Characteristics in trace elements compositions of tephras (B-Tm and To-a) for identification tools

Nara, Fumiko*; Yokoyama, Tatsunori; Yamasaki, Shinichi*; Minami, Masayo*; Asahara, Yoshihiro*; Watanabe, Takahiro; Yamada, Kazuyoshi*; Tsuchiya, Noriyoshi*; Yasuda, Yoshinori*

Geochemical Journal, 55(3), p.117 - 133, 2021/00

https://doi.org/10.2343/geochemj.2.0619

The absolute date of the Millennium Eruption (ME) of Changbaishan Volcano is widely recognized as AD 946. The Baegdosan-Tomakomai (B-Tm) tephra dispersed during the ME is a robust-age key bed. In order to identify the tephra, refractive index and major-element compositions of volcanic glass shards are conventionally used. However, trace-element analysis has been rarely carried out, especially for rare-earth elements (REEs) and for tephra layer bulk sediments. Here we present the datasets of major- and trace-element compositions datasets for the glass shards and bulk sediments of the B-Tm and Towada caldera eruptions (To-a) tephra deposits from the Lake Ogawara sediment core, Tohoku region, northern Japan. The depth profiles of the major and trace elements show the significant peaks for the KO and some trace elements (Zn, Rb, Zr, Nb, Sn, Y, La, Ce, Nd, Th, and U) at the B-Tm tephra layer in the Lake Ogawara sediment core, but no peaks of these elements at the To-a tephra layer. High concentrations of the trace elements in the B-Tm tephra layer were observed in individual glass shards as well as in the bulk sediment. These concentrations are highlighted by the elemental abundance pattern normalized by the crustal abundance. The elemental pattern in individual glass shards from other Japanese tephras showed significant differences from those of the B-Tm tephra, especially in REEs compositions. The trace-element compositions of the glass shards and bulk sediment show strong advantages for distinguishing the B-Tm tephra from other Japanese tephras.

A Geochemical approach for identifying marine incursions; Implications for tsunami geology on the Pacific coast of northeast Japan

Watanabe, Takahiro; Tsuchiya, Noriyoshi*; Yamasaki, Shinichi*; Sawai, Yuki*; Hosoda, Norihiro*; Nara, Fumiko*; Nakamura, Toshio*; Komai, Takeshi*

Applied Geochemistry, 118, p.104644_1 - 104644_11, 2020/07

https://doi.org/10.1016/j.apgeochem.2020.104644

Possible tsunami inundation areas can be predicted from the distribution of paleo tsunami deposits, which are mainly composed of marine-derived sands and muds on land. Such exotic sandy and muddy layers have been identified by multiple approaches. However, there still remain uncertainties and other useful proxies need to be investigated for the identification of tsunami deposits. Here we show the geochemical signatures of modern tsunami deposits from the Pacific coast of Northeast Japan (2011 Tohoku tsunami), as well as those paleo tsunami deposits, which were taken from the Tohoku District (Jogan, ca. 1080 calibrated ages before present [cal BP] and Yayoi, ca. 2000 cal BP). A geochemical ternary diagram (Seawater-Rock-(As+Metals)) enables the weathering trend of tsunami deposits over ca. 2000 years in the Sendai Plain in the Tohoku to be shown. In the paleo tsunami layers from the Tohoku, the Na/Ti atomic ratios markedly increased to 23.4, and the average values were 19.33.0 (Jogan and Yayoi tsunami deposits), which were clearly higher than those of other layers (soil deposits, 10.33.5 on average). These results show that the Na/Ti ratio is a useful indicator of marine incursions in our case. Our rapid and simple method using the Na/Ti ratio can be easily applied to the Tohoku, and it may contribute to the detection of unrecorded muddy tsunami deposits.

Microstructural assessment of damaged materials in FBR assessment of creep damage in weldment

Momma, Yoshio*; *; ; ; ; Aoto, Kazumi

JNC TN9400 2000-044, 22 Pages, 2000/03

JNC-TN9400-2000-044.pdf:1.37MB

ln the past the microstructural observation was mostly applied to understand the materials behavior qualitatively in R&D of the new materials and the life prediction for the fast breeder reactor components. However, the correlation between the changes in properties and microstrutures must be clarified to ensure the structural integrity. Particularly we are interested in the method to correlate the long-term properties and microstructural changes at high temperatures. The current research is to quantify the changes in microstructure of the weld metal for the welded structure of the reactor vessel. ln this research we have conducted creep testing of the weld metals at 823 and 873K up to 37,000h. Two types of the weld metals (16Cr-8Ni-2Mo and 18Cr-12Ni-Mo) were subjected to the creep testing. Based on the areas of the precipitates, the microstructural characterization with time and creep damage was attempted. The creep strength of the 16Cr-8Ni-2Mo weld metal is lower than that of the 18Cr-12Ni-Mo one at higher stresses, shorter times. But there is a trend toward to become similar strength with lower stresses and increasing times. The creep-rupture ductility of the 16Cr-8Ni-2Mo weld metal is superior to that of the 18Cr-12Ni-Mo one. The creep-rupture takes place at the interface of the sigma () phases precipitated in the delta () ferrites at 823K lower stresses and 873K. The amount of precipitates in the 16Cr-8Ni-2Mo weld metal is smaller than that in the 18Cr-12Ni-Mo one at each temperature and stress. Also it is apparent that the amount of the precipitates is primarily responsible to the decomposition of the phase, because the amount of the residual ferrites measured by the Magne-Gauge reduces with times. Using the Larson-Miller parameter it was possible to correlate the amount of the precipitates linearly with the LMP values.

Current status of the new polarized neutron reflectometer (SHARAKU) at J-PARC, and prospects for study on multilayers

Kubota, Masato; Takeda, Masayasu; Yamazaki, Dai; Hayashida, Hirotoshi; Maruyama, Ryuji; Soyama, Kazuhiko; Asaoka, Hidehito; Yamazaki, Tatsuya; Sakasai, Kaoru; To, Kentaro; et al.

no journal, , 

no abstracts in English

The Millennium scale monsoon cycles recorded in a sediment core from alpine Tibetan lake

Watanabe, Takahiro; Nara, Fumiko*; Matsunaka, Tetsuya*; Minoura, Koji*; Kakegawa, Takeshi*; Yamasaki, Shinichi*; Tsuchiya, Noriyoshi*; Nakamura, Toshio*; Junbo, W.*; Liping, Z.*

no journal, , 

Understanding of past environmental and geochemical changes is significant issues to estimate global climate variation. Therefore, these changes have been studied by continuous terrestrial sediments. The high-time resolution past environmental changes, especially monsoon fluctuations, have been reported in previous studies using geochemical signatures in stalagmites from Asian caves. However, continuous climate records in Tibetan plateau have not yet been cleared, which a key area to understand mechanism of monsoon fluctuations. In this study, mean grain size and geochemical proxies from lake sediment cores from south Tibetan plateau were used for estimation of past monsoon changes during Holocene. Spectral analysis of the mean grain size in the Tibetan lake indicated 1000-1500 years climate cycles, which might be caused by the changes in solar activities. These monsoon fluctuations based on the mean grain size were also supported by geochemical proxies in this study.

Estimation of the age with the brackish lake environmental changes using continuous sediment core samples from Lake Ogawara

Nara, Fumiko*; Matsunaka, Tetsuya*; Yamasaki, Shinichi*; Tsuchiya, Noriyoshi*; Watanabe, Takahiro; Yamada, Kazuyoshi*; Yasuda, Yoshinori*

no journal, , 

Lake Ogawara, which is the brackish lake in Aomori prefecture, northern Japan, has been formed by the sea level change. Although the lake formation period is roughly estimated at the late Jomon period, the precise formation period is still unclear. The Lake Ogawara formation is directly connected with the sea level change, therefore, determination of the precise formation period of the Lake Ogawara is very important to understand the sea level history during the Jomon period. In this study, we constructed the precise age model based on the radiocarbon (C-14) for the plant residues and total organic carbon (TOC), Cs-137, Pb-210 and tephra identify in the Lake Ogawara sediment core. Two visible tephras (the Baegdosan-Tomakomai: B-Tm and Towada carudera eruption: To-a) were observed in the sediment core. Since the absolute age of the Millennium Eruption (ME) of Changbaishan volcano is widely accepted as AD 946, the B-Tm tephra in the sediment core can be used as the precice chronological key bed layer. Age profile of the trace element (Br), which was derived from the sea water, in the core showed that the Lake Ogawara started to change to the brackish lake at around 2000 cal BP.