Stable carbon isotope signature in mid-Panthalassa shallow-water carbonates across the Permo-Triassic boundary: evidence for C-13-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 stud y examines stable carbon isotope compositions (delta C-13(carb) and delta C -13(org)) of such open-ocean shallow-water limestone across the Permo-Trias sic boundary (PTB) at Kamura and Taho in southwest Japan. The results show an almost identical secular change in delta C-13(carb) values with a remark able negative spike across the PTB in both sections. This confirms for the first time that the mid-Panthalassa shallow-water carbonates are bio- and c hemo-stratigraphically correlated not with previously studied PTB sections from the peripheries of Pangea. The negative shift in delta C-13(carb) occu rs parallel to that of delta C-13(org) in both sections, and the difference (Delta C-13=delta C-13(carb)-delta C-13(org)) remains nearly constant thro ughout the sections. This implies that the C-13-depleted water should have developed widely, probably in a global extent, throughout the superocean Pa nthalassa across the PTB. These findings suggest that a large input of C-12 -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. (C) 2001 Elsevier Science B.V. All rights re served.