1992 Fiscal Year Final Research Report Summary
Facies analysis of the Upper Cenozoic, western Japan
| Project/Area Number |
02640601
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
地質学一般
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| Research Institution | Ehime University |
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Principal Investigator |
MIZUNO Atsuyuki Ehime Univ Fac of Sci Prof., 理学部, 教授 (60181898)
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| Project Period (FY) |
1990 – 1992
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| Keywords | Western Inner Zone / Upper Cenozoic / Continental fluvial facies / of Southwestern Japan 1-Ma unconformity / 1-Ma tectonic movement / Braid-river facies / alluvial fan facies / Meandering river facies |
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| Research Abstract |
The Upper Cenozoic sediments in the western Inner Zone of South-west Japan, mostly consisting of continental fluvial depositional facies are stratigraphically classified into two horizons, the Pliocene to Lower Pleistocene (PLP) and the Middle Pleistocene (MP). The Tsunozu Group of PLP represented by alternating lagoonal and fluvial facies formed possibly under the control of sea-level change caused by glacial eustacy, as suggested by palyno-floral changes, which provides a significant basis of better understanding of the sea-level changes in Japan during 4-1 Ma.Fluvial depositional facies of PLP sediments in the other areas mostly comprises braided-river facies and additionally alluvial fan- and meandering river facies, excluding their top part which exclusively consits of proximal alluvial facies generally, suggesting marked upheaval of hinterland in its depositional time after regional unconformity called the "1-Ma unconformity" developed in wide areas of the western Inner Zone. The unconformity represents the "1-Ma tectonic movement" in the areas, possibly related to some phase of northwestward movement of the philippine Sea plate. Fluvial depositional facies of the MP sediments was formed mostly under a tectonic control of activity of NE-SW faults prevailing in western Chugoku region, as represented by the Saijo Formation. Thus, the depositional facies of the Upper Cenozoic in the western Inner Zone was formed, influenced partly by sea-level changes by glacial eustacy and mostly by tectonic movement.
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