Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
Volume 93 , Issue 1
Showing 1-7 articles out of 7 articles from the selected issue
  • Hiroshi MACHIDA, Fusao ARAI, Byong-Sul LEE, Hiroshi MORIWAKI, Toshio F ...
    1984 Volume 93 Issue 1 Pages 1-14
    Published: February 25, 1984
    Released: October 13, 2010
    JOURNALS FREE ACCESS
    A trachytic tephra fall deposit, the Ulreung-Oki ash, was first discovered at the Torihama archaeological site, in the northern Kinki district, where it forms whitish ash layer in strata bearing artifacts of the earliest Jomon ceramic culture. Occurrence of alkali feldspar and specific amphibole (probably kaersutite) clearly shows that this tephra is alkalic in composition. Correlatives of this tephra have been recognized at many localities in central Honshu and in piston cores from adjacent to Ulreung island to Oki bank. The grain-size distribution clearly suggests the source to be Ulreung volcano.
    This paper mainly deals with late Quaternary eruptive history of Ulreung volcano based on tephra studies in Ulreung island.
    Ulreung or Dagelet island is a large Quaternary stratovolcano situated in the west Japan Sea, 130km off the eastern coast of the Korean peninsula. Though the volcano has been considerably dissected, it has a remarkable caldera with a longer diameter of 3.5km and a central cone. The caldera has had a series of silicic tephra eruptions, forming a sequence of airfall and airflow deposits in late Quaternary. At least seven coarse-grained airfall units are discriminated and named from upper to lower as U-1, U-2, …and U-7.
    Approximate dating of these tephras is possible because the two time-marker tephras of Kyushu origin are found within the soils between the pumice falls: the Aira-Tn ash (AT, 21, 000-22, 000 YBP) between U-4 and U-5, and the Kikai-Akahoya ash (K-Ah, 6, 300 YBP) between U-1 and U-2.
    These Ulreung tephras are trachytic in composition, containing considerable amounts of alkali feldspar, kaersutite, biotite and clinopyroxene as phenocrysts. Chemical composition of pumiceous glass for these tephras is completely different from that of such subalkalic tephras as AT and K-Ah, etc. However, compositional variation from layer to layer is too small to be distinguished each other.
    In the late Quaternary age before ca. 22, 000 YBP, many plinian type eruptions took place producing such pumice falls as U-5, 6 and 7, which are not well preserved in the island due to erosion but in abyssal sediments in the Japan Sea. The three pumice falls, U-2, -3 and -4, recognized between the AT and K-Ah ashes were respectively formed by plinian, phreato-plinian and plinian eruptions. The last two are associated with pyroclastic flow deposits. This multicyclic explosive volcanism should result in the formation of caldera.
    Of the younger three tephras, U-2 seems to represent the largest recent eruption of the caldera. Distribution and stratigraphic position of this tephra indicates that U-2 can be correlated with the U-Oki ash. Three radiocarbon dates of ca. 9, 300 YBP were obtained at the Torihama site and south port of Osaka for this ash. U-Oki or U-2 is used as an excellent time-marker in analyzing paleo-sea level and paleo -oceanographic environments in the Japan Sea.
    The youngest activity of Ulreung volcano took place after 6, 300 YBP, forming the U-1 scoria falls, Al-bong cinder cone and lava flows.
    Download PDF (2565K)
  • Kazutaka IWASAKI
    1984 Volume 93 Issue 1 Pages 15-29
    Published: February 25, 1984
    Released: December 22, 2010
    JOURNALS FREE ACCESS
    Residual mass curves of annual summer and winter rainfall are examined from 52 widely spread stations in Australia to clarify the spatial difference of long-term rainfall trends. The calendar year is not used to compute the annual rainfall, because the calendar year divides a summer into two. The annual rainfall is defined as the total rainfall of 12 months from December of the year before to November. The summer rainfall is defined as the total rainfall during the 3 months of December, January and February within the defined annual cycle. The winter rainfall, of June, July and August. The quantity plotted in the graphs is given by,
    Xi=100×∑in=1(rn-r/ra)-C
    where rn. is the annual, summer or winter rainfall for the n th year of the record and the mean annual, summer or winter rainfall I has been computed for the standard 60-year period 1920-1979. ra is the mean annual rainfall. By dividing by the mean annual rainfall, the degree of contribution of summer and winter rainfall to annual rainfall can be made clear. The constant C is the summation extending from the beginning of the record to 1919,
    C=100×∑tn=1(rn-r/ra)
    where t is the years from the first record to 1919.
    Residual mass curves are primarily classified into two types:
    Type S: Summer rainfall curve is more similar to annual rainfall curve than winter rainfall curve (Fig. 2-a).
    Type W: Winter rainfall curve is more similar to annual rainfall curve (Fig. 2.b). Each type is classified into sub-types (Fig. 3).
    Type Se: The curve of annual rainfall shows downward trend in the former half of this century. This downward trend continues till 1960's in the region of Se-I. The curve shows upward trend in the latter half of this century in the region of Se-II (Figs. 4-a, b).
    Type Sw: The curve shows upward trend from the end of the 19 th century up to 1920's, then downward trend up to 1960's. Each curve also shows short-term fluctuation as well as long-term trend (Fig. 4-c).
    Type We: The curve shows upward trend in the 19 th century. This trend continues up to 1940's or 1950's in the regions of We-Ia and We-Ib, then the curve turns downward. In the region of We-Ib, downward trend is shown in 1920's and 1930's. The curve shows downward trend in the region of We-II in the former half of this century, then turns upward (Figs. 5-a, b).
    Type Ww: The curve shows downward trend in the 19th century. Upward trend shows in the former half of this century in the region of Ww-I, downward trend again since 1950's. The curve shows upward trend in the beginning of this century then turn downward in the middle of this century, upward again in 1960's and 1970's in the region of Ww-(Figs. 5-c, d).
    It is assumed that the east-west difference in long-term trends of rainfall is explained by the location of the deeper trough among the subtropical anticyclones presented in monthlymean sea-level pressure charts, and the south-north difference in the region W is explained by the difference of the origin of vapor shown in the precipitable water (1000-500 mb) distribution map (Figs. 6, 7, 8).
    Download PDF (2398K)
  • Ryoichi KOUDA
    1984 Volume 93 Issue 1 Pages 30-53
    Published: February 25, 1984
    Released: October 13, 2010
    JOURNALS FREE ACCESS
    Veins, veinlets, and networks occur in and around stratified Kuroko deposits for which the vein-type mineralization is genetically important. It is necessary for the exhalative sedimentary hypothesis of Kuroko deposits to be accompanied by the solution-feeding pass under beneath the stratified massive ore. On the contrary, it was also necessary for the epigenetic replacement hypothesis of them to be associated the veinlets in the hanging wall. This key evidence shows that the mineralization occurs in the hanging wall of stratified massive ore, so that the massive ore itself was considered to be the result of replacement in the underground. According of the sedimentary hypothesis, it is, however, explained that the post-Kuroko mineralization took place after the time of deposition of stratified massive ore which is sedimentary.
    A lot of observations in the Fukazawa Kuroko deposits, Northern Akita Prefecture, depict the various mode of occurrence of the vein-type mineralization in and around the stratified Kuroko deposits. The distributions of massive and vein-type ores are subdivided as follows:
    1) Stratified massive gypsum-anhydrite-(pyrite) ore in the footwall.
    2) Pyrite-quartz veins, copper-rich and zinc-poor veins, and networks of veinlets in the footwall with a strong silicification.
    3) Zinc-rich veins and networks of veinlets in the footwall. They are silicified weaker with clay alteration.
    4) Stratified massive pyrite ore in the bottom of the stratified sulfide bed.
    5) Copper-rich and zinc-poor massive ore in the lower and upper part of the stratified sulfide beds.
    6) Zinc-rich massive ore in the most part of the stratified sulfide beds. Sedimentary textures are most excessive in this mode.
    7) Massive barite lens in the upper part of the stratified sulfide beds.
    8) Hematite-bearing chert lens or veinlets in the hanging wall.
    9) Veinlets in the hanging wall. The boundaries between the different modes of massive ores are always clear and sharp.
    The vein-type mineralizations in the footwall continue about 100 meters to 200 meters long or more to the lower part. They are divided into two main modes; copper rich and zinc-rich. Copper-rich one belongs to normal-type veins or networks of veinlets which configuration shows zonal structures and drusy pipes. Zinc-rich one is more “massive” and compact which has no zonal structure in the internal. The distributions of the two are separated into the central copper-rich and the marginal zinc-rich parts of the stratified extent. The stratified sulfide beds include some powdery are or lenticular copper-rich veins. The powdery “intrusion” of copper-rich are to the zinc-rich massive bed connects with lower and upper part of the massive copper-rich are in part.
    Zinc-rich fragments of massive are and zinc-rich and copper-rich veinlets are frequently observed in the hanging wall, especially in the basaltic lava. Copper-rich fragments also occur in the hanging wall a little, but are rare in the basaltic lava and post-basaltic lava sediments.
    Download PDF (5126K)
  • [in Japanese]
    1984 Volume 93 Issue 1 Pages 54
    Published: February 25, 1984
    Released: October 13, 2010
    JOURNALS FREE ACCESS
    Download PDF (206K)
  • [in Japanese]
    1984 Volume 93 Issue 1 Pages 55
    Published: February 25, 1984
    Released: October 13, 2010
    JOURNALS FREE ACCESS
    Download PDF (186K)
  • [in Japanese]
    1984 Volume 93 Issue 1 Pages 56
    Published: February 25, 1984
    Released: October 13, 2010
    JOURNALS FREE ACCESS
    Download PDF (553K)
  • H. MACHIDA, H. MORIWAKI
    1984 Volume 93 Issue 1 Pages plate1-plate2
    Published: February 25, 1984
    Released: October 13, 2010
    JOURNALS FREE ACCESS
    Download PDF (965K)
feedback
Top