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Volume 64, Issue 1
Displaying 1-11 of 11 articles from this issue
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Tsunemasa Saito1999 Volume 64 Issue 1 Pages 2-15
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSBased on the study of magnetic lineations in normal to active spreading centers of the world's ocean basins, a time scale of geomagnetic reversals was proposed by Heirtzler and others (1968) for the Cenozoic and late Cretaceous using the polarity time scale then known for the last 3.5Ma. Since the accuracy of such a polarity time scale can be refined by improved methods of measuring the distance of magnetic anomalies from axis of the ocean ridges, the geomagne tic reversal time scale has served for the past three decades as the most important correlation standard for biostratigraphic events occurring in various microfossil groups. A review is herein presented with regard to the methodology leading to the establishment of the most refined version of geomagnetic reversal time scale by Cande and Kent (1995), currently referred to as CK 95, and a correlation chart of datum events of diatom, radiolarians, calcareous nannoplankton and planktonic foraminifera, useful for dating Japanese Neogene sediments, is constructed relative to this new CK 95 time scale.View full abstractDownload PDF (1010K) -
Neogene and Quaternary stratigraphy of offshore Joban based on calcareous nannofossilsKoji Kameo, Tokiyuki Sato1999 Volume 64 Issue 1 Pages 16-27
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSThis paper deals with a recent summary of calcareous nannofossil biostratigraphy and an example of biostratigraphic application. According to recent studies of nannofossil biostratigraphy, a total of 60 calcareous nannofossil datums and bioevents can be available for the Neogene and Quaternary. Newly proposed bioevents based on size variations of Reticulofenestra coccoliths are introduced.
Calcareous nannofossils in the exploratory wells in offshore Joban were examined and two major hiatuses were identified in the Miocene sequences, indicating relative sea level drops during the Neogene.View full abstractDownload PDF (796K) -
Advances in biostratigraphic resolutionIsao Motoyama1999 Volume 64 Issue 1 Pages 28-39
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSDuring the last decade, the Neogene radiolarian zonation of Japan has been greatly improved by combination of biostratigraphic studies from both onshore sections and offshore deep-sea cores. This improvement is achieved by advancement of knowledge on taxonomy, the nature of evolutionary lineages, and the paleomagnetic dating of biostratigraphic events. The biostratigraphic framework established here consists of three zones of the tropical area for Lower Miocene and 14 zones and subzones of the subarctic area for Middle Miocene to Pleistocene. These zones provide an average age resolution of about 1.6 m.y. between 16 and 7Ma and about 0.8 m.y. between 7 and 2Ma. The Lower Miocene radiolarian biostratigraphy of Japan is poorly known due to a lack of good reference sections.
These biostratigraphic results revealed that Neogene radiolarian assemblages of Japanese oil-field belong to the subarctic biogeographic province of the North Pacific rather than temperate one. However, due to the presence of many undescribed species and few quantitative assemblage data, details of radiolarian ecological and paleoenvironmental aspects of the Neogene of Japan are not known. Characterization of radiolarian assemblages and paleoenvironmental interpretation will be a considerable subject on the Japanese Neogene in future.
The lower limit of the Eucyrtidium inflatum Zone is modified herein.View full abstractDownload PDF (925K) -
Examples from the Neogene in HokkaidoShiro Hasegawa1999 Volume 64 Issue 1 Pages 40-48
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSBiostratigraphic correlation using benthic foraminifera is discussed in a paleoceanographic point of view. Based on the compiled data on the geographic distribution of shallow-water benthic foraminifera during the Mid-Neogene climatic optimum (MNCO), the coastal seas of the Northwest Pacific at around 16Ma are divided into four paleobiogeographic provinces; subtropical, warm temperate, mild temperate, and cool temperate.
A similar pattern of thermal gradient is recognized in the transition period between the MNCO and the following cooler stage (early Middle Miocene), though each province shifted southward compared with those in the MNCO. This biogeographic trend is a useful guideline to test the validity of inter-regional correlation.View full abstractDownload PDF (689K) -
Akiko Obuse1999 Volume 64 Issue 1 Pages 49-62
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSThe Takinoue Formation and its correlative strata in the central part of Hokkaido are late Early to early Middle Miocene in age and represent a major transgressive phase significant for the regional sedimentary history. They yield characteristic fauna and flora which mark regional warming, and the fossil flora are correlated to the Daijima-type flora. This paleoclimatic signature has been used for subsurface correlation by means of palynological analysis. This paper discusses pollen assemblages from those strata to elucidate their latitudinal changes which will serve as a more detailed template for biostratigraphic interpretation of Miocene pollen assemblages in the middle to high latitude of the northwest Pacific region.
The pollen assemblages from the studied sections are generally dominated by broad-leaved deciduous taxa as well as conifers, with only minor presence of broad-leaved evergreen taxa. This composition implies temperate paleovegetation. There is a clear trend among them that taxa indicative of relatively warm paleoclimate decrease gradually toward the north within Hokkaido. Considering that the coeval pollen assemblages in northernHonshu to the south are composed mainly of broad-leaved evergreen and deciduous taxa, the trend observed in Hokkaido makes a part of overall latitudinal trend of Miocene paleovegetation along the northwestern Pacific coast.View full abstractDownload PDF (1079K) -
Kozo Uto, Osamu Ishizuka1999 Volume 64 Issue 1 Pages 63-71
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSCurrent situation and future possibility of the K-Ar and 40Ar/39Ar dating methods are reviewed focusing their utilization to the Tertiary volcanic rocks. As Tertiary volcanic rocks in general are not completely free from weathering and alteration, special attention should be made in choosing appropriate samples for age analyses. K-Ar and 40Ar/39Ar analytical results are shown for two contemporaneous rocks of Middle Miocene age, one is a porphyritic intrusive rock with holocrystalline groundmass and the other is an extrusive lava with glassy groundmass. The former gives concordant K-Ar and 40Ar/39Ar ages, while the latter shows considerably younger K-Ar and 40Ar/39Ar total gas ages with the obviously disturbed 40Ar/39Ar age spectra in the low temperature fractions. These results suggest that holocrystalline rocks are preferable to glassy rocks in K-Ar and 40Ar/39Ar dating, because glass tends to easily loose the accumulated radiogenic 40Ar not only by decomposition but also by hydration. Accurate and precise age determinations can be achieved by the 40Ar/39Ar incremental heating experiments along with the age spectrum and isochron interpretations. Total fusion 40Ar/39Ar dating for single to a few grains of fresh K-bearing phenocrysts like biotite, sanidine and plagioclase is also useful in knowing the ages for glassy and/or altered rocks. Multiple analyses on such mineral separates ensure the reproducibility of the analyses and reduce the analytical uncertainty by statistical treatments. Systematic 40Ar/39Ar studies are now underway to construct the accurate and precise tectonic history of the Japanese island arc.View full abstractDownload PDF (664K) -
Susumu Kato, Takanori Nakano1999 Volume 64 Issue 1 Pages 72-79
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSStrontium isotopic studies were made on Cenozoic formations in Japan in order to demonstrate the applicability of Sr isotope stratigraphy for petroleum exploration. The conclusions are summarized as follows:
1) Sr isotope stratigaraphy using calcareous foraminiferal tests is a powerful method for the dating of Early Oligocene to Recent marine sediments.
2) This method has several advantages over biostratigraphic methods because only small amounts of calcareous foraminifera, which are benthonic and planktonic speicies with a long range, can be used for analysis.
3) Sr isotope stratigraphy in combination with well data, including microfossils and physical well logs, promises to be a tool for high resolution stratigraphic analysis.
4) Abundant and characteristic species with relatively good preservation shoud be measured to eliminate dropped foraminifera from shallower depth intervals.
5) Continuous and systematic measurements ensure the reliability of Sr isotope ages and the detection of the isotopic alteration of samples.View full abstractDownload PDF (417K) -
Katsuki Kurokawa1999 Volume 64 Issue 1 Pages 80-93
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSCorrelation of the Nanatani to Uonuma Formations of 13Ma-1Ma in the Niigata region on the Sea of Japan side was comprehensively investigated using subaqueous tephra marker layers. The examined areas are the Sado Island, Nishiyama-Chuo Oil Field, Niitsu-Shitada Hills, Higashiyama-Uonuma Hills, Hachikoku Oil Field, Yoneyama region, Higashikubuki Hill, Arai region and Nishikubiki region. The tephrostratigraphical investigation was proved to be effective especially in the sedimentary basin prevailing marked contemporaneous heterotopic facies relations from fluvio-lacustrine to bathyal environments as in the Niigata basin. The age estimation of the predominant ash layers was also attempted based on the correlation of widespread ash layers to those in the Himi, Tokai and Kazusa Groups, and on the data of the magnetostratigraphy and diatom and nannofossil zones. The shallow marine to fluvio-deltaic environments (the Uonuma Group) were appeared initially in the southern Higashikubiki and the Uonuma Hills in 2.4-2.2Ma, and the shallow facies progressively extended toward the Nishiyama-Chuo Oil Field in 2.2-1.0Ma.View full abstractDownload PDF (1457K) -
Takashi Tsuji, Yuichiro Miyata, Masaru Nakamizu1999 Volume 64 Issue 1 Pages 94-106
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSCyclic lithologic changes in sediments can be used a chronometer spanning 1/2 day through 100, 000 of years in the geological column. Here we reviews some examples of cyclic sediments, related to tidal currents, seasonal changes, and glacio-eustacy. Particular attention is paid to the oxygen isotope study of turbidites of the Otadai and Umegase Formations drilled through by the study well TR-3, Boso Peninsula. The data clearly demonstrate that the sedimentation of turbidites was closely related to glacio-eustatic changes.
All these examples of sediment cyclicity are controlled by constant, cyclic movements of astronomical bodies. Therefore, their signatures in sediments should be very stable through time. For this reason, each astronomically-induced cyclicity in sediments represents a definite time interval, which is useful for high-resolution chronostratigraphy. For example, fluctuations in oxygen isotope data from deep-sea pelagic sediments can be interpreted as an end result of astronomically-induced cyclicity of various origin. Recognition of these cyclicities provides a tool for sequencial dating of the sediments. This article reviews the sequencial dating of the TR-3 by determining the interval sedimentation rates. For this calculation, TR-3 oxygen isotope records were correlated to those of DSDP Site 607 which were well interpreted in terms of the astrochronologic method.View full abstractDownload PDF (1212K) -
Hisatake Okada1999 Volume 64 Issue 1 Pages 107-109
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSDownload PDF (217K) -
Masao Hayashi1999 Volume 64 Issue 1 Pages 110-111
Published: 1999
Released on J-STAGE: March 27, 2008
JOURNAL FREE ACCESSDownload PDF (129K)
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