1989 Fiscal Year Final Research Report Summary
Geochronological Study by Use of the Radiochemical Disequilibrium between Nuclides in the Uranium Decay Series
| Project/Area Number |
62470047
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | Kanazawa University |
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Principal Investigator |
OMURA Akio Kanazawa University Associate Professor, 理学部, 助教授 (70019488)
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| Project Period (FY) |
1987 – 1989
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| Keywords | Uranium-Series Method / Kita-Daito Island / Mimami-Daito Island / Yonaguni Island / Riukiu Limestone / Last Interglacial Stage / Tsukui Formation / Rotoehu Ash |
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| Research Abstract |
Results newly obtained during the term of this study are summarized as follows:
(1) A simple and effective technique to separate uranium and thorium isotopes from geologic materials such as silicates and carbonates was developed for the ^<230>Th method of dating.
(2) The distribution of Pleistocene limestone was confirmed at nine locations and the total number of ninety of coral samples were collected for dating by the ^<230>Th/^<234>U method from Kita- and Minami-Daito Islands. As the results of dating, autochthonous limestone bodies on both islands were assigned to the last interglacial. The height of "raised surf bench" relating to the dated limestone was ca. 10 m and 12.2-12.7 m on Kita- and Minami-Daito Islands, respectively. From these facts, both islands are considered to have been uplifted very slowly, at the rate of approximately 0.05 m/ka, since the last interglacial.
(3) The Riukiu Limestone on northwestern part of Yonaguni Island consists of three reef complexes formed during three interglacials, 120-140 ka BP, 200-230 ka BP and ca. 300 ka BP. The height of marine terrace reminds us that this island have been uplifted at the rate of 0.1-0.2 m/ka during the last 130 ka.
(4) Ahermatypic simple corals of six species were collected for age determination from the Tsukui Formation in the southeastern part of Miura Peninsula, Kanagawa Prefecture. ^<230>Th/^<234>U ages of three species are corresponding to the oxygen isotope stage 9.
(5) In order to make sure the eruption age of the Rotoehu Ash, one of wide distributed tephra of New Zealand, ^<230>Th-^<238>U method was applied and obtained the date of 71,000<plus-minus>6,000 years. From this results, marine sediments of Te Papa Terrace in the Bay of Plenty, North Island, is concluded to have been deposited during a global high sea stand at ca. 85 ka.
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