X-ray stereoradiographical method and phytolith analysis were applied to accumulated tephra and granite profiles in northern Japan, in order to investigate the spread-depth, origin and significance of soil macropores whose form resembles a root system. At the tephra section of Hachinohe Tengudai, soil macropore similar to a root system was extensively found in all stratigraphic units underlying sands which are marine in origin. This type of soil macropore was also predominant, and extended to the deep layers, in tephra sections in the northeastern and southeastern areas of the Iwate Volcano. However, the soil macropore was not present in underlying volcanic debris flow deposits. At the granite profile, the soil macropore was limited to 2m in depth from the top of the granite. In addition, the opal phytolith could be identified in almost all the soil layers where the soil macropore was recognized. The results obtained here supports that the soil pore was derived from subterranean parts of plants, and leads to the inference that volcanic ash soils were formed by successive deposits of airborne volcanic ash and soil formation.

View full abstract

Dinoflagellate cyst analysis has been carried out on boring core materials in order to reconstruct the coastal paleoceanography around the Tsushima Island during the Holocene time. Submarine samples were collected at -8.5m depth at the inner part of Mine Bay in Kami-Tsushima. The sediments consist of dark grey sandy to clayey silt including many shell fragments. Two ¹⁴C ages using these shell fragments are dated; 1, 100±110 yrs BP at -4m horizon and 7, 150±³²⁰₃₀₀yrs BP at -24.5m horizon. Such marine palynomorphs as dinoflagellate cysts, microforaminiferal linings, and acritarchs were found in the sediments. The dinoflagellate cysts consist mainly of Gonyaulacoid group of Spiniferites bulloideus, Spin. cf. bentori, Spin. cf. delicatus, Protoperidinioid group of Brigantedinium spp., Selenopemphix quanta, Votadinium carvum, Vot. spinosum, and Gymnodinioid group of Polykrikos schwartzii. On the basis of the occurrence mode of dinoflagellate cysts and microforaminiferal linings, three assemblages are recognized: A: assemblage from -1m to -4m depth is characterized by a moderate abundance of cysts and high species diversity. B: assemblage recorded from -5m to -1.7m depth features a great abundance of cysts and high species diversity, and C: assemblage obtained from -18m to -25m depth has few cysts and lower species diversity. These assemblages reflect the early transgression, climatic optimum, and late regression oceanographic conditions of the Holocene time in ascending order.
Some archaeological sites of the Early Jomon Period (ca. 6, 000yrs BP) on the northwestern coast of Kami-Tsushima Island are now located at -1m to -2m below the present sea level. Both paleoceanographic and archeological evidence suggests that the sea level at the time of the Holocene climatic optimum was not higher than the present one, and that the western part of this island has been subsiding since the middle Holocene.

View full abstract

The stratigraphy of the Pliocene-Pleistocene Osaka Group in Keihanna Hills is summarized as follows,
1. The Osaka Group in this area, about 300 meters thick, is lithologically subdivided into four formations: the Tomigaoka, Tanabe, Seika and Shoudai Formations in ascending order. More than 14 volcanic ash layers and 5 marine clay beds are intercalated in these strata. Among them, 10 volcanic ash layers and 5 marine clay beds are useful as key beds. They are the Kitadani, Higashibata, Fugenji, Takagi, Susudani I, Susudani II, Pink, Azuki, Hacchoike and Kasuri volcanic ash layers, and the Ma1, Ma2, Ma5, Ma6 and Ma 8 beds, in ascending order.
2. On the basis of lithologic data on the volcanic ash layers and magnetostratigraphic data, the Osaka Group in this area can be correlated with the standard stratigraphy from the lower horizon of Mitsumatsu volcanic ash layer to the upper horizon of the Ma 8 bed.
3. This area is subdivided into three areas: the south area to the Fugenji Flexure (characterized by north-south-trending flexures and faults), the north area to the Katano Fault- Nagao Flexure (northeast-southwest-trending flexures and faults) and the area between the Katano Fault-Nagao Flexure and the Sonenji Flexure (the northern part of the Ikoma Range). These flexure and fault structures in the Osaka Group have resulted from the tilting of the basement blocks by foundation folding in the east-west compressional stress.

View full abstract

[in Japanese]

View full abstract