[B-CG04] 地球史解読：冥王代から現代まで

[BCG04-01] Progress of the end-Permian oceanic anoxia in the pelagic Panthalassa

*高橋 聡¹、堀 利栄²、山北 聡³、相田 吉昭⁴、竹村 厚司⁵、池原 実⁶、Xiong Yujin⁷、Poulton Simon ⁷、Wignall Paul⁷、板井 啓明¹、Campbell Hamish ⁸、Spörli Bernard ⁹ (1.東京大学理学系研究科地球惑星科学専攻、2.愛媛大学大学院理工学研究科、3.宮崎大学教育文化学部、4.宇都宮大学農学部、5.兵庫教育大学学校教育研究科　、6.高知大学　海洋コア総合研究センター、7.リーズ大学　地球環境学科、8.ニュージーランド核科学研究所、9.オークランド大学 環境学科)

キーワード：ペルム紀三畳紀境界、大量絶滅、海洋無酸素

The end-Permian mass extinction event (EPME) has been linked with the widespread development of oxygen-poor oceanic conditions. However, information on the spatial extent of anoxia in the Panthalassa super-ocean has been limited. This study reports oceanic redox records from the southern middle-latitude, pelagic Panthalassa across the EPME, based on a deep-sea chert succession (the Waiheke 1 section, WHK 1) from the North Island of New Zealand. Carbon isotope correlation between the study section and the GSSP section for the Permian-Triassic boundary (PTB) indicates that the EPME is recorded in a thin black claystone interbedded between siliceous siltstone beds in WHK 1. Pyrite dominated reactive iron, and high Fe/Al, U/Al and Mo/Al values occur in the black claystone bed and the overlying strata, which comprises the Permian-Triassic transition. These geochemical features suggest that anoxic-sulfidic water developed at that time. Similar redox variations across the EPME boundary have been reported from other Panthalassic deep-sea sections, suggesting widespread sulfidic waters during EPME. However, the onset of the shift to the oxygen-poor and/or sulfidic condition of WHK 1 postdates the change to anoxia in low latitude sections by up to a hundred kilo years. This finding implies the gradual expansion of oceanic anoxia from low to middle-high latitude oceanic regions during the Permian-Triassic transition. As an result of this expansion in ocean anoxia, a significant decrease in seawater trace metals such as Mo is inferred from the earliest Triassic strata of the studied section and other PTB sections. The pre-EPME ocean anoxia that occurred mainly in low latitude regions began after the first Siberian Traps eruption and during terrestrial de-vegetation trends, implying a terrestrial-marine linkage to severe environmental change. The more widespread anoxia at the EPME coincides with extreme global warming. This suggests that rising temperature and associated effects (e.g. change of ocean circulation, marine eutrophication intensified by terrestrial weathering) were critical triggers for ocean deoxygenation and the mass extinction event.