Changing Abundance of Magnetofossil Morphologies in Pelagic Red Clay Around Minamitorishima, Western North Pacific

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  • Yoichi Usui
    Department of Deep Earth Structure and Dynamics Research Japan Agency for Marine‐Earth Science and Technology (JAMSTEC) Yokosuka Kanagawa Japan
  • Toshitsugu Yamazaki
    Research and Development Center for Submarine Resources, JAMSTEC Yokosuka Kanagawa Japan
  • Masafumi Saitoh
    Research and Development Center for Submarine Resources, JAMSTEC Yokosuka Kanagawa Japan

書誌事項

公開日
2017-12
資源種別
journal article
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1002/2017gc007127
公開者
American Geophysical Union (AGU)

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説明

<jats:title>Abstract</jats:title><jats:p>Recent investigations have discovered an unexpected abundance of magnetofossils in oxic pelagic red clays. These have potential to serve as paleoenvironmental tracers in otherwise nonfossiliferous sediments. Here, we report on variations in the abundance and morphology of magnetofossils in red clay from the western North Pacific. Magnetic measurements revealed that magnetofossils dominate the magnetic mineral assemblage of the sediments. An endmember analysis of isothermal remanent magnetization acquisition curves, supplemented by an analysis of S ratios, indicates that the magnetic assemblage can be unmixed into three endmembers, two corresponding to magnetofossils and one to terrigenous magnetic minerals. Direct counting of magnetofossil morphologies under a transmission electron microscope shows that the two magnetofossil endmembers differentiate equant magnetofossils and bullet‐shaped magnetofossils, respectively. The stratigraphic variation of the endmember contributions revealed that the equant magnetofossils are dominant for the most part, while an interval at around 7 m in core depth shows higher abundance of the bullet‐shaped magnetofossils. This may reflect enhanced organic carbon flux to the sediments. The organic carbon content is low throughout the sediments, and it does not show any change corresponding to the increase of bullet‐shaped magnetofossils, pointing at extensive remineralization of the organic carbon. On the basis of lithostratigraphic correlation to nearby drilling sites, we tentatively estimate the age of the bullet‐shaped magnetofossil increase as sometime between ∼75 and 25 Ma. These results suggest that environmental information can be obtained from magnetofossils in pelagic red clay.</jats:p>

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