Carbon Isotope Chemostratigraphy Across the Permian-Triassic Boundary at Chaotian, China: Implications for the Global Methane Cycle in the Aftermath of the Extinction

During the end-Permian extinction, a substantial amount of methane (CH4) was likely released into the ocean-atmosphere system associated with the Siberian Traps volcanism, although fluctuations in the global CH4 cycle in the aftermath of the extinction remain poorly understood. The carbon (C) isotopic composition of carbonate (delta C-13(carb)) across the Permian-Triassic boundary (P-TB) was analyzed at Chaotian, South China. The delta C-13(carb) values decrease from ca. +1 to -2 parts per thousand across the P-TB, possibly caused by a collapse of primary productivity associated with the shallow-marine extinction. The frequent intercalation of felsic tuff layers around the P-TB suggests that a volcanogenic carbon dioxide (CO2) input to the surface oceans may also have contributed to the delta C-13(carb) decline. The magnitude of the delta C-13(carb) decrease (similar to 3 parts per thousand) is substantially smaller than the magnitude of a decrease in C isotopic composition of organic matter (delta C-13(org)) in the same P-TB interval (similar to 7 parts per thousand). This apparent delta C-13(carb)-delta C-13(org) decoupling could be explained by proliferation of methanogen (methanogenic burst) in the sediments. A global delta C-13 compilation shows a large variation in marine delta C-13(org) records, implying that the methanogenic burst according to the Siberian Traps volcanism may have contributed, at least in part, to the delta C-13(org) variability and to the elevated CH4 levels in the atmosphere. The present and previous observations allow us to infer that the global CH4 cycle may have fluctuated substantially in the aftermath of the extinction.

Automated summary

The study investigates the impact of methane release associated with the Siberian Traps volcanism during the end-Permian extinction on the global methane cycle, and analyzes the carbon isotopic composition variations at Chaotian, South China. The research suggests that changes in marine carbon isotopic composition may be influenced by factors such as primary productivity collapse and volcanic activity.