A newly proposed radiolarian zonation for the Jurassic of Japan

Marine Micropaleontology, 11 (1986): 91--105 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

91

A NEWLY P R OP OSE D R A D I O L A R I A N Z O N A T I O N F O R T H E JURASSIC OF JAPAN

ATSUSHI MATSUOKA and AKIRA YAO

Department of Geosciences, Faculty of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558 (Japan) (Received January 10, 1985; accepted July 20, 1985) Abstract Matsuoka, A. and Yao, A., 1986. A newly proposed radiolarian zonation for the Jurassic of Japan. Mar. Micropaleontol., 11: 91--105. Eight radiolarian zones are established on the basis of biostratigraphic investigations on the Japanese Jurassic. These are the Parahsuum sp. C, Archicapsa pachyderma, Laxtorum(?) jurassicum, Tricolocapsa plicarum, Tricolocapsa conexa, Stylocapsa(?) spiralis, Cinguloturris carpatica and Pseudodictyomitra primitiva Zones in ascending order. Biohorizons reflecting evolutionary lineages are utilized, where possible, in defining the zonal boundaries. In the case of absence of adequate lineages, biohorizons of the first or last appearance of characteristic species are applied. The zones are compared with the zones previously proposed by several workers in Japan.

Introduction A n u m b e r o f geologists have recently made it clear t h a t Jurassic marine sediments are widely distributed in t he Japanese Islands. Studies o f Jurassic radiolarian fossils have played an i m p o r t a n t role in clarifying the age o f siliceous and clastic sediments which f o r a long time were believed to be Upper Paleozoic. Since 1979, several workers have made efforts to establish a f r a m e w o r k for the Triassic and J u r a s s i c radiolarian biostratigraphy in S o u t h w e s t Japan. In a previous paper (Yao et al., 1982), we set up eight radiolarian assemblages through the Jurassic period. Although these assemblage-zones are practical and useful f or general correlation and age assignment, a n o t h e r category o f radiolarian zonation, based on biohorizons, is necessary f o r a precise correlation o f sediments. In this paper, we propose a new zonal f r a m e w o r k o f t he Jurassic radiolarian biostratigraphy o f Japan, partly adopting the zones p r o p o s e d by Matsuoka (1983) con0377-8398/86/$03.50

cerning the Middle and Upper Jurassic parts. Biohorizons reflecting evolutionary lineages, which are m ore reliable for correlations than t he o t h e r biohorizons, are utilized in defining zonal boundaries as m uch as possible. In the case o f absence of adequate lineages, biohorizons o f the first o r last appearance o f characteristic species are applied. In addition, we com pare the zones in this paper with the assemblage-zones previously proposed by Yao et al. (1982) and by several o t h e r workers in Japan. Correlation with the zonations established outside o f Japan will be discussed in o t h e r papers. Geologic setting The Japanese Islands are c o m p o s e d of various tectonic units which were i n c o r p o r a t e d into Paleo-Asia during M e s o z o i c - C e n o z o i c times. In the Sout hern Chichibu Terrane (southern part of t he Chichibu Terrane) and the Mino Terrane (Fig. 1), Jurassic sediments are represented by chert--clastic sequences

~© 1986 Elsevier Science Publishers B.V.

92

I

I

I

]

I

Mino Terrane

,JAPAN S E A Chichibu Terrane

©

@

SOUTHWEST JAPAN ~-'~I 10rl S]ILI \ Hisuikyo ~Inuyama CH-2 Pen.

i -

~ Shira i s hKi;:a~c:: hi-1

PACIFIC OCEAN

Kajiki-I

32ON

d~ 130OE t

0 | ~" 1

134OE 1

1

i00 1

200k~ !

138°E 1

Fig. 1. Localities of study sections. and olistostromes which contain wellpreserved radiolarian remains. The Southern Chichibu Terrane is one of the tectono-stratigraphic units in the Outer Zone of Southwest Japan and consists mainly of the Triassic--Jurassic Togano Group, the Jurassic--Lower Cretaceous Sambosan Formation (s.s.), the uppermost Jurassic-lowermost Cretaceous Torinosu Group and their equivalents. In the t y p e area of the Togano Group (Matsuoka, 1984c), central Shikoku, the stratigraphic sequence is composed of bedded siliceous claystone, chert, siliceous mudstone and coarse clastics layers in ascending order. It is tectonicaUy piled up to form an imbricate structure. The Sambosan Formation is mainly represented by an olistostrome facies. Its equivalent is extensively distributed on the western coast of the Kii Peninsula (Yao, 1984). The Torinosu Group consists of clastic rocks associated with

reefal limestones and yields age
93 stratigraphic relationships between zones. These are the Shiraishigawa-1, the Kawanouchi1, the Kaiji and the Kajiki-1 sections of the Togano Group and its equivalents in the Southern Chichibu Terrane and the I n u y a m a CH-2 and the Hisuikyo sections of the sedimentary complex belonging to the turbidite-chert facies in the Mino Terrane. In all sections, the Jurassic sequence conformably overlies the Triassic chert or is in fault contact with it. The lithology of each section is shown in Fig. 2.

Kaiji section This section is located in a road cut 0.3 km north of the Kaiji railway station, Ashikita

Town, K u m a m o t o Prefecture. Preliminary results of the radiolarian biostratigraphy of this section were reported by Sato and Nishizono (1983).

Kajiki-1 section This section is located in a road cut parallel to the Kajiki River, 1.2 km south of Kajiki, Kuma Village, Kumamoto Prefecture.

Shiraishigawa-1 section This section is' located in a road cut 1.5 km east of Shiraishigawa, Niyodo Town, Kochi Prefecture. The lithostratigraphy and radiolarian biostratigraphy o f this section are given in Matsuoka {1983).

/

ZONE Pseudodictgomi tra primltJva

8 Cinguloturris carpatlca

7 St glocapsa (?) spiralls 6 Tri colocapsa conexa

- ----...=-

5 Trlcolocapsa plicarum 4

-__---_Laxtorum (?) jurassicum ,

3 A rchi capsa pachyderm~

/ .

-F"

2

i

Parahsuum sp, C

i0m

i

il ]: 2: 3: 4:

FAB of P. simplum FAB of A. pachgderma FAB of L.(?) jurassicum FEAB of T° plicarum

5: 6: 7: 8:

FEAB of T. conexa FEAB of S.(?) spiralls gr. LAB of T° conexa FAB of Po primitiva

~ ~ ~

sandstone

mudstone

~ ~

siliceous mudstone chert

Fig. 2. Lithology and correlation of the study sections. A: Kaiji section; B: Kajiki-1 section; C: Shiraishigawa-i section; D: Kawanouchi-1 section; E: Inuyama CH-2 section;F: Hisuikyo section.

94

Kawanouchi-1 section This section is exposed along a cliff of an abandoned mine in Kawanouchi, Sakawa Town, Kochi Prefecture. The lithostratigraphy and radiolarian biostratigraphy were briefly reported b y Matsuoka (1984a).

Inuyama CH-2 section This section crops o u t on the bank of the Kiso River, Kagamigahara City, Gifu Prefecture. The biostratigraphy, based on conodonts and radiolarians, of this section was investigated b y Yao et al. (1980). Subsequently, Yao {1982) re-examined the radiolarian biostratigraphy of this section and established three Triassic and one Jurassic radiolarian assemblages in succession. The detailed biostratigraphic distribution of the radiolarians is given in Yao (1982).

Hisuikyo section This section is exposed along the Hida River, Kamiaso, Shichiso Town, Gifu Prefecture. The radiolarian biostratigraphy of this section was carried o u t by Kido (1982), Kido et al. (1982), Matsuda and Isozaki (1982) and Isozaki and Matsuda {1983). Mizutani and Kido ( 1 9 8 3 ) d e s c r i b e d four species of Middle Jurassic radiolarians and Isozaki and Matsuda {1985) describe some Early or Middle Jurassic radiolarians obtained from this section. Biohorizons

Several biohorizons (Fig. 3) are defined on the basis of the first appearance {FA) and the last appearance (LA) of characteristic radiolarian species. The first evolutionary appearance (FEA), which represents the occurrence of divergent speciation in the lineage, is reliable for defining a biohorizon. ( 1 ) T h e first appearance biohorizon of Parahsuum simplum Yao {FAB of P. simplum ) This biohorizon is recognized in the chert

sequence of the Kaiji section {Fig. 2:A), the Inuyama CH-2 section (Fig. 2:E ) and the Hisuikyo section (Fig. 2 :F). (2) The first appearance biohorizon of Archicapsa pachyderma (Tan Sin Hok) (FAB of A. pachyderma) This biohorizon is recognized in the chert-siliceous mudstone sequence of the Kajiki-1 section (Fig. 2 :B). (3) The first appearance biohorizon of Laxtorum (?) jurassicum Isozaki and Matsuda (FAB of L. (?) ]urassicum) This biohorizon is recognized in the siliceous mudstone sequence of the Kajiki-1 section (Fig. 2:B). (4) The first evolutionary appearance biohorizon of Tricolocapsa plicarum Yao (FEAB of T. plicarum ) This biohorizon is defined by the first evolutionary appearance of T. plicarum Yao from its ancestral form, Stichocapsa tegiminis Yao group. In this paper, stichocapsids consisting of four segments with a dish-like basal appendage, and with or without longitudinal plicae on the outer surfaces of shells are assigned to the S. tegiminis Yao group. T. plicarum Yao seems to have arisen from the S. tegiminis Yao group with longitudinal plicae through decrease in number of segments from four to three. This biohorizon is recognized in the siliceous mudstone sequence of the Kajiki-1 section (Fig. 2 :B). (5) The first evolutionary appearance biohorizon of Tricolocapsa conexa Matsuoka (FEAB of T. conexa) This biohorizon is defined by the first evolutionary appearance of T. conexa Matsuoka from its ancestral form, T. plicarum Yao (Matsuoka, 1983). It is recognized in the chert sequence of the Shiraishigawa-1 section (Fig. 2:C) and also in the chert--siliceous mudstone sequence of the Oyashiki-1 and the Yanasegawa-1 sections (Matsuoka, 1983). (6) The first evolutionary appearance biohorizon of Stylocapsa(?) spiralis Matsuoka group (FEAB of S. (?) spiralis group) This biohorizon is defined by the first evolutionary appearance of the S. (?) spiralis

95

0 • ~,~ BIOHORIZON

Period

Pseudodictyomltra primi ti va

iI I

T

Cinguloturris carpatica -J

j

Stylocapsa(?)spiralis T

~D

I,

conexa

I

t~ t~

Tricolocapsa

FAB of

P,

primltiva

LAB of

T.

conexa

I I1 ,'

FEAB of S.(?)

].111

spiralisgr.

FEAB of

T.

FEAB of

T. plicarum

conexa

I

plicarum

lll-

f~ ~D

T

i !

Laxtorum(?)

[

jurassicum

FAB of L.(?) jurassicum

--~ Arehicapsa pachyderma u~

I I

I

i I I

FAB of

A.

FAB of

P. simplum

pachyderma

Parahsuum sp, C

Fig. 3. Radiolarian zones for the Jurassic o f Japan and range chart o f selected radiolarians.

Matsuoka group from its ancestral form, S. (?) hemicostata Matsuoka (Matsuoka, 1983). It is recognized in the chert--siliceous mudstone sequence of the Kawanouchi-1 section {Fig. 2:D), and in the siliceous mudstone sequence o f the Shiraishigawa-1 section (Fig. 2:C), the Yanasegawa-2 and the Yanasegawa-3 sections of the Togano Group (Matsuoka, 1983). (7) The last appearance biohorizon of

Tricolocapsa conexa Matsuoka (LAB of T. conexa) This biohorizon is recognized in the siliceous mudstone--mudstone sequence of the Kawanouchi-1 section (Fig. 2:D). (8) The first appearance biohorizon of Pseudodictyomitra primitiva Matsuoka and Yao (FAB of P. primitiva) This biohorizon is recognized in the clastic sequence of the Torinosu Group and its

96

equivalents. It is not shown in the stratigraphic column of Fig. 2 because it is not sufficiently examined in continuous sequences. Zonation Except for the uppermost one, the zones proposed here are defined as the intervals between two successive biohorizons; that is, the boundaries of these zones are related to biohorizons as signified in the range chart of diagnostic taxa (Fig. 3). Approximate age assignments of the zones described below or assemblage-zones biochronologically equivalent to them, were discussed in other papers (Yao, 1982, 1984; Yao et al., 1982; Matsuoka, 1983, 1984b; Matsuoka and Yao, 1985; Matsuda and Isozaki, 1982; Isozaki and Matsuda, 1985, etc.). Detailed age a~ signments, including correlations with European stages, will be made elsewhere.

Parahsuum sp. C Zone Definition: The interval from the FAB of

Parahsuum simplum to the FAB of Archicapsa pachyderma. Age: early Early Jurassic Remarks: The first appearance biohorizon o f Parahsuum sp. C, diagnostic species of this zone, is the same as that of Parahsuum simplum Yao in the Inuyama CH-2 section (Yao, 1982). P. simplum Yao ranges upward into the higher zone of the middle Lower Jurassic. Chert or siliceous mudstone corresponding to this zone conformably overlies the latest Triassic chert in the Inuyama CH-2 section (Yao et al., 1980; Yao, 1982),

the Hisuikyo section (Matsuda and Isozaki, 1982; Isozaki and Matsuda, 1983) and the Kaiji section (Sato and Nishizono, 1983). In the Inuyama CH-2 section, the chert layers directly under this zone contain late Norian-Rhaetian conodonts, Misikella hernsteini (Mostler) and M. posthernsteini Kozur and Mock, and radiolarian species of the Canoptum triassicum Assemblage, e.g., C. triassicum Yao, Dreyericyrtium sp. A and Palaeosaturnalis bifidus (Kozur and Mostler). Species belonging to the genera Parahsuum, Canoptum, Katroma and Bipedis occur abundantly in this zone.

Archicapsa pachyderma Zone Definition: The interval from the FAB of the FAB of

Archicapsa pachyderma to Laxtorum (?) jurassicum.

Age: middle Early Jurassic Remarks: In this zone, multi-segmented nassellarians, assigned to the genera Parahsuum and Canoptum, occur abundantly as in the underlying zone. Undescribed parahsuids with a large number of segments (more than fifteen) are c o m m o n in the upper part of this zone.

Laxtorum (?) jurassicum Zone Definition: The interval from the FAB of

Laxtorum(?) ]urassicum to the FEAB of Tricolocapsa plicarum. Age: late Early Jurassic Remarks: Unuma echinatus Ichikawa and Yao, Cyrtocapsa(?) kisoensis Yao and Tricolocapsa (?) fusiformis Yao first occur within this zone, which is characterized b y abundant

PLATE I

1. Katroma sp., x 142. 2. Parahsuum simplum Yao, × 200. 3. Parahsuum sp. C, × 200. 4. Bipedis sp., × 142. 5. Archicapsa pachyderma (Tan Sin Hok), × 300. 6. Laxtorum(?) jurassicum Isozaki and Matsuda, × 200.

7. Parahsuum sp. D, × 150. 8. Hsuum hisuikyoense Isozaki and Matsuda, x 150. 9. Cyrtocapsa(?) kisoensie Yao, × 330.

10. Cyrtocapsa mastoidea Yao, x 300. 11. Unuma echinatus Ichikawa and Yao, × 145. 12. Unuma typicus Ichikawa and Yao, x 277. 13. Protunuma fusiformis Ichikawa and Yao, x 250. 14. Tricolocapsa (?) fusiformis Yao, x 375. 15. Stichocapsa tegiminis Yao group, × 300. 16. Tricolocapsa plicarum Yao, × 300. 17. Tricolocapsa conexa Matsuoka, × 300. 18. Tricolocapsa tetragona Matsuoka, × 300.

97

PLATE I

98 multisegmented nassellarians with cephalis surrounded by thick walls, such as Laxtorum (?) jurassicum Isozaki and Matsuda and Hsuum hisuikyoense Isozaki and Matsuda.

Tricolocapsa plicarum Zone Definition: The interval from the FEAB of Tricolocapsa plicarum to the FEAB of Tricolocapsa conexa Age: early Middle Jurassic Remarks: This zone was proposed by Matsuoka (1983), although the base was n o t clearly defined at that time. The FEAB of T. plicarum Yao is now confirmed in the Kajiki-1 section. Cyrtocapsa rnastoidea Yao first appears in the middle part of this zone and disappears near the top. Cyrtocapsa(?) kisoensis Yao and Archicapsa pachyderma (Tan Sin Hok) make their last occurrence near the top of this zone. The following species have their acme within this zone; Unuma echinatus Ichikawa and Yao, Unuma typicus Ichikawa and Yao, Protunuma fusiformis Ichikawa and Yao, Stichocapsa tegiminis Yao, Diacanthocapsa normaUs Y a o and Diacanthocapsa (?) operculi Yao.

Tricolocapsa conexa Zone Definition: The interval from the FEAB of Tricolocapsa conexa to the FEAB of the S ty locapsa (?) spiralis group. Age: late Middle Jurassic Remarks: This zone was defined by Matsuoka (1983); Protunuma turbo Matsuoka and Tricolocapsa tetragona Matsuoka first appear near the base and are characteristic P L A T E II (All figuresX 300 unlessotherwise noted) 1. Stylocapsa lacrimalis Matsuoka. 2. Protunuma ( ?) oehiensis Matsuoka. 3. Lithocampe (?) nudata Kocher. 4. Gongylothorax sakawaensis Matsuoka. 5. Stylocapsa (?) hemicostata Matsuoka. 6. Sty locapsa(?) spiralis Matsuoka. 7. Dictyomitrella(?) kamoensis Mizutani and Kido. 8. Stylocapsa tecta Matmuoka. 9. Dicolocap#a eonoformis Matsuoka. 10. Eucyrtidium (?) ptyctum Riedel and Sanfflippo.

of its lower and middle parts. Protunuma (?) ochiensis Matsuoka, Lithocampe(?) nudata Kocher, Stylocapsa oblongula Kocher, Stylocapsa lacrimalis Matsuoka and Eucyrtidium (?) ptyctum Riedel and Sanfilippo first occur in the middle part of this zone and Dicolocapsa conoformis Matsuoka, Stylocapsa tecta Matsuoka and 8tylocapsa (?) hemicostata Matsuoka first occur in the upper part. Dictyomitrella (?) kamoensis Mizutani and Kido has its acme within this zone.

Sty locapsa (?) spiralis Zone Definition: The interval from the FEAB of the 8tylocapsa(?) spiralis group to the LAB of Tricolocapsa conexa. Age: early Late Jurassic Remarks: This zone was proposed by Matsuoka (1983), though its top was n o t clearly defined. Stylocapsa catenarum Matsuoka first occurs near the base. Lithocampe(?) nudata Kocher, Dicolocapsa conoformis Matsuoka, Stylocapsa tecta Matsuoka and Stylocapsa (?) hemicostata Matsuoka make their last occurrence just above the base. The occurrence of Gongylothorax sakawaensis Matsuoka is confined to within the middle part. Stylocapsa(?) spiralis Matsuoka and Stichocapsa naradaniensis Matsuoka disappear near the top of this zone. Cinguloturris carpatica Zone Definition: The interval from the LAB of Tricolocapsa conexa to the FAB of Pseudodictyomitra primitiva. ,4~e: middle Late Jurassic

11. Stylocapsa catenarum Matsuoka. 12. 8tichocapsa naradaniensis Matsuoka. 13. Trieotocapsa sp. O. 14. Cinguloturris carpatica Dumitrica, × 200. 15. Pseudoeucyrtis reticularis Matmuoka and Yao, × 100. 16. Hsuum maxwelli Pemagno, × 200.

17. Podocapsa amphitrep~era Foreman, x 147. 18. Mtrifusus mediodflabm~ (Rimt), x 100. 19. Pwudodietyomitra primitiva Matsuoka and Yao, x

213.

99 P L A T E II

100

This paper

Yao et al. (1982) modified

Pseudodlctyomitr~ primltiva

Pseudodictyomitra primltiva -Pseudodictyomitra sp. A

Clnguloturris carpatlca

Tricolocapsa sp. 0

Stylocapsa(?) splralls

Gongylothorax sakawaensis m Stlchocapsa naradaniensis

Nishlzono et ai. (1982) Nishlzono & Murata (1983) Sate & Nishlzono (1983)

Kishida & Sugano (1982)

M i z u t a n l et ale (1981) Kido et ale (1982) Mizutanl & Kido (1983

Mirifusus baileyi Andromeda violae Mirlfasus

medlodilatatus

ILithocampe(?) sp. B Tricolocapsa conexa

Lithocampe(?) nudata

Trlcelocapsa plicarum

Unuma echinatus

Dictyomltrella(?) kamoensis Pantanellium foveatum

=K

uo

Unuma echinatus

Unuma echinat~s

e~

....

Zartus jurassicus Archaeodictyomitra

Laxtorum(?) jurassicum

sp. C

Hsuum h i s u i k y o e n s e

Spongocapsula(?) sp. A Parahsuum sp, D Arcbicapsa pachyderma uJ i

Parviclngula(?) sp. A

Parahsuum spo C

Parahsuum simplum

"Archaeodictyomltra" direct~porata -"Eucyrtidium" sp, A

--

Parvicingula(?) sp. B

"Archaeodictyomitra" sp. A

Triassocampe sp. A

Fig. 4. Correlation of the newly defined zones with previously proposed zones in Japan. Broken line indicates the boundary of essemblage-zones. R e m a r k s : T h e base o f this z o n e is r e c o g n i z e d w i t h i n t h e u p p e r part o f t h e K a w a n o u c h i - 1 s e c t i o n (Fig. 2 : D ) . T h e t o p is n o t clearly determined within continuous sequences, but

corresponds approximately to the boundary b e t w e e n t h e T a t e g o F o r m a t i o n and t h e Y u r a F o r m a t i o n in t h e Kii-Yura area, W a k a y a m a Prefecture (Yao, 1984). Cinguloturris

PLATE HI (All figures × 150) 1. Archicapsa pachyderma (Tan Sin Hok). 2.8tichocapsa tegiminis Yao group. 3. Laxtorum (?) ]urauicum Isozaki and Matsuda. 4. Hsuum hisuikyoense Isozaki and Mat~da. 5, Pamhsuum sp. D. 6. Diacanthocapsa normalis Yao. 7. Diaeanthocapsa(?) operculi Yao. 8. Tricolocapsa ( ?) fudformis Yao. 9. Protunuma turbo Matsuoka. 10. Gongylothorax sakawaends Matsuoka. 11. Unuma echinatus Ichikawa and Yao.

12. Unuma typicus Ichikawa and Yao. 13. Dicolocapsa conoformis Matsuoka. 14. Stylocapsa lacrimalis Matsuoka. 15. Trieolocapse pliearum Yao, 16. Pro tunurna ( ?) ochiensis Matsuoka. 17. L ith ocamp e ( ?) nudata Kocher. 18. Trieolocapsa conexa Matsuoka. 19. Stichoeapsa naradaniensis Matsuoka. 20. Styiocapsa (?) spirali~ Matsuoka. 21. Solenotryma(?) ichikawai Matsuoka and Yao. 22. Protunuma japonicus Matsuoka and Yao.

101

P L A T E III

5

102

carpatica Dumitrica, nominal species of this zone, has its acme in this zone and the next younger Pseudodictyornitra primitiva Zone. Tricolocapsa sp. O appears near the base and occurs commonly in this zone. Hsuum maxwelli Pessagno probably has its last occurrence near the top.

Pseudodictyomitra primitiva Zone Definition: The base of this zone is defined by the FAB of Pseudodictyomitra primitiva (cf. preceedin.g paragraph). The top is not defined here, but it does not extend up to. the zone characterized by species of Pseudodictyomitra cf. carpatica Assemblage (Nakatani and Yao, 1980; Matsuoka and Yao, 1981). Age: late Late Jurassic Remarks: Neither the base nor top of this zone are at present clearly determined within continuous sequences. This zone corresponds to the m a i n part of the Torinosu Group and its equivalents. The following species occur commonly: Pseudodictyomitra primitiva Matsuoka and Yao, Solenotryma (?) ichikawai Matsuoka and Yao, Protunuma japonicus Matsuoka and Yao, Pseudoeucyrtis reticularis Matsuoka and Yao, Mirifusus mediodilatatus (R~ist), Cinguloturris carpatica Dumitrica and Podocapsa amphitreptera Foreman. Correlation with other radiolarian zones in Japan In this section, correlation of the above defined zones with other radiolarian zones previously proposed in Japan is discussed. A summary is shown in Fig. 4. Studies on the Jurassic radiolarian biostratigraphy in Japan have been carried out by a number of groups or workers in the last several years. Their preliminary results were reported in the Proceedings of the First Japanese Radiolarian Symposium (Yao et al., 1982; Matsuoka, 1982; Nishizono et al., 1982; Kishida and Sugano, 1982; Kido et al., 1982; Kido, 1982; etc.). They have continued their work since then (Matsuoka, 1983, 1984a, b;

Nishizono and Murata, 1983; Sato and Nishizono, 1983; Mizutani and Kido, 1983). The correlation of these zones is based both on the literature and on investigation of the material on which other workers based their zonations.

Correlation with assemblage-zones of Yao et al. (1982) Since we proposed a zonal scheme (Yao et al., 1982), several nominal species of assemblages have been described (Matsuoka, 1984b; Matsuoka and Yao, 1985; Isozaki and Matsuda, 1985). Our previous zonal scheme by means of radiolarian assemblages is shown in Fig. 4 with modification. Namely, informal names are replaced by formally proposed species names. In establishing the assemblagezones, we inserted three biostratigraphic gaps between certain neighbouring zones, namely; between the Parahsuum simplum and the Parahsuum sp. D assemblage-zones, between the Parahsuum sp. D and the Hsuum sp. B assemblage-zones and between the Gongylothorax sakawaensis- Stichocapsa naradaniensis and the Tricolocapsa sp. O assemblage-zones because we could not directly determine the stratigraphic relationships between the assemblage-zones within continuous sequences. Subsequently, the upper two stratigraphic gaps were covered through investigation in additional continuous sequences. The lower one still remains open and a zone characterized by a certain assemblage is expected to be recognized in this gap. The newly proposed zones can be broadly correlated with the assemblage-zones, except for the following two: the Archicapsa pachyderma Zone is partly correlated with the lower portion of the Parahsuum sp. D assemblage-zone, while the Laxtorum(?) juraasicum Zone corresponds to the Hsuum hisuikyoense assemblage-zone and the upper portion of the Parahsuurn sp. D assemblagezone (Fig. 4).

103 Correlation with zonation o f Nishizono et al. (1982), Nishizono and Murata (1983) and Sato and Nishizono (1983)

Researchers of Kumamoto University have carried out a radiolarian biostratigraphic study, mainly in the Kuma massif, Kyushu. Although their investigation extends from the Paleozoic to the Mesozoic, we refer here only to the Jurassic part of their radiolarian zonation. Nishizono et al. (1982) proposed five Jurassic assemblages which were slightly modified and described in more detail by Nishizono and Murata (1983). They are, in ascending order, "Archaeodictyomitra" sp. A -- Triassocampe sp. A, "Archaeodictyomitra" directiporata - " E u c y r t i d i u m " sp. A, Zartus ]urassicus, A n d r o m e d a violae -Mirifusus mediodilatatus and Mirifusus mediodilatatus - Pseudodictyomitra cf. carpatica assemblages. A type locality was designated for each assemblage and faunal associations from the type localities, which were listed in tables and were called "type assemblages". Their "Archaeodictyomitra" sp. A -Triassocampe sp. A and "Archaeodictyomitra" directiporata -"Eucyrtidium" sp. A assemblages are compared with our Parahsuum simplum assemblage. Sato and Nishizono (1983) clarified the stratigraphic relationship between the "A." sp. A -- T. sp. A and the "A." directiporata -- "E." sp. A assemblagezones in the Kaiji Section. The two assemblagezones correspond to the Parahsuum sp. C Zone, according to a biostratigraphic investigation of this section by one of us (A. Matsuoka). Nishizono and Murata (1983) stated that the Zartus ]urassicus assemblage coincided with the Unuma echinatus assemblage of Yao et al. (1980)and Mizutani et al. (1981). Although the assemblage from the type locality of the Z. ]urassicus assemblage can be compared with the U. echinatus assemblage, other localities assigned to the Z. ]urassicus assemblage include older elements such as H s u u m sp. G (Nishizono and Murata, 1983) which is similar to Parahsuum sp. D or Hsuum

hisuikyoense, a diagnostic species of the H. hisuikyoense assemblage. Therefore, the Zartus jurassicus assemblage may be compared not only with the Unuma echinatus assemblage, but also with the Hsuum hisuikyoense assemblage. The A n d r o m e d a violae -- Mirifusus mediodilatatus assemblage includes H s u u m maxweUi Pessagno and Eucyrtidium(?) p t y c t u m Riedel and Sanfilippo, besides the nominal species. Co-occurrences of these species are recognized in both the Gongylothorax sakawaensis -- Stiehocapsa naradaniensis and the Tricolocapsa sp. O assemblage-zones. At present, it is difficult to determine whether the A. violae -- M. mediodilatatus assemblage can be correlated with the G. sakawaensis S. naradaniensis or the T. sp. O assemblage because of paucity of data. The Mirifusus mediodilatatus -- Pseudodictyomitra cf. carpatica assemblage was proposed as an assemblage indicating latest Jurassic and probably earliest Cretaceous time. The faunal association of this assemblage is not comparable with that of the Pseudodictyomitra primitiva - - P s e u d o d i c t y o m i t r a sp. A assemblage, but with that of the Pseudodictyomitra cf. carpatica assemblage (Nakatani and Yao, 1980; Matsuoka and Yao, 1981, 1985) and that of the Ditrabs sansalvadorensis Zone (Aita and Okada, 1986) which is assigned to earliest Cretaceous time. Correlation with the zonation o f Kishida and Sugano (1982)

Kishida and Sugano (1982) made a biostratigraphic study on Triassic and Jurassic radiolarians of the Southern Chichibu Terrane in Shikoku and Kyusyu. Concerning the Jurassic biostratigraphy, their zonation (Fig. 4) was based mainly on two stratigraphic sections, the Ogawa ch-4 and K o o k u ch-4 sections, located in the Sakawa area, Shikoku. One of us (A. Matsuoka) examined the same sections. A morphologically characteristic species, Spongocapsula (?) sp. A (Kishida and

104 Sugano, 1982) is conspecific with Spongocapsula(?) sp. C (Yao et al., 1982). This species is now described as Laxtorum(?) jurassicum by Isozaki and Matsuda {1985). The first appearance biohorizon of L.(?) jurassicum Isozaki and Matsuda is utilized as zonal boundary both by Kishida and Sugano and by us. On the basis of the biohorizon and stratigraphic relationship to the uppermost Triassic radiolarian zone, their Parvicingula (?) sp. A -- Parvicingula (?) sp. B Zone is correlated with our Parahsuum sp. C and Archicapsa pachyderrna Zones. Kishida and Sugano {1982) divided strata above the FAB of L. (?) jurassicurn Isozaki and Matsuda in the Ogawa ch-4 section into two zones, namely the Spongocapsula{?) sp. A and the Archaeodictyornitra sp. C zones in ascending order. According to our biostratigraphic study of the Ogawa ch-4 section, the same strata are assigned to the L . ( ? ) j u r a s s i c u m Zone. Though it is difficult to correlate our newly proposed zones with their zones exactly, we can compare our assemblage-zones with theirs. Their Unuma echinatus Zone corresponds to our Unuma echinatus assemblagezone by definition. Their Lithocarnpe(?) sp. B Zone may be correlated with our Lithocampe (?) nudata and/or Gongylothorax sakawaensis Stichocapsa naradaniensis assemblage-zone because the L.(?) sp. B assemblage includes Tricolocapsa conexa Matsuoka. Correlation with the zonation o f Mizutani et al. (1981), Kido et al. (1982) and Mizutani and Kido (1983) Dr. Mizutani of Nagoya University and his co-workers recognized three Jurassic radiolarian assemblages in the Mino Terrane, namely the Unuma echinatus, the Dictyornitrella (?) karnoensis -Pantanelliurn foveaturn and the Mirifusus baileyi assemblages in ascending order. Their Unuma echinatus assemblage-zone coincides with our assemblage-zone of the same name because t h e y have the same type area.

According to them, the siliceous shale of the Unuma echinatus assemblage-zone is overlain successively by that of the Dictyomitrella (?) kamoensis -- Pantanellium foveatum assemblage-zone (Kido et al., 1982; Mizutani and Kido, 1983). On the other hand, we clarified the conformable relationship between the Unuma echinatus assemblagezone and the next younger Lithocampe(?) nudata assemblage-zone within continuous sequences in the Southern Chichibu and the Mino terranes (Matsuoka, 1982; Yao et al., 1982). The faunal association of the D.(?) kamoensis -- P. foveatum assemblage-zone presented by Kido et al. (1982} is essentially similar to that of the lower part of the L. (?) nudata assemblage-zone and lacks species characteristic of the upper part of L.(?) nudata assemblage-zone, such as Dicolocapsa conoformis Matsuoka and Stylocapsa tecta Matsuoka. Therefore, the D.(?) kamoensis - - P . foveaturn assemblage-zone is correlated with the lower part of the L.(?) nudata assemblage-zone. The Mirifusus baileyi assemblage presented by Mizutani (1981) includes many species which c o m m o n l y occur in the Tricolocapsa sp. O and the Pseudodictyornitra prirnitiva -- Pseudodictyomitra sp. A assemblage-zones. Hsuum maxwelli Pessagno and Eucyrtidiurn (?) ptyctum Riedel and Sanfilippo, which are elements of the M. baileyi assemblage, disappear at the top of the T. sp. O assemblage-zone and within the lower part of the P. prirnitiva - - P . sp. A assemblage-zone, respectively. Therefore, the M. baileyi assemblage-zone can be generally correlated with the T. sp. O assemblage-zone and the lower part of the P. primitiva - P . sp. A assemblage-zone.

Acknowledgements We wish to thank Prof. K. Ichikawa of Osaka City University for his kind guidance, encouragement and critical reading of the manuscript. We express our thanks to Dr. K. Nakaseko, Dr. S. Mizutani, Mr. S. Kido, Mr. Y. Nishizono, Mr. T. Sato, Mr. Y. Kishida,

105

Mr. Y. I s o z a k i and Dr. T. M a t s u d a f o r valuable discussion o n Jurassic radiolarian biostratigraphy.

References Adachi, M., 1976. Paleogeographic Aspect of the Japanese Paleozoic--Mesozoic Geosyncline. J. Earth Sci. Nagoya Univ., 23/24: 13--15. Aita, Y. and Okada, H., 1986. Radiolarians and calcareous nannofossils from the Uppermost Jurassic and Lower Cretaceous strata of Japan and Tethys regions. Micropaleontology, 32: 97-128. Isozaki, Y. and Matsuda, T., 1983. Early Jurassic radiolarians from bedded chert at Hisuikyo, Kamiaso area, Mino Belt. Proc. Nishinippon Branch, Geol. Soc. Jap., 7 8 : 1 3 (in Japanese). Isozaki, Y. and Matsuda, T., 1985. Early Jurassic radiolarians from bedded chert in Kamiaso, Mino Belt, Central Japan. Earth Sci. (Chikyu Kagaku), 39 : 429--442. Kido, S., 1982. Occurrence of Triassic chert and Jurassic siliceous shale at Kamiaso, Gifu Prefecture, central Japan. News Osaka Micropaleontol., 5: 135--151 (in Japanese, with English abstract). Kido, S., Kawaguchi, I., Adachi, M. and Mizutani, S., 1982. On the Dictyomitrella(?) k a m o e n s i s Pantanellium foveatum assemblage in the Mino area, central Japan. News Osaka Micropaleontol., 5:195--210 (in Japanese, with English abstract). Kishida, Y. and Sugano, K., 1982. Radiolarian zonation of Triassic and Jurassic in outer side of southwest Japan. News Osaka Micropaleontol., 5:271--300 (in Japanese, with English abstract). Matsuda, T. and Isozaki, Y., 1982. Radiolarians around the Triassic--Jurassic boundary from the bedded chert in the Kamiaso Area, Southwest Japan. Appendix: "Anisian radiolarians". News Osaka Micropaleontol., 5 : 9 3 - - 1 0 1 (in Japanese, with English abstract). Matsuoka, A., 1982. Middle and Late Jurassic radiolarian biostratigraphy in the Sakawa and Niyodo areas, Kochi Prefecture, Southwest Japan. News Osaka Micropaleontol., 5: 237--253 (in Japanese, with English abstract). Matsuoka, A., 1983. Middle and Late Jurassic radiolarian biostratigraphy in the Sakawa and Adjacent areas, Shikoku, Southwest Japan. J. Geosci., Osaka City Univ., 26: 1--48. Matsuoka, A., 1984a. Stratigraphic relationship between the Gongylothorax sakawaensis and the Stichocapsa sp. C Subassemblages. Proc. Kansai Branch, Geol. Soc. Jap., 95:11--12 (in Japanese). Matsuoka, A., 1984b. Late Jurassic four-segmented Nassellarians (Radiolaria) from Shikoku, Japan.

J. Geosci., Osaka City Univ., 27: 143--153. Matsuoka, A., 1984c. Togano Group of the Southern Chichibu Terrane in the western part of Kochi Prefecture, Southwest Japan. J. Geol. Soc. Jap., 90(7): 455--477 (in Japanese, with English abstract). Matsuoka, A. and Yao, A., 1981. Jurassic radiolarian assemblages from the Sakawa area, Kochi Prefecture. Proc. Kansai Branch, Geol. Soc. Jap., 89: 4--5 (in Japanese). Matsuoka, A. and Yao, A., 1985. Latest Jurassic radiolarians from the Torinosu Group in Southwest Japan. J. Geosci., Osaka City Univ., 28: 125--145. Mizutani, S., 1981. A Jurassic formation in the Hidakanayama area, central Japan. Bull. Mizunami Fossil Mus., 8: 147--190 (in Japanese, with English abstract). Mizutani, S. and Kido, S., 1983. Radiolarians in the Middle Jurassic siliceous shale from Kamiaso, Gifu Prefecture, central Japan. Trans. Proc. Palaeontol. Soc. Jap., 132: 253--262. Mizutani, S., Hattori, I., Adachi, M., Wakita, IL, Okamura, Y., Kido, S., Kawaguchi, I. and Kojima, S., 1981. Jurassic formations in the Mino area, central Japan. Proc. Jap. Acad., 57: 194--199. Nakatani, T. and Yao, A., 1980. Radiolarian assemblages in the equivalent to the Torinosu Group, Western Shikoku. Proc. Kansai Branch, Geol. Soc. Jap., 86:5--6 (in Japanese). Nishizono, Y. and Murata, M., 1983. Preliminary studies on the sedimentary facies and radiolarian biostratigraphy of Paleozoic and Mesozoic sediments, exposed along the midstream of the Kuma River, Kyushu, Japan. Kumamoto J. Sci. Geol., 12(2): 1--40 (In Japanese, with English abstract). Nishizono, Y., Oishi, A., Sato, T. and Murata, M., 1982. Radiolarian fauna from the Paleozoic and Mesozoic formations, distributed along the midstream of Kuma River, Kyushu, Japan. News Osaka Micropaleontol., 5:311--326 (in Japanese, with English abstract). Sato, T. and Nishizono, Y., 1983. Triassic and Jurassic radiolarian assemblages from two continuous sections in the Kuma massif, Kyushu, Japan. News Osaka Micropaleontol., 1 1 : 3 3 - - 4 7 (in Japanese, with English abstract). Yao, A., 1982. Middle Triassic to Early Jurassic radiolarians from the Inuyama area, Central Japan. J. Geosci., Osaka City Univ., 25: 53--70. Yao, A., 1984. Subdivision of the Mesozoic complex in Kii-Yura Area, Southwest Japan and its bearing on the Mesozoic basin development in the Southern Chichibu Terrane. J. Geosci., Osaka City Univ., 27: 41--103. Yao, A., Matsuda, T. and Isozaki, Y., 1980. Triassic and Jurassic radiolarians from the Inuyama area,

106 Central Japan. J. Geosci., Osaka City Univ., 23: 135--154. Yao, A., Matsuoka, A. and Nakatani, T., 1982.

Triassic and Jurassic radiolarian assemblages in Southwest Japan. News Osaka Micropaleontol., 5:27--43 (in Japanese, with English abstract).