Frequent and intense fires in the final coals of the Paleozoic indicate elevated atmospheric oxygen levels at the onset of the End-Permian Mass Extinction Event

Abstract

Abstract During the End-Permian mass extinction event (EPME) there is extensive evidence for depletion of oxygen in the marine realm. Atmospheric models based upon biogeochemical cycling predict a comparable decline leading up to this event and have been postulated as a possible driver for marine depletion. However, these models contrast with broadly contemporaneous empirical evidence from charcoal in coals. New charcoal data from the temporally well-constrained late Permian Xuanwei Formation coals of eastern Yunnan Province, China, deposited just prior to the onset of the Permian-Triassic Transitional Beds, supports the coarser analysis and further challenges these biogeochemical models. Inertinite group macerals, comprising fusinite, semifusinite, macrinite, inertodetrinite, secretinite, all funginite with elevated reflectance, and some micrinite, are proxies for wildfire activity, and indicate abundant evidence for this phenomenon in the latest Permian and preclude low levels of atmospheric oxygen concentration coevally. Henceforward, we will employ the term ‘inertinite group macerals sensu amplo’ to refer to just these precise macerals, though these encompass what are the overwhelming preponderance of inertinites in most coals. Both inertinite abundance and reflectance indicate an increase in fire activity and intensity towards the End-Permian faunal crisis. Quantitatively, these inertinite data indicate atmospheric oxygen concentration was high and at the close of the Paleozoic was probably elevated to levels well above those of the present-day. The elevated fire activity at this time may have functioned as a causal link to explain some localized oxygen depletion in the marine realm as a result of post-fire increased run-off and erosion. However, globally depressed atmospheric oxygen concentration at the End-Permian was not a driver of extensive marine anoxia at that time.