The fossil periglacial phenomena, involution, mass-movement, and gentle slope (cryopediment) formation, are often observed in the upper Kitakami River basin, northeastern Japan. The tephrochronological studies of late Pleistocene periglacial phenomena are carried out and the Quaternary history in this area is also discussed. At the foot of Mt. Iwate (alt. about 200-300m), involution is dominantly observed on FSc, ISc (about 33, 000y.B.P.), WSc-1, WSc-2, S1P, and S2P, which are the marker beds of the Shibutami and Nishine Volcanic Ash formations erupted from the Nishi-Iwate Volcano. KP (about 13, 500-16, 300y.B.P.) erupted from the Akita-Komagatake Volcano is also disturbed on a small scale. However, OD (about 34, 000y.B.P.) and KwP, which are respectively erupted from the Nishi-Iwate and Akita-Yakeyama Volcanoes, are scarcely disturbed. Involution observed in these marker beds is tephrochronologically estimated to have been formed about 16, 300 to 12, 400 years ago for KP, about 34, 000 to 16, 3000 years ago for FSc and ISc, on the first half of the Würm glacial age for WSc, and on the period of cold climate prior to that for S1P and S2P. At the foot of Mt. Himekami (alt. about 400-700m), the solifluction deposits consisting of granodiorite boulder and volcanic ash are put between VP (or FSc) and OD, and are also observed in the layer directly overlain by OD or in the Nishine Volcanic Ash formation. The mass-movement (the Block Stream) at Mt. Himekami probably took place about 34, 000 to 16, 300 years ago and in the first half of the Würm glacial age and/or on the period of cold climate prior to that. The gentle slope developed in the area of the Sotoyama Plateau (alt, about 700-900m) is covered with AK-h, AK-g, and Holocene tephras. Solifluction deposits rich in an angular gravel are extensively observed in the Shibutami Volcanic Ash formation on the Sotoyama and Hayasaka Plateaus, whichis underla in by the red weathering crust. On the basis of the stratigraphical relationships, they are probably formed about 34, 000 to 16, 300 years ago and may be related to the formation of gentle slope developed in the Kitakami Mountains. According to the pollen analysis, it seems to have been cool to cold in Upper Pleistocene. Therefore, the periglacial environment in Upper Pleistocene would have a great influence upon the landform development in this region.
The Pleistocene to Holocene sediments underlying the Osaka Plain consist of unconsolidated gravels, sands, silt and clay beds of limnic, fluvial and marine origin. IKEBE et al. (1970) and FURUTANI (1978) described the subsurface geology of the Osaka Plain is through the investigation of the drilling cores. From these studies the subsurface stratigraphy of the Osaka Plain summarized as the following sequence, the latest Pleistocene to Holocene formation (Nanba Formation), the upper Pleistocene formation (Ma 11 bed, Ma 12 bed and Tenma Formation) and the Osaka Group in descending order (Figs. 1 and 2). The writer investigated the content of glass fragments in these sediments and also studied the features such as shape and refractive index of glass fragments. The results obtained are the following: 1) The content and the features of glass fragments from the Pleistocene to Holocene sediments are shown in Fig. 3, 4, 5, 6, 7, 8, 9, and 10. 2) On the basis of the vertical variation-diagram (Figs. 3…10), volcanic ash- horizons can be found in these sediments, because the vertical variations of content and features of glass fragments are controlled mainly by the fall of volcanic ash. 3) Five volcanic ash-horizons occur in these sediments and are widely traceable. Among these five horizons, three horizons are in the Ma 12 bed, and two horizons are in the Nanba Formation. 4) The lower ash-horizon in the Nanba Formation can be correlated with the ash layer described by MAEDA (1976) in Core Site 2. The upper ash-horizon in the Nanba Formation can be correlated with the ash layer described by ISHIDA et al. (1969) in the Kyoto Basin.
MIYAGI, HIBINO and KAWAMURA (1979) in their paper published in this journal stated that“The pollen occurrence of vegetation which shows the so-called cold period equals the rockfragment-producing period (periglaciation) (TSUKADA, 1967)”, but this is not how I expressed it in my 1967a paper. Neither“pollen occurrence”nor“periglaciation”is a“period.”Occurrence is a phenomenon that happens or takes place, but is not a portion of time determined by some recurring phenomenon. Periglaciation pertains to the action or process at the area marginal to a frozen or ice-covered region, especially with respect to its climate or the influence of its climate upon geological processes. My 1967 discussion was briefly as follows. Since the present subalpine zone was a treeless alpine environment during the late-glacial period, inorganic particles (clay and fine sands) were probably carried by water into the lake basin. Thus, willow and ericaceous pollen and Lycopodium and Selaginella selaginoides spores from the alpine zone were rich in late-glacial inorganic sediments. As tundra vegetation was subsequently reviewed by TSUKADA and NELSON (1976), S. selaginoides is common in the forest tundra today and was abundant in late-glacial sediments in northern Europe, Hokkaido and highlands of central Japan. In the late-glacial sediments of highlands of central Japan, pollen from trees growing at timberline was also abundant. Gyttja was not formed in this alpine environment because autochthonous organic production was low by comparison to the rapid influx of mineral particles.