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Volume 32 (1993)
- Issue 5 Pages 245-
- Issue 4 Pages 195-
- Issue 3 Pages 129-
- Issue 2 Pages 61-
- Issue 1 Pages 1-
Volume 32, Issue 2
Displaying 1-4 of 4 articles from this issue
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Ikuo Suzuki1993 Volume 32 Issue 2 Pages 61-74
Published: May 31, 1993
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe landforms of central part of Niigata Prefecture can be divided roughly into two parts: high the Echigo Mountains in the east and low mountains, hill, terraces, and alluvial plains in the west. The boundary between these two is referred to as the Shibata-Koide Tectonic Line, which runs approximately trending NNE to SSW.
The Shinano River in Niigata Prefecture flows southwest toward northeast, and finally pours into the Sea of Japan. This region is known for having the shortest wave length of folding and the largest rate of folding in gradient change in Japan.
The studied area is located along the Ikarashi River, a tributary of the Shinano River, and is characterized by active folding and faulting trending NNE to SSW parallel to the Shibata-Koide Tectonic Line. In this area, the author discovered some outcrops of the faults cutting through terrace surfaces and deposits younger than 120-130ka. The most important of these faults is referred to as the Shimoppara Fault, which is a reverse fault and probably belongs to the Shibata-Koide Tectonic Line fault system. Such reverse faulting is the dominant mode of deformation in areas affected by compression. Left-lateral displacement is generally recognized in the northern part of the Shibata-Koide Tectonic Line. However, offset terrace scarps show that the Shimoppara Fault in the central part of the Shibata-Koide Tectonic Line was probably dislocated right-laterally.
Vertical and horizontal displacements amount to about 6.3m (or more) and 48.5m, respectively, in the recent 120-130ka. The mean rate of vertical displacement of the Shimoppara Fault is 0.05m/ka., and its average recurrence interval is estimated to be 25ka.View full abstractDownload PDF (3034K) -
Tomio Nakagawa, Osamu Fukuoka, Shoji Fujii, Toshio Nakamura1993 Volume 32 Issue 2 Pages 75-87
Published: May 31, 1993
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSHolocene shell beds were discovered in the underground of Takahama-cho, Oi-gun, Fukui Prefecture. The sequence of the Holocene strata occurs between 2 and 6m in depth, and was divided into six stratigraphic horizons on the basis of the characteristics of lithology and fossil molluscan assemblages, foraminiferas and ostracodas. In this study, 14C ages of every representative molluscan assemblage were determined. The results indicated that the molluscan assemblages are 1, 000 to 5, 000 years old. According to the shell-assemblage results from synecological analysis, the following paleoenvironmental transitions were clarified: the Takahama area was a mud-depositing intertidal zone 5, 000 years ago, a sand and mud-depositing shallow-water bottom during a minor transgression 4, 000 years ago, an intertidal zone due to gradual lowering of the sea level 2, 000 years ago, a brackish water area 1, 000 years ago, and a swamp-like land influenced by rivers since that time. Assemblage analysis of foraminiferas and ostracodas gave us very similar results.
A 4, 000 to 2, 000 year-old molluscan assemblage contains many subtropical shells such as Clypeomorus coralium, Plicarcularia bellula, Tegillarca granosa, Anomalocardia (Anomalodiscus) squamosa, which cannot be found in the present Wakasa Bay. The analysis of the fossil molluscan asseblages and determination of 14C ages made it clear that a minor transgression took place 4, 000 years ago and that the subtropical shells, which are considered to have been extinct 4, 000 to 5, 000 years ago in the Kanto region, survived in the Takahama area until 2, 000 years ago.View full abstractDownload PDF (1736K) -
Yaeko Igarashi, Tsuneo Igarashi, Hiromu Daimaru, Osamu Yamada, Toyohik ...1993 Volume 32 Issue 2 Pages 89-105
Published: May 31, 1993
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSVegetation history was reconstructed from pollen analysis and 14C dates of almost continuous drilling cores obtained from two inland basins, Kenbuchi Basin in north Hokkaido and Furano Basin in central Hokkaido, north Japan. During the 25, 000-32, 000yrs BP vegetation was a boreal conifer forest, so-called “Taiga” mainly composed of spruce (Picea jezoensis and/or P. glehnii), in both basins. Between 16, 000 and 25, 000yrs BP, steppe with open pine (Pinus pumila)-larch (Larix gmelini) forest developed in Kenbuchi Basin, and “Taiga” composed mainly of pine and larch developed in Furano Basin under cold/dry climatic condition. The vegetation in the Full Glacial are correlated with that distributed in northernmost Sakhalin at present. After a period in which larch forests decreased, 12, 000-16, 000yrs BP, they remarkably increased in both basins under cold climatic conditions during 10, 000-12, 000yrs BP. The newly identified cold age in Hokkaido, the “Kenbuchi Stadial”, could be correlated to the Younger Dryas Stadial. In 8, 000-10, 000yrs BP, larch decreased and disappeared from Hokkaido. During this interval birch-walnut forests flourished in the area along rivers of the central basin under the influence of increased precipitation. At about 8, 000yrs BP, oak abruptly became dominant in many parts of Hokkaido. Though oak decreased a little at 5, 000yrs BP, it has been the main component of the “Pan-mixed Forest” developed in present-day Hokkaido.View full abstractDownload PDF (2068K) -
H. Miura, S. Takaoka1993 Volume 32 Issue 2 Pages 107-114
Published: May 31, 1993
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESS
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