Jour. Geol. Soc. Japan, Vol. 124, No. 2, p , February 2018 doi: /geosoc Devonian chert in the Permian Ko

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1 Jour. Geol. Soc. Japan, Vol. 124, No. 2, p , February 2018 doi: /geosoc Devonian chert in the Permian Kozuki Formation of the Ultra-Tamba Zone, eastern Okayama Prefecture, Southwest Japan Abstract Shizuo Takemura, Atsushi Takemura, Hikaru Ueno, Yoshiaki Sugamori and Hiroshi Furutani Geoscience Institute, Hyogo University of Teacher Education, Hyogo , Japan / Department of Regional Environment, Faculty of Regional Sciences/ Department of Agricultural, life and Environmental Sciences, Faculty of Agriculture, Tottori University, Tottori , Japan Institute of Natural and Environmental Sciences, University of Hyogo, Sanda, Hyogo , Japan : Present address: Muko Elementary School, Sanda, Hyogo , Japan Devonian chert beds in the Permian Kozuki Formation of the Ultra-Tamba Zone are reported from Mimasaka City, Okayama Prefecture, Southwest Japan. The Kozuki Formation consists mainly of Permian clastic rocks and felsic tuffs with basalts, Carboniferous limestone, and Early Permian cherts, and is therefore interpreted as a Permian accretionary complex similar to the other formations of the Ultra-Tamba Zone. The Devonian chert beds are frequently intercalated with black layers composed of magnetite, in which a wellpreserved radiolarian fauna occurs. These magnetite beds with radiolarian shells indicate the sedimentary origin derived from hydrothermal activity on the seafloor. The radiolarian fauna contains Holoeciscus foremanae and H. elongatus, as well as Ceratoikiscum avimexpectans and Archocyrtium sp., indicating the Fammenian Age of Late Devonian. These are the oldest fossils in the Chugoku District and the chert beds represent one of the oldest allochthons within the accretionary complexes of Japan, similar in age to the Devonian chert of the Nedamo Belt in the Tohoku District. Keywords: Devonian radiolarians, Kozuki Formation, Ultra-Tamba Zone, chert, magnetite, Okayama Prefecture Corresponding author: S. Takemura, takesizu@hyogo-u.ac.jp Caridroit et al.1985 Ishiga1986 Fig. 1, 1993Kojima et al., 2000, Ishiga, 1986 Cisuralian Guadalupian Lopingian The Geological Society of Japan Ishiga1990 UT-3UT-2UT-1 3 UT-3 UT-3, 1980, 2009UT-3 UT-3

118 竹村 2018 2 静夫ほかおおい UT-2 亜帯は大飯層広川ほか, 1957; Ishiga, 1986 とその相当層からなるが大飯層に明確に対比される地層は兵庫県東部以東にだけ分布する大飯層および相当層は一般に泥岩砂岩珪質泥岩チャートからなり一部に珪長質凝灰岩を伴う本層のチャート珪質泥岩泥岩からは中期ペルム紀末後期ペルム紀中頃の放散虫化石が産する

, 1985; Ishiga, 1986 とその相当層からなり主に泥岩と緑色砂岩から構成される氷上層相当層は福井県西部から岡山県南部にかけて広く連続的に分布するが鍵層を欠くため正確な層序の対比は困難である本層は中上部ペルム系とさ化石の産出に乏しく詳しい年代れてきたが栗本, 1986 は不明に近い状態にある竹村ほか, 2009 2上月層 Fig. 1. Simplified geological map showing the tectonic units of the Kinki Chugoku region.

2 118 竹村静夫ほかおおい UT-2 亜帯は大飯層広川ほか, 1957; Ishiga, 1986 とその相当層からなるが大飯層に明確に対比される地層は兵庫県東部以東にだけ分布する大飯層および相当層は一般に泥岩砂岩珪質泥岩チャートからなり一部に珪長質凝灰岩を伴う本層のチャート珪質泥岩泥岩からは中期ペルム紀末後期ペルム紀中頃の放散虫化石が産する例えば,, 1988 Ishiga, 1985; 木村ひかみ UT-1 亜帯は氷上層広川ほか, 1957; Caridroit et al., 1985; Ishiga, 1986 とその相当層からなり主に泥岩と緑色砂岩から構成される氷上層相当層は福井県西部から岡山県南部にかけて広く連続的に分布するが鍵層を欠くため正確な層序の対比は困難である本層は中上部ペルム系とさ化石の産出に乏しく詳しい年代れてきたが栗本, 1986 は不明に近い状態にある竹村ほか, 上月層 Fig. 1. Simplified geological map showing the tectonic units of the Kinki Chugoku region. Inset map shows the location of the study area within Japan. 今回新たにデボン紀チャート層の存在が明らかとなった上月層は UT-3 亜帯を代表する地層であり岡山県東部のさようちょう美作市から兵庫県西南部の佐用町にかけて広く分布する本層は主として泥岩珪長質凝灰岩玄武岩類砂岩からな泥りごく少量の石灰岩とチャート礫岩を伴う Fig. 2 岩は一般に珪質またはシルト質で黒色暗灰色で強い剥離 Fig. 2. Simpliﬁed geological map of the Mimasaka Kozuki region after Takemura (1997), showing the location of the Shiramizu outcrop (Loc. A).

地質雑 124 2 119 超丹波帯ペルム系上月層中のデボン紀チャート層 Fig. 3. (a) Photograph of the Shiramizu outcrop and (b) schematic sketch.

3 地質雑超丹波帯ペルム系上月層中のデボン紀チャート層 Fig. 3. (a) Photograph of the Shiramizu outcrop and (b) schematic sketch. 性をもつことが多い珪長質凝灰岩は暗灰色灰緑色を呈化石産出地点の岩相しシルトから細粒砂サイズの火山砕屑物から構成される一般に珪長質凝灰岩は泥岩とともに産し両者は整然とした互層から珪長質凝灰岩が含礫泥岩の礫として含まれる場合しらデボン紀の放散虫化石が産出した露頭は美作市東部の白水に位置し N, E; Fig. 2 南西からみず町西部の稗田などに産し境界部では苦鉄質凝灰岩と互層す北東に流れる小河川沿いに露出する以下, 白水露頭 Fig. 3 白水露頭の水平方向の幅は 24 m 以上あり南西部には 10 m 以上にわたり泥岩北東部には約 14 m の幅で玄武岩ることがあるチャートは泥岩中のブロックまたは玄武岩類とチャートが露出する南西部の泥岩は低角な断層で見類に伴われて産するがその量は少なく一般に再結晶が著掛けの下位にあたる玄武岩類およびチャートと接しているまで産状が連続的に変化する玄武岩類は苦鉄質凝灰岩と変質した玄武岩からなる石灰岩は玄武岩類に付随して佐用ひえだしい兵庫県佐用町最西部の稗田付近に分布する上月層の石灰岩からは Fusulinella sp. など石炭紀を示すフズリナ化石やサンゴ化石が産出している後藤山際, 1973; 猪木, 1969 また同じく稗田付近のチャートからは Pseudoalbaillella bulbosa Ishiga など前期ペルム紀初期の放散虫化石が報告上月層の砕屑岩類からは多くのされた後藤堀, 1985 Fig. 3 本露頭の北東部では玄武岩類はチャートを挟んで北東と南西の両側に分布するが北東端の玄武岩類とチャートの境界は露出状況が悪く両者の関係は不明瞭である一方南西側の玄武岩類とチャートは一部で弱い剪断面で接するものの多くは密着漸移している玄武岩類は変質の進んだ玄武岩と苦鉄質凝灰岩であり灰地点の泥岩と珪長質凝灰岩より Follicucullus charveti Caridroit and De Wever などの中期ペルム紀末後期ペル緑暗灰色または赤褐色を呈することが多い玄武岩に初生ム紀初期の放散虫化石が報告された Pillai and Ishiga, 1987 さらに一部の泥岩からは Albaillella asymmetri- ま果状の集合体を構成しているのが観察される Fig. 4a た二次鉱物として方解石と緑泥石が多く見られ一部の試 ca Ishiga and Imoto など前期ペルム紀末中期ペルム紀中鉱物はほとんど残っていないが鏡下では羽毛状の鉱物が球料にはぶどう石が生じている上月層頃の放散虫化石が報告されており竹村ほか, 1993 チャートは赤茶褐色または灰黒色を呈し色調の変化の形成年代はおよそ中後期ペルム紀であると考えられていによる厚さ数 mm 以下の葉理が発達する多量の放散虫化る竹村ほか, チャートの上位石がチャートには含まれている Fig. 4b

120 竹村静夫ほか 2018 2 Fig. 4. Thin-section photomicrographs of samples from the Shiramizu outcrop. (a) Basalt. Left and right are plane- and cross-polarized light images, respectively.

Radiolarian fossils are not found in the black layer without the boundary region with the chert. (d) Close-up of the boundary between the chert and the black layer.

4 120 竹村静夫ほか Fig. 4. Thin-section photomicrographs of samples from the Shiramizu outcrop. (a) Basalt. Left and right are plane- and cross-polarized light images, respectively. Altered variolitic minerals are scattered throughout the rock mass. (b) Chert. Radiolarian fossils and laminas are observed. (c) Chert and black layer. Radiolarian fossils are not found in the black layer without the boundary region with the chert. (d) Close-up of the boundary between the chert and the black layer. Note that well-preserved radiolarian shells are present in the black layer. 方向は不明であるが全体の層厚は 7 m 以上で N50 70 W N の走向傾斜を示すまたチャートは Fig. 5 厚さ数 mm 十数 cm の黒色層を頻繁に挟在するチャート層内で認められる面構造は前述したチャートの色調変化とこの黒色層により構成されており珪質泥岩を伴う一般的な層状チャートとは産状が異なるこれらの黒色層反射顕微鏡やは薄片においても光を透過しない Fig. 4c EDS エネルギー分散型 X 線分析装置などによる観察分析の結果黒色層は大部分が磁鉄鉱で構成されておりそれに葉理状の磁硫鉄鉱を伴うことが明らかとなったなお放散虫化石はチャートの部分に多く含まれるのに対して黒色ただし黒色層部層部にはほとんど存在しない Fig. 4c 中でもチャートとの境界部には保存良好な放散虫化石が認められる Fig. 4d 産出した放散虫化石とその年代本研究では白水露頭より主にチャートの試料を約 30 カ所泥岩試料を 5 カ所から採取し放散虫化石の抽出を行った Fig. 5. Field occurrence of bedded chert with black layers (white arrows).

5 % 24 Trilonche Albaillellaria 1 12% % Albaillellaria Fig. 6 Albaillellaria Holoeciscus foremanae Chen Holoeciscus elongatus Kiessling and Tragelehn Ceratoikiscum cf. avimexpectans Defrandre Entactinaria Palaeoscendium cladophorum Defrandre Trilonche Triaenosphaera Nassellaria Archocyrtium Popofskyellidae Holoeciscus Foreman1963 Albaillellaria , Cheng, 1986; Aitchison, 1990 Holoeciscus H. foremanae H. elongatus 2 H. foremanae Cheng1986 H. foremanae Maletz, 2011; Schwartzapfel and Holdsworth, 1996 Kiessling and Tragelehn, 1994Wang et al., 1998; Wang et al., 2006 Famennian H. elongatus Kiessling and Tragelehn1994 H. foremanae Schwartzapfel and Holdsworth1996 H. longus H. foremanae Famennian Palaeoscenidium cladophorum Ceratoikiscum avimexpectansarchocyrtium Popofskyellidae Albaillellaria Frasnian Helenifore Albaillella Famennian,, 2009, Fig. 4c Suhaylah Fleet and Robertson, 1980; Alabaster and Pearce, 1985; Hara and Kurihara, 2017 EDS, 1973, Ishiga, 1990, 1993

122 20182 Fig.. Scanning electron microscope images of selected radiolarian fossils. 1 3: Holoeciscus foremanae Cheng, 4 & 5: Holoeciscus elongatus Kiessling and Tragelehn, 6: Ceratoikiscum cf.

6 Fig.. Scanning electron microscope images of selected radiolarian fossils. 1 3: Holoeciscus foremanae Cheng, 4 & 5: Holoeciscus elongatus Kiessling and Tragelehn, 6: Ceratoikiscum cf. avimexpectans Deflandre, 7 & 8: Palaeoscenidium cladophorum Defrandre, 9: Trilonche sp., 10: Triaenosphaera cf. hebes Won, 11: Archocyrtium cf. dilatipes Deflandre, 12: Popofskyellidae, gen. et sp. indet., Scale bars are 50 µm., Kojima et al., 2016, Kammera et al., 1990, Mizutani, 1990 Visean, 2003

7 , 2002 Palmatolepis 3 P. glabra prima Ziegler and Huddle Famennian Palmatolepis crepida P. marginifera H. foremanae Wang et al.,2006 Famennian Palmatolepis crepida P. postera MORB, 2008, 2005;, 2008 Aitchison, J. C., 1990, Significance of Devonian-Carboniferous radiolarians from accretionary terranes of the New England Orogen, Eastern Australia. Mar. Micropaleont., 15, Alabaster, T. and Pearce, T. A., 1985, The interrelationship between magmatic ore-forming hydrothermal process in the Oman Ophiolite. Economic Geol., 80, Cheng, Y. N., 1986, Taxonomic studies on Upper Paleozoic Radiolaria. Natl. Mus. Nat. Sci., Taiwan, Spec. Publ., 1, 311p. Caridroit, M., Ichikawa, K. and Charvet, J., 1985, The Ultra- Tamba Zone, a new unit in the Inner Zone of Southwest Japan-its importance in the nappe structure after the example of the Maizuru area-. Earth Sci.Chikyu Kagaku, 39, Ehiro, M. and Suzuki, N., 2003, Redefinition of the Hayachine Tectonic Belt of Northeast Japan and a proposal of a new tectonic unit, the Nedamo BeltJapan. Jour. Struct. Geol., 47, Fleet, A. J. and Robertson, A. H. F., 1980, Oceanic-ridge metalliferous and pelagic sediments of the S Nappe, Oman. Jour. Geol. Soc. London, 137, Foreman, H. P., 1963, Upper Devonian Radiolaria from the Huron member of the Ohio shale. Micropaleont., 9, Goto, H. and Hori, R., 1985, Geology of northern part of the Kozuki-Tatsuno BeltKamigori Belt, Southwest Japan* 92 92th Annu. Meet. Geol. Soc. Japan, Abstr., 189 Goto, H.,and Yamagiwa, N., 1973, Fusulinids from the Upper Palaeozoic in Kozuki-machi, Sayo-gun, Hyogo Prefecture, Southwest Japan Jour. Geol. Soc. Japan, 79, Hamano, K., Iwata, K., Kawamura, M. and Kitakami Paleozoic Research Group, 2002, Late Devonian conodont age of red chert intercalated in greenstones of the Hayachine Belt, Northeast JapanJour. Geol. Soc. Japan, 108, Hara, K. and Kurihara, T., 2017, Radiolarian age and lithostratigraphy of Late Cretaceous pelagic sediments overlying basaltic extrusive rocks, northern Oman Mountains. Ofioliti, 42, Hirokawa, O., Isomi, H. and Kurokawa, K., 1957, 5 1 Geology of the Obama district. With Geological Sheet Map at 1: 50,000, Geol. Surv. Japan, 31p. Igi, S., 1969, Findings of the Carboniferous corals from the so-called Kamigori Structural Belt, JapanBull. Geol. Surv. Japan, 20, Igi, S. and Wadatsumi, K, 1980, 5 1 Geology of the Kamigori district. With Geological Sheet Map at 1: 50,000, Geol. Surv. Japan, 70p. Ishiga, H., 1985, Discovery of Permian radiolarians from Katsumi and Oi Formations along south of Maizuru Belt, Southest Japan and its significance. Earth Sci.Chikyu Kagaku, 39, Ishiga, H., 1986, Ultra-Tamba Zone of Southwest Japan. Jour. Geosci. Osaka City Univ., 29, Ishiga, H., 1990, Ultra-Tamba Terrane. In Ichikawa, K., Mizutani, S., Hara, I., Hada, S. and Yao, A., eds., Pre-Cretaceous Terranes of Japan. Publ. IGCP 224, Osaka, Kammera, K., Sano, H. and Isozaki, Y., 1990, Akiyoshi Terrane. In Ichikawa, K., Mizutani, S., Hara, I., Hada, S. and Yao, A., eds., Pre-Cretaceous Terranes of Japan. Publ. IGCP 224, Osaka, Kiessling, W. and Tragelehn, H., 1994, Devonian radiolarian faunas of conodont-dated localities in the Frankenwald Northern Bavaria, Germany. Abh. Geol. B.-A. Wien, 50, Kimura, K., 1988, Geology and tectonic setting of the Ultra-Tamba Belt in the western part of Ayabe City, Kyoto Prefecture, Southwest JapanJour. Geol. Soc. Japan, 94, Kojima, S., Kemkin, I. V., Kametaka, M. and Ando, A., 2000, A correlation of accretionary complexes of southern Sikhote- Alin of Russia and the Inner Zone of Southwest Japan. Geosci. Jour., 4, Kojima, S., Hayasaka, Y., Hiroi, Y, Matsuoka, A., Sano, H., Sugamori, Y.,Uchino, T., 2016, 2b Pre-Cretaceous accretionary complexes. In Moreno, T., Wallis, S., Kojima, T. and Gibbons, W., eds., The Geology of Japan, Geol. Soc., London, Kurimoto, C., 1986, Ultra-Tamba Zore in the Fukuchiyama area, Kyoto Prefecture: its constituent rocks and dis-

8 tributionearth Sci.Chikyu Kagaku, 40, Maletz, J., 2011, Tetrentactinia barysphaera Foreman, 1963: skeletal structure and age of a biostratigraphically important FamennianUpper Devonianradiolarian from the Ohio Shale, USA. Paläontol. Z., 85, Mizutani, S., 1990, Mino Terrane. In Ichikawa, K., Mizutani, S., Hara, I., Hada, S. and Yao, A., eds., Pre-Cretaceous Terranes of Japan. Publ. IGCP 224, Osaka, Pillai, D. L. and Ishiga, H., 1987, Discovery of Late Permian radiolarians from Kozuki Formation, Kozuki-Tatsuno Belt, Southwest Japan. Jour. Geol. Soc. Japan, 93, Schwartzapfel, J. A. and Holdsworth, B. K., 1996, Upper Devonian and Mississippian radiolarian zonation and biostratigraphy of the Woodford, Sycamore, Caney and Goddard Formations, Oklahoma. Cushman Foundation for Foraminineral Research, Spec. Publ., 33, Sugamori, Y., 2009,, Ultra-Tamba Terrane in the Kawanishi-Inagawa area, southern part of Hyogo Prefecture, Southwest Japan Jour. Geol. Soc. Japan, 115, Suzuki, N., Aita, Y. and Kurihara, T., 2012, 4, 4.2 Chapter 4, Microfossil world, 4.2 Shape of microfossils: Variety of radiolarian shapes in different geologic ages and habitats Microfossils: Their Microscopic World ExploredTokai Univ. Press, Suzuki, S. and Kiminami, K., 2009, 2., 2.1, 6 Regional Geology of Japan, Part 6: Chugoku, Asakura Publ., Takemura, S., 1997, Folding and related structures of the Maizuru and Ultra-Tamba zones in the Kozuki-Mimasaka area, Southwest Japan. Jour. Geosci. Osaka City Univ., 40, Takemura, S., Sugamori, Y. and Suzuki, S., 2009, Maizuru and Ultra-Tamba zones in eastern Okayama and southwestern Hyogo prefectures, southwest JapanJour. Geol. Soc. Japan, 115, S123 S137. Takemura, S., Suzuki, S. and Ishiga, H., 1993, Albaillella asymetrica Stratigraphy of the Kozuki Formation, Kamigori Zone Southwest Hyogo Prefecture, Japan, reconsideration with the discovery of Albaillella asymmetricaradiolarian fossil and the strucural analysisjour. Geol. Soc. Japan, 99, Uchino, T. Kurihara, T. and Kawamura, M., 2005, Early Carboniferous radiolarians discovered from the Hyachine Teraane, Northwest Japan: the oldest fossil age for clasitc rocks of accretionary complex in JapanJour. Geol. Soc. Japan, 111, Uchino, T., Kawamura, M. and Kawamura, T., 2008, Lithology of the Nedamo Terrane, an Early Carboniferous accretionary complex, and its southern boundary with the South Kitakami TerraneJour. Geol. Soc. Japan, 114, S141 S157. Wang, Y. J., Luo, H. and Aitchison, J. C., 2006, Influence of the Frasnian-Famennian event on radiolarian faunas. Eclogae Geol. Helv., 99, Suppl. 1, Wang, Y. J., Luo, H., Kuang, G. D. and Li, J. X., 1998, Late Devonian-Late Permian strata of cherty facies at Xiaodong and Bancheng counties of the Qinzhou area, SE Guangxi. Acta Micropalaeont. Sin., 15, in Chinese with English abstract. Yano, K., Ishida, K., Namiki, H., Sakamoto, K. and Kato, T., 1993, New findings of a formation corresponding to the Ultra Tamba Zone to the east of the Fossa Magna th Annu. Meet. Geol. Soc. Japan, Abstr., takesizu@hyogo-u.ac.jp takemura@ hyogo-u.ac.jp / sugamori@muses.tottori-u.ac.jp furutani@hitohaku.jp Takemura S., Takemura A., Ueno H., Sugamori Y. and Furutani H., 2018, Devonian chert in the Permian Kozuki Formation of the Ultra-Tamba Zone, eastern Okayama Prefecture, Southwest Japan. Jour. Geol. Soc. Japan,, Holoeciscus foremanae Fammenian

Occurrence of Permian radiolarians from chert pebbles in conglomerate at Yokoo, Nyukawa Village, Gifu Prefecture, central Japan Satoru KOJIMA* Abstrac

Occurrence of Permian radiolarians from chert pebbles in conglomerate at Yokoo, Nyukawa Village, Gifu Prefecture, central Japan Satoru KOJIMA* Abstract Permian Radiolaria including Albaillella levis, Follicucullus