Ng-1 (0.30Ma) is a widespread tephra covering the Tokai, Kinki, and Shikoku areas, and the location of its source vent is assumed to be in the Hida Mountains. However, the existence of proximal deposits of this tephra has not been confirmed around the vent. At the same time, a pumice fall deposit named the Takayama Pumice Layer (Tky) has been distributed in and around the Takayama Basin, west of the Hida Mountains. Some previous studies identified Tky as one of the Omachi A Tephra Layers (APms: 0.33-0.40Ma) derived from a volcano in the Hida Mountains. However, other studies concluded that Tky was derived from the Hakusan Volcano, about 45km west of the Takayama Basin.
This study clarifies that Ng-1 is correlated to Tky, not to APms, and assumes that the source is most likely to be in the Hida Mountains. The following similarities confirm the correlation between Ng-1 and Tky: mineral assemblage, refractive indices of the volcanic glass, hornblende and orthopyroxene, and the chemical composition of titanomagnetite. Moreover, the distributions of Ng-1 and Tky are limited in the southwest area of the Hida Mountains.
The age of Ng-1 is estimated by previous works to be 0.30Ma, which means that Tky provides a significant datum plane of 0.30Ma around the Takayama Basin.

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The stable carbon and nitrogen isotopes were investigated in successive samples of a cumulative Andisol in Miyakonojo basin. The biggest difference of δ¹³C values among the group of horizons was 2.6‰ in the Mi-ike tephra (horizon 3C; Sample No. 26-24), followed by 1.6‰ in Kuroniga (buried humic horizon 2A; No. 16-10) above the Mi-ike tephra and 1.6‰ in horizon 8B2 (No. 64-59) of the lower part of the brown loam layer. The δ¹³C values showed a tendency to become lower in horizons with high organic carbon content, from humic horizon 8A1 existing with the Satsuma tephra up to the surface horizon (1Ap).
The percentages of C₃ and C₄ plant-derived carbon in soil organic matter estimated from δ¹³C values had a relation with those estimated from phytoliths of gramineous plants, although differences in the percentages were observed. Highly positive correlations were observed between the content of C₃ plant-derived carbon and the yield of C₃ plant (Pleioblastus sect.) estimated from phytolith analysis in horizon 5-4 (R²=0.917) above the Akahoya tephra (ca. 6.5ka) and in horizon 3-2, Kuroniga 4A and 2A (R²=0.806) above the Mi-ike tephra layer (ca. 4.2ka). Consequently, it was inferred that soil organic matter in Kuroniga (4A and 2A) was mainly composed of Pleioblastus sect. (Medake and Nezasa), C₃ plants. As higher percentages of C₄ plant carbon were recognized in the horizons above the thickly deposited Mi-ike and Akahoya tephra layers, it was inferred that Miscanthus, a pioneer C₄ plant, first invaded under conditions of devastation of vegetation. It was also suggested that C₄ vegetation, mainly composed of Miscanthus, had been gradually replaced by C₃ vegetation mainly composed of Pleioblastus sect. (Medake and Nezasa).
Since the δ¹⁵N values in the cumulative Andisol, except for some horizons, tend to become high in dry periods and low in wet periods with reference to other proxies, it may be concluded that the δ¹⁵N values partly respond to the soil moisture condition due to climatic change. The low δ¹⁵N value (minimum; 2.9‰) of sample No. 41, humus horizon 7A/C1 including pumice of the Sueyoshi tephra, suggested the possibility that the accumulation of nitrogen was caused by atmospheric nitrogen fixation.

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The purpose of this study is to modify the decomposition coefficient (r) of the reversing Jenkinson's model: Cmax=C/exp-0.000125t applied to humus accumulation in tephra-soil sequence. The decomposing coefficient (r) was optimized by the following procedure. 1) Examine the inorganic colloid components conducted by selective dissolution analysis to understand the state of humus bonding with aluminum that was considered to assign the age limitation for applying the model. 2) Examine the relationship between present climatic condition represented as Humidity index (K, mm/°C) and carbon content of topsoil of Holocene tephra-soil to determine the direction of modifying the decomposing coefficient (r). 3) Determine the decomposing coefficient (r) by applying the enlarged or reduced coefficient (r) to the reversing Jenkinson's model on the assumption that equilibrium carbon content (Cmax) should not exceed 250g·kg^-1. The modified coefficient (r) was obtained for three representative tephra-soil sequences, Aso, Ashitaka and Towada in Japan. Since chronological sequence of Cmax, the equilibrium carbon content, in the Holocene soils resembled to the other proxy data of past environmental change, it may be considered that the equilibrium value of humus accumulation in the buried soils of tephra-soil sequence reflect the strength of the past solar radiation as the background condition of the yield of plants.

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We discovered a tephra in the terrace deposits at the southern foot of Asan Range in Tokushima Prefecture, southwestern Japan, and named it the Nagate tephra. The Nagate tephra is brown to gray-white in color and is composed of sand-and silt-sized grains that include many phenocrysts. The Nagate tephra is compared with Aso-4 tephra in terms of petrography, refractive index of volcanic glass, and chemical composition of pyroxene.
Aso-4 tephra erupted 70 to 90ka BP. The terrace which contains Nagate tephra was completed at the end of the last interglacial stage. The Nagate tephra is important in clarifying the active time of the Median Tectonic Line in the late Pleistocene.

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The present methods of opal phytolith analysis still limits an accurate reconstruction of past environment. In this paper opal phytolith assemblage and its relation with plant biomass was studied. Opal phytolith production of some common grass and tree species was determined mixing leaf blades at different ratios. All plants showed some variability in the production of opal phytoliths, especially for those from Bulliform cells (Fan shape). The results showed that leaf blades of Sasa kurilensis produce about 23 times more Fan shape phytoliths and 27 times more Bambusoid phytoliths than the quantity of Jigsaw-puzzle opal phytoliths produced by Fagus crenata leaves. Generally, to have similar amounts of tree and grass origin opal phytoliths in soils, the quantity of tree leaves should be more than 10 times of that of the grasses. The clear results obtained for the plant species studied show that the determination of opal phytolith ratios between species is a good tool to estimate plant biomass and consequently to achieve a more precise reconstruction of past vegetation.

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The authors clarified the evolution of shallow buried valleys in the Nobi plain, especially in the archaeological sites of Kadomanuma and Mabikiyokote where these valleys typically develop.
The sites are located in the central Nobi plain near the boundary of the alluvial fan and the floodplain area; the buried shallow valleys dissect and develop on the well-developed sand layer which is related to the “upper sand layer” in the coastal region.
Based on close observation and the radiocarbon ages of sediments, the following results are clarified: The sand layer was dissected at ca. 3, 000-2, 400yrs BP, and shallow valleys were formed. These valleys were buried by ca. 2, 400-2, 200yrs BP.
In addition to these results, the authors clarified the geoenvironmental change in the region based on the geomorphic and geologic information from the surrounding areas. The geoenvironmental change in the region surrounding the Kadomanuma and Mabikiyokote sites is divided into the following four stages:
Stage I (3, 300-3, 000yrs BP): End of the deposition of the sand layer which is related to the “upper sand layer” in the coastal region.
Stage II (3, 000-2, 400yrs BP): Formation of shallow valleys on the sand layer. Flood sediments can be seen in the valleys, but the surrounding areas are in a stable condition that is characterized by humic or peaty sediments.
Stage III (2, 400-2, 200yrs BP): Deposition of sediments in the shallow valleys ceases at the end of this period. Environment of the surrounding area is relatively stable and there is less flooding.
Stage IV (2, 200yrs BP-): Active flooding occurs in the region, and the shallow valleys are buried completely.

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