The Chronology and Correlation of the Tephra in the Chugoku Mts. During the Middle and Late Pleisocene

玻璃状火山灰在Chugoku山脉的分布是众所周知的。它们通常分布广泛。由浮石组成的薄壁岩分布面积小，为人所知甚少。它们主要是浮石状火山，起源于大森火山。有些种类的火山产于三别火山。这两座火山都位于Chugoku山脉。通过考察火山玻璃的折射率和矿物组成，可以区分这些浮石状的tephras。这些指标的差异很小，因此需要进行精确的测量。在这项研究中，我对折射率进行了精确的测量，用于色散年代学。为了本研究的目的，我制作了一个有温度值的显微镜舞台，舞台的温度直接通过热电偶测量。热电偶非常精细，在同一显微镜场中可以观察到火山玻璃和热电偶。利用该仪器，对分布在日本中部的火山玻璃进行了逐粒折射率测量。实验结果表明，高精度的测量方法对样品的识别是非常有用的。利用这种方法，我发现了一些来自Daisen火山的tephra和一些来自Sanbe火山的tephra。在这个地区还发现了一些新发现的麻药。这些术语作为季末的时间标记是很重要的。对这些细菌的研究将揭示环境变化的时间。有必要在更大的范围内对这些菌株进行进一步的研究。

The distribution of the glassy volcanic ash in the Chugoku Mountains is well Known. They are usually wide spread tephra. The tephras composed of pumice which are distributed in a small area are little known.They are maninly pumicous tephra and derived form Daisen Volcano. Some group of tephras are derived form Sanbe Volcano. Both of these volcanoes situated in the Chugoku Mountains.These pumicous tephras can be distinguished by examining the refractive indices of volcanic glass and examine the mineral composition. The differences of these indices are very small, so the accurate measurements are needed for this purpose.In this study, I took accurate measurements of the refractive indices for the purpose of tephrochronology. For the purpose of this study, I made a microscope stage which is temperature valuable and the temperature of the stage are measured directly by thermocouple. The thermocouple is so fine that it is observable the volcanic glass and thermocouple in the same microscope field.By this equipment, the refractive index of volcanic glass which are distributed in the Chugoku Mountains are measured grain by grains. As a results, it is found that high accuracy measurement is very useful for discernment of the tephra.Using this method, I revealed that some tephra derived from Daisen and others derived from Sanbe volcano, respectively. And some tephras are newly found in this area.These tephras are important as time markers of late quarterly period. Studies of these tephra will reveal the timing of the environmental change. It is neccessary farther investigations of these tephra in a wide area.