9:45 AM - 10:00 AM
[BCG10-04] Sulfur and carbon isotope profiles for Guadalupian-Lopingian paleo-atoll carbonates in Japan
Keywords:Guadalupian-Lopingian boundary, mass extinction, carbonate associated sulfate
Although the extreme carbonate δ13C values corresponding to the Kamura event were accompanied by high organic matter δ13C values, the isotope differences between carbonate and organic matter (Δ13C) varied and were correlated with carbonate δ13C values throughout the Capitanian (late Guadalupian) and Wuchiapingian (early Lopingian). The Capitanian δ13C-Δ13C correlation can be understood if an unusually large reservoir of dissolved organic carbon (DOC) is assumed2). The decline in carbonate δ13C after the Kamura event indicates enhanced DOC oxidation. As the deep-sea Panthalassa had been well oxygenated during the Capitanian, the large DOC reservoir likely developed as a result of the expansion of mid-depth oxygen minimum zone (OMZ) in Panthalassa.
The Wuchiapingian δ13C-Δ13C correlation, the slope of which differs from that of the Capitanian, can be explained by steady-state models in which incoming and outgoing carbon fluxes are balanced. The lower carbonate δ13C values occurred when the concentrations of atmospheric CO2 were higher, which likely induced global warming that could have suppressed oceanic circulation and, therefore, the supply of oxygen to the seafloor, which could enhance bacterial sulfate reduction. Therefore, the increased input of volcanic CO2 can decrease δ13C in carbonate and increase δ34S in sulfate, producing a negative δ13C-δ34S correlation, which was observed for the Wuchiapingian dataset. The intense volcanic activity might be limited to the G-L boundary and the middle Wuchiapingian, based on the lower δ13C values. As the decline in Middle Permian marine biodiversity began in the earlier half of the Capitanian period, these two volcanic events may not be the cause of the decline in biodiversity. The expansion of the OMZ during the Capitanian could have severely impacted the Middle Permian fauna.
1) Isozaki, Y., Kawahata, H., Ota, A., Glob. Planet. Change 55, 21-38 (2007).
2) Rothman, D.H., Hayes, J.M., Summons, R.E., Proc. Natl. Acad. Sci. 100, 8124-8129 (2003).