[B-CG06] 地球史解読：冥王代から現代まで

[BCG06-P16] Geochemistry of Akasaka and Kamura Limestones and Marine Environment Change at Guadalupian-Lopingian Boundary

*Kaiyu Wu¹、Chiyori Nakajo¹、Yuichiro Ueno^1,2、Yukio Isozaki³、Jakub Surma¹ (1.Department of Earth and Planetary Sciences, Institute of Science Tokyo、2.Earth-Life Science Institute, Institute of Science Tokyo、3.Department of Earth Science & Astronomy, The University of Tokyo)

キーワード：Permian, mass extinction, carbonate, trace element

Just before the Permian-Triassic mass extinction, another extinction event occurred at the Guadalupian-Lopingian Boundary (G-LB, middle-late Permian), the causes of which are still debated. The active volcanism (e.g. large igneous province (LIP) ‘Emeishan Trap’) is thought to be one possible reason (Wignall et al. 2009), but its mechanism on a global scale is doubted. Here, we newly report records of major, trace and rare earth elements from Kamura and Akasaka sections, Japan, that are both mid-oceanic atoll limestones deposited crossing the G-LB. Both two section are characterized by a relative depletion in heavy rare earth pattern, indicating the influence of hydrothermal fluids. The significant negative cerium anomaly and positive europium anomaly at the G-LB may suggest intensive hydrothermal or volcanic contributions. In addition, we determined accurate barium concentrations of calcite fractions in the samples through a stepwise leaching procedure with acetic acid. The Ba concentrations in both sections show a significant drop in the late Capitanian (end of Guadalupian), which may reflect a decrease in overall seawater Ba concentration. This variations in dissolved Ba may have been controlled by increasing seawater sulphate concentrations and, hence, fixation of Ba in insoluble barite (BaSO₄). This would be in agreement with the enhanced volcanic and hydrothermal input that we observe in REEs, further endorsing their importance to global changes in the marine environment and corresponding mass extinction at the G-LB.

References:
Wignall P.B., Sun Y.D., Bond D.P.G., Izon G., Newton R.J., Védrine S., Widdowson M., Ali J.R., Lai X.L., Jiang H.S., Cope H. and Bottrell S.H. (2009)
Volcanism, Mass Extinction, and Carbon Isotope Fluctuations in the Middle Permian of China Science, 324, 1179-1182.