[B-CG07] 顕生代の生物多様化：放散と絶滅

[BCG07-05] ペルム紀パンサラッサ海Sr収支変化

*可児 智美¹、磯崎 行雄²、三澤 啓司³、石川 晃⁴、米田 成一⁵ (1.熊本大学大学院自然科学研究科（理学）、2.東京大学大学院総合文化研究科、3.極地研究所、4.東京工業大学理学院、5.国立科学博物館理工学研究部)

キーワード：δ88Sr、87Sr/86Sr、炭酸塩、海水

The radiogenic Sr isotopic composition (⁸⁷Sr/⁸⁶Sr) of the Phanerozoic seawater has been fluctuated according to global tectonics and/or climate change. The major Sr fluxes to drive ⁸⁷Sr/⁸⁶Sr in seawater are three-fold; i.e., weathering of highly radiogenic continental silicates, non-radiogenic submarine hydrothermal fluid, and weathering of less radiogenic carbonates and basalts from island arc/oceanic island. During the Phanerozic, seawater ⁸⁷Sr/⁸⁶Sr changed most dramatically around the Middle/Late Permian boundary marked by a major mass extinction. Stable Sr isotope (δ⁸⁸Sr) in seawater is recently recognized as an useful proxy for estimating ancientburial/dissolution of marine carbonate. The δ⁸⁸Sr values were consistently low in the Middle Permian and began to increase during the Late Permian. The timing of thistrend change across the G-LB corresponds to that of ⁸⁷Sr/⁸⁶Sr. This significant change of ocean Sr budget in the Phanerozoic might be explained by increase/decrease of carbonate weathering on continental shelves with respect to the long-term cooling/warming associated with global sea level change.