巻号一覧
38 巻 (2004)
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38 巻, 2 号
選択された号の論文の9件中1～9を表示しています
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Anto Raukas2004 年 38 巻 2 号 p. 101-106
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーThe soil in and around the Kaali meteorite craters in the SE part of Saaremaa Island contains a large number of micrometeorites and abounds in pulverized extraterrestrial and impactite matter. The explosion with accompanying high temperatures resulted in the formation of glassy silicate spherules. These spherules were distributed over a large area, and allow to estimate the age of the impact at about 7500 years BP and correlate separated sequences. The extraterrestrial and explosive material in the Kaali area is diverse in form, colour and composition. The spherules may be of different origin, including industrial. From the methodological point of view, it is especially important to study spherules in the geologically established crater fields and their surroundings. The Kaali area provides an excellent polygon for this kind of studies.抄録全体を表示PDF形式でダウンロード (1479K) -
François Marini, Anto Raukas, Reet Tiirmaa2004 年 38 巻 2 号 p. 107-120
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーThe Kaali crater field (1 sq. kilometre, 9 craters) offers a unique opportunity to recover large amounts of magnetic fines still partly preserved from late-stage weathering. SEM studies of these materials reveal an unusually wide spectrum of derivatives from the initial iron meteorite body, including minor amounts of unmelted metal fragments, and an abundance of more evolved products resulting from primary oxidation processes. Most of these products are sprays and splashes of liquid iron oxides, and some particles may be ascribed to oxide condensates from a vapor phase, as a result of both atmospheric ablation and vaporization upon impact. This wide range reflects varied impact conditions, due to variable masses and velocities of fragments after atmospheric disruption of the original meteoritic body. The large spectrum of magnetic fines from Kaali should provide an excellent probe into the chemical- and isotopic-fractionation of elements over a range of impact processes, from atmospheric entry to post-impact alteration. Magnetic fines from other sites of multiple impacts may have the same potential, and deserve more systematic attention.抄録全体を表示PDF形式でダウンロード (2351K) -
Gilberto Athayde Albertão, Alexandre De Azevedo Grassi, Fran&cc ...2004 年 38 巻 2 号 p. 121-128
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーDuring the last 10 years some important results have been reached after extensive research performed on some Brazilian basins relating to the Cretaceous-Tertiary Boundary (KTB) matter. This paper presents some of these results mainly focused on the spherule content of the sediments. The preliminary analysis carried out without strong constraints have not revealed any distinguishing and typical characteristics known for the KTB. These geochemical analysis were performed on ditch samples, from subsurface data, submitted to statistical tests such as factor and discriminant analysis. The result of the factor analysis indicated general trends in the concentration of chemical elements while the discriminant analysis showed a very clear discontinuity of the chemical data between the Cretaceous and Tertiary periods. The first occurrence of spherules was found in sediments from the KTB of Pernambuco-Paraiba Basin (PE-PB). Despite other impact-derived characteristics present in this sedimentary section these spherules do not show any direct evidence of an impact origin. On the other hand, the study of microspherules recovered from a drilling core of Campos Basin has probably revealed the first documented occurrence of tektites in South America.抄録全体を表示PDF形式でダウンロード (1684K) -
Tatsuo Maekawa2004 年 38 巻 2 号 p. 129-138
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーIsotopic fractionation of oxygen and hydrogen in water caused by gas hydrate formation was investigated experimentally. Two different gas hydrates in structures, Structure I hydrate and Structure II hydrate, were formed with methane and krypton gases in a NaCl solution. Isotopic fractionation during gas hydrate formation was observed by measuring oxygen and hydrogen isotopic compositions in the solutions sampled before and after gas hydrate formation. Heavy isotopes of oxygen and hydrogen in water were depleted in the solution resulting from that those isotopes were concentrated in the gas hydrate. The isotopic fractionation was larger as increasing amounts of gas hydrates that were calculated from both the decrease of gas pressure and increase of NaCl concentration in solution. The isotopic fractionation factors of oxygen and hydrogen in water between gas hydrate and liquid water were determined to be 1.0023-1.0032 and 1.014-1.022, respectively. The significant difference of the gas hydrate structures was not observed beyond the analytical errors. These factors are similar to those between ice and liquid water.抄録全体を表示PDF形式でダウンロード (867K) -
Jincheng Zhou, Xiaolei Wang, Jiansheng Qiu, Jianfeng Gao2004 年 38 巻 2 号 p. 139-152
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーMeso- and Neoproterozoic mafic-ultramafic rocks from northern Guangxi show mainly calc-alkaline features. The mafic rocks have (Nb/La)pm1) = 0.13∼0.51, (Th/La)pm = 0.85∼3.3, Ti/Ti∗2) = 0.29∼0.79 and show negative Nb and Ti anomalies in primitive mantle normalized diagrams. The Mesoproterozoic mafic rocks have lower εNd(T) than those of Neoproterozoic, -1.99 ∼ -5.13 vs. -0.74 ∼ 2.4, respectively. They plot in the field of volcanic arc basalt in tectonic discrimination diagrams and display geochemical signatures of island arc volcanics. The mafic-ultramafic rocks are thought to be the products of magmatism of convergent plate boundary rather than derived from mantle plume. Therefore, they can not be regarded as an indicator of breakup of Rodinia supercontinent.抄録全体を表示PDF形式でダウンロード (1108K) -
Yoshinori Takano, Junya Kudo, Takeo Kaneko, Kensei Kobayashi, Yukishig ...2004 年 38 巻 2 号 p. 153-161
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーCore samples of sediments at depths of 0-300 cm at Rikubetsu, Hokkaido, Japan were analyzed for total organic carbon (TOC) concentration, total hydrolyzed amino acids (THAA) and density of viable microorganisms. TOC, THAA and density of viable microorganisms were greatest at the surface and decreased with the depth: THAA showed 62 μmol/g at a depth of 0-5 cm. The correlation coefficients (r) for TOC and THAA versus cell density were 0.97 and 0.98, respectively. The alteration of dicarboxylic amino acids, aspartic acid and glutamic acid, to β-alanine and γ-aminobutyric acid respectively, via specific decarboxylation due to diagenesis were observed. Rate constant of aspartic acid racemization, kASP was determined to be 3.8 × 10-5 at 4, 420 yrBP and 2.6 × 10-5 at 9, 290 yrBP. Some anomalies in vertical distribution of THAA and cell density in the core sediment may indicate the presence of the past warmer period called “Hypsithermal” in Rikubetsu, Hokkaido, Japan.抄録全体を表示PDF形式でダウンロード (608K) -
Aninda Mazumdar, S. K. Bhattacharya2004 年 38 巻 2 号 p. 163-175
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーCarbonate rocks of late Neoproterozoic-early Cambrian (?) age occur in two extremities of the Nagaur-Ganganagar basin in western India: in east as part of Bilara hills (type locality) and in west as part of Baghewala oil field. These rocks have close stratigraphic correlation with the Ara Formation (Huqf Group, south Oman salt basin) which transgresses the late Neoproterozoic-early Cambrian boundary. Sedimentological and stable isotopic studies of these rocks show prevalence of arid and evaporitic conditions during their depostion. Close resemblance of C-isotopic profiles of Hanseran evaporites and Bilara carbonates allows intra-basinal correlation and suggests that they are coeval facies variants. There are several characteristic carbon isotopic excursions one of which can be tentatively correlated with the globally recorded excursion close to the late Neoproterozoic-early Cambrian boundary. In contrast other peaks are possibly of regional significance and can be attributed to fluctuations in bioproductivity, correlatable with variation in nutrient supply on a basinal scale. Highly depleted carbon isotopic composition of the organic matter in subsurface organic-rich carbonates (Upper carbonate Formation, Baghewala-II core) has been ascribed to incorporation of biomass synthesized by chemoautotrophic bacteria under anoxic or eutrophic basinal condition caused by salinity stratification.抄録全体を表示PDF形式でダウンロード (1750K) -
Qinhong Hu, Robert C. Trautz, Joseph S. Y. Wang2004 年 38 巻 2 号 p. 177-189
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーField tracer experiments were conducted at an underground tunnel—the Exploratory Studies Facility (ESF)—at Yucca Mountain, Nevada, to investigate the localized preferential flow and transport resulting from multiple episodic liquid-release tests in unsaturated fractured tuff. Liquid was released into an isolated test interval (0.30 m long) within a borehole drilled along ESF. Out of 60 liquid-release tests, 36 contained tracers (mostly food and fluorescent dyes) to help us to elucidate the flow paths in unsaturated tuff. After the tracer-migration test, an array of 12 boreholes was drilled into the test area to collect rock samples. These samples were then analyzed to delineate the extent of tracer migration. Complementary laboratory column transport studies using crushed rock showed that the dye tracers were—at most—very weakly sorbed to the tuff matrix. We found that the tracer-migration test, with a limited release volume of 1.5 L, resulted in a localized distribution of tracers, most likely confined to a 1.0 × 1.6-m area directly below the test interval (over a vertical experimental length of about 0.65 m). This conclusion was corroborated by detecting dyes that had been introduced during previous liquid-release seepage tests either before or after niche excavation; the spatial distribution of all dyes was near their individual release intervals. Limited lateral spreading of the dyes occurred, even when several non-dye-containing seepage tests were intermittently conducted following dye release. This work also demonstrates the utility of applying multiple tracers (including food and fluorescent dyes) to help delineate transport characteristics in unsaturated fractured rock.抄録全体を表示PDF形式でダウンロード (2688K) -
Xiaoping Xia, Min Sun, Guochun Zhao, Huimin Li, Meifu Zhou2004 年 38 巻 2 号 p. 191-200
発行日: 2004/04/20
公開日: 2008/04/08
ジャーナル フリーA method for precise determination of 207Pb/206Pb and 206Pb/238U ratios of zircon was developed, using an ICP-MS with 213 nm Nd-YAG laser ablation system. Compared with the conventional 266 nm laser, the 213 nm laser has advantages of high absorption of energy and effective reduction of U-Pb elemental fractionation. The maximum fractionation during the first 80 seconds is about 1.3 times the initial value. In addition, by using a linear fit of 206Pb/238U ratios acquired during a depth profile analysis, U-Pb elemental fractionation can be further corrected and the precision of 206Pb/238U ratio measurement is improved to around 3% (2σ).抄録全体を表示PDF形式でダウンロード (1182K)
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