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Volume 105, Issue 7
Displaying 1-6 of 6 articles from this issue
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Yoshiro Ishihara, Yuichiro Miyata1999 Volume 105 Issue 7 Pages 461-472
Published: July 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Middle Pleistocene (∼0.5 Ma) Hiruzen-bara Formation exposed in Hiruzen-bara Highland, Okayama Prefecture, consists of lacustrine varved diatomite. It is composed of alternation of about 2 mm thick couples of light-colored and dark-colored laminae. Because light-colored laminae is made mostly of Stephanodiscus sp. breeding in winter season, and dark-colored lamina of Cyclotella comta, a single couplet of these laminae is suggested to represent an annual deposit. Thickness of 8000 varves are sequentially measured for photo film under microscope. Time series variations of lamina thickness indicating productivity of diatoms are examined by spectral analyses, and environmentally induced fluctuations were extracted. Modified time series of thickness variations by numerical filters are examined by spectral analysis (FFT : fast Fourier transformation), and dominant periods were obtained as 9-10.5 and 32 years, which are, however, not always significant through the sequence.To improve precision and quality of the thickness data, the digital images of the varves are also analyzed, where more distinct 4-5, 9.1-11.6, 22 (FFT), 34-36 and 100 year periods (MEM : maximum entropy method) are detected. However, the amplitude of 11 years periodicity even in the most distinct interval is less than 20% of the total variations, and is fluctuating from hundred to several hundred years interval. The potential factor causing 11 year periodicity in the varved diatomite is sunspot cycle, which varies from 9 to 13 years. As the pure diatomite of the Hiruzen-bara formation is a highly sensitive record of the lake environments in the past, the dominant periods obtained from microscopic measurement as well as image analysis demonstrates the time series fluctuations of diatom blooming, which is most likely affected by climatic change due to periodic solar activity, even masked by other non-periodic environmental changes.View full abstractDownload PDF (1584K) -
Toyoki Aoki, Katsuki Kurokawa1999 Volume 105 Issue 7 Pages 473-479
Published: July 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe T 1 and T 4 volcanic ash layers in the Sarumaru Formation around Nagano City were correlated to the Ykp ash layer in the lower Hamatsuda Formation and the SK 110 ash layer in the Uonuma Group in the Niigata region respectively. The T 1 and Ykp ash layers are crystal-vitric, and hornblende and hyperthene are dominant as heavy minerals. Glass shards are fibrously vesiculated. Chemical composition of glass shards, hornblende (mg*=0.70-0.72) and hypersthene (mg*=0.60-0.65) is coincident. The T 4 and SK 110 ash layers contain biotite as dominant heavy mineral and shape and chemical composition of glass shards are coincident. Thus, the Sarumaru Formation can be correlated to the Hamatsuda (lower Nishiyama) Formation at base and to the Uonuma Group in the Niigata region, which indicates the Sarumaru Formation to be from lower Pliocene to lower Pleistocene (about 3.9-1.6 Ma) in age.View full abstractDownload PDF (1577K) -
Hiroki Hayashi, Yukio Yanagisawa, Noritoshi Suzuki, Yuichiro Tanaka, T ...1999 Volume 105 Issue 7 Pages 480-494_1
Published: July 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSFor the purpose of refining Neogene microbiostratigraphic time scale useful for dating marine strata distributed in and around Japan, studies were undertaken on middle and late Miocene marine and terrestrial sedimentary sequences distributed in the Shimokurosawa district, Ichinoseki City, Iwate Prefecture, Northeast Japan. These sequences are divided into three formations in ascending order ; the Shimokurosawa (largely consisting of sandstone and granular conglomerate, interbedded with tuff layers), the Kamikurosawa (sandstone with tuff interbeds), and the Genbi (consisting characteristically of welded tuff accompanied by some sandstone and granular conglomerate beds) Formations. The Shimokurosawa Formation is partial overlain unconformably by the Kamikurosawa Formation and the latter is in turn unconformably overlain by the Genbi Formation.Planktonic foraminifera, calcareous nannofossil, diatom and radiolarians were detected successively from the Shimokurosawa and Kamikurosawa Formations. These Formations are correlatable with planktonic foraminiferal zones from N. 10 to N. 14 of Blow (1969), CN 5 a to CN 5 b calcareous nannofossil zones of Okada and Bukry (1980), NPD 4 Bb to NPD 5 C diatom zones of Yanagisawa and Akiba (1998), and the radiolarian Eucyrtidium inflatum A to Lychnocanoma magnacornuta zones of Motoyama and Maruyama (1998).View full abstractDownload PDF (2426K) -
[in Japanese], [in Japanese], [in Japanese]1999 Volume 105 Issue 7 Pages 496-507
Published: July 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThis paper describes conformable relationship between the Mizuyagadani and Sorayama Formations in the Fukuji area, Hida-gaien Tectonic Zone, and occurrence of Middle Permian fusulinids from the matrix of limestone conglomerate of the Sorayama Formation.The Mizuyagadani Formation consists mainly of tuffaceous clastic rocks, sandstone and mudstone, whereas the Sorayama Formation is composed mainly of mafic to intermediate pyroclastic rocks. Field observations of the boundary strata between the two formations exposed in the Iranodani Valley strongly indicate the conformable relationship. The reasons are as follows ; 1) no faults exist between the two formations, 2) the Mizuyagadani Formation is stratigraphically lower than the Sorayama Formation, since the sedimentary structures observed in the Mizuyagadani Formation indicate northward facing, 3) bedding planes of the two formations are parallel to subparallel to each other, 4) the Mizuyagadani Formation is intercalated with mafic tuff layers, and felsic tuff of the Mizuyagadani Formation contains many basaltic volcanic fragments similar to the basalts of the Sorayama Formation, and 5) lithology between the two formations is gradual change.Middle Permian fusulinids (Nankinella sp., Parafusulina sp. aff. gigantea and Russiella pulchra) are found from the matrix of conglomerate in the Sorayama Formation along the Kashiatedani Valley about 1 km east of the Iranodani Valley. The age of the sedimentation of the Sorayama Formation is regarded as of the same age of fusulinids, because the felsic to intermediate tuffaceous materials similar to the matrix of conglomerate fill chambers of the most of fusulinid shells remains.View full abstractDownload PDF (3095K) -
Makoto Ito1999 Volume 105 Issue 7 Pages 508-520
Published: July 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSA fundamental framework of the concept of sequence stratigraphy is discussed in this paper. Development of a depositional sequence is interpreted to be controlled by interaction between relative changes in sea level and sediment supply. Transgression-and-regression cycles and changes in paleowater depth are also a result of the two major controls, but are commonly misinterpreted to be equivalent to relative changes in sea level. The interaction of relative changes in sea level and sediment supply also control spatial variation in the onset of a regressive highstand deposit. This indicates that a maximum flooding surface is not necessarily synchronous. Variation in sediment supply is commonly estimated based on sedimentation rates. However, sedimentation rates are a result of aggradational stacking of deposits and are, in general, controlled by subsidence rates rather than only by sediment supply. Detailed identification and interpretation of depositional facies in stratigraphic successions seem to be critical to predict spatial and temporal variations in sediment supply in a sedimentary basin.View full abstractDownload PDF (2363K) -
Yasuhiko Makino, Takahiro Masuda, Gen Matsumoto, Kazuma Fujimagari1999 Volume 105 Issue 7 Pages XIII-XIV
Published: 1999
Released on J-STAGE: November 26, 2010
JOURNAL FREE ACCESS
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