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1 Diatom 27: December 2011 Diatoms from the Oidawara Fm Diatom biostratigraphy of the middle Miocene Oidawara Formation in the Mizunami area, Gifu Prefecture, central Japan Keita Kawamura 1, Itsuki Suto 2 and Yukio Yanagisawa 3 1 Nissei Gakuen, 2739 Hattaino, Hakusan-cho, Tsu, Mie , Japan 2 Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi , Japan suto.itsuki@a.mbox.nagoya-u.ac.jp 3 Institute of Geology and Geoinformation, Geological Survey of Japan/AIST, Higashi, Tsukuba, Ibaraki , Japan Abstract We examined fossil diatoms in the middle Miocene Oidawara Formation distributed in Mizunami City, Gifu Prefecture, central Japan, to determine the precise sedimentation age. Well preserved fossil marine diatoms with high diversity have been found in the diatomaceous mudstone of the Oidawara Formation. The diatom assemblage of the formation can be assigned to the short interval between diatom biohorizons D41 the last occurrence of Denticulopsis praelauta, 15.8 Ma and the first occurrence of Actinocyclus ingens f. nodus 15.7 Ma in the diatom zone NPD 4A Denticulopsis lauta Zone of the Neogene North Pacific diatom zonation. As a result, the sedimentation age of the Oidawara Formation was determined to be between 15.8 and 15.7 Ma. Reversed magnetic polarity reported from the Oidawara Formation corresponds to chron C5Br. Key index words: biostratigraphy, fossil, middle Miocene, Mizunami, Oidawara Formation Fig Fig. 2 Received 28 July 2011 Accepted 20 October Yanagisawa Akiba et al , Sugiyama & Furutani Saito Hayashida Hiroki & Matsumoto Yanagisawa Ma =megaan-

2 18 Keita Kawamura et al. Fig. 1. a. Map showing the location of Mizunami City, Gifu Prefecture, Japan. b. Map showing the localities of the Shuku stratigraphic section see detail in Fig. 3 and the bore hole examined in this study, with distribution of the Oidawara Formation shaded area in Mizunami City after Itoigawa 1974, num, million years before present Hayashida 1986 Hiroki & Matsumoto Akiba 1986 Yanagisawa & Akiba 1998 Watanabe & Yanagisawa 2005, Fig. 2 Fig. 2. The stratigraphy of the Neogene sediments in the Mizunami area Itoigawa 1974, 1980.

3 Diatoms from the Oidawara Fm. 19 Fig. 3. Route map of the Shuku stratigraphic section , m 70 m 135 m 30 m 30 m 30 m 30 m Fig Fig. 4. Stratigraphic distribution of selected diatom species in the Shuku stratigraphic section. Diatom zonation after Akiba 1986 and Yanagisawa & Akiba 1998.

4 20 Keita Kawamura et al. Fig. 5. Stratigraphic distribution of selected diatom species in the boring core. Diatom zonation after Akiba 1986 and Yanagisawa & Akiba m 160 m Fig. 3 Fig Figs 1, 3 Fig m 10 cm 20 cm 47 m 4 m 1 m 16 m 20 cm m 20 m

5 Diatoms from the Oidawara Fm. 21 Table 1. Occurrence chart of fossil diatom species from the Shuku stratigraphic section. Preservation, G: good, M: moderate, P: poor. Abundance, A: abundant, C: common, R: rare; Occurrence, +: present. Sample SHK A s 3s 5s 8s 10s 12s 14s Preservation G G G G G G G G G G G G G G G G G G G G G G G Abundance A A A A M A A A A A A A A A A A A A A A A A A Actinocyclus ingens Rattray emend. Whiting et Schrader A. cf. kisselevii Makarova 1 + Actinoptychus senarius (Ehrenberg) Ehrenberg A. splendens (Shadbolt) Ralfs in Pritchard + + A. vulgaris Schumann Arachnoidiscus spp Asteromphalus sp Azpeitia endoi (Kanaya) P.A.Sims et G.A.Fryxell in G.A.Fryxell et al. Cavitatus exiguus Yanagisawa et Akiba in Akiba et al C. jouseanus (Scheschukova-Poretzkaja) D.M.Williams C. linearis (Scheschukova-Poretzkaja) Akiba et Yanagi- sawa in Akiba et al. C. miocenicus (Schrader) Akiba et Yanagisawa in Akiba et al. Cocconeis californica (Grunow in Cleve et Möller) 0.5 Grunow in Van Heurck C. californica var. kerguelensis Heiden in Heiden et Kolbe C. costata Gregory C. scutellum Ehrenberg C. vitrea Brun + C. spp Coscinodiscus asterompharus Ehrenberg C. lewisianus Greville + C. marginatus Ehrenberg C. radiatus Ehrenberg C. spp. + + Cymatosira cf. lorenziana Grunow Delphineis angustata (Pantocsek) Andrews D. miocenica (Schrader) Andrews D. penelliptica Andrews Denticulopsis ichikawae Yanagisawa et Akiba D. lauta (Bailey) Simonsen Diploneis bombus Ehrenberg + D. smithii (Brébisson in W.Smith) Cleve 1 + Grammatophora spp Hemiaulus bipons (Ehrenberg) Grunow in Van Heurck Hyalodiscus obsoletus Scheschukova-Poretzkaja Kisseleviella carina Scheschukova-Poretzkaja Macrora stella (Azpeitia) Hanna + Mediaria magna Yanagisawa M. splendida f. splendida Scheschukova-Poretzkaja M. splendida f. tenera Schrader Neodelphineis pelagica Takano Nitzschia challengeri Schrader Odontella aurita (Lyngbye) Agardh Paralia sulcata (Ehrenberg) Cleve Pseudodimerogramma elliptica Schrader in Schrader et Fenner Raphidodiscus marylandicus Christian Rhabdonema spp Rhaphoneis elegans (Pantocsek) Hanna Rhizosolenia hebetata Bailey R. miocenica Schrader R. styliformis Brightwell 1 Rouxia spp. + + Stellarima microtrias (Ehrenberg) Hasle et P.A.Sims + Stephanopyxis turris (Greville et Arnott) Ralfs in Pritchard S. spp. Thalassionema nitzschioides (Grunow) Mereschkowsky Thalassiosira cf. leptopus (Grunow in Van Heurck) Hasle et G.A.Fryxell T. manifesta Scheschukova-Poretskaja + T. cf. marujamica Scheschukova-Poretzkaja T. mizunamiensis Yanagisawa T. cf. nidulus (Tempére et Brun in Brun et Tempére) Jousé Thalassiosira cf. yabei (Kanaya) Akiba et Yanagisawa + T. spp Thalassiothrix longissima Cleve et Grunow in Grunow Triceratium condecorum Ehrenberg Total of valves counted Nonmarine diatoms Resting spores of Chaetoceros

6 22 Keita Kawamura et al. Table 1. continued. Sample SHK- 16s 41A A 46C 46D Preservation G G G G G G G G G G G G G G G G G G G G G G G G Abundance A A A A A A A A A A A A A A A A A A A A A A A A Actinocyclus ingens Rattray emend. Whiting et Schrader A. cf. kisselevii Makarova 1 1 Actinoptychus senarius (Ehrenberg) Ehrenberg A. splendens (Shadbolt) Ralfs in Pritchard A. vulgaris Schumann Arachnoidiscus spp Asteromphalus sp Azpeitia endoi (Kanaya) P.A.Sims et G.A.Fryxell in G.A.Fryxell et al. Cavitatus exiguus Yanagisawa et Akiba in Akiba et al C. jouseanus (Scheschukova-Poretzkaja) D.M.Williams C. linearis (Scheschukova-Poretzkaja) Akiba et + + Yanagisawa in Akiba et al. C. miocenicus (Schrader) Akiba et Yanagisawa in Akiba et al. Cocconeis californica (Grunow in Cleve et Möller) Grunow in Van Heurck C. californica var. kerguelensis Heiden in + Heiden et Kolbe C. costata Gregory C. scutellum Ehrenberg C. vitrea Brun C. spp. Coscinodiscus asterompharus Ehrenberg + + C. lewisianus Greville + C. marginatus Ehrenberg C. radiatus Ehrenberg + C. spp. Cymatosira cf. lorenziana Grunow Delphineis angustata (Pantocsek) Andrews D. miocenica (Schrader) Andrews D. penelliptica Andrews 1 + Denticulopsis ichikawae Yanagisawa et Akiba D. lauta (Bailey) Simonsen Diploneis bombus Ehrenberg D. smithii (Brébisson in W. Smith) Cleve + Grammatophora spp Hemiaulus bipons (Ehrenberg) Grunow in Van Heurck Hyalodiscus obsoletus Scheschukova-Poretzkaja Kisseleviella carina Scheschukova-Poretzkaja Macrora stella (Azpeitia) Hanna Mediaria magna Yanagisawa M. splendida f. splendida Scheschukova-Poretzkaja M. splendida f. tenera Schrader + Neodelphineis pelagica Takano Nitzschia challengeri Schrader Odontella aurita (Lyngbye) Agardh Paralia sulcata (Ehrenberg) Cleve Pseudodimerogramma elliptica Schrader in Schrader et Fenner Raphidodiscus marylandicus Christian + Rhabdonema spp Rhaphoneis elegans (Pantocsek) Hanna Rhizosolenia hebetata Bailey R. miocenica Schrader 1 + R. styliformis Brightwell Rouxia spp Stellarima microtrias (Ehrenberg) Hasle et P.A.Sims + Stephanopyxis turris (Greville et Arnott) Ralfs in Pritchard S. spp Thalassionema nitzschioides (Grunow) Mereschkowsky Thalassiosira cf. leptopus (Grunow in Van Heurck) Hasle et G.A.Fryxell T. manifesta Scheschukova-Poretzkaja + + T. cf. marujamica Scheschukova-Poretzkaja T. mizunamiensis Yanagisawa T. cf. nidulus (Tempére et Brun in Brun et Tempére) + + Jousé Thalassiosira cf. yabei (Kanaya) Akiba et Yanagisawa + T. spp Thalassiothrix longissima Cleve et Grunow in Grunow Triceratium condecorum Ehrenberg Total of valves counted Nonmarine diatoms Resting spores of Chaetoceros

7 Diatoms from the Oidawara Fm. 23 Table 2. Occurrence chart of fossil diatom species from the boring core. Preservation, G: good, M: moderate, P: poor. Abundance, A: abundant, C: common, R: rare; Occurrence, +: present. Sample No. - cod Preservation G G G G G G G G G G G G G G G G G G G G G Abundance A A A A A A A A A A A A A A A A A A A A A Actinocyclus ingens f. ingens + planus A. cf. kisselevii Makarova Actinoptychus senarius (Ehrenberg) Ehrenberg A. splendens (Shadbolt) Ralfs in Pritchard + + A. vulgaris Schumann Arachnoidiscus spp Asteromphalus sp Azpeitia endoi (Kanaya) P.A.Sims et G.A.Fryxell in G.A.Fryxell et 1 al. Cavitatus exiguus Yanagisawa et Akiba in Akiba et al C. jouseanus (Scheschukova-Poretzkaja) D.M.Williams C. linearis (Scheschukova-Poretzkaja) Akiba et Yanagisawa in Akiba et al. C. miocenicus (Schrader) Akiba et Yanagisawa in Akiba et al Cocconeis californica (Grunow in Cleve et Möller) Grunow in Van Heurck C. californica var. kerguelensis Heiden in Heiden et Kolbe + C. costata Gregory C. scutellum Ehrenberg C. vitrea Brun C. spp. + Coscinodiscus asterompharus Ehrenberg C. lewisianus Greville C. marginatus Ehrenberg C. radiatus Ehrenberg 2 C. spp. Crucidenticula cf. kanayae Akiba et Yanagisawa + Cymatosira cf. lorenziana Grunow Delphineis angustata (Pantocsek) Andrews D. miocenica (Schrader) Andrews Denticulopsis ichikawae Yanagisawa et Akiba D. lauta (Bailey) Simonsen Diploneis bombus Ehrenberg + D. smithii (Brébisson in W. Smith) Cleve Grammatophora spp Hemiaulus bipons (Ehrenberg) Grunow in Van Heurck Hemidiscus spp. Hyalodiscus obsoletus Scheschukova-Poretzkaja Kisseleviella carina Scheschukova-Poretzkaja Koizumia adaroi (Azpeitia) Yanagisawa Macrora stella (Azpeitia) Hanna Mediaria magna Yanagisawa M. splendida f. splendida Scheschukova-Poretzkaja M. splendida f. tenera Schrader Melosira spp Neodelphineis pelagica Takano Nitzschia challengeri Schrader N. heteropolica Schrader + Odontella aurita (Lyngbye) Agardh + Paralia sulcata (Ehrenberg) Cleve Pseudodimerogramma elliptica Schrader in Schrader et Fenner Pyxilla spp. + Raphidodiscus marylandicus Christian Rhabdonema spp. + + Rhaphoneis elegans (Pantocsek) Hanna R. paralis Hanna Rhizosolenia hebetata Bailey R. miocenica Schrader R. styliformis Brightwell 1 + Rouxia spp Stellarima microtrias (Ehrenberg) Hasle et P.A.Sims + + Stephanopyxis turris (Greville et Arnott) Ralfs in Pritchard S. spp. Thalassionema nitzschioides (Grunow) Mereschkowsky T. spp. + Thalassiosira grunowii Akiba et Yanagisawa T. leptopus (Grunow in Van Heurck) Hasle et G.A.Fryxell + T. cf. leptopus (Grunow in Van Heurck) Hasle et G.A. Fryxell T. manifesta Scheschukova-Poretzkaja + + T. cf. marujamica Sheshukova-Poretzkaja T. mizunamiensis Yanagisawa T. cf. nidulus (Tempére et Brun in Brun et Tempére) Jousé + 1 T. spp Thalassiothrix longissima Cleve et Grunow in Grunow Triceratium condecorum Ehrenberg Total of valves counted Nonmarine diatoms Resting spores of Chaetoceros

8 24 Keita Kawamura et al. Table 2. continued. Sample No. - cod Preservation G G G G G G G G G G G G G G G G G G G G G Abundance A A A A A A A A A A A A A A A A A A A A A Actinocyclus ingens f. ingens + planus A. cf. kisselevii Makarova 1 1 Actinoptychus senarius (Ehrenberg) Ehrenberg A. splendens (Shadbolt) Ralfs in Pritchard + + A. vulgaris Schumann Arachnoidiscus spp Asteromphalus sp Azpeitia endoi (Kanaya) P.A.Sims et G.A.Fryxell in G.A.Fryxell et al. Cavitatus exiguus Yanagisawa et Akiba in Akiba et al C. jouseanus (Scheschukova-Poretzkaja) D.M.Williams C. linearis (Sheshukova-Poretzkaya) Akiba et Yanagisawa in Akiba et al. C. miocenicus (Schrader) Akiba et Yanagisawa in Akiba et al. Cocconeis californica (Grunow in Cleve et Möller) Grunow in Van Heurck C. californica var. kerguelensis Heiden in Heiden et Kolbe + + C. costata Gregory C. scutellum Ehrenberg C. vitrea Brun + + C. spp Coscinodiscus asterompharus Ehrenberg C. lewisianus Greville C. marginatus Ehrenberg C. radiatus Ehrenberg C. spp. + Crucidenticula cf. kanayae Akiba et Yanagisawa Cymatosira cf. lorenziana Grunow Delphineis angustata (Pantocsek) Andrews D. miocenica (Schrader) Andrews Denticulopsis ichikawae Yanagisawa et Akiba D. lauta (Bailey) Simonsen Diploneis bombus Ehrenberg + D. smithii (Brébisson in W. Smith) Cleve + Grammatophora spp Hemiaulus bipons (Ehrenberg) Grunow in Van Heurck Hemidiscus spp. Hyalodiscus obsoletus Scheschukova-Poretzkaja Kisseleviella carina Scheschukova-Poretzkaja Koizumia adaroi (Azpeitia) Yanagisawa Macrora stella (Azpeitia) Hanna 1 Mediaria magna Yanagisawa M. splendida f. splendida Scheschukova-Poretzkaja M. splendida f. tenera Schrader Melosira spp Neodelphineis pelagica Takano Nitzschia challengeri Schrader N. heteropolica Schrader + Odontella aurita (Lyngbye) Agardh 1 Paralia sulcata (Ehrenberg) Cleve Pseudodimerogramma elliptica Schrader in Schrader et Fenner Pyxilla spp. Raphidodiscus marylandicus Christian + 1 Rhabdonema spp. + + Rhaphoneis elegans (Pantocsek) Hanna R. paralis Hanna Rhizosolenia hebetata Bailey R. miocenica Schrader R. styliformis Brightwell Rouxia spp Stellarima microtrias (Ehrenberg) Hasle et P.A.Sims Stephanopyxis turris (Greville et Arnott) Ralfs in Pritchard S. spp. Thalassionema nitzschioides (Grunow) Mereschkowsky T. spp. Thalassiosira grunowii Akiba et Yanagisawa T. leptopus (Grunow in Van Heurck) Hasle et G.A.Fryxell T. cf. leptopus (Grunow in Van Heurck) Hasle et G.A. Fryxell T. manifesta Sheshukova-Poretskaya + + T. cf. marujamica Sheshukova-Poretskaya T. mizunamiensis Yanagisawa T. cf. nidulus (Tempére et Brun in Brun et Tempére) Jousé T. spp. + + Thalassiothrix longissima Cleve et Grunow in Grunow Triceratium condecorum Ehrenberg Total of valves counted Nonmarine diatoms Resting spores of Chaetoceros

9 Diatoms from the Oidawara Fm. 25 Table 2. continued. Sample No. - cod Preservation G G G G G G G G G G G G G G G G G G G G G Abundance A A A A A A A A A A A A A A A A A A A A A Actinocyclus ingens f. ingens + planus A. cf. kisselevii Makarova 1 + Actinoptychus senarius (Ehrenberg) Ehrenberg A. splendens (Shadbolt) Ralfs in Pritchard + A. vulgaris Schumann Arachnoidiscus spp Asteromphalus sp Azpeitia endoi (Kanaya) P.A.Sims et G.A.Fryxell in G.A.Fryxell et al. Cavitatus exiguus Yanagisawa et Akiba in Akiba et al C. jouseanus (Scheschukova-Poretzkaja) D.M.Williams C. linearis (Scheschukova-Poretzkaja) Akiba et Yanagisawa in Akiba et al. C. miocenicus (Schrader) Akiba et Yanagisawa in Akiba et al. Cocconeis californica (Grunow in Cleve et Möller) Grunow + + in Van Heurck C. californica var. kerguelensis Heiden in Heiden et Kolbe C. costata Gregory C. scutellum Ehrenberg C. vitrea Brun C. spp. + + Coscinodiscus asterompharus Ehrenberg C. lewisianus Greville + C. marginatus Ehrenberg C. radiatus Ehrenberg + + C. spp. + + Crucidenticula cf. kanayae Akiba et Yanagisawa Cymatosira cf. lorenziana Grunow Delphineis angustata (Pantocsek) Andrews D. miocenica (Schrader) Andrews Denticulopsis ichikawae Yanagisawa et Akiba D. lauta (Bailey) Simonsen Diploneis bombus Ehrenberg D. smithii (Brébisson in W. Smith) Cleve Grammatophora spp Hemiaulus bipons (Ehrenberg) Grunow in Van Heurck Hemidiscus spp. Hyalodiscus obsoletus Scheschukova-Poretzkaja Kisseleviella carina Scheschukova-Poretzkaja Koizumia adaroi (Azpeitia) Yanagisawa Macrora stella (Azpeitia) Hanna Mediaria magna Yanagisawa M. splendida f. splendida Scheschukova-Poretzkaja M. splendida f. tenera Schrader Melosira spp Neodelphineis pelagica Takano Nitzschia challengeri Schrader N. heteropolica Schrader + Odontella aurita (Lyngbye) Agardh + Paralia sulcata (Ehrenberg) Cleve Pseudodimerogramma elliptica Schrader in Schrader et Fenner Pyxilla spp. Raphidodiscus marylandicus Christian Rhabdonema spp. + + Rhaphoneis elegans (Pantocsek) Hanna R. paralis Hanna + Rhizosolenia hebetata Bailey R. miocenica Schrader R. styliformis Brightwell 1 Rouxia spp Stellarima microtrias (Ehrenberg) Hasle et P.A.Sims Stephanopyxis turris (Greville et Arnott) Ralfs in Pritchard S. spp. + Thalassionema nitzschioides (Grunow) Mereschkowsky T. spp. Thalassiosira grunowii Akiba et Yanagisawa + + T. leptopus (Grunow in Van Heurck) Hasle et G.A.Fryxell T. cf. leptopus (Grunow in Van Heurck) Hasle et G.A.Fryxell T. manifesta Scheschukova-Poretzkaja T. cf. marujamica Sheshukova-Poretzkaja T. mizunamiensis Yanagisawa T. cf. nidulus (Tempére et Brun in Brun et Tempére) Jousé + + T. spp. Thalassiothrix longissima Cleve et Grunow in Grunow Triceratium condecorum Ehrenberg Total of valves counted Nonmarine diatoms Resting spores of Chaetoceros

10 26 Keita Kawamura et al. Table 2. continued. Sample No. - cod Preservation G G G G G G G G G G G G G G G G G G G G G G Abundance A A A A A A A A A A A A A A A A A A A A A A Actinocyclus ingens f. ingens + planus A. cf. kisselevii Makarova + 1 Actinoptychus senarius (Ehrenberg) Ehrenberg A. splendens (Shadbolt) Ralfs in Pritchard + + A. vulgaris Schumann Arachnoidiscus spp Asteromphalus sp Azpeitia endoi (Kanaya) P.A.Sims et G.A.Fryxell in G.A.Fryxell et al. Cavitatus exiguus Yanagisawa et Akiba in Akiba et al C. jouseanus (Scheschukova-Poretzkaja) D.M.Williams C. linearis (Scheschukova-Poretzkaja) Akiba et Yanagisawa in Akiba et al. C. miocenicus (Schrader) Akiba et Yanagisawa in Akiba et al Cocconeis californica (Grunow in Cleve et Möller) Grunow in Van Heurck C. californica var. kerguelensis Heiden in Heiden et Kolbe C. costata Gregory C. scutellum Ehrenberg C. vitrea Brun C. spp. Coscinodiscus asterompharus Ehrenberg C. lewisianus Greville + + C. marginatus Ehrenberg C. radiatus Ehrenberg C. spp Crucidenticula cf. kanayae Akiba et Yanagisawa Cymatosira cf. lorenziana Grunow Delphineis angustata (Pantocsek) Andrews D. miocenica (Schrader) Andrews Denticulopsis ichikawae Yanagisawa et Akiba D. lauta (Bailey) Simonsen Diploneis bombus Ehrenberg D. smithii (Brébisson in W.Smith) Cleve + + Grammatophora spp Hemiaulus bipons (Ehrenberg) Grunow in Van Heurck Hemidiscus spp. Hyalodiscus obsoletus Scheschukova-Poretzkaja 1 + Kisseleviella carina Scheschukova-Poretzkaja Koizumia adaroi (Azpeitia) Yanagisawa Macrora stella (Azpeitia) Hanna + Mediaria magna Yanagisawa M. splendida f. splendida Scheschukova-Poretzkaja M. splendida f. tenera Schrader Melosira spp Neodelphineis pelagica Takano Nitzschia challengeri Schrader N. heteropolica Schrader 1 Odontella aurita (Lyngbye) Agardh Paralia sulcata (Ehrenberg) Cleve Pseudodimerogramma elliptica Schrader in Schrader et Fenner Pyxilla spp. Raphidodiscus marylandicus Christian Rhabdonema spp Rhaphoneis elegans (Pantocsek) Hanna R. paralis Hanna Rhizosolenia hebetata Bailey R. miocenica Schrader R. styliformis Brightwell 1 + Rouxia spp. + Stellarima microtrias (Ehrenberg) Hasle et P.A.Sims + + Stephanopyxis turris (Greville et Arnott) Ralfs in Pritchard S. spp. 1 Thalassionema nitzschioides (Grunow) Mereschkowsky T. spp. Thalassiosira grunowii Akiba et Yanagisawa T. leptopus (Grunow in Van Heurck) Hasle et G.A.Fryxell + T. cf. leptopus (Grunow in Van Heurck) Hasle et G.A Fryxell T. manifesta Scheschukova-Poretzkaja T. cf. marujamica Scheschukova-Poretzkaja T. mizunamiensis Yanagisawa T. cf. nidulus (Tempére et Brun in Brun et Tempére) Jousé + T. spp. + + Thalassiothrix longissima Cleve et Grunow in Grunow Triceratium condecorum Ehrenberg Total of valves counted Nonmarine diatoms Resting spores of Chaetoceros

11 Diatoms from the Oidawara Fm. 27

12 28 Keita Kawamura et al. 20 cm 2 km Fig. 1 4 m Fig. 5 2 m 100 m Fig Fig Akiba Chaetoceros 100 present + Tables 1, present SHK Figs 6 42, Table 1 Thalassionema nitzschioides Grunow Mereschk % Denticulopsis lauta Bailey Simonsen 13 40% D. ichikawae Yanagisawa et Akiba 0 27% Fig. 4 Cavitatus exiguus Yanagisawa et Akiba C. jouseanus Schesh.-Por. D.M.Williams 0 10% Yanagisawa 1994 Mediaria magna Yanagisawa M. splendida f. splendida f. tenera 1% 86 cod Figs 6 42, Table 2 Fig. 5 Figs Fossil diatoms from the Oidawara Formation in the Mizunami area. Figs 6, 7. Mediaria magna Yanagisawa, sample SHK-16 same specimen in different focus. Figs 8, 9. Mediaria splendida f. splendida Shesh.-Por., sample cod-6 same specimen in different focus. Figs 10, 11. Denticulopsis lauta Bailey Simonsen, sample cod-23 same specimen in different focus. Figs 12, 13. Denticulopsis ichikawae Yanagisawa et Akiba, sample SHK-46D same specimen in different focus. Fig. 14. Thalassiosira mizunamiensis Yanagisawa, sample SHK-46D. Figs 15, 16. Cavitatus exiguus Yanagisawa et Akiba, sample SHK-12s same specimen in different focus. Figs 17, 18. Cavitatus jouseanus Shesh.-Por. D.M.Williams, sample SHK-1s same specimen in different focus. Figs 19, 20. Cavitatus linearis Shesh.-Por. Akiba et Yanagisawa, sample cod-62 same specimen in different focus. Fig. 21. Cavitatus miocenicus H.-J.Schrad. Akiba et Yanagisawa, sample SHK-46D. Figs 22, 23. Thalassiosira cf. yabei Kanaya Akiba et Yanagisawa, sample SHK-16 same specimen in different focus. Fig. 24. Coscinodiscus lewsianus Grev., sample cod-71. Figs Fossil diatoms from the Oidawara Formation in the Mizunami area. Fig. 25. Actinocyclus ingens Rattray, sample SHK-16. Fig. 26. Actinoptychus senarius (Ehrenb.) Ehrenb., sample SHK-16. Fig. 27. Eunotia sp., sample SHK-13. Fig. 28. Actinoptychus splendens (Shadbolt) Ralfs ex A.Pritch., sample SHK-46D. Fig. 29. Asteromphalus sp., sample cod-19. Fig. 30. Cymatosira cf. lorenziana Grunow, sample cod-26. Fig. 31. Macrolla stella (Azpeitia) Hanna, sample cod-65. Fig. 32. Neodelphineis pelagica Takano, sample cod-85. Figs 33, 34. Grammatophora spp., sample SHK-13. Fig. 35. Gemellodiscus cingulus var. longus Suto (fossil resting spore of Chaetoceros), sample cod-57. Fig. 36. Thalassionema nitzschioides (Grunow) Van Heurck, sample SHK-36. Fig. 37. Pyxilla sp., sample cod-85. Fig. 38. Paralia sulcata (Ehrenb.) A.Cleve, sample SHK-17. Fig. 39. Dispinodiscus pilusus var. pilusus Suto (fossil resting spore of Chaetoceros), sample cod-57. Fig. 40. Liradiscus bipolaris Lohman (fossil resting spore of Chaetoceros), sample cod-57. Fig. 41. Delphineis miocenica (H.-J.Schrad.) G.W.Andrews., sample SHK-16. Fig. 42. Stephanopyxis turris (Grev. et Arn.) Ralfs in A.Pritch., sample SHK-46D.

13 Diatoms from the Oidawara Fm. 29

14 30 Keita Kawamura et al. Fig. 43. Ranges of stratigraphically useful diatoms in the early to middle Miocene of the middle- to high latitude North Pacific. The Oidawata Formation is assigned to the shaded time interval in the lower part of the Denticulopsis lauta Zone NPD4A. Ages of diatom zones and biohorizons of Akiba 1986, Yanagisawa & Akiba 1998 and Watanabe & Yanagisawa 2005 are reevaluated based on the geomagnetic polarity time scale of Gradstein et al FO: first occurrence, LO: last occurrence, LCO: last common occurrence, Ma: megaannum million years before present.

15 Diatoms from the Oidawara Fm. 31 Denticulopsis lauta D. hyalina H.-J.Schrad. Simonsen Akiba 1886 Yanagisawa & Akiba 1998 NPD 4A D. lauta Fig. 43 D. ichikawae D. praelauta Akiba et Koizumi Actinocyclus ingens f. nodus Baldauf M.C.Whiting et H.-J.Schrad. D. praelauta D41; 15.8 Ma A. ingens f. nodus 15.7 Ma D. lauta NDP 4A Fig Yanagisawa Akiba et al Yanagisawa 1994 NPD 4A Hayashida Hayashida 1986 Hiroki & Matsumoto 1999, 2003 C5Bn1r Hiroki & Matsumoto 1999, 2003 Berggren et al Ma 2006 C5Br Fig. 43 Gradstein et al NPD 4A Denticulopsis lauta D41 D. praelauta Actinocyclus ingens f. nodus Ma 2 Akiba, F Middle Miocene to Quaternary diatom biostratigraphy in the Nankai Trough and Japan Trench, and modified Lower Miocene through Quaternary diatom zones for middle-to-high latitudes of the North Pacific. In: Kagami, H. et al. Initial Reports of the Deep Sea Drilling Project, U. S. Goverment Printing Office, Washington D. C. 87: Akiba, F., Hiramatsu, C. & Yanagisawa, Y A Cenozoic diatom genus Cavitatus Williams; an emended description and two new biostratigraphically useful species, C. lanceolatus and C. rectus from Japan. Bulletin of the National Science Museum, Tokyo, Series C 19: Berggren, W.A., Kent, D.V., Swisher III, C.C. & Aubry, M.-P A revised Cenozoic geochronology and chronostratigraphy. In: Berggren, W.A., et al. Geochronology, Time Scales and Global Stratigraphic Correlation, Society for Sedimentary Geology SEPM, Special Publication, 54: Gradstein, F., Ogg, J. & Smith, A A Geologic Time

16 32 Keita Kawamura et al. Scale, 589 pp. Cambridge University Press, Cambridge K Ar FT Hayashida, A Timing of rotational motion of Southwest Japan inferred from paleomagnetism of the Setouchi Miocene Series. Journal of Geomagnetism and Geoelectricity 38: Hiroki, Y. & Matsumoto, R Magnetostratigraphic correlation of Miocene regression-and-transgression boundaries in central Honshu, Japan. Journal of Geological Society of Japan 105: Hiroki, Y. & Matsumoto, R Correlation of Miocene Ma sequence boundaries in central Japan to major Antarctic glaciation events. Sedimentary Geology 157: In 4 pp V 1: : : In pp IGCP-114, National Working Group of Japan, : Saito, T Miocene planktonic foraminifera from Honshu, Japan. Science Reports of the Tohoku University, Second Series Geology 35: : : : : Sugiyama, K. & Furutani, H Middle Miocene radiolarians from the Oidawara Formation, Mizunami Group, Gifu Prefecture, central Japan. Bulletin of the Mizunami Fossil Museum 19: : Watanabe, M. & Yanagisawa, Y Refined early to middle Miocene diatom biochronology for the middle- to high-latitude North Pacific. Island Arc 14: Yanagisawa, Y Thalassiosira mizunamiensis Yanagisawa sp. nov., a new fossil Thalassiosira species from the early Middle Miocene Oidawara Formation in Mizunami area, central Japan. Diatom 8: Yanagisawa, Y Mediaria magna Yanagisawa, sp. nov., a new fossil raphid diatom species useful for Middle Miocene diatom biostratigraphy. Transaction and Proceedings of the Palaeontological Society of Japan, New Series 174: In pp Yanagisawa, Y. & Akiba, F Refined Neogene diatom biostratigraphy for the northwest Pacific around Japan, with an introduction of code numbers for selected diatom biohorizons. Journal of the Geological Society of Japan 104: