Geochemical characteristics of deposits from the 2011 Tohoku‐oki tsunami at Hasunuma,Kujukuri coastal plain,Japan          下载免费PDF全文

Tetsuya Shinozaki  Yuki Sawai  Junko Hara  Minoru Ikehara  Dan Matsumoto  Koichiro Tanigawa 《Island Arc》2016,25(5):350-368

We examined the geochemical characteristics and temporal changes of deposits associated with the 2011 Tohoku‐oki tsunami. Stable carbon isotope ratios, biomarkers, and water‐leachable ions were measured in a sandy tsunami deposit and associated soils sampled at Hasunuma, Kujukuri coastal plain, Japan, in 2011 and 2014. At this site, the 2011 tsunami formed a 10–30 cm ‐thick layer of very fine to medium sand. The tsunami deposit was organic‐poor, and no samples contained any detectable biomarkers of either terrigenous or marine origin. In the underlying soil, we identified hydrocarbons and sterols derived from terrestrial plants, but detected no biomarkers of marine origin. In the samples collected in 2011, concentrations of tsunami‐derived water‐leachable ions were highest in the soil immediately beneath the tsunami deposit and then decreased gradually with depth. Because of its finer texture and higher organic content, the soil has a higher water‐holding capacity than the sandy tsunami deposit. This distribution suggests that ions derived from the tsunami quickly penetrated the sand layer and became concentrated in the underlying soil. In the samples collected in 2014, concentrations of water‐leachable ions were very low in both soil and sand. We attribute the decrease in ion concentrations to post‐tsunami rainfall, seepage, and seasonal changes in groundwater level. Although water‐leachable ions derived from seawater were concentrated in the soil beneath the tsunami deposit following the tsunami inundation, they were not retained for more than a few years. To elucidate the behavior of geochemical characteristics associated with tsunamis, further research on organic‐rich muddy deposits (muddy tsunami deposits and soils beneath sandy tsunami deposits) as well as sandy tsunami deposits is required.  相似文献   

Phylogeny and phylogeography of the land hermit crab Coenobita purpureus (Decapoda: Anomura: Coenobitidae) in the Northwestern Pacific Region          下载免费PDF全文

Katsuyuki Hamasaki  Chikako Iizuka  Tetsuya Sanda  Hideyuki Imai  Shuichi Kitada 《Marine Ecology》2017,38(1)

Hermit crabs of the family Coenobitidae comprise the land hermit crabs, with 16 Coenobita species, and the coconut crab Birgus latro. They are terrestrial but spend their marine life as planktonic larvae. Some coenobitid crabs are widely distributed in the Indo‐West Pacific region, and some species occupy narrower ranges. To improve our knowledge of coenobitid crab speciation and geographical distribution patterns, we examined the phylogenetic relationship between Coenobita purpureus, which has a narrow distribution in the Northwestern Pacific, and its more widely distributed coenobitids including B. latro, Coenobita brevimanus, Coenobita cavipes, Coenobita perlatus, Coenobita rugosus and Coenobita violascens based on the mtDNA cytochrome c oxidase subunit I (COI) and 16S rDNA genes. We also assessed the phylogeography of Co. purpureus populations based on the COI gene. Our phylogenetic and phylogeographical analyses revealed that (i) Co. purpureus clustered with Co. rugosus and (ii) the Co. purpureus population in the Ogasawara Islands was genetically distinct from those in other regions, which showed genetic panmixia. It has been hypothesized that Co. purpureus evolved in the isolated landmasses of the Ryukyu region during the Pliocene, and that its population expanded and colonized the Ogasawara Islands in the late Pleistocene. Further phylogeographical studies on Coenobita species with relatively narrow distributions coupled with characterization of their phylogenetic relationships with widely distributed congeners will advance our knowledge of the speciation and geographical distribution history of coenobitid crabs.  相似文献   

A speculation on the structure of the D″ layer: The growth of anti-crust at the core–mantle boundary through the subduction history of the Earth   总被引：1，自引：1，他引：0  

Tetsuya Komabayashi  Shigenori Maruyama  Shuji Rino 《Gondwana Research》2009,15(3-4):342-353

The growth curve of the continental crust shows that large amounts of continental crust formed in the early part of the Earth history are missing. In order to test a hypothesis that the former crust was subducted to the deep mantle, we performed phase assemblage analysis in the systems of mid-oceanic ridge basalt (MORB), anorthosite, and tonalite–trondhjemite–granite (TTG) down to the core–mantle boundary (CMB) conditions. Results show that all these materials can be subducted to the CMB leading to the development of a compositional layering in the D″ layer. We speculate that there could be five layers of FeO-enriched melt from partial melting of MORB, MORB crust, anorthosite, TTG, and slab or mantle peridotite in ascending order. Although the polymorphic transformation of perovskite to post-perovskite in (Mg,Fe)SiO₃ may explain the seismic discontinuity at the top of the D″ layer (D″ discontinuity), the effects of solid solution on the sharpness of the transformation suggest that the compositional layering is more plausible for the origin of the D″ discontinuity. The D″ layer can be an “anti-crust” made up mostly of TTG + anorthosite derived from the former continental crust. Tectonic style of the anti-crust at the CMB is similar to that at the surface. At both places, chemically distinct layers are density stratified and are also characterized by the processes of accretion, magmatism, and metasomatism.  相似文献   

Refinement of the Micro‐Distillation Technique for Isotopic Analysis of Geological Samples with pg‐Level Osmium Contents     

Nao Nakanishi  Tetsuya Yokoyama  Akira Ishikawa 《Geostandards and Geoanalytical Research》2019,43(2):231-243

In recent years, the ¹⁸⁷Re–¹⁸⁷Os isotope system has been increasingly used to study samples containing very small quantities of Os. For such samples, optimisation of measurement procedures is essential to minimise the loss of Os before mass spectrometric measurements. Micro‐distillation is a necessary purification step that is applied after the main Os chemical separation procedure, prior to Os isotope ratio measurements by negative‐thermal ionisation mass spectrometry (N‐TIMS). However, unlike the other separation steps, this procedure has not yet been optimised for small samples. In this study, we present a refined micro‐distillation method that achieved higher yields and allowed high‐precision R(¹⁸⁷Os/¹⁸⁸Os) expressed as ¹⁸⁷Os/¹⁸⁸Os measurements for small‐sized geological samples that contain only a few pg Os. The Os recovery in the micro‐distillation step was tested by changing the operating conditions including heating time and temperature, and amounts of oxidant and reductant. Recoveries were measured by the isotope dilution ICP‐MS method after the addition of ¹⁹⁰Os‐enriched spike solution. We found that the most critical factor controlling the chemical yield of Os during micro‐distillation is the extent of dilution of the reductant (HBr) by H₂O evaporated from the oxidant. A refined micro‐distillation method, in which the amount of oxidant solution is reduced from the conventional method, achieved an improved chemical yield of Os (~ 90%). This refined method was applied to the measurement of ¹⁸⁷Os/¹⁸⁸Os by N‐TIMS of varying test portions of the geological reference material BIR‐1a. The resulting ¹⁸⁷Os/¹⁸⁸Os ratios of BIR‐1a matched the literature data, with propagated uncertainties of 0.2, 1.1 and 11% digested sample quantities containing 150, 10 and 1 pg of Os, respectively.  相似文献   

Development of partial factor design method on bearing capacity of pile foundations for Japanese Specifications for Highway Bridges     

Toshiaki Nanazawa  Tetsuya Kouno  Gaku Sakashita  Kazunori Oshiro 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(3):166-175

ABSTRACT

This paper shows the development of a partial factor design method on the bearing capacity of pile foundations for Japanese Specifications for Highway Bridges. Firstly, estimation design equations on the bearing capacities of pile foundations are improved by analysis of pile load test results and uncertainties in the bearing capacities are evaluated. Secondly, the reliabilities of pile foundations designed by the former specifications are evaluated based on reliability analysis considering the uncertainties in the bearing capacities and coefficients of subgrade reaction. Finally, a partial factor design method is developed based on the target reliability index obtained based on the conventional pile installation method by the pile installation methods. The factors are different for each pile installation method.  相似文献   

Infrared photometry of Venus: Variation during 10 years?     

Tetsuya Nagata  Shuji Sato  Tadashi Mukai  Sonoyo Mukai 《Icarus》1985,63(2):217-221

The infrared flux of Venus has been observed with a narrowband filter (λ = 3.6 μm, Δλ = 0.08 μm) from 1982 through 1984, covering a range of the phase angle α from 27 to 94°. Normalized values of flux at the Venus-Earth distance of 1 AU were (4.0–5.4) × 10^?17W/cm²/cm^?1 and the α dependence of the data is rather weak. Furthermore, when the evening terminator of Venus was seen, lower values of flux were obtained in contrast with higher values at the morning terminator. The α dependence is quite different from that of J.V. Martonchik and R. Beer (1975, J. Atmos. Sci.32, 1151–1156). Since we cannot find any significant problem in the two observational methods, the difference might suggest an intrinsic time variation of haze particles during these 10 years in the upper haze layer of the Venus cloud.  相似文献   

River processes after rapid valley-filling due to large landslides     

Hiroshi Shimazu  Takashi Oguchi 《GeoJournal》1996,38(3):339-344

A three-stage model is proposed to describe river processes after rapid valley-filling due to large landslides, based on surveys on the Shirayuki river basin in northeast Japan. At Stage I slightly entrenched debris avalanche deposits get covered with fluvial sediments. At Stage II the river along the upper reaches deeply cuts into fill deposits while fan aggradation occurs along the lower reaches. At Stage III river incision occurs along all the courses. This sequence of river processes reflects the changing amounts of post-landslide debris supply from the landslide scar and river banks. The three-stage model is also applicable to other examples of post-landslide river processes, although some lack the Stage I. Morphometric analyses suggest that the presence or absence of the Stage I depends on the ratio of debris supply from the landslide scar to river competence of sediment delivery.  相似文献   

Enrichment Ratio-Tonnage Diagrams for Resource Assessment     

Shoji  Tetsuya 《Natural Resources Research》2002,11(4):273-287

The enrichment ratio (ER), defined as the ratio of grade of a metal element in a deposit to the crustal abundance of the metal, is proposed for assessing mineral resources. According to the definition, the enrichment ratio of a polymetallic deposit is given as a sum of enrichment ratios of all metals. The relation between ER and the cumulative tonnage integrated from the high ER side of about 4750 deposits in the world is approximated by the combination of three exponential functions crossing at ER values of 16 · 10³ and 600. High ER deposits are expected for the commodities Ag, Pb, and Au+Ag, and for epithermal, mesothermal, unconformity-related and vein types. In contrast, low ER deposits are typical for the commodities Cu, Mn, Mo, Ni, and U, and for chemically precipitated, Cyprus, laterite, orthomagmatic, pegmatite, placer, porphyry, and sandstone deposits. The critical ER value of the low ER class (the differential metal amount decreases with decreasing ER in the regions lower than the value) is 250 in all deposits, 610 in W+Mo, 2800 in Pb+Zn and 360 in Au+Ag, 530 in massive sulfides, 160 in the orthomagmatic type, 170 in placers, 220 in the porphyry type, 1900 in the replacement type, 580 in the stratabound type, 3400 in the unconformity-related type, and 1700 in vein type deposits. The frequency proportion determined by a keyword and a commodity provides valuable suggestions for mineral exploration: for example, the exploration target for chromite is a deposit characterized as orthomagmatic, whereas the expected commodity of a newly developed orthomagmatic deposit is chromite.  相似文献   

Precise determination of ferrous iron in silicate rocks     

Tetsuya YokoyamaEizo Nakamura 《Geochimica et cosmochimica acta》2002,66(6):1085-1093

We have developed a highly precise method for the determination of ferrous iron (Fe²⁺) in silicate rocks. Our new method is based on Wilson’s procedure (1955) in which surplus V⁵⁺ is used to oxidize Fe²⁺ into Fe³⁺ while equivalently reducing V⁵⁺ into V⁴⁺. Because V⁴⁺ is more resistant to atmospheric oxidation than Fe²⁺, Fe²⁺ in the sample can be determined by measuring unreacted V⁵⁺ by adding excess Fe²⁺ after sample decomposition and then titrating the unreacted Fe²⁺ with Cr⁶⁺. With our method, which involves conditioning the sample solution with 5 M H₂SO₄ in a relatively small beaker (7 mL), the oxidation of Fe²⁺ or V⁴⁺ that leads to erroneous results can be completely avoided, even in 100-h sample decompositions at 100°C. We have measured the concentration of FeO in 15 standard silicate rock powders provided by the Geological Survey of Japan (GSJ). Analytical reproducibility was better than 0.5% (1σ) for all but those samples that had small amounts of Fe²⁺ (<1.5 wt.% of FeO). Fourteen of these samples gave FeO contents significantly higher than the GSJ reference values. This likely indicates that the GSJ reference values, obtained by compiling previously published data, contain a large number of poor-quality data obtained by methods with lower recovery of Fe²⁺ caused by oxidation or insufficient sample decomposition during analyses. To achieve accurate determinations of Fe²⁺ in our method, several factors besides the oxidation must be considered, including: (1) long-term variations in the concentration of Fe²⁺ solution must be corrected; (2) excess use of the indicator must be avoided; and (3) the formation of inert FeF⁺ complex must be avoided during titration when using boric acid as a masking agent.  相似文献   

Petroloy of the Taga Volcano Group,Izu Peninsula,Central Japan     

Dr. Mitsuo Shimazu  Dr. Kazuhiro Kurihara 《Mineralogy and Petrology》1989,41(1):11-24

The Taga Volcano Group of the Izu Peninsula is divided into four volcanoes: Older Taga, Atami, Shimo-Taga and Himenosawa. Each volcano consists of basalt-andesite lavas and volcaniclastic sediments, mainly of low alkali tholeiite composition.The activity of the Shimo-Taga Volcano is divided into three stages (early, middle and later). Rocks of the first two stages consist of lavas and volcaniclastic sediments of olivine basalt, phyric and aphyric basaltic andesite. The later stage rocks consist of volcaniclastic sediments which were erupted as mudflow deposits.Basalts and andesites of the first two stages are considered to have been derived from a zoned magma chamber. They were produced by fractional crystallization, which involved the gravitational separation of plagioclase, olivine and/or pyroxene crystals. Eruption of aphyric and phyric basaltic andesite from the upper part of the chamber occurred first, followed by olivine basalt from lower parts of the chamber.

---

Zusammenfassung Die Taga-Vulkan Gruppe besteht aus dem älteren Taga, dem Atami, dem Shimo-Taga und dem Himenosawa Vulkan. Jeder dieser Vulkane wird aus basaltisch-andesitischen Laven und vulkano-klastischen Sedimenten, hauptsächlich subalkalisch tholeiitischer Zusammensetzung, aufgebaut.Die Eruptionstätigkeit des Shimo-Taga Vulkans läßt sich in drei Phasen, eine Früh-, Mittel- und Spätphase untergliedern. Laven und vulkanoklastische Sedimente der ersten beiden Phasen bestehen aus Olivinbasalten, sowie aus basaltischen Andesiten mit porphyrischem und nichtporphyrischem Gefüge. Während des letzten Stadiums wurden vulkanoklastische Sedimente in Form von vulkanoklastischen Schlammströmen eruptiert.Die Basalte und Andesite der ersten beiden Stadien werden als Produkte einer zonierten Magmenkammer gedeutet. Sie entstanden durch fraktionierte Kristallisation und durch die gravitative Abtrennung von Plagioklas, Olivin und/oder Pyroxenkristallen. Der Eruption der porphyrischen und nichtporphyrischen basaltischen Andesite aus dem obersten Teil der Magmakammer folgte die Eruption von Olivinbasalten aus dem tieferen Teil der Magmakammer.

  相似文献