The Quaternary Research (Daiyonki-Kenkyu)

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In Echizen province of Fukui Prefecture many manors were distributed from the late Asuka period to the Heian period (ca. seventh to twelfth century). These manors belonged to the Imperial Household and such temples as the Tôdai-ji, Kôfuku-ji and Iwashimizu Temples. The Manor Chimori-no-shô, which belonged to the Tôdai-ji Temple and existed in the Nara period (ca. eighth century), was situated in the vicinity of Mt. Asuwa-yama in the southwestern part of Fukui City. It is estimated on the basis of the ancient rice-field map and the old documents which are deposited in the National Shôsôin Historical Museum in Nara City. This area is the alluvial lowland formed by the Asuwa and Hino Rivers, tributaries of the Kuzuryû River. The ancient rice-field mould, waterways and flumes formed during the Manor Chimori-no-shô age are overlain by the Holocene fluviatile deposits transported by these tributaries. Consequently, although the locality of this manor was well known, the horizon of the ancient rice-field mould and the localities of the ancient waterways and flumes was not clear for long years.
The writer determined the horizon of the ancient rice-field mould and the localities of the ancient waterways and flumes, based on the following methods: (1) palynological investigation, especially of the existence and ratio of Gramineae, (2) degree of survival of plant fragments and carbonaceous materials, (3) degree of survival of siliceous phytogenic particles (plant opal), (4) horizon of cracked soil, (5) soil color, and (6) thickness and horizontal extent of dark bluish gray soil.
The results of the palynological investigation, and the degree of survival of plant fragments, carbonaceous materials and siliceous phytogenic particles are shown in Figures 11, 12, 14, 15, 17, 18, 21, 22, 24 and 26. These figures will be helpful to realize the horizon of the ancient rice-field and the locations of the ancient waterways and flumes in the Manor Chimori-no-shô age.

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A tephra layer that conformably underlies the hitherto defined Shimosueyoshi Loam unit is recognized in the moutainous drainage area along the Sagami River and its adjacent east which occupies the western part of the South Kanto plain in central Japan. The lithology of the upper part of the tephra resembles to that of Shimosueyoshi Loam; accordingly the lower limit of the Shimosueyoshi Loam unit is desirable to place at a lower horizon than has been placed. The lower part of the tephra does not, however, resemble to Shimosueyoshi Loam, and moreover pumice layers within this part cannot be correlated to those within Tama Loam. Accordingly a new name “Suarashi Loam” is proposed for this part of the tephra. The Suarashi Loam unit must be younger than the Tama Loam unit because the tephra in question is stratigraphically continuous with the so-called “Shimosueyoshi Loam” unit.
In the mountainous area along the Sagami River, four fill terraces were formed during the period from the time just before the deposition of Suarashi Loam down to Musashino Loam age. Since the Tachikawa Loam age, down-cutting of the valley has essentially dominated.

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