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Volume 41 (1987)
- Issue 6 Pages 297-
- Issue 5 Pages 253-
- Issue 4 Pages 205-
- Issue 3 Pages 151-
- Issue 2 Pages 81-
- Issue 1 Pages 1-
Volume 41, Issue 4
Displaying 1-7 of 7 articles from this issue
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Toshikazu SUZUKIArticle type: Article
1987 Volume 41 Issue 4 Pages 205-220a
Published: July 25, 1987
Released on J-STAGE: June 06, 2017
JOURNAL OPEN ACCESSThe Asso Formation of the Miocene Tanabe Group comprises thick conglomeratic sediments in the northern marginal part. This article deals with the sedimentological characteristics and sedimentary environments of these sediments. The sediments in Member Alt which occupies the lower part of the Asso Formation, is classified into 5 lithotypes, namely lithotypes A, B, C, D and E. Lithotype A consists of mudstone with coal seams and coal flakes. Lithotype B consists of alternation of conglomerate and mudstone. Lithotype C consists of thick-bedded conglomerate accompanied with thin mudstone intercalations. Lithotype D consists of massive conglomerate without mudstone intercalations. Lithotype E is characterized by stratified conglomerate with sandy matrices. Conglomerates in lithotypes B, C and D show no clear laminations and internal stratifications, and are composed of subangular gravels and muddy matrices, showing a distinctive contrast to conglomerates in lithotype E. In Member A_1, distinctive three fan-shaped sedimentary bodies, which are composed of lithotypes A, B, C and D, can be recognized. Each body shows the general tendency of fining stratigraphically upward and laterally away from the apex. That is, within each sedimentary body, lithotype D is developed at the basal part and the apex of the fan. Away from lithotype D, lithotypes C, B and A are distributed in this order vertically and laterally. The paleocurrent system, which are deduced from clast-fabrics of conglomerates, comprises three radially dispersing flow systems. It is worthy to note that lithotype D develops at the apex of each dispersing system. At the stage of deposition of Member A_1; the closed and stagnant sea area was existed in the study area. This closed sea was separated from the open sea by a presumable barrier complex, and in the back-barrier area mud and coaly materials were deposited quietly. From the land area situated to the north, large amount of gravels were transported into this closed sea, and dispersed radially. The intermittent supply of gravels resulted in the alternation of conglomerate and mudstone. The conglomeratic sediments of Member A_1 had been deposited as marginal gravels of Tanabe sedimentary basin, under the influence of upheaval movement in the hinterland and of the gradual transgression in the sedimentary basin.View full abstractDownload PDF (2790K) -
Katsuki KUROKAWA, Yusuke YAJIMA, Makoto KABA, Hideru MAKINO, Katsuya T ...Article type: Article
1987 Volume 41 Issue 4 Pages 221-230a
Published: July 25, 1987
Released on J-STAGE: June 06, 2017
JOURNAL OPEN ACCESSThe Ashio Belt in the Oshirakawa area consists of four sedimentary units; (I) the Kuromatagawa chert-black shale unit (500-600 m), (II) the Kakinoki shale-sandstone alternation unit (600-800 m), (III) the Irihirose greenstone-chert unit (200-300 m) and (IV) the Oshirakawa pebbly shale-greenstone-chert unit (1500-2000 m) in ascending order of apparent sequence. The Kuromatagawa chert-black shale unit is dominantly composed of bedded and massive cherts, interbedded by black shale. The cherts are occasionally gradational to black shale. This unit is folded and thermally metamorphosed by Cretaceous granites. The Kakinoki shale-sandstone alternation unit refers to the shaly flysh accompaning basaltic greenstones. The lower half of the Irihirose greenstone-chert unit comprises basaltic greenstones, and the upper half is dominantly composed of bedded and massive cherts, characterized by the occurrence of the bedded red cherts. The Oshirakawa pebbly shale-greenstone-chert unit occupies the upper half of the surveyed area. Olistostrome facies are predominant in the unit with olistoliths of siliceous sandstones, cherts, greenstones and limestones. Middle Permian fusulinids such as Neoschwagerina and Chusenella were found in the limestone olistoliths. Besides, laterally extending strata of cherts, greenstones and sandstones are intercalated. Some greenstones accompany limestones and skarns at their top. Layered sandstones commonly contain 5-15% potash feldspar, while in sandstone olistoliths, they are scarcely found. The early Jurassic radiolarian assemblage (the Parahsuum simplum assemblage) (YAO, 1984) was detected from the layered bedded chert situated at the middle horizon of the unit, interbedded in the olistostrom.es. From the Kuromatagawa chert-black shale unit, the middle Permain to late Triassic conodonts were reported. Thus, the Ashio Belt in the Oshirakawa area is composed of the piles of the sedimentary bodies of different facies and ages, at least from middle Permian to early Jurassic. These apparent successions are almost similar to those in the Tanba and northern Mino Belts in southwest Japan, and the middle Jurassic might also be expected in the surveyed area.View full abstractDownload PDF (1685K) -
Case study in Lake BiwaYoshio INOUCHIArticle type: Article
1987 Volume 41 Issue 4 Pages 231-241
Published: July 25, 1987
Released on J-STAGE: June 06, 2017
JOURNAL OPEN ACCESSA method to estimate mass sedimentation rate is proposed in the following procedure; 1. drafting of isopach map of sediment based on the depth of specific reflector in acoustic (UNIBOOM) record, 2. making vertical prone of standard water content in sediments at selected point(s) in the area, 3. conversion of the data of water content into those of dry weight and cumulative dry weight of sediments, 4. age determination of the critical reflector, (in general, some of reflectors are age-known tephras.) 5. making a standard curve of " thickness versus sedimentation rate" through dividing cumulative dry weight in each depth by sedimentary age of the reflector, 6. conversion of thickness of sediments into sedimentation rate by using that curve. In Lake Biwa, depths of reflectors beneath the bottom coincide with those of the top of corresponding sediment layers which contain more than 1% of sand. Consequently, thickness of sediment can be caluculated easily based on the acoustic record. Vertical profile of water content is obtainde using drilled samples in the area. It is converted into that of dry weight and cumulative dry weight profiles, assuming that specific gravity of sediment grains to be 2.65 and that all pores in sediments are filled with water. In Lake Biwa, the top of Kikai-Akahoya tephra (K-Ah; aged ca. 6300 Y. B. P.) makes a good reflector. Mean sedimetation rate in the whole area of Lake Biwa, obtained by this method, is 38.2 mg/cm_2/year. Comparison between the results and the rates by 210Pb, 137Cs and specified tephra methods shows good correlation, with a few exceptions. The result of isotope method show a little smaller values than those of acoustic method. There are several factors to make an error in this methd. They are; 1. difference between sediment thickness obtaind through acoustic record and the real thickness, caused by vertical change of acoustic velocity (This is, however, negligible in Lake Biwa.), 2. areal difference of water content, 3. difference in degrees of compaction with time and depth, 4. age determination error (As for 14C dating, they are within a few percent.), 5. sporadic sedimentation, such as turbidite, 6. change of sedimentation rate in recent years caused by the anthropogenic deformation of surrounding land area. As there are many active and non active volcanoes in Japan, many volcanic ash seams can be found in the lake and shallow sea sediments. Consequently, this method will be applied in various lakes and shallow sea areas with muddy sediments.View full abstractDownload PDF (1244K) -
Osamu INAWASHIROArticle type: Article
1987 Volume 41 Issue 4 Pages 242-243
Published: July 25, 1987
Released on J-STAGE: June 06, 2017
JOURNAL OPEN ACCESSDownload PDF (840K) -
Mitsuru NAKAGAWA, Nirei NAKANOArticle type: Article
1987 Volume 41 Issue 4 Pages 244-247
Published: July 25, 1987
Released on J-STAGE: June 06, 2017
JOURNAL OPEN ACCESSDownload PDF (536K) -
14C age of the Quaternary deposits in Japan (165)Kiyohara HOSIMI, Hirosi MORIOKAArticle type: Article
1987 Volume 41 Issue 4 Pages 248-250
Published: July 25, 1987
Released on J-STAGE: June 06, 2017
JOURNAL OPEN ACCESSDownload PDF (441K) -
14C Age of the Quaternary Deposits in Japan (166)Ikuo ONISHI, Saburo AKAGI, Tamaki MIYOSHIArticle type: Article
1987 Volume 41 Issue 4 Pages 251-252
Published: July 25, 1987
Released on J-STAGE: June 06, 2017
JOURNAL OPEN ACCESSDownload PDF (293K)
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