Fossil ostracod faunas from the Katsuta Group of the Setouchi Geologic Province in southwestern Japan and their paleobiogeography during the mid-Miocene Climatic Optimum

Abstract

A total of 52 ostracod species were found in 24 samples collected from four sites of the Yoshino Formation of the Katsuta Group, which were deposited in the Setouchi Geologic Province of southwestern Japan during the mid-Miocene Climatic Optimum (16.9–14.7 Ma). Q-mode cluster analysis revealed five sample clusters (ostracod biofacies), suggesting that the paleoenvironments included enclosed bay, middle to lower sublittoral bay, and upper bathyal sea, in ascending order, during the transgression. R-mode cluster analysis revealed seven species clusters (ostracod bioassociations) that reflect the paleoecology of ostracod species. Fossil ostracod assemblages are paleobiogeographically characterized by a mixture of tropical taxa (e.g. Cibotoleberis, Pacambocythere, and Paijenborchella), cosmopolitan taxa (e.g. Cytherella, Neonesidea, and Xestoleberis), and the taxa that survived or evolved around the Japanese islands since the Paleogene (e.g. Acanthocythereis, Munseyella, Pseudoaurila, and Trachyleberis). All taxa entered the study area after the opening of the Sea of Japan during 18–17 Ma. Cool-temperate species, such as Elofsonella, Hemicythere, and Laperousecythere, which have been reported from the Lower Miocene deposits in Japan, were not detected in the study area. Three new trachyleberidid species, Acanthocythereis kunihiroi sp. nov., Cibotoleberis tsuyamensis sp. nov., and Pacambocythere ishizakii sp. nov., are described.

ZooBank registration: urn:lsid:zoobank.org:pub:35693991-2F1D-414C-96EF-487CD8FBF96C