Current research in Japanese Palaeolithic archaeology and anthropology has four main objectives: (1) radiometric dating of Early and Middle Palaeolithic sites; (2) criteria distinguishing the Middle Palaeolithic from the Early and Late Palaeolithic; (3) understanding of settlement, procurement of raw materials, and regional variation of culture in the Late Palaeolithic; and (4) dating of hominid remains from the Late Pleistocene. Thermoluminescence dates suggest that people first reached the Japanese Islands as much as 0.5 million years ago. Increasing number of AMS radiocarbon dates and their calibration opens a new horizon of man-environment interaction in the later phase of the Last Glacial, and the Pleistocene-Holocene transition patterning. But few hominid remains preserved in Japan are older than the Last Glacial maximum.
Studies of sequence stratigraphy in Japan began in the early 1990s with the Quaternary successions, especially the Plio-Pleistocene of the southern Kanto area. Comprehensive geologic researches in this area provided a framework for the application of the sequence-stratigraphic principles to the onshore outcrops. The outcome of such studies represents one type of variation in the standard sequence-stratigraphic model. In particular, such studies have clarified some kinds of variations in the sequence-stratigraphic tenet. That is (1) diachroneity of systems tracts, (2) spatial and temporal relationship between high-frequency depositional sequences and parasequences, (3) relative timing of turbidite deposition in a submarine fan environment, and (4) contemporaneity of lowstand depositional systems. Furthermore, sequence-stratigraphic classification of the Quaternary successions, together with tentative correlation of sequence boundaries with the oxygen isotopic sea-level index, permits detailed chronostratigraphic correlation of such successions developed in the Osaka and Boso areas. Recently, detailed measurements of depositional rates in a Holocene sequence has been available. Such measurements identified several different patterns of depositional rates that characterize each of a wide range of shallow marine and coastal depositional systems.
Many widespread Quaternary tephras have been identified in and around Japan. Recent developments in tephra characterization and dating methods have provided a regional stratigraphic framework for Quaternary studies as well as for determining the nature and effects of explosive eruptions. This paper stresses on the importance of tephra catalog compilation and shows a simplified example from Japan.
Detailed secular variation records of geomagnetic field direction during the Holocene, derived from archeomagnetic and sedimentary magnetic studies in Japan, can be used as a time scale for intervals of 102-103 years. Accumulated paleointensity data for the last 50kyr, from baked earth and volcanic rocks using the Thellier method, provide reliable age constraints for time intervals of 103-104 years. The geomagnetic excursions and short reversal events found in Japan, which mostly coincided with paleointensity minima at intervals of 104-105 years in the Pacific, are also useful for dating. Besides its chronological applications, magnetic analyses of sediments are useful in other areas of Quaternary studies.
This article presents that our investigations based on Paleobiology have good progress in understanding how environmental conditions changed and fluctuated during Quaternary, of fossils themselves as well, for these ten years. Major results are as follows: (1) Sedimentary facies and molluscan fossil contents of Quaternary sediments were originated from glacio-eustacy with the period of orbital precession and/or obliquity by the Milankovitch cycles. (2) Four stages in warm molluscan and diatom assemblages were recognized during the Holocene in Hokkaido. They can be correlated with the periods of strong northward inflow of the warm Tsushima Current. (3) The rising of averaged temperature by 2-3°C and sea-level by 2-3m were recognized at the Hyperthermal and Last Interglacial age. (4) Tsunami deposits, which consist of sand and sandy gravel with mixed environmental molluscan shells and wood fragments, generated by earthquakes were found along the Boso and Miura peninsulas. (5) A cold-seep chemosynthetic community, which is composed of the articulated bivalves Conchocela bisecta and Lucinoma spectabilis, were found in the lower Pleistocene Koshiba Formation, Yokohama City. (6) Living fossils were observed in seafloor caves, in deep water, or in singular area around spouting thermal spring on the ocean floor.
Because the Japan Sea is a semi-enclosed marginal sea surrounded by a continent and an island arc, its oceanographic condition during late Quaternary has been influenced by many factors including climate in central to east Asia and Japan, oceanographic condition of northwestern Pacific, and glacioeustatic sea level changes. Consequently, its sedimentary record is complicated and difficult to interpret. However, the record preserves a wealth of information both terrestrial and marine, and is suited for linking the terrestrial climate in central to east Asia and the oceanography of the Japan Sea and surrounding oceans. Recent progress revealed intimate linkage between the Asian climate and the Japan Sea paleoceanography on millennial time-scale.
Teleconnections between the East Asian Monsoon and North Atlantic circulation are being clarified through Japanese Quaternary studies affiliated with an international program on global changes. Monsoonal history is well known from loess and intercalated soils in China. Recent findings where, of what kind show that the summer monsoon became stronger soon after Heinrich events of the North Atlantic region. Conversely, the winter monsoon strengthened, as shown by eolian dust in Japanese peat, during cold phases probably correlative with Heinrich events. Heinrich events and Dansgaard-Oeschger cycles have been further correlated with changes of surface temperature of the Japan and South China Seas, as inferred from cores from those waters. Current hypotheses include a linkage between monsoons and a summertime subtropical jet near the Tibetan Plateau.
We review the progress on coral reef terrace studies in Japan since 1990. We first summarize recent progress in the study of paleo-sea-level indicators which are based on the present-day coral assemblage in the Ryukyu Islands. Five coral assemblages as different water depth indicators are used for analysis of coral terraces in the Ryukyu Islands and also in the Huon Peninsula, Papua New Guinea. In addition to the water depth analysis, an accurate dating of corals by the alpha-spectrometric method resulted in revision of paleo-sea-level heights on the Huon Peninsula, which has been used as one of the standards for Quaternary sea level studies. We also point out the finding of isotope stage 3 corals at rapidly uplifting Kikai Island. Heights of stage 5e coral terraces show differential tectonic uplift among islands on the overriding Eurasian plate and on the subducting Philippine Sea plate. Japanese contributions on overseas coral terrace studies are summarized, emphasizing coseismic uplift as a major cause of tectonic uplift.
Annually laminated (varved) lacustrine sediments provide a potentially continuous, high-resolution records of the last glacial and Holocene paleoenvironments. In 1991-1993, long sequences of laminated lacustrine sediments were successfully taken from two lakes in southwestern Japan, Lake Suigetsu and Lake Tougouike. Based on lamina counting and AMS 14C dating, we clarified that these laminated sediments were varves. Clay mineral composition in these varved sediments would be reflected by eolian dust concentrations, transported from Chinese Loess Plateau, and by precipitations around both lakes. Also, formation of iron sulfides and carbonates in varves would be caused by cyclic changes of sea-water invasion, originated from sea-level changes. Annual to decadal oscillations of dust and iron mineral concentrations since the last glacial were detected in varved sequences of both lake sediments. These detailed sedimentological analysis of these sediments revealed varve chronology, process of varve formation and annual to decadal changes of sea-level and climate. Some of the climatic changes may correlate with abrupt changes (Younger Dryas and Heinrich events) observed in Greenland ice cores and marine sediments.
Pedological studies contributed to the reconstruction of Quaternary environment of Japan and eastern Asia in 1990s. Study of the material in the Red-Yellow soil, a representative relict paleosol in Japan, improved understandings of the soil's genesis. The origin of Japanese Red-Yellow soils confirmed to be aeolian dust from the Asian continent and can be characterized as a transitional soil between a tropical and a warm regime, which has been developed by weathering during 103kyr. Studies of weathered volcanic ash layers improved the understanding of the formation of tephra-soil sequences widely distributed in Japan. The development of tephra-soil has occurred succestively during intervals between volcanic activity by the addition of weathered tephra and aeolian dust. Interpretations of environmental change in Holocene and late Pleistocene by investigations on tephra-soil and loess-soil sequences were supported by these findings.
We review progress of geological and geomorphological approaches in paleoseismology in Japan during the this decade. We emphasize the growth of active fault studies since the 1995 Kobe earthquake. Two examples of intensive trenching studies, one on the Itoshizu-Tectonic Line in central Japan, and the other on the Miura Peninsula south of Tokyo, are briefly discussed with special reference to fault segmentation and the probability of large earthquakes. Studies of coastal morphology and deposits which are used for the reconstruction of paleoearthquakes are also reviewed. Japanese scientists have contributed much to paleoseismological studies overseas through collaborative international projects including identification of coseismic uplift, subsidence and tsunami deposits along the Pacific coasts as well as studies of inland faults.
Japanese activities on Quaternary research for the inter-congress period from 1995 to 1999 is summarized in this report. Japan Association for Quaternary Research and the National Committee for Quaternary Research of Japan are main organizations for promoting Quaternary research in Japan. Japan Association for Quaternary Research have conducted each year annual and spring meetings on Quaternary research and published a regular journal entitled “The Quaternary Research” (Daiyonki-Kenkyu) with 5 issues a volume. Articles and review papers on various aspects of Quaternary research in English or in Japanese with English summary were published in “The Quaternary Research”. One issue has been usually allocated for a special issue on symposium held in the annual meeting. The National Committee for Quaternary Research of Japan is located in the Science Council of Japan and is the contact point for international activities on Quaternary research including International Union for Quaternary Research (INQUA). Japan Association for Quaternary Research and/or National Committee for Quaternary Research have organized and supported the national and international symposia and workshops on Quaternary research.