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Volume 52 (1998)
- Issue 6 Pages 431-
- Issue 5 Pages 341-
- Issue 4 Pages 251-
- Issue 3 Pages 171-
- Issue 2 Pages 69-
- Issue 1 Pages 1-
Volume 52, Issue 3
Displaying 1-10 of 10 articles from this issue
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Genjyu Yamamoto, Mitsuo ShimazuArticle type: Article
1998 Volume 52 Issue 3 Pages 171-187
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSThe Kurosawa, Takahagi basalt members and Kamimura volcanic member of the Nishiyatsushiro Group mainly consist of basaltic pillow lavas and hyaloclastites erupted in the lower bathyal and abyssal zone, and were intruded by a large number of basaltic dikes of the same age. Plotting on the TiO_2-FeO/MgO, TiO_2-MnO-P_2O_5, and 2Nb Zr/4-Y diagrams, and patterns in the N-MORB-normalized diagram indicate that tholeiites of the Kurosawa and Takahagi basalt members have petrochemical character similar to back-arc basin basalt rather than island-arc tholeiite. Alkali basalt dykes have oceanic island alkali basalt-like character similar to alkali basalt of the Takakusayama Formation. These tholeiites and alkali rocks have relatively low Sr isotopic ratios and high Nd isotopic ratios which are similar to those of alkali rocks from the Takakusayama Formation and basalts from the Izu-Ogasawara arc. Therefore, these basalts seem to have been derived from slightly depleted mantle beneath the back-arc region. On the Y/Nb-Zr/Nb diagram, tholeiites are plotted both in the N-MORB and OIB fields near T-MORB field, and alkali basalt dykes and alkali rocks of the Takakusayama Formation are plotted more OIB side than the tholeiites. Accordingly, these rocks may have been formed in relation to mixing of N-MORB and OIB. Bimodal volcanism of basalt and dacite in the Nishiyatsushiro Group of middle Miocene occurred in relation to deep fracture formed in the back-arc side of the proto-Izu-Bonin arc. After the volcanism, collision of the Misaka and Tanzawa blocks onto the Honshu arc took place.View full abstractDownload PDF (2025K) -
Early to Middle Permian radiolarians from the Kuhfeng Formation in southeastern Guangxi, South ChinaWenchen Xian, Ning ZhangArticle type: Article
1998 Volume 52 Issue 3 Pages 188-202
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSWell-preserved Early to Middle Permian radiolarians were abundantly recovered from chert beds of the Kuhfeng Formation at Bancheng of southeastern Guangxi, China. Fifteen species and 3 genera of Albaillellaria, 8 species and 5 genera of Latentifistulicea, and 2 species and 1 genera of Follicucullacea were distinguished. One of them was described as a new species. Two radiolarian zones, Albaillella sinuata and Pseudoalbaillella banchengensis zones were recognized here firstly in South China. Therefore, the six assemblage zones have been recognized from the Kuhfeng Formation of South China, namely, Pseudoalbaillella scalprata zone, Albaillella sinuata zone, P. banchengensis zone, P. globosa-P. fusiformis zone, Follicucullus monacanthus zone and F. scholasticus zone. The ages of the Kuhfeng Formation in the different regions of South China are not same.View full abstractDownload PDF (2897K) -
Masaki UmedaArticle type: Article
1998 Volume 52 Issue 3 Pages 203-209
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSLate Silurian radiolarians were extracted from the Joryu Formation of the Yokokurayama Group in the Kurosegawa Terrane, Kochi Prefecture. The fauna includes the genera Pseudospongoprunum, Devoniglansus and Praespongoceolia which are regarded as the key taxa for the Upper Silurian radiolarian biostratigraphy. Five radiolarian species, including two new species, of the genera are described in this paper. The species are useful for age determination because of their characteristic shape.View full abstractDownload PDF (1428K) -
Tomio Otsuka, Nobuyuki Takahama, Hiroomi Nakasato, Satoshi Nomura, Ter ...Article type: Article
1998 Volume 52 Issue 3 Pages 210-224
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSIn the Karasu River Valley of Gunma Prefecture, central Japan, the authors have discovered an active mega-landslide, 2.8km wide and 1.5km long. This landslide occurred during the late Pleistocene before deposition of the Aira-Tanzawa tephra, and is reactivated at the present. We call the landslide the Yudonosan Mega-landslide. The landslide mass and its bed rocks are composed of andesitic tuff breccia and welded tuff of the late Miocene to Pliocene. In the upper portion of the landslide mass, horsts and grabens are observed to be arranged in echelon pattern, which was formed by ancient landslide cracks. However, compared with the strata of surrounding areas, the strata in the lower portion of the landslide is sheared into pieces and their bedding planes are disturbed. Furthermore, there are tension cracks in the upper portion, and irrigation facilities and flood control measures are now collapsing in the lower portion. These facts suggest that the landslide is reactived now. There is a large possibility that the Yudonosan Mega-landslide was reactivated at least twice in the past. One reactivation occurred about 10,000yrs BP and the other occurred between 1108 and 1783 AD. It has become clear that these two reactivations at the same times as liquefaction in the tephra layer of the landslide and surrounding areas. From this it can be inferred that earthquakes triggered the reactivations of those ancient landslides. However, since the present reactivation has no clear relation to any earthquakes, it should be studied in detail in further. In addition, there is a possibility that this mega-landslide might have dammed up the Karasu River in the past. Therefore, further studies on the damming will give us a considerable amount of useful information for predicting disasters. The disaster prevention measures against the Yudonosan Mega-landslide, which is on a geological scale in both time and space, should be considered in all aspects, providing landslide prevention measures and informing the inhabitants about the details of the landslide. However, since prevention measures for mega-landslide have not been implemented yet, it is essential to reveal the entirety of the landslide as it exists, and to offer the area's inhabitants a great deal of information about the landslide. This can be done through detailed investigations independent of prevention measures.View full abstractDownload PDF (4188K) -
Takashi Okajima, Hirofumi Yamamoto, Tomio Nakagawa, Fusao Arai, Shiro ...Article type: Article
1998 Volume 52 Issue 3 Pages 225-228
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSDownload PDF (758K) -
Jiri FrydaArticle type: Article
1998 Volume 52 Issue 3 Pages 229-234
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSDownload PDF (1396K) -
Naotoshi Yamada, Toru Sakamoto, Kazuo KanekoArticle type: Article
1998 Volume 52 Issue 3 Pages 235-239
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
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Tomio NakagawaArticle type: Article
1998 Volume 52 Issue 3 Pages 240-243
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSDownload PDF (794K) -
Hiromitsu YamagishiArticle type: Article
1998 Volume 52 Issue 3 Pages 244-245
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSDownload PDF (1097K) -
Article type: Appendix
1998 Volume 52 Issue 3 Pages 250-
Published: May 25, 1998
Released on J-STAGE: July 11, 2017
JOURNAL OPEN ACCESSDownload PDF (103K)
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