The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 107, Issue 9
Displaying 1-6 of 6 articles from this issue
  • Shigeyuki Suzuki, Daniel K. Asiedu, Tamiaki Fujiwara
    2001 Volume 107 Issue 9 Pages 541-556
    Published: September 15, 2001
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Lower Cretaceous successions distributed in the Nariwa Area, Okayama Prefecture, have been redefined as the Hayama Formation. The type locality is Hayama Village, which is situated at the center of the study area. The Hayama Formation is characterized by stacking of fining-upward units which are composed of conglomerate, sandstone and reddish mudstone from bottom to top. The sandstone parts are poorly developed and often lack in the sedimentary cycles. The formation itself shows a fining upward succession as a whole and is divided into two members ; the lower Eda Conglomerate Member and the upper Sora Mudstone Member. The Eda Conglomerate Member is dominated by conglomerate parts of the units. On the other hand, the Sora Mudstone Member is mainly composed of reddish mudstone parts of the units. The boundary between these two members is not clear but gradational. The deposits of the formation are interpreted as fluvial deposits based on sedimentary facies analysis. Semi-arid type climatic environment is supported by the occurrence of carbonate concretions which are formed in the floodplain mudstone. Fission-track dating was carried out by analyzing a felsic tuff sample from the Sora Mudstone Member and 101±4 Ma indicating Albian age was obtained. Paleotopography was reconstructed by tracing out the bottoms of the Hayama Formation. Obtained contour map demonstrates a north to south trending valley, and imbrication of gravels indicate paleocurrents to the south. The valley was filled with 300 m-thick fluvial deposits of the Hayama Formation during Albian time.
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  • Yuichiro Tanaka, Masaki Takahashi
    2001 Volume 107 Issue 9 Pages 557-564
    Published: September 15, 2001
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The size distribution pattern of calcareous nannofossil genus Reticulofenestra and its stratigraphic change were examined for the Middle Miocene marine sequence of the Kobana Formation, lower part of the Arakawa Group, distributed in Tochigi Prefecture. The 4-5 μm-size Reticulofenestra dominated throughout the Kobana Formation. The first occurrence of a large Reticulofenestra (>9 μm) is recognized between the Kb2 and Kb3 key tuff beds, and is estimated to be about 13.8 Ma based on the K-Ar ages of tuff layers. The first occurrence of the larger Reticulofenestra (>10 μm) was identified at a few meters above the Kb7 tuff layer, and is estimated to be 13.1 Ma. This appearance occurs simultaneously with the recalculated age of the Miocene isotope event 4 (13.0 Ma or somewhat younger). The abundant occurrence of very small Reticulofenestra (<2 μm) from 13.6 to 13.2 Ma are associated with periods of higher primary productivity.
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  • Satoshi Hanagata, Isao Motoyama, Chikara Hiramatsu, Kazue Watanabe, Ta ...
    2001 Volume 107 Issue 9 Pages 565-584
    Published: September 15, 2001
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Planktonic and benthic microfossils, including radiolarians, diatoms, calcareous nannofossils and foraminifers from the onshore sections of the Jouetsu-Chuetsu district, Niigata Prefecture, northeastern Japan, were studied with the objective of constructing a time-stratigraphic framework for the Upper Miocene and Pliocene strata. These are characterized by interbedded hemipelagic mudstones and turbiditeic sandstones. Radiolarian and benthic foraminiferal biostratigraphies indicate that the Miocene/Pliocene boundary in the Teradomari and Nishiyama areas corresponds approximately to the upper boundaries of the Teradomari and Shiiya Formations, both of which have been used as standard stratigraphic units in the Niigata Oil and Gas field region. Moreover, the boundary is traced to the upper part of the Ogaya Formation in the Yoneyama area and to the Sugawa Formation in the Higashikubiki area.Biostratigraphic analyses show that three volcanic ash layers, namely the Natsudo Pumice Tuff (Ndp), the Ogaya Pumice Tuff (Ogp) and the Iriyamagawa Tuff (Iy), are positioned at different stratigraphic horizons ; the Ndp is younger than Ogp, and the Iy is the youngest among the three. These three layers was recognized as the same tephra maker in previous studies. Furthermore, estimated ages of the Ndp and the Ogp based on the biostratigraphy are significantly younger than the ages estimated for the same ash layers based on fission track dating. This suggests that these ash layers contain or consist of reworked minerals and sediments derived from older pyroclastic deposits. Consequently, this study points out that the stratigraphic correlation and chronology established based mainly on fission track dating of such ashes in the Jouetsu-Chuetsu district require considerable revisions.
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  • Osamu Takano, Shigehiro Moriya, Mizue Nishimura, Fumio Akiba, Masanori ...
    2001 Volume 107 Issue 9 Pages 585-604
    Published: September 15, 2001
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    We carried out sequence stratigraphic analyses for the Neogene Shiiya and Nishiyama Formations in the Kitakambara Area of the Niigata Sedimentary Basin in the northern part of Niigata Prefecuture, central Japan. The objective was to clarify the characteristics of depositional sequences in a tectonically active area. Fourteen 4th order depositional sequences (S1∼S5, N1∼N9) and two 3rd order depositional sequences are recognized in the strata by integrating data from surface geology, well log patterns, seismic sections and microfossils. Characteristic relationships between the depositional sequences and fossil foraminifers are recognized as follows ; No. 2 and No. 3 Globorotaria inflata beds correspond to HST (highstand systems tract) of the 3rd order sequences, and dextral-coiling Neogloboquadrina pachyderma dominant zones (SD-1 and SD-3 Zone of Moriya, 1995) correspond to HST and TST (transgressive systems tract). Spatial distribution maps of depositional systems of each 4th order depositional sequence indicate that there were several sediment supply systems, forming submarine fan systems in the basin. Along with these sediment supply systems, coarse clastics were deposited, whereas slope to basin floor mud facies tend to be developed between these supply systems.Compared to the sequence stratigraphic model in a passive margin, the following unique sedimentation is pointed out in the Neogene strata in the Kitakambara Area ; a) As sediment supply frequently varied and shelf territory was narrow, submarine fan systems were prominently developed even in HST of the 3rd order sequences at the basin center. b) Local uplift and fault zones in the basin such as Niitsu Hills, were active during deposition, and then caused areal tectonic onlap surface, submarine hiastus, erosional surface and chaotic sedimentation.Consequently, it is suggested that tectono-stratigraphic analyses should be carried out simultaneously with conventional sequence stratigraphic analysis when analyzing tectonically active basins.
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  • Akira Miyake
    2001 Volume 107 Issue 9 Pages 605-608
    Published: September 15, 2001
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
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  • Takehisa Tsubamoto, Hisashi Suzuki, Naoko Egi, Masanaru Takai, Nobuo S ...
    2001 Volume 107 Issue 9 Pages XVII-XVIII
    Published: 2001
    Released on J-STAGE: November 26, 2010
    JOURNAL FREE ACCESS
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