Ryuji Asami

Research Field

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

10.5281/zenodo.3941816

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Within‐shell variations in carbon and oxygen isotope compositions of two modern brachiopods from a subtropical shelf environment off Amami‐o‐shima, southwestern Japan

Geochemistry Geophysics Geosystems (2010)

Kazuyuki Yamamoto Ryuji Asami Yasufumi Iryu

This study examines the fidelity of carbon ( δ 13 C) and oxygen ( δ 18 O) isotope compositions of two modern brachiopod species ( Kikaithyris hanzawai and Basiliola lucida ) to use as proxies of δ 13 C values of total dissolved inorganic carbon and temperature and/or δ 18 O values of seawater, respectively. Well‐preserved shells of K. hanzawai and living individuals of B. lucida were collected from a subtropical shelf environment off Amami‐o‐shima, southwestern Japan. Some portions of the shells are in isotopic equilibrium with the ambient seawater, while other portions are not. The degree of disequilibrium differs between the two species and between different portions of each shell. Statistically significant positive correlations are recognized between the δ 13 C and δ 18 O values of these samples, which can be ascribed to a kinetic fractionation effect. Far from the posterior shell edge and along the axis of shell growth, the δ 18 O values of the secondary shell layer of K. hanzawai mostly fall within the expected range of equilibrium calcite. The δ 13 C values from the inner surface of the secondary shell layer in both species are relatively constant and are equivalent to or very close to equilibrium calcite. Therefore, these portions of the shells are most suitable for collecting reliable environmental proxy data. Although the δ 13 C and δ 18 O values of modern brachiopod shells are predominantly controlled by a kinetic fractionation effect, the appropriate selection of species and shell portions that reflect the isotopic composition of ambient seawater can facilitate the reconstruction of secular variations in oceanic δ 13 C or δ 18 O values.

δ18O

10.1029/2010gc003190

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Within- and inter-shell variations of carbon and oxygen isotope composition in Permian brachiopod shells from the Indochina terrane in Thailand

Annual Meeting of the Geological Society of Japan The 122nd Annual Meeting(2015' Nagano) (2015)

Mamoru Takizawa Techapinawat Lapone Hideko Takayanagi Thasinee Charoentitirat Ryuji Asami

Carbon fibers

10.14863/geosocabst.2015.0_599

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Speleothem-inferred paleoclimate records at 570-450 thousand years ago from northern Mediterranean