Trans. Proc. Palaeont. Soc. Japan, N.S.. No. 53. pp. 179-193. pls. 27, 28. Apr. 10, 1964 466. CARBONIFEROUS CONODONTS FROM THE OMI LIMESTONE, NIIGATA PREFECTURE. CENTRAL JAPAN (STUDIES OF ASIAN CONODONTS, PART I)* HISAYOSIII IGO and TOSHIO KOIKE Institute of Geology and Mineralogy. Tokyo University of Education 青 海 石 灰 岩 か ら発 見 され た 石 炭 紀 の コ ノ ドン トにつ い て;新 潟 県 西 頸 城 郡 青 海町 ・青海 電 化 株 式 会社 の青 海 ∫ll沿いの 西 山 採 石 場 に 露 出 す るC1層(Millerella Zone)の 石 灰 岩 か ら発 見 され た コ ノ ドン トの うち,11属16睡 を 記 蔵 した 。 また これ らの コ ノ ドン トに も とつ い て, C1層 の地 質 時 代 を険 討 し た.猪 郷 久 義 ・小 池 敏 夫 which was rather vague before our study. Introduction and Acknowlegments This paper is the first report of our continuous work on conodonts from Ja- The Omi Limestone is distributed in pan and other Asian districts. Nishikubiki County, Niigata Prefecture. Acknowledgments are due to Drs. Central Japan. It has been studied by Haruyoshi FUJIMOTO, professor emeritus many workers. such as HAYASAKA (1921), of the Tokyo University of Education, KAWADA (1954) and FUJITA (1958), but Wataru HASHIMOTO, professor of the no comprehensive paleontological study same university, Teiichi KOBAYASHI,. has been published except for HAYA- professor emeritus of the University of SAKA'S classical work. We have been Tokyo and Teturo HANAI, assistant pro- studying various fossils from this huge fessor of the same university, for their limestone mass and are very fortunate suggestions and encouragements. During to find an excellently preserved rich the senior author's stay in Illinois he conodont fauna in the lower part of this was indebted to Dr. Charles COLLINSON, limestone. There has been no report of geologist of the Illinois State Geological a rich conodont fauna in Japan except Survey, for his guidance for the cono- for recent brief note of HAYASHI (1963). dont study. We also thank Mr. Hide- We studied this newly found conodont toshi TOGASHI of the Omi Denka Co. fauna with keen interest. As the result Ltd., for his help to our fossil collection of the study we discriminated eleven in the field. A part of expenses of this genera and sixteen species and became work was defrayed from the Scientific to believe that this conodont fauna ap- Expenditure Fund, Ministry of Education, parently indicates Early Pennsylvanian Japanese Government. or Late Namurian in age. This conclusion must be noted about the geological age of the lower part of the Omi Limestone Stratigraphic Summary * Received Jan. 6. 1961; read at the Annual The Omi Limestone is a thick lime- Meeting of the Society at Tokyo, Sep. 7. 1963. stone mass ranging from the Early Car- 179 18(1 Hisayoshi IGO and Toshio KOIKE boniferous (Tournaisian) to late Middle Eoasianites from the certain horizon 01 Permian in age. According to KAWADA CI and they briefly discussed about the (1954) and FUJITA (1958) this limestone geological age of CI. Judging from can be subdivided into five lithogenetic these evidence, KAWADA'S Coral-Bra- units as follows in descending order. chiopod Zone or FUJITA's Millerella- Coral-Brachiopod Zone is thought to be P2•c•c Parafusulina and Neoschcogerina equivalent to the Tournaisian to Bashi- Zones kirian. P1•c•cPsendofusulina and Pseudoschina- We collected many specimens of bra- gerina Zones chiopods. ammonites, corals and others C3•c•cTriticites Zone Finnlinella-FusulinaC2•c•c Zone from about 100 m. below of the SAKA- Millerella-Coral-Brachiopod C1•c•c Zone GAMI'S Profusulinella-limestone. They are not throughly worked out, but we The representing conodonts were col- discriminated the following ammonites lected from C1 of KAWADA and FUJITA. in addition to Eoasianites sp., such as The geological age of CI was very ob- Gastrioceras sp.. aff. G. reticulatus Yin scure, but HAYASAKA once discriminated and Paralegoceras sp.. These ammonites the following fossils, such as Amygdalo- may indicate the Reticuloceras Zone of phyllum giganteum MAYASAKA), Cor- western Europe. The Reticuloceras Zone enia ? omiensis (HAYASAKA). Axophyl-w is the Upper Namurian and thought to um gracile HAYASAKA. Lithostrotionl be equivalent to the Lower Pennsylvanian somaense YABE and HAYASAKA, Stvlido- (MOORE, 1948; ELIAS. 1956). Our cono- phyllum sp.. Chaetetes sp.. Giganlopro- dont fauna was obtained from this am- ductus edelburgensis (PHILLIPS), Avonia monite-bearing limestone, and as will be cfr. aculeatus (MARTIN), Echinoconchus discussed later the geological age of punctatus var.. Produclus semireticulatus this conodont fauna also indicates ex- MARTIN. Camarophoria globulina PHIL- actly same age with the preliminary LIPS, Martinia glabra decora PHILLIPS, conclusion from these ammonites and Reticularia lineata MARTIN, Syringothyris brachiopods. cuspidalus MARTIN, Megistocrinus sp.. Actinocrinus aff. globrus PHILLIPS and Faunal Summary of Conodonts others. Unfortunately precise stratigraphic The collections were made in the Nishi- positions of these fossils are still obscure. yama quarry of the Omi Denka Co. Ltd. It seems to be necessary further inves- along the Omigawa River (Text-fig. I). tigation of these fossils from CI based Stratigraphic position of conodont-bear- upon the present progressed paleon- ing bed is about 100 m. below of the tology. The occurrence of Syringothyris SAKAGAMI'S Profusulinella-limestone. cuspidalus from CI indicates Tour We have succeeded to separate numer- naisian age, and Gigantoproductus and ous specimens of conodonts from gray -others are thought to be the Visean. to white sparry limestone by acetic acid Recently SAKAGAMI (1962) proved the treatment and discriminated the follow- •occurrence of Profusulinella from the ing species. namely :-Hindeodella asia- upper part of CI and described several tica IGO and NOIRE. n. sp., H. paradeli- 'Carboniferous bryozoa . KATO and NAKA (Willa IGO and KOIKE, n. sp. II. saka- AIURA 1962) reported the occurrence of gamii IGO and NOIRE, n. sp.. Synprionio- 466. Carboniferous Conodonts from Central Japan 181 Text-fig. 1. Map showing the fossil locality. dina microdenta ELLISON, S. collznsoni Ilindeodella are very abundant through- IGO and KOIKE. n. sp., Euprioniodina out the collections, and they are related dentata IGO and KOIKE, n. sp.. Ligonodina to the mentioned American species which hanaii IGO and KOIKE, n. sp.. Roundya range from the Desmoinesian to Missou- subacordus (GUNNELL), Lonchodina ? nip- rian. Owing to the fragmentary state ponica IGO and KOIKE, n. sp.. Ozarkodina of these described foreign specimens. orientate IGO and KOIKE, n. sp.. Spatho- detailed comparison seems to be difficult. gnathodus echigoensis IGO and KOIKE, Thus we proposed new species herein sp.. Idiognathodus togashii IGO and KOIKE, based upon many complete specimens. n. sp., Streptognathodus japonicus IGO and The genus Synprioniodina is known KOIKE, n. sp., S. expansus IGO and KOIKE, from the Lower Devonian to Upper Car- n. sp., Gnathodus opimus IGO and KOIKE, boniferous, but it is rather common in n. sp. and Gnathodus sp. the Devonian and Mississippian rocks. Hindeodella asiatica and IL sakagamii S. microdenta is very abundant in the resemble H. armata STAUFFER and PLUM- treated material and it is similar to the MER which was described from the East American specimens which were de- Mountain Shale member, Mineral Wells scribed from the Cherokee Shale through formation, Texas. II. paradelicatula is the Deer Creek Limestone (ELLISON, also closely related with IL delicatula 19411) and also from the Middle Dimple STAUFFER and PLUMMER from the Gra- formation (Morrowan) in Texas (ELLISON ford and Mineral Wells formation in and GRAVES. 1941). ROHDES (1952) de- Texas. These three new species of scribed Synprioniodina-assemblage from 182 Hisayoshi IGO and Toshio KOIKE the Pennsylvanian of Illinois and his Spathognathodus echigoensis is a rather illustrated specimens quite agree with common species in this fauna and it our specimens. S. collinsoni is rather slightly resembles S. minutus (ELLISON) rare, but having unique denticles and is discriminated from the Desmoinesian to very distinct from other previously de- Rig Blue Series. scribed species. Idiognathodus togashii is a rather rare Euprioniodina dentata is not so com- throughout our collection. This new mon in our collections. The genus species seems to be a primitive type Euprioniodina is rather long-ranged cono- among this genus and resembles I. deli- dont and has been known from the catus GUNNELL persisting in the Desmo- Lower Carboniferous to Triassic. Our inesian to Lower Virgilian in Kansas new species resembles E. Pulcella YOUNG- and Missouri. QUIST and DOWNS described from the Two forms of Streptognathodus are Lower Pennsylvanian of Iowa. discriminated from this fauna. S. japo- Ligonodina is also a long-ranged genus nicus is very abundant and is a charac- of Coleodontidae and has been reported teristic representative in this fauna , but from the Ordovician up to the Triassic it differs from many American species. rocks. L. hanaii is a rare species in S. expansus is rare, but it resembles S. our collection and it may he related wabaunsensis GUNNELL and other Pen- with L. typa (GUNNELL) and also with nsylvanian species of U.S. A.. L. lexingtonensis (GUNNELL) reported Gnathodus opimus is fairly common in from the Desmoinesian and Missourian our collection, but it differs from most of North America. of the American and European species. Roundya subacodus (GUNNELL) is also As mentioned above the Omi conodont a rare species in this fauna . Detailed fauna is dominated by Streptognathodus comparison between our forms and the japonicas, Gnalhodus opimus, three new American ones seems to he difficult. but species of Hindeodella, Synprioniodina they stand very close each other . Ac- microdenta Spathognalhodus echigoensis cording to ELLISON (1941), R. subacodus and Ozarhodina orientate. ranges from the Desmoinesian through Up to date a few papers treated the Virgilian. Lower Pennsylvanian or Upper Namu- Lonchodina ? nipponica is also a rare rian conodonts were published, therefore, .