Stable carbon isotope signature in mid-Panthalassa shallow-water carbonates across the Permo–Triassic boundary: evidence for 13C-depleted superocean

Abstract

The Jurassic accretionary complex in southwest Japan contains exotic blocks of the Permo–Triassic limestone primarily deposited on ancient mid-oceanic seamounts in an ancient Pacific Ocean or superocean Panthalassa. This study examines stable carbon isotope compositions (δ13Ccarb and δ13Corg) of such open-ocean shallow-water limestone across the Permo–Triassic boundary (PTB) at Kamura and Taho in southwest Japan. The results show an almost identical secular change in δ13Ccarb values with a remarkable negative spike across the PTB in both sections. This confirms for the first time that the mid-Panthalassa shallow-water carbonates are bio- and chemo-stratigraphically correlated not with previously studied PTB sections from the peripheries of Pangea. The negative shift in δ13Ccarb occurs parallel to that of δ13Corg in both sections, and the difference (Δ13C=δ13Ccarb−δ13Corg) remains nearly constant throughout the sections. This implies that the 13C-depleted water should have developed widely, probably in a global extent, throughout the superocean Panthalassa across the PTB. These findings suggest that a large input of 12C-enriched carbon into the ocean–atmosphere system has occurred and may have caused a global environment change probably relating to the greatest mass extinction in the Phanerozoic.