The old burial mound“Komatsu Kofun, ”which has been buried under the River Tone alluvial soil, was discovered at Hanyu City in Saitama Prefecture. The bottom of the chamber is situated 3 meters below the surface. It is considered that the mound was sunk by the Kanto Basin-forming movement, and has been buried by river sediments.
In this study, the location of Kofun ground was defined by pedological analyses of soil just under the chamber. The following conclusions can be drawn by making a comparison between these data and the characteristics of nearby Kanto loam terraces.
1) The basement of the burial mound is Tachikawa loam formation (tephra layer), which was formed in the Late Pleistocene, and Kofun was constructed on Kanto loam terrace. The formation is tephra in situ, not banked.
2) As there is no soil horizon A (Kuroboku soil) at the bottom of the chamber, it is estimated that the chamber was set on Tachikawa loam formation, which acquires bearing capacity by stripping coarse structural Kuroboku soil.
3) Tachikawa loam formation of the Kofun ground is air-borne and air-laid tephra, and non-tephra particles are also included in it. This mixed-particle tephra is not so extensive as to change the pedological characteristics of the Tachikawa loam formation.

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We found that the basal age of Kuroboku Soils is younger than ten thousands years and it varies at each tephra profiles in Yunodai, the area of Holocene Towada Volcanic ashes, according to opal phytolith analysis and humus analysis, utilizing some time marker tephras such as Towada-a Ash (To-a) and Chuseri Pumice (Cu). Moreover, we concluded that vegetation and human activities have strongly effected to form Kuroboku Soils. 1. Three soil units were recognized at Yunodai 1 and 2 sites. Unit III soil as brown weathered volcanic ash (BWT) soil at Yunodai 1 has formed under a vegetation of cool broad leaved forest with Bambusoideae (S as a) in the forest floor. (A) horizon of the BWT soil (III(A)b) shows yellow-brown color, low PQ value with P_<+++> type humic acid. We concluded this soil as a Brown Forest Soil. Unit II soil, named Chuseri (Cu) soil is characterized by type-A humic acid and has black mull A horizon. This II Ab horizon has formed under the grassland vegetation of Bambusoideae-dominant with Panicoideae, which formed high humic black humus. We concluded that the Cu soil as a Kuroboku soil. The Unit I , present soil as the A horizon of To-asoil (I A) has black mull humus and shows B type humic acid which is slightly similar to A type. The vegetation which offered Soil formation is a grassland of Panicoideae-dominant with fern plants. Since these facts we estimate the former humic acid as A type before artificially forested. We also concluded this soil as a Kuroboku Soil. 2. Unit III soil as A horizin (III(A)b) of BWT soil and Unit n soil as A horizon (IIAb) of Cu soil at Yunodai 2 shows dark yellow and dark brown colors, with poor humus and P_<+++> type humic acid. The vegetation type which formed these soils was cool broad leaved forest with Bambusoideae in the forest floor. We concluded it as a Brown Forest Soil. The Unit I , To-a soil has A horizon of black mull humus (I A) which is characterized by A type humic acid. The vegetation which offered soil formation has been a grassland of Panicoideae and fern plants. We concluded this soil as a Kuroboku Soil. As mentioned above, soil formation of each unit is strongly effected by vegetation. It is to say that Brown Forest Soils has formed under the forest and Kuroboku Soils has formed under the grassland. 3. We clarified the basal age and duration of soil formation utilizing time marker tephras. BWT soil of Unit IE had formed since Late Glacial to Middle Holocene (the end of Early Jomon Era), with its duration five thousands years. Cu soil of Unit n had formed between the end of Early Jomon to Heian Era with its duration 4,400 years. To-a soil of Unit I started to form 1, 000 years ago. Both Unit IE and Unit n soils of each sites are covered with Cu and To-a tephras respectively and are interpreted as fossil soils since they have not suffered form any soil formation after buried. 4. The basal age of Kuroboku soil is 5, 400 y.B.P. (Unit II, Cu) at Yunodai 1 whether 1,000 y.B.P. (Unit III To-a) at Yunodai 2. These facts shows that the basal age of Kuroboku Soils is not always the begining of Holocene, moreover it varies at every sites. 5. Vegetation have changed after Cu soil at Yunodai 1 and after To-a at Yunodai 2. Each of them change form forest to grassland of dominant Bambusoideae or Panicoideae. The appearance of grassland are estimated by deforestation by human activities rather than by natural succession. Human activities on forests in Yunodai area started too later than other areas. The reason must be a severe climate which prohibited human actibities in the area. It delayed the change of vegetation which forms the Kuroboku Soils. We gave the same reason why basal age of the Kuroboku Soil in Yunodai 2 is later than Yunodai 1. We clarified that the basal age of Kuroboku Soils in Yunodai area near Towada Volcano is far younger than 10,000 years ago and it varies at each site. We suspect that the

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Using opal phytolith analysis and humus analysis, we have determined the relationship between humus properties and vegetation history on accumulated volcanic ash soils at Tsutanuma, Towadako-cho, in the area of Holocene Towada volcanic ash. These data coupled with time marker tephras allow a discussion of the basal age of the Kuroboku Soils (Andosols) and the human impact on forests. After the Late glacial substage, Brown weathered tephra (B. W. T.), Chuseri pumice (Cu, about 5,400 y. B. P.) and Towada a tephra (To-a, about 1,000 y. B. P.) accumulated at Tsutanuma. Here, the section is divided into three soil stratigraphic units with each of the tephras as the basal horizon. The three soil units are called the Tsutanuma B. W. T. Soil (Unit III), the Tsutanuma Chuseri Soil (Unit II) and the Tsutanuma Towada a Soil (Unit I). Every soil unit did not show Kuroboku Soils characteristics and developed under a broad leaf forest. Therefore, all units are Brown Forest Soils-like volcanic ash soils. This indicates that Brown Forest Soils-like volcanic ash soils formed under broad leaf forest at Tsutanuma during the Holocene. At present, the Tsutanuma area is covered by forest which dose not result in Kuroboku Soils. It seems, therefore, that the formation of Kuroboku soils at Tsutanuma will depend on a change from forest to grassland in the future. The continuation of forest vegetation during the Holocene at Tsutanuma depended on no human impact. As human advancement to the Tsutanuma area was very late (because of an unfavorable environment), the climax of natural vegetation was maintained. Volcanic activity, resulting in accumulation of tephra at a few thousand intervals, only caused transitory damage to forest vegetation and could not be the decisive factor that controlled the change in the vegetation pattern.

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We clarified the relationship among the basal age of Kuroboku Soils, the humus properties of volcanic ash soils and the vegetation environment, according to the opal phytolith analysis and the humus analysis utilizing time marker tephras on the cumulative volcanic ash soils in Akasaka, Sannohe and in Kawamukai, Takko, the area of Towada volcanic ashes. Moreover, we examined the formation process of volcanic ash soils. 1. Kuroboku soils have been formed from Nb (Nanbu pumice) soil of Unit III in Kawamukai and from NA (Ninokura volcanic ash) soil of Unit IV in Akasaka. According to the ages of marker tephras, the basal age of Kuroboku soils is between 8,600 y. B. P. and 5,400 y. B.P. in Kawamukai and between 9,500 y. B. P. and 8,600 y. B. P. in Akasaka. Moreover, these ages corresponded with the time when the vegetation changed from forest to grassland. The basal ages of Kuroboku soils in Kawamukai and Akasaka are older than in Yunodai, Towadako (Hosono et al., 1992), where the relationship between the basal age of Kuroboku Soils and the change of vegetation was recognized also. We estimated that Kuroboku Soils formation following the formation of grassland had relation to human activities on forests and the older basal age of Kuroboku Soils in Kawamukai and Akasaka than in Yunodai accounted for earlier human activities on forests in the former than the latter, according to lower height and genialer climate of Kawamukai and Akasaka. Besides, the difference of the basal age between Kawamukai and Akasaka has relation to other factors, because both climate conditions are almost equal. 2. Both the Nb soil, Unit IK in Kawamukai and the NA soil, Unit TV in Akasaka had the sections of A/BC/C. The BC horizons of both soils were recognized the (A) horizons of Brown Forest Soils, according to vegetational career of broadleaved forest with Bambusoideae (Sasa). Therefore, both of soils cumulated (A) horizons of Brown Forest Soils and A horizons of Kuroboku Soils. We estimated that these cumulus were formed when atmospheric dust composed mainly from volcanic ash had been cumulating slowly under each other vegetation. We propose to call such soils as have cumulated plural soil units while soil forming factor changed on the process of soil formation and slow cumulus of parent material progressing side by side "Accumulatin Polygenic Soil".

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Opal phytolith analysis using A horizons of present and buried soils at Te Ngae Road Tephra Section in Rotorua Basin, New Zealand, was carried out to clarify the relationship between vegetation and volcanic ash soils during the last 20, 000yrs. Silica bodies in some New Zealand native trees were also examined. The results are summarized as follows.
1) For the period between 20, 000 and 11, 250y.B.P. grass was the main source of phytolith. The very low amount of phytolith in soils formed before the deposition of the Rerewhakaaitu Ash (14, 700y.B.P.) indicates that these soils developed under scattered grassland or in forests poor in phytolith-supplying trees. During the formation period of soil in the Waiohau Ash (11, 250-7, 330y.B.P.) the main sources of phytolith were grasses and trees. The clear rise of cauliflower-head-like phytolith originating from trees suggested that the climate was wetter and milder than at an earlier stage. Between 7, 330 and 930y.B.P. tree-origin phytolith was dominant. This indicates that forest vegetation completely covered soils. After the deposition of the Kaharoa Ash (930y.B.P.), grass, trees, and ferns were sources of phytolith. The increase of grasses and ferns was due to Polynesian settlements with a resultant reduction in forest cover and increase in fernland and grassland.
2) Holocene volcanic ash soils buried beneath the Kaharoa Ash contain very low amounts of humus because these soils developed under forest vegetation without grasses and ferns. After the deposition of the Kaharoa Ash, widespread grassland and fernland introduced by Polynesian settlements provided the volcanic ash soils with a black humus horizon.
3) It is said that volcanic ash soils with thick black humus horizons (Koroboku soils) were formed under grass vegetation and slow tephra deposition of slow rate. The fact that few Kuroboku soils are distributed in New Zealand might be explained by the fact that until the deposition of the Kaharoa Ash (930y.B.P.) there was little human activity which destroyed forests and induced grass vegetation.
4) Small cauliflower-head-like phytoliths were found in the leaves of Rewarewa (Knightia excelsa) and the wood of Kohekohe (Dysoxylum spectabile). These trees seemed to be one of the sources of tree-origin phytolith (small grain type) in the soils of New Zealand.

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