Abstract
We carried out high-resolution phytolith analysis on the Tachikawa and Musashino Loam formations (Late Pleistocene air-laid tephric soils) in the areas close to Mount Fuji volcano : Sagamino Upland, Ooiso Hill, and the eastern foot of Mt. Fuji, Central Japan.
Fluctuations of bambusoid phytolith assemblage were very likely to synchronize with global climate changes since the marine isotope stage (MIS) 5.1 (5a). The phytolith of Pleiobrastus, a warm temperature dwarf bamboo, dominated in the two layers : 1) the boundary layer between the Shimosueyoshi Loam formation (SL) and the Musashino Loam formation (ML) below Hakone-Anjin tephra (Hk-AP) and 2) upper part of the ML above Hakone-Sanshokuki (Hk-SP). The first warm phase corresponded to the formation of Misaki marine terrace, which correlated with the MIS5.1, and the second corresponded to the Nakatsuhara (Tachikawa-1) fluvial terrace, which correlated with the MIS3.3. On the other hand, the phytolith of Sasa, a cool temperature dwarf bamboo, dominated in the lower part of the ML between Hk-AP and Hk-SP, and in the upper part of the Tachikawa Loam formation (TcL), which starts from Aira-Tn tephra (AT). These two significant cool phases were equivalent to the MISs 4 and 2, stadials in the Last Glacial, respectively. In addition some short warming and cooling phases were recognized in the lower part of the TcL, suggesting fluctuations of climate in the younger period of MIS 3.
Non-bambusoid grass phytolith significantly increased in humic soil layers called black bands in the TcL. This might suggest expansion of grassland vegetation possibly caused by human activity in the Paleolithic era. On the other hand, the phytolith of deciduous broadleaved trees continuously appeared in brown soil layers, which intercepted the formation of humic soil layers.
