JpGU-AGU Joint Meeting 2017

Presentation information

[EJ] Oral

B (Biogeosciences) » B-PT Paleontology

[B-PT05] [EJ] Decoding the history of Earth: From Hadean to Modern

Wed. May 24, 2017 10:45 AM - 12:15 PM 201B (International Conference Hall 2F)

convener:Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Chairperson:Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo)

11:15 AM - 11:30 AM

[BPT05-21] Origin of deep-sea sediments within the Minamitorishima EEZ based on downhole variation of bulk chemical composition and neodymium isotopic ratios

*Erika Tanaka1, Kazutaka Yasukawa1,2, Kentaro Nakamura1, Takashi Miyazaki3, Bogdan S Vaglarov3, Koichiro Fujinaga2,1, Hikaru Iwamori3,4, Yasuhiro Kato5,1,2,3 (1.Sys. Innovation, Univ. of Tokyo, 2.Chiba Institute of Technology, 3.JAMSTEC, 4.Dept. of Earth and Planetary Sciences, TITECH, 5.FRCER, Univ. of Tokyo)

Keywords:Nd isotopes, Chemostratigraphy, Deep-sea Sediments, Minamitorishima EEZ, REY-rich mud

In 2011, the deep-sea sediments containing a high concentration of rare-earth elements and yttrium (REY) were discovered in the Pacific Ocean [1]. Moreover, the presence of "highly/extremely REY-rich mud" was confirmed within the Japanese exclusive economic zone (EEZ) surrounding Minamitorishima Island in 2013 [2].
On the basis of geochemical characteristics in major- and trace-elemental composition, it was reported that the deep-sea sediment layers within the Minamitorishima EEZ can be classified into several distinct groups including the highly/extremely REY-rich mud, although they are apparently very similar pelagic brown clay [3]. However, the origin and formation mechanism of the highly/extremely REY-rich mud has not been completely unraveled yet.
To elucidate the origin of deep-sea sediment including REY-rich mud within the Minamitorishima EEZ, isotopic composition of neodymium (one of the rare-earth elements), together with major and trace element compositions, can provide an important constraint. We aim to decipher geochemical end-members characterized by distinctive chemical compositions and isotopic ratios that enable us to specify their sources, fluxes and processes of supply [4, 5]. Here, we investigated (1) bulk chemical compositions by XRF and ICP-MS analyses and (2) bulk Nd isotopic ratios using Thermal Ionization Mass Spectrometry (TIMS) throughout a piston core, KR13-02 PC05 of 11.45 m in length, which contains the Extremely REY-rich mud and the other several characteristic layers. We report the downhole variations of bulk chemical composition and neodymium isotopic ratios, and discuss the origin of the highly/extremely REY-rich mud on the basis of their geochemical features.

[1] Kato et al. (2011) Nature Geoscience 4, 535-539.
[2] Iijima et al. (2016) Geochemical Journal 50, 557-573.
[3] Nakamura et al. (2016) JpGU2016
[4] Goldstein, O’Nion and Hamilton (1984) Earth and Planetary Science Letters 70,221-236.
[5] Grousset and Biscaye (2005) Chemical Geology 222, 149-167.