15:30 〜 15:45
[SCG52-16] 深層学習に基づくイクチオリス画像検出システムを用いた南鳥島レアアース泥の化学層序の年代制約
キーワード：イクチオリス、生層序、化学層序、深海堆積物、深層学習、レアアース泥
In recent years, the demand for rare-earth elements and yttrium (REY) has increased globally with the promotion of renewable energy and the spread of electric vehicles. As a new promising resource for these industrially critical elements, Kato et al. [1] discovered deep-sea sediments enriched in REY, or REY-rich mud, in the Pacific Ocean. Furthermore, Takaya et al. [2] estimated that several hundred times the annual world demand for REY lie in the promising area of about 2,500 km2 in the southern part of Japan's exclusive economic zone (EEZ) around Minamitorishima Island.
Tanaka et al. [3] established a chemostratigraphy based on multi-elemental features in bulk chemical composition of 49 sediment cores collected in the area, resulting in a classification of the sediments into five units and three REY peaks. This chemostratigraphy enabled the apparently homogeneous pelagic clay layers including REY-rich mud to be correlated with each other.
To decipher the entire depositional history of the Minamitorishima REY-rich mud, age-determination of each chemostratigraphic unit is essential. However, the depositional ages of each chemostratigraphic unit remain poorly constrained. The common dating methods such as siliceous and calcareous microfossil biostratigraphy or palaeomagnetic stratigraphy are hardly to be applied to the REY-rich mud, or barren pelagic clay in lithology, due to a great water depth that dissolves most fossils and a low sedimentation rate that obscures geomagnetic polarity reversals. For this reason, it has not even been verified whether each chemostratigraphic unit in this area were temporally coincident with one another or not.
The only biostratigraphy that can be applied to REY-rich mud is the ichthyolith stratigraphy. Ichthyolith is a type of microfossils composed of fish teeth and denticles [4]. They consist of calcium phosphate that is less dissolvable than carbonate or silica (biogenic opal), resulting in being well preserved in pelagic clay [5]. In order to efficiently determine the depositional ages of pelagic clay, Mimura et al. [6] recently established a method to automatically detect ichthyoliths in microscopic images using a deep learning technique. We applied this method to several cores collected from the Minamitorishima EEZ to examine the depositional ages of the chemostratigraphic units. The preliminary results will be discussed in the presentation.
References: [1] Kato et al. (2011) Nature Geoscience 4, 535-539. [2] Takaya et al. (2018) Scientific Reports 8, 5763. [3] Tanaka et al. (2020) Ore Geology Reviews 119, 103392. [4] Doyle and Riedel (1985) Init. Repts. DSDP 86, 349-366. [5] Sibert and Norris (2015) Proceedings of the National Academy of Sciences 112(28), 8537-8542. [6] Mimura et al. (2022) Applied Computing and Geosciences 16, 100092.
Tanaka et al. [3] established a chemostratigraphy based on multi-elemental features in bulk chemical composition of 49 sediment cores collected in the area, resulting in a classification of the sediments into five units and three REY peaks. This chemostratigraphy enabled the apparently homogeneous pelagic clay layers including REY-rich mud to be correlated with each other.
To decipher the entire depositional history of the Minamitorishima REY-rich mud, age-determination of each chemostratigraphic unit is essential. However, the depositional ages of each chemostratigraphic unit remain poorly constrained. The common dating methods such as siliceous and calcareous microfossil biostratigraphy or palaeomagnetic stratigraphy are hardly to be applied to the REY-rich mud, or barren pelagic clay in lithology, due to a great water depth that dissolves most fossils and a low sedimentation rate that obscures geomagnetic polarity reversals. For this reason, it has not even been verified whether each chemostratigraphic unit in this area were temporally coincident with one another or not.
The only biostratigraphy that can be applied to REY-rich mud is the ichthyolith stratigraphy. Ichthyolith is a type of microfossils composed of fish teeth and denticles [4]. They consist of calcium phosphate that is less dissolvable than carbonate or silica (biogenic opal), resulting in being well preserved in pelagic clay [5]. In order to efficiently determine the depositional ages of pelagic clay, Mimura et al. [6] recently established a method to automatically detect ichthyoliths in microscopic images using a deep learning technique. We applied this method to several cores collected from the Minamitorishima EEZ to examine the depositional ages of the chemostratigraphic units. The preliminary results will be discussed in the presentation.
References: [1] Kato et al. (2011) Nature Geoscience 4, 535-539. [2] Takaya et al. (2018) Scientific Reports 8, 5763. [3] Tanaka et al. (2020) Ore Geology Reviews 119, 103392. [4] Doyle and Riedel (1985) Init. Repts. DSDP 86, 349-366. [5] Sibert and Norris (2015) Proceedings of the National Academy of Sciences 112(28), 8537-8542. [6] Mimura et al. (2022) Applied Computing and Geosciences 16, 100092.