| Project/Area Number |
12440139
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geology
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| Research Institution | Nagasaki University |
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Principal Investigator |
MURO Tetsuji Nagasaki University, Faculty of Environmental Studies, Associate professor, 環境科学部, 助教授 (70212248)
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| Project Period (FY) |
2000 – 2002
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| Project Status |
Completed (Fiscal Year 2002)
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| Budget Amount *help |
¥8,400,000 (Direct Cost: ¥8,400,000)
Fiscal Year 2002: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2001: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2000: ¥5,700,000 (Direct Cost: ¥5,700,000)
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| Keywords | sequence / shoreline autoretreat / delta / flume experiment / sea-level changes / sediment supply / slope break / subaqueous terraces / 段丘 / 海岸線自動後退理論 / 水槽実験 / 陸棚 / 深海堆積系 / 陸棚デルタ |
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| Research Abstract |
The present research was to investigate how the development of deep-water, coarse-grained clastic environments is related to shoreline autoretreat. This problem has been solved by means of flume experiments and theoretical examinations, summarized as below.
Deepwater clastic depositional systems can respond sensitively with shoreline autoretreat River deltas cannot prograde over hundreds of kilometers across their shelves during the interval of highstand systems tract development. Even if unlimited time is available to delta growth, there is a clear limit in delta progradation owing to a mechanism ('autobreak') inbuilt in a delta evolving during relative sea-level rise. The termination of the progradation may be far landward of shelf edge. The main factors controlling the limit of delta progradation and the occurrence time of the autobreak event include shelf width, rate of sediment supply, rate of relative-sea level rise, and geometrical parameters of the delta and shelf. It is not abs
… More
olutely impossible for shelf-edge deltas to be built during slightly rising relative sea level. However, stillstand and falling relative sea level much favor the development of shelf-edge deltas and of sand supply to deep-marine areas, in terms of the delta's travel time to shelf edge. The present study therefore supports the maintenance of the conventional sequence stratigraphic interpretation that sand-rich deep-marine systems are most easily developed during falling and lowstand of relative sea level.
A comprehensive understanding of the autogenic response of fluvial deltas to the steady forcing is provided from the theory of shoreline autoretreat. Besides, both autoincision and autobreak represent the moment at which the delta has to lose its original geometry. Any of autostepping and autogenic terrace formation comes out from the effect of the principle of shoreline autoretreat combined with its autocyclic behavior. Allocyclic changes of dynamic conditions only enhance or reduce the inbuilt process of delta systems. Less
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