Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*
JAEA-Testing 2021-001, 49 Pages, 2021/08
JAEA-Testing-2021-001.pdf:3.86MB
To make a contribution to safety assessment for geological disposal of high level radioactive and/or TRU waste, we need to assess long-term stability of geological environment and predict long-term changes of geotectonic events that will occur in the future, especially for Quaternary period (
2.6 million years ago-present). In the most case, we investigate chronological data of geological events by radiometric dating. When some geological samples have no objects to which radiometric dating method can be applied (e.g., zircon, biotite, wood fragments and plant residues), we can use tephrochronology, which is geological dating method using each layer of tephra (erupted volcanic ash), for dating of geological layers. This chronological method is essential in Japan, where volcanism is very active. Tephra is usually characterized by petrographic characteristics and/or chemical composition (mainly major elements) of volcanic glasses and/or minerals in tephra. In Tono Geoscience Center (Japan Atomic Energy Agency), we develop an analytical technique of chemical composition including trace elements of volcanic glasses for detailed tephra identification. In this paper, we report a sample preparation procedure and analytical methods of chemical compositions of individual volcanic glass shards by using an electron probe microanalyzer and a laser ablation-inductively coupled plasma-mass spectrometer.
Ueki, Tadamasa; Niwa, Masakazu; Yonaga, Yusuke
no journal, ,
no abstracts in English
Ueki, Tadamasa; Niwa, Masakazu; Yonaga, Yusuke; Iwano, Hideki*; Danhara, Toru*
no journal, ,
no abstracts in English
Kagami, Saya; Yokoyama, Tatsunori
no journal, ,
no abstracts in English
Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*
no journal, ,
Tephrochronology is one of the geochronological techniques for Quaternary and generally used as well as radiocarbon dating. A catalogue of wide-spread tephras provides fundamental criteria for the establishment of a regional chronostratigraphy. Tephras have been identified by petrographic characteristics, types of volcanic glass shards in tephra, and major elements compositions of them. Major element analyses of volcanic glass shards are usually carried out by EPMA. Recently, it has been reported that the some tephras which were quite similar to others in major element compositions were distinguishable by trace element compositions. Although trace element data of volcanic glass shards are important for tephra identification, the data are still lack in a catalogue of wide-spread tephras. To measure trace element abundances of the glass shards, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a powerful method because individual glass shards can be analyzed. In this study, we performed trace element analysis of tephras using LA-ICP-MS at Tono Geoscience Center, JAEA. We analyzed the concentration of 41 elements with the internal standard element of Si and two calibration standards of NIST SRM 612 and 614. Three tephra samples were prepared: Aso-4, Aira-Tn (AT), and Akogi (identified to Znp-Ohta) tephras. While a fused glass bead of Aso-4 was prepared, the others were mounted on epoxy resin. In Aso-4 and AT tephra samples, the concentrations of trace elements (Rb, Sr, Y, Zr, Ba, La, and Ce), by which tephras are especially identified, were consistent with those in the previous studies (RSD:10%). We obtained the pattern of trace element compositions of Akogi tephras, which was similar to that of Znp-Ohta tephras. This analytical method will contribute to establish the detailed catalogue of tephras.
Nishio, Gaku*; Kagami, Saya; Yokoyama, Tatsunori; Kariya, Yoshihiko*; Kojima, Satoru*
no journal, ,
We attempt to use local tephra derived from nearby volcanoes as an age marker. The Kamikochi area in the southern part of the Northern Alps is strongly affected by the Yakedake volcano. We prepared distinctive tephras, (1) one sample of glassy volcanic ash in hand auger boring cores drilled at the near-shore Kinugasanoike Pond, about 4.7 km northeast of Mt. Yakedake and (2) two samples of glassy volcanic ash in the Nakao pyroclastic flow deposites, which is considered to be a product of the last magmatic eruption about 2,300 years ago, distributed about 1.5 km north-northwest of Mt. Yakedake. We investigated the clast composition of these tephras and the chemical composition and refractive index of volcanic glass. Approximately 70% of the clasts were volcanic glasses, and most of them were vesicular and blocky types. These glasses were characterized by high SiO
, K
O, NaO and low AlO
, FeO, which were clearly distinguishable from the volcanic glasses in Quaternary widespread tephras. The refractive indices of 30 volcanic glasses for each tephra were 1.4958-1.5011 with a peak in the range of 1.497 to 1.499. The results of this study indicate the tephra from Kinugasanoike Pond were erupted from Mt. Yakedake about 2,300 years ago. Therefore, the tephra with the above characteristics can be used as a useful age marker for the southern part of the Northern Alps about 2,300 years ago.
Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*; Yasue, Kenichi*; Niwa, Masakazu; Furusawa, Akira*; Tamura, Itoko*
no journal, ,
Tephrochronology is important to understand geotectonic events for the last few Myr. Tephra is usually characterized by petrographic characteristics and chemical compositions (mainly major elements) of volcanic glass shards. When tephras similar in the characteristics are discriminated, trace element compositions are valid for identification of tephra. We focus on the enrichment of the database of trace elements compositions in widespread tephras, which is not reported enough. We used EPMA and LA-ICP-MS for major and trace element concentration of volcanic glass shards in Znp-Ohta tephra and Tng tephra, of which major elements similar to Znp-Ohta tephra. In this study, it was clear that Znp-Ohta tephra had zirconium concentration [Zr] = 44-58 ppm and Zr/Pb = 2.5-3.4, while Tng tephra had [Zr] = 70-81 ppm and Zr/Pb = 3.8-4.6. Znp-Ohta and Tng tephras were discriminated not only by characteristic type, Ba/La, and La/Y of glass shards (Tamura and Yamazaki, 2004) but also by Zr-Pb correlation. In the future, we compare the trace element concentrations of Znp-Ohta tephra in multiple sites for evaluation of secondary effect during the deposition.
Kagami, Saya; Yasue, Kenichi*; Nagata, Mitsuhiro; Yokoyama, Tatsunori; Tamura, Itoko*
no journal, ,
The Kurehayama Hills consist to the Pliocene-Pleistocene sedimentary layers, where the Znp-Ohta tephra was found. The Znp-Ohta tephra is one of the wide-spread tephras and an important Early Pliocene marker tephra. In this study, we reevaluated the tephrostratigraphy in the type locality of the Teramachi (Trm) tephra corresponded to the Znp-Ohta tephra in Kurehayama Hills. Observations of the outcrop in the type locality of the Trm tephra revealed three tephra layer 1), 2), and 3) in an ascending order, and gravel bed sandwiched between the layers 2) and 3). Based on tephra characteristics (major and trace element composition and refractive index of volcanic glass), it is most likely that the tephra units 1), 2) and 3) correlate with the Tsuribe1 (4.2 Ma), Znp-Ohta (3.9 Ma), and Taniguchi (2.2 Ma) tephras, respectively. Previously, the Znp-Ohta tephra had been only identified at the type locality of the Trm tephra. This study clarified that the tephra deposits from 4.2 to 2.2 Ma were overlying in this outcrop of several meters. In addition, no other outcrops have been found where three tephra layers could be continuously identified. The results in this study are important to understand the formation history of the Kurehayama Hills. Furthermore, the gravel bed was found between the tephra layer 2) and 3), and the age gap between these layers was 
1 Myr. This unconformity suggests that the Znp-Ohta tephra in this area was thicker than the currently deposited layer thickness. In the future, we plan to conduct zircon U-Pb dating for three tephra layers to determinate more precise age. The identification of absolute ages will contribute to improve chronological importance of these tephra as tephra marker in tephrochronology.
Komatsu, Tetsuya; Hongo, Misao*; Furusawa, Akira*; Tsukahara, Yuzuko; Kawamura, Makoto; Nishiyama, Nariaki; Kanno, Mizuho*; Yasue, Kenichi*
no journal, ,
Elucidating formation ages of marine terraces located higher than that correlated with Marine Isotope Stage (MIS) 5e, so-called higher marine terraces, is a key to understand the uplift rate over a period longer than ~100,000 years. To acquire knowledge about chronological limitation of higher marine terraces, we conducted a case study in the northern side of Nanao Bay, Noto Peninsula, where higher marine terraces are well-preserved in Japan. Cryptotephra and pollen analysis of terrace-forming material was carried out in a higher-marine terrace, previously correlated with MIS 13 estimated from its morphostratigraphical position. The results suggest that the higher marine terrace was created during an interglacial period before MIS 19, possibly MIS 21.