[B-CG04] Decoding the history of Earth: From Hadean to the present

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

*Satoshi Takahashi¹, Rie Hori², Satoshi Yamakita³, Yoshiaki Aita⁴, Atsushi Takemura⁵, Minoru Ikehara⁶, Yujin Xiong⁷, Simon W. Poulton⁷, Paul B. Wignall⁷, TAKAAKI ITAI¹, Hamish J. Campbell⁸, Bernard K. Spörli⁹ (1.Department of Earth and Planetary Science, University of Tokyo, 2.Department of Earth Sciences, Graduate School ofScience and Engineering, Ehime University , 3.Department of Earth Sciences, Faculty of Culture, Miyazaki University, 4.Department ofGeology, Faculty ofAgriculture, Utsunomiya University, 5.Geosciences Institute, Hyogo University ofTeacher Education, 6.Center for Advanced Marine Core Research, Kochi University, 7.School of Earth and Environment, University of Leeds, 8.GNS Science, 9.School of Environment, The University of Auckland)

Keywords:Permian-Triassic boundary, Mass extinction, Ocean anoxia

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.