63 MIOCENE FORAMIiNIFERA IN CHUGOKU, JAPAN . By Shigeo MURATA* Abstract: No one has ever reported on the smaller foraminifera in the Miocene sediments of Chugoku, Japan. The writer discovered it in the Tortonian, the Helvetian and the Burdigalian in the Miocene of Chugoku. Here, the writer wants to present some of his researches concerning the stratigraphical, micro' paleontological and paleo-ecological significance of tho Miocene foraminifera in this district. The new species is described. INTRODUCTION The Miocene sediments in Chugoku, hitherto, have heen investigated in •detail on the stratigraphy and paleontology, except on the foraminiferology. Since his micropaleonte- logical study have been tried on the Miocene formations in the vicinity of Matsue City, shimane Pref., the writer has started on some researches by the foraminifera in the Miocene of Chugoku. In the present paper, the Miocene foraminifera . frem Chugoku and their stratigraphical, micropaleontological and paleo-ecologicql significances are dealt with. These were collected by the writer from l951 to 1953, and are now kept in the cellection of the Mining Department, . Kyushu Institute of Technology. Here the writer would like to express his cordinal thanks to Dr. K. Asano of the Inst- itute of Geology and Paleontology, Tohoku University, Sendai, for his kind advices and comments, and Prof. G. Imamura of the Institute of Geology, Hirds' hima University, Hiro• shima, for his 'kind encouragements and suggestions given to the writer to the present study. He is particularly grateful to Dr. S. Jizaimaru of the Kyushu Institute of Technology for his criticism and for reading the manuscript. ' MIOCENE STRATIGRAPHY OF CHUGOKU •' The inVestigation of the Miocene stratigraphy in Chugoku has made very great progress, ewing to the researches done by Dr. Y. Otuka, Dr. T. Tomita and G. Imamura and hi$ fellows. By these recent studies, the Miocene stratigraphy in thig di$trict has heen estab- lished as shown in Table 1. The Kimitani, the Naheyama and the Yatadani group deyeloped aleRg the coast frenting the Japan Sea in Chugoku, and the lower member of the Miyoshi and the Katsnta group . in the Miyoshi and the Tsuyama basin among the mountains of the aferementiosted district are the coal bearing formations which censtitute the Kimitani, the Shimane, the Kekubu} the Futami and the Tsuyama coal field, respectively. The Koura series, including the above mentioned group, consists mainly of sandgtone, *Mining Department, Kyushu Institute ef Technology, { 64 shigeo Murata shale and conglamerate with intercalated lignites, which contains the comptoneipdyllum- ttguidamber flora, a characteristics of the Burdigalian, lying uneonformal)ly above the Paleozoic, tihe gneiss, the granite and the quartz-porphyty etc. As to the geological age, the terrestrial sediments just eited, unconformably overlain by the Opercude'na-Miogypsincb-Vicarya zone mqntig.necl belQw, may be, •assigned to the lewe; Burdigalian, the lower Miocene. Th,q Tany}azukuri serieg includes the upper shale and the lower sandstone and conglome-. rate member with the 0perculina-Miogypsina-Vicarora fauna, which contains the tuff zone in the middle part. The sediments corespond to the Tamazukuri series in Hiroshima and Okayama ' Pref. have the aforementioned fauna, while in the Tamazukuri group and its equivalent formations in Shimane and Yamaguchi Pref. developed along the coast of the Japan Sea this fauna have not been found. The Iast mentioned sediments, however, included the characteristic species of the Opmczslt'na-IMogypsina horizon in Toyama PreÅí, namely Siraton'a siratoriensis (OT(JKA), Thptasira n. sp. and Venenicardia (Cptclocardia) n. sp. etc., and also the same species as that of the Miyoshi ' and the Tsuyama btisin, namely &'ratoria siratoriensis, Pecten kagnnzianus and Pecten kimurai etc. Therefore, the last ment! ion'ed group may be correlated with the Operculina-Miogorpsina zone. There has been found E'thothamm'um ramosissiumum REuSS, a characteristics of the Miocene of Japan, in the Kaw'ajiri formation, ' the upper member of the Yuyawan group equivalent to the ahove pieriti'oned group. ' - Judging from the similarity of these faunas, the intercalation of the tuff in the middle part of these sediments and the change of the deposition indicating the same transgressien stBge in each group, the Tamazukuri series may be referred to the upper Burdigalian in the'European standard.. These marine groups include the great number of the foraminifera mentioned,s. below. ' L T,he Fujina series in S'himane Pref. consists of sandstone, shale and conglomerate with the so-called ""Fujina fauna", a characteristics of the Tortonian of Japan, uneonfoimably lying above the Omori series mentioned below. Desmostylus 1'apombus TOKUNAGA, found , inahorizonalttle higher than the 0perculina-Miogypsiua horizon in Japan, has been discovered in the 'lower Fujina series near Wakayama, south of the Shinzi Lake, Shimane PreÅí The Fujina series, therefore, is marine in origin, and may be correlated with the Tortonian. The Omori series in this district consists of basaltic, liparitic and andesitic rocks and their pyroclastics with intercalated sandstone and shale with a few foraminifera. The Omori Series which Iies between the Fujina and the Tamazukuri, therefore, may be referred to the Helvetian'stage. The Matsue series, the uppermost Miocene in Chugoku, unconformably lying above the' Fujina geries, consists of shale, and sandstone with intercalated basaltic rock and it's pyroclastics with the molluscan faunule. This series belongs to a shallow water facies, arid' may be 'referred to 'the Sarmatian, the upper Miocene. The complete Miocene formations are .the Shinzi group in the Shimane Peninsula, -- MJ'oeene Foraminifera •i Chugoku, Japan 65 S"himane Pref. It has been said that the Shinzi' group, thickness up to 2ooem., had been depesiKed in the se-called ""Shinzi geesyncline" during the Miocene age in that area. By his rece'nt stratigraphical and paleontological $tudies, Y. Tai referred the Koura sandstone, the Josoji shale, the Ushikiri alternation, the Furue mudstone and the Matsue sandstone formation in this group approximately to the lower Burdigalian, the upper Burdigalian, the Helvetian, the Tortonian and the Sarmatian stage respective!y. MIOCENE FORAMINIFERA IN CHUGOKU The Miecene fossi'1 remains of the smaller foraminifera in Chugoku were found by the writer in three stages, namely the Tortonian, the Helvetian and the Burdigalian. The T6rtonian foraminifera was collected from the Shimane Peninsula, the vicinity of Matsue City, the southern area of the Shinzi Lake and lzumo City in Shimane Pref. These distriets include the .following species. Cyelammiua caneelZata BRADy vr C. incisa (STACHE) r 'C. 7'apaiNkra AsANo c C. erbiczslan's BRADy r . `' '' Haplophragnicles cornpressam LFRoy c 4 H. renzi ASANO' f Trochammina mobensis AsANo vr 'Mastinottiella commune's diORBIGNY c Plectina sp. ' ' r Gaucbyt'ua sp. , r QitangzseZoculina sp. vr. lagenonodosaria scaim's (BATseH) vr Nedosaha sp. , vr Eponides pp. vr Anomaliua sp. vr Among them, Cyclamunv'na irutsa, C. orbicularis, C. pasigla, C. (xmcezatua, C. ]'aporNeca, Haplophragmoides compressum, H. renzi, Trochamnina nebe7ut's and MavtinottieZla communis are the characteristic species of the Miocene in JRpan. The abundant occurrence of Cptclammina ]' aponica, C. pasiZla, Haplophragnoictes campressum, H. rend and Martimottiella communis has been reported in the Tortonian sediments of Akita, Niigata and Toyama Pref. etc. These may be considered to have been affected by the colder Kurile current (er Oyashiro-current). And alse this assemblage hag very great number of the apenaceous 66 - • Shigeo Murata forms, namely C.ieclammina, llapZophragmoides, Trechamm'ua and MartinottielZa etc., and few calcareo"s forms, such as Lagenonedes(uria and ATmbsan'a etc. Desmostylus ]'apani(xss ToKVNAGA, a colder water species in Japan, has been discovered in the vicinity ef Wakayama, south of the g. hinzi Lake. Judging from these facts, it seems reasonable to conclude that the Tortonian age must have been under the influence of the colder KuriIe current in the abeve mentioned district. This conclusion harmonise well with that from the study of the molluscan faunule by Y. Otuka and Y. Tai. The foraminifera of the Helvetian age has been discovered very poorly in the Shimane Peninsula, the southern area of the Shinzi Lake and Izumo City, Shimane Pref. These are only two following species, which aTe rarely found and only the arenaceous form. Cyclamnziua incisa (STACHE) r As already stated, the Omori series in the Helvetian consists of basaltic, liparitic and andesitic rocks and their pyroclastics with intercalated sandstone, shale and conglomerate. In the Helvetian, an intense volcanicity took place in the above mentiened district, probably along the present coast of the Japan Sea in Chugoku. The above mentioned facts have been recognized also in Akita Pref. and Hokkaido ete. These suggest that the larger form Cyclammina prefers an abnormal condition due to the volcanic activity. Judging from these facts, it may be concluded that the Helvetian sediments in this dis- ' trict indicate a colder water condition affected by more intense volcanicity than that of the Tortonian age. The Burdigalian foraminifera were found numerous in Chugoku, which may be divided into three types aS follows. The first assemblage of the Burdigalian was discovered by the writer from the Miyoshi and the Tsuyama basin among the mountains