The Japan Association for Quaternary Research published the“Quaternary Maps of Japan”, with an explanatory text, through the University of Tokyo Press, in 1987. This paper presents an outline of the publication together with a discussion of its contents, including the characteristics of Japanese Quaternary phenomena, and a comparison of the maps presented with various other Quaternary maps published by other organizations around the world.
The Japanese Islands consist of several island arcs which compose a part of tectonically active belts surrounding the western Pacific. Then, a greater part of land areas of the islands is composed of mountains with not less number of volcanoes, and of separated intermontane basins and coastal plains. Therefore, the Quaternary system in the islands consists substantially of fluvio-lacustrine, volcanic and marine sequences. Generally, the Lower Pleistocene deposits are distributed in and around hilly districts in the Japanese islands, which lie conformably on the Pliocene sequences. They are represented by marine sequences of the Kazusa Group, the Kitaura Formation and the Soga Group; fluvio-lacustrine ones of the Osaka Group, the Uonuma Group and the Nanaorezaka Formation; volcanic sequence of the Yachio Group. Based on bio-, chrono- and magnetostratigraphy, those deposits are correlated with each other. Although the Middle Pleistocene deposits mainly cover the Lower Pleistocene sequences conformably, some of them in inland areas form fresh sequences in newborn basins. As representatives of them, the Shimonopporo Formation, the Ogasa Group and the Minami-Saku Group are examined stratigraphically. The Upper Pleistocene are composed of a variety of sediments such as marine, river terrace, lacustrine, volcanics, aeolian etc. Among them, the Shimosueyoshi Formation is taken as a typical sequence for marine terrace of the last interglacial, while the Nojiriko Formation in northern Central Japan is referred to a representative lacustrine sequence of the Last Glacial. Most of the Holocene deposits form the upper part of alluvial plains, valley plains and coastal dunes. They consist of the filling up sediments in drowned valley which has been formed during the last glacial stage.
This paper presents an overview of the development of tephrochronology in Japan, and discusses several problems regarding the Japanese Quaternary. The impact of developments in such subjects as soil science, archaeology, radiometric dating and many other disciplines of Quaternary research has stimulated the tephrochronology in studies of earlier periods. However, recent advances seem more closely related to indigenous factors. Since the early 1970's, systematization of tephrochronology and fundamental characterizations for the identification of widespread tephras, occuring in and around the Japanese Islands, have initiated revision and refinement of regional stratigraphies, revolutionary studies of tephra for determining the nature and effects of explosive eruptions, and new applications to several aspects of Quaternary studies. A compilation of tephra catalogue for the Japan region provides fundamental data for correlations on land and in sea and for determining the recurrence period of cataclysmic explosive volcanism.
Various geomagnetic phenomena have been revealed by paleomagnetic and archeomagnetic studies on the Japanese Quaternary. Archeo-secular variations of the geomagnetic field in Japan are clarified for the past 2, 000 years. Fairly big local gradients in the geomagnetic direction are found within Japan. Studies on tephra layers and marine and lake sediments, revealed that several geomagnetic events or excursions occurred during the Brunhes normal polarity epoch. These events and excursions will provide very good time markers to correlate with the middle and late Quaternary strata. Age of paleo-earthquakes can be determined by using remanent direction of sediments squeezed out by ancient earthquakes, because their magnetization recorded the geomagnetic field at the time when the earthquakes occurred.
We review in this paper the recent trend of active fault studies in Japan. The Japanese Islands, including the continental shelves and slopes surrounding them, form an active tectonic belt. The overall distribution and regional characteristics of Quaternary faults have recently been clarified, and are now being supplemented in detail. Some topics, including the studies of active faults on shallow sea and lake bottoms, the geomorphic and structural evolution of and the surface defromation associated with thrust faults, and the excavation of active faults with or without historic activity, are also reviewed.
The recent progress of late Quaternary shoreline studies in Japan are reviewed. In the first half, outcomes of the estimation of ages and elevations of shorelines during high sea-level stand of the late Pleistocene are exemplified for five localities, Hateruma Island in the Ryukyus, Matsumae Peninsula of Hokkaido, Tanegashima Island to the south of Kyushu, Noto Peninsula in the Japan Sea side of Chubu district, and Muroto Peninsula of southeastern Shikoku. The latter half is a summary, mainly as to the elevation of shorelines of the last interglacial, and gives some informations on younger (isotope stages 5c or 5a) and the penultimate interglacial (isotope stage 7) shorelines in the Japanese Islands. There it is evidenced not only how to confirm the elevation of each shoreline but also how to determine the age of it.
Recent progress in Holocene sea-level studies and studies on coastal evolution in Japan are reviewed. Several studies recorded either a slight fall or slow rise of sea-level in the early Holocene, and some studies recognized minor regressions after the culmination of rapid postglacial transgression. Coastal landforms have changed remarkably during the Holocene. Many drowned valleys were formed in the middle Holocene, and the coast lines in Japan were very rugged at the time. Various types of coastal evolution have been reported in numerous studies. Some of the studies were carried out as cooperative research using a variety of research techniques.
Oceanic paleoenvironmental studies in Japan have been performed on marine sediment cores retrieved from the Japan Sea, northwest Pacific Ocean, and East China Sea using different approaches such as sedimentological, micropaleontological, and geochemical methods. In particular, about fifty papers on paleoenvironments of the Japan Sea have been published since the end of the 1960's. Consequently, a detailed paleoenvironmental changes in the Japan Sea over the last 85, 000 years was reconstructed. On the other hand, there are not so many papers on paleooceanogaphy of the northwest Pacific Ocean and East China Sea. Several important studies, however, are included in these papers dealing with global problems related to the climatic changes in the late Quaternary. From these studies, it is suggested that a multidisciplinary study of sediment cores is a very valid method for detailed reconstruction of oceanic paleoenvironments.
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.
The faunal succession of Japanese Quaternary mammals is described within the stratigraphic framework provided mainly by KAMEI, KAWAMURA and TARUNO (1988). Descriptions are given separately for Hokkaido, Honshu-Shikoku-Kyushu and the Ryukyu Islands. In Hokkaido, Pleistocene mammalian remains are too scarce to provide a detailed faunal succession, but abundant remains of Holocene age suggest that the fauna was almost identical to that of the present day. Large mammals recorded for the Late Pleistocene are therefore considered to have been extinct by the Holocene. In Honshu-Shikoku-Kyushu, the Early Pleistocene fauna is of temperate forest type, and related to those of north China. Almost all the components are, however, assigned to extinct endemic species. The Middle Pleistocene fauna is characterized by the presence of extant species. In fact, they exceed half of the components in the middle Middle Pleistocene fauna, and are still more common in the later faunas. This fauna is also dominated by temperate forest elements and endemic species. Immigration from south China in the middle Middle Pleistocene is more limited than previously thought, and only a few forms migrated from north and northeast China in the late Middle Pleistocene. The Late Pleistocene fauna is basically identical with that of the Middle Pleistocene except for the absence of several extinct species and several exotic species which still survive in other regions. Although the fauna seems to have been isolated from those of the adjacent continent in the early Late Pleistocene, immigration of large herbivores from the northern part of the continent was recognized in the late Late Pleistocene. Most of the extinct and exotic species were eliminated from the fauna between 20, 000 and 10, 000 years BP, and thus the fauna became almost identical with that of the present day by the early Holocene. In the Ryukyu Islands, Early and Middle Pleistocene faunas are almost unknown, while Late Pleistocene and Holocene ones are relatively well recorded. The Late Pleistocene fauna is of insular type, and includes several species endemic to the islands. Some of them are extinct species. From the end of the Pleistocene to the Holocene, insularity of the fauna was enhanced by the extinction of major species and by extreme reduction in habitat areas of the survivors.
The skeletons of Minatogawa Man, found on Okinawa Island in 1970, have been morphologically reevaluated. The skulls of Minatogawa Man are characterized by a low and wide face with rectangular orbits, a projected glabellar region, a depressed nasal root and deep temporal fossae, which more or less resemble those of the late Pleistocene men from Zhoukoudian Upper Cave and Liujian and early Holocene Jomon people in Japan. In Minatogawa Man, however, the development of these characteristics is very pronounced. In the Minatogawa and Jomon skulls the zygomatic bones protrude anteriorly and the zygomatic arches are thin and flared, which are different from the features of the Upper Cave and Liujian men. Besides the skulls, the Minatogawa postcranial bones stand apart from those of the Zhoukoudian Upper Cave, Liujian, Jomon Japanese, and are close to Zhoukoudian Homo erectus, in some characteristics. Therefore, Minatogawa Man should be assigned to the oldest type of Mongoloids or modern Homo sapiens in East Asia. We infer that he might be a direct ancestor of Jomon people, but not an ancestor of the Upper Cave and Liujian men.
Reconstruction of paleodiets for hunter-gatherers in Japan is carried out using the major nutritive elements. (1) Carbohydrate sources are examined using carbon isotope data from charcoal in burnt “cookies” and pottery residues. Measurements of charcoal in burnt cookies indicated no evidence of C4 plant use during the prehistoric age in Japan. (2) Protein sources are identified using carbon and nitrogen isotope ratios measured on collagen extracted from human bones. Among hunting-fishing-gathering people in Japan, marine protein intake was about 70-90% for people in Hokkaido including the Ainu people, while Jomon people in Honshu and Kyushu had a wider variation of 20-60% between coastal and inland people. (3) Lipid sources are identified from fatty acids and sterols extracted from pottery residues and coprolites by GC and GC-MS. Coprolites and pottery sherds from shellmidden sites indicated that animal foods were dominant lipid sources in the diet, and marine food resources were not constantly, but occaisionally used.