GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
Volume 53 , Issue 2
Showing 1-6 articles out of 6 articles from the selected issue
  • Katsuhito Soda, Tetsuji Onoue
    Type: research-article
    2019 Volume 53 Issue 2 Pages 91-102
    Published: 2019
    Released: April 05, 2019
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    The Middle Triassic has been interpreted as the epoch of the biotic recovery phase from the end-Permian mass extinction. In particular, the early Middle Triassic (Anisian) oceanic anoxic events are thought to be important as the final ones before the rebuilding of marine ecosystems with complex trophic levels such as modern. However, details of global environmental and biotic changes during the Anisian oceanic anoxic events remain unclear. In this study, we applied multivariate analysis to extract geochemical components controlling chemical compositional changes on the high resolution geochemical stratigraphy of the Middle Triassic (Anisian) bedded chert sequence in central Japan, which deposited in a pelagic deep seafloor in a low- to mid-latitude zone of the Panthalassic Ocean. Two geochemical components were extracted from the major elemental compositions. The first component explained the chemical weathering intensity, whose statistics indicate that the chemical weathering intensity increased before and decreased within or after the anoxic conditions. The second component represented the biogenic apatite accumulation, whose statistics suggest that the higher biogenic apatite accumulation during the oxic conditions and the minor variations in this dataset. Integrated stratigraphic data suggest that the chemical weathering intensity controlled the timings and the durations of the middle Anisian oceanic anoxic events and these situations affected the biogenic apatite accumulation.

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  • Sebastian Oscar Danielache, Chisato Yoshikawa, Mizuo Kajino, Satoshi I ...
    Type: research-article
    2019 Volume 53 Issue 2 Pages 103-118
    Published: 2019
    Released: April 05, 2019
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    We present a numerical study conducted using a regional Lagrangian model to account for the transport, deposition and radioactive decay of 35S in sulfur dioxide and sulfate aerosols emitted into the atmosphere during the Fukushima Dai-ichi Nuclear Power Plant incident. The model is a Eulerian-Lagrangian hybrid system that accounts for chemical conversion of SO2 into SO42− in a Eulerian manner. The simulations were compared to field measurements of atmospheric 35S in sulfate collected at Kawamata, Tsukuba, Kashiwa, Fuchu and Yokohama, Japan. The 35S emission scenario that best replicated the field measurements followed the same temporal variation pattern as the 134/137Cs emissions. These results suggest that 35S and 134/137Cs follow a similar release pattern. Among the considered emission scenarios, a maximum flux of emitted chemical compounds was assumed to be either 100% 35SO42− or 100% 35SO2, with values of 4.0 × 1019 molecules/hour and 4.0 × 1020 molecules/hour, respectively on March 14th. These emission scenarios reflect the findings reported in the literature, where traces of 35SO2 were measured along with 35SO42−, so the actual emission is expected to be a combination of both chemical forms. The Kawamata measurements (Figs. 5 and 6) presented a large concentration in the July–August period, several months after emissions decreased by more than an order of magnitude. To explain this anomaly, re-suspension ratios were calculated for the Kawamata site, which ranged between 0.1 and 1.5% and partially, but not fully, explain the large measured concentrations. Furthermore, they show large discrepancies with 134/137Cs re-suspension values for measurements at the town of Namie. This situation indicates a lack of understanding of the transformations of 35S that occurs after deposition and the mechanisms involved in the 35S re-suspension process.

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  • Hirotaka Nishino, Tasuku Akagi
    Type: research-article
    2019 Volume 53 Issue 2 Pages 119-137
    Published: 2019
    Released: April 05, 2019
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    To examine the hypothesis that vertical distribution of rare earth elements (REEs) in the oceans are controlled by surface plankton, a self consistent algorithm was developed, in which reported vertical profiles of REEs and nutrients (Si or P) are given variables with the REE composition of surface plankton being one of the solutions. In the calculations the composition of surface plankton (primary scavenging) was tuned such that the sum of two relative standard deviations (RSDs), i.e., the RSD of partitioning pattern of secondary scavenging at sampling depths of all REEs and the RSD of discrepancy of the reproduced vertical profiles from those observed at all depths, is minimized, where the partitioning pattern of scavenging is obtained by averaging the obtained partitioning pattern of scavenging at all depths. In the Pacific Ocean the calculation was successful in both the Si- and P-based calculations; whereas in the Indian and Atlantic Oceans the calculation was much more successful in the P-based calculation than the Si-based calculation. This implies that diatom frustules and organic components in surface plankton comprise primary scavengers: the former mainly in the Pacific Ocean and the latter possibly in all three oceans examined. In the successful calculations the results were consistent: the calculated composition of surface plankton is typically enriched with heavier (H) REEs against that of shale; the obtained partitioning patterns of the scavenging consistently showed maxima around lighter (L) + middle (M) REEs and slight increases toward Lu. In the North Pacific Ocean, if Si is regarded as a representative nutrient, the composition of surface plankton thus calculated is almost identical to the reported composition of diatom frustules. Carbonate/oxide and organic matter are considered to be the main secondary scavengers of L+M and H REEs, respectively. The residence times of REEs can be calculated relative to the turnover rate of nutrient. Those of M+HREEs are typically in the range of 1000–2500 years in the three oceans; the residence times of LREEs in the Pacific Ocean (1000–2500 years) are longer than those of the other two oceans (<1000 years).

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  • Kotaro Toyama, Yasutaka Terakado
    Type: research-article
    2019 Volume 53 Issue 2 Pages 139-150
    Published: 2019
    Released: April 05, 2019
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    The practical partition coefficients of rare earth elements (REEs) between limestone and seawater were examined by comparing the data of some young limestones, present-day biogenic carbonates, and those experimentally obtained. The plausible REE partition coefficients for the limestone studies were obtained from the REE data of Quaternary limestones and modern seawaters. The inferred partition coefficients range from 214 for La to 327 for Ce, and show a nearly flat REE pattern. These REE partition coefficients were applied to some Carboniferous to Quaternary limestone samples that have been considered to involve a lesser amount of non-carbonate materials (i.e., clay, apatite, and Fe-Mn oxyhydroxide). The estimated REE patterns of the paleoseawaters show various sizes of negative Ce anomalies and LREE depletions, and these features are similar to those seen in modern seawaters regardless of the limestone ages.

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  • Jessica Larissa Lima, Ricardo Scholz, Cristiano Lana, Glaucia Queiroga ...
    Type: research-article
    2019 Volume 53 Issue 2 Pages 151-170
    Published: 2019
    Released: April 05, 2019
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    Geochemical studies on mica and tourmaline and boron isotopic analysis on tourmaline from pegmatites of the Conselheiro Pena Pegmatitic District—Eastern Brazilian Pegmatite Province—were conducted in order to: 1) analyze their relationship with the Urucum granite, believed to be their source pluton; 2) investigate their origin and evolution; and 3) assess their economic potential. Considering the fractionation from a granitic pluton as the most accepted model for pegmatite genesis, some factors suggest the study pegmatites do not represent residual magmas from the Urucum suite fractionation: the granites from this suite cannot be classified as fertile according to the chemical composition of its facies; the emplacement of rare element pegmatites around and within the Urucum granite is inconsistent with the model of evolution as they fractionate from a common granitic intrusion; and there are no clear geochemical trends among mineral separates from the pegmatites and the Urucum suite. Boron isotope analysis measured on tourmaline crystals yielded δ11B values in the range of –16.3 to –11.3‰ (n = 86) for the pegmatites, –13.8 to –11.5‰ (n = 8) for the São Tomé Formation host schists and –14.0 to –13.1‰ (n = 6) for the Córrego do Onça facies (tourmaline-bearing) of the Urucum suite. This extremely similar isotopic composition suggests all the analyzed rocks come from a common source, but more studies are needed to determine which source may it be. Most pegmatites are classified as complex and some (Boca Rica, Cigana and Pomarolli) are Li-bearing, with spodumene, triphylite and/or amblygonite. However, mica and tourmaline chemical compositions are inconsistent with the presence of such Li-minerals in that where these are present, mineral separates show low values of Li, Rb, Cs and Sn, while mica and tourmaline from pegmatites without Li-minerals (Urucum, Sapo and Jonas) show higher amounts of such elements. Therefore, chemical analysis of these mineral separates seems, in this case, uncorrelated to the economic potential for Li exploration, and the data should be used with caution. Nevertheless, pegmatites are economically attractive for gems and collection minerals, being two of them (Sapo and Itatiaia) potentially suitable for Ta exploration.

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Express Letter
  • Tung Thanh Phan, Atsuko Yamazaki, Hong-Wei Chiang, Chuan-Chou Shen, La ...
    Type: research-article
    2019 Volume 53 Issue 2 Pages e1-e7
    Published: 2019
    Released: April 05, 2019
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    The offshore flow of the Mekong River is strongly governed by the East Asian monsoon (EAM). Monthly-resolved skeletal carbonate Sr/Ca, Ba/Ca and oxygen isotope (δ18Oc) data from 1980 to 2005 of a Porites coral from Con Dao Island, ~90 km from the Mekong River mouth, were analyzed for capturing the past flood events and the signal of East Asian winter monsoon. Ba/Ca time series is characterized with intra-annual double peaks, the first large one in March during the dry season and relative small one in August during the wet season. The low values of seawater δ18O (δ18Osw), deduced from both the Sr/Ca ratio and δ18Oc, in the wet season resulted from precipitation and/or freshwater input from the Mekong River. The difference in the seasonal characteristics of Ba/Ca and δ18Osw between flood and no-flood years could be attributed to the seasonal reversal of the regional ocean current derived from the EAM.

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