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Volume 125 (2016)
- Issue 6 Pages 775-
- Issue 5 Pages 647-
- Issue 4 Pages 431-
- Issue 3 Pages 299-
- Issue 2 Pages 185-
- Issue 1 Pages 1-
Volume 125, Issue 2
Displaying 1-8 of 8 articles from this issue
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Cover
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2016 Volume 125 Issue 2 Pages Cover02_01-Cover02_02
Published: April 25, 2015
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSThe Paleozoic strata deposited in the shallow sea and dunes along the western margin of Pangea occur as almost horizontal beds, ornamenting the 2,000 m high Colorado plateau surface. Rapid uplift induced a pre-existing meandering river system to incise rocks quickly, carving a V-profiled canyon. The uplift has likely been driven by an uprising movement in the upper mantle; nonetheless, the well-known steep cliffs will soon change into boring gentle slopes immediately after this uplift stops. In contrast to the magnificent view of various strata at a glance, the strata themselves are not unique, as they can be traced extensively in the surrounding areas.
Turing off Interstate Highway 40 （the old Route 66） to the north, visitors can easily reach the southern rim of the canyon by car, traveling to the Mather Point and/or Bright Angel Trailhead, and enjoy the familiar authentic views. By driving east for one hour or less, visitors can reach Desert View to observe the eastern part of the Grand Canyon and can see the meandering stream of the Colorado River itself in a widened valley. The evening view from this vista point will give a slightly different impression of the Grand Canyon. Some visitors may recognize the Great Unconformity between the horizontal Cambrian beds and the underlying Precambrian units.
（Photograph and explanation: Yukio ISOZAKI）View full abstractDownload PDF (1405K)
Original Articles
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Teruaki ITO, Kenichi UENO2016 Volume 125 Issue 2 Pages 185-199
Published: April 25, 2016
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSChanges in precipitation distribution associated with a surface temperature rise in the late 1980s, which accompanied a climatic regime shift, are investigated using Automated Meteorological Data Acquisition System (AMeDAS) data of the Japan Meteorological Agency, and their relations with the variability of surface pressure patterns are revealed. After the temperature rise, the frequency of winter monsoon pressure patterns did not decrease. According to the classification of pressure patterns, long-term variations of surface pressure pattern frequencies showed negative relations between the winter monsoon and high-pressure patterns before 1992, which subsequently changed to the negative relations between the winter monsoon and traveling low-pressure systems. After the temperature rise, in years when low-pressure patterns prevailed, precipitation increases were observed in western Japan due to low-pressure systems traveling over the Pacific coast, and in wider areas from central Japan to Kyusyu areas due to low-pressure systems traveling over the Sea of Japan. Recently, the frequency of stationary front patterns has been increasing with precipitation increasing in the Setouchi area of western Japan. In years with a warm winter, precipitation increased in wider areas of the Pacific coast to inland areas of central Japan. In cold winters, low-pressure systems traveling over the Pacific coast decreased precipitation in central to western Japan. However, after a temperature rise, low-pressure systems traveling over the Sea of Japan decreased precipitation at the coast of the sea of Japan from central Japan to Hokkaido.View full abstractDownload PDF (3289K) -
Shigeru SUEOKA, Koji UMEDA, Ken-ichi YASUE, Masakazu NIWA, Koji SHIMAD ...2016 Volume 125 Issue 2 Pages 201-219
Published: April 25, 2016
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSIn this study, multi-system thermochronology, i.e., fission-track (FT), K-Ar and U-Pb methods are used to identify the cooling and denudation history of the Tsuruga body of Kojaku granite, southwest Japan. Apatite FT age of 51.8 ± 6.5 Ma, zircon FT age of 70.4 ± 2.0 Ma, biotite K-Ar ages of 66.7–62.0 Ma, and zircon U-Pb age of 68.5 ± 0.7 Ma were obtained for granitic samples, whereas plagioclase K-Ar ages of 19.1–18.8 Ma and whole-rock K-Ar age of 19.0 ± 2.9 Ma were inferred for the basaltic dyke intruding into the granite. The zircon FT lengths are not significantly shorter than their initial lengths, implying rapid cooling at the zircon FT partial annealing zone (PAZ). On the other hand, the apatite FT length distribution shows a typical pattern for granitic pluton without reheating, indicating a slow cooling history at the apatite FT PAZ. Based on the results of these thermochronometric analyses, inverse thermal calculations using the FT data, and simple thermal conduction modeling of the granitic body, the cooling and denudation histories of the Tsuruga body are reconstructed: (1) the Tsuruga body intruded at ca. 68 Ma, late Cretaceous, at a depth of several kilometers, (2) rapidly cooled to below the zircon FT PAZ by heat conduction within a few million years or less, and (3) slowly cooled due to peneplanation during the past 50–60 million years. On the other hand, the whole-rock Rb-Sr age previously reported for the Kojaku body is younger than when the cooling curve of the Tsuruga body obtained by this study intersects with the closure temperature of the whole-rock Rb-Sr system. This may imply a time lag between the formation ages of these bodies, but more thermochronometric studies are required to draw a definitive conclusion. The K-Ar ages of the basaltic dyke are interpreted as its formation age, indicating that dyke intrusion was associated with the Green Tuff movement.View full abstractDownload PDF (1662K) -
Kyoko KAGOHARA, Yoshinori TASHIRO, Hideki KOSAKA, Kohei ABE, Eiji NAKA ...2016 Volume 125 Issue 2 Pages 221-241
Published: April 25, 2016
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSWe should understand the earthquake potential in and around Quaternary fault zones, in view of recent destructive inland earthquakes at previously unknown active fault zones in Japan. The Senpoku Plain and its surrounding areas are characterized by high seismic activity in northeast Japan, highlighted by four destructive earthquakes, M 6.8 in 2008, M 6.4 in 2003, M 6.5 in 1962, and M 7.0 in 1900, which occurred during the past 100 years, although few geomorphic features indicate active faulting. A comprehensive survey was conducted on the tectonic geomorphology in the area to understand the structural and geomorphic expression of the Ichinoseki–Ishikoshi Flexure Line (IIFL), which suggests Quaternary activity. Geological and geomorphical mapping shows that the IIFL is located between the Kitakami Lowland Fault Zone and the Senpoku Plain. The IIFL extends about 30 km from Isawa to Ishikoshi with a slightly sinuous trace. A high-resolution seismic reflection profile and a gravity profile define the subsurface geometry of the IIFL. The IIFL is interpreted to be a steeply west-dipping reverse fault. The Pliocene Kazawa and Yushima Formations typically dip 40° to 20°E along the IIFL, and are overlain by the Pleistocene Mataki Formation, which becomes thinner toward the fold axis of the IIFL, and their dips decrease progressively upward. This suggests that the Mataki Formation was deposited concurrently with fault activity of the IIFL. Fission-track dating of a tuff layer within the uppermost section of the Kazawa Formation indicates that active reverse faulting of the IIFL began at about 2 Ma. At least 280 m of the tectonic uplift is consumed by active faulting and the average uplift rates are estimated to be 0.14–0.08 mm/yr. Vertical separations of Hh surface are about 15 to 40 m. Heights of fold scarps on L1 surface are about 2 m. Their ages are determined to be 0.4–0.5 Ma for Hh and 24–12 ka for L1, respectively. Therefore, the Quaternary average uplift rates of the IIFL are estimated to be 0.03–0.17 mm/yr. Quaternary activity of the IIFL is weak, but there are differences in the magnitude of dissection in the Iwai Hills between the hanging-wall and the footwall of the IIFL.View full abstractDownload PDF (9274K)
Short Article
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Daisuke ISHIMURA, Takahiro MIYAUCHI, Ryosuke HAYASE, Keiichi OHARA, Ts ...2016 Volume 125 Issue 2 Pages 243-256
Published: April 25, 2016
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSRradiocarbon dates of organic bulk sediment samples, as well as animal and plant fossil samples, from Holocene coastal lowland sediments are compared to clarify characteristic differences between the dates of both samples and estimate the true age of sedimentation. The samples were collected from drilled cores obtained from two sites. An OSN-Br core was drilled at a river mouth in Kuji City, Iwate Prefecture, and consisted of marine sediments showing sea-level rise during the Holocene. Two KYD-Br cores were drilled at a small valley in Yamada Town, Iwate Prefecture, and consisted of peaty sediment and interbedded event deposits (e.g., tephra and tsunami deposits). Based on a comparison with the dates of samples collected from the same horizon or ages of tephras, radiocarbon dates of organic bulk sediment samples of the OSN-Br core showed a systematic age difference between the dates of animal and plant fossil samples and tephras. These organic bulk sediment samples were interpreted to include old carbon derived from the hinterland, particularly from Paleogene to Cretaceous sedimentary rocks. On the other hand, radiocarbon dates of organic bulk sediment samples of the KYD-Br cores agree with dates of in-situ plant fossil samples (seed and leaf) and are consistent with the age of tephras. Therefore, it can be assumed that the dates of organic bulk sediment samples represent the true age of sedimentation.View full abstractDownload PDF (1233K)
Letters
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Naotoshi YAMADA, Michiko YAJIMA2016 Volume 125 Issue 2 Pages 257-267
Published: April 25, 2016
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSEdmund Naumann (1854–1927), the first professor of the Geological Institute, Science Department, the University of Tokyo, presented a proposal to found the Geological Survey of Japan to Hirobumi Ito, Minister of the Home Affairs of Japan, in 1879. The Japanese Government immediately accepted this proposal, so Naumann resigned his post as a professor of the university and returned to Germany, in order to find the necessary specialists and items for the upcoming survey. During his stay in Germany, on January 3rd, 1880 he gave an invitation lecture on Japan, which was published in “die geologische Verhandlungen der Gesellschaft für Erdkunde zu Berlin” as a paper titled “Ueber die wirthschaftlichen Verhältnisse Japans und die geologische Aufnahme des Landes” (The economic situation of Japan and the Geological Survey of Japan). This paper introduced the feudal system, which had controlled Japan through the Middle to Modern ages, the economic situation of Japan after the Meiji Restoration, especially for agriculture, means to promote Japanese agriculture and industry, and the purpose and tasks of the Geological Survey of Japan. The paper, which we have now translated into Japanese, is important because it is similar to the Japanese translation of the above proposal handwritten in 1879, and the original text of the proposal, probably written in German, has now been lost.View full abstractDownload PDF (557K) -
Editorial Committee of History of Geosciences in Japan, Tokyo Geograph ...2016 Volume 125 Issue 2 Pages 269-290
Published: April 25, 2016
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSThe Editorial Committee of the History of Geosciences in Japan, set up by the Tokyo Geographical Society, is publishing “Trends of Geosciences after the Pacific War in Japan, 1945 to 1965 Part 4”. It provides a history of oceanology and volcanology.View full abstractDownload PDF (743K) -
Kenichi UENO, Teiji WATANABE2016 Volume 125 Issue 2 Pages 291-298
Published: April 25, 2016
Released on J-STAGE: May 12, 2016
JOURNAL FREE ACCESSThe international conference “Perth III: Mountains of Our Future Earth” was held in Perth, Scotland on Oct. 4-8, 2015. International trends in mountain studies observed at the meeting are examined, following a brief history of recent international mountain studies. Field trips and educational activities associated with the meeting are also introduced, and future perspectives are proposed to activate mountain studies in Japan.View full abstractDownload PDF (1021K)
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