]ournal of Geosciences， Osaka City Uaiversity Vol. 23， Art. 4， P. 135-154 March， 1980

Triassic and! Jurassic Radiolar.ians from the IIiI.uyama Area， Cen危ralJapan

Akira YAO穴TetsuoMATSUDA* and Yukio ISOZAKI*

(with 4 Figures， 1 Table and 3 Plates)

Abstract

Four radiolarian assemblages were distinguished， namely Di{;tyomitreZla sp. A assemblage， D. sp. B assemblage， D. sp. C・Archaeodictyomitrasp. A assemblage and Unuma eGhinatus as-

semblage in ascending order， in the geosynclinal sequence of the Inuyama area， Central J apan.

The first three of the assemblages are successively obtained from a single sequence of chert. With

reference to the range of coexisting conodonts， the D. sp. A assemblage is assigned to Ladinian

and ear1y Carnian， and the D. sp. B assemblage to Late Triassic in age. The D. sp. C -A. sp. A

assemblage is probably Early Jurassic in age. The Unuma echinatus assemblage， which is coト

tained in the mudstone bed， possibly indicates the late Middle Jurassic age.

Introdiuction'

The Mino-Tanba belt of Southwest J apan is occupied extensively by late Paleozoic

and Mesozoic geosynclinal sequences composed of clastic sedimentary rocks， limestone，

chert and submarine volcanic rocks. Age determination of the geosynclinal sequences

was formerly based mainly on dfl.ta of fusulinids and corals obtained from limestone

bodies or blocks in clastic sedimentary rocks and in submarine volcanic-pyroclastic rocks.

Since ten years ago， Triassic c∞onodontおshave been discovered from several areas of Sout仏h圃

weωst J apan in che釘r匂 rocksthat were previously considered to be of late Paleozoic age (cf.

KOIKE， 1979). Some radiolarian assemblages of Mesozoic aspect have been found from

th.e so-called late Paleozoic mudstones (ICHIKAWA & YAO， 1979; NAKASEKO et al.， 1979; SUGANO et al.， 1979; YAO， 1972， 1979a， b). Fossil wood of Mesozoic aspect has also

been reported from the so-called late Paleozoic sandstone (NISHIDA et al.， 1974). The oc-

currence of these Mesozoic fossils suggests that the geosynclinal sequences have formed

the complicated history and structure beyond expectation. In stratigraphical approach

on the late Paleozoic and Mesozoic strata in ，Southwest Japan， it is now necessary to

determine the geological age of not only limestone but also chert and rnudstone of each

layer enclosed in the strata， and to settle the sedimentological and tectonical relationship among rocks involved.

The purpose of the present research is to set up a Triassic-J urassic biostratigraphy

of chert恒 mudstonesequence by means of both conodonts and radiolarians， and to deter・帽

• Department of Geosciences， Osaka City University， Osaka 558， Japan.

136 Akira Y AO， Tetsuo 島iATSUDAand Yukio ISOZAKI

mine the geological age of the geosynclinal sequences on the basis of the biostratigraphical

result. In the Inuyama area， the geosynclinal sequence composed of clastic sedimentary rocks and chert is exposed continuously along the Kiso River， and forms gently a large

synform. Geologic relationship among the beds of sandstone， mudstone and chert can be

well observed on the bank of the Kiso River. Moreover， Triassic conodonts and Meso-zoic radiolarians are contained in chert bed， and the latter also occurs in mudstone bed.

In this paper， the authors intend to offer some data on the detailed biostratigraphy of both Triassic conodonts and Mesozoic radiolarians， and to discuss the age determina-tion of the strata in the Inuyarna area. Conodonts and radiolarians from the area will

be described paleontologically in other papers.

Geologica，l setting

The Inulama area occupies the southern part of the Mino belt， Inner Zone of South田

west Japan. The so-called Mesozoic strata distributed in the northern part of the Inu圃

yama area are composed of thick beds of chert， sandstone and mudstone， forming a

large synform structure plunged to the west (MIZUTANI， 1964). The beds strike N

600-800 E and steeply dip NNE， partly SSW， on the southern limb of the synform.

Four beds of chert， namely CH-1， CH・2，CH・3and CH-4 beds， crop out broadly on

the bank of the Kiso River in the area (Fig，. 1). Chert beds are c∞∞omr

with in凶te灯rcωalat旬edthinner siliαous mudstone. The thickness of each layer of bedded

chert is about 2-5 centimeters. Chert beds form scarcely minor intraformational foldings.

Mudstone beds consist of readish and greenish siliceous one and grey to black non-sili圃

ceous one; the forlner locally contains manganese carbonate ore concretions and the

latter is rarely interbedded with thin beds of fine grained sandstone. The siliceous mud-

stone grades upward into the non-siliceous mudstone which is conformably overlain by

the sandstone bed with thin interbeds of mudstone. The manganese nodules reported

by YAO (1972) are from the reddish siliceous mudstone distributed between the CH-1 bed

and CH-2 bed.

F ossil records hitherto reported from the area are reviewed as :follows: KOIKE et al.

(1971) reported Late Triassic conodonts， represented by Paragondolella navicula and Epなondolellaabnφ的， from the chert exposed at the roadside cutting on the right side

of the Kiso River (Loc. C: Fig. 1). The locality of those conodonts is situated at the middle

part of the CH...4 bed. SATO (1974) described a late Middle or Late Jurassic ammonite， Cαhqザグαtωia(伊Sub伊'gr削，

creek c∞onfluen此twith the valley of the Kiso River， north of Inuyama (Loc. A: Fig. 1). NISHIDA et al. (1974) reported fossil fragment of petrified wood obtained from the sand圃

stone on the right side of the Kiso River， north of Inuyarna (Loc. W: Fig，. 1). lt was

identHied with a species of Taxaceoxy'lon which belongs to the民fωozoictaxaoeous plant.

In addition to the above-mentioned fossils， Mesozoic radiolarian assemblage was found

from the manganese nodules in reddish siliceous mudstone exposed at the bank of the

Triassic and Jurassic Radiolarians from Inuyama area 137

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Fig. 1. Geologiじalsketch map of the northern part of the Inuyama area， showing the distribution of chert beds. Rectangular portion in the middle part of the CH圃 2bed is sketched in Fig. 2. Localities of the previously reported fossils:

A， late Middle or Late Jurassic ammonite (SATO， 1974). C， Late Triassic conodonts (KOIIffi et al.， 1971).

R， Mesozoic radiolarians (YAO， 1972， 1979a; ICHTKAWA & YAO， 1976).

Kiso River (YAO， 1972， 1979a; ICHIKAWA & YAO， 1976: Loc. R: Fig.1). The radiolarian

assemblage is characterized by numerous species， more than 150 species， which include many forms closely related to late Mesozoic radiolarians.

The stratigraphical relationship between the chert containing the Late Triassic

conodonts and the sandstone yielding the late Middle or Late J urassic ammonite was

explained in two ways; one was a conformity and the other was in fault contact. The

former was held by KONDO & AnACHI (1975)， who interpreted that the chert was the

product of resedimentation during Late Jurassic time with a mixed faunal assemblage of

Middle to Late Traissic conodonts. On the other hand， IIJIMA et al. (1978) asserted

the latter interpretation based on their field survey. According to the research of the

present authors， the Middle and Late Triassic conodonts occur in succession， being not mixed， and the chert containing conodonts is not the resedimented Late Jurassic

rocks. Furthermore， the presumably Early Jurassic chert and the Middle-Late Jurassic

clastic rocks are recognized by means of radiolarian assembalges. All of the chert bed

(CH・I・CH-4)include Triassic chert containing both conodonrts and radiolarians， and

presumably Early J urassic chert with radiolarians which lies conformably ahove the

Triassic chert. They are， therefore， nearly contemporaneous in age， and are repeated

in occurrence by certain tectonical or sedimentological reason which is doubtful. Mud-

stone beds which are intercalated among the chert beds contain some similar radiolarian

assemblage which is assigned to Middle-Late Jurassic age. The sandstone beds

the youngest formation in this area， and lie confortnably above the mudstone beds.

Akira YAO， Tetsuo 酌iATSUDAand Yukio ISOZAKI 138

are

39 38 37 36

35

34

33 32

31 30

29

28

27 26

2'5 214 23

22

21 20 19 18

17 16 15

14 13 12 11 110

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marker bed (white chert)

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白日圏一日。

Sketch of the bedded chert in the middle part of the CH圃 2bed， showing the localities 1-39.

Fig. 2.

140 Akira YAO， Tetsuo MATSUDA and Yukio ISOZAKI

contact with the mudstone beds at both the southern and the northern margins. Within

the CH・2bed， two faults parallel to the strike of the bed are inferred because successive occurrence of late Triassic conodonts and radiolarians is repeated three times in the sec-

tion. Therefore， the CH-2 bed is not stratigraphically a single bed.

The chert samples of about 2 kilograms per one locality were collected respectively

from less than 3 succeeding layers of bedded chert， namely within a limit of about 10

centimeters， in total thickness， in order to avoid a mixing of fossil assemblage of different

ages. The samples were treated with 10 to 20 % hydroBuoric acid for 3 to 10 hours.

The primary residue was washed through a 10S-micron screen， and dried. The heavy

liquid separation technique was applied to it. Conodont elements in the secondary

residue were picked out under a binocular. Radiolarian remains were usually concentra-

ted su伍cientlyin the primary residue so that glass slides for the optical microscope were

prepared without picking. Concerning mudstone samples， the treatment with 10 % hydroBuoric acid was applied to each sample of about 1 kilogram in order to detect radio-

larian remain. As a result of the treatment for 3 to 10 hours， radiolarian remains could be separated in all cases. The concentrated radiolarian remains were mounted o，n glass

slides with the synthetic medium “Entel1an new".

In this research， the authors under close cooperation did the fieldwork and treated the rock samples in the laboratory. The junior authors (MATSUDA， T. and ISOZAKI， Y.) jointly examined and identified the conodonts obtained from the chert samples， while the examination of radiolarians was carried out by the senior author (Y AO， A.).

，

Conodonts

'Triassic conodonts occurred in many chert sarnp:]es fr，ωn the area. Tbe description

in this chapter is focussed on the occurrence of conodonts， both platform-and compound-

type， from the measured section of the CH-2 bed. Fig.2 shows the localities of the chert

samples 1-39 in the middle part of the CH-2 bed along the right side of the Kiso River.

Each level of the samples is given in the columnar section (Fig. 3). Table 1 gives the

distribution of representative species of conodont and radiolaria from the measured sec圃

tlon.

Sample 3 includes one specimen of Gondolella sp. cf. G. huckriedei (BUDUROV & STE-

FANOV)・G.huckriedei is originally described in the lower Ladinian of Bulgaria (BUDUROV

& STEFANOV， 1973). 8amples 7，9， 10 and 11 contain Gondolella spp.， and the last one is accompanied by Neoゆathodussp. and many compound圃 typeconodonts. Sample 8 yields

a few specimens of Glad:忽ondolellasp. cf. G. tethydis (HUCKRIEDE). Gondolella polygnathi-

formis BUDUROV & STEFANOV is found i，n samples 13 and 14. This species has been re-

ported from the Carnian of Europe， North America etc. (SWEET et al.， 1971; KOZUR &

MOSTLER， 1972b). Ep~なgo仰ndlゐOんωuμaηnodゐosωa (HAYASHI)， which is believed to occur in uppe釘r

CωarInm1

s鈎ample1臼S. Sample 16 is characterized by abundance of conodonts classified as Epなondo・

List of important species oI conodonts and radiolarians in each sample. Table 1.

同ユ抽よね句旬礼町ぬ芯丸、位、ぬ句句片見

anm。宮司よね暗号、ささ

NSQQSQaミぬ

】{恥H

. 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 samp1e / species 2 3 4 5 6 7 8 9

CONODONT

x Gondo1e11a cf. huckr、iedei

X G1adigondole11a cf. tethydis

x x Gondo1e11a pOlygnathiformis x Epigondo1e11a nodosa

x x E. abneptis x x X ‘ E. postera x X X E. bidentata

X X X X Misike11a hernsteini • 阿. posthernsteini × X × x X ×

RADIOLARIA x x × x Xiphosphaera? sp. B

× x X x x X X × X X E11ipsoxiphus sp. × x x X X Staurosphaera? sp. A

x X X χ X X S. ? sp. B X X X Capnodoce? sp.

X x X X x X x Triactoma sp. B X x X Spongosaturnalis multidentatus

X x S. tenuispinosus X X X X X x X X x S. graci1is

X x X x x S. ? sp. A X x x S. ? sp. B

X x x x X X x X x Poulpus? sp. x x Eucyrtidium? sp.

X x x x Syringocapsa? sp. A χ χ S. ? sp. B

x X x x x x X X X x X X x Dictyomitrel1a sp. A x x X x x x X x x X X X x x X D. sp. B

X x x D. sp. C X x χ Archaeodictyomitra sp. A x X X Stichocapsa sp.

Dictyomitrella sp. A Dictyomitrella sp. B D.sp.C-A.sp.A assemblage RADIOLARIAN ASSEMBLAGE assemb1age assemblage

142 Akira YAO， Tetsuo MATSUDA and Yukio ISOZAKI

たllaabnψtゐ(HUCKRIEDE)，E. postera {KOZUR & MOSTLER) and E. bidentata MOSHER. E.

abneptゐoccursalso in sample 17， E. postera in samples 18 and 21， and E. bidentata in sarnples 18 and 24. These species have been reported from various parts of the world by

many workers (e.g. SWEET et al.， 1971; KOZUR & MOSTLER， 1972b). According to them， E. abneptゐoccursin uppermost Carnian ~ middle Norian， E. postera in Norian， and E. bidentata in upper Norian. Misikella hernsteini (MOSTLER) is found in samples 18， 24， 27 and 28. This species has been reported from lJpF>ermost Norian in Europe (SWEET

et al.， 1971; KOZUR & MOSTLER， 1972b). Samples 24，26，27，29， 30 and 31 contain Misi-kella posthernsteini KOZUR & MOCK. This species has been reported from uppermost

Norian and Rhaetian in Europe and Papua New Guinea (KOZUR & MOCK， 1974; SKWAR-KO et al.， 1976; GAznzIcKI， 1978; GAZDZICKI et al.， 1979). Sample 31 is situated at the

uppermost horizon of conodont-bearing chert in the measured section.

Radiolarian assemblage

Radi'O.1arians were obtained from rnost samples taken from both chert beds and

mudstone beds. Three assemblages of radiolarians are broadly distinguished in chert

beds， namely Dic砂omitrellasp. A assemblage， D. sp. B assemblage and D. sp. C -Archaeo四

dic抄omitrasp. A assemblage in ascending order. While in mudstone beds， Unuma echinatus assemblage is present. The first three of these assemblages are obtained suc-

cessively from the middle part of the CH-2 bed. 'Tbe distribution of important species

of radiolarians obtained from the measured section is shown in Table 1. The species com-

mon to the three assemblages and unidentified species are not listed in Table 1. Among

them are Cenoψhaera sp.， X争hoψhaera?sp. A， Triactoma sp. A (Pl. 1， :fig. 4)， Acantho-φhaera sp." Melitoψhaera spp.， Plagmoψhaera? sp.， Spongodiscus sp.， Paronaella? spp. and Saitoum? spp. (Pl. 1， :figs. 7-8). Generic names of radiolarians are here applied in a

very broad sense or in a rather conventional way. A ful1 description of new taxa with

scanning micrographs is in preparation.

Dic砂omitrellasp. A assemblage is found in samples 1-13. The species most

diagnostic oI the assemblage is Dictyomitrella sp. A (PL 1， :figs. 9-11)， which has a slender

cylindrical multisegmented shel1 with well田 developedtransverse ridges at the joint parts

of segments. Application of the generic name Dic砂omitrellato this form is tentative

as in the case of Dicかomitrellasp. B and C. In addition to the species mentioned above， X1μoφhae宮-a?sp. B (Pl. 1， :fig. 1)， Stauroゆhaera?'sp. A (PL 1， ug. 5) and Ell争soxiphus

sp. (Pl. 1， :figs. 2-3) characterize this assemblage. The occurrence of significant mem-

bers of this assemblage is restricted to the horizon of samples 1-13 except for Stauro-

φhaera? sp. B which is present in sample 14. This radiolarian assemblage occurs to-

gether with following conodonts， namely Gondolella cf. huckriedei in sample 3， Gladなon-dolella cf. tethydis in sample 8 and Gondolella polygnath約rmisin sample 13. Beside the

measured section， this radiolarian assemblage was present at the southern parts of both the CH-1 bed and the CH・2bed， and at the middle part of the CH-4 bed on the southern

Tri，αssic and Jurassic Radiolarians.fiγomlγluyama a~γea 143

limb.

Dicかomitrellasp. B asselnblage is obtained from samples 14-34. This assemblage

is characterized by a large number of species. The most significant member of this

assemblage is Dic砂omitrellasp. B (P1. 3， figs. 1-3)， which is similar to D. sp. A men-

tioned above， but di百ersfrom the latter in the conical shell and in having broad transverse

ridges arranged in short interva1. This species has also a strong resemblance to the

species， Dic砂omitrellasp. A， reported by DE WEVER et al. (1979) from Carnian or early

Norian limestone in Greece. The other members of this assemblage are Capnodoce?

sp. (P1. 2， fig. 1)， Triactoma sp. B， Spongosaturnalis multidentatus KOZUR & MOSTLER

(Pl. 2，五g.2)， S. tenuispinosus~(DoNOFRIO & MOSTLER) (Pl. 2，五g.3)， S. gracilis KOZUR &

MOSTLER (Pl. 2， fig. 4)， S. sp. A (Pl. 2.，五g.5)， S. sp. B， Poulpus? sp. (Pl. 2， fig. 6)， Eucyr圃

tidium? sp. (Pl. 2， fig.7) and Syringocapsa sp. A (Pl. 3， fig.4)， most of which have an analogy with the species of Late Triassic radiolarians reported by DE WEVER et al.

(1979)， KOZUR & MOSTLER (1972a， 1979) and PESSAGNO et al. (1979). These species are

not always present throughout samples 14-34， but are restricted to certain samples. A

further subdivision of this assemblage is therefore possible， but this paper is concerned with the recognition of major aspect of the assemblage. The characteristic members of

this assemblage do not occur together with members of both the D. sp. A assemblage

mentioned above and the D. sp. C -Archaeodicかomitrasp. A assemblage to be mentioned

below. Except f01i samples 32-34 which yield no conodont element， this radiolarian assemblage coexists with Late Triassic conodonts， narnely Gondolella polygnath約rmis，Epigondolella nodosa， E. abneptゐ，E. postera， E. bidentata， Misikella hernsteini and M.

posthernsteini. Dictyomitrella sp. B assemblage was also found in the middle part of

the CH-1 bed， and in the southern parts of both the CH-2 bed and the CH-4 bed.

Dic砂omitrellasp. C -Archaeodic砂omitrasp. A assemblage is found in samples

35-39. This assemblage is characterized by abundance of nassellarians， such as Dic砂0-

mitrella sp. C (Pl. 3， figs. 5-6)， Archaeodic砂omitrasp. A (Pl. 3， figs. 7-9)， Stたhocapsasp.

(Pl. 3， figs. 12-13) and Syringocapsa sp. B (Pl. 3， figs. 10-11)， and the first two are the most diagnostic species of the assemblage. Dic砂omitrellasp. C is similar to D. sp. B， but differs from the latter in having inconspicuous transverse ridges. Archaeodicかomitra

sp. A has a slender multisegmented test on which longitudinal ribs are developed with

one row of pores between them. Primary pores are arranged in tetragonal system. The

shel1 is conical in its main part， and is slightly constricted toward the aperture. This

species belongs to an undescribed genus， but is here provisional1y assigned to Archaeodic・

砂omitra. This assemblage was additionally found in the northern parts of both the CH-1

bed and the CH-2 bed， and in the basal part of the CH岨 4bed.

Unuma echinatus assemblage is from mudstone beds which are in fault contact with

the chert beds containing the three radiolarian assemblages mentioned above. 1t com-

prises a large number of nassel1arian species. 1mportant members of the assemblage

are Unumaか'Picω ICHIKAWA& YAO， U. echinatlls ICHIKAWA & YAO， Archaeodic砂omitra

sp. cf. A. rigida PESSAGNO， Hsuum sp. B， Tricolocapsa plicarum YAO， T. sp. cf. T. rUsti

~

144 Akira YAO， Tetsuo MATSUDA and Yukio ISOZAKI

T AN SIN HOK， Stichocapsa convexa YAO and Cyrtocapsa mastoidea YAO， al1 of which

have been reported from the manganese nodu】esin reddish siliceous mudstone (Loc. R

in Fig. 1!: cf. YAO， 1979a). The constituent element of the assemblage is more numerous

in the reddish and greenish siliceous mudstone in comparison with the grey to black

noか siliceousmudstone.

Discussion on age

The order of successive occurrence of conodonts in the measured section is generally

consistent v/ith those reported from the Middle and Late Triassic rocks in Europe and

North America (SWEET etal.， 1971; KOZUR & MOSTLER， 1972b; KOZUR & MOCK， 1974). It is biostratigraphically significant in J apan that the Middle to Late Triassic conodont

sequence was recognized within a single sequence of chert， and that the presence of the probable Rhaetian was newly suggested through the present study. From this， it is

inferred that the cOllodont田 bearingchert in the measured section (salnples 1-31) is a

sequence of the Middle-Late Triassic rocks without tectonic break. Recently， a simi1ar

conodont sequence of the Late Triassic was found from a chert of the geosynclinal se-

quence in the southern part of the Tanba belt， Southwest Japan (ISOZAKI & MATSUDA，

1980).

On the basis of conodonts， the age of the chert bed is considered as follows: The

horizon yielding Gondolella cf. huckriedei (sample 3) is referred to the Ladinian. In the

middle part of the measured section (samples 13-31)， the successive occurrence of cono~ donts indicates that the Late' Triassic is liepresented here. The boundary between the

Ladinian. and the Carnian is set below the horizon of sample 13. The CarniarトNorian

boundary is estimated at the horizon between sample 15 and sample 16. Although

opinions are diversed concerning the Rhaetian problem， including the validity of the stage name Rhaetian， the horizon bearing only Misikella posthernsteini without M. heren圃

steini (samples 29-31) correlated with the early Rhaetian according to the opinion pro-

posed by KOZUR & MOCK (1974).

Concerning radiolarians， age of the three radiolarian assemblages are considered as fol1ows with reference to the coexisting conodonts (Table 1; Fig. 3): The Dたかomitrella

sp. A assemblage may indicate the Ladinian and the early Carnian prior to the appearance

of Etigondoんlla. rriactoma sp. D from the southern part of the CH-2 bed (outside the

list iB Table 1) of this assemblage resembles Venωsa.ψongus subφhaericus KOZUR & Mos帽

TLER described from the lower Carnian of Gostling， Austria (KOZUR & MOSTLER， 1979).

The Dたかomitrellasp. B assemblage is Late Triassic in age with exception of the early

Carnian. As remarked already in the preceding chapter， this assemblage includes cer輔

tain species which closely resemble the species from the Carnian or lower Norian of

Greece (DE WEVER et al.， 1979)， frorn the Norian of Austria (KOZUR & MOSTLER， 1972a)

1979)， and from the upper Carnian to upper NOI匂nof Baja California (PESSAGNO et al.， 1979). The assemblage in samples 32-34 does not coexist with conodont element， but

Trzassic a:悦dJurassic Radiolarz:α~ns from Inuyαmααγea 145

it is inferred to be of late Rhaetian in age under the scheme that biohorizon of disappearance

of Mz"sikella posthernsteini marks the end of the early Rhaetian (KOZUR & MOCK， 1974).

The Dic砂omitrellasp. C -Archaeodic砂omitrasp. A assemblage is probably of Early

Jurassic age because the chert containing the assemblage conformably overlies the Late

Triassic chert in the measured section， because no radiolarians， characteristic of the Trias圃

sic， is identi:fied， and because the assemblage consists mainly of the nassellarians closely aUied to the previously reported J urassic forms. The exact position of the Triassic-J urassic

boundary cannot be clarified owing to a lack of reliable paleontological evidence other

than radiolarians. However， based on the above-mentioned discussion on the radiolarian

assemblages， it is provisionally drawn at the boundary between the horizons of sample 34 and sample 35.

The Unuma echinatus assemblage comprises many species closely related to the

Late Jurassic-Cretaceous forms. DONOFRIO & MOSTLER (1978) remarked that the strati-

graphic position of the radiolarian assemblage described by YAO (1972) has to be regard-

ed as an Upper Jurassic one. Nevertheless， the assemblage is possibly of the late Middle Jurassic age because it is accompanied by probably ancestral forms of cryptothoracic

tricyrtids， such as Tricoゐcapsasp. cf. T. rUsti T AN SIN HOK and T. sp. cf. T. par1.ゆora

TAN SIN HOK described by YAO (1979a)， and those of certain parvicingulid with transverse

ridges at chamber joints on which numerous small spines or projections are arranged，

such as Parvicingula? sp. a il1ustrated by ICHlKAWA & YAO (1979， no. 55-328， figs. 7-8). The presence of such unique form as Unuma should be also taken into account. This

age assignment is supported by BAUMGARTNER (in press) based on the detailed study of

hagiastrids. Further consideration on the age of the last two assemblages is necessary

before the conclusion is formed.

Additionally， the age of the sandstone bed in the Inuyama area is considered as

fol1ows: The sandstone bed conformably overlies the grey to black n01トsiliceousmudstone

bed which poorly includes radiolarians of the Unuma echinatus assemblage. Except

for the petrified wood， no fossil has been discovered from the sandstone bed. However，

an ammonite iden凶t“ifieda鈴sC，αhqザグat均ia(伊Sub伊'tr削.

from this bed. For a while， it is assumed that the sandstone bed is of Late Jurassic or

late Middle J urassic age.

On the basis of the above四 mentioneddiscussion about the age， the strata in the Inu-yama area are provisionally divided into five major units， namely the Middle Triassic，

the Upper Triassic， the Lower Jurassic， the Middle Jurassic and the Upper Jurassic. Fig. 4 shows the distribution of the units along the Kiso River and the geological rela-

tionships among the units. This result shows that repeated occurrence of strata through

tectonic andfor sedimentary rearrangement of the norlllal stratigraphical sequence was

quite conspicuous in the Inuyama area. It is much more complicated than the result

given by IIJIMA et al. (1978). The problem of rearrangement of strata wilI be discussed

ln a separate paper.

Akira YAO， Tetsuo MATSUDA and Yukio ISOZAKI 146

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Tentative map showing the distribution of five major units along the Kiso River.

S¥1m.mary

Fig.4.

A biostratigraphical research of conodont and radiolaria was carried out on the geo・

synclinal sequence in the Inuyama area， Central Japan. Successive occurrence of La-

dinian， Carnian， Nrorian and “Rhaetian'" conodonts was established in a section of chert

(CH-2 bed). Four radiolarian assemblages were d~istinguished ， namely Dic砂omitrella

sp. A assemblage， D. sp. B assemblage， D. sp. C -Archaeodicかomitrasp. A assemblage

and Unuma echinatus assemblage in ascending order. For an age assignment， the first two are correlated with reference to coexisting conodonts， and the last two are broadly

•

Tγiassic and ]urasslc Radiolαγians fiγom Inuyamaαγea 147

compared with the p，reviously reported radiolarian assembiages. Thus， the Dic砂omふ

trella sp. A assemblage is Ladinian and early Carnian， the D. sp. B assemblage is Late

Triassic in age. The D. sp. C -Archaeodic砂omitrasp. A assemblage is probably Early

Jurassic in age. These three assemblages are successively obtained from a single se-

quence of chert. The Unuma echinatus assemblage is contained in the mudstone bed，

and it possibly indicates the late Middle J urassic age.

Acknowledgement

The authors wish to thank Prof. K. ICHIKAWA of Department of Geosciences， Osaka City University for valuable discussion and critical reading of the manuscript. The

authors are also much indebted to Dr. K. NAKASEKO of Osaka University for helpful

advice.

References

BAUMGARTNER， P.O. (in press): Late Jurassic and Early Cretaceous Radiolaria from the Argolis

Peninsula (Peloponnesus， Greece): Hagiastridae RIEDEL， emended (Spumellariina incertae sedis) and Patulibracchiidae PESSAGNO， emended (Spongodiscacea). Micropaleontology.

BUDUROV， K.J. and STEFANOV， S.A. (1973): Etliche neue Plattform-Conodonten aus der Mitteltrias

Bulgariens. Comptes rendus de l' Acad. bulgare SC1..， 26， no. 6， p. 803-806. DE WEVER， P.， SANFILIPPO， A.， RIEDEL， W.R. and GRUBER， B. (1979): Triassic radiolarians fJ..om

Greece， Sicily and Turkey. Micropaleontology， 25， no. 1， p. 75-110， pl. 1-7.

DONOFRIO， D.A. and MOSTLER， H. (1978): Zur Verbreitung der Saturnalidae (Radiolaria) im

Mesozoikum der t.Jordlichen Kalkalpen und Sudalpen. Geol. Palaont. Mitt. lnnsbruck， 7， no. 5， p. 1-55.

GA土DZICKI，A.(1978):Conodontsof tpe genus Misthella kOZUR&MOCK，1974from the Rhae圃

tian of the Tatra Mts (West Carpathian). Acta Palaeont. Pol.， 23， p. 341-350. GAZDZICKI， A.， KOZUR， H. and MOCK， R. (1979): The Norian-Rhaetian boundary in the light of

micropaleontological data. Geologija， 22， p. 71-122. ICHlKAWA， K. and YAO， A. (1976): Two new genera ofMesozoic cyrtoid radiolarians from Japan.

ln Progress in Micropaleontology (ed. TAKAYANAGI， Y. and SAlTO， Tふ Micropaleontology

Press， p. 110-117. ICHIKAWA) K. and YAO， A. (1979): Mesozoic radiolarian fossils from Japan 1-6. Atlas 01 ]apanese

Fossils， Tsukiji Shokan， no. 55， s. 325-330.

IIJIMA， A.， KAKUWA， Y.， YAM AZAK 1 ， K. and YANAGIMOTO， Y. (1978): Shallow-Sea， Organic Origin of the Triassic Bedded Chert in Central Japan. Jour. Fac. Sci.， Univ. Tokyo， sec. 2， 19， no. 5， p. 369-400.

lSOZAKI， Y. and MATSUDA， T. (1980): Age of the Tamba Group along the Hozugawa“Anticline" ， Western Hills of Kyoto， Southwest Japan. Jour. Gosci.， Osaka City Univリ 23，p. 115-134.

KOIKE， T. (1979): Biostratigraphy of Triassic Conodonts. ln Biostratigraphy of Permian and

Triassic Conodonts and Holothurian Sclerites in J apan (Prof. Mosaburo I<ANUMA memorial

volume)， p. 21-77. KOlKE， T.， IGo， H.， TAKIZAWA， S. and KINOSHITA， T. (1971): Contribution to the geological

history of the Japanese Islands by the conodont biostratigraphy. Pt. II. Jour. Geol. Soc. Japa1!ιJ

77， no. 3， p. 165-168. . KONDo， N. and ADACHI， M. (1975): Mesozoic strata of the area north of Inuyama， with special

reference to the Sakahogi conglomerate. Jour. Geol. Soc. Japan， 81， no. 6， p. 373-386.

148 Akira YAO， Tetsuo MATSUDA and Yukio IS0ZAKI

KOZUR， H. and MOSTLER， H. (1972a): Beitrage zur Erforscl】ungder mesozoischen Radiolarien.

Teil 1: Revision der Oberfamilie Coccodiscacea HAECKEL 1862 emend. und Beschreibung

ihrer triassischen Vertreter. Geol. Palaont. Mitt. Innsbruc九2，no. 8/9， p. 1-60. KOZUR， H. and 1¥任OSTLER，H. (1972b): Die Bedeutung der Conodonten fur stratigraphische und

palaogeographische Untersuchungen in der Trias. Mitt. Ges. Geol. Bergbaustudリ 21，p. 777-810， p1. 1-4.

KOZUR， H. and MOSTLER， H. (1979): Beitrage zur Erforschung der mesozoischen Radiolarien.

Teil 111: Die Oberfamilien Actinimmacea HAECKEL 1862 emend.， Artiscacea HAECKEL 1882， Multiarcusel1acea nov. der Spumellaria und triassische Nassellaria. Geol. Palaont. Mitt. Inns-

bruck， 9， no. 1/2， p. 1-132. KOZUR， H. and MOCK， R. (1974): Misikella tosthernsteini D. sp.， die jungeste Conodontenart der

tethyalen Trias. Casopis Miner. Geol.， 19， p. 245-250. KRYSTYN， L. (1973): Zur Ammoniten-und Conodonten..Stratigraphie der Hallstatter Obertrias

(Salzkammergut， Osterreich). Verh. IGeol. B.-A. 1973/1， p. 113-153. MIZUTANI， S. (1964): Superficial folding of the Palaeozoic system of Central Japan. ]our. Earth

Sci.， Nagの'aUnivリ 12，no. 1， p. 17-83. NAKASEKO， K.， SUGANO， K. and NISHIMURA， A. (1979): Triassic radio】ariansfrom the Sanbosan

belt and the Mino belt. In Abst. Program， 1979 Annual Meet. Geo1. Soc. Japan， p. 238. NISHIDA， M.， AnACHI， M. and KONDO， N. (1974): Fossil fragments of petrified wood from pre・

Tert1ary formatioDs in the northern area of lnuyama City， Aichi Prefecture， and their bearing on geology. _Iour. ]ap. But.， 49， no. 9. p. 265-272.

PESSAGNO， E.A." FINCH，羽T.and ABBOTT， P.L. (1979): Upper Triassic Radiolaria from the San

Hipolito Formation， Baja California. Micropaleontοlogy， 25， no. 2， p. 160-197， pL 1-9. SATO， T. (1974): A Jurassic ammonite from near Inuyama， north of Nagoya. Trans. Proc. Palaeont.

Soc. Japan， N. S.， no. 96， p. 427-432. SKWARKO， S.， NICOLL， R.S. and CAMPBELL， K.S.W. (1976): The Late Triassic mol1uscs， cono・

donts and brachiopods of the Kuta Formation， Papua New Guines. BMRJ. Aust. Geol. Geo-

phys.， 1， p. 219-230. SUGANO， K.， NAKASEKO， K. and WAKIMOTO， R. (1979): Jurassic radiolar加 lSfrom the Sanbosan

belt and the恥1inobelt. In Abst. Program， 1979 Annual Meet. Geo1. Soc. Japan， p. 237. 8WEET， W.C.， MOSHER， L.C.， 'CLARK， D.iL..， 00札LLI江INSωON刊， J

Conodont biostratigra勾phy0ぱfthe Tr討iassiたc. In Symposium on conodont biostratigraphy (ed.

SWE打， W.C. and BERGSTROM， S.MふGeol.Soc. Amer.， Mem. 127， p. 441-465， 1 pl.

YAO， A. '(1'972): Radioiarian Fauna from tbe Mino Belt in th.e Northern PaFt of the Inuyama

Area， Central Japan. Part 1: Spongosaturnalids. ]our. Geosci.， Osaka City Univ.， 15， p. 21-64. YAO， A. (1979a): Radiolarian Fauna form the Mino Belt in the Northern Part of the Inuyama

Area， Central Japan. Par'C 11: NasserIaria 1. Jour. Geosci.， Osaka City Univ.， 22， p. 21-72. YAO， A. (1979b): Triassic and J urassic radiolarians from the Honshu geosynclinal sequences. In

Abst. Program， 1979 Annual Meet. Geol. Soc. J apan， p. 148.

•

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152

Fig.1. Cap符odoce?sp.

Explanation. of Plate 2

Dic砂omitretZasp. B assemblage

(All figures x 200)

I-UNM16-3 (26/86)， middle part of the CH-2 bed.

Fig.2. Spo得 osaturnalismultidentatus KOZUR & MOSTLER

I-UNM35-1 (45/87)， middle part of the CH-4 bed (northern limb).

Fig. 3. Spongosaturnalis tenuispinosus (DONOFRIO & MOSTLER)

I-UNM15-1 (41/82)， sample 18， rnIJddle part of the CH・2bed.

Filg.4. Sponglosaturnalis gralcilゐK0ZUR&乱I:[OS'FLER

I-UNM35-1 (3'9/90)， midd]e part of the 'CH-4 bed (north.ern Hmb).

Fig.5.SpongosatZ4771afis?宅p.A

1-UNM17 -2 (37/82)， middle part of the CH岨 2bed.

Fig. 6. Poulpus? sp.

III-UNM5-1 (40/84)， sample 29， middle part of the CH-2 bed.

Fig. 7. Eucyrtidium? sp .

. II-UNM16-4 (28/97)， sample 17， middle part of the CH-2 bed.

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• •

154

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Dictyomitrella sp. B assemblage (Figs. 1-4) and D. sp. C

圃 Archaeodictyomitrasp. A assernblage (Figs. 5-13)

(AH fAIguli，es X 2，00)

Figs. 1-3. Dictyomitrella sp. B

1. 11-UNM16-2 (38/90)， sample 17， middle part of the CH-2 bed. 2. 11-UNM16-2 (29/102)， sample 17， middle part of the CH-2 bed. 3. 11-UNM16-2 (33/99)， sample 17， middle part of the CH-2 bed.

Fig. 4. Syringocapsa? sp. A

111-UNM6-2 (44/103)， sample 31， middle part of the CH-2 bed.

Figs. 5-6. Dictyomitrella sp. C

5. 1II-UNM11-1 (27/94)， saJmpl，e 38， middle part of the CH-2 bed. 6. I1-UNM10-2 (46199)， sample 31， mid:dle part of the CH-2 bed.

Figs.フ-9. Archaeodictyomitra sp. A

7. 1-UNM36-2 (31/90)， middle part of the CH-4 bed (northern lirnb). 8. 1-UNM36-'1 (47/93)， middle part of the CH-4 bed (northern limb). 9. 1-UNM36-2 (31/86)， middle part of the CH-4 bed (nQrthern limb).

Figs. 10-11. Syringocapsa? sp. B

10. 1-UNM18-1 (25/97)， middle part of the CH-2 bed. 11. 1-UNM18-2 (25/88)， middle part ofthe CH-2 bed.

Figs. 12-13. Stichocapsa sp.

12. 1-UNM18-3 (34/83)， middle part of the 'CH-2 bed. 13'. 11田 UNM9-1(32/89)， samplle 3'9， middle paltt of the CH-2 bed.

A. Y AO et al. : Triassic and J urassic Radiolarians from Inuyama area Plate 3

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