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During the end-Permian extinction, a substantial amount of methane (CH 4 ) was likely released into the ocean-atmosphere system associated with the Siberian Traps volcanism, although fluctuations in the global CH 4  cycle in the aftermath of the extinction remain poorly understood. The carbon (C) isotopic composition of carbonate (δ 13 C carb ) across the Permian-Triassic boundary (P-TB) was analyzed at Chaotian, South China. The δ 13 C carb  values decrease from ca. +1 to –2‰ 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 (CO 2 ) input to the surface oceans may also have contributed to the δ 13 C carb  decline. The magnitude of the δ 13 C carb  decrease (∼3‰) is substantially smaller than the magnitude of a decrease in C isotopic composition of organic matter (δ 13 C org ) in the same P-TB interval (∼7‰). This apparent δ 13 C carb -δ 13 C org  decoupling could be explained by proliferation of methanogen (“methanogenic burst”) in the sediments. A global δ 13 C compilation shows a large variation in marine δ 13 C org  records, implying that the “methanogenic burst” according to the Siberian Traps volcanism may have contributed, at least in part, to the δ 13 C org  variability and to the elevated CH 4  levels in the atmosphere. The present and previous observations allow us to infer that the global CH 4  cycle may have fluctuated substantially in the aftermath of the extinction.

frontiers in earth science

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