[B-PT27_28PM1] 顕生代生物多様性の変遷：絶滅と多様化

[BPT27-09] 中・後期ペルム紀の海水Sr同位体比変動および氷床増減との関連

*可児 智美¹、小福田 大輔²、磯崎 行雄² (1.熊本大学大学院自然科学研究科、2.東京大学大学院総合文化研究科)

キーワード：Permian, Sr isotope, seawater, limestone

We report the detailed secular change of the Middle to Late Permian seawater ⁸⁷Sr/⁸⁶Sr ratio for the Akasaka and Iwato limestone in SW Japan. The studied two sections were originally deposited as paleo-atoll complexes on the low-latitude, mid-Panthalassa seamounts. We also analyzed coeval sections at Sizipo and Liangshan deposited on the shallow marine shelf of South China. Commonly in the four studied sections, extremely low values (<0.7069; the lowest values of the Phanerozoic) continued from upper Wordian (middle Middle Permian) to the topmost Capitanian (upper Middle Permian) immediately below the Middle-Late Permian boundary. The ⁸⁷Sr/⁸⁶Sr ratios increased to 0.7072 in the early Late Permian. This increase recorded the most rapid in the entire Phanerozoic. The ca. 5 m.y.-long minimum interval and the following rapid increase in Sr isotope ratio can be explained by the remarkable changes in continental erosion/weathering rate; in particular, by the onset of glaciation and the following deglaciation, that is supported by global sea level change, in addition to the initial doming/rifting of Pangea. After the Capitanian cooling, the long-term climatic regime shifted to a warmer one during which covering ice was removed from continents to expose crustal silicates for to erosion/weathering. The continental rifting with new drainage systems likely increased decisively the highly radiogenic continental flux to the superocean.