[B-CG10] 顕生代生物多様性の変遷：絶滅と多様化

[BCG10-03] δ⁸⁸Sr and ⁸⁷Sr/⁸⁶Sr variations in Middle-Upper Permian seawater

*可児 智美¹、磯崎 行雄²、三澤 啓司³、石川 晃²、米田 成一⁴ (1.熊本大学大学院先端科学研究部、2.東京大学大学院総合文化研究科、3.極地研究所、4.国立科学博物館理工学研究部)

キーワード：炭酸塩、海水、Sr同位体

The lowest value of seawater ⁸⁷Sr/⁸⁶Sr in the Phanerozoic called “the Capitanian minimum” represents an extremely unusual condition in the global Sr cycle, which may have been linked to the global environmental changes with major mass extinction at the end-Guadalupian (Middle Permian). We newly measured δ^88/86Sr values of shallow marine carbonates for the same Middle-Upper Permian interval by TRITON TIMS, with correction of isotope fractionation during mass spectrometry with ⁸⁷Sr-⁸⁴Sr double spike. The δ^88/86Sr values started to decrease in the Early Permian, and reached to the Phanerozoic lowest value at the end of Capitanian (Late Guadalupian). In turn, the values started to increase across the Middle-Late Permian boundary (G-LB), and kept increasing throughout the early Late Permian. This trend across the G-LB is similar to that of ⁸⁷Sr/⁸⁶Sr, even though there is no overall correlation between seawater δ^88/86Sr and ⁸⁷Sr/⁸⁶Sr through the Phanerozoic. The extremely low δ^88/86Sr value in seawater may reflect a unique balance between two fluxes to seawater from marine carbonate sources in global-scale; i.e., increase by dissolution and decrease by deposition of carbonates.