1997 Fiscal Year Final Research Report Summary
Eustatic, sedimentary supply, tectonic controls on sequence stratigraphy of Paleo-Tokyo Bay
| Project/Area Number |
07640613
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | Natural History Museum and Institute, CHIBA |
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Principal Investigator |
KUMASHIRO Hiroko (岡崎 浩子) Nat.Hist.Mus.& Inst.Chiba, Dept.Earth Sci., Resercher, 地学研究科, 学芸研究員 (10250135)
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| Project Period (FY) |
1995 – 1997
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| Keywords | Pleistocene / Paleo-Tokyo Bay / depositional sequences / glacio-eustatic sea-level change / sediment supply / tectonic movement |
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| Research Abstract |
The Kamiizumi, Kiyokawa and Yokota Formations, Shimosa Group, which crop in the Shimosa Upland, were deposited in the middle Pleistocene Paleo-Tokyo Bay (c.250 - 150 KaBP). Paralic and shallow marine depositional systems (fluvial, estuarine, delta, tidal sand bars, shoreface-beach, tidal inlet and lagoon-bay) are recognezed in the formations and constitute two depositional sequences. These sequences are interpreted to have developed during the stage 8 - 6 of the oxygenisotope curve and been primarily controlled by glacio-eustatic sea level changes. Spatial variation in depositional systems, inferred from the mapping of a chronostratigraphical surface marked by some volcanic ash layrs, are recognizable in the depositional sequences of the formations. In Paleo-Tokyo Bay, valleys were incised by rivers during the low sea-level stage in the glacial period. The subaerial unconformity shows a sequence boundary. Two different types of depositional systems were formed during early transgressive through highstand stages of the relative sea level in the interglacial period : estuarine-delta and tidal sand bars systems, and estuarine - barrier island systems. The spatial variation is interpreted in terms of differences in sedimentation supply and tectonic movement in Paleo-Tokyo Bay area. Consequently, two types of depositional sequence developed in the Kamiizumi, Kiyokawa and Yokota Formations : a high subsidence-high sediment flux type of sequence and a low subsidence-low sediment flux type of sequence.
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