The vegetational changes which occurred during the Last Glacial Age in Hokkaido were clarified by studies of plant macrofossils and pollen and spore assemblages. Five major pollen zones, one of which contained 2 subzones, were distinguished. (1) Picea-Abies-Betula Zone Before ca., 40, 000y.B.P., mixed forests dominated by spruce, fir and birch trees were continuously developed under cooler climatic conditions than those of the present. (2) Picea-Abies-Larix Zone During ca., 40, 000-26, 000y.B.P., Picea glehnii and/or Picea jezoensis and Abies sachalinensis were dominant and coexisted with Larix gmelini and Betula around moor lands under colder and moister conditions than those of the present. However, two short-lived warm spells, Betula-Tsuga-Quercus subzone and Betula-Abies-Ulmus subzone, were newly recognized from samples of pollen and spore assemblages and molluscan faunas which are believed to have existed ca., 34, 000y.B.P. and ca., 31, 000y.B.P. respectively. (3) Abies-Picea-Ulmus Zone Another comparatively small scale warm spell was identified by the increase of Abies and Ulmus during ca., 26, 000-25, 000y.B.P.. (4) Picea- Larix Zone Larix gmelini became dominant in most parts of Hokkaido during ca., 25, 000-12, 000 y.B.P. and formed boreal forests together with Picea glehnii and/or Picea jezoensis. However, in the eastern and the northern parts of Hokkaido, forest tundra may have existed at the same time under colder and drier climatic condition than those of the present. (5) Abies-Juglans Zone In the Ishikari Plain, another comparatively warm climatic period which was characterized by a sudden increase of Juglans, Ulmus and Quercus appeared to have occurred during ca., 12, 000-11, 000y.B.P..
The Quaternary strata in the environs of Takine town in the central part of the Abukuma Mountains can be classified as shown in Table 1 and Figure 3. The Saru-uchi I Formation and the Saru-uchi II Formation are considered assignable to the Last Glacial Age on the basis of radiocarbon dates, regional tephra, paleomagnetic data and plant fossil assemblages (macroscopic and pollen fossils), and the Ishigami Formation to Early Holocene in age on the basis of radiocarbon date and plant fossil assemblages (macroscopic and pollen fossils). The Saru-uchi I Formation can be represented by a plant fossil assemblage zone Sr-1 of local significance. The Saru-uchi II Formation is classified into three local plant fossil assemblage zones, Sr-2, Sr-3 and Sr-4, in ascending order. The plant fossil assemblages characterizing the Sr-1 and Sr-4 zones seem to represent stadial floras and the one characterizing the Sr-2 zone an interstadial flora, all during the Last Glacial Age in the southern Tohoku District. And, the plant fossil assemblages characterizing the Sr-3 zone may represent a flora with intermediate characters between the stadial and interstadial floras. The Sr-2 zone is nearly suited to the Ts-b magnetozone containing an excursion, and assigned to ages of about 34, 000 to 30, 000 years B.P. as the results of radiocarbon dating. The plant fossil assemblages in the zones of Sr-1 and Sr-4 may represent the vegetation closely resembling to that of the subalpine zone in the central Honshu, and those in the zone of Sr-2 may represent a vegetation composed of taxas of the subalpine and montane zones in the central Honshu of Japan. The plant fossil assemblages in the zone of Sr-3 may represent the vegetation which contains the elements of the subalpine zone more abundantly than those of the montane zone. Finally, the characters of flora and vegetation in the southern Tohoku District during the Last Glacial Age are tentatively considered, based on the plant fossil assemblages from some areas.
The Late Pleistocene period in Central Japan is subdivided into the following four periods based on climatic changes. (1) Last interglacial: R/W Interglacial (before 65, 000yr.B.P.) This period is characterized by the dominance of the elements of temperate coniferous forest, including Cryptomeria, and deciduous broad-leaved trees, including Fagus. The climate is estimated to have been warmer and wetter than that of the present. (2) Early Würm Glacial (from 65, 000 to 55, 000yr.B.P.) In the early half of this period, two interstadials are inferred by the dominance of the elements of temperate coniferous forest, including Cryptomeria, Sciadopitys, Ulmus-Zelkova and Corylus. The later half of this period is characterized by the subarctic forest which is estimated to have been 5°C to 6°C lower than present in average annual temperature. (3) Middle Würm Glacial (from 55, 000 to 25, 000yr.B.P.) Cool climate prevailed throughout this period, intervening a remarkable warm climate which reached a maximum about 37, 000 years ago. In Nobi coastal plain, the Atsuta Surface was formed by the transgression during the warm climate. (4) Late Würm Glacial (from 25, 000 to 10, 000yr.B.P.) This period was dominated by subarctic forest. Periglacial agency acted at places higher than 1, 000m above sea-level in the Kiso valley during the early half of this period.
Lake Nojiri is located in the northern part of Nagano Prefecture at lat. 36°49′N, long. 138°12′E. It is a unique site where a wealth of mammalian fossils and many Paleolithic artifacts have been unearthed from the lacustrine sediments. The first Lake Nojiri Excavation was undertaken in 1962 on the shore of the lake to identify the stratigraphic horizon of the fossil molar tooth of Palaeoloxodon naumanni, which had been found there by a proprietor of the lakeside hotel. Thereafter, six excavations on the shore and three excavations on the hill site near the lake have been carried out until 1979. These excavations have marked a highly significant step in establishing a satisfactory connection between geology and archeology in Japan on the basis of precise stratigraphic research works. It set out to reconstruct a standard history of Late Pleistocene men and its nature around them in Japan. The voluminous report entitled “The Paleolithic Site and Paleoenvironment in and around Lake Nojiri” was published in the Memoirs of the Geological Society of Japan, No. 19 (1980). The present paper is a brief report of the Lake Nojiri Excavation Research work, focussing on a paleoenvironmental change of Late Pleistocene around Lake Nojiri. Stratigraphic successions of lacustrine deposits at the lake shore as well as of aeolian deposits on the western hillside of the lake were established. The complete correlation between these two sedimentary sequences was done by the precise stratigraphic studies of the tephra intercalations therein. Fig. 5 summarizes the stratigraphic successions with the important data including absolute ages, Paleolithic artifacts, fossil faunas and floras, paleoclimate, volcanic activities and lake-water level. Several paleogeographic maps around Lake Nojiri during Late Pleistocene and thereafter are shown in Fig. 4. 14C age determinations suggest that the deposits in and around the lake are of Late Pleistocene in age, ranging from 10 to 50 thousand years B.P. The coldest period of Late Glacial Stage corresponds to the deposition of the Upper Nojiri-ko Member. This is suggested by an examination of fossil floras including pollen therein. The upper part of the Lower Nojiri-ko Member to the upper part of the Middle Nojiri-ko Member possibly corresponds to the Aurignacian period of Europe, indicating a Late Paleolithic culture with a relic from the Neanderthaloid. Some part of the Upper Nojiri-ko Member and the Upper Nojiri Loam (Volcanic ash) Member are assignable to the Mesolithic period, and the Kashiwabara Black Ash Formation to the Johmon (Neolithic) period and later.
This article deals with introducing some problems being debated by the members of the Research Group, relating to the fauna and flora of the Japanese Islands in the Last Glacial time. Though nowhere in Japan the precise chronostratigraphy of this age has been established yet, a tentative clasification based on litho- and biostratigraphy in central Japan by J. SAKAI and others is proposed with tephrochronology and radiometric dating. According to them, the Early stage began with the regression and advent of cold phase of ca. 65, 000yr.B.P., and further with the Middle stage chracterized by climatic ossilation, some peculiar warm phases were corporated. In the Late stage between 25, 000yr.B.P. and 10, 000yr.B.P. was intercalated the maximal cold phase of ca. 20, 000yr. B.P.. Concerning the reconstruction of paleoenvironment, I. HIURA made biogeographical and ecological consideration by paying his attention to the species and subspecies distribution of non-dispersal plants and insects like as tribe ASAREAE and tribe CARABINI respectively. On the other hand, the vegetation of the Japanese Islands and its adjacent areas was investigated from the recent and Last Glacial plant geography by M. HOTTA and T. NASU respectively. They suggest significance of the distribution of plant communities to the seasonal structure of precipitation rather than to the temperature control. Summing up those results collectively, the environmental and vegetational studies on the Last Glacial seem to indicate the presence of more arid and extensive steppe-like environment which is absent in the present Japanese Islands. It is characteristic that some of the arctic mammals migrated into Honshu through northern land connection during the Last Glacial. Therefore, the mammalian fauna in that time was composed of arctic immigrants and temperate endemics, that is the mixed fauna. In this sence, that mixed fauna may resemble to the present of mammals in the Maritime Province (Siberia) and Manchuria of the continent. The immigration of those arctic mammals might be undertaken before the maximal phase of ca. 20, 000yr.B.P. In connection with this, the sea level change of those days was discussed. It may probable to say that the lowest sea level was -100m± as being discussed by M. HOSHINO and that the southern land connection did not happen at that time.
In the Japanese Islands, alluvial fans had developed best during the period corresponding to the last glaciation of the glaciated regions of high latitudes and high altitudes in the world. Many alluvial fans of this age cover aggradationally the inland parts of the older fluvial and coastal plains, though the base-level of gradation prevailed along the coasts and rivers was lowered consistently with lowered sea level. Temperature on land indicated by the fossil flora was lower than the present, but no significant glaciation occurred in Japan. Possibly climate controlled mass-wasting and fluvial processes with unbalanced precipitation besides low temperature.
The purpose of this paper is twofold: to establish a tephrochronological framework for the sediments of the Japan Sea on the basis of the identification of the abyssal tephra layers and to examine the paleo-oceanographic conditions of the Japan Sea during the last 60, 000 years, based on the foraminiferal biostratigraphy and 18O record in two piston cores. Accurate determinations of the refractive indices of volcanic glass shards and minerals, together with other data, have enabled successful characterization of several tephra layers and permitted correlation to be made between cores. Of the five marker-tephras described in this paper, three can be correlated with the dated widespread tephras which originated from eruptions of gigantic caldera volcanoes in Kyushu. They are: the Akahoya ash, the Aira-Tn ash and the Aso-4 ash. The Akahoya ash (Kikai caldera, 6, 300Y.B.P.) occurs in cores from the southern part of the Japan Sea. The Aira-Tn ash (Aira caldera, 21, 000-22, 000Y.B.P.) is the most prominent marker, found in cores from the whole area of the sea. The Aso-4 ash (Aso caldera, approximately 50, 000Y.B.P.) is found in cores from the central and southeastern part of the sea. The other two marker-tephras, the Oki ash and the Yamato ash, are the products of major eruptions of Holocene and Late Pleistocene age, and have probably originated from the Ulreung-do Island in South Korea. This estimate is based on their peculiar petrographic nature and distribution. The Oki ash is found in a stratigraphic horizon between the Akahoya ash and the Aira-Tn ash in cores from a tract extending from the area adjacent to the Ulreung-do to the Kinki district of central Honshu, where three radiocarbon ages of around 9, 300Y.B.P. were obtained for the eruption. The Yamato ash occurs in cores from areas to the east of the Ulreung-do. A reliable age for this tephra has not yet been determined, although its stratigraphic relationship to the overlying Aira-Tn ash and the underlying Aso-4 ash, suggests that it must occur within a range of between 25, 000 and 35, 000Y.B.P. Vertical changes in the lithological, foraminiferal and oxygen isotope characteristics of the two tephrochronoiogically dated cores from the Oki bank in the Japan Sea occur at about 6, 500-9, 500Y.B.P., 13, 000 and 23, 000Y.B.P. The paleo-oceanographic conditions of the Japan Sea between these ages are reconstructed from the data of paleosalinity and paleo-temperature, which were calculated on the basis of the 18O values of the benthonic and planktonic foraminiferal tests in the cores. The water of the Japan Sea seems to have been of relatively constant salinity (33-34‰) and low temperature (8-10°C) in the period between 60, 000Y.B.P. and 23, 000Y.B.P. Relatively minor amounts of Pacific sea water flowed into the Japan Sea during this period. A conspicuous, continuous decrease in the salinity of the sea water took place in the period from 23, 000Y.B.P. to 13, 000Y.B.P., as inferred from the decrease of the 18O values of the planktonic foraminiferal tests. It seems probable that the inflow of water from the open sea was checked by some paleogeographic changes at the straits, caused by lowering of sea level during this glacial stage. The 18O values of the planktonic foraminifera tests increased suddenly at about 13, 000Y.B.P. Subsequently, the benthonic foraminiferal fauna which live today in the shallow water of the Northwest Pacific coast appeared in the cores of the Japan Sea. These facts suggest that a remarkable inflow of the Oyashio current through the Tsugaru Straits into the Japan Sea began about 13, 000Y.B.P. The coiling direction of Globigerina pachyderma changed from sinistral to dextral approximately 8, 000Y.B.P. Then warm water planktonic foraminifera appeared in the cores, and the temperature of the surface water of the sea increased abruptly by 7-8°C.
To delineate the paleoceanography of the Sea of Japan since the last glacial maximum, I first tried to formulate the relationship between the present-day distribution and physico-chemical properties of surface water masses and the diatom flora in the modern sediments collected at 78 stations which are widely distributed in the sea. Then the results from this examination were applied for the upper portion of eight piston cores with the assistance of key tephra and its 14C age for a time scale. The floral analysis of the diatoms in modern sediments is performed by principal components analysis employing the Q-mode variance-covariance matrix. On floral analysis, two species associations are defined by the second principal component; species association in the warm-current region (Pseudoeunotia doliolus, Melosira sulcata and Thalassiosira oestrupii) and one in the cold-current region (Denticulopsis seminae, Thalassiosira sp. 1 and Thalassiosira nordenskioeldii), From relative frequency of these species at a random count of about 200 diatom specimens for each sample, R value was obtained to facilitate the application of the results from the diatoms in modern sediment samples to core samples. The value is defined as: R=(P. doliolus+M. sulcata+T. oestrupii)/(P. doliolus+M. sulcata+T. oestrupii+D. seminae+T. sp. 1+T. nordenskioeldii) The value are generally constant below a certain surface water masses classified by their physico-chemical properties. From interpretation of the third principal component, the relative frequencies of Pseudoeunotia doliolus and Melosira sulcata provide a useful clue to estimate the degree of the influence of low saline water of the upper surface water in the southern part of the sea; Pseudoeunotia doliolus is dominant in samples from the high saline area, and Melosira sulcata in those from the low saline area. The paleoceanography of the Sea of Japan since the last glacial maximum are deduced on the basis of these criteria as follows: 1) The supply of the warm water which have a similar oceanographic structure to the present-day Tsushima Warm Current, began about 7, 000-8, 000y.B.P. 2) The frontal zone in the eastern half of the Sea of Japan was to the south of its present position, and its southern boundary reached at least as far as the eastern offing of the Oki Islands during a period, from about 15, 000 to 9, 000y.B.P. in conservative estimation, following decrease of the sea water supply through the Tsushima Straits. 3) The zone at that time was probably formed between the low saline water brought from the East China Sea and the cold water which occupied the northern part of the sea. 4) The low saline water probably occupied the surface layer of the southern part of the sea at the last glacial maximum.
The Tsushima Strait are consists of broad continental shelves, connecting the Japanese Islands with the Asian Continent. Systematic sea bottom surveys of this area with two-mile spacing soundings were carried out by Hydrographic Department of Japan from 1973 to 1976. From the seismic profiling, it was revealed that the center of broad continental shelves are surfaced with thick Quaternary sediments where longitudinal depressions lie, trending in the NE-SW direction. In 1977 and 1978, with 0.5-mile-spacing soundings more detailed surveys were conducted by Hydrographic Department in the areas from the southern coast of Tsushima Island to the north of Iki Island and near Shiro-se off the west coast of the Goto Islands, respectively. The distinct depositional terraces were detected at depths of -90m to -110m and -110m to -130m in the Shiro-se area. Along these terrace edges there are sand bars, suggesting the ancient shore lines, and inward shallow depressions. It is noticeable that the basement of the longitudinal depression is buried by sediments which form the depositional terrace at the depths of -110m to -130m. This fact means that the longitudinal depression represents an uncovered portion of the basin reclaimed by shelf sediments. The present topography of the longitudinal depression is modified, however, by currents indicated by a pair of caldrons excavated from the bottom of the depression on the west of Korai-sone. On the other hand, a lot of submarine sand ridges were found in the Tsushima East Channel. These submarine sand ridges are classified into two types: one is a U-type, developing in the narrowest part of the channel between the southern coast of Tsushima Island and Iki Island, and the other is a longitudinal type with a NE trend, developing abundantly in the vast area behind the U-type sand ridge area. From the relations between regular distribution patterns of the sand ridges, and distributions of current velocity and grain size of sediments, the author concluded that these sand ridges are not growing at the present with the Tsushima Current, but have been made by tidal currents in the past when sea level lowered to a depth of -80m. These sand ridges cover the submarine terraces at depths of -90m to -120m. Accordingly, the abundant submarine sand ridges are formed at a certain stage of the sea level rising after the Würm glacial stage when the -110m to -120m terrace was presumably cut. A more detailed survey on a scale of 1/10000 was carried out by Hydrographic Department of Japan in the area off the west coast of Tsushima Island. From the survery, distinct five submarine terraces and fifteen buried shelf channels were discovered. The second terrace, -20m to -35m deep, is a depositional plain covered by Alluvium of 5m to 20m thickness. On the other hand, the fourth terrace at -60m to -70m depths is an erosional plain with a veneer of coarse sediments. The buried shelf channels start from the land river mouths and continue to a depth of about 100m. It is noticeable that the course of the buried shelf channels are interrupted at the fourth terrace, and arc crossed by the second terrace. As a result, the author summarized evolution of the continental shelves as follows. During the Würm glacial stage, the coast line regressed to the present depth of about -100m, and the marine terrace was formed by wave abrasion at that level. Many rivers extended to that coast and cut new dried land. And then sea level rose toward the present sea level. At a certain stage of the sea level rising the sea level stayed at the present depth of about -80m, and many submarine sand ridges were formed in the ancient Tsushima East Channel as in the case of the present Malacca Strait. After the rising of sea level from -80m, the sea level stayed again at the present depth of about -60m. At that time, wave abrasion made the fourth terrace and scratched the submarine valleys out on it.