Abrupt warming in the latest Permian detected using high-resolution in situ oxygen isotopes of conodont apatite from Abadeh, central Iran

Climate warming, probably as a result of massive degassing of greenhouse gases from the Siberian Traps magmatism, has often been acclaimed as a major cause of the end-Permian mass extinction. Indeed, several studies have documented a sudden rise in seawater temperatures during the latest Permian-earliest Triassic, as evidenced by oxygen isotopic records measured on conodont apatite. However, whether such a rapid increase in seawater temperatures occurred before, during, or after the mass extinction remains controversial. Moreover, the pattern of this rise in seawater temperatures and its timing relative to the latest Permian-earliest Triassic carbon cycle disruption, mass extinction, as well as the Siberian Traps magmatism still need to be rigorously examined in various regions. In this study, we present high-resolution oxygen isotopic records of conodont apatite (δ18Oapatite) from the Upper Permian-lowermost Triassic interval at the Abadeh section, central Iran that are analyzed with in situ secondary ion mass spectrometry (SIMS) method. The δ18Oapatite results from Abadeh demonstrate a clear pattern consisting of three phases: (1) From the lower Wuchiapingian Clarkina dukouensis Zone to the end-Permian mass extinction horizon, δ18Oapatite values are relatively stable, fluctuating in the range of 18.28-20.15‰ with an average of 19.44‰. (2) δ18Oapatite value remains high as 19.26‰ at the mass extinction horizon. Above this horizon, a sudden decrease occurs in the Clarkina hauschkei Zone and reaches a low value of 17.05‰ close to the Permian-Triassic boundary. (3) In the lowermost Triassic, δ18Oapatite values maintain a low baseline in the range of 16.92-17.39‰ with an average of 17.11‰. Overall, the most dramatic change in δ18Oapatite values (i.e., a decrease of ~2‰), converting into an abrupt warming of ~10 °C, occurred above the mass extinction horizon and below the Permian-Triassic boundary at Abadeh. The Abadeh δ18Oapatite record is consistent with previous results documented in South China, Iran, and Armenia in terms of the timing and magnitude of a substantial warming, and therefore represents a global signature. If applying the high-precision temporal framework established in the well-dated Meishan GSSP section to Abadeh, the abrupt warming of ~10 °C took only a maximum duration of ~37 kyr (thousand years). By projecting the carbon cycle change, temperature rise, mass extinction at the Abadeh and Meishan sections, and the temporal evolution of the Siberian Traps magmatism onto a unified timescale, the temporal correlation strongly suggests that the switch from dominantly extrusive eruptions to widespread sill intrusions is probably the most annihilating phase of the Siberian Traps magmatism, and is temporally consistent with the end-Permian mass extinction.