著者

岩井 淳一 高柳 洋吉 中川 久夫

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.52, pp.3-15, 1961-03-27

著者

斎藤 靖二

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.62, pp.55-67, 1966-03-30

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The Paleozoic System distributed in the Setamai district, southern Kitakami massif, is classified on the ba-5is of rock facies as follows; Toyoma Formation Permian Kanokura Formation Sakamotozawa Formation ~Unconformity~ Nagaiwa Formation Onimaru Formation Carboniferous ~Unconformity~ Odaira Formation Arisu Formation Orikabe Formation The Orikabe, Arisu, and Odaira Formations are composed chiefly of "schalstein" and black slate. The acidic to andesitic pyroclastics intercalated in the Orikabe Formation indicate the former existence of volcanic activities. The Arisu Formation and the lower part of the Odaira Formation are composed mostly of andesitic pyroclastics, which decrease in thickness upwards to the middle part of the Odaira Formation. This shows that intense volcanism was periodic during deposition of those formations. The formations other than mentioned above do not show such intense volcanic activity. The Paleozoic System of this area is folded and faulted into blocks and thus their structures are complicated. The Hizume-Kesennuma tectonic line which extends in NNW-SSE direction is situated in the western part of the area and the eastern margin is defined by the grandodiorite which metamorphosed the sedimentaries in contact ther with. The most striking feature of the geology of this district is the structural differences between the Carboniferous and the Permian Systems. This unconformity was discovered by Minato (1942) at the base of the Permian Sakamotozawa Formation in the Setamai district who said that it represents the "Setamai folding" of thee Late Carboniferous. The folding axes of the Carboniferous System trend nearly N-S, whereas that of the Permian System is generally NNW-SSE in direction, being parallel with the Hizume-Kesennuma tectonic line. The Permian System is distributed in the northeastern, southeastern and central parts of the district and along the tectonic line. In the central part, in general, the Permian strata form a large-syncline, with NNW-SSE trend plunging to the south and parallel with the tectonic line. On the other hand the Carboniferous System which is restricted in distribution to the eastern side of the tectonic line, is developed on the outerside of the large-syncline. In the east of Komata it occurs in the Permian System as a block uplifted by faulting. The Orikabe Formation is distributed along the western wing of the syncline extending from Orikabe to Okuhinotsuchi in north to south direction though it is separated into several blocks by faults. The Arisu Formation is developed on the outerside of the Orikabe Formation which follows the syncline. The Odaira Formation is distributed generally farther to the outerside than the lower formations though it is directly overlain with unconformity by the Sakamotozawa Formation at the west of Mt. Odaira, and is bordered by the Onimaru Formation on its outerside. Concerning the Carboniferous System it seems that each of the formations is developed on the westward and eastward sides of the central part of the area in ascending order, and all of them are covered with unconformity by the Permian Sakamotozawa Formation. Furthermore, the Carboniferous System sometimes develops a large-anticline and gently dipping fluted homoclines, features which cannot be seen in the intensely folded Permian System. It seems that these evidences reflect not only the lithofacies but also the geologic structures of the Carboniferous System before the deposition of the Sakamotozawa Formation. The differences of the geologic structures between the Carboniferous and the Permian Systems, as mentioned above, are the results of the "Shizu folding" and the "Setamal folding" of Minato (1942). Therefore it is supposed that a large-anticline with axis of nearly N-S trend might have been formed and denuded in the Setamai district before the deposition of the Sakamotozawa Formation. The geological structures must have been fairly complicated, but concerning the details more precise investigation must be undertaken.

著者

中川 久夫 土井 宣夫 白尾 元理 荒木 裕 Hisao Nakagawa Nobuo Doi Motomaro Shirao Yu Araki 東北大学理学部地質学古生物学教室 日本重化学工業株式会社盛岡工業所 (盛岡市) 徳本寺 (東京都台東区西浅草) 長谷地質調査事務所 (仙台市)

出版者

東北大學

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 = Contributions from the Institute of Geology and Paleontology Tohoku University (ISSN:00824658)

巻号頁・発行日

vol.84, pp.1-22, 1982-03-29

被引用文献数

2

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Ishigaki-jima and Iriomote-jima are the largest two islands of Yaeyama Gunto in the westernmost part of the Ryukyu Islands. Major startigraphic units on them are pre-Eocene Ishigaki Group, Upper Eocene Miyara Group, Lower Miocene Yaeyama Group, Sonai Conglomerate of unknown age, Pleistocene Ryukyu Group and the recent coastal and fluvial deposits. The Ishigaki Group comprises the Tomuru and Fusaki Formations. The Tomuru Formation occurs in the northeastern, east central and northwestern parts of Ishigaki-jima and in the eastern part of Iriomote-jima. Rocks are glaucophane schist, graphite schist, quartz-mica schist, phyllite, green and black schists and basalt. Maximum thickness is 2100 m. The Fusaki Formation crops out in the west central to southwestern part of Ishigaki-jima and on Taketomi-Jima, a small island to the southwest of Ishigaki-jima. It consists of sandstone, shale, phyllite, chert and limestone. The measured section in the southwestern part of the island is about 400 m. No fossils have been found in the Ishigaki Group. The sedimentary rocks of the Fusaki Formation are bounded on the east and northwest by the metamorphic rocks of the Tomuru Formation, but the relation between them remains uncertain because of poor exposure along the boundary. The estimated boundaries pass through the central part of Ishigaki-jima in north direction and the northwestern part in northeast direction. In the central part of the island, the boundary extends northward to the eastern margin of the granitic intrusion, along which dunite crops out in a few places. The Miyara Group comprises the Miyaragawa and Nosoko Formations. The Miyaragawa Formation unconformably overlies the Ishigaki Group in many places of Ishigaki-jima and in a small area in the eastern part of Iriomote-jima. It consists of conglomerate, an alternation of sandstone and siltstone and limestone. The limestone is biogenic and cotains well preserved fossils of the Late Eocene age. Fossils occur also in the conglomerate, sandstone and siltstone. Thickness of the Miyaragawa Formation is about 80 m. The Nosoko Formation overlies conformably the Miyaragawa Formation and unconformably the Ishigaki Group. The Nosoko Formation is distributed mainly in the northeastern and northwestern parts of Ishigaki-jima and in the eastern part of Iriomote-jima. It consists largely of andesite, dacite and tuff breccia, but includes conglomerate and sandstone, which yielded fossils. The pyroclastic rocks of the Nosoko Formation are altered and colored green ; they closely resemble the so-called green-tuff of the Early to Middle Miocene in the mainland of Japan. However, the fossils from the interbedded conglomerate and sandstone indicate the Late Eocene age. Total thickness of the Nosoko Formation is about 400 m. Granitic rocks intrude the Ishigaki and Miyara Groups in the northwestern part of Ishigaki-jima. The rocks are biotite adamellite and biotite granite which are accompanied by biotite-hornblende-augite quartzdiorite, granodiorite, dacite and rhyolite. In contact with the intrusions, the rocks of the Ishigaki and Miyara Groups are metamorphosed into hornfels. K-Ar age of the biotite adamellite is 21 Ma. The Yaeyama Group includes the Iriomote Formation, which occupies most part of Iriomote-jima. The Iriomote Formation consists of conglomerate, sandstone and siltstone. By the predominant lithofacies, the Iriomote Formation is subdivided into seven beds ; they are called with the letters A to G, in ascending order. Among them, the bed F is characterized by coal layers interbedded with an alternation of siltstone and silty sandstone, and is named the Uchiba-narejima Coal-bearing Member. The conglomerate and sandstone yielded molluscan and other fossils. The sandstone of the bed C and G are partly fossiliferous, and in places they grade into calcarenite and shell-limestone which form small lenses. Total thickness of the Iriomote Formation amounts to 700 m. The Sonai Conglomerate is distributed in several places in the north central to western part of Iriomote-jima. It unconformably overlies the Iriomote Formation. The conglomerate consists mostly of rounded cobbles, but includes pebbles and boulders in palces. Predominant rocks of cobbles are sandstone in the northern part and limestone and sandstone in the western part of the island, most of which are derived from the Iriomote Formation. The limestone cobbles contain larger foraminifera of the Early Miocene age. Maximum thickness of the conglomerate is 80 m. The Ryukyu Group includes the Ohama Formation on Ishigaki-jima and the Sumiyoshi Formation on Iriomote-jima. The Ohama Formation overlies the Nosoko and older formations with unconformity, and the Sumiyoshi Formation overlies the Sonai Conglomerate and older formations with unconformity. Distribution of the Ryukyu Group is limited to the area less than 70 m above sea level. In the inland area of Ishigaki-jima, the Ohama Formation consists of gravel, sand and clayey silt. The main part of the formation in the coastal area consists of detrital, foraminiferal, algal and coral limestones. The Ohama Formation occupies large area on Ishigaki-jima. Depositional surface is preserved between 20 and 70 m above sea level. The Sumiyoshi Formation is distributed in small areas along the coast of Iriomote-jima except the south coast. It consists of detrital, algal and coral limestones. Depositional surface is between 20 and 40 m above sea level. The Ryukyu Group on Ishigaki-jima and Iriomote-jima is correlated with the younger part of the Ryukyu Group in Amami-Okinawa Gunto. The recent deposits include coral reefs, beach sand and gravel, dune sand, fluvial clay, sand and gravel and residual soils. Deposits of cave and fissure in the limestone of the Ohama Formation yielded various remains of land animals.

著者

永広 昌之

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.77, pp.1-37, 1977-03-25

被引用文献数

7

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The present study is undertaken to elucidate the movement of the Hizume-Kesennuma fault extending from Hizume on the north to Kesennuma on the south which is one of the major faults traversing the Southern Kitakami Massif in a NNW-SSE trend (Fig. 1). Along the southern half of the Hizume-Kesennuma fault, highly deformed sedimentary rocks ranging their age from Carboniferous to Jurassic are distributed (Fig. 2). The stratigraphic succession of these formations is shown in Fig. 3 and the geologic structure in Fig. 11. The characteristics of the geologic structures in this area are as follows : On the western side of the Hizume-Kesennuma fault the Permian is folded with NNE-SSW trending axis which plunge southward. The folds are associated with longitudinal faults and traversed by left lateral strike-slip faults of a NNW-SSE trend. On the eastern side a thick sequence of the Carboniferous to Jurassic rocks forms a N-S trending large synclinorium with an axis plunging southward. The folds which constitute the synclinorium are associated with longitudinal faults and traversed by left lateral strike-slip faults of a NW-SE to NNW-SSE trend like on the western side. Furthermore, the folds are traversed by ENE-WSW trending faults in the southern area. Most of the folds in the studied area were formed during the Oshima orogeny (in Early Cretaceous) and the faults associated with these folds are formed during or shortly after the folding. The Hizume-Kesennuma fault, originated in Early Cretaceous Period, had been developed during the Oshima orogeny as well. The Hizume-Kesennuma fault is characterized by a steeply dipping fault plane, straight trace, many smaller associated faults trending in NW-SE to NNW-SSE direction in echelon arrangement and other parallel faults. En echelon faults have the left lateral strike-slip component like the faults of a NW-SE to NNW-SSE trend which developed on the both sides of the Hizume-Kesennuma fault. The latter are thought to be the second order faults associated with the main fault. The strain picture of the Hizume-Kesennuma faults is quite similar to those reported on a few precedents of strike-slip faults and model experiments. Considering this similarity, as well as the nature of second order faults associated with the Hizume-Kesennuma fault and the distribution pattern of the formations along the fault, it may be concluded that the Hizume-Kesennuma fault is a left lateral strike-slip fault. The strike-slip displacement of the fault is estimated at about 30 km from the following evidences : (1) strike separation indicated by the synclinal structure composed of Jurassic and Lower Cretaceous formations (Karakuwa belt) and (2) strike separation of the Permian Ubaishi Formation and its equivalent mainly consisting of tuff (Fig. 15). The dip-slip displacement is very little as compared with the strikeslip one and is estimated to be less than 1 km.

著者

今泉 力蔵

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.78, pp.1-61, 1978-02-15

著者

樋口 雄

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.61, pp.1-48, 1964-12-24

被引用文献数

1

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The gas field in Chiba Prefecture occupies the main part of the gas-producing area of the southern Kanto region, and is one of the largest gas fields in Japan. Stratigraphically the majority of the gas-producing strata in the area are restricted to the marine Kazusa group which consists of 10 formations. These formations are mainly composed of alternations of sandstone and siltstone, and were deposited in a large sedimentary basin of Pliocene to early Pleistocene age. The writer had studied the Kazusa group from the view points of microbiostratigraphy and economic geology, for several years examining many cores collected from the gas wells and surface cuttings in Chiba Prefecture. The purpose of the present article is to summarize the lithologic variation, microbiostratigraphy, paleoecology, depositional history and some economic problems of the field. From the detailed study of the foraminiferal faunas and rocks collected from many wells in this area, the following facts were recognized : 1. Eleven foraminiferal zonules are discriminated in the Kazusa group of the area. The sequence and dominant species of these zonules are shown in Table 1. 2. The lithologic character of the Kazusa group in the Kujukuri coastal plain changes from southwest to northeast. However, the biofacies of the Foraminifera are stable, and correlation of the wells by means of the foraminiferal zonules is easy. 3. The thickness of the formainiferal zonules generally converges toward the northeast in the Kujukuri section, and some changes in the dominant species of the assemblages characterizing the zonules are recognized. Especially, the Lower Kokumoto faunule is not discriminated at the northeast end of this section, because of the faunule thinning out. 4. As shown in the isopach maps (figs. 11-15) of each formations of the Kazusa group, the center of deposition of the group migrated from the southern part of the Kujukuri coastal plain area towards the northwest, during the deposition of respective formations. 5. The isolith maps (sandstone : figs. 16-19) and sandstone percentage maps (figs. 20-24) of these formations show the following facts. The sandstones are developed regularly in the Ohara, Namihana and Katsu-ura formations, but irregularly in the Kiwada, Otadai and Umegase formations. In the Kokumoto formation, the sandstone again shows a regular distribution pattern. From these facts the writer has concluded that the sandstones of the Ohara, Namihana, Katsu-ura and Kokumoto formations were deposited in shallow water under the normal sedimentary process, but the ones of the Umegase and Otadai formations were secondarily transported to deep water. 6. The paleoecologic conditions of these formainiferal zonules may be explained from the Recent distribution of Foraminifera around Japan. The biofacies maps (figs. 7-10) summarize s the regional variation of these paleoecologic conditions. The depositional history of the Kazusa group is as follows : At the beginning of deposition of the group, its sedimentary environment was of relatively shallow water and the basin unstable. During the depositional stages from the Kiwada to Umegase formations, the environment was relatively deep and the basin was in a stable bathyal condition. During the Umegase stage the sea water attained the maximum coverage in Chiba Prefecture. Regression might have begun with the Kokumoto stage. This may be explained from the dominance of neritic species of the Kokumoto and its superjacent formations. The foraminiferal assemblage of the Kasamori formation indicates the most shallow water habitat throughout the deposition of the Kazusa group 7. The argillaceous sediments in the stable bathyal sea bottom are most favourable as the mother rocks of natural gas. The siltstone layers of the Otadai and Umegase formations are good examples of them. On the other hand, the sandstone layers intercalated in them are very good gas-reservoirs, because they are composed of sand grains excellently sorted and graded as a result of secondary transportation such as by turbidity currents. The natural gas accumulations of high potentiality in these formations are on the east side area of Chiba City. In the west side area of Chiba City, the foraminiferal assemblages of these fornrations indicate shallow water-environments, and the geological characters of these formations are somewhat different from those of the east side. The different characters between the east and west side areas of Chiba City cause the different mode of accumulations of natural gas.

著者

北里 洋

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.75, pp.17-49, 1975-03-31

被引用文献数

19

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The present study is undertaken to clarify the age of deposition and extent of geographic distribution of the younger Cenozoic strata (Fig. 2) developed in the Oga Peninsula, Akita Prefecture (Fig. 1). Detailed tephrochronological investigation of the sedimentary rocks was done to trace the geographic distribution of the strata. A total of thirty key beds were traced over the Oga Peninsula area and a few of them were traced further to the Akita oil fields lying southeast of the Oga Peninsula (Fig. 9). Lithologic descriptions and type localities of the key tuff beds are given in Table 1. Magnetostratigraphy, microbiostratigraphy and radiometric dating assumed as the principal means to establish the geochronology of the strata. However, these methods were not accompanied by each other in most of previous works. Accordingly, an attempt was made to apply these methods to the same sections simultaneously and to synthesize their results for comparison. Two routes, the Oga Peninsula main route and the Sarukawa route, were selected in the Oga Peninsula for study. Along these routes, collected were 149 samples for paleomagnetic measurement, 30 samples for microfossil study and 4 samples for radiometric dating. The sampling localities and stratigraphic position in columnar sections are shown in Figs. 4 and 5. Magnetostratigraphy : -In the laboratory, samples were demagnetized in the alternation field of 150 Oersted to remove the unstable secondary components and then the samples were demagnetized in 200℃ thermal field. These samples were measured at every 45° around three axes of the sample with the automatic parastatic-type magnetometer. All numerical values obtained from the measurement were processed by an electric computer, NEAC 2200, Model 500, at the Computer Center of the Tohoku University. The result of measurements are shown in Fig. 6-a, b. The paleomagnetic studies indicate that the lowermost Kitaura, upper half of the middle Kitaura and upper Kitaura to Shibikawa formations are normaly magnetized and the uppermost Funakawa and lower to lower half of the middle Kitaura are reversely magnetized. The rest of the Funakawa Formation is interpreted as being remagnetized and unreliable for magnetostratigraphy. In order to magnetostratigraphic classification, these magnetic reversal patterns are named as AKOG-A, AKOG-B, AKOG-C, AKOG-D, AKOG-E at the Oga Peninsula main route, while AKSK-B, AKSK-C, AKSK-D, AKSK-E, AKSK-F at the Sarukawa route in descending order. Microbiostratigraphy : -Samples for microfossil study were used for planktonic foraminifera and Radiolaria. A part of samples used for paleomagnetic measurement were examined in calcareous nannoplankton and diatom. The results are shown in Figs. 7-a, b. The faunal and floral assemblages are generally monotonous in composition, as same as the present-day biota living in the North Pacific. Among them, species were found to be significant for biostratigraphical correlation, though they occurred sporadically both in the northern and southern sections : they are, planktonic foraminifera : -Globoquadrina asanoi, Globoquadrina kagaensis, Globoquadrina himiensis ; calcareous nannoplankton : -Gephyrocapsa spp. ; Radiolaria : - Eucyrtidium matuyamai, Ommatartus antepenultimus, Ommatartus penultimus, Ommatartus tetratharamus ; diatom : -Actinocyclus oculatus, Pseudoeunotia doliolus and Rhizosolenia praebergonii. Correlation : -Correlation of the magneto-zones with the Cenozoic magnetic time scale of marine sediments (Opdyke, 1972) were accomplished by correlating the associated micro-biostratigraphic events to those recognized already in the paleomagnetic polarity sequence of deep-sea cores (Fig. 8). From the interval of AKSK-F, occurence of Actinocyclus oculatus and Globoquadrina asanoi were recorded. Because of the first appearance of Actinocyclus oculatus and the last appearance of Globoquadrina asanoi, AKSK-F is correlated to the Matuyama reversed Epoch below the "Olduvai" event. Globoquadrina asanoi, Globoquadrina kagaensis, Globoquadrina himiensis, Actinocyclus oculatus and Rhizosolenia praebergonii were found in the intervals of AKOG-E, AKSK-F. The first appearance of Actinocyclus oculatus and Globoquadrina himiensis and the last appearance of Globoquadrina asanoi, Globoquadrina kagaensis, GloBoquadrina himiensis and Rhizosolenia praebergonii indicate that AKOG-E and AKSK-E are correlated to the "Olduvai" event. Within the interval of AKOG-D, AKSK-D, Gephyrocapsa spp., Eucyrtidium matuyamai, Pseudoeunotia doliolus and Actinocyclus oculatus were recognized. The first appearance of Gephyrocapsa spp., Eucyrtidium matuyamai and Pseudoeunotia doliolus and the last appearance of Actinocyclus oculatus and Eucyrtidium matuyamai assure that AKOG-D, AKSK-D can be correlated to the Matuyama reversed Epoch between "Olduvai" event and Jaramillo event. Correlation of the rest of magneto-zones are reserved because of poor occurrence in microfossils. Radiometric dating : -Dating was carried out by K-Ar method at the laboratory of Prof. Y. Uyeda of the Tohoku University. Measured minerals were biotite. The results of measurement are shown in Table 2. A distinct discrepancy is noticed between the radiometric age obtained and the results of magnetostratigraphic and microbiostratigraphic correlation.

著者

小貫 義男 柴田 豊吉 三位 秀夫

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.52, pp.16-27, 1961-03-27

著者

北村 信 小高 民夫 片岡 純

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.52, pp.28-40, 1961-03-27

被引用文献数

1

著者

今野 円蔵

出版者

東北大学

雑誌

東北大學理學部地質學古生物學教室研究邦文報告 (ISSN:00824658)

巻号頁・発行日

vol.52, pp.1-"2-3", 1961-03-27