GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
47 巻 , 4 号
選択された号の論文の8件中1~8を表示しています
  • YUTARO TAKAYA, KENTARO NAKAMURA, YASUHIRO KATO
    2013 年 47 巻 4 号 p. 385-396
    発行日: 2013/08/20
    公開日: 2013/11/26
    ジャーナル フリー
    Basaltic aquifers have the potential to provide secure option for CO2 sequestration. Because basaltic rocks are widely distributed around the world, their capacity for storage of anthropogenic CO2 emissions is enormous. In addition, geochemical trapping of CO2 injected into basaltic aquifers occurs quickly, because basaltic rocks contain many cations that react with CO2 to form stable carbonate minerals. Two types of large-scale basaltic aquifers may be suitable for sequestering huge amounts of anthropogenic CO2: continental flood basalt aquifers and deep-sea basalt aquifers. Here, we assess the potential of these two CO2 sequestration options from geological, geochemical and social-scientific perspectives. From a geological and geochemical viewpoint, both continental flood basalt and deep-sea basalt aquifers have excellent CO2 storage potential. In deep-sea basalt aquifers, however, storage of injected CO2 may be more secure than in continental flood basalt aquifers, because leakage of CO2 to the atmosphere is minimized by geological, geochemical and physical barriers associated with the deep-sea environment. In addition, from a social-scientific point of view, several current CO2 injection projects in continental flood basalts have encountered problems due to groundwater depletion, and large-scale implementation of CO2 storage in continental flood basalt aquifers might cause contamination of freshwater resources needed for domestic and agricultural use. In striking contrast to continental flood basalts, deep-sea basalts can be used for CO2 storage without encountering critical problems, because deep-sea basalt aquifers have no economic value. We conclude, therefore, that deep-sea basalt aquifers are a better option for CO2 storage than continental flood basalt aquifers.
  • ASSEM O. BARAKAT, BARBARA M. SCHOLZ-BÖTTCHER, JÜRGEN RULLK&O ...
    2013 年 47 巻 4 号 p. 397-407
    発行日: 2013/08/20
    公開日: 2013/11/26
    ジャーナル フリー
    The distribution of free sterols in a sulfur-rich lacustrine sediment of Miocene age deposited in the ancient crater lake of the Nördlinger Ries (southern Germany) was investigated and compared with the corresponding distributions of esterified and kerogen-bound sterols. The three fractions exhibited the same suite of principal sterols, with 4α,24-dimethyl-5α-cholestan-3β-ol, dinosterol and dinostanol displaying the highest concentrations and relative abundances. The distributions of sterols, steroidal ketones, n-alkanols and isoprenoid alcohols suggest a prevalent deposition of autochthonous aquatic organic matter under saline conditions. In particular, the high abundance of 4α,24-dimethyl-5α-cholestan-3-one, dinosterone and dinostanone and the corresponding 4-methyl sterols indicates the importance of dinoflagellate productivity in this former crater lake and its significant contribution to the sedimentary lipids in the Nördlinger Ries sediment. The similarity in structures and relative abundance of the major 4-methyl sterols and the corresponding steroidal ketones suggest that they are biosynthetically linked.
  • HIROSHI AMAKAWA, HIROFUMI TAZOE, HAJIME OBATA, TOSHITAKA GAMO, YUJI SA ...
    2013 年 47 巻 4 号 p. 409-422
    発行日: 2013/08/20
    公開日: 2013/11/26
    ジャーナル フリー
    We report two vertical profiles of the concentration and isotopic composition of neodymium (Nd) in seawater samples collected at 20°S and 30°S along a longitude of 170°W in the Southwest Pacific Ocean. At depths below 500 m, Nd isotopic composition values are less radiogenic than those obtained from the subtropical North Pacific. The minimum εNd values of -8.0 and -6.9 at depths of 800 to 1000 m correspond to Antarctic Intermediate Water (AAIW). The differences in εNd values between upper deep water (2000-3000 m) and lower deep water (>4000 m) seem to be associated with Upper and Lower Circumpolar Deep Waters (UCDW and LCDW, respectively). The radiogenic Nd supply to AAIW from the Society Islands is estimated to be 30 ± 22 tons Nd/yr, which is consistent with the estimates from previous studies conducted in the same location and the oceanic region close to the Hawaiian Islands. Our study demonstrates the uniqueness of Nd isotopic composition distributions in the Southwest Pacific Ocean. These results may be valuable for tracing present and past ocean circulation in this region.
  • GALIP YUCE, LUTFI TASKIRAN
    2013 年 47 巻 4 号 p. 423-435
    発行日: 2013/08/20
    公開日: 2013/11/26
    ジャーナル フリー
    The aim of this study was to understand geochemistry of thermal fluids circulating in the basin at the southwest of Tekman (Erzurum, Turkey) Geothermal Province in Eastern Anatolia as well as to estimate reservoir temperature and its heat source by assessment of helium and carbon isotopic compositions of liquid and gas samples. Deep thermal and cold shallow groundwaters are NaCl type (Cerme and Ilipinar springs) and Ca-Mg-HCO3 type, respectively. The discharge temperatures of thermal waters vary between 29 and 57°C. The reservoir temperatures were estimated by solute silica and cation geothermometers vary from 80 to 110°C. CO2 is the dominant gas in geothermal fluids with variable amounts of nitrogen, helium and CH4. The isotopic ratios of helium that range from 1.03 to 1.54Rac show a range crustal to magmatic-type values. The isotopic composition of carbon (CO2) obtained from the bubbling and dissolved gases shows the variation from -0.2 to 3.4‰ vs. PDB. The mantle derived fluids interact at shallower levels with circulating meteoric waters and originate geothermal systems from which equilibration temperatures were estimated up to 192°C by gas geothermometers.
  • EMANUELA BAGNATO, GIANCARLO TAMBURELLO, ALESSANDRO AIUPPA, MARIO SPROV ...
    2013 年 47 巻 4 号 p. 437-450
    発行日: 2013/08/20
    公開日: 2013/11/26
    ジャーナル フリー
    There have been limited studies to date targeting mercury emissions from volcanic fumarolic systems, and no mercury flux data exist for soil or fumarolic emissions at Santorini volcanic complex, Greece. We present results from the first geochemical survey of Hg and major volatile (CO2, H2S, H2O and H2) concentrations and fluxes in the fumarolic gases released by the volcanic/hydrothermal system of Nea Kameni islet; the active volcanic center of Santorini. These data were obtained using a portable mercury spectrometer (Lumex 915+) for gaseous elemental mercury (GEM) determination, and a Multi-component Gas Analyzer System (Multi-GAS) for major volatiles. Gaseous Elemental Mercury (GEM) concentrations in the fumarole atmospheric plumes were systematically above background levels (~4 ng GEM m-3), ranging from ~4.5 to 121 ng GEM m-3. Variability in the measured mercury concentrations may result from changes in atmospheric conditions and/or unsteady gas release from the fumaroles. We estimate an average GEM/CO2 mass ratio in the fumarolic gases of Nea Kameni of approximately 10-9, which falls in the range of values obtained at other low-T (100°C) volcanic/hydrothermal systems (~10-8); our measured GEM/H2S mass ratio (10-5) also lies within the accepted representative range (10-4 to 10-6) of non-explosive volcanic degassing. Our estimated mercury flux from Nea Kameni’s fumarolic field (2.56 × 10-7 t yr-1), while making up a marginal contribution to the global volcanic non-eruptive GEM emissions from closed-conduit degassing volcanoes, represents the first available assessment of mercury emissions at Santorini volcano, and will contribute to the evaluation of future episodes of unrest at this renowned volcanic complex.
  • YUAN BAO, CHONGTAO WEI, CHAOYONG WANG, LAICHENG LI, YIMIN SUN
    2013 年 47 巻 4 号 p. 451-458
    発行日: 2013/08/20
    公開日: 2013/11/26
    ジャーナル フリー
    Six woody peat samples were heated to 150, 250, 300, 350, 370, and 400°C to determine their geochemical characteristics and identify whether the coal bed methane (CBM) was thermogenic or secondary biogenic. The experiments were conducted in a closed pyrolysis system, from which the generated pyrolysis gas was collected. The composition of the gas and its carbon and hydrogen isotope concentrations were also determined. The results indicate that methane and carbon dioxide were the main hydrocarbon and non-hydrocarbon gases generated from the samples. The carbon isotopic compositions of the generated methane, ethane, and propane became initially lighter and then heavier with increasing experimental temperature; conversely, the hydrogen isotopic composition of the generated methane and the carbon isotopic composition of the generated carbon dioxide became gradually heavier. Therefore, a strong positive correlation exists between the aforementioned parameters. In addition, relationships have been established between carbon and hydrogen isotopic contents and Ro values, and a model for the identification of the maturity and relative content of thermogenic CBM is proposed. Then, the model was applied in a case study to evaluate the gas source of CBM in the Luling CBM field in Anhui Province, China.
  • XIAOPING XIA, ZHONGYUAN REN, GANGJIAN WEI, LE ZHANG, MIN SUN, YUEJUN W ...
    2013 年 47 巻 4 号 p. 459-468
    発行日: 2013/08/20
    公開日: 2013/11/26
    ジャーナル フリー
    A method for in situ rutile U-Pb dating was developed using a multiple-collector (MC) ICPMS coupled to an excimer laser-ablation system. Compared with single collector Quadruple ICPMS used by previous in situ rutile U-Pb dating studies, the Neptune Plus MC-ICPMS used in this study has higher sensitivity and is capable of simultaneous acquisition of all the isotope signals required for rutile U-Pb dating. These advantages are important to achieve precise and reproducible in situ U-Pb dating results for rutiles, which typically contain low abundances of U and radiogenic Pb. The analytical results in this study on three reference rutile standards (R10, JDX and DXK) and one nature rutile sample (07RU3) agree with literature/known values, thereby demonstrating that this technique can yield precise and accurate U-Pb dating results for Paleozoic to Paleoproterozoic rutile, even with ~1 ppm U.
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