11:30 〜 11:45
[BPT05-22] 全岩化学組成に基づく北太平洋の遠洋性深海堆積物層序
キーワード：遠洋性粘土、化学層序、レアアース泥、北太平洋、ODP Site 1149、ODP Site 1179
Pelagic clay, referred to as red clay, is one of the common types of seafloor sediment, especially in the Pacific Ocean floor [1]. It is known that the pelagic clay deposits at remote areas in the ocean with considerably slow sedimentation rates of only 0.1-0.5 cm/kyr. Recently, this type of sediment is also recognized as a new deep-sea mineral resource. In 2011, Kato et al. [2] reported that some parts of the deep-sea pelagic clay in the Pacific Ocean contain high concentrations of rare-earth elements and yttrium (REY). They defined the pelagic clay containing more than 400 ppm of total REY as “REY-rich mud” and concluded that this sediment could be a prospective resource for the critical elements.
Pelagic clay is, however, not so well studied as other types of sediments, such as carbonate and neritic sediments, probably due to the lack of visible features and little availability of microfossils to determine its depositional age. Therefore, detailed stratigraphy of the pelagic clay layers including REY-rich mud is not well understood, although it deposited throughout the Cenozoic era [3]. To clarify the stratigraphy of the pelagic clay layers including REY-rich mud, analyses of long and fully recovered deep-sea sediment cores are needed. Here we focused on the ODP Sites 1149 and 1179 in the North Pacific Ocean, both of which were recovered continuously from seafloor to basement rock.
In this study, we provide the results of bulk chemical analyses of sediment samples from the ODP cores. By comparing the multi-elemental compositions of these cores and those of GPC3-LL44 [4], we constructed a general chemostratigraphy of pelagic clay layers in the North Pacific Ocean. We also quantified the relative contributions of each geochemical end-member causing the chemostratigraphic variations of the pelagic clay layers. Based on the results, we discuss the deposition processes of pelagic clays including REY-rich mud in the North Pacific Ocean.
References
[1] Dutkiewicz et al. (2015) Geology 43, 795-798.
[2] Kato et al. (2011) Nature Geoscience 4, 535-539.
[3] Yasukawa et al. (2016) Scientific Reports 6, 29603.
[4] Kyte et al. (1993) Geochemica et Cosmochimica Acta 57, 1719-1740.
Pelagic clay is, however, not so well studied as other types of sediments, such as carbonate and neritic sediments, probably due to the lack of visible features and little availability of microfossils to determine its depositional age. Therefore, detailed stratigraphy of the pelagic clay layers including REY-rich mud is not well understood, although it deposited throughout the Cenozoic era [3]. To clarify the stratigraphy of the pelagic clay layers including REY-rich mud, analyses of long and fully recovered deep-sea sediment cores are needed. Here we focused on the ODP Sites 1149 and 1179 in the North Pacific Ocean, both of which were recovered continuously from seafloor to basement rock.
In this study, we provide the results of bulk chemical analyses of sediment samples from the ODP cores. By comparing the multi-elemental compositions of these cores and those of GPC3-LL44 [4], we constructed a general chemostratigraphy of pelagic clay layers in the North Pacific Ocean. We also quantified the relative contributions of each geochemical end-member causing the chemostratigraphic variations of the pelagic clay layers. Based on the results, we discuss the deposition processes of pelagic clays including REY-rich mud in the North Pacific Ocean.
References
[1] Dutkiewicz et al. (2015) Geology 43, 795-798.
[2] Kato et al. (2011) Nature Geoscience 4, 535-539.
[3] Yasukawa et al. (2016) Scientific Reports 6, 29603.
[4] Kyte et al. (1993) Geochemica et Cosmochimica Acta 57, 1719-1740.