Earth Science (Chikyu Kagaku)

Tectonic deformation of soft sediments of the Otonashigawa Group in the Shimanto Terrain, Ku Peninsula, southwest Japan(Photo)

Kazuyoshi Nakamura

Article type: Article
1988 Volume 42 Issue 1 Pages i-ii
Published: January 25, 1988
Released on J-STAGE: June 06, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.42.1_i

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Plio-Pleistocene Tokai Group between the Suzuka and Yoro Mountains, central Japan

Late to latest sediments of the Tokai Sedimentary Basin

Fumio Yoshida

Article type: Article
1988 Volume 42 Issue 1 Pages 1-16
Published: January 25, 1988
Released on J-STAGE: June 06, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.42.1_1

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The upper to uppermost sediments of the Tokai Group are distributed between the Suzuka and Yoro Mountains. The geology of the Tokai Group in this area is summarized as follows: 1. The Tokai Group attaining to 950 m thick is divided into the Biroku (composed of gravel), Kono (mud and sand), Ichinohara (gravel and mud), Ohizumi (mud and sand), Tara (gravel and mud) and Komeno (gravel) Formations in ascending order. Among them, the Ohizumi and Tara Formations interfinger. The sediments of the Ichinohara, Tara and Ohizumi Formations are gradually finer southward. 2. In general, the Tokai Group dips 10-20° to the west, and strikes parallel to the piedmont lines of the Suzuka and Yoro Mountains. 3. The Tokai Group yielded Stegodon akashiensis from three localities, and their horizons have been revealed to be restricted to the Ohizumi and (lower part of) Tara Formations. 4. The depocenter in the Tokai Group shifted northward, and the accumulation of the Tokai Sedimentary Basin finished during the period ranging from 0.90 Ma to 0.70 Ma with the deposition of the Komeno Formation. 5. The sediment source areas are inferred as follows: (a) The Biroku Formation was supplied from the Yoro Mountains, (b) the Ichinohara, Tara and Ohizumi Formations were transported from about 50 km northern area beyond the Yoro Mountains, and (c) the Komeno Formation was supplied from the Suzuka Mountains.

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Organic matter in siliceous shale and chert of the Onverwacht Group, South Africa

Yuuko Itihara, Toshiro Morikiyo, Masae Omori

Article type: Article
1988 Volume 42 Issue 1 Pages 17-24
Published: January 25, 1988
Released on J-STAGE: June 06, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.42.1_17

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Contents of various forms of carbon and nitrogen in siliceous shale and chert of the Onverwacht Group (Hooggenoeg F. and Theespruit F.), 3300-3500 Ma old, and elemental composition, graphitization degree and ¹³C/¹²C ratio of their kerogen have been determined. These rocks contain various quantity of organic carbon (1.84% for the siliceous shale and 0.27-0.43% for the chert), but practically do not contain insoluble nitrogen which consists of organic nitrogen in the kerogen structure and ammonium nitrogen in minerals. δ¹³C values of their kerogens are -27.7‰ and -35.5‰ for the Hooggenoeg Formation and -17.0‰ and -15.9‰ for the Theespruit Formation. On the other hand, analytical results of carbon and nitrogen contents for the Gunflint chert, 1800-2100 Ma old, which were examined for reference in this study, show that the Gunflint chert contains 8.7ppm insoluble nitrogen in spite of the low organic carbon content (0.06%). The lack of insoluble nitrogen in the Onverwacht siliceous shale and chert is characteristic in comparison with the data of the Gunflint chert and the Phanerozoic siliceous shale and chert which have been determined in a previous study. Taking the δ¹³C values of the kerogens into consideration, the lack of insoluble nitrogen in the Onverwacht siliceous shale and chert seem to be due to the difficulty of the nitrogen fixation into the kerogen structure (e. g. Simple chemical character of the early life caused the rapid elimination of the nitrogen from the sedimentary organic matter as ammonium ion, and the low rate of sedimentation in Archean time promoted the elimination of the nitrogen from the sediments).

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Discovery and significance of the perified forest around the piedmont of Komagatake Volcano, southwestern Hokkaido

Seiji Yanai, Yoshihiro Ganzawa

Article type: Article
1988 Volume 42 Issue 1 Pages 25-28
Published: January 25, 1988
Released on J-STAGE: June 06, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.42.1_25

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14C ages of Naumann's elephant Palaeoloxodon naumanni (Makiyama) from the sea bottom off the San'in district in the Sea of Japan by accelerator mass spectrometry (Datum)

14C age of the Quaternary deposits in Japan (168)

Masahiko Akiyama, Tadao Kamei, Nobuyuki Nakai

Article type: Article
1988 Volume 42 Issue 1 Pages 29-31
Published: January 25, 1988
Released on J-STAGE: June 06, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.42.1_29

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On the volcanoes in Northeast China (Introduction)

Mitsuo Shimazu

Article type: Article
1988 Volume 42 Issue 1 Pages 32-40
Published: January 25, 1988
Released on J-STAGE: June 06, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.42.1_32

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