09:45 〜 10:00
[BCG10-04] Sulfur and carbon isotope profiles for Guadalupian-Lopingian paleo-atoll carbonates in Japan
キーワード：ペルム紀中期‐後期境界、大量絶滅、炭酸塩置換体硫酸
The mass extinction event that occurred around the Guadalupian–Lopingian (or Middle-Late Permian) boundary (G-LB; 260 Ma) followed extremely high carbonate δ13C values (up to + 6 ‰) 1). This carbon isotopic signal was named the “Kamura event,” after the Kamura section in Japan1. To elucidate the environmental conditions during the G-LB mass extinction, we analyzed the sulfur isotope ratios of carbonate-associated sulfate (CAS) and the carbon isotope ratios of organic carbon in the Middle-Upper Permian carbonates of an accreted mid-oceanic paleo-atoll complex at Kamura in central Kyushu, Japan, which is where the Kamura event was first documented.
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).
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).