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Volume 107, Issue 1
Displaying 1-8 of 8 articles from this issue
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Katsura Yamada, Toshiaki Irizuki, Sachie Nakajima2001 Volume 107 Issue 1 Pages 1-13_1
Published: January 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe lower part of the Lower Miocene Arakida Formation, Tomikusa Group (ca. 18 Ma), central Japan, is divided into seven sedimentary facies (SF I to SF VII) : SF I, alternating beds of pebbly sandstone and mudstone ; SF II, well-sorted arkose sandstone ; SF III, muddy fine-grained sandstone ; SF IV, well-sorted medium-grained sandstone ; SF V, muddy medium-grained sandstone ; SF VI, alternating beds of sandstone and dark gray mudstone ; SF VII, massive dark gray mudstone. At least 65 ostracode species are identified in 31 samples, which are grouped into five clusters (A∼E) on the basis of Q-mode cluster analysis. These five clusters have characteristics as follows : A is dominated by inner bay species ; B contains middle deep bay species ; C is characterized by warm-water shallow species with inner to middle bay forms ; D is characterized by an increase of warm-water shallow species in upward sequence and the absence of embayment forms ; E is dominated by shallow rocky shore species. The depositional environments of the study area based on the seven sedimentary facies and five clusters are estimated in ascending order as follows : fluvial, bay coast, inner to middle bay, outer bay influenced by open warm currents, slope and offshore basin-floor in the upper bathyal zone. Two different attributes of the examined interval imply that high topographic relief of the basement existing both in the northern and southern parts of the study area led to an intermittent supply of coarse grained material into depth as well as such spatial heterogeneity of lithofacies.View full abstractDownload PDF (2146K) -
Makoto Yamasaki, Motoyoshi Oda, Kazumi Akimoto, Yuichiro Tanaka2001 Volume 107 Issue 1 Pages 15-25
Published: January 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe foraminiferal flux from the shelf edge to the slope of the East China Sea was studied through conventional and time series sediment trap experiments during 27 October to 4 November, 1995. Well preserved planktic foraminifers, poorly preserved planktic foraminifers and benthic foraminifers were observed in both types of sediment traps. Such fact indicates that these foraminifers were suspended from the surface sediments. We also found that the benthic foraminiferal species in the surface sediments at the shelf edge and the uppermost slope site were captured by the sediment trap moored at the shelf edge station, and those in the surface sediment sites from the uppermost slope to the Okinawa Trough were captured by the traps at the uppermost slope station and the upper slope station. Furthermore, based on the foraminiferal flux observation by time series sediment traps at the continental slope, we infer that a great number of foraminifers from the surface sediments were suspended by internal tides, and then some of these foraminifers reached the sediment traps through lateral transportation.View full abstractDownload PDF (1551K) -
Nao Kusuhashi, Atsushi Yamaji2001 Volume 107 Issue 1 Pages 26-40
Published: January 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSDid intra-arc deformations in SW Japan occur associated with the opening of the Japan Sea back-arc basin? To answer this question, we studied the Lower Miocene Kuma Group, central SW Japan. The Group is shown to be alluvial fan deposits. The sedimentary basin of the Kuma Group may have been formed as half grabens. The multiple inverse method was applied to mesoscale faults of the Kuma Group and detected six stresses from in situ and from tilt corrected fault-slip data. One stress state determined from the tilt corrected data is consistent with the paleostress that formed the E-W trending half grabens in the Kuma Group. One other stress is consistent with that inferred from 15 m.y. old dike swarm in this area. Accordingly, this area was subject to extensional tectonics in the Early to early Middle Miocene.View full abstractDownload PDF (2244K) -
Toshiyuki Yoshikawa, Masaki Takahashi, Toshinori Okada2001 Volume 107 Issue 1 Pages 41-45
Published: January 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSIn the eastern margin of the Ashio Mountains, Tochigi Prefecture, central Japan, middle Miocene volcanic rocks are distributed with few reliable chronological data. This paper includes newly measured whole rock K-Ar dates of the Kazamiyamada Andesite in the Utsunomiya area and the Hinata Formation in the Kanuma area. The pyroxene andesite lavas of the Kazamiyamada Andesite give 15.78±0.64, 16.61±0.84, 15.26±0.40 and 15.02±0.39 Ma, which are thought to be the eruption age. The basaltic andesite lavas of the Hinata Formation yield 16.8±2.1, 17.3±2.0, 15.6±2.2 and 15.3±2.4 Ma, and these lavas correspond to the Kazamiyamada Andesite by the lithofacies and stratigraphic evidences. This means chronologically the Kazamiyamada Andesite and the Hinata Formation are correlated to the hiatus between the Yamanouchi and Motegi Formations in the Motegi area in western part of the Yamizo Mountains. According to lithofacies and microfossil data of overlying marine beds, Motegi Formation, Nagaoka/Oya Formations in the Utsunomiya area and Fukaiwa Formation in the Kanuma area are correlated to each other.View full abstractDownload PDF (901K) -
Minoru Ikehara2001 Volume 107 Issue 1 Pages 46-63
Published: January 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Southern Ocean is known to play an important role in the global climate system, because the Antarctic cryosphere represents the largest accumulation of ice on the Earth's surface. The latitudinal migration of the oceanic fronts and sea-ice coverage in the Southern Ocean should have an influence on the surface water circulation, as well as primary productivity, heat transport, and temperature gradient. Recent paleoceanographic studies on deep sea sediments from the Southern Ocean have demonstrated the latitudinal migration of the Subtropical Convergence (STC) and Antarctic Polar Front (APF) during the glacial/interglacial cycles and the larger drop in sea surface temperatures (SST) than SST change estimation by the CLIMAP project. Paleoproductivity in the Subantarctic Southern Ocean, which is north of the present APF, increased during the glacials due to a northward shift of the circum-Antarctic biogenic silica belt and an enhanced dust input. On the other hand, the surface water south of the APF was presumably stratified due to extended sea ice coverage. The stratification of the Antarctic surface water blocked CO2 emission from the intermediate and deep waters to the atmosphere. Variations in the biological pump and stratification in the Southern Ocean surface water and its associated drawdown of atmospheric CO2 have been proposed as a forcing mechanism for the global climate changes.View full abstractDownload PDF (2499K) -
Takenori Kato2001 Volume 107 Issue 1 Pages 64-67
Published: January 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSDownload PDF (592K) -
Kazue Tazaki, Hiroaki Ishiga, Kaori Dozen, Masahide Akasaka, Ryuji Asa ...2001 Volume 107 Issue 1 Pages 68-78
Published: January 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSAn earthquake (M=7.3) hit the western part of Tottori Prefecture on the 6th October on 13 : 30, 2000. Liquefaction occurred on reclaimed lands in Tottori and Shimane Prefectures. A large amount of the boiling sands and water are found at Takenouchi industrial area and at Nishikihama. The character of the boiling sand and water were chemically, physically and mineralogically studied. High NaCl contents in the boiling sand and water correspond to pH 6-7 and high EC. The boiling sand consisting mainly of silicate minerals and feldspars, with grain size of approximately 30-40 μm at Takenouchi and 130-178 μm at Nishikihama were examined. After ethylene glycol treatment, swelling smectite and halloysite identified by XRD method. In the boiling sand crater, coccus and bacillus bacteria inhabited in yellowish-brown biofilms at Takenouchi. The microorganisms in the biofilms are capable of concentrating of heavy metals in the boiling sand crater.View full abstractDownload PDF (2844K) -
Takenori Kato2001 Volume 107 Issue 1 Pages I-II
Published: 2001
Released on J-STAGE: November 26, 2010
JOURNAL FREE ACCESSInterference colors provide one of fundamental criteria for identification of minerals in petrological studies. Therefore, it is important to have an interference color chart with reliable color reproduction and without degra dation. A computer program that pre cisely reproduces normal interference colors has been implemented (Fig.1). It synthesizes interference color charts from some standard illuminants using a colorimetric approach (Fig.2). Details of the program and the mean ings of the technical terms are described in Kato (2000). The interfer ence color chart synthesized from the CIE standard illuminant D55 corre sponding to the light from a halogen lamp through a blue CB filter is pre sented here for the petrological purpose(Fig.3)View full abstractDownload PDF (7849K)
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