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

玻璃状火山灰在中部山区的分布是众所周知的。它们通常是广布的非洲菊。分布在小范围内的浮石组成的冰盖鲜为人知，它们是源于代森火山的男性浮石冰盖。一些短语派生于桑贝火山。这两座火山都位于初国山脉，可以通过检查火山玻璃的折射率和矿物成分来区分这些浮石冰盖。这些折射率的差异很小，因此需要精确的测量。在这项研究中，我为了年代学的目的，对折射率进行了精确的测量。为了本研究的目的，我制作了一个具有温度价值的显微镜工作台，该工作台的温度是用热电偶直接测量的。这种热电偶非常精细，可以在同一显微镜下观察到火山玻璃和热电偶。利用该设备，可以逐粒测量分布在中部山区的火山玻璃的折射率。结果发现，高精度的测量方法对于识别火山灰是非常有用的。利用这种方法，我发现了一些来自戴森的火山灰和另一些来自桑贝火山的火山灰。此外，该地区还发现了一些新发现的时间短语，它们是季末时期的重要时间标志。对这些特弗拉的研究将揭示环境变化的时间。因此，有必要对其进行更大范围的深入研究。

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.