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Volume 107, Issue 12
Displaying 1-8 of 8 articles from this issue
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Kazuo Kaneko2001 Volume 107 Issue 12 Pages 729-748
Published: December 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSLower to middle Miocene Yatsuo Group distributed in the eastern part of Toyama Prefecture, central Japan, is divided into the Nirehara, Iwaine, Iozen, Kurosedani/Fukuhira, Higashi-bessho Formations in ascending order. The Iwaine, Iozen, and Fukuhira Formations consist mainly of subaqueous volcanic rocks occasionally interbedded with subaerial volcanic rocks in several horizons. The volcanic rocks vary from basaltic andesite to rhyolite. In the studied area, normal faults are developed with N to S and NNE to SSW trends, and are intersected by some faults at almost right angles. Such a fault system must have formed a sedimentary basin in which the Yatsuo Group were deposited. The tectonic setting is similar to that of a continental rift, such as the Rio Grand Rift and the rift zone of the Akita-Yamagata oil field. The K-Ar ages of six volcanic rock samples from the Yatsuo Group range from 16.50 My to 12.19 My. This indicates that the volcanism occurred during the spread of the Japan Sea. In conclusion, the studied area was situated at peripheral parts of the rift zone.View full abstractDownload PDF (3030K) -
Keiji Arita, Shizuo Takemura, Atsushi Takemura, Toshiharu Nishimura2001 Volume 107 Issue 12 Pages 749-754
Published: December 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Kozaki Formation belonging to the Kurosegawa Terrane had been assigned to the Middle Permian in age judging from fusulinids. The purposes of this study are establishment of the lithostratigraphy and re-examination of the age based on radiolarian fossils.The Kozaki Formation, about 700m thick, is divided into three members. The Lower Member consists of conglomerate, sandstone, mudstone with limestone. The Middle Member is mainly composed of conglomerate and pebbly sandstone. The Upper Member consists of pebbly mudstone, mudstone and sandstone. The Lower and Upper members yield radiolarian fossils. The radiolarians of the Lower Member indicate Early Permian, and these of the Upper Member denote earliest Late and later Late Permian. Fossil evidence suggests that the Kozaki Formation ranges in age from Early to Late Permian. The Upper Member of the Kozaki Formation probably corresponds to the Kuma Formation.View full abstractDownload PDF (1038K) -
R. Shi Guang, Jun-ichi Tazawa2001 Volume 107 Issue 12 Pages 755-761
Published: December 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSTwo Permian brachiopod genera, Rhynchopora King and Blasispirifer Kulikov, are reported for the first time from the Middle Permian, lower part of the Moribu Formation in the Hida Gaien Belt, central Japan. The Moribu species are closely compared with similar forms from the Middle Permian Barabash Formation (lower Chandalaz Series) in the Barabash area of South Primorye, Russian Far East. The discovery of these two genera, which exhibit close relationships with Middle Permian brachiopod faunas of South Primorye and the broad Boreal Realm, implies that tha Hida Gaien Belt was paleobiogeographically and paleogeographically close to the western part (Voznesenka Belt) of South Primorye, both situated in a middle latitudinal setting in the Northern Hemisphere on the southeastern side of the Bureya Block and lay proximal to and slightly northeast of the Sino-Korea Block during the Permian.View full abstractDownload PDF (1149K) -
Yoshihiro Ganzawa, Naomi Porat, Jun-ichi Araya, Takashi Shiina2001 Volume 107 Issue 12 Pages 762-772
Published: December 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSAn investigation on TL/IRSL dating of poly-mineral 4-11μm component of aeolian deposits, so called "loam", collected from seven beds near Ottomo in north-east Japan was performed as a first attempt in Japan. The clay layers, composed of fine particles of quartz and feldspars, are favorable material for TL/IRSL dating because they had been exposed to sunlight sufficiently through transportation process from inland China to Japan. Two apparatuses, Ris ∅ Reader and NK 95, were employed for TL/IRSL measurements with filters combination of Schott BG-39 (2 mm) and Corning 7-59(6mm) or U-340 (5 mm). The De (equivalent dose) of TL/IRSL determined by two methods, the additive dose method (AD) and the regeneration method (RG), show values from 40 Gy, to 209 Gy according to the geological horizon at the sampling site. Annual Dose rates of samples, measured by both atomic absorption analysis (AAS) and neutron activation analyses (NAA), indicated 1.2 mGy/year to 2.5 mGy/year, taking into account the water content calculated by DBD (Dry Bulk Density). The IRSL and TL ages younger than 50 ka coincided well with the estimated ages derived from the intercalated tephra layers. Moreover, TL additive dose ages show good agreement with the estimated ages over 50 ka to 120 ka. However, IRSL and TL regeneration method show "age short fall" compared with the estimated ages over 50 ka.View full abstractDownload PDF (1192K) -
Mitsuo Shimada, Tomoaki Sumii, Masayuki Torii2001 Volume 107 Issue 12 Pages 773-783
Published: December 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSWe report new paleomagnetic directions from six Middle Miocene andesite sites in Takanawa peninsula, Shikoku, Southwest Japan. These andesites were divided into three groups in terms of their K-Ar ages. One dyke is dated as 12.0+/-0.2 Ma. Two dykes and two necks are dated in the range between 14 to 15 Ma. Rest one shows relatively older age as 15.8+/-0.2 Ma. The paleomagnetic directions of the younger five sites (12 Ma to 15 Ma) do not show any significant deflection from that of the present geomagnetic field. On the other hand, a clockwise deflected declination (52.2°) is revealed at the older site. Local tectonic disturbances and geomagnetic secular variation are inadequate to explain the deflected direction of this site. These results, in conjunction with the previous study on the Miocene Mizunami/Kani Groups (18 Ma to 15 Ma), can delineate the continuous record of the clockwise rotation of the Southwest Japan block. We provide further evidence for beginning of the block rotation at about 16 Ma and its termination at about 15 Ma or 14 Ma.View full abstractDownload PDF (1552K) -
Yoshiaki Ishida, Toshihiko Fujita2001 Volume 107 Issue 12 Pages 784-791_2
Published: December 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSSpecimens of the extant species Ophiura sarsii sarsii Lutken, collected from the late Middle Miocene to early Late Miocene Wakkanai Formation and from the middle Late Miocene to Early Pliocene Koetoi Formation in north Hokkaido (latitude ca. 45°N), are described herein. The Wakkanai specimens represent the oldest fossil record of this species. The fossil ophiuroids from both locations are found in dense aggregations suggesting that they formed high-density populations on the sea bottom of the lower shelf and the upper slope as in those of Recent ones. The maximum sizes of the fossil ophiuroids from both formations were larger than those from the Late Miocene to Middle Pleistocene formations in Honshu, north to central Japan (latitude ca. 35-39°N). This regional trend of larger body size northward resembles that of Recent Ophiura sarsii sarsii. Size structure of the ophiuroids from the Wakkanai Formation was bimodal, and the percentage of animals larger than 20 mm in disc diameter was larger in the Wakkanai Formation than in the Koetoi Formation. Such a difference in size structure may be explained by the difference in water depth.View full abstractDownload PDF (3054K) -
Ken-ichi Yoshidomi, Yasuko Inoue2001 Volume 107 Issue 12 Pages 794-797
Published: December 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSCorals, nerineid gastropods, bivalves and cidarid echinoids were discovered from limestones in western Yamaguchi Prefecture. The fauna is comparable to the Torinosu Fauna widely distributed in the Chichibu Belt, Outer Zone of SW Japan.These limestones have been regarded as lacustrine facies belonging to the Lower Cretaceous Wakino Subgroup (Kanmon Group). The formation containing limestones is divided into four members in ascending order ; Lower Mudstone Member, Middle Sandstone and Mudstone Member, Upper Limestone Member and Uppermost Sandstone and Mudstone Member. Uppermost Sandstone and Mudstone Member is correlated with the Yoshimo formation (Toyonishi Group) with brackish fauna, accordingly, it is concluded that conformably underlies Upper Limestone Member also belongs to the Toyonishi Group. Coral-limestone indicates that the Tethys Sea expanded to studied area in Early Cretaceous.View full abstractDownload PDF (1028K) -
Mutsuki Aoya, Takao Hirajima, Akira Takasu, Masaki Enami, Simon Wallis ...2001 Volume 107 Issue 12 Pages XXI-XXII
Published: 2001
Released on J-STAGE: November 26, 2010
JOURNAL FREE ACCESS
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