The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 112, Issue 12
Displaying 1-6 of 6 articles from this issue
Articles
  • Yu'suke Kubo, James P. M. Syvitski, Susumu Tanabe
    2006 Volume 112 Issue 12 Pages 719-729
    Published: 2006
    Released on J-STAGE: May 29, 2007
    JOURNAL FREE ACCESS
    HYDROTREND, the hydrologic model suggested by Syvitski and his colleagues, is applied to the paleo-Tonegawa to reconstruct sediment discharge to the Kanto Plain and Tokyo Bay area for the last 13,000 years. HYDROTREND provides a numerical simulation of water and sediment discharges of modern and ancient rivers, on the assumption of climate conditions and drainage basin characteristics. The model is applied (1) first to the modern Tonegawa with measured precipitation and temperature as inputs, to determine values and coefficients of the involved variables, (2) second to verify the model applicability using data obtained from modern hydrologic conditions, and (3) third to the paleo-Tonegawa with changing climate and sea level conditions of the past. The numerical results, after a calibration of the local factor of snowmelt, show an agreement with the measured discharge in dam-free, mountainous part of the uppermost drainage. The predicted discharge for the whole basin is comparable to the observations as well. The predicted sediment supply, where effects of changes in annual average temperature, annual precipitation and drainage area were taken into account, agrees with the estimates from the measured data obtained from the area. In the predictions, sediment discharge is relatively stable through 13,000 years, because increase in sediment supply at high temperature compensates decrease in drainage area during the 7.000 - 0 yrBP higher sea level period. The results indicate that daily precipitation controls sediment discharge more effectively than the Holocene climate change. The maximum daily sediment load reaches 10 times of the annual mean. The paleo-Tonegawa is most likely to produce hyperpycnal with a recurrence interval of hundreds of years during the 7,000 - 0 yrBP sea level highstand. The present study supports the actual applicability of HYDROTREND to Japanese river systems of the past.
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  • Shoichi Kiyokawa
    2006 Volume 112 Issue 12 Pages 730-748
    Published: 2006
    Released on J-STAGE: May 29, 2007
    JOURNAL FREE ACCESS
    The Albion Formation, which is located in the southeastern region of the Yucatan Peninsula, is identified as the outer portion of the continuous ejecta blanket of the Chicxulub crater. Three locations where Albion Formation is preserved are 1) the Quintana Roo to Ramonal region along the eastern border of Mexico, 2) the Albion region of northwestern Belize and 3) the Armenia region of central Belize. They are situated 330˜350 km, 370 km and 470 km from the Chicxulub crater respectively. In this paper, I review the recent works on the Albion Formation and discuss the ejecta from the Chixulub crater based on my own field work.
    The Albion Formation, which is preserved on the uppermost Cretaceous shallow dolomite sequence, forms two sequences: spheroid and diamictite beds. The spheroid bed consists of dolomite and clay spheroids and smectite clay fragments, within a fine carbonate matrix. The dolomite spheroid is formed by dolomite fragments surrounded by fine calcite crystal, which are melted to the host rock. The clay spheroid and clay fragments are identified as an altered impact glass. Sedimentary structures indicate a high flow regime with a paleocurrent NNW to SSE trend, indicating the flow coming from the Chicxulub crater. The diamictite bed is characterized by accreted boulder-size dolomite blocks and a coarse-grained calcareous matrix containing altered glass, striated, polished cobbles, and shocked quartz. The boulder-size dolomite blocks are formed by accreted calcite crystal layers, which are identified as fall deposits within a highly concentrated vapor cloud of carbonate formed after passing of the ejecta blanket.
    These stratigraphic characteristics of the Albion Formation indicate that the formation is formed by impact-related ballistic sedimentation from the Chicxulub crater. The ejecta bed and accreted block sequences provide the key evidence in recognizing the flow conditions and ejecta transport mechanism at peripheral sites from the giant impact crater.
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  • Kohsaku Arai, Yukinobu Okamura, Ken Ikehara, Juichiro Ashi, Wonn Soh, ...
    2006 Volume 112 Issue 12 Pages 749-759
    Published: 2006
    Released on J-STAGE: May 29, 2007
    JOURNAL FREE ACCESS
    Single- and multi-channel seismic reflection analyses allow us to better understand the seismic stratigraphy of the forearc region in the eastern Nankai Trough and provide a crucial clue for the reconstruction of the tectonic framework. The lowest Kodaiba Group is composed of the middle to upper Miocene forearc basin fill. Since deposition of the Kodaiba Group the forearc basin had uplifted and then widely eroded over the study area. The main part of the outer arc high is likely to uplift during the deposition of the late Pliocene to early Pleistocene Atsumi-oki Group. In addition the central uplift zone has started to develop particularly in the accumulation stage of the uppermost of the group. During the unconformity between the underlying Atsumi-oki and the overlying Hamamatsu-oki Groups, numerous minor conjugate normal faults had developed and the tilting of the upper forearc slope toward southeast had been proceeded. Normal faults, on the other hand, to run parallel to the Nankai Trough axis with 70-80º dipping toward north were activated on the shelf to the upper shelf slope area off Hamamatsu. The normal faults have been active since onset of the deposition of the Hamamatsu-oki Group because some displaced the shelf surface floor to be made by the sea level falling in the last glacial maximum. An average of maximum vertical displace component of the normal faults may reach up to several ten cm/1000 years. Considering the time and space, a development of the normal faulting was synchronized with the tilting of the upper forearc slope, probably caused by ridge subduction to progress along the Nankai decollemant fault in the study area.
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  • Toshiyuki Yoshikawa
    2006 Volume 112 Issue 12 Pages 760-769
    Published: 2006
    Released on J-STAGE: May 29, 2007
    JOURNAL FREE ACCESS
    The Middle Miocene felsic volcanic rocks are widely distributed in the northern part of Tochigi Prefecture, central Japan. The Iiyama Formation and Otaki Tuff Breccia in Imaichi area are composed mainly of rhyolite pyroclastic rocks and lavas and zircon fission-track age determination was carried out for each unit. Age of the pyroclastic flow deposit of the Iiyama Formation is 14.8±0.7 Ma (1σ) which is thought to indicate eruption age of the pyroclastic flow. Age of the Otaki Tuff Breccia corresponds to 13.4±0.6 Ma (1σ), which is obtained from matrix of the debris avalanche deposit. Age of the Otaki Tuff Breccia is disqualified by the chi-square test implying contamination of the zircon from the Iiyama Formation or other factor which disturbs Poisson distribution law. Age of the Otaki Tuff Breccia remains still unclear.
    Each dating sample includes detrital zircon possibly from the Late Cretaceous volcanic rocks. Over 20 m thick pyroclastic flow deposit of the Iiyama Formation might be emplaced at relatively low temperature not enough to anneal the tracks in detrital zircon. Although paleo-environment of this area is not fully clarified, low temperature pyroclastic flow is indicative of much water as coolant especially for such a thick deposit. Sporadic occurrence of marine fossils in the Iiyama Formation also implies that sea area might prevail during Middle Miocene. The Middle Miocene felsic volcanic rocks seem to have occurred at different places and ages on the basis of the radiometric age data, however the correlation is still problematic because of the confusion between age data and stratigraphy or dating methods in Utsunomiya area.
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Prompt Report
  • Masao Kametaka
    2006 Volume 112 Issue 12 Pages 770-773
    Published: 2006
    Released on J-STAGE: May 29, 2007
    JOURNAL FREE ACCESS
    Permian radiolarian fossils were discovered from greenish gray felsic tuff of the Nagato Tectonic Zone, at Soegasako in the Nishiichi area, Yamaguchi Prefecture, Southwest Japan. The radiolarian fauna is composed of Follicucullus sp. cf. F. porrectus, Pseudoalbaillella sp. aff. P. longicornis, Cauletella manica, Raciditor gracilis, Pseudotormentus kamigoriensis and others. It indicates late Middle to Late Permian in age. The lithology of felsic tuff, age of radiolarian fauna and characteristics of sponge spicule fauna look similar to those of the clastic rocks of the Akiyoshi terrane. Therefore, Paleozoic formation in the Nagato Tectonic Zone of the Nishiichi area corresponds to the Akiyoshi terrane.
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