日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 B (地球生命科学) » B-CG 地球生命科学複合領域・一般

[B-CG08] 顕生代生物多様性の変遷:絶滅と多様化

2019年5月28日(火) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:磯崎 行雄(東京大学大学院総合文化研究科広域科学専攻広域システム科学系)、澤木 佑介(東京大学大学院総合文化研究科)

[BCG08-P02] パンサラサ海における後期三畳紀レーチアンのコノドント化石層序と三畳紀末コノドントの絶滅

*山﨑 栞奈1山下 大輔2尾上 哲治1 (1.熊本大学、2.薩摩川内市役所)

キーワード:後期三畳紀、化石層序、コノドント、層状チャート、美濃帯、パンサラサ海

The Rhaetian stage of the Triassic was a period characterized by intense biological, climate and environmental changes, ending with the break-up of the supercontinent Pangaea and the occurrence of the End-Triassic mass Extinction (ETE), one of the big five extinctions documented during the Phanerozoic. It is noteworthy that the ETE seems to be associated with significant d13C perturbations (CIEs), commonly related to the CAMP eruptive phases. The stratigraphic record of these environmental changes has been recently reported from the Upper Triassic bedded chert successions in Japan, deposited within a Paleo-Pacific (Panthalassa) deep basin. The chronology for the Rhaetian pelagic in the Panthalassa Ocean is based on the radiolarian zonation, which is well established in the Upper Triassic bedded chert successions in the Mino Belt, central Japan. Although accurate calibration for the chronostratigraphic stages and substages are established basically by means of ammonites and conodonts, most of the Japanese radiolarian zones were calibrated through correlation with zonal schemes established in other regions, and have not been calibrated conodont biostratigraphy.

Here we present Upper Norian to Rhaetian conodont biostratigraphy of an Upper Triassic bedded chert succession from the Mino belt, central Japan, where the radiolarian biostratigraphy has been investigated (Hori, 1992; Sugiyama, 1997). Based on the stratigraphic distributions of marker species, four conodont zones were defined: the Mocina bidentata Zone, the Misikella hernsteini Zone, the M. posthernsteini zone, and the M. ultima zone, in ascending order. These conodont zones are comparable to the standard Late Norian and Rhaetian conodont zones of western Tethys. The Norian/Rhaetian boundary in the study section is tentatively placed between the last occurrence of a Norian radiolarian species (Betraccium deweveri) and the first occurrences of Rhaetian conodont species (M. posthernsteini). The intercalibrated conodont—radiolarian biostratigraphy from the section accurately calibrates the radiolarian zones in Japan with standard chronostratigraphic stages and substages.