[B-CG07] Decoding the history of Earth: From Hadean to the present

[BCG07-11] Composite ages of REE-rich mud in the western North and South Pacific Ocean

*Erika Tanaka¹, Kazuhide Mimura², Junichiro Ohta³, Takashi Miyazaki⁴, Bogdan Stefanov Vaglarov⁴, Kazutaka Yasukawa³, Kentaro Nakamura³, Yasuhiro Kato³ (1.Kochi University, 2.Chiba Institute of Technology, 3.The University of Tokyo, 4.JAMSTEC)

Keywords:Pelagic clay, REE-rich mud, Ichthyolith biostratigraphy, Sr isotope stratigraphy, Chemostratigraphy

Deep-sea sediments containing a high concentration of rare-earth elements (REE), termed REE-rich mud, are widely distributed in the North and South Pacific [1]. The REE-rich mud has been stimulating our interest as a new promising mineral resource for REE as well as media recording the past climate and oceanic environments [2]. The REE-rich mud is generally categorized into “pelagic clay” in terms of lithology, whose age assignment is quite difficult. Common biostratigraphic methods using microfossils could not perfectly determine the depositional age of pelagic clay, because calcareous and siliceous microfossils rarely occur in it [3]. In addition, it often contains erosions and hiatus without any visible features [4], and thus, magnetostratigraphy can constrain the age intervals for only up to several million years [5, 6]. Therefore, to discuss the formation mechanism of REE-rich mud and the recorded environmental information, we need to establish a precise dating method for pelagic clay.
Here, we applied ichthyolith biostratigraphy, fish-teeth Sr isotope stratigraphy, and chemostratigraphy using bulk chemical compositions to three drilling cores composed of pelagic clay: Ocean Drilling Program Hole 777B, and Integrated Ocean Discovery Program Holes U1366C and U1370D, in the western North and South Pacific Ocean, respectively. All of them contain the REE-rich mud. In this study, we constrain the formation ages of the REE-rich mud based on their composite ages.

[1] Kato, Y. et al. (2011) Nature Geoscience, 4, 535–539. [2] Ohta, J. et al. (2020) Scientific Reports, 10, 9896. [3] Doyle, P. S. & Riedel, W. R. (1979) Micropaleontology, 25, 337–364. [4] Tanaka et al. (2020) Ore Geology Reviews, 119, 103392. [5] Asahara, Y. (1999) Earth and Planetary Science Letters, 171, 453–464. [6] Usui, Y. & Yamazaki, T. (2021). Earth, Planets and Space, 73, 2.