The Wisdom of Ancient People

  • Bulletin of Gunma Archaelogical Research Foundation
  • Glossary
  • English Summaries from the Bulletin of Gunma Arcaherological Research Foundation
  • Guide to events

English SummariesBulletin of Gunma

Tephra Stratigraphy of the Middle-Late Pleistocene loess deposits
-In the North-western part of Gunma Prefecture-
YAGUCHI Hiroyuki

The Middle-Late Pleistocene tephras distributed round Nakanojo basin are composed of the pyroclastics from the volcanic atmosphere of Mt. Haruna and of many other volcanoes round the border of Gunma and Nagano Prefecture.
In this analysis of the characteristics and the identification of the old soils, the tephras and the tephra loess deposits are divided into eight types as follows; 1. Nakanojo Loam, 2. Lower Agatsuma Loam, 3. Middle 4. Agatsuma Loam, 5. Upper Agatsuma Loam, 6. Numata Loam, 7. Middle Loam and 8. Upper Loam from below.
The broad range of tephras such as vitric volcanic ashes from Kyusyu and the Crystal Ash of central Japan are found in the tephra loess deposits and in the lake deposits in the research area.
The geological age of the tephras corresponds proportionately to the thickness of tephra loess deposit.
Hence, the correlation between these can be regarded as the key factor for estimating the geological age of the tephra loess deposits.
The tephras found in this survey are made up of C P, Kb-Ks, ODA, A1-6 P-UPm, Kkt and Ata-Th.
The thickness of the tephra loess deposit is estimated to be 42 mm per 1000 year in accordance with the tephra geological age.
A trial for the comparison was made between the tephra loess deposits and the lake deposits round Nakanojo basin based on the tephra characteristics by which the geological period for the accumulation was counted.
The lake deposits in the Nakanojo basin were directly affected by the volcanic activities and they conform simultaneously to the climatic curved line of changes while they were forming.
The strati graphical boundaries of the tephric loess deposits were associated with the formation in the periods of the volcanic activities and the geographical deformation in the surrounding areas.
The sectional cycle is apparently similar to the curved line of the climatic changes.

Key words: Nakanojo Loam; Agatsuma Loam; Numata Loam; Tephric loess deposit; Crystal Ash; Middle Pleistocene; Haruna Volcano

BackPage Top