[B-PT27_28PM1] 顕生代生物多様性の変遷：絶滅と多様化

[BPT27-04] 前期三畳紀極端温暖化直後の全球的海洋酸化イベント

*海保 邦夫¹、高橋 聡²、ゴージャン ポール³、チェン ツォンチャン⁴、トン ジンナン⁴ (1.東北大学大学院理学研究科地学専攻、2.東京大学、3.ワシントン大学、4.中国地質大学)

キーワード：前期三畳紀, 海洋溶存酸素, 硫黄同位体

Biotic recovery after the largest mass extinction at the end of the Permian (252.3 million years ago, Ma) became evident in early Spathian (250.1 Ma), Early Triassic, and was eventually completed in middle-late Anisian (ca. 244 Ma), early Middle Triassic. Recent studies showed that this much delayed recovery was impacted by several biocrises and associated environmental and climatic stresses during the Early Triassic. For instance, the end-Smithian extinction and associated thermal maximum and Smithian oceanic anoxia may have prevented biotic recovery initiated in early Smithian (251 Ma). Our new study not only confirmed the oceanic anoxia in late Smithian but also found an oxygenation event just after the Smithian thermal maxima (STM) using sulfur isotope fractionation between sulfate and sulfide. Newly obtained sulfur isotope ratios of carbonate-associated sulfate (d34SCAS) in the surface water and sulfide (d34Ssulfide) in the Panthalassic deep water during the late Permian to the Early Triassic compiled with published data show a significant increase in fractionation between the d34SCAS and d34Ssulfide during the early Spathian (41-51 permil to 62 permil). The latter indicates an increase in global oceanic dissolved oxygen levels, which also coincided with a climatic cooling and may have facilitated biotic recovery in late Early Triassic.