著者
田辺団体研究グループ
出版者
地学団体研究会
雑誌
地球科學 (ISSN:03666611)
巻号頁・発行日
vol.47, no.1, pp.1-16, 1993-01-25
被引用文献数
2

The Miocene Tanabe Group, which consists of shallow-marine siliciclastic sediments, is distributed in the southwestern part of the Kii Peninsula, Japan. The group is about 1,500m thick, and is divided into the Asso and the Shirahama Formations in ascending order. The Asso Formation is mainly composed of mudstone and conglomerate, and the Shirahama Formation of sandstone, mudstone and alternating beds of them. A thick conglomeratic sedimentary wedge, which was deposited in a fan-delta system (the Shimomisu Fan-delta), is developed in the northern area of the distribution of the group. To clarify the sedimentary history of the fan-delta, at first, sedimentary facies were recognized and classified based mainly on grain-size and sedimentary structures. Consequently, the facies associations and the sedimentary bodies were recognized and defined based on the occurrence and combinations of sedimentary facies. The spatial and stratigraphic interrelationship among sedimentary facies, facies associations and sedimentary bodies were analyzed in detail. The following results are obtained. The sediments of the Shimomisu Fan-delta consist of 3 sedimentary bodies, which are in turn consist of 6 facies associations. The sedimentary history of the Shimomisu Fan-delta is summarized as follows: STAGE OF GENESIS: The drowned valleys facing to the ocean were formed as the sea-level rise began. The debris flow deposits and marsh muds, and then sands and rounded gravels in the neritic environments were deposited in the valley. STAGE OF PROGRADATION: After the burial of valleys, the rate of the sea-level rise decreased. Gravely deposits supplied from the north formed a fan-delta system which prograded toward the south. Gravely deposits were deposited as foreset beds, resting on a downlap surface, which were underlain by the bottomset muds. The fan-delta divided the sedimentary basin into embayed sea in the northern margin and open shelf in the resting area. STAGE OF AGGRADATION: The rate of the sea-level rise again increased, and the supply of sediments were continued. Therefore, the rate of the progradation decreased, and sediments were accreted vertically in the neritic area, forming the topset beds of the fan-delta. STAGE OF ABANDONMENT: The rapid increase in the rate of the sea-level rise took place in the later half of Blow's N 8 stage, and the fan-delta system was abandoned and the shelf mud facies covered throughout the basin.
著者
Hendarmawan 三田村 宗樹 熊井 久雄
出版者
地学団体研究会
雑誌
地球科學 (ISSN:03666611)
巻号頁・発行日
vol.59, no.3, pp.155-166, 2005-05-25

研究地域では,水資源を湧水に依存しているため,湧水の環境保全は非常に大切である.それ故,湧水についての浸透量・涵養量・流出量の理解が必要である.本研究では,インドネシア,Java島西部のLembangとその周辺において,涵養地域と流出地域に各地域を区分する目的で,地質学的背景と湧水の電気伝導度と温度の傾向を総合的に検討した.断層の発達と時代の新しい累層,古い累層は,それぞれ異なる電気伝導度と水温度の湧水の形成に影響していた.乾季と雨季における電気伝導度と温度の違いは,降雨からの涵養水や表層水の影響が大きいと考えられた.以上の結果,大きく異なる湧水の電気伝導度と水質の特徴により,研究地域は3つの地域に区分することができる.
著者
大藤 弘明 赤井 純治
出版者
地学団体研究会
雑誌
地球科學 (ISSN:03666611)
巻号頁・発行日
vol.59, no.2, pp.103-110, 2005-03-25

20面体構造をとる物質は自然界において極めて稀である.また,並進対称を満たさない5回対称軸を伴うため,鉱物(単結晶)においても原則的に禁じられた構造である.しかし近年,堆積岩中などに広く産するフランボイダルパイライト(黄鉄鉱の木苺状集合体)中から20面体の対称を示すドメイン構造が見出された.本論では,その特異な構造について概説するとともに,天然・合成物質における類似構造体との比較検討を行った.フランボイダルパイライトにおける20面体構造は,中心で頂点を共有して集合した20個の四面体ユニットより構成される.各ユニット内において,マイクロクリスタルは互いの結晶方位を共有し,立方パッキングを形成している.このような多粒子の緻密な集合によって造られる20面体構造は,天然においても他に例がなく,ミクロスケールにおける鉱物の結晶化の新たな一面を示しているといえる.一方,実験合成物,特にクラスターなどのナノスケールの物質においては,20面体パッキング構造は比較的普通に認められる.特に,構成粒子のサイズ,属性こそ大きく異なるが,Au微粒子などに代表される多重双晶粒子と20面体型フランボイダルパイライトとの間に,構造的な共通点が多く認められた.この事実は,ナノスケールからミクロスケール,さらにはマクロスケールに至るまでの微粒子の一連の挙動,クラスターの形成から粒子の成長,結晶相への転移など,を理解する上でも重要な手がかりとなる可能性がある.
著者
永尾 隆志
出版者
地学団体研究会
雑誌
地球科學 (ISSN:03666611)
巻号頁・発行日
vol.30, no.2, pp.110-121, 1976-03-20

In the Chugoku and Shikoku provinces, are extensively distributed various kinds of the late Cenozoic volcanic rocks as follows. (1) Calc-alkaline volcanic rocks derived by the volcanism associated with the "Gree Tuff Crustal Movement" in the San'in and Setouchi districts (middle to late Miocene). (2) Alkaline volcanic rocks mainly composed of basalts in the San'in district (the so called "Circum Japan Sea Alkaline Petrographic Province") and the Chugoku mountainland (late Miocence to Recent). (3) Calc-alkaline volcanic rocks which formed the volcanoes beloging to the so called Daisen Volcanic Zone in the San'in district (Quaternary). The middle to late Miocene volcanic activity might have been controlled by the structure in the direction of the Honshu arc. On the other hand, in the Pliocene to Recent time (especially middle Pleistocene to Recent) the volcanic activity has occurred mainly in relation to the structure of north-south trend, which crosses the Honshu arc direction. These evidences may suggest that the volcanisms of the above two periods have occurred in relation to the different crustal movement, respectively. Considering from many published chemical analyses, it is possible to point out the following chemical differences among the late Cenozoic volcanic rocks in these provinces. (1) There is a clear distinction of the chemical features between the middle to late Miocenct calc-alkaline volcanic rocks occurring in the San'ir and Setouchi districts. The latter have highei contents of alkalies, especially K2O, than those from the former. (2) Similar chemical difference is also observed in the alkaline volcanic rocks from the Pliocene to Recent in the Chugoku province. In this case alkaline volcanic rocks from the Sanyo district are richer in alkali contents than those from the San'in district. (3) It may be noticed, moreover, that the Pliocene to Recent calc-alkaline volcanic rocks in the San'in district have higher alkali contents than those of the middle to late Miocene in the same district. The above first two evidences may conflict with the general tendency in the chemical character of the island arc volcanic rocks, and seem to be inconsistent with the genetical interpretation based on plate tectionics held by JAKES-WHITE (1968,1972) and many others.
著者
Vasiliev Boris I. Yugov Ivan V.
出版者
地学団体研究会
雑誌
地球科學 (ISSN:03666611)
巻号頁・発行日
vol.60, no.3, pp.185-196, 2006-05-25
被引用文献数
4

35年間におよぶ海洋地質研究にもとづいて,太平洋の基本構造を解明し,もっとも信憑性のある太平洋の起源論を提案する.太平洋巨大海盆の基本構造は,3つの地質-構造ステージからなる.第1ステージは,始生代にさかのぼる超塩基性岩類(塑性流動を履歴)と変成岩類に代表され,それぞれ,海洋島火山岩中の包有物として産出し,海溝・断裂帯・海台などに露出する.第2ステージは,三畳紀〜ジュラ紀を中心とする海洋性トラップ層(層状塩基性貫入岩類と玄武岩類のコンプレックス)であり,海盆下のほぼ全域に伏在する.第3ステージは,海盆底や海山・海台を構成するジュラ紀後期〜現世の火山岩類と堆積層であり,ブロック運動による深海化を記録する.太平洋巨大海盆は,地球最大のユニークな地形-地質構造であり,おもに苦鉄質な地殻をもつ.(1)その原型は,地球-月システムをうみだした約45億年前の天体事件によって形成され,その後,(2)周縁の大陸から数10億年間にわたって供給された厖大な量の陸源物質が,海盆底の火山噴出物や伏在する超塩基性岩類とともに変成-溶融し,少量の酸性岩類を形成した.さらに,中-新生代における全地球的海洋形成作用にともなって,(3)三畳紀〜ジュラ紀を中心に海盆のほぼ全域にトラップ層が形成され,(4)ジュラ紀後期にはじまるブロック沈降による深海化と火山活動-堆積作用が現海盆の複雑な地形-地質構造を形成した.