In this paper, the results of a detailed stratigraphical study on air-fall pyroclastics (the Osakada Loam Formation, the Hata Loam Formation and the Omachi Loam Formation) are outlined. Especially valuable as marker beds are nine Ontake volcano pumice falls in the Osakada Loam Formation, six Ontake scoria falls in the Hata Loam Formation and two pumice falls that are inferred to originate from the Tateyama volcano which is intercalated in the Omachi Loam Formation. The Ontake Pm-1', Pm-1A, Pm-2A, Pm-2B and Pm-3D beds and the Tateyama Dpm and Epm beds are each subdivided into several sedimentary units which are widely recognized by their grading structure or lithofacies. The stratigraphic positions of fine-grained ash beds are determined by stratigraphical survey of subaquatic sediments that intercalate the upper Pleistocene air-fall pyroclastics. KIGOMA ash and vitric N-Tf, K-Tf, O-Tf, and T-Tf ashes are well sorted, and the thickness of these beds are constant. It is assumed that these ashes were supplied by anomalous volcanoes. Tracing these wide-spreading pumice or scoria beds together with the ashes as sets of marker beds made it possible to correlate stratigraphic successions of separated areas. It appears that the Osakada Loam Formation, the Upper Omachi Loam Formation II, the Middle and Upper Saku Loam Formation (originating from the Yatsugatake volcano) and the Nojiri and Kaisaka Loam Formations (originating from the Kurohime and Myoko volcanoes) have accumulated during the 50, 000-10, 000 years before the present.
The climatic change during the Late Pleistocene in Central Japan is characterized as follows. (1) Palaeoclimate during the Last Interglacial Epoch is supported as warm and moist, because of that the Fagus pollen content is high rate in sediment. (2) At the early stage of the Last Glacial Epoch, coniferous forest of the subarctic zone had been extended. So that climate during the Last Glacial Epoch is estimated as considerable cold. And it is large possibility that the Japanese Island had been connected to the continent by land-bridge. (3) During the middle stage of the Last Glacial Epoch, it is a transgression stage (=warm period) forming of Atsuta Tarrace in Nobi Plain. Fagus had been increased even in inland basin. (4) During the next cold stage, it is large possibility that the first glacier had been formed on the Central Alps (Kiso Range). (5) During the cold climatic stage of the end of Last Glacial Epoch, the coniferous forest of the sudarctic zone had been extented widely.
The following chronostratigraphic pollen zones and climatic changes are established based on published papers of pollen analyses covering the period since the last glacial age in Japan. WE (Würm Earlyglacial) zone (ca. 120, 000-70, 000 years B.P.). This zone corresponds to Earlyglacial. High values of Cryptomeria constitute a characteristic feature of this zone. WP (Würm Pleniglacial) I zone (ca. 70, 000-50, 000 years B.P.). This zone corresponds to a stadial of the lower Pleniglacial. An increase in Picea, Abies, Tsuga and Betula suggests climatic deterioration. WPII zone (ca. 50, 000-33, 000 years B.P.). This zone corresponds to an interstadial of the middle Pleniglacial. Cryptomeria show high values like those of the WE zone, indicating a cool and moist climate. WPIII zone (ca. 33, 000-28, 000 years B.P.). This zone corresponds to a stadial of the upper Pleniglacial. Dominance of Pinus subg. Haploxylon, Picea, Abies and Tsuga suggests a cold and dry climate. Climatic deterioration of this stadial played an important role in the evolution of Japanese Paleolithic culture. WPIV zone (ca. 28, 000-25, 000 years B.P.). This zone corresponds to a small interstadial of the upper Pleniglacial. Climate showed a temporary warming. WPV zone (ca. 25, 000-13, 000 years B.P.). This zone corresponds to the maximum stadial of the upper Pleniglacial and is sub-divided into three sub-zones: WPVa sub-zone (ca. 25, 000-21, 000 years B.P.). WPVb sub-zone (ca. 21, 000-18, 000 years B.P.) and WPVc sub-zone (ca. 18, 000-13, 000 years B.P.). The WPVb sub-zone is the coldest epoch of the last glacial age. WL (Würm Lateglacial) zone (ca. 13, 000-10, 000 years B.P.). This zone corresponds to a Lateglacial. The climate became warm by the beginning of deposition of this zone, and an obvious increase in humidity appeared after 13, 000-12, 000 years B.P. H (Holocene) zone (after about 10, 000 years B.P.). This zone is Holocene. Deciduous broad-leaved trees like Fagus and Quercus flourished in the warm and moist climate. This zone is sub-divided into the five sub-zones HI, HIIa, HIIb, HIIIa and HIIIb. These climatic changes for the last 120, 000 years in Japan are discussed in comparison with results from southern Europe.
Although there has been some discussion of paleoclimate during the Last Glacial Age in Japan, there are still unclear points. This paper discusses the Last Glacial paleoclimate in Central Japan (Fig. 1), considering mainly the vertical changes of morphogenetic zones at two maximal phases of glaciation (i.e., 50, 000y.B.P. and 20, 000y.B.P.: Fig. 2). The results are summarized as follows: (1) Temperatures at 50, 000y.B.P. were much colder than those at 20, 000y.B.P. in the Hida Mountain Range (Mt. Shirouma and Mts. Yari-Hotaka). In the Kiso Mountain Range (Mt. Kisokoma), however, temperatures at 20, 000y.B.P. were much colder than those at 50, 000y.B.P. Temperatures at 50, 000y.B.P. and 20, 000y.B.P. in the Chichibu Mountains (Mt. Kinpu) are regarded as approximately the same range (Table 1). (2) The snowfall at 50, 000y.B.P. was nearly equal to that at 20, 000y.B.P. in the Hida Mountain Range. In the Kiso Mountain Range, however, snowfall at 50, 000y.B.P. was much greater than that at 20, 000y.B.P. (3) It seems that the location of the climatic boundary between the Japan Sea Coast type climate and the Pacific Coast type was nearly the same at 50, 000y.B.P. as it was at 20, 000y.B.P. (Figs. 2 and 3).
Pleistocene paleogeography and paleoenvironment of the Japan Sea have been investigated by several authors on the basis of the geological and geomorphological records on the surrounding land areas as well as of sediment core analyses. Recent works have elucidated the paleo-oceanographic history of the Japan Sea from the last Würm glacial to the postglacial by means of dated marker tephras, microfossils and oxygen isotope analyses of some piston-core samples. According to OBA (1983), the Tsushima warm current had begun to flow into the Japan Sea by 8, 000 years B.P. Before then, the Japan Sea was an enclosed cold sea (60, 000 to 30, 000 years B.P.) or a cold sea of low salinity (30, 000 to 20, 000 years B.P.), and an influx of the Oyashio cold current had begun to flow into the Japan Sea at 20, 000 years B. P. (Fig. 6).
The paleoenvironmental studies of the Japan Sea are mainly based on the analyses of the piston cores taken from the southern part of the sea. The lithological feature and oxygen isotopic curves of planktonic and benthic foraminiferal tests in a core taken from the eastern part of the sea are completely the same as those of the cores from the southern part. This indicates that the paleoenvironmental reconstruction of the Japan Sea based on the cores from the southern part is reasonable and applicable to much wider area of the Japan Sea.
In Central Japan, many archaeological excavation sites are located around the plains of Toyama, along the middle courses of the Shinano River, at the foot of Mt. Yatsugatake and around Lake Suwa, at the foot of Mt. Ontake, along the Tenryu basin, at the foot of Mt. Atago, and on the Iwatahara tableland. At the Tategahana site and the Nakamachi site by Lake Nojiri, many cultural layers are found, from the Lower Nojiri-ko Member III (about 40, 000y.B.P.) to the Kashiwabara black ash (Holocene, about 2, 000y.B.P.). Therefore these are the most important sites for the Palaeolithic chronology in the middle courses of the Shinano River. The Sugikubo A site is a type site for the Sugikubo Culture that occupied North East Japan. The culture layer of the Sugikubo A site corresponds to the Upper Nojiri-ko Member III (about 15, 000y.B.P.). The Black Band of Upper Nojiri Loam Member I is the oldest culture layer except for the Tategahana site; its Carbon-14 age is about 20, 000 years. Palaeolithic chronology in the Nojiri-ko site group and the middle reaches of the Shinano River is divided as follows. Phase I: “Najiri-ko Culture”. Nojiri-ko Tategahana site. From Lower Nojiri-ko Member III to Upper Nojiri-ko Member I, about 40, 000-24, 000y.B.P. Phase II: “Backed-blade Culture”. (Phase IIa) Seimeidai site and Shogetsudai site. Black Band of Upper Nojiri Loam Member and lower part of Yellowish Brown Loam. (Phase IIb) Nakamachi site and others. Upper part of Yellowish Brown Loam. Phase III: “Micro-blade Culture”. Nakamachi site and Mukoushinden site. “Kimoya”, uppermost part of Upper Nojiri Loam Member II Phase IV: “Incipient Jomon Culture”. Nakamachi site and Kitsunekuho site. Upper part of “Kimoya” and “Kuromoya”, uppermost part of Upper Nojiri Loam Member II According to this chronology, palaeolithic cultures of Toyama Prefecture and the southern part of Nagano Prefecture correspond to Phase IIa and later, and that of Niigata Prefecture corresponds to Phase IIb and later. The stratigraphy of Tategahana and Nakamachi sites is very important for the palaeolithic chronology of Central Japan. Considering the correspondence of culture layers, “Nuka-I” tuff near Lake Nojiri corresponds to “AT” tuff of Toyama Prefecture, and not to “AT” tuff of the South Kanto district. In Central Japan, there is clear evidence that man has been dwelling by Lake Nojiri since about 40, 000 years ago and in Toyama Prefecture and the southern part of Nagano Prefecture since about 20, 000 years ago.
Ontake Volcano was one of the most active volcanoes in Japan, producing many extensive sheets of tephras during the late Pleistocene. These sheets are very useful for the cor- relation and chronology of the late Pleistocene deposits distributed in central Japan. The authors established the stratigraphy of the Younger Ontake tephra group by careful investigation along the Kiso valley and on the eastern foot of Ontake volcano. The Younger Ontake tephra group is classified into 17 formations by buried soils and intervening unconformities. In addition, the tephra ages are estimated using the radiometric ages of related sediments, the stratigraphic positions of widespread marker tephras, and the geologic histories of well-investigated areas in central Japan. The following are the new results obtained from this investigation. 1) Among the many marker tephras originating from the Ontake volcano, Katamachi pumice layer (On-KtP) extends to the Takada coastal plain on the Sea of Japan, Ina pumice layer (On-Inp) to southern Kanto, Nagawa pumice layer (On-NgP) to the northern part of Gunma Prefecture and Tatsuno pumice layer (On-Ttp) to the Nobi plain. Therefore, these extensive pumice layers make it possible to correlate the geomorphic surfaces and the late Pleistocene deposits which are distributed in areas separated by great distances. 2) The upper part of the Atsuta formation in the Nobi plain is correlated to the upper part of the Katamachi sand bed in the Takada plain. These two beds were deposited during the marine regression stage from 90, 000 to 60, 000 years ago, after the culmination of the last interglacial transgression. 3) Kisogawa mudflow deposits from the Ontake and Komaki gravels in the Nobi plain are considered to have been accumulated about 45, 000 years, which makes them much older than the previously estimated age of 27, 000 years. 4) The maximum phase of the Kumazawa glacial stadial in the Central Japan Alps is estimated to be older than 57, 000 years.