[M-IS30] 遠洋域の進化

[MIS30-05] 美濃帯上部三畳系層状チャートの有機炭素同位体比変動

*尾上 哲治¹、池原 実²、曽田 勝仁¹、山下 大輔¹ (1.熊本大学自然科学研究科、2.高知大学海洋コア総合研究センター)

キーワード：三畳紀, 層状チャート, 炭素同位体

The Late Triassic was characterized by several marine and terrestrial biotic turnover events prior to the end-Triassic mass extinction. The causes of the end-Triassic mass extinction and these Norian to Rhaetian biotic turnover events are still the subject of debate. In order to infer the Norian to Rhaetian (Late Triassic) environmental changes in a pelagic realm of the Panthalassa Ocean, the stratigraphic variations of TOC and δ13C_org of the bedded chert succession in the Sakahogi section were examined. The Sakahogi section (~26 m in thickness) crops out in the Mino Belt, central Japan, and consists of the red to greenish-gray bedded chert. The radiolarian biostratigraphy indicates a middle Norian to Rhaetian age of the bedded chert. The bedded chert of the Sakahogi section is reconstructed as a deep-sea sediment of pelagic facies forms in an open ocean realm of the Panthalassa Ocean. Our analysis shows that the middle Norian samples record stable vaues until the late middle Norian. This stability is disturbed by a small negative δ13C_org excursion at the middle Norian ejecta layer (Sakahogi ejecta). TOC values increase across the middle and upper Norian boundary interval. This interval is marked by a minor increase in δ13C_org value (~1 ‰).