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Chronological Significance of the Late Pleistocene Marker Tephra on the Lowest Terminal Moraine in the Yari-Hotaka Range, Nothern Japanese Alps

1989; Association of Japanese Geographers; Volume: 62; Issue: 6 Linguagem: Inglês

10.4157/grj1984a.62.6_438

2185-1735

Mahito Ito, Tomoyuki MASAKI,

Landslides and related hazards

The Yokoo, Ninomata, and Ichinomata moraines, which are located in the Yari-Hotaka Range, Northern Japanese Alps, constitute the lowest moraine systems of the Yokoo glacial age (the Ichinomata stage) which has been considered the greatest glacial advance in the Yari-Hotaka Range (Iozawa, 1962, 1972, 1979; Ito, 1982a, b; Ito and Vorndran, 1983). The recent trenching of the surface deposits of these moraines revealed the occurrence of the marker tephra, the Omachi-E pumice (Tateyama volcano), in the volcanic ash layer directly covering the uppermost till of the Ichinomata moraine. The total thickness of the volcanic ash layer overlying the till is 120cm, and the horizon of the Omachi-E pumice is about 115cm below the ground surface. The marker tephra was identified by the examination of petrographic properties, such as heavy mineral composition and refractive indices of glass, orthopyroxene, and hornblende. According to the inferred age of the Omachi-E pumice (Machida and Arai, 1979; Machida, 1980), the age of the greatest glacial advance in the Yokoo glacial (the Ichinomata stage) is estimated to be a little older than 60, 000 y. B. P.