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Dendrochronological study of past volcanic activity with fossil petrified wood.

用化石硅化木对过去火山活动进行树木年代学研究。

基本信息

批准号：
04452064
负责人：
YAMAOKA Koshun
金额：
$ 4.16万
依托单位：
Nagoya 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：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04452064/
关键词：
volcano petrified woods Mount Asama the 1783 eruption of Asama dendrochronology 富士山炭化木

项目摘要

Tree rings of petrified woods in volcanic sediments were analyzed to resolve a volcanic activity of 20 Ma ago with a relative accurcy of 1 yr. Field observations indicate that these petrified woods are the fossils of the trees that were carried away from their growth sites with volcanic breccia ejected upon explosive eruption and included in it. Using a dendrochronological procedure we measured the relative years of the last rings of the petrified woods. The relative years of the last rings are concentrated in 17 yrs, where the ring-width patterns show an anomalous behavior similar to one observed in firs growing in the area devastated by Mt.St.Helens. We suggest that the last-formed tree ring of a petrified wood is a record of volcanic eruption and that the activity of volcano continued over a period of 17 yrs, in which eruption occurred at least five times.A fossil wood found in volcanic sediments of the 1783-eruption of Asama volcano is used to test the usefulness of tree-ring records for high resolution dating of an eruption event. The dendrochronological dating is first applied by using the Chamaecyparis master chronology. High correlation is found at the position of 1783 AD as tree death though some other years have also high correlation. In order to overcome the difficulty to give uniqueness of dating the 14C dating was then applied. We extracted 14C age variation within the fossil wood, and then searched the matching position between this 14C age variation and the calibration curve of Stuiver and Becker (1993). Uncertainty of the calendar year of death of the fossil wood was greatly reduced by this procedure compared with the conventional method. In combination of the results of dendrochronological dating and of 14C dating it is suggested that the death of the fossil wood occured in 1783 AD, a date consistent with document records. Our result indicates the usefulness of tree-ring records for high resolution dating of an eruption event.

通过对火山沉积物中石化木的树木年轮分析，确定了20 Ma前的火山活动，相对精度为1a。野外观察表明，这些石化木是由火山爆发时喷出的火山角砾岩从生长地带走并包埋在其中的树木化石，我们用树木年代学方法测定了石化木最后年轮的相对年代。最后一个年轮的相对年份集中在17年内，此时年轮宽度模式显示出异常行为，类似于在圣海伦斯山破坏地区生长的冷杉中观察到的行为。我们认为木化石的最后形成的树轮是火山喷发的记录，火山活动持续了17年，其中至少发生了5次喷发。首次应用Chamaesthenoparis主年表进行树木年代测定。尽管其他一些年份也有高相关性，但在公元1783年树木死亡的位置发现了高相关性。为了克服确定年代唯一性的困难，采用了14 C测年法。我们提取了化石木材中的14 C年龄变化，然后寻找该14 C年龄变化与Stuiver和Becker（1993）的校准曲线之间的匹配位置。与传统方法相比，该方法大大降低了化石木死亡年份的不确定性。结合树木年代学和~（14）C测年的结果，推测化石木的死亡时间为公元1783年，与文献记载一致。我们的研究结果表明，有用的树轮记录的高分辨率测年的喷发事件。