35 0 0 0 OA 大河川デルタの地形と堆積物
- 著者
- 堀 和明 斎藤 文紀
- 出版者
- Tokyo Geographical Society
- 雑誌
- 地学雑誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.112, no.3, pp.337-359, 2003-06-25 (Released:2009-11-12)
- 参考文献数
- 141
- 被引用文献数
- 9 14
Large rivers with high sediment discharge, such as the Amazon, Ganges-Brahmaputra, and Huanghe (Yellow) rivers, have formed mega-deltas at their mouths. This paper reviews morphology and sediments of mega-deltas and their Holocene evolution in relation to sea-level changes, channel avulsion, and past-sediment discharge. Application of various radiometric dating techniques to delta deposits, especially since the 1980's has made it possible to clarify delta evolution dynamically on 10-to 1000-year time scales. Most of the deltas are located in developing countries, and have environmental problems principally caused by human activities. For the evaluation of current status and human activities in deltas and drainage basins, both natural and anthropogenic changes of deltas should be analyzed from the viewpoints of geology, sedimentology, and their evolution.
1 0 0 0 東京湾の環境資源(<特集>環境地質学)
- 著者
- 大嶋 和雄 斎藤 文紀
- 出版者
- 地学団体研究会
- 雑誌
- 地球科学 (ISSN:03666611)
- 巻号頁・発行日
- vol.47, no.3, pp.213-231, 1993
Tokyo Bay is badly polluted, but would be in much worse shape were in not for sewage treatment and regulation. Such management techniques for water quality have rid the bay of toxic mercury sludge, and have made the average water quality of the bay head up to Class C rating, which indicates no unpleasant effects on everyday life. The bay still yields fishery products; a 30,000-ton catch in 1990. However, its yield is less than only a third of the maximum of the past fisheries yield. There is a limit, however, to technology. To bring the water quality rating of the entire bay up to Class B, suitable for fishing, would require that treated sewage dumped into the bay be able to support marine life. The construction of sewage treatment plants to perform such a feat would be prohibitively expensive, and the cost of the treatment would be a continuing liability, not a one-time fix. In other words, though technology can keep death at bay, it alone cannot restore Tokyo's coastal area to health. A Tokyo-Bay restoration project must harness the area's natural ability to recover from environmental damage. That recovery is accomplished through three mechanisms; sea-water exchange, sedimentation, and biological production. The coast is the interface between land and sea, where its ecosystem has developed over thousand of years. Technology works to fight pollution, but only to a point. Coastal restoration projects must be designed to work with the powerfull cleaning system of the bay itself if they are to assist truly sustainable development.
1 0 0 0 OA 東シナ海陸棚における最終氷期の海水準
- 著者
- 斎藤 文紀
- 出版者
- Japan Association for Quaternary Research
- 雑誌
- 第四紀研究 (ISSN:04182642)
- 巻号頁・発行日
- vol.37, no.3, pp.235-242, 1998-07-31 (Released:2009-08-21)
- 参考文献数
- 55
- 被引用文献数
- 36 50
東シナ海における最終氷期の海水準を明らかにするため,今までに報告されている350を超える放射性炭素年代値と最近の音波探査などの報告を検討した.この結果,50,000~25,000yrs BPについては,黄海や東シナ海において三角州の発達が認められ,当時の海水準は黄海で-80±10m,東シナ海で-90±10mと推定された.また最終氷期最盛期については,海成層と陸成層の分布深度や海底地形などから,最低位海水準は-120±10mと推定された.これらの値は従来報告されている値よりも浅い.
1 0 0 0 シーケンス層序学入門
1 0 0 0 OA 沿岸域の堆積システムと海水準変動
- 著者
- 斎藤 文紀
- 出版者
- 日本第四紀学会
- 雑誌
- 第四紀研究 (ISSN:04182642)
- 巻号頁・発行日
- vol.50, no.2, pp.95-111, 2011-04-01 (Released:2012-04-01)
- 参考文献数
- 59
- 被引用文献数
- 1 5
現在の沿岸域の地形や堆積物,または地層に残された沿岸域の堆積物から海水準変動への応答や古環境変遷を解析するには,これらを堆積システムとして捉えることが重要である.これは堆積相解析やシーケンス層序学的な解析を行う際の基本となる.現在見られる沿岸域の堆積環境や沖積層を堆積システムの視点から解析することは,過去の地層の理解に役立つばかりでなく,将来の環境予測への鍵となる.
1 0 0 0 陸棚堆積物の区分と暴風型陸棚における堆積相
- 著者
- 斎藤 文紀
- 出版者
- Tokyo Geographical Society
- 雑誌
- 地学雑誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.98, no.3, pp.350-365, 1989
- 被引用文献数
- 25 16
The criteria for the classification of present shelf sediments are summarized, and the classification of sedimentary environments and the facies of their sediments in a stormdominated shelf are presented.<BR>The present shelf sediments are classified by the seven criteria as follows.(1) Are the sediments modern or relict? and when were the sediments supplied? (2) Are the sediments palimpsest or not? (3) By which kind of physical processes were they deposited? (e. g. density currents, flood, tidal currents, geostrophic currents, oceanic currents, tsumanis, etc.)(4) What type of sedimentary environment? (e. g. foreshore, shoreface, inner shelf, outershelf, etc.)(5) What is the grain size? (6) What is the natur e of the constituents? (e. g. authigenic, biogenic, volcanic, clastic, etc.)(7) What is the sedimentary structure or bedform of the sediments? These classification criteria of the present shelf sediments are the key to the interpretation of the environment of ancient sedimentary rocks.<BR>The storm-dominated and siliciclastic shelf sediments are divided into nearshor e (foreshore and shoreface), inner shelf and outer shelf facies. Foreshore is the zone of beach and the facies is characterized by well-sorted sand and seaward dipping, low-angle wedge-shaped cross- or parallel-bedding. Upper shoreface is the zone in which longshore bars and troughs are recognized within water depth of less than about 6m, and the facies consists of coarse to pebbly sand with cosets of high -angle tabular or trough cross-bedding of 10 to 100cm thickness. Lower shoreface is the zone which is between 6 to about 20m of water depth, and the facies is comprised of well-sorted fine to very fine sand with amalgamated hummocky cross- or parallel-stratification. Inner shelf is the zone which ranges from 20 to about 70m of water depth, and the facies is made up of interbedded sand and mud. Also, hummocky cross-stratification is recognized in the sand beds deposited in a zone less than about 50m of water depth. Outer shelf is the zone below about 70m of water depth, and the facies is composed of bioturbated mud. The boundary between shoreface and innershelf corresponds to the mean fairweather wave base and the boundary between inner shelf and outer shelf to the mean storm wave base.