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

中国山的玻璃状火山灰的分布是众所周知的。它们通常是广泛分布的火山灰。小范围分布的由浮石组成的火山灰鲜为人知，主要是由戴森火山衍生的浮岩火山灰。一些火山岩群是从桑贝火山中衍生出来的。这两座火山都位于中国山脉。通过检查火山玻璃的折射率和矿物成分，可以区分这些浮石火山岩。这些折射率的差异很小，因此需要精确的测量，在本研究中，我对这些折射率进行了精确的测量。为了进行本研究，我制作了一个具有测温功能的显微镜载物台，利用热电偶直接测量载物台的温度。该热电偶非常精细，可以在同一显微镜视野内观察到火山玻璃和热电偶。利用该设备，对分布在中国山脉的火山玻璃进行了逐粒测量。结果发现，高精度的测量是非常有用的火山灰的识别。使用这种方法，我发现，一些火山灰来自戴森和其他来自山边火山，分别。在本区新发现了一些火山岩，这些火山岩是晚第四纪的重要时间标志。对这些火山灰的研究将揭示环境变化的时间。对这些火山灰的进一步研究具有重要意义。

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.