14:45 〜 15:00
[MIS28-05] Os同位体比層序に基づく南鳥島周辺深海堆積物の複数のレアアース濃度ピークの堆積年代
キーワード：深海堆積物、レアアース、レアアース泥、南鳥島、年代決定、Os同位体比
Deep-sea sediments highly enriched in rare-earth elements and yttrium (REY), lying in the Japanese exclusive economic zone around Minamitorishima Island, are expected as a promising new resource for the industrially critical metals [1-4]. Multi-elemental chemostratigraphic correlation revealed that the deep-sea sediments around Minamitorishima Island have three distinct layers with >2000 ppm of total REY concentrations. These layers were named as the 1st, 2nd, and 3rd REY peaks from shallow to deep [4]. Using marine osmium isotope ratio (187Os/188Os), a previous study [5] revealed that the 1st REY peak was formed at 34.4 Ma and proposed that an enhanced northward flow of bottom water associated with the late Eocene event, a temporal expansion of Antarctic ice sheet, caused the upwelling of deep-ocean nutrients along with topographic highs, such as large seamounts. This upwelling could have stimulated the biological productivity and resulted in an increased fish productivity, leading to the substantial deposition of fish debris that accumulate REY on the seafloor [5].
In contrast to the detailed investigation of the 1st REY peak from a paleoceanographic perspective, the depositional ages and causes of the 2nd and 3rd REY peaks still remain uncertain. Here, we will report new results of the Os isotope analysis on the sediment samples from MR15-E01 PC07 core that clearly contains three REY peaks. The depositional ages of the REY peak of MR15-E01 PC07 core were estimated based on the osmium isotope stratigraphy. In the presentation, we will discuss the possible causes of the REY peaks based on their depositional ages.
[1] Kato et al. (2011) Nature Geoscience 4, 535-539. [2] Iijima et al. (2016) Geochemical Journal 50, 557-573. [3] Takaya et al. (2018) Scientific Reports 8, 5763. [4] Tanaka et al. (2020) Ore Geology Reviews 119, 103392. [5] Ohta et al. (2020) Scientific Reports 10, 9896.
In contrast to the detailed investigation of the 1st REY peak from a paleoceanographic perspective, the depositional ages and causes of the 2nd and 3rd REY peaks still remain uncertain. Here, we will report new results of the Os isotope analysis on the sediment samples from MR15-E01 PC07 core that clearly contains three REY peaks. The depositional ages of the REY peak of MR15-E01 PC07 core were estimated based on the osmium isotope stratigraphy. In the presentation, we will discuss the possible causes of the REY peaks based on their depositional ages.
[1] Kato et al. (2011) Nature Geoscience 4, 535-539. [2] Iijima et al. (2016) Geochemical Journal 50, 557-573. [3] Takaya et al. (2018) Scientific Reports 8, 5763. [4] Tanaka et al. (2020) Ore Geology Reviews 119, 103392. [5] Ohta et al. (2020) Scientific Reports 10, 9896.