Chemostratigraphic Correlations of Deep-Sea Sediments in the Western North Pacific Ocean: A New Constraint on the Distribution of Mud Highly Enriched in Rare-Earth Elements

Erika Tanaka,Kentaro Nakamura,Shiki Machida,Yasuhiro Kato,Koichiro Fujinaga,Koichi Iijima,Junichiro Ohta,Kazutaka Yasukawa,Tatsuo Nozaki,Kazuhide Mimura

doi:10.3390/min10060575

Abstract

Deep-sea sediments with total rare-earth elements and yttrium (ΣREY) concentrations exceeding 400 ppm, which are termed REY-rich mud, are widely distributed in the world oceans. Specifically, deep-sea sediments within the Japanese exclusive economic zone (EEZ) surrounding Minamitorishima Island in the western North Pacific have attracted significant attention as a new REY resource, because they contain REY-enriched layers exceeding 2000 ppm of ΣREY. However, neither the sediments deeper than 15 m below the seafloor (mbsf) nor those outside the Minamitorishima EEZ have ever been studied. Recently, a number of distinct geochemical features which are aligned in stratigraphic order were recognized in these sediments, based on multi-elemental composition data. Chemostratigraphy enables us to laterally correlate three REY peaks among apparently featureless pelagic clays. Here, we apply chemostratigraphic correlation to 19 new cores collected from the northern Pigafetta Basin and several small basins within the Marcus-Wake Seamounts. This study revealed that the REY-enriched layers occur at greater depths than the piston core length in a wider area than previously investigated (e.g., ~20.5 mbsf at Ocean Drilling Program Site 801A). This finding suggests that the depositional environments in these areas were basically similar, although local geographic conditions could have affected the continuity of REY peaks.

Highlights

Rare-earth elements and yttrium (REY) have unique magnetic and optical characteristics, and can be used to produce important industrial materials such as high-power permanent magnets and various fluorescent substances [1]
For the piston cores collected during Cruise MR16-07, REY peaks (ΣREY > 2000 ppm) were observed in only two cores: MR16-07 PC07 and PC10
The samples newly analyzed in this study showed distinct positive correlations on the ΣREY–P2 O5 and ΣREY–CaO diagrams, but not on the ΣREY–Fe2 O3 * diagram (Figure 4)

Summary

Introduction

Rare-earth elements and yttrium (REY) have unique magnetic and optical characteristics, and can be used to produce important industrial materials such as high-power permanent magnets and various fluorescent substances [1]. Nowadays, they are indispensable to various high- and green-tech products, including electric vehicles, wind power generators, and light-emitting diodes. Considering the long-term economic growth of emerging countries, the global demand for REY will increase over the coming decades. To satisfy the increasing demand, exploring for new sources is crucial [1,2]. Deep-sea sediments containing high concentrations of REY were reported by

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Discussion

Conclusion