[B-PT27_28PM1] Phanerozoic biodiversity change: Extinction and diversification

[BPT27-10] A unique low-latitude-type molluskan assemblage from the Permian Iwaizaki limestone in the S. Kitakami belt, NE Japan

*Yukio ISOZAKI¹, Tomoki KASE² (1.Dept. Earth Science & Astronomy, University of Tokyo, 2.National Science Museum)

Keywords:Permian, bivalve, gastropod, South Kitakami belt, South China

Permian large gastropod "Pleurotomaria" yokoyamai was found for the first time from the Capitanian (Upper Guadalupian) Iwaizaki limestone in the South Kitakami belt, NE Japan. A smaller planispiral gatropode Porcellia sp. was also associated. These taxa have been scarcely reported, except from the coeval Akasaka limestone in SW Japan. The Akasaka Limestone was deposited as a low-latitude atoll on a mid-Panthalassan seamount, whereas the Iwaizaki limestone as a patch reef within terrigenous clastics-dominant facies on a shallow marine continental shelf. The occurrence of this unique gastropod assemblage, together with large bivalves and large-tested fusulines, suggests that the Iwaizaki Limstone was originated also in a Permian low-latitude domain, and that the South Kitakami belt likely formed a part of the continental margin of South China representing its eastern extension to NE Japan.