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Volume 36, Issue 1
Displaying 1-7 of 7 articles from this issue
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Genji Saito, Hiroshi Shinohara, Kohei Kazahaya2002 Volume 36 Issue 1 Pages 1-20
Published: February 20, 2002
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSUp to 15 fumarolic gas samples were collected successively within a few hours at Satsuma-Iwojima and Kuju volcanoes, southwest Japan, with the aim to evaluate the naturally occurring short-term variations in the chemical and isotopic compositions. Variations in the concentrations of the major gas components (CO2, total S, SO2 and H2S) and in the hydrogen, oxygen (H2O) and carbon (CO2) isotopic compositions were relatively small and were within the analytical errors. Exceptions were HCl at both volcanoes, CO2 at Satsuma-Iwojima, and D/H and 18O/16O ratios of water at Kuju volcano. Large variations were found for the minor gas components, i.e., N2, Ar, CH4 and CO. The observed variations in HCl and CO concentrations probably relate to sampling and analytical procedures. Variations in HCl, N2, Ar and CH4 concentrations, and D/H and 18O/16O ratios of water may result from processes such as gain or loss of HCl-rich liquid, sporadic additions of air and hydrothermally-derived CH4 and change of mixing ratio between magmatic and meteoric waters. Precision associated with the gas sampling and analytical techniques used in this study were estimated by making the hypothesis that the chemical and isotopic compositions of the fumarolic gases did not change during the sampling period. The estimated precision was 1–3% for CO2, H2S and SO2, 6–11% for HCl, 1–6% for H2, 4–6% for N2, 5–9% for Ar, 2% for CH4 and 7–27% for CO. The precision of the isotopic analyses was estimated to be 0.05–0.2‰ for 13C/12C ratio of CO2. Also the precision was 0.9 and 0.05–0.11‰ for D/H and 18O/16O ratios of the condensates, respectively. The results in this study suggest that careful sampling and analysis of volcanic gases provide reliable chemical and isotopic compositions that can be used to monitor volcanic activities.View full abstractDownload PDF (389K) -
Hailong Lu, Ryo Matsumoto2002 Volume 36 Issue 1 Pages 21-30
Published: February 20, 2002
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe stability conditions of methane hydrate in a nannofossil-rich claystone column have been investigated using a temperature-controllable pressure vessel. Careful analyses of the reaction process of the experiments confirmed the formation of methane hydrate in sediments, then the pressure-temperature stability conditions of methane hydrate were recognized from the beginning and end of each hydrate dissociation step. The results show that the stability condition of methane hydrate at a given pressure in the test sediment column is shifted to the lower temperature field by 0.4°C and 1.5°C relative to those in sea water and pure water, respectively.View full abstractDownload PDF (260K) -
Hikaru Yabuta, Hajime Mita, Akira Shimoyama2002 Volume 36 Issue 1 Pages 31-49
Published: February 20, 2002
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSForty five mono and 12 bicyclic alkanes were detected in a sedimentary sequence from Miocene to Pliocene in the Shinjo basin, northeastern Japan. The monocyclic alkanes included polyalkylcyclohexanes (C9, C10, C11, and C13), a series of n-alkylcyclohexanes (C9–C26) and a series of n-alkylcyclopentanes (C12–C26). The bicyclic alkanes were from C9 to C12, including cis- and trans-hydrindanes, cis- and trans-decalins, and methyl- and dimethyldecalins. These cyclic alkanes were detected at a level of 0.01–1 nmol g-1. Concentrations of 2-alkyl-1, 1, 3-trimethylcyclohexanes (C11 and C13), a major portion of n-alkylcyclohexanes (C11–C26), all n-alkylcyclopentanes, and methyl- and dimethyldecalins showed a maximum in the lower part of the sequence which has been known to be an oil generation zone. n-Alkane (C15–C38) concentration as well as that of pristane and phytane also showed a maximum in the lower part. Concentrations of 1, 1, 3-trimethyl-, and 1, 1, 2, 3-tetramethylcyclohexanes, a minor portion of n-alkylcyclohexanes (C9 and C10), cis-hydrindane, cis- and trans-decalin showed a maximum in the middle part of the sequence. Only trans-hydrindane showed a maximum concentration in the upper part of the sequence, as did perylene. The molecular distributions of series of n-alkylcyclohexanes (C15–C26) and n-alkylcyclopentanes (C15–C26) showed a predominance in a range from C15 to C18 in the upper part of the sequence, whereas that of n-alkanes did from C27–C31 in the part. However, the distributions of the three series became relatively smooth in the lower part, reflecting the further progress of diagenetic maturation resulting from the oil generation in the part.View full abstractDownload PDF (944K) -
Masahiro Oba, Hajime Mita, Akira Shimoyama2002 Volume 36 Issue 1 Pages 51-60
Published: February 20, 2002
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSKerogen recovered from Neogene Shinjo sediments was heated from room temperature to 800°C using a thermogravimetric analyzer (TG). Organic compounds released from kerogen during heating were trapped and analyzed by a gas chromatograph (GC)-mass spectrometer (MS). Among these compounds, benzene, hexane, toluene, phenol, heptane, and indene were selected to determine temperatures at which maximum release of these compounds occurred based on TG-MS peak profiles. This analysis was carried out using programmed heating rates (Hr) of 5, 10, 20, 30, and 60°C min-1 and five temperatures at peak tops (Tmax in absolute temperature) were determined for each compound. The plot of 1/Tmax vs. ln(Hr/(Tmax)2) for each compound showed a good straight line with a high correlation coefficiency. Accordingly, a mean activation energy (E0) and pre-exponential factor (A) at E0 for each compound on the release from kerogen were calculated, using the equation of the approximate method (or Gaussian E-distribution method) by Braun and Burnham (1987), ln(Hr/(Tmax)2) = −E0/RTmax + ln(AR/E0) where R is the ideal gas constant. The activation energies and pre-exponential factors of these compounds were in a range of 43.1 to 60.9 kcal/mol and of 3.56 × 1010 to 1.21 × 1016 s-1, respectively. The averages of the activation energies and pre-exponential factors obtained from the five kerogens had decomposition rates in order of indene > benzene, toluene > phenol > hexane, heptane, which indicated that hexane and heptane were more strongly bound to kerogen than the three aromatic hydrocarbons.View full abstractDownload PDF (184K) -
Etsuo Uchida, Teppei Sakamori, Jin Matsunaga2002 Volume 36 Issue 1 Pages 61-72
Published: February 20, 2002
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSIn order to obtain the stepwise formation constants of tri-chloro complexes of Pb2+ and Sn2+, experiments on the effect of NaCl concentration on the ion exchange equilibria in the systems PbS–ZnS–PbCl2–ZnCl2–H2O and CaWO4–SnWO4–CaCl2–SnCl2–H2O were carried out. The experiments were conducted at 500°, 600°, 700° and 800°C (800°C is only for Sri2+), 1 kbar and also at 600°C, 0.5 kbar using 2 m aqueous chloride solutions. In all the experiments, the Σm(Pb)/(Σm(Pb) + Σm(Zn)) ratio of the aqueous chloride solutions in equilibrium with both PbS and ZnS and the Σm(Ca)/(Σm(Ca) + Σm(Sn)) ratio of the aqueous chloride solutions in equilibrium with both CaWO4 and SnWO4 decrease with the increase of NaCl concentration. The experimental results were analyzed thermodynamically using the previously published dissociation constants for NaClaq, CaCl2aq and ZnCl3-aq. As a result, the stepwise formation constants (log K) for PbCl3-aq (PbCl2aq + Cl-aq = PbCl3-aq) were obtained to be −0.1 at 500°C and 1 kbar, 0.9 at 600°C and 1 kbar, 1.4 at 700°C and 1 kbar, and 1.3 at 600°C and 0.5 kbar. The stepwise formation constants (log K) for SnCl3-aq (SnCl2aq + Cl-aq = SnCl3-aq) were obtained to be 0.5 at 500°C and 1 kbar, 1.4 at 600°C and 1 kbar, 2.0 at 700°C and 1 kbar, 2.6 at 800°C and 1 kbar, and 1.9 at 600°C and 0.5 kbar. The stepwise formation constants (log K) of tri-chloro complexes of Pb2+, Sn2+, Fe2+, Mn2+, Co2+, Ni2+, Zn2+ and Cd2+ vary with sixfold coordinated ionic radius showing a parabola-shaped curve with a maximum between Mn2+ and Cd2+. This may suggest that the best ionic radius for tri-chloro complex exists between Mn2+ and Cd2+.View full abstractDownload PDF (397K) -
Hideyoshi Yoshioka, Ryoshi Ishiwatari2002 Volume 36 Issue 1 Pages 73-82
Published: February 20, 2002
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSAn infrared (CO2) laser micropyrolysis system for analyzing organic matter in rock was developed and applied to a Green River shale sample. A series of n-alkanes (C8–C33), isoprenoids (C18–C20), triterpenoids (C27–C31), and steranes (C27–C29), as well as β-carotane (C40), were detected as the main compounds in the laser pyrolysates without serious degradation. These results indicate that infrared laser micropyrolysis is superior to short-wavelength laser micropyrolysis in determining the original molecular composition of organic matter in a rock sample. By comparing the infrared laser pyrolysates with the solvent-extractable organic matter from the shale and the conventional flash pyrolysates of the macromolecules (kerogen) in the rock, we concluded that the infrared laser pyrolysates come from thermal evaporation of solvent-extractable organic compounds and pyrolytic fragmentation of the macromolecules. Roughly equal amounts of the thermal extracts of bitumen in the sample and the pyrolysis products were produced under the experimental conditions.View full abstractDownload PDF (336K) -
K. Gopalan2002 Volume 36 Issue 1 Pages 83-89
Published: February 20, 2002
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSIt is shown that two internal reference isotopic ratios of an element permit direct and exact power law correction for mass fractionation of its isotopically spiked ratios from dynamic multicollector measurements. Applications of this method to spike calibration and a few elements of geochronological interest are discussed.View full abstractDownload PDF (36K)
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