Earth Science (Chikyu Kagaku)
Online ISSN : 2189-7212
Print ISSN : 0366-6611
Volume 57, Issue 1-2
Displaying 1-9 of 9 articles from this issue
  • Masahiko HASHIMOTO
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 1-2
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
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  • Takashi SASE, Mamoru HOSONO, Masaaki SUZUKI, Kikuko TANINO
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 3-5
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
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  • Takaharu SATO
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 7-22
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
    Greenstones commonly occur within the Jurassic accretionary complex of the Chichibu terrane (central Kii Peninsula, Southwest Japan). In Gobanseki pass and Dorogawa areas, sharp contacts between the metagabbro with adjacent chert are exposed. Long axes of the metagabbro intrusive bodies are less than several ten meters in diameter, and makes stock or sheet. Field relationships indicate that metagabbro exhibited chilled margin and wavy, sometimes irregular boundary surface against chert. In the contact zone, the metagabbro changed to become dark green chilled margin, sometime a white glassy rock about 1cm from the boundary. Field occurrences and relationships indicate that the metagabbro intruded into unconsolidated pelagic sediments. The K-Ar age on kaersutite yielded age around 220±5.9 Ma. The metagabbro shows holocrystalline textures and is mainly composed of euhedral titanaugite, kaersutite, plagioclase, apatite and Fe-Ti oxide minerals. Some kaersutite grains overgrowth with titanaugite. Some metamorphic minerals including chlorite, albite, epidote, sphene and actinolite are present in the metagabbro, indicating that they have been affected by greenschist facies conditions. Their occurrence and petrography suggest they are of magmatic origin rather than representing tectonic blocks metamorphosed under amphibolite facies conditions. The chemical composition of the metagabbro is characterized by high contents of alkali (Na_2O+K_2O=1.9-6.8wt%), TiO_2 (2.5-7.8wt%), P_2O_5 (0.6-1.0wt%), Nb (66-113ppm) and Zr (262-414ppm). The geochemical characteristic suggests that they are similar to OIB-type alkali basalt and basalt originating from superplume.
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  • Miyabi SUGAWARA, Yoshihiro UJIIE
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 23-30
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
    Living spores of Athyrium niponicum were heated at 62 to 302℃ for 24 hours under the atmosphere in the laboratory to investigate the changes in physical and chemical characters of spores and hydrocarbon generation from spores during artificial heating experiments. It was shown that the heated spores have decreasing trends of weight, size, atomic H/C ratio and brightness (stTAI; Ujiie 2001) with increasing heating temperature, but an increasing trend of atomic N/C ratio, especially in the range of high temperature. It is concluded from the judgment of decreasing trend of the atomic H/C ratio in the heating experiments that hydrocarbon generation from spores should take place in the temperature range of about 159 and 237℃.
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  • Collaborative Researth Group on the Matsukawa-ura
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 31-48
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
    The authors studied the benthic fauna living on the tidal flat at six survey locations in Matsukawa-ura, Fukushima Prefecture: the north side of Junihonmatsu (A), the west side of Kikaijima (B), Ushirowada (C), the mouth of Udagawa River (D), northwest of Unoosaki (E) and the north-west side of Oosu bar (F). Their composition and exo- and endogenic lebensspuren were observed. A quadrangle survey of the benthic fauna was carried out to determine weight of biomass, population density, co-existent fauna and depositional environment of the substratum of the lebensspuren at each survey point. Thirty-two species benthic animals were identified at A-E survey points. On the mouth of the Udagawa River (D) and northwest of Unoosaki (E), numbers of species is smaller than those at the other three locations. Ten bio-zones are recognized by dominant species (dominant benthos zones) from low to high tidal levels. The Scopimera globosa zone occurred at high tidal level has fewer biomass, while the Ilyoplax pusillus and Macrophthalmus (Mareotis) japonicus zones occurred at low tidal level have more biomass. The authors described the lebensspuren of nine kinds of benthic fauna, including crustaceans, bivalves, gastropods and nereids in terms of their apertures, digging structures, feeding pellets, vertical sections, surface of inner walls and lining of burrows and relationship between burrows and substrates. These data cannot be obtained by plaster casting method. The authors studied not only individual lebensspuren but also following related subjects: comparing the similarly-shaped burrows, for example, Macrophthalmus (Mareotis) japonicus and Helice tridens tridens, Scopimera globosa and Ilyoplax pusillus; difference in population density; modification of Ilyoplax pusillus burrows in the Ilyoplax pusillus-Helice tridens tridens zone; population density in the Ilyoplax pusillus-Macrophthalmus (Mareotis) japonicus zone; the existence of lining of inner walls. Conceptual model was made to show a cross-section of the lebensspuren assemblage. Diatom flora were preliminarily investigated on the portions of lebensspuren (aperture, lining material, digging structures, feeding pellets) and their surrounding bottom material.
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  • Yoshiki KODA, Yukio YANAGISAWA, Yoshikazu HASEGAWA, Hiroyuki OTSUKA, M ...
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 49-59
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
    A fossil elephantoid mandible was found in a mudstone boulder on the riverbed of the Nakagawa river at Katsura village, Ibaraki Prefecture, eastern Japan. This specimen (Katsura specimen) is assigned to a left mandible of the genus Stegolophodon. It is made of broken ramus with three molars in situ. The first molar is only represented by a tip of tooth-root, and the second one is severely abraded, but the last one is rather well preserved. The mandible is presumed to be derived from the lower part of the Asakawa Formation distributed around the fossil site. The geological age of the fossil is assigned to the earliest middle Miocene based on fission track dating and chronostratigraphic data.
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  • Atsuyuki OHTA, Noboru IMAI, Takashi OKAI, Hidenori ENDO, Takemasa ISHI ...
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 61-72
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
    Seventy-three sediment samples were collected in Sendai City, and their bulk components and soluble components in 0.1N HC1 were analyzed by AAS, ICP-AES and ICP-MS. The data are expressed graphically on geochemical maps and used to estimate natural background of respective elements and find the pollution enhanced by human activity. The characteristics of geochemical maps for bulk components reflect the geology of background area. The elemental concentrations are controlled mainly by the underlying mineral substrate in the study area such as sedimentary rock with acid tuff and andesite-basalt lava. The geochemical maps of soluble components in 0.1N HC1 have the similar trends to those of bulk components. Although the unstable phase is only a fraction of the stream sediments, the 40-70% of the contents of Cu, Zn and Pb in stream sediments is attributable to this phase. The application of geochemical maps to environmental assessment reveals the influence of agricultural pollution in the area of rice field where P concentrations in the bulk and acid soluble components are very high. However, we did not find any anomalous distributions of elemental concentrations in the urban area where many anthropogenic materials are found in stream sediments and river water is tainted by human activity.
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  • Tomio OTSUKA
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 73-82
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
    Derorinatio ndsuc to liguefactie nin peat bcds are describc di'ru itnhrec localit ; Takasaki City and Itakura Town, Gumma Prefecture and Echigo-Kawaguti Town, Niigata Prefecture. The liquefaction in Takasaki occurs in a late Pleistocene pumice bed, part of the Maebashi Peat Formation, originated from Asama Volcano. The thickncss of the pumice bed is laterally hig}hly variable showing flame-like structure in places. The age of the liquefaction is estimated to be 16 thousand years BP from radiometric ages of the peat bed and overlying pumice fall. The liquefaction trace at Itakura Town is observed in the Holocene peat and sand beds. Due to lateral flow of sand bed at the time of liquefaction, wedge and ball structures are formed. At Echigo-Kawaguchi, structures due to lateral movement of sand bcds within peat beds of thc river terrace deposits are observed. In all the cases clear upward-intrusions and sand dikes are not seen, but the deformation of peat beds accompanying lateral movement of liquefied materials are observed resulting in chaotic structures. It is impossible to make a conclusion that these structures have been formed by paleo-earthquakes. but there is a large poessibililty left. The recognition of these characteristic features may be effective to clarify a local seismic history.
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  • Kazuo OHTAKE, Ryuichi YASHIMA
    Article type: Article
    2003 Volume 57 Issue 1-2 Pages 83-88
    Published: March 15, 2003
    Released on J-STAGE: July 14, 2017
    JOURNAL OPEN ACCESS
    The authors have examined structures, mode of occurrence, lithology, radiometric ages and arrangement of volcanic bodies to demonstrate the existence of 'Late Miocene to Pliocene volacanic front' in Northeast Japan (e.g. Yashima and Ohtake 1998; Yashima et al. 1999). Ten rock bodies of acidic volcanics have been identified in the northwestern part of the Iizaka district, Fukushima City. Because these lava domes have been weathered and eroded intensively, they are herein called as 'volcanic bodies'. K-Ar dating of six rock bodies of the acidic volcanics gives ages around 8 and 6 Ma, and indicates that the volcanic activity is correlative with the Late Miocene epoch. The Akagawa Formation, which consists largely of non-marine acidic pyroclastic deposits, is distributed around the rock bodies of acidic volcanics. It has been confirmed by field observations that the Akagawa Formation is an eruptive product of a series of volcanic activities that generated the rock bodies of acidic volcanics. Generally speaking, two volcanic processes, that is, deposition of the acidic pyroclastics and intrusion and or extrusion of the acidic volcanics, seem to have proceeded alternatively for a long period of time. The authors regard the newly aquired age data as a supportive evidence of the possible existence of the Late Miocene to Pliocene volcanic front.
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