Recurrent and Long-Term Oceanic Anoxia Contributed to Aborted Biotic Recovery Following the Permian-Triassic Crisis.

Abstract

The influence of ocean chemistry on Early Triassic biotic recovery is poorly understood in the Chaohu Area. Here, we evaluate the influence of ocean chemistry following the Permian-Triassic crisis using pyrite content, δ¹³C_org, and S isotopic composition of pyrite. The pyrite content, V/(V + Ni) ratio, and S isotopic composition of pyrite in the Early Triassic from the northern Pingdingshan section of the Chaohu area in eastern China reveal recurrent and long-term ocean anoxia and two episodes of oxic conditions that occurred in the earliest Spathian and the late early Spathian. A positive δ¹³C_org shift of ~4‱ around the Smithian/Spathian boundary (SSB) in the lowermost Spathian was associated with significant biotic recovery, coincident with a positive δ³⁴S excursion of ~25‱ and a low V/(V + Ni) ratio. The results suggest that the oxic conditions contributed to this recovery. Enhanced global ocean circulation during the SSB climate cooling may also have promoted this recovery. Frequent environmental perturbations may have aborted the biotic recovery, although the second episode of oxic conditions occurred in the late early Spathian. Sustained recovery did not appear in the Early Triassic because of the recurrent and long-term ocean anoxia.