[B-PT27] 原生代末／顕生代生物多様性変遷：絶滅と多様化

[BPT27-05] ペルム紀中期末の生相・環境変化：中緯度での応答

*磯崎 行雄¹、林 隆太郎¹、可児 智美² (1.東京大学大学院、2.熊本大学)

キーワード：ペルム紀, キャピタン世, 寒冷化, Sr同位体比, 南部北上, 陸棚石灰岩

The Guadalupian-Lopingian boudnary (Permian) recorded the most significant environmental change in the Paleozoic on all aspects; i.e. major global cooling, biodiversity decline, ocean chemistry, and even geomagnetism. Previous studies focused mostly on the fossiliferous limetones deposited in low-latitude domains both in peri-Pangean shelves and mid-oceanic atoll complexes. In order to check the relevant environmental changes in mid-latitude, the Iwaizaki Limestone in the South Kitakami Blet, NE Japan, was analyzed in litho-, bio-, and isotope stratigraphy. In particular, the top part of the limestone, ca. 50 m-thick interval, recorded the collapse of a patch reef complex. Except the Capitanian fusulines from the basal part of this interval, most of the interval lacks index fossil. The present Sr isotope analysis newly identified the uniquely low Sr-ratio, as low as 0.7068, throughout the interval, confirming the Capitanian age. The collapse of reef occurred during the Capitanian in accordance with the Kamura cooling event, but probably much earlier than the low-latitude domains.