Japan Geoscience Union Meeting 2015

Presentation information


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

[M-IS34] Paleoclimatology and paleoceanography

Wed. May 27, 2015 4:15 PM - 6:00 PM 301A (3F)

Convener:*Kazuyoshi Yamada(Museum of Natural and Environmental history, Shizuoka), Minoru Ikehara(Center for Advanced Marine Core Research, Kochi University), Tomohisa Irino(Faculty of Environmental Earth Science, Hokkaido University), Akira Oka(Atmosphere and Ocean Research Institute, The University of Tokyo), Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University), Ikuko Kitaba(Research Centre for Palaleoclimatology, Ritsumeikan University), Akihisa Kitamura(Institute of Geosciences, Faculty of Science, Shizuoka University), Masaki Sano(Research Institute for Humanity and Nature), Takeshi Nakagawa(Ritsumeikan University), Akira Hayashida(Department of Environmental Systems Science, Doshisha University), Chair:Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University)

5:15 PM - 5:18 PM

[MIS34-P01] Paleoenvironmental changes in NW Panthalassa through the Toarcian OAE: Stratigraphy and geochemistry of the Toyora area

3-min talk in an oral session

*Kentaro IZUMI1, David KEMP2 (1.Center for Environmental Biology and Ecosystem Studies, NIES, 2.Department of Geology and Petroleum Geology, University of Aberdeen)

The early Toarcian (Early Jurassic) oceanic anoxic event (T-OAE) was a significant palaeoenvironmental perturbation that led to marked changes in ocean chemistry and climate, and which also had a severe impact on marine ecosystems. In addition, this event is characterized by the widespread occurrence of a ~3?7‰ negative excursion in the carbon-isotope (δ13C) composition of marine organic and inorganic matter and terrestrial plant material. This feature of the event indicates a pronounced perturbation to the global carbon cycle. Despite such global impacts of the event, the precise palaeoenvironmental changes during the event from sections outside of the Boreal and Tethys realms are uncertain. Thus, to resolve this issue and further expand our understanding of the nature of the event, here we investigated the Nishinakayama Formation of the Toyora area, southwest Japan, which represents shallow-marine strata deposited at the northwestern margin of the Panthalassa Ocean. First, we established high-resolution carbon-isotope chemostratigraphy. A characteristic δ13C negative excursion was recognized around the middle part of the Nishinakayama Formation, allowing accurate international correlation. Then, we carried out geochemical analyses to reconstruct palaeoenvironmental conditions at the northwestern Panthalassic margin. Our results indicate that in the studied succession, organic-matter enrichment persisted through the early Toarcian, but elemental redox proxies and ichnofabrics do not support persistent bottom-water anoxia through the δ13C excursion. Analysis of terrigenously derived major and trace element abundances and palynology, coupled with sedimentological observations, revealed an increase in coarse-grained sediment, phytoclast size, and terrestrial organic-matter close to the onset of the δ13C negative excursion. These lines of evidence potentially suggest a marked strengthening of detrital sediment flux and hence hydrological cycling and continental weathering. This is consistent with previously published evidence from Boreal and Tethys realms.