Re-examination on formation and emergence process of Holocene coral terraces at Kikai Island, Nansei Islands (Ryukyus), southwestern Japan
| Project/Area Number |
08458027
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
自然地理学
|
|---|
| Research Institution | Senshu University |
|---|
Principal Investigator |
OTA Yoko Senshu University, Department of Geography, Professor, 文学部, 教授 (80017714)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
OMURA Akio Kanazawa University, Department of Geosciences, Professor, 理学部, 教授 (70019488)
|
|---|
| Project Period (FY) |
1996 – 1997
|
| Project Status |
Completed (Fiscal Year 1997)
|
| Budget Amount *help |
¥6,200,000 (Direct Cost: ¥6,200,000)
Fiscal Year 1997: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1996: ¥4,900,000 (Direct Cost: ¥4,900,000)
|
|---|
| Keywords | Kikai Island / Holocene coral terrace / drilling / coseismic uplift / U-series date / Postglacial transgression / 完新世 / サンゴ礁段丘 / 海面変化 |
|---|
| Research Abstract |
Kikai Island is located close to the Ryukyu Trench as a convergent plate boundary and has been uplifted with the highest rate in Japan since isotope stage 5e. Hence, it is fringed by Holocene coral terraces. The aim of this study is to re-examine the formation and emergence process of Holocene terraces of this island. Surface observation of Holocene coral terraces and drilling through the reef complex underlain by Holocene terraces were carried out at Shidooke coast on the northeast of the Kikai Island. Main results are summarised as follows : 1) The Holocene terrace is subdivided into four from I to IV in descending order. 2) Terrace I is underlain by beach deposits or detrital limestone, indicating that the formation of coral reefs did not proceed with the Holocene sea level rise. Terrace II was formed as a fringing reef with broad moat and outward crest. Terrace III and IV are narrow wave cut surfaces with some younger coral reefs. 3) The oldest date of Holocene coral is 9.9 ka, which is seen 800 m from the inner margin of the Holocene. Coral was grown upward associated with sea level rise since that time, but not rapid enough to correspond to sea level rise. Since ca 7. ka coral was grown outward. 4) The time of emergence at Shidooke was 5.3 ka for Terrace II,and 2.9 for III,and younger than 2.6 ka for Terrace IV.No age was obtained from Terrace I.Intermittent uplift is probably resulted from repeated coseismic uplift. 5) Isochron of Holocene reefs is drawn to understand coral structurte. The width of each terrace is controlled by coral structure and initial morphology of the reefs, and does not directly reflect the time of sea level stillstand. 6) Holocene coral terraces at Kikai is compared with those at Huon Peninsula, Papua New Guinea, and considerable difference between them and reasons are discussed.
|
Report
(3 results)
Research Products
(4 results)
