The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 61, Issue 712
Displaying 1-3 of 3 articles from this issue
  • Saburo IWASA
    1955 Volume 61 Issue 712 Pages 1-18
    Published: January 25, 1955
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    From lithological characteristics the Isizawagawa group, the principal oil-bearing strata in Honjo and its environs in Akita Prefecture, is classified into four formations as shown in Figure 1., Biostratigraphical studies were concentrated on these formations based upon the smaller Foraminifera., About 250 species of benthonic Foraminifera were discriminated in the 288 samples taken from the area., From the foraminiferal assemblages and stratigraphic distribution of some of the characteristic forms, a total of four zonules and 11 subzonules (Figure 3) were distinguished within the formations recognized., These zonules and subzonules have uniform distribution within the area studied (Figure 5)., The foraminiferal fauna of the Isizawagawa group indicates a cool thermal condition contrary to the underlying Sugota formation, which contains a fauna of warm thermal waters., From the faunal evidence and geology of the area, it is considered that the major transgression which resulted in the deposition of the Isizawagawa group, commenced with the deposition of the Toridame formation; this formation occupies the lowest position in the said group., From the sequence of the foraminiferas it is inferred that the transgression reached an inundation phase during the Tate formation., A gradual regressive phase was initiated towards the latter part of Tate time., The foraminiferal assemblages in the basal part of the Minaminomata and Osawa formations include a few reworked, shallow water species of Foraminifera, which have distorted and water worn shells., From such evidence it is inferred that there were two orogenic movements within the geosyncline during the regressive phase, at least in the area studied.,
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  • Motoki EGUCHI, Rikii SHOJI
    1955 Volume 61 Issue 712 Pages 19-29
    Published: January 25, 1955
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    During the course of the present study, we have recognized the following three important facts : 1) In six areas where two workable coal seams are developed, the lower of about one meters thick and 20∼30 meters above the basement, and the upper about two meters thick and 15∼20 meters above the lower, and the whole about 200 meters distant from a buried hill, the following facts were confirmed., The strata underlying the lower coal seam, that between the lower and upper coal seems, the coal seams themselves and also the partings within the coal seams all tend to become thinner as the buried hill is approached where these strata abut against the buried hill they follow the general inclination of the hill, but thin out completely at the top of the hill., 2) From the fact that blocks of amphibolite and amphibole mica schist as large as 20×10×3cm in size are abundantly contained in the above mentioned sequence in areas neighboring the buried hill, it is inferred that they were derived from the basement which consists of similar rocks during sedimentation., It is noteworthy that the quantity and size of the blocks both diminish rapidly as the distance from the buried hill increases., The calcite crystals found embedded in the coal seams and shales above and below are considered to be recrystalized weathered products of the amrhibolite and amphibole mica schists above mentioned., 3) From the paleogeological map constructed from observations in coal pits, numerous bore-core data and seismic prospecting, it is confirmed that the basement in the present district consists of at least two buried hills, each trending in NW-SE-direction, and separated from one another at their broadest eastern extremity by 3 to more than 6 kilometers., The promontories of these hills at their eastern extremities measures from about or to more than 500 meters., The coal seams above referred to belong to the Hanakawa formation and were deposited in these inlets or small bays or embayments., The respective coal seams can be traced from one basin to another, and are actually being mined., The number of cycles within the Hanakawa formation developed in each district of the Joban coal-field have been studied in detail, and the relationship existing between number of cycles for each independent field with that of other fields has been worked out to an advantageous stage.,
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  • Kunio KOBAYASHI, Teruo HIRABAYASHI
    1955 Volume 61 Issue 712 Pages 30-47
    Published: January 25, 1955
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Matsumoto Basin, situated between the Hida Ranges and the mountain ranges occupying the western margin of the Fossa Magna, is bordered by fault lines along its western margin, and is probably a structural basin., It is partially filled by rather thick fanglomeratic deposits of Pleistocene Epoch., Fluviatile boulders on the mountain have been called "Yamajari" or "Mountain gravel" in Japan, and have been attributed by NAKAMUMA (1927) to represent a past pluvial or torrential deposit., HOMMA (1927) recognized mountain gravels on the eastern side of the Matsumoto Basin., The Mountain gravels are named "Omine gravels" or "boulders" in strict sense, and among them are found some that attain three meters in diameter; these are residual., The Omine boulders are composed mainly of granitic rocks and have been considered to be derived from the Hida Ranges by remote transportation., The possible derivation of these boulders from the Hida- Ranges may be an evidence that consequent streams from the Hida Ranges traversed the Matsumoto Basin., The mechanisms of transportation are suggested by the following evidences: (1) The boulders observed are almost subrounded granitic rocks measuring 3∼0., 5 meters in diameter., (2) The surface previous to the deposition are represented by small relief of the Omine erosion surface, and therefore, the stream gradient on this surface must have been considerably reduced., Therefore, without crustal movement or heavy precipitation, previous to or at the time of deposition of the Omine gravel, large boulders could not have been transported by the streams flowing over the Omine erosion surface., The deposition of boulders indicates the commencement of a new phase of stream regimen, in other words, an increase of stream gradient took place., Rapid uplift of the Hida Ranges occurred in the middle of the Pleistocene, resulting in the rejuvenation of the upper drainage of the river and an increase of the stream gradient., The scarcity of boulders exceeding one meter in diameter indicates that they have not been transported by normally flowing streams, but by some occasional and accidental floods., Although the Omine boulders may have been transported by occasional heavy rainfall, it can not be proved that their deposition was during the pluvial age., The reference of the Omine gravel to early upper Pleistocene age is from that its deposition was during the second interglacial or in the third glacial ages., From the studies on the particle size distribution of the present fan of the Takase, the writers conclude that the large boulders among the Omine gravel were transported by rapid streams, influenced by the increased gradient of the upper drainage of the river and by occasional heavy rainfalls during the rainy season (summer time) of the glacial or interglacial age.,
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