If the natural radioactive nuclides of uranium or actinouranium series existed at one time of the past in the situations of the enrichment of either the parent nuclide or the daughter nuclide, the age determination of Quaternary sample in such system can be made by using either the growth of the daughter nuclide to the radioactive equilibrium with its parent or the exponential decay of the daughter nuclide, respectively. The historical review of the applications of these methods to various samples and the discussions of their results are given in the order of the following themes together with the brief description of the methods for the determinations of the concerning nuclides. I. Uranium or Actinouranium enriched systems or Uranium isotopes disequilibrium system. 1) Ionium (Radium) growth method: (a) coral and oolite, (b) mollusc shell, (c) fossil bone, fossil soil, peat and others, (d) volcanic rocks. 2) Protactinium growth method. 3) Uranium isotopes ratio method. II. Daughter nuclides enriched system. 1) Ionium decay method and 230Th/232Th ratio method. 2) Ionium-Protactinium ratio method. 3) Protactinium decay method. 4) 210Pb (210Po) decay method. III. Methods for the separation and the determination of the nuclides.
During the past few years, considerable attention has been given to the possibility of dating by fission tracks and alpha-particle recoil tracks. In this paper, it was described the principle and application for Quaternary period. Ages of a few obsidians and old man made glasses were measured by the fission track method. The volcanic glass which was extracted from the deep sea core (V-20-130), was determined of its age and it was compared with the paleomagnetic result. According to the experimental result of this method, the difficulty and the usefulness wcre discussed
Principles and current instrumental techniques of K-Ar dating method are briefly reviewed. Possible errors which might appear in final age results in the case of K-Ar dating method are discussed in details. Several examples of the application to some geophysical and geological problems, such as the dating of sediments, chronology of some Cenozoic Japanese volcanic rocks and ages of some dredged basalts from the Pacific are also given.
The errors in radiocarbon age determination on the wood samples are estimated from the possible variations in the concentration of radiocarbon in the atmosphere. Recent results of measurements on the secular variation of the atmospheric 14C are presented and compared in order to find a general variation. Based on this general variation a correction curve for conventional radiocarbon ages to calender years is computed.
The principle and the present status of the thermoluminescent (TL) dating are reviewed. The method is still in research stage. There exist a number of problems to be solved concerning various factors affecting TL light output. Among them, the effect of radiation quality (sometimes called the LET effect), non-linearity of the relation between the light output and the absorbed dose, fading of TL during burial or storage, bleaching of TL by irradiation of light, the pressure effect, the effect of grinding of the sample, the effect of oxygen atmosphere during TL measurement, change of the susceptibility by initial heating, inhomogeneity in the sample structure, the radioactive disequilibrium in uranium series, and the effect of temperature gradient in the sample during heating are mentioned and possible solutions are described.
A number of attempts have been made to estimate the relative geological age of fossil human bones by chemical analyses. Fluorine dating method plays at present a main part among them, sometimes combined with those by other elements. In this paper this method was reviewed, and several problems concerned were considered.
On the problem of dating method by means of obsidian artifact, an important contribution from petrology to archaeology has been presented by FRIEDMAN and SMITH (1960). Obsidian is a homogeneous natural glass which contains a small amount of water, usually less than 0.3%. While the obsidian is exposed to the atmosphere or buried in the soil, its surface will be hydrated. Other conditions being equal, the time required to form the hydration layer would be proportional to the squares of thickness of the layer. The hydration rate may be controlled mainly by two factors, temperature of circumstances and petrographic character of obsidian. In order to obtain a reliable result by this method, a working curve based upon radiocarbon date is required at each climatic region, and obsidian samples must be similar in their petrographic features. Under the special caution above mentioned, a nearly linear working curve (Fig. 1) was prepared based upon 6 sites of nonceramic to after-Jomon cultures excavated from Hokkaido, Japan. A significant increase of the hydration rate from the late Pleistocene to the Holocene is found. It would be attributed to the warming of climate in the Holocene. Even though other factors are the same, the working curve at any region would not bear a simple linear relation due to the climate change in the Quaternary.
The main constituents of wood (i. e. cellulose, hemicellulose and lignin) are soluble in acetylbromide, but humin transformed from these is not attacked by the reagent. Turning their attention to this fact, Y. ITIHARA and the writers (1966) treated fossil-woods with acetylbromide and found that the solubility of fossil-woods in acetylbromide decreases with increasing duration of burial. In this paper, the technique of the acetylbromide-treatment for fossil-wood is explained. Also, in relation to the assumed absolute ages, the analytical results obtained from 26 samples by this method are shown in Fig. 2.
The author has found a new age-indicator of a bone in its manganess, which increases remarkably in the course of geological and archaeological time. Points plotted in log. paper in combination with the age presumed archaeologically and the manganese content of bones from several districts of Japan and Korea Formosa (Taiwan) give a smooth curve. And, the content of manganese in bone is especially useful to determine the difference between the recent bone and the old bone. Manganese form less soluble compound in the ordinary natural condition. For this reason, the manganese dissolve in ground water by the almost constant amount. When the manganese ion come into contact with bone, they are absorbed and become locked in bone. Perhaps, this fact brings that the effectiveness of this manganese dating method does not depend on the difference of place from which bone are dug up. In this report, the diagram showing the relation between the manganese content and the age of bones in the range of 2, 000 to 500, 000 years has been prepared.
Principle and experimental method of paleotemperature analysis were reviewed. The temperature coefficient of equilibrium constant of exchange reaction of oxygen atom between water and carbonate is large enough to enable us to calculate temperature of formation of carbonate in water. By the recent development of mass spectrometric and experimental techniques for the measurement of isotopic ratio of oxygen, paleotemperature can be measured within the experimental error of ±0.5°C and the development is completely attributed to the effort of Urey group. Japanese mass spectrometer such as Hitachi RMU-6 and RMS-4 can be used satisfactorily for this purpose. The development of other temperature scale such as phosphateand silicate-scale is strongly desired to eliminate the hypothesis that the old ocean water had the same oxygen-18 content as that of the present day.
Most tephrochronological studies based upon absolute ages are derived from historical records of eruption and radiocarbon dates from Holocene and Pleistocene times. However, unless associated with some organic matters whose ages are younger than 35, 000 years old, tephra layers usually could not be dated. Recently Kigoshi explored the possibility that Ionium dating could be applied to igneous rocks whose ages are not so older as compared with the half-life of Ionium. The method is expected, when the informations would be increased, to elaborate the chronology of the later part of the Pleistocene period. Momose has shown that the Curie temperature of titanomagnetite in a solid solution series between TiFe2O4 and Fe3O4, seems likely to reflect the composition of associated magma and is taken as a clue for identification of tephra. Certain topics on tephrochronology hitherto carried in Europe and in Japan are introduced.
In this paper the relation between stratigraphy of the Postglacial deposits and their carbon-14 datings is discussed. Besides, the Postglacial Epoch in the Japanese Islands is preliminarily divided using the sea level changes as a basis, into seven ages: Haijiman, Yurakuchoan I, Ariakean, Yurakuchoan II, Numan, Uozuan and “Historic”, as shown in Table 2 and Fig. 1. The question about the age of the highest sea level in the Postglacial Epoch is discussed and the writer concludes that the data from the Japanese Islands show that the sea level at the Numan age must have been several meters higher than the present one.
One can estimate the age of pyroclastic fall unit by means of the observation of soil profile on it. At first each fall unit must be distinguished, and next the age of each unit should be determined based on the following principles. 1) When living trees are found on the uppermost pyroclastic soil unit, the age of this unit can be estimated by means of the dendrometry. 2) The age of pyroclastic fall unit can be roughly estimated by the degree of soil profile development on it as shown by the following standard. Age of weathering Soil horizon sequence Within 100 years C or (A)/C 100-500 years (A)/C, A/C or A/(B)/C 500-1500 years A/(B)/C or A/B/C Over 1500 years Complete A/B/C profile 3) The humus content of the volcanic soils must be responsible for the weathering age of it, so the humus content or the value of the humic acid extracted from the humic layer may be useful to estimate the weathering age of pyroclastic fall unit, though the mass-wasting and the artificial disturbance of soil materials should be kept in mind. 4) When the pyroclastic fall unit is intercalated within peat layer, one can estimate the age of the unit by determining the depth of the peat layer on it, supposing that the accumulating rate of peat is constant (1cm per 10 years). According to the same way, the age of the pyroclastic unit overlain by the aceolian soil layer can be estimated. 5) When any carbonized materials or prehistoric implements including obsidian tools. made by aborigines are found within the volcanic soil unit, the age of the pyroclastics can be estimated by means of 14C dating, the thickness of hydration layer of obsidian tool and the cultural chronology of the implements, etc. 6) Moreover, if one can obtain the ancient record of volcanic activity, the chronology of the pyroclastic fall unit determined by the above mentioned methods can get undoubtedly more accuracy.
Current works of the dating of shallow-water biogenic calcium carbonates and öolites by means of natural alpha-radioactive nuclides are reviewed in terms of Late Quaternary eustatic change of sea level and local tectonism. It is compared with the results of 230Th and 231Pa dates of the corals and Tridacna shells from the Ryukyu Islands. Based on the ecological evaluation of the fossils dated, altitude of the locality, and the radioactive age geochemically checked and, if necessary, corrected, the range of sea level change in a given time can be limited (Text-figure 1). Thus the rate of vertical displacement can be calculated as shown in Table 6. The conclusion is drawn that Kikai-jima of the Ryukyu Islands has been rather uniformly upheaved tectonically with the rate of 1.5-2.0mm·y-1 during the last 70, 000 years.
The use of radio-isotope has made it possible and as prevalent as now to determine the absolute date of a marine sediments. Among works so far made public in this specific field of marine geology those pertinent to the Quaternary are reviewed in the present paper. Dating of sediments from the continental shelves by C14 revealed that the continental shelves were formed in the Würm Glacial Age. The fact suggests that sea-level abruptly rose sometime 15, 000 years ago. Some of the works reviewed here discuss about chronological process and climatic changes in the Pleistocene on the basis of C14 or Io/Pa dating of deep-sea sediments in association with micropalaeontology.
It is essential for the magnetic dating of archaeological remains and sites that the changes in geomagnetic elements are known with regard to the relevant period in the past. Secular variation curves of the direction of geomagnetism in historic and protohistoric times in Japan have been set up by means of the natural remanent magnetism of baked earth from ceramic kilns, lava flows and tuffs, the absolute dates of them being determined by archaeological and documentary evidences. As to the Yayoi and Jomon period, charcoal was occasionally found from the dwelling pit where baked earth samples were collected so that the radiocarbon date determined from the charcoal was directly connected with the geomagnetic direction obtained from the baked earth. Change in the intensity of geomagnetism in the past has also been traced back into the Jomon period. Magnetic dating may be achieved more effectively, if the change in the intensity is taken into account together with that in the direction of geomagnetism.
Since the charcoal and shells from the shell mound of Natsushima yielded the radiocarbon dates more than 9000 years B. P., the age of Jomon pottery has been subjected to controversy among archaeologists in Japan. While some archaeologists, particularly Prof. Sugao Yamanouchi, threw doubt to the radiocarbon dates, the author regards them as acceptable from the view point of a new concept, “the group of pottery types”. The concept depends upon that several succeeding pottery types have some basic traits in common which underwent change in the course of time, and such group of pottery types can be taken as the unit of assumed cycle of the change. Eleven groups of pottery types in total are assigned to the Stone Age of Japan and the distribution of them among the subdivisions of the age indicates that the older is the subdivision, the larger number of groups belongs to it suggesting the longer time duration of the subdivision. Comparison of the archaeological framework of these groups of pottery types with the radiocarbon dates is presented on Table 1 in the text.