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Volume 67 (2013)
- Issue 6 Pages 183-
- Issue 5 Pages 159-
- Issue 4 Pages 119-
- Issue 3 Pages 89-
- Issue 2 Pages 63-
- Issue 1 Pages 1-
Volume 67, Issue 3
Displaying 1-3 of 3 articles from this issue
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Shigenori KAWANO, Toshiaki IRIZUKI, Ritsuo NOMURAArticle type: Article
2013 Volume 67 Issue 3 Pages 89-99
Published: May 25, 2013
Released on J-STAGE: May 16, 2017
JOURNAL OPEN ACCESSThe Manzeki-Seto Strait is an artificial strait excavated between Asou Bay and Miura Bay, Tsushima Island, Nagasaki Prefecture, Southwest Japan, in 1900 and was extended in 1975. A short sediment core was obtained from the inner part of Asou Bay near the Manzeki-Seto Strait to clarify the temporal change of the depositional environment. We conducted 210Pb and 137Cs dating, CHN analysis, grain size analysis, and meiobenthos (Ostracoda) analysis. As a result, the sedimentation rate based on 210Pb and 137Cs dating was 0.105 cm/year. The results of several analyses revealed that temporal changes of total organic carbon (TOC) and total nitrogen (TN) contents, the ratio of TOC and TN, and ostracode assemblages are closely related to the excavation and extension of the Manzeki-Seto Strait. Before the excavation the study site was stagnant environment and Bicornucythere bisanensis, which can survive in oxygen-poor bottoms, dominated other ostracodes. After the excavation, several species increased or invaded the study site, and the relative abundance of B. bisanensis gradually decreased. Thus, the environment gradually changed for a continuous inflow of the open sea water. Moreover, the extension of the Manzeki-Seto brought an inflow of more open sea water and the study site changed to open bay environment.View full abstractDownload PDF (7899K) -
Kikuji MATSUOKAArticle type: Article
2013 Volume 67 Issue 3 Pages 101-112
Published: May 25, 2013
Released on J-STAGE: May 16, 2017
JOURNAL OPEN ACCESSThe Kashiwagi Unit of the Northern Chichibu Belt, distributing in the northeastern Kanto Mountains, is divided into the Tate and the Hagidaira Subunits. The Tate Subunit corresponds to the usual Kashiwagi Unit. The Hagidaira Subunit, being composed of Lower Cretaceous mixed rocks, corresponds to the formerly defined Kazahaya-toge Unit of the survey area by lithological characters, geologic age, grade of deformation and metamorphism. It is considered that the upper part of the Mikabu Unit, the Tate and the Hagidaira Subunits have been stacked up to form a low-angle piled nappe structure during subduction of an oceanic plate from latest Jurassic to Early Cretaceous time.View full abstractDownload PDF (10232K) -
Yasuo IKEDA, Keita SHIMIZUArticle type: Article
2013 Volume 67 Issue 3 Pages 113-116
Published: May 25, 2013
Released on J-STAGE: May 16, 2017
JOURNAL OPEN ACCESSThe Kutcharo volcano is situated in the southwestern part of the Akan-Shiretoko volcanic chain. The somma of the Kutcharo caldera exhibits a nearly circular wall of 500-1000 m above sea level constructed of thick piles of somma lavas and pyroclastic rocks on the basement Tertiary rocks. Age of the somma lava was determined by K-Ar method. The isotopic age determination on a specimen indicates a Pliocene age (3.7 Ma). The K-Ar age shows one of oldest age in the volcanic chain and is almost same age of somma lava of Akan volcano. These suggest that volcanic activity began at ca 4 Ma at Akan and Kutcharo volcanoes of the southwestern end of the volcanic chain.View full abstractDownload PDF (617K)
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