Massive volcanism at the Permian–Triassic boundary and its impact on the isotopic composition of the ocean and atmosphere

Abstract Bulk carbonate and conodonts from three Permian–Triassic (P–T) boundary sections at Guryul Ravine (Kashmir), Abadeh (central Iran) and Pufels/Bula/Bulla (Italy) were investigated for δ 13 C and δ 18 O. Carbon isotope data highlight environmental changes across the P–T boundary and show the following features: (1) a gradual decrease of ∼4‰ to more than 7‰ starting in the Late Permian (Changhsingian) C. bachmanni Zone, with two superimposed transient positive excursions in the C. meishanensis – H. praeparvus and the M. ultima – S. ? mostleri Zones; (2) two δ 13 C minima, the first at the P–T boundary and a higher, occasionally double-minimum in the lower I. isarcica Zone. It is unlikely that the short-lived phenomena, such as a breakdown in biological productivity due to catastrophic mass extinction, a sudden release of oceanic methane hydrates or meteorite impact(s), could have been the main control on the latest Permian carbon isotope curve because of its prolonged (0.5 Ma) duration, gradual decrease and the existence of a >1‰ positive shift at the main extinction horizon. The P–T boundary δ 13 C trend matches in time and magnitude the eruption of the Siberian Traps and other contemporaneous volcanism, suggesting that volcanogenic effects, such as outgassed CO 2 from volcanism and, even more, thermal metamorphism of organic-rich sediments, as the likely cause of the negative trend.