from the Permian–Triassic global stratotype at Meishan, China, indicates the late Permian mass extinction is closely associated with a dramatic decline of benthic oxygen levels. Sizes and abundances of the framboids were determined from acid residues and in situ on polished sections of the samples. The framboids are abundant in the thin pyrite lamina on the top of Bed 24e (the upper layer of Bed 24), and Beds 25, 26 and 29, rare in Bed 24e and Bed 28, but absent in Bed 27. They have narrow size distributions with average diameters from 4.6 μm to 8.7 μm which are similar to those formed under anoxic/dysoxic conditions. The abundances and mean diameters of the pyrite framboids indicate redox conditions of deposition changing from upper dysoxia (Bed 24e) and lower dysoxia (pyrite lamina, Beds 25 and 26) to oxygenation (Bed 27), and again to upper dysoxia (Bed 28) and lower dysoxia (Bed 29). Our discovery confirms a worldwide dysoxic marine event during the Permian–Triassic transition, suggestive of a direct relationship with the Permian–Triassic marine mass extinction.