Japan Geoscience Union Meeting 2014

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Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS30_28PM2] Paleoclimatology and paleoceanography

Mon. Apr 28, 2014 4:15 PM - 6:00 PM 501 (5F)

Convener:*Kazuyoshi Yamada(School of Human Sciences, Waseda University), Minoru Ikehara(Center for Advanced Marine Core Research, Kochi University), Tomohisa Irino(Faculty of Environmental Earth Science, Hokkaido University), Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University), Ikuko Kitaba(Kobe University Research Center For Inland Seas), Akihisa Kitamura(Institute of Geosciences, Faculty of Science, Shizuoka University), Masaki Sano(Research Institute for Humanity and Nature), Ryuji Tada(Department of Earth and Planetary Science, Graduate School of Science, The Univeristy of Tokyo), Masakazu Yoshimori(Atmosphere and Ocean Research Institute, University of Tokyo), Chair:Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University)

5:30 PM - 5:45 PM

[MIS30-22] Paleoceanographic evolution of Miocene to Pliocene mud sea in the Ryukyus based on calcareous nannofossil assemblages

*Ryo IMAI1, Tokiyuki SATO2, Yasufumi IRYU1 (1.Institute of Geology and Paleontology, Graduate School of Science, Tohoku University, 2.Institute of Applied Earth Sciences, Faculty of Engineering and Resource Science, Akita University)

Keywords:calcareous nannofossil, Miocene, Pliocene, Ryukyu Islands

The Cenozoic sedimentary succession in Okinawa-jima, including the upper Miocene to Pleistocene siliciclastic deposits (Shimajiri Group) and the Pleistocene reef to shelf deposits (Ryukyu Group), suggests a drastic paleoceanographic change from a mud sea to a coral sea. To delineate the paleoceanographic evolution of the mud sea, we quantified the stratigraphic distribution of the calcareous nannofossil assemblages from the Shimajiri Group in a 2119.49 m-deep well (Nanjo R1 Exploratory Well) drilled in southern Okinawa-jima (Ryukyu Islands, southwestern Japan). Four late Miocene and Pliocene datum planes were found in the studied interval. The calcareous nannofossil assemblages suggest the existence of oligotrophic conditions between 5.3 and >8.3 Ma followed by eutrophic conditions and a return to oligotrophic conditions at 3.5 Ma. Micropaleontological evidence suggests that these oceanographic changes were likely caused by local tectonic movement (shallowing of the sedimentary basin in which the Shimajiri Group was deposited). We will report calcareous nannofossil records from two exploratory wells drilled in southern Okinawa-jima in 2013–2014 as well.