The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 105, Issue 5
Displaying 1-7 of 7 articles from this issue
  • Shoichi Shimoyama, Hiroko Kinoshita, Momo Miyahara, Yukari Tanaka, Tos ...
    1999 Volume 105 Issue 5 Pages 311-331
    Published: May 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Data from the ancient shorelines along the present-day coastline of Kyushu Island, Western Japan, show that the island can be divided into several regions on the basis of modes of vertical crustal movements during the past 125, 000 years. The heights of the ancient shorelines have been determined using paleodepth indicators such as molluscan faunas, trace fossils and sedimentary structures. The chronology of the sediments and of the tectonic events have been deduced from the well-documented history of volcanic ash events (tephrostratigraphy) of southwestern Japan.The difference between the most uplifted and subsided areas in the island during the past 125, 000 years is about 190 meters. Although it was previously thought that the whole of Kyushu Island was an uplifting region throughout this time, the present work has shown that there were marked differential movements.Northern and southwestern Kyushu were steadily subsiding areas, but rapid uplift occurred locally in the southeastern part of the island. A subsiding axis (the Saeki-Sendai Subsiding Axis) crosses the island with a NE-SW trend, and an E-W trending structural depression (the Beppu-Shimabara Graben) is present in central Kyushu.There is a clear correlation between the present-day coastal landforms of the island and the differential tectonic movements that have occurred during the past 125, 000 years.
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  • Shusaku Yoshikawa, Muneki Mitamura
    1999 Volume 105 Issue 5 Pages 332-340
    Published: May 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Quaternary sediments of the Osaka Plain are composed mainly of unconsolidated sand, gravel, silt and clay intercalated with a number of volcanic ash layers. These sediments are divided into three units, the late Pliocene to early Pleistocene Miyakojima Formation, early Pleistocene to late Pleistocene Tanaka Formation and late Pleistocene to Holocene alluvial deposits. The Miyakojima Formation is of freshwater facies, while freshwater facies of the Tanaka Formation and the alluvial deposits are frequently intercalated with strata of shallow marine facies. Twenty marine clay beds, namely Ma-1, Ma 0, Ma 0.5, Ma 1, …Ma 12, are recognized in the Minato Formation and Ma 13 marine clay bed in the alluvial deposits.We have made correlation between Quaternary stratigraphy of the Osaka Plain and oxygene isotope record from deep sea cores, on the basis of a combination of litho-, bio-, magneto- and tephro-stratigraphy. The results are summarized as follows.1) The twenty-one marine clay beds, each of which represents marine transgression in the Minato Formation and alluvial deposits, were deposited during interglacial high·sea-level periods from Oxygen Isotope Stage 37 to Stage 1.2) The horizons of Ma 3, Ma 6, Ma 9, Ma 10 and Ma 12 beds, which are characterized by warm-temperate paleoclimate and high sea-level environment, can be regarded as the most useful marker-horizons for Pleistocene correlation.
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  • Atsushi Aoki, Kenji Shuto, Tetsumaru Itaya
    1999 Volume 105 Issue 5 Pages 341-351
    Published: May 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Tertiary volcanic rocks in the Hamamasu area along the Japan Sea coast in northwestern Hokkaido are lithologically divided into three formations. These are, in ascending order, the Iwao, Horo and Hamamasu Formations. The Iwao Formation is composed mainly of lavas and pyroclastic rocks of basalt and andesite with subordinate amounts of debris flow deposits and fluvial deposits. The Formation is divided into six units, which are in ascending order, A, B, C, D, E and F units. K-Ar ages include 3.8±0.1 Ma for andesite from the A unit and basalts from the B and C units as well as an andesite dike intruding the B unit. The andesites of the D and F units are dated to be 3.7±0.1 Ma, and a basalt lava of the Hamamasu Formation to be 2.6±0.1 Ma.These stratigraphical results and K-Ar age determinations show that volcanic rocks from the Iwao Formation, and the dike were derived from a volcano which has been erupted during a relatively short period of 3.7 to 3.8 Ma in the eastern part of this area, and the volcano seems to have collapsed, resulting in debris flow deposits and fluvial deposits. After completion of the volcano, the fluvial deposits accumulated on the southern part of this area. Thereafter, at 2.6 Ma the basaltic lavas overlay the volcanic products formed during the 3.7-3.8 Ma volcanic activity, mainly at the southern and northern parts of this area.The geochemical characteristics of basalts from this area, different from those of the Pliocene to Quaternary basalts from the NE Japan arc and the Quaternary basalts from the Kurile arc, may suggest a different origin of the magma from those in the NE Japan and Kurile arcs.
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  • Hisashi Tanaka, Yuichiro Miyata
    1999 Volume 105 Issue 5 Pages 352-363
    Published: May 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Effect of strain rate on deformation style of soft-sediments was examined for artificially compacted kaolin clay. The clay specimens with approximately 52 % water content were sheared by plane strain compression with strain rates between 2.0×10-4 and 3.0×100 s-1 which are higher than those by previous workers.As a result, it was clarified that strain rate is one of the major factors controlling shear plane characteristics as well as deformation style. Flow deformation becomes dominant under higher strain rate. At low strain rate, selected shear planes grow and cut across the specimen before axial strain reached 20 %. Shear zones, where clay particles are well rearranged, are distinguished from intact part with primary sedimentary fabric under cross polar. On the other hands, a specimen deformed at high strain rate shows axial shortening and lateral expansion by pure shear without any distinct major shear plane even though axial strain reached 40 %, but it shows many minute, indistinct fracture after failure, where clay particles are insufficiently rearranged.With increasing strain rate, strain localization is suppressed, and development of shear planes, and a peak strength occur at higher axial strain up to 40 %. A natural slump structure in the Pleistocene lacustrine sediments also exemplified contrast failure styles due to different strain rate. Localization of shear strain observed at earlier stage of deformation is not only the trigger of shear plane but also a probable factor controlling deformation style under various strain rates.
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  • Mitsuru Okuno, Mitsuhiro Yoshimoto, Ken-ichi Arai, Toshio Nakamura, Ta ...
    1999 Volume 105 Issue 5 Pages 364-369
    Published: May 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The Ko-f tephra is one of the prominent tephra layers from Hokkaido-Komagatake volcano, southwestern Hokkaido, Japan. It consists of Plinian pumice fall and pyroclastic flow deposits. Previous studies have estimated that the Ko-f tephra was erupted at approximately 3.0 kyr BP, on the basis of a radiocarbon date of 2750±110 yr BP(GaK-2836) for paleosol sample just above the Ko-f tephra. However, we suspect that this age is not acceptable, because 14C dates of paleosol just above a tephra layer are often far younger than its eruption age. In order to determine the eruption age of the Ko-f tephra accurately, we performed 14C dating of paleosol samples just below the tephra (Samples A and B) and charcoal fragments below and above the tephra (Samples C and D, respectively), using a Tandetron accelerator mass spectrometer at Nagoya University.The obtained 14C dates of paleosol, 5480±90 yr BP (NUTA-5783) for Sample A and 5530±80 yr BP (NUTA-5785) for Sample B, are identical within measurement errors. This agreement indicates that the organic matter in both samples was put in a closed system simultaneously when the Ko-f tephra deposited. Thus, it seems that these 14C dates represent the eruption age of the Ko-f tephra. Consequently, the age of the Ko-f is revised to be 5.5 kyr BP. This age is also supported by two 14C dates of charcoal fragments, 5730±80 yr BP (NUTA-5384) for Sample C and 5050±100 yr BP (NUTA-5842) for Sample D. From two soil 14C dates, we can calibrate to calendar year of about 6.3 cal kyr BP.
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  • Ayumu Nojo, Shiro Hasegawa, Hisatake Okada, Yoshihiro Togo, Akihiko Su ...
    1999 Volume 105 Issue 5 Pages 370-388
    Published: May 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Litho- and biostratigraphical studies have been carried out on the Pleistocene Setana Formation distributed in the Oshima Peninsula, southwestern Hokkaido. The Setana Formation is redefined and subdivided into the following six members ; Hanaishi Conglomerate, Chinkobe Sandstone, Hatakenosawa Conglomerate, Natsuji Conglomerate, Nakasato Conglomerate, and Soebetsu Sandstone. The Hanaishi Conglomerate, Natsuji Conglomerate, and Nakasato Conglomerate Members are correlated with the lower part of the Setana Formation, and the Chinkobe Sandstone, Hatakenosawa Conglomerate, and Soebetsu Sandstone to the upper part. These members yield planktonic foraminifera and calcareous nannofossils, and the fossils indicate that the lower and upper part of the Setana Formations were deposited about 1.2 to 1.0 Ma and about 1.0 to 0.6 Ma, respectively. The lower Setana Formation was deposited in shallow sea where cold-water dominated, whereas the upper part was formed in a deeper and expanded sea in which warm-water intruded periodically under the glacial eustatic sea-level controls. Biostratigraphical study reveals that the Setana Formation can be correlated with the Daishaka Formation, upper part of the Kitaura Formation, the Haizume Formation, and middle to upper parts of the Omma Formation in the Japan Sea side of the Honshu Island, as well as to the Tomikawa Formation in southwestern Hokkaido.
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  • Ken Nakayama, Nihat Kaya
    1999 Volume 105 Issue 5 Pages IX-X
    Published: 1999
    Released on J-STAGE: November 26, 2010
    JOURNAL FREE ACCESS
    In the Pontides belt of northern Turkey, a number of ophiolites, which represent the paleo-Tethys oceanic crust-mantle of the Permian to Jurassic and active continental margin sequences of the Permian to early Jurassic are juxtaposed along the Tethyan suture (Sengor et al., 1980). Around the Kure mine dismembered ophiolite lacking sheeted dike complex is chaotically jumbled among terrigenous sedimentary rocks. In the Kure open pit, blocks of massive and stockwork sulfide ore associated with hyaloclastite ranging from a few tens of centimeters to few hundred meters in diameter are inlaid in scaly argillite with a prominent tectonic contact; so-called melange. The oceanic crust of paleo-Tethys overlain by a Cyprus type deposit is thought to be mingled with trench-fill terrigenous sediments and accreted to the continent. Although VMS deposits in sedimentary settings such as a back arc basin or marginal sea have been defined as Besshi type deposits (e. g., Slack, 1993), what would be the product if allochthonous VMS deposits, such as in this case, were introduced to a deeper level within the subduction zone and consequently undergone high P/T metamorphism ?
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