The Quaternary Research (Daiyonki-Kenkyu)
Online ISSN : 1881-8129
Print ISSN : 0418-2642
ISSN-L : 0418-2642
Volume 37, Issue 5
Displaying 1-7 of 7 articles from this issue
  • Keiichi Sasaki, Akio Omura, Yoko Ota, Takashi Murase, Takashi Azuma, M ...
    1998 Volume 37 Issue 5 Pages 349-360
    Published: December 31, 1998
    Released on J-STAGE: August 21, 2009
    JOURNAL FREE ACCESS
    A history of Holocene terrace formation is discussed through detailed topographic and geologic surveys and α-spectrometric 230Th/234U dating of fossil corals along the northern Shiooke coast, Kikai Island. A depositional part of the Holocene coral limestone, a wave cut surface of the Holocene coral limestone, and a shore platform cutting the Pleistocene rhodolith limestone compose a Holocene marine terrace sequence at the northern Shidooke coast. 230Th/234U ages of corals from depositional and abrasional parts of the Holocene coral limestone demonstrate the following history of terrace development in this area.
    Offlapping growth of the Holocene reef tract and the following erosion near the mean hightide level have formed regressive terraces, during intermittent emergence at 4.0-5.1ka and 2.6-2.9ka after the maximum Holocene transgression. Relative sea levels are estimated to stand at altitudes of 4.0-4.8, 2.6-2.9, and 1.1-1.6m (mean low-tide level) from elevations -1.6m (mean low-tide level) from elevation of depositional parts of the Holocene coral limestone and wave-cut terraces of the Pleistocene rhodolith limestone. Shapes of the transgressive systems tract developed during the post-glacial sea level rise control the subsequent formation of two types of regressive reef terraces, deposition-dominated at the Nakaguma and abrasion-dominated at the northern Shidooke coasts on Kikai Island.
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  • Deduced by the Analyses on a Piston Core from the Ryukyu Trench Slope, Northwest Pacific Ocean
    Shuntaro Oka
    1998 Volume 37 Issue 5 Pages 361-370
    Published: December 31, 1998
    Released on J-STAGE: August 21, 2009
    JOURNAL FREE ACCESS
    A piston core (RN95-PC4) collected from the central Ryukyu Trench slope is investigated concerning the down-core fluctuations in planktic and benthic δ18O and δ13C values, total organic carbon contents (TOC), organic carbon/nitrogen (C/N) ratios, calcium carbonate contents, benthic foraminiferal crops, and planktic foraminiferal fauna. Based upon the oxygen isotope stratigraphy and three AMS14C dates, this core reveals a continued sedimentation for the past -60ka; from the early oxygen isotope Stage 3 to the present. The primary production in surface water increased during the last glacial period, particularly in Stage 2, judging from the significant signals in down-core changes of benthic δ13C values, TOC, C/N ratios, and so on. Analysis of planktic foraminiferal fauna suggests that the increased primary production in Stage 2 might be ascribed to relative development of upwelling with cold water invasion.
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  • Tadashi Nakajima, Junko Fujii
    1998 Volume 37 Issue 5 Pages 371-383
    Published: December 31, 1998
    Released on J-STAGE: August 21, 2009
    JOURNAL FREE ACCESS
    Paleomagnetic measurements were made of the Aso pyroclastic flows of middle to late Pleistocene age in central Kyushu, and of the Aso-4 ashes in the Chubu-Kanto-Tohoku district. The Aso pyroclastic flows are divided into four major cycles: the Aso-1, -2, -3, and -4 flows in ascending order. The paleomagnetic directions obtained are characteristic of the individual cycles, and are all of normal polarity. The mean directions of the Aso-1 (Dm=3.4°E, Im=49.0°, α95=5.2°) and the Aso-4 (Dm=5.2°W, Im=42.0°, α95=5.2°) flows are similar to that of the present geomagnetic field (D=6°W, I=45°). On the other hand, the direction of the Aso-2 flow is characterized by a very steep inclination (Dm=2.5°W, Im=72.7°, α95=13.6°), and that of the Aso-3 flow by an extremely easterly declination (Dm=35.7°E, Im=51.2°, α95=3.7°).
    The Aso-4 pyroclastic flow in Oita Prefecture is subdivided into two units: the Aso-4A and the Aso-4B flows in ascending order. The mean inclination of the Aso-4B flow is shallower than that of the Aso-4A flow by 5 degrees. Assuming that this directional difference was caused by geomagnetic secular variation (GSV), we can estimate the time interval between the Aso-4A and the Aso-4B flows to be about 50 years or more based on the standard GSV curve for southwestern Japan over the past 2, 000 years.
    The directions of the Aso-4A welded tuffs in Oita Prefecture are consistent with those of the Aso-4 non-welded pyroclastic flow deposits in Miyazaki Prefecture, and with those of the Aso-4 co-ignimbrite ashes in the Chubu-Kanto-Tohoku district. This comparison was made on declination and inclination values for each flow reduced from their virtual geomagnetic poles (VGPs) to a reference point at 131°E, 33°N. The declination values have a range limited between 0.5°W and 5.4°W, and the inclination values are between 44.4° and 45.9°. Identical paleomagnetic directions for the widespread Aso-4 tephra indicate that the magnetizations were acquired in a field dominated by the same geomagnetic dipole field (DF) component in all three regions of the Japanese islands; the pole of the DF at the time of eruption is inferred to coincide with the mean VGP (A95=2.1°, N=21) located at 22.8°W, 83.3°N.
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  • Allocation of Extant Species to Historically-based Categories
    Mike Dobson, Yoshinari Kawamura
    1998 Volume 37 Issue 5 Pages 385-395
    Published: December 31, 1998
    Released on J-STAGE: August 21, 2009
    JOURNAL FREE ACCESS
    Consideration of the historical development of the mammal fauna on the major Japanese Islands allows six categories of species to be recognised, on the basis of their origins and current geographical distribution within Japan, which are modified from the original seven categories of Dobson (1994). The six categories are clearly defined, but allocation of species within them requires a full understanding of taxonomic relationships and a good fossil record and is, therefore, tentative for certain species. We here attempt to allocate the recent terrestrial non-flying mammals of Japan to the six categories. In cases where allocation is uncertain, due to a lack of appropriate evidence, we provide our reasoning for decisions made. We have, therefore, been able to highlight gaps in the knowledge of the biogeographical history of the Japanese mammal fauna.
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  • Yasuhiro Kumahara
    1998 Volume 37 Issue 5 Pages 397-409
    Published: December 31, 1998
    Released on J-STAGE: August 21, 2009
    JOURNAL FREE ACCESS
    In Northwestern Shikoku, the Hiji River flows through the outer zone of Southwest Japan (Figs. 1 and 2). The fluvial terrace surfaces along the Hiji River are classified into four levels: Terrace H1, H2, M, and L in descending order (Fig. 3). Based on the correlation of these terraces, this paper discusses the development of the terraces and the tectonic movement indicated by deformed terrace profiles.
    The H1 terrace is most extensively distributed along the Hiji River and its tributaries, while the lower terraces are limited to inside the Nomura, Uchiko, and Ozu basins. As the H1 terrace sediment contains an Ng-1 tephra (erupted about 300ka) layer about 5m below the terrace surface at Nomura (Mizuno and Kikkawa, 1991), the age of the H1 terrace is roughly estimated to be 250 to 300ka.
    H1 and H2 terraces are distributed in the valley from Shimo to Ozu through Uchiko basin to the north of Mt. Kannan; these terraces are not found along Hiji River south of Mt. Kannan. The course of the Hiji River presumably shifted from Shimo to Ozu after the formation of the H2 terrace (Fig. 8).
    The relative altitude of the H1 terrace surface above the present river bed is 75m at Nomura and 120m at Sakaishi (Fig. 9). This indicates westward tilting by 5.6‰ in the middle reach; and this tilt is cumulative since the formation of the H1 terrace surface in this area. Based on the estimated age of the H1 terrace (250-300ka), the rate of westward tilting is estimated as 1.8-2.2×10-8/yr. In the lower reach, the largest relative altitude of the H1 terrace above the present river is 210m at 6km upstream from the river mouth, while it is 170m at Ozu (Fig. 9). This southeastward tilting indicated by the longitudinal profile of the H1 terrace is attributed to the regional uplift of the mountains to the south of Median Tectonic Line. Based on the estimated age of the H1 terrace (250-300ka), the rate of westward tilting in the lower reach is estimated as 2.0-2.4×10-8/yr.
    Because these uplift rates are comparable to the average rate of uplift over a million years (Ohmori, 1990), it appears that mountains have been uplifted at a constant rate in northwestern Shikoku during the latter part of the Quaternary.
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  • Takeyuki Ueki, Shuji Iwata, Sumiko Tsukamoto
    1998 Volume 37 Issue 5 Pages 411-418
    Published: December 31, 1998
    Released on J-STAGE: August 21, 2009
    JOURNAL FREE ACCESS
    Petrographic composition of the early Pleistocene Fukuji Tuff Breccia are comparable with the distribution of bedrocks in the area of Mt. Hotaka and the Hida Mountains to the east. Clast fabrics of the formation generally represent westward and southward paleocurrent directions. These facts indicate that in the early to middle Pleistocene, a “paleo-Azusa River”, by which the Fukuji Tuff Breccia was deposited, flowed westward from Kamikochi to Takayama. At that time, the volcanoes around Mt. Yake were much lower in elevation than at present.
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  • Tadahiro Arakawa, Noriko Yamazaki
    1998 Volume 37 Issue 5 Pages 419-424
    Published: December 31, 1998
    Released on J-STAGE: August 21, 2009
    JOURNAL FREE ACCESS
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