The upper Permian Takatsuki Formation in the Ultra-Tamba Zone, presumed to be forearc basin sediments. The mode of occurrence and geochemistry of greenstones from the base part of the Takatsuki Formation were studied. These greenstones are composed of pillow basalt, pillow breccia and hyaloclastite. The mode of occurrence of greenstones which adhere to sandstone of the Takatsuki Formation in Kawakubo area surely indicates in-situ greenstones, as the "basaltic dike" intruded into the boundary between the greenstones and the unconsolidated terrigenous clastic sediments and in which hyaloclastite is intercalated with black shale. Geochemical features suggest that the greenstones are similar to mafic lava at a volcanic arc. We infer that the eruption of the greenstones resulted from igneous activity in the island-arc (volcanicarc) area.

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Aso Caldera in Central Kyushu is a large depression formed after the huge pyroclastic eruption of Aso Volcano. In the northern half of the depression called Asodani (Aso valley), sediments have been deposited in lake, river, swamp and fan conditions. We analyzed the fossil diatom of samples taken from cores and an outcrop of nine sites in the northern Aso Caldera area in order to reconstruct the aquatic environments since the Last Glacial. A fluvial condition assumed to be coarse sand and gravel in the western area of Asodani, was deposited in the latter part of the Last Glacial. Above it, the diatom assemblages become dominated by planktonic genera such as Auracoseira, Cyclotella and Stephanodiscus, showing that a lake condition started around 21,000yBP and lasted to 8,800yBP at the Hosenbashi site, 8,200yBP at the Kario site and about 7,900yBP at the Senchomuta site. Then, the gradual shift in the diatom assemblage in the overlying horizons indicates that the lake condition changed to the present-day condition. After a period of ongoing decrease in depth, the lake disappeared. The diatom assemblages of such sediments are composed of epithyte genera, such as Fragilaria, Synedra and Cocconeis, and benthic genera such as Navicula, Gomphonema, Nitzchia and Neidium. Whereas in eastern Asodani, a fan condition has continued since the Last Glacial, as indicated by dominance of the epiphyte and benthic diatom genera. On the rim plain, environmental conditions were mainly eolian, but sediments from the Sanno site, contain the diatom assemblages of some epiphyte and benthic genera showing river and/or swamp conditions. At the Zogahana site, swamp conditions have existed since 1,000years ago.

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Fission track (FT) dating was carried out on samples collected from the lower part of a Miocene sequence in the northern part of the Chichibu sedimentary basin, northern Kanto Mountains. In order to eliminate the effect of detrital zircons, ages were determined by deleting older single-grain ages one by one until P(χ2) exceeded 5%. Two taffaceous samples from the Shirasu Sandstone Member of the Ushikubi Formation yielded ages of 16.7±0.6Ma (051103-1) and 18.2±0.6Ma (051103-3), respectively. The ages obtained range from late Early Miocene to the Early/Middle Miocene boundary. In addition, a zircon FT age of 63.2±2.2Ma was determined for rounded rhyolitic conglomerate clast (051103-2) embedded within the Shirasu sandstone. This result and the petrographical characteristics of the clast suggest it was derived from the Yorii Acidic Rocks. Detrital zircon grains showing a mode of 50-60Ma in probability distribution histograms are common in most samples in the lower Chichibu sedimentary Basin. The older component suggests that the detrital zircons were probably derived from surrounding Paleogene igneous basement.

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