Late Quaternary tephrostratigraphy of Baegdusan and Ulleung volcanoes using marine sediments in the Japan Sea/East Sea     

Chungwan Lim  Kazuhiro Toyoda  Ken Ikehara  David W. Peate 《Quaternary Research》2013

Only Ulleung and Baegdusan volcanoes have produced alkaline tephras in the Japan Sea/East Sea during the Quaternary. Little is known about their detailed tephrostratigraphy, except for the U–Oki and B–Tm tephras. Trace element analysis of bulk sediments can be used to identify alkaline cryptotephra because of the large compositional contrast. Five sediment cores spanning the interval between the rhyolitic AT (29.4 ka) and Aso-4 (87 ka) tephras were analyzed using an INAA scanning method. Source volcanoes for the five detected alkaline cryptotephra were identified from major element analyses of hand-picked glass shards: Ulleung (U–Ym, and the newly identified U–Sado), and Baegdusan (B–J, and the newly identified B–Sado and B-Ym). The eruption ages of the U–Ym, U–Sado, B–J, B–Sado, and B–Ym tephras are estimated to be 38 ka, 61 ka, 26 ka, 51 ka, 68–69 ka, and 86 ka, respectively, based on correlations with regional-scale TL (thinly laminated) layer stratigraphy (produced by basin-wide changes in bottom-water oxygen levels in response to millennium-scale paleoclimate variations). This study has allowed construction of an alkaline tephrostratigraphical framework for the late Quaternary linked to global environmental changes in the Japan Sea/East Sea, and improves our knowledge of the eruptive histories of Ulleung and Baegdusan volcanoes.  相似文献   

Sea surface temperature record off central Japan since the Last Glacial Maximum using planktonic foraminiferal Mg/Ca thermometry     

Takuya Sagawa  Kazuhiro Toyoda  Tadamichi Oba 《第四纪科学杂志》2006,21(1):63-73

We conducted paired measurements of the Mg/Ca ratio and δ¹⁸O of planktonic foraminifera, Globigerina bulloides, from a sediment core (MD01‐2420) off central Japan in the northwest Pacific, to reconstruct current movements since the Last Glacial Maximum (LGM). These methods make it possible to determine the magnitude and timing of the sea surface temperature (SST) changes and to reconstruct the variations of the past seawater δ¹⁸O (δ¹⁸Ow) off central Japan. The amplitude of Mg/Ca‐based SST changes between the Holocene and the LGM was about 10°C. The strong resemblance of the SSTs estimated from both methods, Mg/Ca‐based and δ¹⁸O‐based, suggests that the SST changes were caused primarily by latitudinal displacement of the Kuroshio–Oyashio currents and no distinct change in the carbonate dissolution of the core. The southward migration of the water mass was 5–6° in latitude at the LGM. The values for regional δ¹⁸Ow changes, which were obtained by subtracting the ice volume contribution from the calculated δ¹⁸Ow, describe the millennial‐scale water mass migration over the last 30 kyr. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Carbon isotopic thermometry calibrated by dolomite-calcite solvus temperatures   总被引：1，自引：0，他引：1  

Hideki Wada  Kazuhiro Suzuki 《Geochimica et cosmochimica acta》1983,47(4):697-706

The temperature dependence of carbon isotopic fractionations between calcite and graphite, and between dolomite and graphite are calibrated by the calcite-dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the Kasuga area, central Japan. The carbon isotopic fractionations (Δ¹³C_Cc-Gr and Δ¹³C_DoGr) systematically decrease with increasing metamorphic temperature. The concordant relationships between the fractionations and solvus temperatures are approximately linear with T^?2 over the temperature range. 400° to 680°C: Δ¹³C_CcGr (%.) = 5.6 × 10⁶ × T^?2 (K) ? 2.4 Δ¹³C_DoGr (%.) = 5.9 × 10⁶ × T^?2 (K) ? 1.9 These systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases. The equation for the calcite-graphite system has a slope steeper than Bottinga's (1969) results. It is, however, in good agreement with that of Valley and O'Neil (1981) in the temperature range from 600° to 800°C.Because of the relatively high sensitivity to temperature, these isotopic geothermometers are useful for determining the temperatures in moderate- to high-grade metamorphosed carbonate rocks.  相似文献   

Optical identifications of southern rosat EUV and soft X-ray sources     

David A. H. Buckley  Kazuhiro Sekiguchi  Darragh O'Donoghue  Walter W. Wargau 《Astrophysics and Space Science》1995,230(1-2):117-130

This paper discusses the first all-sky surveys of cosmic extreme ultra-violet and soft X-ray sources, discovered by ROSAT. Details of the surveys are presented, with comparisons made to previous selected surveys in the X-ray regime. The subsequent optical identification programs are described, and the major results summarized. We then discuss the main classes of EUV emitters: active chromosphere stars and hot white dwarfs, and describe the importance of EUV observations in understanding the astrophysics of these objects. Many bright, and relatively nearby, sources have been identified as hitherto unrecognized active stars, representing the extremes in chromospheric and coronal activity, be it binary or age related. Many new hot DA white dwarfs have also been indentified, and the most exciting result in this area is the discovery that significant traces of heavier elements (e.g. C, N, O, Si, Fe and Al) exist in their atmospheres, substantially increasing their EUV opacities. The importance of hot white dwarfs as standard candles in probing the local interstellar medium is also discussed. Miscellaneous counterparts (AGN, PNN, O-B stars and CVs) that make up the rest of the sample of EUV sources are also briefly mentioned. We finish with a discussion of the on-going ROSAT Galactic Plane Survey (RGPS) identification program.  相似文献   

A ROSAT observation of the dipping, flaring and eclipsing polar MN Hya (RX J0929.1–2404)     

David A. H. Buckley  Paul E. Barrett  Frank Haberl  & Kazuhiro Sekiguchi 《Monthly notices of the Royal Astronomical Society》1998,299(4):998-1006

We present the results of a 22.5 ks pointed ROSAT PSPC observation of the 3.4-h period eclipsing polar MN Hya (RX J0929.1−2404). The X-ray light curve exhibits a 'double-humped' shape, with a secondary minimum occuring at φ∼ 0.45, a morphology consistent with two-pole accretion. Strong aperiodic flaring activity, with flux enhancements of ∼ 6 × the quiescent level, is also observed. A pre-eclipse 'dip' occurs in the phase interval φ= 0.87–0.95 with the X-rays becoming harder, indicative of photoelectric absorption by the pre-shock flow. There is also evidence of a secondary spectrally hard 'dip' near φ = 0.45–0.55, which might be associated with a second accretion stream flowing to the other magnetic pole.   The X-ray spectrum is best represented by a combination of a ∼50 eV blackbody and a thermal bremsstrahlung component of kT 1.6 keV, with a total absorption column of N _H  = 2.9 × 10²⁰ cm⁻².   The primary maximum (φ∼ 0.65) has a slightly larger column and normalization compared to the secondary maximum. Although there are few photons, the dip spectrum is very flat in comparison to other phases, and is best represented by a single bremsstrahlung component. This is indicative of the spectral hardening seen in the light curves attributed to photoabsorption. The ratio of unabsorbed bremsstrahlung and blackbody luminosities is ∼ 0.1 for the best-fitting average spectral models. This implies a magnetic field strength  30 MG on the basis of the empirical L _hard/ L _soft −  B relationships, although consideration of the cyclotron flux and aspect effects could allow for an even higher field (55 MG).  相似文献   

Petrology and CHIME geochronology of Pan-African high K and Sr/Y granitoids in the Nkambe area, Cameroon   总被引：1，自引：1，他引：0  

Samuel Tetsopgang  Kazuhiro Suzuki  Emmanuel Njonfang 《Gondwana Research》2008,14(4):686

The Central African Belt in the Nkambe area, northwestern Cameroon represents a collisional zone between the Saharan metacraton and the Congo craton during the Pan-African orogeny, and exposes a variety of granitoids including foliated and massive biotite monzogranites in syn- and post-kinematic settings. Foliated and massive biotite monzogranites have almost identical high-K calc-alkaline compositions, with 73–67 wt.% SiO₂, 17–13 wt.% Al₂O₃, 2.1–0.9 wt.% CaO, 4.4–2.7 wt.% Na₂O and 6.3–4.4 wt.% K₂O. High concentrations of Rb (264–96 ppm), Sr (976–117 ppm), Ba (3680–490 ppm) and Zr (494–99 ppm), with low concentrations of Y (mostly< 20 ppm with a range 54–6) and Nb (up to 24 ppm) suggest that the monzogranites intruded in collisional and post-collisional settings. The Sr/Y ratio ranges from 25 to 89. K, Rb and Ba resided in a single major phase such as K-feldspar in the source. Garnet was present in the source and remained as restite at the site of magma generation. This high K₂O and Sr/Y granitic magma was generated by partial melting of a granitic protolith under high-pressure and H₂O undersaturated conditions where garnet coexists with K-feldspar, albitic plagioclase. CHIME (chemical Th–U-total Pb isochron method) dating of zircon yields ages of 569 ± 12–558 ± 24 Ma for the foliated biotite monzogranite and 533 ± 12–524 ± 28 Ma for the massive biotite monzogranite indicating that the collision forming the Central African Belt continued in to Ediacaran (ca 560 Ma).  相似文献   

Full-scale dynamic testing of response-controlled buildings and their components:concepts,methods,and findings     

Kazuhiko Kasai  Kazuhiro Matsuda 《地震工程与工程振动(英文版)》2014,(Z1)

A series of shake-table tests was conducted by inserting and replacing 4 different types of dampers,or by removing them in a full-scale 5-story steel frame building. The objective is to validate response-control technologies that are increasingly adopted for major Japanese buildings without being attested to-date by a major earthquake. Test results are briefly described,and good performance of the dampers and frame demonstrated. The concepts of the full-scale building tests and various contributions are discussed. The difficulty associated with full-scale dynamic testing is explained.  相似文献   

Field measurement and modeling of near-bed sediment transport processes with fluid mud layer in Tokyo Bay     

Yasuyuki Nakagawa  Kazuo Nadaoka  Hiroshi Yagi  Ryuichi Ariji  Haruo Yoneyama  Kazuhiro Shirai 《Ocean Dynamics》2012,62(10-12):1535-1544

Tokyo Bay is one of the estuaries in Japan with a high population of almost 26 million people in the basin area. One of the major concerns for the environment in this water area is the decreasing ecosystem functions including the deterioration of water and sediment qualities caused by various anthropogenic activities. Since the bottom sediments around almost the entire area of the inner bay consist of fine materials with a high organic content, which cause the deterioration of water quality through processes such as hypoxia, an understanding of the fine sediment dynamics in the Bay is crucial for an environmental assessment of the water area. This paper proposes a model for the key processes of fine sediment dynamics, which reflects field data about muddy bed structures and their dynamics obtained during the monitoring campaign in 2007. One of the specific features of the sediment in the Bay at present is the persistent existence of fluid mud layers (water content over 300?%) with a thickness of around a few decimeters, which might be caused by deposition of abundant organic particles due to eutrophication. The present study shows that diffusion flux model delivers quite reliable results for estimating erosion flux from the top of fluid mud layers after calibrating the model parameter against the time series data of vertical flux measured by an acoustic Doppler velocimeter system. This study also derives analytical solutions, based on the Bingham fluid concept, of advection flux in the fluid mud layer on which external shear stress force is applied.  相似文献   

Co-inoculation of Capitella sp. I with its synergistic bacteria enhances degradation of organic matter in organically enriched sediment below fish farms     

Wada M  Zhang D  Do HK  Nishimura M  Tsutsumi H  Kogure K 《Marine pollution bulletin》2008,57(1-5):86-93

A polychaete, Capitella sp. I has been shown to degrade organics actively in organically enriched sediment below fish farms. Our aim of the present study is to enhance the biological treatment of sediment by co-inoculation of Capitella sp. I with bacterial isolates that possess high degrading potential for organic matter. We isolated a total of 200 bacterial strains from fecal pellets, burrow lining, worm body, and sediment, and selected six of them for the degradation experiments in the sediment microcosms. With two out of the six isolates, tentatively identified as Vibrio sp. and Vibrio cyclitrophicus by 16SrDNA sequence, we found the TOC reduction rate was stimulated in sediment co-inoculated with the worms and each of the bacteria. In contrast, this was not observed in sediments inoculated only with the worms or the bacterium. These results strongly suggest that co-inoculation of Capitella sp. I with bacteria improves biodegradation.  相似文献   

Geological relationship between Anyui Metamorphic Complex and Samarka terrane,Far East Russia     

Satoru Kojima  Kazuhiro Tsukada  Shigeru Otoh  Satoshi Yamakita  Masayuki Ehiro  Cheikhna Dia  Galina Leontievna Kirillova  Vladimir Akimovich Dymovich  Lyudmila Petrovna Eichwald 《Island Arc》2008,17(4):502-516

The Anyui Metamorphic Complex (AMC) of Cretaceous age is composed of metachert, schist, gneiss, migmatite and ultramafic rocks, and forms a dome structure within the northernmost part of the Jurassic accretionary complex of the Samarka terrane. The two adjacent geological units are bounded by a fault, but the gradual changes of grain size and crystallinity index of quartz in chert and metachert of the Samarka terrane and the AMC, together with the gradual lithological change, indicate that at least parts of the AMC are metamorphic equivalents of the Samarka rocks. Radiolarian fossils from siliceous mudstone of the Samarka terrane indicates Tithonian age (uppermost Jurassic), and hence, form a slightly later accretion. This signifies that the accretionary complex in the study area is one of the youngest tectonostratigraphic units of the Samarka terrane. The relationship between the Samarka terrane and AMC, as well as their ages and lithologies, are similar to those of the Tamba–Mino–Ashio terrane and Ryoke Metamorphic Complex in southwest Japan. In both areas the lower (younger) part of the Jurassic accretionary complexes were intruded and metamorphosed by Late Cretaceous granitic magma. Crustal development of the Pacific‐type orogen has been achieved by the cycle of: (i) accretion of oceanic materials and turbidites derived from the continent; and (ii) granitic intrusion by the next subduction and accretion events, accompanied by formation of high T/P metamorphic complexes.  相似文献