权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

A Study on concordias in the Uranium-Series Method for Dating

铀系测年法中协和的研究

基本信息

批准号：
02640607
负责人：
OMURA Akio
金额：
$ 1.41万
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 (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

Two kinds of concordias, [^<230>Th/^<234>U]-[^<234>Th/^<238>U] and [^<230>Th/^<234>U]-[^<231>Pa/^<235>U] diagrams, in the uranium-series dating, are examined in terms of a criterion to evaluate a ^<230>Th/^<234>U date of fossil coral. Because they are most useful to check if a coral sample has been preserved in appropriate condition for dating.More than 70% isotopic data on corals from the Pleistocene Riukiu Limestone (Hanzawa, 1935), were not consistent with the [^<230>U/^<234>U]-[^<234>U/^<238>U] concordia, but were plotted in the higher ^<234>U/^<238>U range. That is, the initial ^<234>U/^<238>U activity ratio estimated from those corals, is not necessarily agreeable with 1.144<plus-minus>0.002 as the value of the present-day sea water, reported by Chen et al. (1986). These facts imply that ^<234>U/^<238>U activity ratio of sea water at the time when fossils grew was somewhat (1 to 2%) higher than the value of Chen et al., or that the uranium isotopes were redistributed in those sam … More ples during their diagenetic alteration, as pointed out by Ku et al. (1990).The reliability of some ^<230>Th/^<234>U dates were critically evaluated by using the [^<230>Th/^<234>U]-[^<231>Pa/^<235>U] concordia. All results on isotopic analyses were plotted on the concordia for wellpreserved corals (of 100 to 95% aragonite) from Kikai Island, whereas those for partly recrystallized or calcite-cemented samples were not on it. Data points from a group of fossil corals seemed, however, to give significantly a straight line. In the case that such line was regarded as a discordia, two ages, namely ages of death and alteration of those samples, can be estimated to 230+50-30 ka and 4<plus-minus>4 ka, respectively. Therefore, the[^<230>Th/^<234>U]-[^<231>Pa/^<235>U] concordia has a possibility to give a reliable uranium-series date for other carbonate-secreting organisms like echinoderms and molluscs, which have been considered not to be appropriate materials for uranium-series dating, due to the open system for uranium isotopes after death of organisms. Less

本文对铀系定年中的两种协心图[^<230>Th/^<234>U]-[^<234>Th/^<238>U]和[^<230>Th/^<234>U]-[^<231>Pa/^<235>U]进行了研究，并以此作为评价珊瑚化石的^<230>Th/^<234>U定年标准。因为它们对于检查珊瑚样品是否保存在适当的条件下以进行测年是最有用的。来自更新世留丘石灰岩（半泽，1935）的珊瑚的70%以上的同位素数据与[^<230>U/^<234>U]-[^<234>U/^<238>U]一致性不一致，但绘制在较高的^<234>U/^<238>U范围内。也就是说，根据这些珊瑚估算出的初始^<234>U/^<238>U放射性比值与<plus-minus>Chen等人（1986年）报告的1.144 0.002的现代海水值并不一定一致。这些事实意味着<234><238>化石生长时海水的^ U/^ U活度比比比比Chen等人的值略高（1 ~ 2%），或者说铀同位素在这些 ...更多信息利用<230>[^ Th/^ U]-[^ Pa/^ U]一致性，对某些~（18）Th/<234>~（18）U年龄的可靠性进行了严格的评价<230><234><231><235>。对于保存完好的纪海岛珊瑚（100 - 95%的文石），同位素分析的所有结果都被标绘在Concordia上，而部分重结晶或方解石胶结样品的同位素分析结果则没有标绘在Concordia上。然而，来自一组珊瑚化石的数据点似乎明显地给出了一条直线。在将该品系视为不一致线的情况下，可将其死亡年龄和变异年龄分别估算为230 ± 50-30 ka和<plus-minus>4.4ka。因此，[^<230>Th/^<234>U]-[^<231>Pa/^<235>U] concordia有可能为其他分泌碳酸盐的生物（如棘皮动物和软体动物）提供可靠的铀系定年，这些生物由于生物死亡后铀同位素的开放系统而被认为是不适合铀系定年的材料。少

项目成果

期刊论文数量（13）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

河名俊男・平良初男・棚原朗・青木大茂・大田陽子・大村明雄・木庭元晴: "南・北大東島の後期更新世サンゴ化石の非破壊ガンマ線測定による ^<226>Ra/ ^<238>U年代" 地学雑誌.

Toshio Kawana、Hatsuo Taira、Akira Tanahara、Daishige Aoki、Yoko Ota、Akio Omura、Motoharu Kinaba：“南大东岛和北大东群岛更新世晚期珊瑚化石的非破坏性伽马射线测量 ^<226>Ra/ ^<238> U的地球科学杂志。