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Synopsis of Japanese Neogene stages
Palaeogeography, Palaeoclimatology, Palaeoecology, 46 (1984): 1--10 Elsevier Science Publishers B.V., Amsterdam Printed in The Netherlands
SYNOPSIS OF JAPANESE NEOGENE STAGES
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NOBUOIKEBE' andRYUICHITSUCHP 'Tezukayarna University, Nara 631 (Japan) aGeoscience Institute, Faculty of Science, Shizuoka University, 836, Ohya, Shizuoka 422 (Japan) (Received July 15, 1983; accepted October 25, 1983) ABSTRACT
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Ikebe, N. and Tsuchi, R., 1984. Synopsis of Japanese Neogene stages. Palaeogeogr., Palaeoclimatol., Palaeoecol., 46 : 1--10, Japanese Neogene stages are examined in the light of recent biostratigraphic and chronologic studies. Precise biochronologic positions of respective stratotypes are elucidated by utilizing planktonic foraminifers within the framework of the radiometric time scale. The late early Miocene Haranoyan, middle Miocene Tozawan, Kaburan and Fujian, late Miocene~early Pliocene Yuian, and late Pliocene--early Pleistocene Totomian, Suchian, Kechienjian and Yuzanjian Stages are now effective for the chronostratigraphic division of Neogene sequences in Japan. Some related problems are also discussed. The Kaburan and Fujian Substages are elevated to Stages. INTRODUCTION J a p a n e s e N e o g e n e stages w e r e e s t a b l i s h e d b y M a k i y a m a ( 1 9 3 1 , 1939) on t h e basis of t h e l i t h o s t r a t i g r a p h y a n d b e n t h i c faunal b i o s t r a t i g r a p h y o f the K a k e g a w a a n d s o m e o t h e r areas in central J a p a n . T h e six stages are: " e a r l y M i o c e n e " Asagaian a n d O i g a w a n , " m i d d l e M i o c e n e " T o g a r i a n , " l a t e M i o c e n e " Y u i a n , a n d " P l i o c e n e " D a i n i t i a n and K e t i e n z i a n (or K e c h i e n j i a n ; M a k i y a m a , 1939). L a t e r the " l a t e m i d d l e M i o c e n e " T o z a w a n and " l a t e P l i o c e n e " Y u z a n j i a n w e r e a d d e d , a n d t h e Dainitian was r e p l a c e d b y the S u c h i a n (Makiy a m a , 1 9 4 7 , 1 9 5 2 ; M a k i y a m a a n d S a k a m o t o , 1957). A f t e r w a r d s , t h e " e a r l y P l i o c e n e " T o t o m i a n was p r o p o s e d b y T s u c h i ( 1 9 6 1 ) o n the basis o f t h e m o l l u s c a n faunal succession, a n d the early M i o c e n e stages LM-1 a n d LM-2 a n d t h e m i d d l e M i o c e n e K a b u r a n were p r o p o s e d b y I k e b e a n d A s a n o ( 1 9 7 3 ) a n d I k e b e et al. ( 1 9 7 7 ) b a s e d p r i m a r i l y on p l a n k t o n i c f o r a m i n i f e r a l biostratigraphy. R e c e n t studies o n b i o s t r a t i g r a p h y a n d b i o c h r o n o l o g y h a v e p e r m i t t e d m o r e precise i n t e r r e g i o n a l c o r r e l a t i o n o f N e o g e n e m a r i n e s e q u e n c e s and m o r e precise c h r o n o l o g i c p o s i t i o n s o f stage s t r a t o t y p e s b y utilizing d a t u m levels o f p l a n k t o n i c microfossils. R e e x a m i n a t i o n a n d e v a l u a t i o n of m a n y N e o g e n e stages, t h e r e f o r e , b e c a m e n e c e s s a r y . T h e p r e s e n t s t a t u s o f b i o s t r a t i g r a p h i c a n d c h r o n o s t r a t i g r a p h i c s t u d i e s o f J a p a n e s e N e o g e n e stages are briefly s u m m a r i z e d a n d s o m e r e l a t e d p r o b l e m s are discussed in this article. 0031-0182/84/$03.00
© 1984 Elsevier Science Publishers B.V.
BIOSTRATIGRAPHIC AND CHRONOLOGIC SYNOPSIS OF THE NEOGENE STAGES (Fig.l)
Early Miocene stages The Asagaian, the stratotype of which is the Asagai Sandstone in the J o b a n coal field, is characterized by the cold-water Asagai molluscan fauna. As some typical elements of the fauna are found mixed in the Ashiya fauna of the late Oligocene Ashiya Group in north Kyushu (Tsuchi et al., 1983a), the Asagai Formation is considered to be of late Oligocene age. Planktonic microfossils are scarce in the Asagai Formation. The Oigawan has the Oigawa Group in the Kakegawa area as its type. The Oigawa Group consists of the lower Lepidocyclina-bearing Megami Formation and the upper flysch-type Horai Formations. According to planktonic foraminiferal studies, the Megami is synchronous with the t y p e Tozawan (Saito, 1963;Ujii~, 1975), and the Horai is partially assigned to the Oligocene (Saito, 1960). The amendment of the definition of the Oigawan is a future problem. F o r the early Miocene stages, Ikebe et al. (1977) proposed the tentatively named LM-1 and LM-2, which were provisionally defined as the interval from the Globigerinoides base datum to the Globigerinatella insueta base datum and the following interval to the Praeorbulina datum, respectively. The early part of the early Miocene sequences have scarcely been recognized in Japan. However, the LM-1 may be represented by the upper part of the Nichinan Group in eastern Kyushu, in which occurrences of Globigerinoides primordius, G. quadrilobatus immaturus and Globoquadrina dehiscens have been reported (Shuto, 1963; Nishi in Kammera et al., 1983). The LM-2 is represented b y the Kurami Group in the Kakegawa area. Recently, Tsuchi et al. (1983b) proposed the name Haranoyan for replacing the provisional LM-2, on the basis of the planktonic foraminiferal biostratigraphy of the section of the Kurami Group along the River Haranoyagawa (Ibaraki et al., 1983). The Kurami Group is predominantly siliceous siltstone and extends biostratigraphically from the Globigerinatella insueta base datum to the level a little above the Globigerinoides sicanus base datum, of late early Miocene age, though the base is not yet clearly defined owing to the paucity of microfossils.
Middle Miocene stages The Togarian stratotype is the Miogypsina-bearing Togari Formation in the Mizunami area, northeast of Nagoya, the stratigraphy of which has, however, been revised subsequently. From studies on planktonic foraminifers, the A k e y o Formation of the Mizunami Group, which is nearly equivalent to the Togari, is correlative with the type Tozawan (Saito, 1963; Ibaraki, 1981).
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T h e T o z a w a n s t r a t o t y p e comprises the Saigo Group, which rests confo r mab ly on the Kurami G r o u p and is u n c o n f o r m a b l y overlain by the Sagara Group. T h e Saigo G r o u p is characterized by occurrences of Lepidocyclina and Miogypsina. Ikebe et al. (1977) defined the T ozaw an as the interval from the Praeorbulina da t um to the Orbulina datum. T he Saigo G roup
ranges, however, from a little below the Praeorbulina datum up to the horizon a little below the Orbulina datum (Ibaraki et al., 1983), being latest early Miocene or earliest middle Miocene age. Biostratigraphic studies by means of calcareous nannoplankton have also been made in the Pacificside areas. The Saigo Group is assigned to the calcareous nannoplankton zones CN 3 or CN 4 (Honda, 1981, 1982). The Kaburan stratotype is a section of the middle part of the Tomioka Group along the River Kaburagawa in the Tomioka area. Ikebe et al. (1977) and Ikebe (1978) defined the Kaburan as the interval from the Orbulina datum to the Globorotalia acostaensis base datum, consisting of the Kaburan Substage for the interval from the Orbulina datum to the Globigerina nepenthes base datum, and the Fujian Substage for the rest of the interval. The Tomioka Group consists of several formations and includes successive datum levels: Praeorbulina, Orbulina, the base of Globorotalia peripheroacuta, the base of Sphaeroidinellopsis subdehiscens and the base of Globigerina nepenthes. The Orbulina and Globigerina nepenthes datums are, respectively, recognized in the basal part of the Haratajino Formation and the middle of the Yoshii Formation (Chiji and Konda, 1978). Takayanagi et al. (1978) have pointed out a hiatus within the type sequence and uncertainties over the stage boundaries. The Orbulina datum is estimated at 15.5 Ma from interpolation of K-Ar ages obtained from the Tozawan volcanic rocks in the Hokuriku area and the Kaburan acidic intrusives in Kii Peninsula (Ikebe et al., 1972; Tsuchi et al., 1981). The Globigerina nepenthes base d a t u m is estimated at 11.6 Ma from K-Ar ages of the Fujiki T u f f of the Tomioka Group (Shibata et al., 1979). The horizons from the Globigerina nepenthes datum to the Globorotalia acostaensis datum are recognized not in the Tomioka area but in the Daigoyama Formation of the Nishiyatsushiro Group in the Minobu area, west of Mount Fuji. This is the stratotype of the Fujian.
Late Miocene--early Pliocene stages The Yuian stratotype was originally the entire succession of the Sagara Group in the Kakegawa area. The Yuian was partially amended by Tsuchi (1961) on the basis of a revision of the lithostratigraphy and biostratigraphy of the Sagara Group. The group is characterized by a calcareous sponge Sagarites (Makiyama, 1931) and the warm water Sagara molluscan fauna, the age of which ranges from Zone N.14, middle Miocene, to Zone N.19, early Pliocene (Ujii6 and Hariu, 1975; Tsuchi and Ibaraki, 1981). The lower part of the group is, therefore, nearly equivalent to the Fujian. Ikebe et al. (1977) redefined the Yuian as the upper part of the Sagara Group corresponding to the interval from the Globorotalia acostaensis datum up to a little below the G. tosaensis base datum. As the original Yuian covers such a long interval of middle Miocene to early Pliocene time, it is proposed to establish the Fujian Stage and define the lower part of the Sagara Group as
the parastratotype of the Fujian. The Kaburan and Fujian are here redefined and elevated to the rank of full stages. Late Pliocene---early Pleistocene stages The Totomian, Suchian and Kechienjian stratotypes are assigned to the lower, middle and upper part of the Kakegawa Group, respectively. The Kakegawa Group, conformably lying on the Sagara Group, can be stratigraphically divided by well-defined key pyroclastic layers into three parts, which have been closely tied to planktonic foraminiferal datum levels as well as molluscan faunal changes. The Yuzanjian stratotype is the Soga Group which conformably lies on the Kakegawa Group and is unconformably overlain by the Pleistocene Ogasayama Gravels. Makiyama (1931) provisionally used infra-Dainitian for a part of the Totomian. The Suchian, Kechienjian, and Yuzanjian were slightly amended by Tsuchi (1961) and the planktonic foraminiferal biostratigraphy was examined by Tsuchi and Ibaraki (1978). The Totomian is characterized by forerunners of the Kakegawa molluscan fauna, corresponding to horizons from the base of the group up to the Iozumi Tuff, namely from a little below the Globorotalia tosaensis base datum to slightly above the horizon of coiling change from dextral to sinistral in Pulleniatina spp., or the Pulleniatina DS datum. Fission track ages of 3.3 Ma have been obtained from the Arigaya Tuff, which is at a slightly higher horizon than the Globorotalia tosaensis datum (Nishimura, 1977). The Suchian, the acme of the Kakegawa molluscan fauna, corresponds to horizons from the Iozumi T u f f to the Hosaya Tuff, namely from the level a little above the Pulleniatina DS datum up to the Globorotalia truncatulinoides datum. The Kechienjian characterized by a modification of the Kakegawa molluscan fauna, corresponds to the interval from the Hosoya T u f f to the top of the Kakegawa Group, namely the Globorotalia truncatulinoides datum to the Pulleniatina SD datum, being Pliocene--Pleistocene in age. The Hosoya Tuff has been dated at 1.9 Ma by the fission track m e t h o d (Nishimura, 1977). The Yuzanjian, being characterized by the disappearance of the tropical elements of the Kakegawa molluscan fauna and also by the appearance of the Recent Kuroshio fauna, corresponds to the entire succession of the Soga Group, namely horizons from the Pulleniatina SD datum to the level a little below the Globorotalia tosaensis top datum, being early Pleistocene in age. Magneto-stratigraphic studies have also been made in the Kakegawa and Soga sections (Yoshida and Niitsuma, 1976 ; Ishida et al., 1980). Biochronologic positions of stratotypes of valid Neogene stages and related biohorizons are shown in Fig.2. The microplanktonic time scale here used is that given by Tsuchi et al. (1984). Correlation of Japanese Neogene stages with the Mediterranean stages is also attempted.
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G|oborotalia iosaensis B
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. D_ai_ji_ma_F .
Nish~urosawa F.
Onnagawa F.
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AKITA
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PROBLEMS OF JAPANESE NEOGENE STAGES As m e n t i o n e d above, nine stages are n o w e f f e c t i v e f o r t h e c h r o n o s t r a t i graphic division o f N e o g e n e s e q u e n c e s in J a p a n . T h e s e are: late early M i o c e n e H a r a n o y a n , m i d d l e M i o c e n e T o z a w a n , K a b u r a n and Fujian, late M i o c e n e - early Pliocene Yuian, and late P l i o c e n e - - e a r l y P l e i s t o c e n e T o t o m i a n , Suchian, K e c h i e n j i a n and Y u z a n j i a n . S e q u e n c e s assignable to the early p a r t of the early M i o c e n e including t h e P a l e o g e n e / N e o g e n e b o u n d a r y have n o t y e t b e e n fully e x a m i n e d in J a p a n , t h o u g h s o m e earliest M i o c e n e p l a n k t o n i c f o r a m i n i f e r s have b e e n r e c o v e r e d f r o m t h e so-called ' P a l e o g e n e ~' c o m p l e x on the Pacific side o f s o u t h e r n J a p a n ( S h u t o , 1 9 6 3 ; Saito, 1 9 8 0 , Nishi in K a m m e r a et al., 1983). T h e e s t a b l i s h m e n t of t h e earliest N e o g e n e stages is y e t t o be achieved. H a r a n o y a n e q u i v a l e n t s are r e c o g n i z e d s p o r a d i c a l l y on t h e Pacific side o f s o u t h e r n J a p a n in Boso, Miura and Kii Peninsulas, as p r e d o m i n a n t l y siliceous s e d i m e n t s . B e n t h i c faunal successions have n o t y e t b e e n described. T h e T o z a w a n correlatives are e x t e n s i v e l y k n o w n f r o m m a n y areas in J a p a n as Lepidocyclina a n d / o r Miogypsina-bearing and t h e t r o p i c a l - s u b t r o p i c a l K a d o n o s a w a m o l l u s c a n f a u n a - b e a r i n g f o r m a t i o n s . This stage is, t h e r e f o r e , a p p l i c a b l e t o a l m o s t all of J a p a n . B i o s t r a t i g r a p h y o f p l a n k t o n i c f o r a m i n i f e r s disclosed a large hiatus s p a n n i n g n e a r l y 4 Ma during m i d d l e M i o c e n e t i m e in m a r i n e s e q u e n c e s o n t h e Pacific coast of s o u t h e r n J a p a n . H e n c e , the K a b u r a n was p r o p o s e d . T h e areal distrib u t i o n of t h e K a b u r a n e q u i v a l e n t s and d e f i n i t i o n o f t h e i r b e n t h i c faunal c h a r a c t e r s are i m p o r t a n t f o r t h e N e o g e n e h i s t o r y o f J a p a n . T h e N e o g e n e m a r i n e f a u n a s in J a p a n are clearly divided into w a r m - and c o l d - w a t e r assemblages. T h e f o r m e r d o m i n a t e s s o u t h e r n J a p a n and t h e l a t t e r e x t e n d s into n o r t h e r n J a p a n and the Sea o f J a p a n side, respectively. Intraregional c o r r e l a t i o n o f N e o g e n e s e q u e n c e s in s o u t h e r n J a p a n has b e e n m a d e m o s t l y b y m e a n s o f p l a n k t o n i c f o r a m i n i f e r s . In n o r t h e r n J a p a n and o n the Sea o f J a p a n side, h o w e v e r , it has b e e n achieved m a i n l y b y using d i a t o m s . T h e stages established in s o u t h e r n J a p a n are, t h e r e f o r e , difficult to a p p l y d i r e c t l y to s e q u e n c e s in n o r t h e r n J a p a n and t h e Sea o f J a p a n side. In t h e oil field regions o f A k i t a and Niigata o n t h e Sea o f J a p a n side, l i t h o s t r a t i g r a p h i c n a m e s h a v e f r e q u e n t l y b e e n used as stages in p r a c t i c e , and p l a n k t o n i c f o r a m i n i f e r a l z o n e s f o r t h e s e regions have b e e n p r o p o s e d (Maiya et al., 1976). F o r m a l stages b a s e d u p o n t h e l i t h o s t r a t i g r a p h y and biostratiFig.2. Biochronologic positions of Japanese Neogene stages, stratotypes and key biohorizons. Planktonic foraminiferal zones are those of Blow (1969). The microplanktonic time scale here used is that given by Tsuchi et al. (1984), slightly revised from Tsuchi et al. (1981). Correlation of Japanese Neogene stages with the Mediterranean stages is attempted. Lithostratigraphy of the oil field regions of Niigata and Akita is shown at the right side of the figure. Legend: G. = group; F. = formation; B = base datum; T = top datum; DS, SD = horizons of coiling change from dextral to sinistral or sinistral to dextral in planktonic foraminiferal species.
graphy of the oil field regions may prove to be necessary (Fig.2). More precise interregional correlation between southern Japan and northern Japan requires integrated biostratigraphic studies of respective stratotypes by means of various taxa of planktonic microfossils. ACKNOWLEDGEMENTS Dr. N. d e B . H o r n i b r o o k o f N e w Z e a l a n d G e o l o g i c a l S u r v e y r e a d a n d r e v i s e d t h e m a n u s c r i p t . D e e p a p p r e c i a t i o n is d u e t o all t h e m e m b e r s o f t h e IGCP-114 National Working Group of Japan for their helpful co-operation. REFERENCES Blow, W. H., 1969. Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In: P. BrSnniman and H. H. Renz (Editors), Proceedings of First International Conference on Planktonic Microfossils, Geneva, 1967, 1: 199--422. Chiji, M. and Konda, I., 1978. Planktonic foraminiferal biostratigraphy of the Tomioka Group and the Nishiyatsushiro and Shizukawa Groups, central Japan, with some consideration on the Kaburan Stage (Middle Miocene). In: K. Huzita et al. (Editors). Cenozoic Geology of Japan, Prof. N. Ikebe Memorial Volume, Osaka, pp. 73--92 (in Japanese with English abstract). Honda, N., 1981. Kakegawa area (2). In: R. Tsuchi (Editor), Fundamental Data on Japanese Neogene Bio- and Chronostratigraphy - - S u p p l e m e n t , IGCP-114 National Working Group of Japan, pp. 5--6 (in Japanese with English captions). Honda, N., 1982. Calcareous nannoplankton biostratigraphy of upper Cenozoic sequences on the Pacific side areas in Japan. In: Abstr. Pap., Annu. Meet. Geol. Soc. Jpn., Niigata, 1982, p. 178 (in Japanese). Ibaraki, M. 1981. Geologic ages of "Lepidocyclina" and Miogypsina horizons in Japan as determined by planktonic foraminifera. In: Proc. IGCP-114 International Workshop on Pacific Neogene Biostratigraphy. Osaka, 1981, pp. 118---119. Ibaraki, M., Tsuchi, R. and Takayanagi, T., 1983. Early Neogene planktonic foraminiferal biostratigraphy in the Kakegawa area, the Pacific coast of central Japan. Rep. Fac. Sci., Shizuoka Univ., 17: 101--116. Ikebe, N., 1978. Bio- and chronostratigraphy of the Japanese Neogene, with remarks on paleogeography. In: K. Huzita et al. (Editors), Cenozoic Geology of Japan. Prof. N. Ikebe Memorial Volume, Osaka, pp. 13--34 (in Japanese with English abstract). Ikebe, N. and Asano, K., 1973. Interregional correlation of the Neogene based on planktonic datum levels and radiometric datings. Mem. Geol. Soc. Jpn., 8 : 2 0 3 - - 2 1 4 (in Japanese with English abstract). Ikebe, N., Takayanagi, Y., Chiji, M. and Chinzei, K., 1972. Neogene biostratigraphy and radiometric time scale of Japan - An a t t e m p t at intercontinental correlation. Pac. Geol., 4: 39--78. Ikebe, N. and Working Group, 1977. Summary of bio- and chronostratigraphy of the Japanese Neogene. In: Proc. First International Congress on Pacific Neogene Stratigraphy, T o k y o , 1976, pp. 93--114. Ishida, S., Makinouchi, T., Nishimura, A., Takemura, K., Danhara, T., Nishimura, K. and Hayashida, A., 1980. Middle Pleistocene of Kakegawa district, central Japan. Quaternary Res., 1 9 : 1 3 3 - - 1 4 8 (in Japanese with English abstract). Kammera, K., Sakai, T., Tsuji, R. and Nishi, H., 1983. Geology of the southern and eastern part of the Nichinan mountainous area. In: Guidebook for Excursion, Annu. Meet. Geol. Soc. Jpn., Kagoshima, 1983, pp. 23--26 (in Japanese).
Maiya, S., Saito, T. and Sato, T., 1976. Late Cenozoic planktonic foraminiferal biostratigraphy of northwest Pacific sedimentary sequences. In: Y. Takayanagi and T. Saito (Editors), Progress in Micropaleontology. Spec. Publ. Am. Mus. Nat. Hist., pp. 395--422. Makiyama, J. 1931. Stratigraphy of the Kakagawa Pliocene in Totomi. Mere. Coll. Sci., Univ. Kyoto, Ser. B, 7: 1--53. Makiyama, J., 1939. The Neogenic stratigraphy of the Japan Islands. In: Proc. 6th Pac. Sci. Congr., pp. 641--649. Makiyama, J., 1947. Two stages of the middle Miocene in Japan. Mem. Coll. Sci., Univ. Kyoto, Ser. B, 19: 33--36. Makiyama, J., 1952. On the mutation of the fossil Glycymeris rotunda. Trans. Proc. Palaeontol. Soc. Jpn., N.S., 5: 131--138. Makiyama, J. and Sakamoto, T., 1957. Geological map and explanatory text of the geological map of Japan, Mitsuke and Kakezuka, 1:50,000. Geological Survey of Japan, Tokyo, pp. 1--45 (in Japanese with English abstract). Nishimura, S., 1977. Re-examination of the fission track age of volcanic tuff. Rep. Kansai Branch, Geol. Soc. Jpn., 8 0 : 8 (in Japanese). Saito, T., 1960. Tertiary stratigraphy of the Kakegawa district, central Japan, and its planktonic foraminifera. Contrib. Inst. Geol. Paleontol., Tohoku Univ., 5 1 : 1 - - 4 5 (in Japanese with English abstract). Saito, T., 1963. Miocene planktonic foraminifera, Honshu, Japan. Sci. Rep. Tohoku Univ., 2nd Set. (Geol.}, 35: 123--209. Saito, T., 1980. An Early Miocene (Aquitanian) planktonic foraminiferal fauna from the Tsuro Formation, the youngest part of the Shimanto Supergroup, Shikoku, Japan. In: T. Taira and M. Tashiro (Editors), Geology and Paleontology of the Shimanto Belt. Selected Papers in Honor of Prof. J. Katto, pp. 227--234. Shibata, K., Uchiumi, S. and Nakagawa, T., 1979. K-Ar results -- 1. Bull. Geol. Surv. Jpn., 3 0 : 6 7 5 - - 6 8 6 (in Japanese). Shuto, T., 1963. Geology of the Nichinan area, with special reference to the Takachiho disturbance. Mere. Fac. Sci., Kyushu Univ., Ser. D, 6 : 1 3 5 - - 1 6 6 (in Japanese with English abstract). Takayanagi, Y., Sakai, T., Oda, M., Takayama, T., Oriyama, J. and Kaneko, M., 1978. Problems relating to the Kaburan Stage. In: K. Huzita et al. (Editors), Cenozoic Geology of Japan. Prof. N. Ikebe Memorial Volume, Osaka, pp. 93--112 (in Japanese with English abstract). Tsuchi, R., 1961. On the late Neogene sediments and molluscs in the Tokai region, with notes on the geologic history of the Pacific coast of Southwest Japan. Jpn. J. Geol. Geogr., 32: 437--456. Tsuchi, R. and Ibaraki, M., 1978. Late Neogene succession of molluscan fauna on the Pacific coast of southwestern Japan,with reference to planktonic foraminiferal sequence. Veliger, 21: 216--224. Tsuchi, R. and Ibaraki, M., 1981. Kakegawa area. In: R. Tsuchi (Editor), Neogene of Japan -- Its biostratigraphy and Chronology. IGCP-114 National Working Group of Japan, pp. 37--41. Tsuchi, R., Takayanagi, Y. and Shibata, K., 1981. Neogene bio-events in the Japanese Islands. In: R. Tsuchi (Editor), Neogene o f J a p a n - - I t s B i o s t r a t i g r a p h y and Chronology. IGCP-114 National Working Group of Japan, pp. 15--32. Tsuchi, R., Shuto, T. and Ibaraki, M., 1983a. Geologic ages of the Ashiya Group and the Ashiya fauna as determined by planktonic foraminifera. In: Abstr. Pap., Annu. Meet. Geol. Soc. Jpn., Kagoshima 1983, p. 125 (in Japanese). Tsuchi, R. and IGCP-114 National Working Group of Japan, 1983b. Neogene chronostratigraphy and bio-events in the Japanese Islands. In: Abstr., 15th Congr., Pac. Sci. Assoc., Dunedin, 1 9 8 3 , p . 242. Tsuchi, R. and IGCP-114 National Working Group of Japan, 1984. Neogene chronostratigraphy and bio-events in the Japanese Islands. Palaeogeogr., Palaeoclimatol., Palaeoecol., 4 6 : 3 7 - - 5 1 (this issue).
10 Ujii6, H., 1975. An early Miocene planktonic foraminiferal fauna from the Megami Formation, Shizuoka Prefecture. Bull. Natl. Sci. Mus.,Tokyo, Ser. C (Geol.), 1: 83--92. Ujii6, H. and Hariu, S., 1975. Early Pliocene to middle Miocene planktonic foraminifera from the type section of the Sagara Group, central Japan. Bull. Natl. Sci. Mus., Tokyo, Ser. C (Geol.), 1: 37--54. Yoshida, K. and Niitsuma, N., 1976. Magnetostratigraphy in the Kakegawa district. In: R. Tsuchi (Editor), Guidebook for Excursion 3, Kakegawa District. First Int. Congr. Pacific Neogene Stratigraphy, T o k y o , 1976, pp. 54--59.
SYNOPSIS OF JAPANESE NEOGENE STAGES
1
NZ ~ 1 9 8 3
NOBUOIKEBE' andRYUICHITSUCHP 'Tezukayarna University, Nara 631 (Japan) aGeoscience Institute, Faculty of Science, Shizuoka University, 836, Ohya, Shizuoka 422 (Japan) (Received July 15, 1983; accepted October 25, 1983) ABSTRACT
c
3
s
Ikebe, N. and Tsuchi, R., 1984. Synopsis of Japanese Neogene stages. Palaeogeogr., Palaeoclimatol., Palaeoecol., 46 : 1--10, Japanese Neogene stages are examined in the light of recent biostratigraphic and chronologic studies. Precise biochronologic positions of respective stratotypes are elucidated by utilizing planktonic foraminifers within the framework of the radiometric time scale. The late early Miocene Haranoyan, middle Miocene Tozawan, Kaburan and Fujian, late Miocene~early Pliocene Yuian, and late Pliocene--early Pleistocene Totomian, Suchian, Kechienjian and Yuzanjian Stages are now effective for the chronostratigraphic division of Neogene sequences in Japan. Some related problems are also discussed. The Kaburan and Fujian Substages are elevated to Stages. INTRODUCTION J a p a n e s e N e o g e n e stages w e r e e s t a b l i s h e d b y M a k i y a m a ( 1 9 3 1 , 1939) on t h e basis of t h e l i t h o s t r a t i g r a p h y a n d b e n t h i c faunal b i o s t r a t i g r a p h y o f the K a k e g a w a a n d s o m e o t h e r areas in central J a p a n . T h e six stages are: " e a r l y M i o c e n e " Asagaian a n d O i g a w a n , " m i d d l e M i o c e n e " T o g a r i a n , " l a t e M i o c e n e " Y u i a n , a n d " P l i o c e n e " D a i n i t i a n and K e t i e n z i a n (or K e c h i e n j i a n ; M a k i y a m a , 1939). L a t e r the " l a t e m i d d l e M i o c e n e " T o z a w a n and " l a t e P l i o c e n e " Y u z a n j i a n w e r e a d d e d , a n d t h e Dainitian was r e p l a c e d b y the S u c h i a n (Makiy a m a , 1 9 4 7 , 1 9 5 2 ; M a k i y a m a a n d S a k a m o t o , 1957). A f t e r w a r d s , t h e " e a r l y P l i o c e n e " T o t o m i a n was p r o p o s e d b y T s u c h i ( 1 9 6 1 ) o n the basis o f t h e m o l l u s c a n faunal succession, a n d the early M i o c e n e stages LM-1 a n d LM-2 a n d t h e m i d d l e M i o c e n e K a b u r a n were p r o p o s e d b y I k e b e a n d A s a n o ( 1 9 7 3 ) a n d I k e b e et al. ( 1 9 7 7 ) b a s e d p r i m a r i l y on p l a n k t o n i c f o r a m i n i f e r a l biostratigraphy. R e c e n t studies o n b i o s t r a t i g r a p h y a n d b i o c h r o n o l o g y h a v e p e r m i t t e d m o r e precise i n t e r r e g i o n a l c o r r e l a t i o n o f N e o g e n e m a r i n e s e q u e n c e s and m o r e precise c h r o n o l o g i c p o s i t i o n s o f stage s t r a t o t y p e s b y utilizing d a t u m levels o f p l a n k t o n i c microfossils. R e e x a m i n a t i o n a n d e v a l u a t i o n of m a n y N e o g e n e stages, t h e r e f o r e , b e c a m e n e c e s s a r y . T h e p r e s e n t s t a t u s o f b i o s t r a t i g r a p h i c a n d c h r o n o s t r a t i g r a p h i c s t u d i e s o f J a p a n e s e N e o g e n e stages are briefly s u m m a r i z e d a n d s o m e r e l a t e d p r o b l e m s are discussed in this article. 0031-0182/84/$03.00
© 1984 Elsevier Science Publishers B.V.
BIOSTRATIGRAPHIC AND CHRONOLOGIC SYNOPSIS OF THE NEOGENE STAGES (Fig.l)
Early Miocene stages The Asagaian, the stratotype of which is the Asagai Sandstone in the J o b a n coal field, is characterized by the cold-water Asagai molluscan fauna. As some typical elements of the fauna are found mixed in the Ashiya fauna of the late Oligocene Ashiya Group in north Kyushu (Tsuchi et al., 1983a), the Asagai Formation is considered to be of late Oligocene age. Planktonic microfossils are scarce in the Asagai Formation. The Oigawan has the Oigawa Group in the Kakegawa area as its type. The Oigawa Group consists of the lower Lepidocyclina-bearing Megami Formation and the upper flysch-type Horai Formations. According to planktonic foraminiferal studies, the Megami is synchronous with the t y p e Tozawan (Saito, 1963;Ujii~, 1975), and the Horai is partially assigned to the Oligocene (Saito, 1960). The amendment of the definition of the Oigawan is a future problem. F o r the early Miocene stages, Ikebe et al. (1977) proposed the tentatively named LM-1 and LM-2, which were provisionally defined as the interval from the Globigerinoides base datum to the Globigerinatella insueta base datum and the following interval to the Praeorbulina datum, respectively. The early part of the early Miocene sequences have scarcely been recognized in Japan. However, the LM-1 may be represented by the upper part of the Nichinan Group in eastern Kyushu, in which occurrences of Globigerinoides primordius, G. quadrilobatus immaturus and Globoquadrina dehiscens have been reported (Shuto, 1963; Nishi in Kammera et al., 1983). The LM-2 is represented b y the Kurami Group in the Kakegawa area. Recently, Tsuchi et al. (1983b) proposed the name Haranoyan for replacing the provisional LM-2, on the basis of the planktonic foraminiferal biostratigraphy of the section of the Kurami Group along the River Haranoyagawa (Ibaraki et al., 1983). The Kurami Group is predominantly siliceous siltstone and extends biostratigraphically from the Globigerinatella insueta base datum to the level a little above the Globigerinoides sicanus base datum, of late early Miocene age, though the base is not yet clearly defined owing to the paucity of microfossils.
Middle Miocene stages The Togarian stratotype is the Miogypsina-bearing Togari Formation in the Mizunami area, northeast of Nagoya, the stratigraphy of which has, however, been revised subsequently. From studies on planktonic foraminifers, the A k e y o Formation of the Mizunami Group, which is nearly equivalent to the Togari, is correlative with the type Tozawan (Saito, 1963; Ibaraki, 1981).
~0
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/ Fig.1. I n d e x m a p o f s t r a t o t y p e s a n d r e l a t e d areas o f J a p a n e s e N e o g e n e stages.
T h e T o z a w a n s t r a t o t y p e comprises the Saigo Group, which rests confo r mab ly on the Kurami G r o u p and is u n c o n f o r m a b l y overlain by the Sagara Group. T h e Saigo G r o u p is characterized by occurrences of Lepidocyclina and Miogypsina. Ikebe et al. (1977) defined the T ozaw an as the interval from the Praeorbulina da t um to the Orbulina datum. T he Saigo G roup
ranges, however, from a little below the Praeorbulina datum up to the horizon a little below the Orbulina datum (Ibaraki et al., 1983), being latest early Miocene or earliest middle Miocene age. Biostratigraphic studies by means of calcareous nannoplankton have also been made in the Pacificside areas. The Saigo Group is assigned to the calcareous nannoplankton zones CN 3 or CN 4 (Honda, 1981, 1982). The Kaburan stratotype is a section of the middle part of the Tomioka Group along the River Kaburagawa in the Tomioka area. Ikebe et al. (1977) and Ikebe (1978) defined the Kaburan as the interval from the Orbulina datum to the Globorotalia acostaensis base datum, consisting of the Kaburan Substage for the interval from the Orbulina datum to the Globigerina nepenthes base datum, and the Fujian Substage for the rest of the interval. The Tomioka Group consists of several formations and includes successive datum levels: Praeorbulina, Orbulina, the base of Globorotalia peripheroacuta, the base of Sphaeroidinellopsis subdehiscens and the base of Globigerina nepenthes. The Orbulina and Globigerina nepenthes datums are, respectively, recognized in the basal part of the Haratajino Formation and the middle of the Yoshii Formation (Chiji and Konda, 1978). Takayanagi et al. (1978) have pointed out a hiatus within the type sequence and uncertainties over the stage boundaries. The Orbulina datum is estimated at 15.5 Ma from interpolation of K-Ar ages obtained from the Tozawan volcanic rocks in the Hokuriku area and the Kaburan acidic intrusives in Kii Peninsula (Ikebe et al., 1972; Tsuchi et al., 1981). The Globigerina nepenthes base d a t u m is estimated at 11.6 Ma from K-Ar ages of the Fujiki T u f f of the Tomioka Group (Shibata et al., 1979). The horizons from the Globigerina nepenthes datum to the Globorotalia acostaensis datum are recognized not in the Tomioka area but in the Daigoyama Formation of the Nishiyatsushiro Group in the Minobu area, west of Mount Fuji. This is the stratotype of the Fujian.
Late Miocene--early Pliocene stages The Yuian stratotype was originally the entire succession of the Sagara Group in the Kakegawa area. The Yuian was partially amended by Tsuchi (1961) on the basis of a revision of the lithostratigraphy and biostratigraphy of the Sagara Group. The group is characterized by a calcareous sponge Sagarites (Makiyama, 1931) and the warm water Sagara molluscan fauna, the age of which ranges from Zone N.14, middle Miocene, to Zone N.19, early Pliocene (Ujii6 and Hariu, 1975; Tsuchi and Ibaraki, 1981). The lower part of the group is, therefore, nearly equivalent to the Fujian. Ikebe et al. (1977) redefined the Yuian as the upper part of the Sagara Group corresponding to the interval from the Globorotalia acostaensis datum up to a little below the G. tosaensis base datum. As the original Yuian covers such a long interval of middle Miocene to early Pliocene time, it is proposed to establish the Fujian Stage and define the lower part of the Sagara Group as
the parastratotype of the Fujian. The Kaburan and Fujian are here redefined and elevated to the rank of full stages. Late Pliocene---early Pleistocene stages The Totomian, Suchian and Kechienjian stratotypes are assigned to the lower, middle and upper part of the Kakegawa Group, respectively. The Kakegawa Group, conformably lying on the Sagara Group, can be stratigraphically divided by well-defined key pyroclastic layers into three parts, which have been closely tied to planktonic foraminiferal datum levels as well as molluscan faunal changes. The Yuzanjian stratotype is the Soga Group which conformably lies on the Kakegawa Group and is unconformably overlain by the Pleistocene Ogasayama Gravels. Makiyama (1931) provisionally used infra-Dainitian for a part of the Totomian. The Suchian, Kechienjian, and Yuzanjian were slightly amended by Tsuchi (1961) and the planktonic foraminiferal biostratigraphy was examined by Tsuchi and Ibaraki (1978). The Totomian is characterized by forerunners of the Kakegawa molluscan fauna, corresponding to horizons from the base of the group up to the Iozumi Tuff, namely from a little below the Globorotalia tosaensis base datum to slightly above the horizon of coiling change from dextral to sinistral in Pulleniatina spp., or the Pulleniatina DS datum. Fission track ages of 3.3 Ma have been obtained from the Arigaya Tuff, which is at a slightly higher horizon than the Globorotalia tosaensis datum (Nishimura, 1977). The Suchian, the acme of the Kakegawa molluscan fauna, corresponds to horizons from the Iozumi T u f f to the Hosaya Tuff, namely from the level a little above the Pulleniatina DS datum up to the Globorotalia truncatulinoides datum. The Kechienjian characterized by a modification of the Kakegawa molluscan fauna, corresponds to the interval from the Hosoya T u f f to the top of the Kakegawa Group, namely the Globorotalia truncatulinoides datum to the Pulleniatina SD datum, being Pliocene--Pleistocene in age. The Hosoya Tuff has been dated at 1.9 Ma by the fission track m e t h o d (Nishimura, 1977). The Yuzanjian, being characterized by the disappearance of the tropical elements of the Kakegawa molluscan fauna and also by the appearance of the Recent Kuroshio fauna, corresponds to the entire succession of the Soga Group, namely horizons from the Pulleniatina SD datum to the level a little below the Globorotalia tosaensis top datum, being early Pleistocene in age. Magneto-stratigraphic studies have also been made in the Kakegawa and Soga sections (Yoshida and Niitsuma, 1976 ; Ishida et al., 1980). Biochronologic positions of stratotypes of valid Neogene stages and related biohorizons are shown in Fig.2. The microplanktonic time scale here used is that given by Tsuchi et al. (1984). Correlation of Japanese Neogene stages with the Mediterranean stages is also attempted.
25 ~
t~
I
EPOCH & PLANKT. MEDITERR/~EAN FORN4 STAGE Ma SUBEPOCH ZONE "
JAPANESE NEOGENE STAGE
I
KAKEGANA
MINOBU
S~RATO~PE TOMIOKA
\
B
Nanatani F, I
Teradomaril F.
Shiiya F. I
Nishiyama I F.
.H_aiz_u_meF_.~
NIIGATA
Globigerinita dissimilis T , GIobigerinita unicava T Globigerinatella insueto B
Globigerinoides sicanus B
suturalis B
nepenthes B
GloborotQlie o c o s t a e n s i s s . s . B
Pulleniatina SD
G|oborotalia iosaensis B
~-- P u l l e n i o t i n a D S
Globorotalia truncatulinoides
Puileniatina SD
Globorotalia tosaensis T
KEY BIOHORIZON
. D_ai_ji_ma_F .
Nish~urosawa F.
Onnagawa F.
Funakawa F.
Tentokuji F
Sasaoka F.
AKITA
25
PROBLEMS OF JAPANESE NEOGENE STAGES As m e n t i o n e d above, nine stages are n o w e f f e c t i v e f o r t h e c h r o n o s t r a t i graphic division o f N e o g e n e s e q u e n c e s in J a p a n . T h e s e are: late early M i o c e n e H a r a n o y a n , m i d d l e M i o c e n e T o z a w a n , K a b u r a n and Fujian, late M i o c e n e - early Pliocene Yuian, and late P l i o c e n e - - e a r l y P l e i s t o c e n e T o t o m i a n , Suchian, K e c h i e n j i a n and Y u z a n j i a n . S e q u e n c e s assignable to the early p a r t of the early M i o c e n e including t h e P a l e o g e n e / N e o g e n e b o u n d a r y have n o t y e t b e e n fully e x a m i n e d in J a p a n , t h o u g h s o m e earliest M i o c e n e p l a n k t o n i c f o r a m i n i f e r s have b e e n r e c o v e r e d f r o m t h e so-called ' P a l e o g e n e ~' c o m p l e x on the Pacific side o f s o u t h e r n J a p a n ( S h u t o , 1 9 6 3 ; Saito, 1 9 8 0 , Nishi in K a m m e r a et al., 1983). T h e e s t a b l i s h m e n t of t h e earliest N e o g e n e stages is y e t t o be achieved. H a r a n o y a n e q u i v a l e n t s are r e c o g n i z e d s p o r a d i c a l l y on t h e Pacific side o f s o u t h e r n J a p a n in Boso, Miura and Kii Peninsulas, as p r e d o m i n a n t l y siliceous s e d i m e n t s . B e n t h i c faunal successions have n o t y e t b e e n described. T h e T o z a w a n correlatives are e x t e n s i v e l y k n o w n f r o m m a n y areas in J a p a n as Lepidocyclina a n d / o r Miogypsina-bearing and t h e t r o p i c a l - s u b t r o p i c a l K a d o n o s a w a m o l l u s c a n f a u n a - b e a r i n g f o r m a t i o n s . This stage is, t h e r e f o r e , a p p l i c a b l e t o a l m o s t all of J a p a n . B i o s t r a t i g r a p h y o f p l a n k t o n i c f o r a m i n i f e r s disclosed a large hiatus s p a n n i n g n e a r l y 4 Ma during m i d d l e M i o c e n e t i m e in m a r i n e s e q u e n c e s o n t h e Pacific coast of s o u t h e r n J a p a n . H e n c e , the K a b u r a n was p r o p o s e d . T h e areal distrib u t i o n of t h e K a b u r a n e q u i v a l e n t s and d e f i n i t i o n o f t h e i r b e n t h i c faunal c h a r a c t e r s are i m p o r t a n t f o r t h e N e o g e n e h i s t o r y o f J a p a n . T h e N e o g e n e m a r i n e f a u n a s in J a p a n are clearly divided into w a r m - and c o l d - w a t e r assemblages. T h e f o r m e r d o m i n a t e s s o u t h e r n J a p a n and t h e l a t t e r e x t e n d s into n o r t h e r n J a p a n and the Sea o f J a p a n side, respectively. Intraregional c o r r e l a t i o n o f N e o g e n e s e q u e n c e s in s o u t h e r n J a p a n has b e e n m a d e m o s t l y b y m e a n s o f p l a n k t o n i c f o r a m i n i f e r s . In n o r t h e r n J a p a n and o n the Sea o f J a p a n side, h o w e v e r , it has b e e n achieved m a i n l y b y using d i a t o m s . T h e stages established in s o u t h e r n J a p a n are, t h e r e f o r e , difficult to a p p l y d i r e c t l y to s e q u e n c e s in n o r t h e r n J a p a n and t h e Sea o f J a p a n side. In t h e oil field regions o f A k i t a and Niigata o n t h e Sea o f J a p a n side, l i t h o s t r a t i g r a p h i c n a m e s h a v e f r e q u e n t l y b e e n used as stages in p r a c t i c e , and p l a n k t o n i c f o r a m i n i f e r a l z o n e s f o r t h e s e regions have b e e n p r o p o s e d (Maiya et al., 1976). F o r m a l stages b a s e d u p o n t h e l i t h o s t r a t i g r a p h y and biostratiFig.2. Biochronologic positions of Japanese Neogene stages, stratotypes and key biohorizons. Planktonic foraminiferal zones are those of Blow (1969). The microplanktonic time scale here used is that given by Tsuchi et al. (1984), slightly revised from Tsuchi et al. (1981). Correlation of Japanese Neogene stages with the Mediterranean stages is attempted. Lithostratigraphy of the oil field regions of Niigata and Akita is shown at the right side of the figure. Legend: G. = group; F. = formation; B = base datum; T = top datum; DS, SD = horizons of coiling change from dextral to sinistral or sinistral to dextral in planktonic foraminiferal species.
graphy of the oil field regions may prove to be necessary (Fig.2). More precise interregional correlation between southern Japan and northern Japan requires integrated biostratigraphic studies of respective stratotypes by means of various taxa of planktonic microfossils. ACKNOWLEDGEMENTS Dr. N. d e B . H o r n i b r o o k o f N e w Z e a l a n d G e o l o g i c a l S u r v e y r e a d a n d r e v i s e d t h e m a n u s c r i p t . D e e p a p p r e c i a t i o n is d u e t o all t h e m e m b e r s o f t h e IGCP-114 National Working Group of Japan for their helpful co-operation. REFERENCES Blow, W. H., 1969. Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In: P. BrSnniman and H. H. Renz (Editors), Proceedings of First International Conference on Planktonic Microfossils, Geneva, 1967, 1: 199--422. Chiji, M. and Konda, I., 1978. Planktonic foraminiferal biostratigraphy of the Tomioka Group and the Nishiyatsushiro and Shizukawa Groups, central Japan, with some consideration on the Kaburan Stage (Middle Miocene). In: K. Huzita et al. (Editors). Cenozoic Geology of Japan, Prof. N. Ikebe Memorial Volume, Osaka, pp. 73--92 (in Japanese with English abstract). Honda, N., 1981. Kakegawa area (2). In: R. Tsuchi (Editor), Fundamental Data on Japanese Neogene Bio- and Chronostratigraphy - - S u p p l e m e n t , IGCP-114 National Working Group of Japan, pp. 5--6 (in Japanese with English captions). Honda, N., 1982. Calcareous nannoplankton biostratigraphy of upper Cenozoic sequences on the Pacific side areas in Japan. In: Abstr. Pap., Annu. Meet. Geol. Soc. Jpn., Niigata, 1982, p. 178 (in Japanese). Ibaraki, M. 1981. Geologic ages of "Lepidocyclina" and Miogypsina horizons in Japan as determined by planktonic foraminifera. In: Proc. IGCP-114 International Workshop on Pacific Neogene Biostratigraphy. Osaka, 1981, pp. 118---119. Ibaraki, M., Tsuchi, R. and Takayanagi, T., 1983. Early Neogene planktonic foraminiferal biostratigraphy in the Kakegawa area, the Pacific coast of central Japan. Rep. Fac. Sci., Shizuoka Univ., 17: 101--116. Ikebe, N., 1978. Bio- and chronostratigraphy of the Japanese Neogene, with remarks on paleogeography. In: K. Huzita et al. (Editors), Cenozoic Geology of Japan. Prof. N. Ikebe Memorial Volume, Osaka, pp. 13--34 (in Japanese with English abstract). Ikebe, N. and Asano, K., 1973. Interregional correlation of the Neogene based on planktonic datum levels and radiometric datings. Mem. Geol. Soc. Jpn., 8 : 2 0 3 - - 2 1 4 (in Japanese with English abstract). Ikebe, N., Takayanagi, Y., Chiji, M. and Chinzei, K., 1972. Neogene biostratigraphy and radiometric time scale of Japan - An a t t e m p t at intercontinental correlation. Pac. Geol., 4: 39--78. Ikebe, N. and Working Group, 1977. Summary of bio- and chronostratigraphy of the Japanese Neogene. In: Proc. First International Congress on Pacific Neogene Stratigraphy, T o k y o , 1976, pp. 93--114. Ishida, S., Makinouchi, T., Nishimura, A., Takemura, K., Danhara, T., Nishimura, K. and Hayashida, A., 1980. Middle Pleistocene of Kakegawa district, central Japan. Quaternary Res., 1 9 : 1 3 3 - - 1 4 8 (in Japanese with English abstract). Kammera, K., Sakai, T., Tsuji, R. and Nishi, H., 1983. Geology of the southern and eastern part of the Nichinan mountainous area. In: Guidebook for Excursion, Annu. Meet. Geol. Soc. Jpn., Kagoshima, 1983, pp. 23--26 (in Japanese).
Maiya, S., Saito, T. and Sato, T., 1976. Late Cenozoic planktonic foraminiferal biostratigraphy of northwest Pacific sedimentary sequences. In: Y. Takayanagi and T. Saito (Editors), Progress in Micropaleontology. Spec. Publ. Am. Mus. Nat. Hist., pp. 395--422. Makiyama, J. 1931. Stratigraphy of the Kakagawa Pliocene in Totomi. Mere. Coll. Sci., Univ. Kyoto, Ser. B, 7: 1--53. Makiyama, J., 1939. The Neogenic stratigraphy of the Japan Islands. In: Proc. 6th Pac. Sci. Congr., pp. 641--649. Makiyama, J., 1947. Two stages of the middle Miocene in Japan. Mem. Coll. Sci., Univ. Kyoto, Ser. B, 19: 33--36. Makiyama, J., 1952. On the mutation of the fossil Glycymeris rotunda. Trans. Proc. Palaeontol. Soc. Jpn., N.S., 5: 131--138. Makiyama, J. and Sakamoto, T., 1957. Geological map and explanatory text of the geological map of Japan, Mitsuke and Kakezuka, 1:50,000. Geological Survey of Japan, Tokyo, pp. 1--45 (in Japanese with English abstract). Nishimura, S., 1977. Re-examination of the fission track age of volcanic tuff. Rep. Kansai Branch, Geol. Soc. Jpn., 8 0 : 8 (in Japanese). Saito, T., 1960. Tertiary stratigraphy of the Kakegawa district, central Japan, and its planktonic foraminifera. Contrib. Inst. Geol. Paleontol., Tohoku Univ., 5 1 : 1 - - 4 5 (in Japanese with English abstract). Saito, T., 1963. Miocene planktonic foraminifera, Honshu, Japan. Sci. Rep. Tohoku Univ., 2nd Set. (Geol.}, 35: 123--209. Saito, T., 1980. An Early Miocene (Aquitanian) planktonic foraminiferal fauna from the Tsuro Formation, the youngest part of the Shimanto Supergroup, Shikoku, Japan. In: T. Taira and M. Tashiro (Editors), Geology and Paleontology of the Shimanto Belt. Selected Papers in Honor of Prof. J. Katto, pp. 227--234. Shibata, K., Uchiumi, S. and Nakagawa, T., 1979. K-Ar results -- 1. Bull. Geol. Surv. Jpn., 3 0 : 6 7 5 - - 6 8 6 (in Japanese). Shuto, T., 1963. Geology of the Nichinan area, with special reference to the Takachiho disturbance. Mere. Fac. Sci., Kyushu Univ., Ser. D, 6 : 1 3 5 - - 1 6 6 (in Japanese with English abstract). Takayanagi, Y., Sakai, T., Oda, M., Takayama, T., Oriyama, J. and Kaneko, M., 1978. Problems relating to the Kaburan Stage. In: K. Huzita et al. (Editors), Cenozoic Geology of Japan. Prof. N. Ikebe Memorial Volume, Osaka, pp. 93--112 (in Japanese with English abstract). Tsuchi, R., 1961. On the late Neogene sediments and molluscs in the Tokai region, with notes on the geologic history of the Pacific coast of Southwest Japan. Jpn. J. Geol. Geogr., 32: 437--456. Tsuchi, R. and Ibaraki, M., 1978. Late Neogene succession of molluscan fauna on the Pacific coast of southwestern Japan,with reference to planktonic foraminiferal sequence. Veliger, 21: 216--224. Tsuchi, R. and Ibaraki, M., 1981. Kakegawa area. In: R. Tsuchi (Editor), Neogene of Japan -- Its biostratigraphy and Chronology. IGCP-114 National Working Group of Japan, pp. 37--41. Tsuchi, R., Takayanagi, Y. and Shibata, K., 1981. Neogene bio-events in the Japanese Islands. In: R. Tsuchi (Editor), Neogene o f J a p a n - - I t s B i o s t r a t i g r a p h y and Chronology. IGCP-114 National Working Group of Japan, pp. 15--32. Tsuchi, R., Shuto, T. and Ibaraki, M., 1983a. Geologic ages of the Ashiya Group and the Ashiya fauna as determined by planktonic foraminifera. In: Abstr. Pap., Annu. Meet. Geol. Soc. Jpn., Kagoshima 1983, p. 125 (in Japanese). Tsuchi, R. and IGCP-114 National Working Group of Japan, 1983b. Neogene chronostratigraphy and bio-events in the Japanese Islands. In: Abstr., 15th Congr., Pac. Sci. Assoc., Dunedin, 1 9 8 3 , p . 242. Tsuchi, R. and IGCP-114 National Working Group of Japan, 1984. Neogene chronostratigraphy and bio-events in the Japanese Islands. Palaeogeogr., Palaeoclimatol., Palaeoecol., 4 6 : 3 7 - - 5 1 (this issue).
10 Ujii6, H., 1975. An early Miocene planktonic foraminiferal fauna from the Megami Formation, Shizuoka Prefecture. Bull. Natl. Sci. Mus.,Tokyo, Ser. C (Geol.), 1: 83--92. Ujii6, H. and Hariu, S., 1975. Early Pliocene to middle Miocene planktonic foraminifera from the type section of the Sagara Group, central Japan. Bull. Natl. Sci. Mus., Tokyo, Ser. C (Geol.), 1: 37--54. Yoshida, K. and Niitsuma, N., 1976. Magnetostratigraphy in the Kakegawa district. In: R. Tsuchi (Editor), Guidebook for Excursion 3, Kakegawa District. First Int. Congr. Pacific Neogene Stratigraphy, T o k y o , 1976, pp. 54--59.