地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
118 巻 , 2 号
選択された号の論文の10件中1~10を表示しています
表紙
  • 2009 年 118 巻 2 号 p. Cover02_1-Cover02_2
    発行日: 2009/04/25
    公開日: 2010/04/01
    ジャーナル フリー
     ゾルンホーフェンは南ドイツのミュンヘンとニュールンベルグの中間に位置する小さな町で,その名を世界的に有名にしているのは,中生代ジュラ紀後期(約1億5000万年前)の石灰岩とそこから産出する化石である.この石灰岩は,表紙写真のように板状で緻密なためにローマ時代から壁や床などの建築材料として使用され,また1793年からはリトグラフ用の石版石としても使用されてきた.大規模な採石がされるようになると,保存のよい化石が多数発見されるようになった.そのなかでも最も有名なのは始祖鳥化石で,現在までに10標本がゾルンホーフェンから発見されている.
     ゾルンホーフェンの駅前には2008年に改築された化石展示を中心とした博物館(Bürgermeister-Müller-Museum)があり,40km西方のロマンチック街道沿いの中世都市ノルトリンゲンにはリースクレーター博物館がある.南ドイツに行く機会があればぜひ訪れてほしい地質系博物館である.
    (写真・文:白尾元理)
論説
  • 西井 稜子
    2009 年 118 巻 2 号 p. 233-244
    発行日: 2009/04/25
    公開日: 2010/04/01
    ジャーナル フリー
     Linear depressions and associated uphill-facing scarps, which result from the gravitational deformation of rock slopes, have widely developed along the main ridge in the Mt. Eboshi area, northern Japanese Alps. The role of landslides in the development of linear depressions in granitic rocks is evaluated from the distribution of linear depressions, characteristics of landslides (form, magnitude and frequency) and characteristics of bedrock (geology, discontinuity, degree of weathering and rock mass strength). The morphology of landslides and changes in the areas of landslides from 1958 to 2004 are compared to the development of linear depressions. Most linear depressions lie parallel to the main ridge and the strike of major rock joints, although their distribution differs between the northern and southern areas. In the northern study area, linear depressions are concentrated on the gentle upper slopes and landslides have intensively occurred on the lower slopes. In contrast, the southern area shows sporadic occurrences of linear depressions on the middle to upper slopes and has experienced only minor landslides. The intensive occurrences of landslides and linear depressions in the northern area are considered to result basically from debuttress and stress-release caused by the landslide activity. In addition, the lower rock mass strength in the northern study area also promotes the development of linear depressions.
  • 石川 智, 鈴木 毅彦, 中山 俊雄, 鹿島 薫
    2009 年 118 巻 2 号 p. 245-260
    発行日: 2009/04/25
    公開日: 2010/04/01
    ジャーナル フリー
     We analyzed core samples from two sites in the Tokyo lowland to clarify paleoenvironmental changes that occurred during the Holocene in the northern Tokyo Bay area. The samples are from (1) Core HK, which was bored at Hibiya Park, Chiyoda Ward, Tokyo, and from (2) Core DK, which was bored at Civil Engineering Center Tokyo Metropolitan Government in Koto Ward, Tokyo. Both cores belong to Civil Engineering Center Tokyo Metropolitan Government. Analyses of both lithofacies and diatom assemblages of the cored samples found the following paleoenvironmental changes.
     The first distinct regression occurred in the early Holocene (11,450-10,600 cal. yrBP) and was followed by one in the high-stand relative sea-level stage at 7,300-6,250 cal. yrBP. Subsequently, two small-scale regressions occurred at 3,600-1,200 cal. yrBP and 1,000 cal. yrBP, respectively. These two regressions were documented by temporal variations in diatom assemblages from marine to brackish-water diatoms to brackish and fresh-water diatoms. During the high-stand stage (7,300-6,250 cal. yrBP), the Hibiya embayment area was inundated with seawater and became part of Paleo-Okutokyo Bay. The marine transgressions and regressions inferred from diatom assemblages in both cores might be correlated with small-scale sea-level fluctuations at one- or two-thousand-year intervals during the Holocene, such as a minor regression during the middle Jomon period, Yayoi regression, and Heian transgression.
  • 加田平 賢史, 森脇 洋, 吉川 周作, 七山 太, 山本 攻
    2009 年 118 巻 2 号 p. 261-279
    発行日: 2009/04/25
    公開日: 2010/04/01
    ジャーナル フリー
     In this study, concentrations of heavy metals and anions of natural origin were investigated using boring core obtained from the north bank of the Shin-yodogawa River in the northern part of Osaka City. A leaching test and a content test in compliance with Soil Contamination Countermeasures Law in Japan were applied. The leaching test is a method by which soil in ten times its volume of water is shaken for 6 hours, and considers the risk of ingestion of groundwater contaminated by hazardous substances eluted from contaminated soil. The content test is the method of eluting hazardous substances from 6 g of soil by shaking the sample in 200 mL of 1 mol/L hydrochloric acid for 2 hours, and considers the risk of the direct ingestion of contaminated soil. Concentrations of heavy metals obtained by the content test were lower than stipulated in the Japanese regulations, while some samples showed higher concentrations than stipulated in the regulations when using the leaching test.
     Metal concentrations were also observed by a microwave extraction method (MEM), which approached those of the total content analysis. The relationships between ratios of leaching amounts to the concentrations obtained by MEM and solution pH were used to discuss leaching characteristics. Because there were good correlations among concentrations of heavy metals and anions obtained by the leaching test, boron concentration could also be estimated from Cl- concentration, and F- concentration could be estimated from both concentrations of SO42- and Ca. There is a possibility that total amounts of Pb and Cr of natural origin in soil could be estimated using relationships with total amounts of other metals such as Ni, V, Mn, Zn and Mg, because their concentrations obtained by MEM showed good correlations.
資料
解説
  • 松田 博貴
    2009 年 118 巻 2 号 p. 297-308
    発行日: 2009/04/25
    公開日: 2010/04/01
    ジャーナル フリー
     Dolomite (dolostone) is a common carbonate rock in the geological records and is also a very important carbonate reservoir rock, which stock about 40% of global oil reserves. Most of the dolomites in the geological record are considered to be of replacement origin, although some were precipitated directly from pore-fluids. A variety of dolomitization models in different diagenetic environments are currently proposed for interpreting ancient dolomites: (1) evaporative dolomitization including sabkha and seepage-reflux models, (2) mixed-water dolomitization, (3) marine dolomitization, (4) burial dolomitization, (5) hydrothermal dolomitization. The dolomites formed by each dolomitization model have different geological, petrographical, mineralogical and geochemical features. Based on these features, we can, therefore, identify dolomitization models and diagenetic environments of ancient dolomites.
     A dolomite reservoir is often of as good quality as a limestone reservoir. Dolomitization affects carbonate reservoir characteristics, such as porosity and permeability, and, as a result, reservoir characteristics are significantly changed from those of primary carbonate rocks. The important factors associated with dolomitization and controlling the characteristics of carbonate reservoir rocks are: (1) increasing crystal size (2) decreasing porosity due to a net addition of dolomite, (3) developing moldic pores, (4) increasing resistance to compaction, and (5) increasing fractures. Dolomitization and diagenetic history of individual carbonate reservoirs differ from each other and result in the complexity of reservoir characteristics. It is, therefore, indispensable to understand the processes that formed each dolomite reservoir.
  • 金丸 龍夫
    2009 年 118 巻 2 号 p. 309-310
    発行日: 2009/04/25
    公開日: 2010/04/01
    ジャーナル フリー
     In August 2008, I visited some rift zones, volcanoes, and glaciers in Iceland, and was impressed with Iceland's nature and Icelandic activities for harnessing it. I would like to introduce you to some of the geological tourist attractions in Iceland.
地学クラブ講演報告
  • 篠田 謙一
    2009 年 118 巻 2 号 p. 311-319
    発行日: 2009/04/25
    公開日: 2010/04/01
    ジャーナル フリー
     Modern DNA—maternally inherited mitochondrial DNA and paternally inherited Y-chromosomal DNA in particular—is now routinely used to trace ancient human routes. It appears that genetic data can actually offer a means of better understanding ancient population movements. The DNA patterns of present-day world populations indicate that modern humans emerged from Africa at least 150,000 years ago. These populations dispersed from Africa to most other parts of the world at least 60,000 years ago along the tropical coasts of the Indian Ocean to Southeast Asia and Australasia.
     Genetic data support a model for the peopling of the New World in which Native American ancestors diverged from the Asian gene pool and experienced a gradual population expansion as they moved into Beringia. After a long period in greater Beringia, these ancestors rapidly spread into the Americas at least 15,000 years ago.
     Examinations of ancient human bones using molecular genetic techniques provide direct access to genetic information on past populations. The retrieval and analysis of ancient DNA is more difficult than that of modern DNA. However, this technique holds great potential for inferring the origins of the Japanese people. The distribution of mitochondrial DNA haplogroups among the Jomon, Yayoi, and modern Japanese populations suggests that the formation of the Japanese population was not the result of a population expansion. Distinctively different frequencies of mitochondrial DNA haplogroups among Jomon and Yayoi populations indicate significantly different population histories for these groups. However, both populations have contributed to the formation of the modern Japanese population. An eastward population expansion from the Asian Continent during the Yayoi period resulted in the admixture of these people with the indigenous Jomon people and led to the formation of the basic pattern seen in modern Japanese people.
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