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Ebihara, Mitsuru*; Shirai, Naoki*; Osawa, Takahito; Yamaguchi, Akira*
Geochimica et Cosmochimica Acta, 389, p.200 - 210, 2025/01
Times Cited Count：14 Percentile：97.68(Geochemistry & Geophysics)The 15 elements including most major elements of 12 carbonaceous chondrites collected in Antarctica were quantified using neutron-induced prompt gamma-ray analysis. While some of these samples were observed to share affinities with CI or CM chondrites, they do not exhibit the same characteristics as the known CI or CM chondrites. As a result, a new group named "CY" has been proposed for these meteorites. Common among the 12 meteorites is the depletion of volatile elements H and chlorine, showing a correlation and being depleted compared to non-Antarctic CI levels. Based on the abundance of moderately volatile elements Mn and S, the 12 meteorites can be divided into two groups: one with levels similar to non-Antarctic CI and the other with intermediate levels between CI and CM. These results suggest that CY chondrites originate from distinct parent bodies (materials), and considering two different parent bodies (materials) is necessary.
Onoue, Tetsuji*; Sato, Honami*; Nakamura, Tomoki*; Noguchi, Takaaki*; Hidaka, Yoshihiro*; Shirai, Naoki*; Ebihara, Mitsuru*; Osawa, Takahito; Hatsukawa, Yuichi; Toh, Yosuke; et al.
Proceedings of the National Academy of Sciences of the United States of America, 109(47), p.19134 - 19139, 2012/11
Times Cited Count：50 Percentile：74.92(Multidisciplinary Sciences)The 34 million year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. As with the Chicxulub impact event at the Cretaceous/Paleogene boudary, the Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., the Triassic/Jurassic boundary). However, the causal link between these impact events and a mass extinction event in the Late Triassic remains controversial because of a lack of stratigraphic records of their ejecta deposits. Here we report evidence for an impact event (platinum group elements anomaly, nickel-rich magnetite and microspherules) deposited within a Paleo-Pacific basin in the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridium anomaly may be found on a global scale. The middle Norian age of the ejecta deposit suggests that the impact event that produced the 100-km-wide Manicouagan crater in Canada8 is most likely related to its deposition. Our analysis of siliceous microfossils shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine fossils. However, such an event has been reported among terrestrial tetrapods and floras in North America. We therefore hypothesize that the Manicouagan impact caused the catastrophic collapse of terrestrial ecosystems near the impact site, but not within the marine realm.
Osawa, Takahito; Shirai, Naoki*; Ebihara, Mitsuru*
no journal, ,
Asteroid Ryugu samples provided from JAXA were analyzed using the prompt gamma-ray analysis system (PGA) installed at JRR-3. This talk will present a preliminary report on the analysis results of the powder sample provided in the third international call for samples.
Inagaki, Makoto*; Takamiya, Koichi*; Miura, Tsutomu*; Washiyama, Koshin*; Akiyama, Kazuhiko*; Osawa, Takahito; Kasamatsu, Yoshitaka*; Shirai, Naoki*; Tsuchiya, Kunihiko; Yoshida, Tsuyoshi*; et al.
no journal, ,
no abstracts in English
Niihara, Takafumi*; Konishi, Riku*; Hojo, Momoka*; Nagaoka, Hiroshi*; Nakauchi, Yusuke*; Shirai, Naoki*; Yokoyama, Tatsunori; Kagami, Saya
no journal, ,
Developing in situ analytical instruments is crucial for the next generation of deep space exploration, which aims to obtain lunar resources and scientific data. To obtain accurate data from crewed and uncrewed missions, instruments must be calibrated using terrestrial or actual lunar samples. One target material for instrument calibration is lunar meteorites. However, there are significant differences in sample shape between petrological measurements in a laboratory and in situ measurements on the lunar surface. Petrological studies often use polished sections for optical and scanning electron microscopes (SEM) with energy dispersive spectroscopy (EDS) and electron microprobes (EPMA). These polished sections are coated with carbon to prevent charging during SEM and EPMA measurements. These observations connect petrological structures and mineral compositions. Therefore, we must make a direct comparison between the quantitative data obtained from polished sections and the quantitative data obtained from rough-surface rock slabs in order to calibrate in situ instruments. We are trying to establish reference material for instrument calibration. This data includes high-quality quantitative data obtained from polished sections, as well as mineral distribution maps for rough surfaces. We have collected a variety of terrestrial rocks and lunar meteorites. We plan to create archives including mineral composition, mineral maps, and petrological information for engineering use.
