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Geochronological Study by Use of the Radiochemical Disequilibrium between Nuclides in the Uranium Decay Series

利用铀衰变系列中核素之间的放射化学不平衡进行年代学研究

基本信息

批准号：
62470047
负责人：
OMURA Akio
金额：
$ 4.48万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

项目摘要

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.

（1）建立了从硅酸盐、碳酸盐等地质材料中分离铀、钍同位素的简便有效的方法，用于~（13）<230>Th定年。(2)更新世石灰岩的分布在9个地点得到确认，从北大岛和南大东岛收集了90个珊瑚样品，用^<230>Th/^<234>U法测定了年龄。作为定年的结果，两个岛屿上的原地石灰岩体被分配到末次间冰期。与测年灰岩有关的“凸起冲浪台”高度约为1000米。北大岛和南大东岛分别为10米和12.2-12.7米。根据这些事实，这两个岛屿被认为是非常缓慢的上升，在约0.05米/ka的速度，因为最后一次间冰期。(3)与那国岛西北部的柳丘灰岩由三个礁复合体组成，它们分别形成于120-140 ka BP、200-230 ka BP和约200 - 300 ka BP的三个间冰期。距今30万年。海阶地的高度表明，在过去的130 ka中，该岛屿以0.1- 0.2m/ka的速率隆升。(4)在神奈川县三浦半岛东南部的津井组中采集了6种无造礁型单珊瑚。三<230><234>个物种的~（13）Th/~（13）U年龄均对应于氧同位素第9阶段。(5)为了确定新西兰分布较广的火山灰之一-罗托胡火山灰的喷发年龄，采用~（13）<230>Th-~（14）<238>U法测定了其喷发年龄，得到的年龄为71000 ~ <plus-minus>6000年。从这一结果，海洋沉积物的Te Papa梯田在丰盛湾，北岛，得出的结论是已经沉积在全球公海站在约。85 ka.