| Project/Area Number |
60300021
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| Research Category |
Grant-in-Aid for Co-operative Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
広領域
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| Research Institution | University of the Ryukyus |
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Principal Investigator |
UJIIE Hiroshi Dept. of Marine Sciences, Univ. of the Ryukyus; Professor, 理学部, 教授 (60000113)
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| Co-Investigator(Kenkyū-buntansha) |
KOBA Motoharu Faculty of Literature, Kansai Univ.; Associate Professor, 文学部, 助教授 (40141949)
MATSUDA Shinya Faculty of Education, Univ. of the Ryukyus; Assistant Professor, 教育学部, 助手 (30157317)
KAWANA Toshio Faculty of Education, Univ. of the Ryukyus; Associate Professor, 教育学部, 助教授 (60044955)
TOKUYAMA Akira Dept. of Chemistry, Univ. of the Ryukyus; Associate Professor, 理学部, 助教授 (50045001)
YAMAMOTO Satoshi Dept. of Marine Sciences, Univ. of the Ryukyus; Assistant Professor, 理学部, 助手 (50124855)
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| Project Period (FY) |
1985 – 1986
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| Project Status |
Completed (Fiscal Year 1986)
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| Budget Amount *help |
¥7,600,000 (Direct Cost: ¥7,600,000)
Fiscal Year 1986: ¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1985: ¥4,800,000 (Direct Cost: ¥4,800,000)
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| Keywords | Ryukyu Island Arc / Recent coral reef / Sekisei-sho / Sea-water composition / Sediments / Uni-boom survey / Tilting / タービダイト・エプロン |
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| Research Abstract |
"Sekisei-sho" is provided with a large lagoon which is developed over the area of ca.15km (north-southly) by ca. 25km (east-westerly) between Ishigaki-jima and Iriomote-jima of the southern Ryukyu Island Arc. This is a typical Recent coral reef developed at the active ocean margin.
STD survey and chemical analysis of sea water reveal a considerably homogeneity of envrionmental condition within the lagoon and also a distinct but areally restricted influence of fresh water invasion by two rivers. Various analyses of 90 sediment samples indicate that calcareous organic remains (particularly hexacorals) rule over the characters of the lagoon sediments whereas terrigeneous materials affect on those of sediments in the outside of the lagoon.
The uni-boom survey suggests that the base of this Recent reef may be located around 25m in water depth with a trend slightly deepening toward the north. This northward tilting during the Holocene preiod is more clearly shown in the altitudinal deistribution and age-assignment of many emerged notchs and beach rocks in the adjacent islands. According to geological re-examination of a number of air-gun seismic profiles, the late Pleistocene reefal formation (Ryukyu Limestone) also tilts northwards in accompanying with two step faults on the northern side (i. e. Okinawa Trough side) of Sekisei-sho. On the other hand, the southern side shows a steep slope composed essentially of the pre-Pleistocene basements and some turbidite aprons are well developed at the slope base which terminates in the Sakishima Deep-sea Terrace. All of these facts indicate that the tilting movement characterizes the Holocene tectonics of this island arc region as a meaningful aspect of the Okinawa Trough spreading.
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