²³⁰Th/²³⁴U and ¹⁴C dating of a lowstand coral reef beneath the insular shelf off Irabu Island, Ryukyus, southwestern Japan     

Keiichi  Sasaki  Akio  Omura  Tetsuo  Miwa  Yoshihiro  Tsuji  Hiroki  Matsuda  Toru  Nakamori  Yasufumi  Iryu  Tsutomu  Yamada  Yuri  Sato  Hiroshi  Nakagawa 《Island Arc》2006,15(4):455-467

Abstract   High-resolution seismic reflection profiles delineated the distribution of mound-shaped reflections, which were interpreted as reefs, beneath the insular shelf western off Irabu Island, Ryukyus, southwestern Japan. A sediment core through one of the mounded structures was recovered from the sea floor at a depth of −118.2 m by offshore drilling and was dated by radiometric methods. The lithology and coral fauna of the core indicate that the mounded structure was composed of coral–algal boundstone suggesting a small-scaled coral reef. High-precision α-spectrometric ²³⁰Th/²³⁴U dating coupled with calibrated accelerator mass spectrometric ¹⁴C ages of corals obtained reliable ages of this reef ranging from 22.18 ± 0.63 to 30.47 ± 0.98 ka. This proves that such a submerged reef was formed during the lowstand stage of marine oxygen isotope stages 3–2. The existence of low-Mg calcite in the aragonitic coral skeleton of 22.18 ± 0.63 ka provides evidence that the reef had once been exposed by lowering of the relative sealevel to at least −126 m during the last glacial maximum in the study area. There is no room for doubt that a coral reef grew during the last glacial period on the shelf off Irabu Island of Ryukyus in the subtropical region of western Pacific.  相似文献   

High-Mg diorites derived from sanukitic HMA magmas, Kyushu Island, southwest Japan arc: evidence from clinopyroxene and whole rock compositions   总被引：21，自引：0，他引：21  

Atsushi Kamei  Masaaki Owada  Takashi Nagao  Keiichi Shiraki 《Lithos》2004,75(3-4):359-371

High-Mg diorites that have similar whole rock composition to high-Mg andesites (HMAs) should not be simply interpreted as rocks solidified from the HMA magmas, because the high-Mg diorites may be mafic cumulates derived from a different magma from the HMAs.

The HMAs contain unique clinopyroxenes with higher Mg# and Si than those of other sub-alkaline series igneous rocks. The Mg# and Si are controlled by the source magma composition rather than its crystallized conditions such as pressure and temperature. The chemical composition of clinopyroxenes would present important information for the investigation of the source of high-Mg diorites.

We considered the source of Early Cretaceous high-Mg diorites on Kyushu Island, southwest Japan arc, based on their clinopyroxene and whole rock compositions. The clinopyroxenes have similar chemical characteristics to those in HMAs rather than those in other sub-alkaline rocks. Moreover, the whole rock compositions are equivalent to the sanukitic HMA and do not show features of mafic cumulates. This indicates that the high-Mg diorites solidified from sanukitic HMA magmas. It is generally believed that the sanukitic HMA magmas involve the subduction of a young and/or hot oceanic slab was situated in their genesis. Therefore, the occurrence of the high-Mg diorites suggests that Kyushu was situated in the tectonic setting of young and/or hot slab subduction in the Early Cretaceous.  相似文献   

Morphological transitions for pore water and pore air during drying and wetting processes in partially saturated sand     

Kido  Ryunosuke  Higo  Yosuke  Takamura  Fukushi  Morishita  Ryoichi  Khaddour  Ghonwa  Salager  Simon 《Acta Geotechnica》2020,15(7):1745-1761

Acta Geotechnica - Water retention characteristics are important for modeling the mechanical and hydraulic behavior of partially saturated sand. It is well known that the soil water characteristic...  相似文献   

The build-up of the colour–magnitude relation as a function of environment     

Masayuki Tanaka  Tadayuki Kodama  Nobuo Arimoto  Sadanori Okamura  Keiichi Umetsu  Kazuhiro Shimasaku  Ichi Tanaka  Toru Yamada 《Monthly notices of the Royal Astronomical Society》2005,362(1):268-288

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High-resolution terrestrial carbon isotope and planktic foraminiferal records of the Upper Cenomanian to the Lower Campanian in the Northwest Pacific     

Reishi Takashima  Hiroshi Nishi  Toshiro Yamanaka  Keiichi Hayashi  Amane Waseda  Akiko Obuse  Takashige Tomosugi  Naoki Deguchi  Sunao Mochizuki 《Earth and Planetary Science Letters》2010,289(3-4):570-582

Making Upper Cretaceous biostratigraphic correlations between the Northwest Pacific and Tethyan–Atlantic sections have been difficult because of rare frequencies of age-diagnostic macro- and microfossils in the sequences in the Northwest Pacific region. In order to correlate these sections precisely, an integrated planktic foraminiferal and bulk wood carbon-isotope stratigraphy from the upper Cenomanian to the lower Campanian succession (the middle–upper part of the Yezo Group) of Hokkaido, northern Japan is established with an average resolution of 50 k.y. The δ¹³C curves from bulk wood of the Yezo Group and from bulk carbonate of English Chalk show remarkably similar patterns of isotopic fluctuation, allowing the correlation of 22 carbon isotopic events between these sections. This high-resolution correlation greatly improves the previous micro- and macrofossil biostratigraphic schemes in the Northwest Pacific region, and reveals that global events, such as the oxygen depletion at the OAE 2 horizon, the constant decrease in pCO₂ during the Late Cretaceous, and the eustatic sea-level falls in the late middle Turonian, Santonian/Campanian Boundary and early Campanian, are recorded in the Upper Cretaceous sequence of the Northwest Pacific.  相似文献   

Amplification of coastal-trapped waves resonantly generated by wind around Sado Island,Japan     

Yosuke Igeta  Keiichi Yamazaki  Tatsuro Watanabe 《Journal of Oceanography》2015,71(1):41-51

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Isolation and characterization of low molecular weight carbohydrates dissolved in seawater     

Hiroshi Sakugawa  Nobuhiko Handa  Keiichi Ohta 《Marine Chemistry》1985,17(4):341-362

Chemical characterization and quantitative determination of dissolved low molecular weight carbohydrates in Mikawa Bay near Nagoya, Japan were conducted. The water samples were collected during the period of algal bloom of the dinoflagellate Prorocentrum minimum on 31 May 1980.Low molecular weight carbohydrates in seawater samples from depths of 1 and 6 m were first retained on a charcoal column and then eluted with aqueous ethanol. The carbohydrates obtained were permethylated and then isolated into each of the components by thin layer chromatography. The sugars isolated were characterized by gas chromatography (GC), combined gas chromatography and mass spectrometry (GC-MS), proton nuclear magnetic resonance spectroscopy (¹H-NMR) and some chemical analyses. Laminaribiose, laminaritriose, sucrose, raffinose, , were fully characterized and quantified with ranges from 2.3 to 27.7 μg l⁻¹ and from 0.5 to 17.8 μg l⁻¹.These low molecular weight carbohydrates were also identified, with some difference in their relative abundance, in particulate matter consisting mainly of dinoflagellate cells collected on the same occasion from this bay. These results indicate that low molecular weight carbohydrates dissolved in seawater are directly derived from those of phytoplankton through extracellular release or cell lysis.  相似文献   

Outline of the JNLT project     

Keiichi Kodaira 《Astrophysics and Space Science》1989,160(1-2):137-144

The Japanese National Large Telescope (JNLT) is a 7.5 m reflector with a monolithic thin meniscus main mirror, having the candidate construction site on the northwest cone of the Mauna Kea, Hawaii.The present concept of JNLT has the characteristics of a third generation infrared telescope, which should be capable of various observations of high spatial resolution in the optical-infrared region.Although the project is still under examination from the financial and administrative point of view, a wide range of technical studies were carried out by the JNLT Working Group with the collaboration of specialists from the academic and the industrial sectors.Paper presented at the symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.  相似文献   

Gamma-Ray Bursts and magnetar-forming Supernovae     

Ken’ichi Nomoto  Keiichi Maeda  Masaomi Tanaka  Tomoharu Suzuki 《Astrophysics and Space Science》2011,336(1):129-137

The connection between long Gamma Ray Bursts (GRBs) and Supernovae (SNe) have been established through the well observed cases. These events can be explained as the prompt collapse to a black hole (BH) of the core of a massive star (M≳40M _⊙). The energies of these GRB-SNe were much larger than those of typical SNe, thus these SNe are called Hypernovae (HNe). The case of SN 2006aj/GRB060218 appears different: the GRB was weak and soft, being called an X-Ray Flash (XRF); the SN is dimmer and has very weak oxygen lines. The explosion energy of SN 2006aj was smaller, as was the ejected mass. In our model, the progenitor star had a smaller mass than other GRB-SNe (M∼20M _⊙), suggesting that a neutron star (NS) rather than a BH was formed. If the nascent NS was strongly magnetized as a magnetar and rapidly spinning, it may launch a weak GRB or an XRF. The peculiar light curve of Type Ib SN 2005bf may also be powered by a magnetar. The blue-shifted nebular emission lines of 2005bf indicate the unipolar explosion possibly related to standing accretion shock instability (SASI) associated with a newly born NS.  相似文献   

Mira variables in the Galactic bulge with OGLE-II data     

Noriyuki Matsunaga  Hinako Fukushi  Yoshikazu Nakada 《Monthly notices of the Royal Astronomical Society》2005,364(1):117-125

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