The Murasakino (or Isawa) Terrace developed in the middle Kitakami River basin, northeastern Japan is covered with the Kurosawajiri Volcanic Ash (KVA). Its marker bed, the Murasakino Pumice is divided into two pumice beds different in an eruptive cycle, namely the Kitakami Pumice and the Isawa Pumice. The Isawa Pumice is older than the Kitakami Pumice. The Kitakami Pumice bed is composed of three fall units, MKP-I, II, and III, and the Isawa Pumice bed is composed of four fall units, MIP and three solidified volcanic ash beds (SVA-1, 2, and 3). Among them, MKP-II and MIP are distributed extensively in the northeastern and southeastern directions from the Mt. Yakeishi, respectively. SVA overlain by MIP is distributed in the eastern and southeastern directions from Mt. Yakeishi and the distribution is limited in the narrow area. The bedding plane between the Murasakino Pumice beds (MKP-II, MIP) and volcanic ash layers of the KVA formation is often disturbed irregularly. This disturbance would be attributed to cryoturbation (involution) in the glacial age. Judging from the stratigraphical relationships between the Murasakino Pumice beds and the terrace surfaces, and the red weathering crusts, the fossil periglacial phenomena observed on MKP-II and MIP, and the degree of weathering in ash layers of the KVA formation, the Murasakino Pumice beds would be erupted in the Alt-Würm subglacial age (about 40, 000-70, 000 years ago). The heavy mineral (s.g.>2.90) content is about 50-90% for MKP-I-III, and about 20-60% for MIP and SVA-1-3, respectively. The heavy mineral composition is in the order of magnetite≥hypersthene>augite for MKP-I-III, and hypersthene≥magnetite>augite>hornblende for MIP and SVA-1-3, respectively. MIP and SVA-1-3 contain a comparable amount of quartz, but MKP-II contains it scarcely. Chemical components, Fe, Ti, Mn, V, and Zn, of ferromagnetic minerals purified from tephra deposits were determined. On the basis of the relationships between V-Zn belt and the content of SiO2 of tephra deposits (Shoji et al., 1975), it is estimated that MKP-I-III and SVA-1-3 are andesitic, and MIP is dacitic in rock type. The greater part of tephra deposits composing the KVA formation is erupted from the Yakeishi Volcano, and is andesitic to dacitic in rock type. However, the upper ash layers of the KVA formation may be contaminated with rhyolitic ashes, probably erupted from the Kurikoma Volcano.
Plant opal analysis on the buried soil directly under the Hachinohe pumice bed distributed in the eastern foothill of the Towada Volcano was carried out. The time of the soil formation is about 13, 000 years B.P. (14C date), that is, late Glacial substage. The plant opal assembleages in the soil are characterized by plant opals originated from Gramineae such as the Festucoid, the Point and the Elongate types and those of coniferous trees such as Picea, Abies and Pinus. This means that the Gramineae plant was Poaceae, the dominant grass in the subarctic zone but Miscanthus sinensis (Panicoideae) and Zoysia japonica (Eragrostoideae) are dominant grasses at present in the surveyed area locating under the cool-temperate climate. Therefore, the climate indicated by the plant opal assemblages is considered to have been, cooler than the present one.