The purpose of this paper is to investigate the amount and mode of crustal movement in the Hidaka mountains, Hokkaido Island. It is known that longitudinal proflies of almost all rivers have changed in accordance with periodic changes in climate and sea level during the Quaternary. In the upper reaches, an erosional river bed formed in the Last Interglacial Age correspond to the bottom of the Last Glacial fill terrace deposit, and its longitudinal profile is often parallel to that of the present one. Therefore the author hypothesized that homologic river profiles were formed in two periods with similar climatic conditions and sea level heights, corresponding to the Last Interglacial Age and the Post Glacial Age. Based on this hypothesis, the difference in height between the Last Interglacial buried valley bottom and the present river bed is explained by the amount of uplift during this period. Fluvial and marine terraces are well developed, and their surfaces are covered with a number of marker tephra layers around the Hidaka mountains (Table 2). Figure 9 shows the difference between the height of the Last Interglacial buried valley bottom and that of the present river bed in the study field. The difference in height between the Last Glacial terrace surface and the Penultimate Glacial terrace surface (Fig. 10) is also useful for cross-checking of the data on height differences between interglacial profiles. The characteristics of crustal movement in the study field are summarized as follows. Almost all of the region on the east side of the Umaoi hills has a tendency to uplift. The uplift rate of the mountainous and hilly region on the west side of the Hidaka mountain range is estimated to have been 0.2-0.4mm/yr., and the rate increases toward the western Hidaka coast. This tendency is also supported by evidence that the shoreline heights of the Last Interglacial marine terrace along the Hidaka coast decrease toward the Erimo cape, where the present coast traverses the axis of the Hidaka mountain range. The east side of the Hidaka mountain range and the Tokachi plain have slowly upheaved at the rate of 0.1mm/yr. Short wave deformation of fluvial terrace surfaces accompanied by rapid uplift (more than 0.7mm/yr.) is expected around the Yubari mountains.
Radiocarbon ages have been measured for charred deposits on the surface of large-sized buried pottery jars (35-50cm in height, 30-40cm in diameter), which were collected during the 1986 excavation at the Morinoshita site, one of the archeological sites in Asahi-mura, Ohno-gun, Gifu Prefecture, using a Tandetron accelerator mass spectrometer at the Radioisotope Center, Nagoya University. According to archeological estimates, the buried jars were used in the Jomon period, first as vessels for boiling foods such as gathered nuts and vegetables and hunted animals, and then as containers for burying the bodies of stillborn babies and infants, as well as placentae of newborns, at the entrances of dwellings. The ages measured for the 10-300mg of charred materials, most likely the food residues of ancient people, collected from the surface of each of seven pottery jars ranged from 3, 940 to 4, 450y.B.P. The average of the seven ages was 4, 180±90y.B.P. In addition, wood charcoal collected in an excavation of the residence site at Morinoshita, which had probably been used as part of the wood materials for constructing a house, was dated as 4, 140±140y.B.P. These dates suggest that the pottery jars were used, and the house built, in the late part of the Middle Jomon. This estimation is consistent with the results from typological studies of the jars: some of the jars have been identified as belonging to the Sori-III type (late Middle Jomon). Stable-isotope ratios of carbon (13C/12C) have also been measured for four samples of the carbonaceous residues on the inner surface of the pottery jars to investigate the diet in the Jomon period, yielding δ13CPDB values from -24.0 to -25.6‰. The δ13CPDB values suggest that C3 plants, which use the Calvin-Benson photosynthetic pathway, and animals feeding on C3 plants can be the sources of the carbonaceous residues, but that the contributions to such residues from C4 plants (the Hatch-Slack photosynthetic pathway), animals feeding on C4 plants, and seafood may be negligible.
The Tama River flows from the Kanto Mountains, 1, 000 to 2, 000 meters high, and across the Kanto Plain into Tokyo Bay. Fluvial terraces from the Late Pleistocene are well developed along the river. They are classified into four groups according to the differences in the relative height above the river floor and in the tephra-cover. These are, from older to younger, the Musashino (80ka-60ka), Tachikawa (30ka), Aoyagi-Haijima (20ka-15ka), and Lower terraces (15ka-). Concerning the longitudinal profile of the terraces along the river, the Aoyagi-Haijima terrace, whose profile is steeper than those of the Musashino terrace and the present river-floor, crosses both of them and converges into the Tachikawa terrace in the upstream direction. Moreover, the Aoyagi-Haijima terrace is assigened downstream to the buried valley floor beneath the recent formations in and around Tokyo Bay. Further, in the gorge of the Kanto Mountains in the upper reaches of the river, a prior buried valley bottom is exposed under terrace deposits, which tends to be assigned downstream to the Musashino terrace in the lower reaches of the river. On the basis of the above results, the author interprets fluvial processes and terrace formation along the Tama River. The results are as follows. 1) In the upper reaches of the Tama River, the profiles of the Aoyagi-Haijima terrace diverge from the prior buried valley bottom in the upstream direction. This is attributed to the fact that fill deposits in the prior valley accumulated more thickly in the upper reaches, and that the increase in gradient is larger in the upper reaches. This is because the amounts of debris which were yielded in this drainage area were in excess of stream capacity at that time. This accumulation in the upper reaches took place from 80ka to 50ka. 2) In the upper reaches, the valley remained filled for a lengthy period of time, from 50ka to 20ka in terms of tephrochronology. Meanwhile the valley wall was worked backwards by lateral erosion. Afterwards major terracing by vertical erosion occrred, resulting in an undersupply of debris during Post Glacial time. 3) Although the drainage basin of the Tama River was in a non-periglacial region, fluviatile accumulation took place during the transition from interglacial to glacial because of an increase of sediment yield in the upper reaches. Therefore the terraces are climatic terraces. The phenomena of crossing terraces are related to the difference in terrace type between climatic terraces in the upper reaches and thalassostatic terraces in the lower reaches.