The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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Volume 111, Issue 1
Displaying 1-9 of 9 articles from this issue
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Articles
  • High-resolution chronology of the lower Pleistocene Otadai and Umegase Formations of the Kazusa Group, Boso Peninsula, central Japan -Chronostratigraphy of the JNOC TR-3 cores based on oxygen isotope, magnetostratigraphy and calcareous nannofossil-
    Takashi Tsuji, Yuichiro Miyata, Makoto Okada, Isao Mita, Hiroshi Nakag ...
    2005 Volume 111 Issue 1 Pages 1-20
    Published: 2005
    Released on J-STAGE: April 28, 2005
    DOIhttps://doi.org/10.5575/geosoc.111.1
    JOURNAL FREE ACCESS
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    Detailed oxygen isotope stratigraphy using benthic foraminifers (Bolivina robusta, Bulimina aculeata and Melonis pompilioides) from cored hemipelagic mudstones enables the lower Pleistocene Otadai and Umegase Formations of the Kazusa Group in the Boso Peninsula, central Japan, a turbidite sequence with high depositional rate (average depositional rate of hemipelagic mudstone: 0.9m/k.y.), to be correlated with astronomically tuned pelagic sequences. Remarkable correlation between this isotope curve and those from DSDP Site607 from the North Atlantic, and ODP Site 677 and Site 849 from the tropical Pacific is well demonstrated magnetostratigraphically based on the Jaramillo normal Subchronozone. Numerical age model can be addressed to each oxygen isotope event in the studied sequence applying the age for correlative event in the deep sea sequence.
    As a result of this study, the ages of events are determined as follows; 1) the first occurrence of Gephyrocapsa parallela: 1038-1041 ka, 2) the marker tephra layers O7, O11, O12 and O16: 1050-1056 ka, 1067-1070 ka, 1073-1078 ka and 1101-1105 ka, respectively, 3) the base of the Jaramillo normal Subchronozone: 1068-1084 ka, and 4) the boundary between the Otadai and Umegase Formations: 1011-1017 ka. The maximum error of the age determination is about 6 k.y.. Average sedimentary rates of turbidite sandstones, hemipelagic mudstones and total sediments are 1.9 m/k.y., 0.9 m/k.y. and 2.8 m/k.y., respectively.
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  • Depositional environment of the upper Jurassic-lower Cretaceous reef limestone in western Yamaguchi Prefecture, Southwest Japan
    Fumito Shiraishi, Ken-ichi Yoshidomi
    2005 Volume 111 Issue 1 Pages 21-28
    Published: 2005
    Released on J-STAGE: April 28, 2005
    DOIhttps://doi.org/10.5575/geosoc.111.21
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    Coral-dominated reef assemblage occurs in several limestone beds of the Toyonishi Group (upper Jurassic-lower Cretaceous) in Murotsu area, Yamaguchi Prefecture. The corals mostly show upright growth positions and form reef frameworks. They occur throughout in the limestone facies and are expanded even in the intercalated mudstone facies. The corals are divided into two types by their growth forms; the massive type indicating a relatively high-energy condition, and the branching type implying a low-energy condition. The latter is accompanied by dasycladacean algae, which are indicative of calm water. The limestone differs from the other Japanese Upper Jurassic to Lower Cretaceous limestone (e.g. the Torinosu Group) in showing abrupt lithologic change from the underlying calcareous sandstone to the reefal limestone, and lacking stromatoporoids, calcareous sponges, hydrozoans, microencrusters, and ooids.
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  • Relationship between the tectonic relief and the subsurface geological structure related to strike-slip displacement: a case of the en échelon faults
    Ken-ichi Yasue, Daisuke Hirouchi, Takayuki Nakano, Hideo Sakai, Koji O ...
    2005 Volume 111 Issue 1 Pages 29-38
    Published: 2005
    Released on J-STAGE: April 28, 2005
    DOIhttps://doi.org/10.5575/geosoc.111.29
    JOURNAL FREE ACCESS
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    This paper clarifies the relationship between the tectonic relief and the subsurface geological structure under several meters, and also we consider the structure in three dimensions and the tectonic formation process around the strike-slip fault. The study site is Mimayano district in the south-central part of the Gero fault of the Atera fault system, which is one of the prominent faults in central Japan. We have carried out topographical and geological explorations, drawing up of detail counter map, trench excavation investigation, and ground penetrating radar exploration. The results of these investigations show that the tectonic relief and the shallow geological structure have the Riedel shear structure as the order from several meters to dozens of meter. We conduced that the strike-slip displacement on the Gero fault in the basement rocks formed the right-handed Riedel-shear type faults in soft-sediment overlying the rocks. A small-scale tectonic relief as linear scarps, narrow depressions in right-stepping en échelon, and pressure ridges of several meters in wave-length are distributed on the ground surface along the arrangement of the Riedel-shear type faults.
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  • Paleoenvironmental change and age of the Miocene Kanomatazawa Formation in the Shiobara area, Tochigi Prefecture, central Japan
    Toshiyuki Yoshikawa
    2005 Volume 111 Issue 1 Pages 39-49
    Published: 2005
    Released on J-STAGE: April 28, 2005
    DOIhttps://doi.org/10.5575/geosoc.111.39
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    The Miocene Kanomatazawa Formation consists of lower and upper parts. The lower part is mainly composed of volcaniclastic sediments which were formed by the growth of submarine andesitic to dacitic volcano. The upper part is bedded sandstone to siltstone including many marine molluscan fossils (the Shiobara-type fauna) and foraminifera. Zircon fission-track ages of the pumice-lapilli tuff (the uppermost bed of the lower part) are 11.9±0.7 (ED2) and 10.4 ±0.3 Ma (ED1). Considering the geological conditions and experimental reliability, the age of 10.4±0.3 Ma (ED1) is assigned to this sample. The planktonic foraminifera in the upper part indicate the age of the lower to middle part of Zone N.16.
    Although the Shiobara-type fauna is known as a cool temperate fossil assemblage, the effect of warm current can be recognized in the upper part of the Kanomatazawa Formation according to the study of foraminifera assemblage. The Shiobara-type fauna in this area occurs under the intertidal part of a marine bay to shallow open marine condition and is prosperous after 10 to 10.5 Ma.
    The relationship between the Kanomatazawa and underlying Fukuwata Formations has not been determined to date. However, based on the fission-track age of this study and the age of corresponding formation to the Fukuwata Formation, it is proposed that the relationship of these formations should be an unconformity.
    The lithofacies difference between the lower and the upper parts of the Kanomatazawa Formation implies the environmental change related to the regression and ensuing transgression. Continuous activity of submarine volcano should be assigned to one of the reason of regression. Considering the same situation of the paleoenvironmental change in adjacent area at the almost equivalent age, the transgression may reflect relative sea-level change.
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Prompt Report
  • Newly found granulites from the western part of Sefuri Mountains, North Kyushu
    Masaaki Owada, Ryoichi Hada, Jun Yada, Mai Nakamura, Yasuhito Osanai
    2005 Volume 111 Issue 1 Pages 50-53
    Published: 2005
    Released on J-STAGE: April 28, 2005
    DOIhttps://doi.org/10.5575/geosoc.111.50
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    Newly found metamorphic block (c. 3 km × 1 km) within the Cretaceous granitic rocks in the Mt. Uki-dake area, northwest Kyushu, consists of two-pyroxene rock, garnet-orthopyroxene-cordierite gneiss and orthopyroxene tonalite being associated with layers or lenses of calcsilicate and ultramafic rocks. Geothermobarometries yield granulite-facies metamorphic conditions, approximately at 800 to 900°C and 400 to 500 MPa. On the basis of the similarity of the lithology and the metamorphic conditions, we propose that the present granulite-facies block and the neighboring amphibolite-facies block at the western part of Sefuri Mountains can be correlated to the high-grade sequence of the Higo metamorphic terrain in west-central Kyushu.
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Note
  • On the English expression of the Hida Gaien belt
    Satoru Kojima, Makoto Takeuchi, Kazuhiro Tsukada
    2005 Volume 111 Issue 1 Pages 54-55
    Published: 2005
    Released on J-STAGE: April 28, 2005
    DOIhttps://doi.org/10.5575/geosoc.111.54
    JOURNAL FREE ACCESS
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    The Hida Gaien belt, one of the Paleozoic-Mesozoic geologic units in central Japan, has been expressed in various ways in English, such as Hida "Gaien" belt, Hida marginal belt, Circum-Hida terrane, Circum-Hida tectonic zone, etc. When the special issue of this journal entitled "Recent progress and future perspective of research on the Hida Gaien belt" was edited for publication, as invited editors we recommended the authors to use the expression of Hida Gaien belt in order to avoid misunderstanding of the geologic characteristics of this belt by foreign researchers. This note summarizes the discussion between the authors during the process of deciding which is the best expression.
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