Glacial and Periglacial Paleoenvironments in the Japanese Islands1)
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第 四 紀 研 究 (The Quaternary Research) 30 (2) p. 203-211 July 1991 Glacial and Periglacial Paleoenvironments in the Japanese Islands1) Yugo ONO2) The paper reviews three main topics of recent studies of Quaternary glacial and periglacial environments in Japan: chronology of glaciations, showline elevation, and permafrost distribution in the Last Glacial age. Two glaciations have been recognized in the Japanese high mountains during the Last Glacial age. The younger one corresponds to the isotope stage 2, and the older one to the stage 4. The alpine glacier attained its maximum extension in stage 4, because of more favorable snowfall conditions in this stage. The oldest glaciations which have been morphologically defined correspond to the isotope stage 5d or 6. The distribution of snowline elevation during stage 4 in eastern Asia shows (1) an abrupt increase of snowline elevation at the eastern margin of Qinghai-Xizang Plateau; (2) no possibility of Quaternary glaciation in the Mt. Lushan area in Southeast China; (3) existence of snowline trough which streches from Formosa towards the mountains of the Japan Sea side of Japan, and (4) the high snowline elevation in Central and Northern Hokkaido, suggesting the winter dryness. The research of present alpine permafrost environment on Mts. Daisetsuzan, central Hokkaido, and the fossil periglacial phenomena in the lowland of Hokkaido have revealed that the island was mostly in the discontinuous permafrost zone in the Last Glacial age. studies. Many authors have attempted year I. Introduction round measurements of the rate of solifluction, Studies of Quaternary glacial and periglacial frost creep and alpine debris flow, together with environments have shown considerable progress air and soil temperatures on the summit areas of during the decade since ONO (1980) reviewed the the Japan Alps and Daisetsuzan Mountains in research before 1980. KOAZE(1984) briefly Hokkaido, as ONO and FUKUDA (1987) and IWATA summarized the history and major results of (1989) have reviewed in detail. studies of Quaternary glaciations in Japan. In The aim of this paper is, therefore, to sum- the explanatory text for the "Quaternary Maps of marize three main topics of recent studies which Japan", IWATA(1987), KOAZE(1987) and KOAZE have not been treated by the review papers and IWATA (1987) synthesized the distribution of mentioned above: chronology of glaciations, glacial landforms and fossil periglacial features, snowline elevation, and permafrost distribution such as ice-wedge casts, cryoturbations and in Last Glacial age. block streams which had been reported before the middle the 1980's. II. Chronology of glaciations Fossil periglacial features were studied mainly Progress in tephrochronology supports in Northern Japan, although some were reported chronological research on glacial deposits in from the southwestern part of the country. Japan. Before the 1980's, only a few moraines Process-oriented research into present were dated by the marker tephra which were periglacial actions in the alpine belt of the occasionally exposed in outcrops of glacial and Japanese high mountains is another important fluvioglacial deposits. During the 1980's, many field closely connected to Quaternary periglacial researchers began to dig trenches into moraine 1) Received 30 April 1991. Accepted 24 May 1991. 2) Graduate School of Environmental Science, Hokkaido University, 060 Sapporo. 204 The Quaternary Research Vol. 30 No. 3 July 1991 at an altitude of about 1,750m, (Fig. 1) represent the Ichinomata stage. ITO and MASAKI (1989) found pumice E from Tateyama Volcano, labeled EPm, in a trench on the lowermost moraine ridges (point J in Figure 1), although they did not find it on other moraine ridges (points A-K in Figure 1). Since EPm directly covers the till of the lowest moraine, they concluded that the outermost ridge of the Ichinomata stage was formed just before the fall of EPm, which was dated about 60ka by MACHIDA and ARAI (1979). This was the first occasion in the Northern Japan Alps, when the age of moraines was determined directly from marker tephra. MACHIDA and ARAI (1979) thought that the till of the Murodo Glacial antedates the fall of DKP in the Mt. Tateyama area. However, as ONO (1980) commented, the stratigraphical relation between DKP and the Murodo Glacial till cannot be determined in the field. The glacial advance corresponding to the Ichinomata stage (named the Yokoo Glacial: IOZAWA, 1962, and including the Babadaira stage) is widely recognized in the Japanese high mountains (Table 1). It is called the Nishimata stage in the Mt. Kashimayari area (ITO and Fig. 1 Trench sites (A-J) on the terminal MASAKI,1987), the Iwatake stage in the Mt. moraines of Ichinomata stage, in Shirouma area (KOAZE et al., 1974), the Murodo Yarisawa and Yokoo Valleys, Mts. Glacial on Mt. Tateyama (FUKAI, 1975; MACHIDA Yari-Hotaka area, Northern Japan and ARAI 1979; ONO, 1980), the Nakagosho Alps stage I and II in the Central Japan Alps (after ITO and MASAKI, 1989). (YANAGIMACHI, 1983) and the Poroshiri Glacial (Stade) in the Hidaka Range in Hokkaido (ONO ridges, even where there are no outcrops. and HIRAKAWA, 1975). The Northern Japan Alps, where Quater- This significant glacial advance represents a nary glaciation was the most extensive in Japan, cold phase of oxygen isotope stage 4. The and where the marker tephra from Daisen, Aso glacier extended much further downstream in and Tateyama Volcanos cover wide areas of the this stage than in a later one, corresponding to glaciated terrain, provide the most favorable isotope stage 2, in the Japanese high mountains. fields for such studies. The reason why the glacier attained its maxi- In the Mts. Yari-Hotaka area, ITO (1982) mum extension in stage 4 in Japan is because of recognized four glacial stages in the Gamata more favorable surface temperature conditions Valley: Takidani, Yaridaira, Hidazawa I and of the Japan Sea for generating snowfall (ONO II, from older to younger, respectively. They and HIRAKAWA, 1975; ONO, 1984b): the warm correspond to the Ichinomata, Babadaira, and Tsushima current still flowed into the Japan Sea Yarisawa I and II stages in the Yarisawa Valley in stage 4, while it did not in stage 2 because of (ITO and VORNDRAN, 1983). the sea level lowering. However, analyses of Well preserved lowest terminal moraine ridges deep sea cores obtained in the southern part of 1991年7月 第 四 紀 研 究 第30巻 第3号 205 Table 1 Tentative chronological table of mountain glaciations in Japan the Japan Sea demonstrate that the warm and SHIMIZU, 1982; ONO, 1984a; YANAGIMACHI, current did not enter the Japan Sea between 1983). about 60 and 8ka (ARAI et al, 1981). The glacial advance corresponding to isotope ONO (1988) suggested that the sea surface stage 2 is called the Karasawa Glacial in the Mts. temperature became cooler in stage 2 than in Yari-Hotaka area (IOZAWA, 1962), the Kitamata stage 4. The decrease in sea surface tem- stage in the Mt. Kashimayari area (ITO and perature diminishes the evaporation from the MASAKI,1987), the Tateyama Glacial in Mt. sea surface, minimizing snowfall from the Tateyama (FUKAI,1975), the Nakagosho III in winter monsoon. There is also a possibility the Central Japan Alps (YANAGIMACHI, 1983) that sea ice covered the surface in the northern and the Tottabetsu Glacial (Stale) in the part of the Japan Sea, according to the indicated Hidaka Range (ONO and HIRAKAWA, 1975). sea surface temperature. In the Mts. Yari-Hotaka area, the Karasawa The beginning date for the stage 4 glacial Glacial is subdivided into two substages called advance is still unknown, but it probably Hida (Hidazawa) I and II. In the Mt. Shiro- postdates 70ka, for ITO and SHIMIZU (1987) did uma area, KOAZEet al. (1974) recognized three not find Aso-4 pumice (from Aso Volcano in substages corresponding to the advance of stage Kyushu; dated by fission track method to 2: Akakurazawa, Kanayamazawa and Shirou- 70ka) on the moraine ridge of the Iwatake stage, mazawa, from older to younger. The till of the while it covers the older moraine of the Akakurazawa substage gave a 14C age of Yoshiwara stage. 25,150±210 years B.P. The end date of the stage 4 glacial advance In the Hidaka Range, pumice A of Eniwa seems to be around 55ka, because pumice IV of Volcano (En-a, dated about 15-18ka) is inter- Ontake Volcano (PmIV), whose fall age is esti- calated in the outwash deposits of the Tottabetsu mated about 55ka, directly covers the Nakagosho Stade (ONO and HIRAKAWA, 1975). As the till of stage moraine in the Central Japan Alps (ONO this stale is covered with pumice D of Tarumae 206 The Quaternary Research Vol. 30 No. 3 July 1991 Fig. 2 Changes of morphogenetic environments in the Japanese high mountains since the middle Pleistocene Uplift rates of mountains: A and B: 2mm/year, C: 1mm/year, D: 0.5mm/year. snowline I: snowline elevation in Pacific side, snowline II: snowline elevation in Japan Sea side, Large figures apply to Japan Alps, Central Honshu, and small ones to Hokkaido. (after KOAZE,1988) Volcano (Ta-d, dated about 9,000 years B.P), is about 100ka (MACHIDA, 1980), the exact age the deglaciation of stage 2 occurred between 15 is still not clear. Table 1 shows, therefore, and 9ka in the Hidaka Range. two possible chronological positions for The existence and extent of older glaciations in the Chogatake Glacial, the Otanihara and the Japanese high mountains are still in debate. Yoshiwara stages. SAKAGUCHI (1988) suggested However, a glacial advance prior to stage 4 is that they correspond to isotope stage 5d. verified in the Northern and Central Japan An older moraine found in the Kurokawa Alps. Valley, Central Japan Alps, is also covered In the Northern Japan Alps, ITO (1983) with a reddish-colored weathered volcanic ash proposed the Chogatake Glacial on the basis of (ONO and SHIMIZU,1982; ONO, 1984a).