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1 July 2013 Miocene Ostracods from the Itahana Formation in the Tomioka District, Gunma Prefecture, Central Japan: Paleoenvironmental Significance and Systematics
Gengo Tanaka, Yoshikazu Hasegawa
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Abstract

Sixty-two podocopid ostracod species belonging to 37 genera were identified during the analysis of 57 samples from the Miocene Itahana Formation (ca. 11.0 to 10.5 Ma) in the Tomioka district, Gunma Prefecture, central Japan. Two assemblages were recognized in the lower member of the Itahana Formation: Assemblage I is characterized by Aurila joushuensis, Loxoconcha nozokiensis, Paracytheridea neolongicaudata, Callistocythere spp., and Cythere omotenipponica; Assemblage II is characterized by Krithe sp., Acanthocythereis sp., Ambtonia takayasui, Ambtonia tamayuensis, and Argilloecia sp. Assemblage II indicates a depositional environment of muddy bottoms in the upper bathyal open sea, while for the species of Assemblage I a habitat of sandy bottoms in warm shallow open seas is indicated, suggesting that the depositional environment of the lowermost Itahana Formation was bathyal and that the ostracods of Assemblage I were transported to that environment by turbidity currents. Fifteen new species are described in this study.

© by the Palaeontological Society of Japan
Gengo Tanaka and Yoshikazu Hasegawa "Miocene Ostracods from the Itahana Formation in the Tomioka District, Gunma Prefecture, Central Japan: Paleoenvironmental Significance and Systematics," Paleontological Research 17(2), 138-172, (1 July 2013). https://doi.org/10.2517/1342-8144-17.2.138
Received: 23 February 2012; Accepted: 1 September 2012; Published: 1 July 2013
JOURNAL ARTICLE
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KEYWORDS
early Late Miocene
Itahana Formation
new species
Ostracoda
paleoenvironment
systematics
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