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Volume 34, Issue 2
Displaying 1-9 of 9 articles from this issue
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Shoji HORIE1973 Volume 34 Issue 2 Pages 49-54
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSIn this paper, the writer has described the academic history of the paleolimnological studies in Lake Biwa-ko during the last twelve years. The writer already obtained 6m and 12m cores in that lake in 1965 and 1967, but in 1971 the new interdisciplinary organization of paleolimnological investigations succeeded to get a 200m core at the water depth of 65m. This is the longest continuous core ever obtained in any oligotrophic lake in the world. The analytical results of each element to be determined in this core will be announced step by step.
The writer has stressed the importance of his idea and plan as an international project for new and much deeper boring to be operated in Lake Biwa-ko in future.View full abstractDownload PDF (1388K) -
Katsumi YASKAWA1973 Volume 34 Issue 2 Pages 55-62
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSIt has become an undoubted fact that there were repetitions of geomagnetic fieldreversal in the geological past. An absolute chronology of these reversals has been established back to about 4.5 million years ago, and a name has been given for each magnetic polarity epoch and event. BRUNHES normal polarity, epoch has continued these 690 thousand years, and MATUYAMA reversed polarity epoch had been regarded as the latest geomagnetic reversal until a few years ago. Recently two short reversals were reported in BRUNHES normal polarity epoch, namely LASCHAMP and BLAKE events, On the other hand, the existence of three short reversed polarity events was also recognized through the palaeomagnetic investigation of the core 200 m long taken from the deep region of Lake Biwa-ko. The discovery of such a short and quick polarity change as these reversed polarity events seems to become quite easy with the stable magnetization of the sediments, of which sedimentation rate is much greater than that at the deep sea bottom. Moreover, the detailed measurements of these sediments give us the informations about the variation of the past geomagnetic field such as the geomagnetic secular variation and the mode of polarity change.View full abstractDownload PDF (1167K) -
Atsuyuki YAMAMOTO, Seiichi KANARI, Yoshiaki FUKUO1973 Volume 34 Issue 2 Pages 63-74
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSGrain size and particle density of the core were measured for every subsample of 5 cm thick at the interval of 50 cm from the uppermost 40 m, and for every subsample of 5 cm thick at the interval of 5 m between 40 m and 200 m. Furthermore, the bulk density was measured for each sample of about 1 m long over whole core sample.
The core sample had the mean density of particles 2.6 gr/cm3 and the phi-median diameter 6.2 on the average. It was also found that the vertical variation of particle density showed close parallelism with that of finer grain contents than 8φ, and that, at the horizon of the reversal of geomagnetic field, the particle density changed abruptly from higher maximum to lower minimum. At the same time, the fractions of grains coarser than 4.5φ also increased rapidly. There revealed conspicuous peaks at the depths of 30, 50, 85 and 130 m in the vertical variation of coarser grain contents. Because of the fact that the increase of precipitation would generally strengthen the river discharge and bottom currents resulting in the transport of coarser sediments to the boring site, the peaks of coarser fraction might indicate pluvial periods and those values might offer the method estimating the intensity of past precipitation.
The vertical distribution of bulk density was analysed on the basis of concept of consolidation which caused the squeeze of pore water between particles in underlying layers by the increase of the weight of sediments settled out successively on the surface of lake bottom. This analysis enables us to estimate the age of each layer in a continuous core sample. We conducted this estimation by integrating the measured bulk density, assuming a constant rate of deposition. Then we obtained the results of 1.35×105 and 3.35×105 years B. P. at the depths of 50 m and 100 m respectively. It was shown that the observed rate of deposition of 1.8 mm per year which was reported from Lake Biwa-ko (TOYODA et al., 1968) agreed well with the estimated value of 1.74 mm per year which was obtained by combining both results of C14 dating and of the integration of the bulk density.View full abstractDownload PDF (1769K) -
Tadashiro KOYAMA, Nobuhiko HANDA, Ryoshi ISHIWATARI, Kazuko OGURA, Ats ...1973 Volume 34 Issue 2 Pages 75-88
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSA deep core sample of 197.2 meters in length was obtained by the technical assistance of MIZUNO and AOKI from the bottom of about 65 m in water depth at the central part of Lake Biwa-ko. Chemical analyses were conducted about the organic components and the inorganic elements in the core sample and the following results were obtained :
1). The content of total carbon (Ct) ranges from 4.4 to 14.7mgC/g of dry sediments and varies with core depth periodically showing four remarkable peaks at 15m, 90m, 140m and 180m. The vertical profile of the content, however, shows a decreasing tendency with depth.
2). Ratio of total carbon (Ct) to total nitrogen (Nt) ranges from 4.3 to 9.8 and fluctuates with core depth showing two remarkable peaks at 130m and 180m.
3). Total carbon (CH2O2) and total nitrogen (NH2O2) in the samples treated with H2O2 indicates carbonate carbon and ammonium nitrogen included in clay mineral lattices respectively. Ratio of CH2O2 to NH2O2 fluctuates vertically in a range from 1.8 to 8.9. This vertical distribution shows four remarkable peaks at 56m, 85m, 130m and 180m in core depth. Each of the former three peaks corresponds to each of the palaeomagnetic reversals of Blake, Biwa I and Biwa II discovered by KAWAI et al. (1972) respectively. These peaks also correspond to the peaks of percentage of sediment particles coarser than 44μ, which were found by YAMAMOTO.
4). The contents of organic carbon (Corg.) and organic nitrogen (Norg.) were estimated as follows : Corg.=Ct-CH2O2 and Norg.=Nt-(NH2O2+NNH4), where NNH4 denotes ammonium nitrogen.
The content of Corg. varies similarly to Ct showing four remarkable peaks at 15m, 90m, 140m and 180m. The former three peaks correspond to the warm periods which were recognized by FUJI through his palynological study (FUJI and HORIE, 1972). The four peaks also correspond to the minimum values of Corg./Norg. ratio. This fact suggests that the four sediment layers corresponding to the four peaks are rich in proteinous substances, thus relatively high production of this substances has arisen in the lake water in the warm periods.View full abstractDownload PDF (1752K) -
Nobuyuki NAKAI1973 Volume 34 Issue 2 Pages 89-96
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSOrganic carbon contents and the stable carbon isotope compositions of 200 meters core samples were determined to attempt to trace the depositional history of sediments in Lake Biwa-ko.
The carbon in organic materials has δ13C values ranging -31 to -38‰ relative to PDB, and the organic carbon contents range 0.3 to 1.2% in dry samples. The 12C enriched values of the sediments indicate the large contribution of plankton residues to sedimentary organic materials. The positive relation between organic carbon contents and the δ13C values was found through the core samples; that is, the isotopic composition of organic carbon becomes heavy with an increase in the organic carbon content. The isotopic variation in the organic carbon in the column is undoubtedly controlled with kinetic isotope effect by temperature at which the plankton grew. In an warm climate, the production rate of organic materials such as plankton and their accumulation rate in the sediments are relatively higher, resulting relatively higher 13C enrichment than those in a cold climate.
On the other hand, paleoclimate estimated by pollen analysis shows an excellent correlation with the carbon contents and the δ13C values. From this geochemical study, it can be concluded that there were three or four warm and cold periods in the depositional history of Lake Biwa-ko sediments after 50 to 60 × 104 years B. P.
Paleomagnetic investigation reveals several magnetic reversals in these samples from 200 m core. During a normal magnetic period, organic carbon contents and its δ13C values of sediments show a linear relationship, which makes up different lines after and before a reversal period.View full abstractDownload PDF (1209K) -
Norio FUJI1973 Volume 34 Issue 2 Pages 97-102
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSIn this paper, the present writer deals with the change of paleoclimate of Lake Biwa-ko during the past 0.6 million years. The purpose of the writer is to clarify paleoclimate and to establish the late Quaternary chronology which is comparable to European and American chronological time-tables, from the viewpoints of paleontological and chemical studies of the present core samples of nearly 12 meters and 200 meters in length.
On the basis of palynological study, though temperature during the late glacial age is regarded as several degrees in centigrade lower than the present one, the temperature during the Flandrian transgression of the Postglacial age is about two degrees in centigrade higher than the present one.
The analysis of the 200 meters core sample showed that most of the samples contained fossil pollen grains and/or spores of about 40 genera and/or families. As a result of the analysis of the pollen and spore assemblages, ten cold climatic stages (co-1, co-2, ……, co-10) were recognized throughout the boring core. In the same core, warm climatic stages (w-1 and w-2) were found two times including the Postglacial climatic optimum. It is true that the warm climatic stage shown by the abbreviation w-1 and cold climatic stage shown by co-1 in Fig. 2 are correlated with the Atlantic age and the last stage of the Würm glacial age respectively.
On the basis of pollen analysis of about 12 meters core sample, the pollen grains of Oryza are found in the samples of 0-3.4 meters below the present lake bottom as shown in Fig. 4. Judging from the radiocarbon dating, the horizon of 3.4-3.7 meters deep is inferred to be about 2, 900 3, 000 years before the present. In addition, many grass pollen grains and spores are also found in the samples of 0-3.7 meters (about 3, 000 years B. P.). Their frequency in the above-mentioned horizons is higher than that of the other horizons. Such phenomena of the ancient flora indicate an influence of ancient man upon natural vegetation in the latest Jomonian and/or early Yayoian period.View full abstractDownload PDF (911K) -
Sadami KADOTA1973 Volume 34 Issue 2 Pages 103-106
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESS1) This paper reports the quantitative study of microfossils remained in the core sample of Lake Biwa-ko.
2) In the core, 13 species of animal microfossils were found, dominated by Cladocera-9, Protozoa-2, Insecta-1 and Platyhelminthes-1 species in order. The gauntitatively important microfossil species were Turbellaria (egg capsules) in Platyhelminthes, Bosmina, Monospilus in Cladocera and Chironomdiae (larvae) of Insecta.
3) Regarding plant microfossils other than pollen and diatoms, Pediastrum and Staurastrum of green algae were found in the layers lower than 85 m. The quantity of the former (66.0%) was, however, a little more than the latter (34.0%).
4) The changes of vertical distribution of Cladocera agree well with those of the whole animal microfossils, i, e., when the latter decrease, the former also becomes to small numbers. In the other words, the increase of Cladocera brings the increase of total animal microfossils. Turbellaria and Insecta, however, show opposite tendency to the Cladocera in vertical distribution.
5) When Lake Biwa-ko was under warm climatic conditions, several hundred thousand years ago, green algae dominated too much to allow the propagation of animals. Green algae, however, gradually decreased while the warm and cold climatic ages repeated and entirely disappeared in the cold time. On the other hand, the animals increased gradually not only in the species but also in their quantity in the layers upper than 85 m at which no more green algae were found. They showed a tendency of remarkable increase in the layers upper than 15 m. However, the propagation of the green algae was not allowed in the cold climatic conditions and animals were found at least abundance in that age.View full abstractDownload PDF (2303K) -
Takuo YOKOYAMA1973 Volume 34 Issue 2 Pages 111-118
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSIt is significant in Quaternary geology of Japan that a 200m core sample was obtained from the bottom of Lake Biwa-ko. The core is mainly composed of clayed sediments including a number of inserted volcanic ash layers. The geohistory of late-Quaternary period in Lake Biwa-ko may be reconstructed firstly by the success of this boring and complete investigations of the core samples, which may cover surely the whole time since 0.5 million years ago. Up to the present time, no geologic research of the surrounding hill lands has been successful to establish a whole geohistory in the area in question.
The Quaternary system around Lake Biwa-ko is roughly divided into three units : Plio-Pleistocene Kobiwako Group, Pleistocene Terrace Deposits and Alluvium. These sediments do not continue through whole ages, because they are accumulated uncomfortably each other. The 200m core sample, however, consists of a continuous series of sediments. It is extremely useful for the reconstruction of whole geohistory of ancient Lake Biwa-ko in the late Quaternary.
In this paper, the writer deals with the characteristics of volcanic ashes found in the upper part of the 200m core sample and discusses the correlation between those ashes and the volcanic ash layers in the Kobiwako Group. The volcanic materials in the core are divided into two types, andesitic and trachytic. The former contains two pyroxenes, hornblende and abundant volcanic glass flakes as the constituent minerals. The latter is chiefly composed of orthorhombic pyroxene, hornblende, biotite, quartz, volcanic glass flakes and small pumice grains. The individual volcanic seam is distinguishable from the differences in some features as shown in Tables 2 and 3. The writer hopes to establish the tephrochronology of whole Quaternary deposits around Lake Biwa-ko by making clear the characteristics of volcanic materials in this core sample and in the Kobiwako Group. It is the writer's expectation that geohistory of Lake Biwa-ko will become wealthy by the investigations carried out on the basis of tephrochronology.View full abstractDownload PDF (1153K) -
1973 Volume 34 Issue 2 Pages 119
Published: April 01, 1973
Released on J-STAGE: October 21, 2009
JOURNAL FREE ACCESSDownload PDF (147K)
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