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