Journal of Geosciences， Osaka City University Vol. 26， Art. 3， p. 65-86 March， 1983

M'IdCl，I.e alild' lLate， TrIas's.Ic' Conodonts from 8edded Chert Sequences In the M'ino-Tamba Bel.t， Southwest Japan

Part 1: Misikella' and Parvigondolella

Yukio ISOZAKI* and Tetsuo MATSUDA料

(with 2 Figures， 3 Tables and 4 Plates)

Introduction

Part 2 of this study deals with paleontological description of Late Triassic three

conodont species， namely Misikella hernsteini (MOSTLER)， M. posthernsteini KOZUR &

MOCK and Parむなondolellaandrusovi KOZUR & MOCK， from Hozukyo and Inuyama areas in the Mino四 TambaBelt， Southwest Japan. Stratigraphic columns of the study sections

and distribution of these species are shown in Part 1 of this study.

Age assignment of these uppermost Triassic conodonts is rather conlplicated due

to the problem of Rhaetian Stage. So， in the appendix of this paper， definition and lower boundary of the Rhaetian Stage are briefly discussed mainly from the viewpoint

of conodont biostratigraphy.

Acknowledgement

The present authors wish to thank Prof. Koichiro ICHlKAWA of Osaka City Univer-

sity for his valuable suggestions and critical reading of the manuscript. Authors are

also indebted to Dr. Akira YAO of the same university for his cooperation in the joint

work in the Inuyama area， to Dr. Yasunori MIURA of Yamaguchi University for allow-

ing them to use ion-sputter and to Mr. Hiroyuki NAGAO of Osaka City University for

joining in discussion on the problem of Rhaetian Stage.

Systematic Paleontology

Horizons of study samples in detail， register and depository of described specimens

are shown in Part 1 of this study (ISOZAKI & MATSUDA， 1982). Measurement of de四

scribed specimens is given in Tables 1-3. Letters L， W， H and N in these tables

represent length， width， height of unit in millimeter and number of carina denticles， respectively.

• Present address: Department of Geology and Mineralogical Sciences， Faculty of Science， Yamaguchi University， Yamaguchi 753， ]apan.

•• Department of Geosciences， Faculty of Science， Osaka City University， Osaka 558， ]apan.

66 Yukio ISOZAKI and Tetsuo MATSUDA

Order CONODONTOPHORIDAE EICHENBERG， 1930

Genus MISIKELLA KOZUR & MOCK， 1974

Misikella hernste'ini (MOSTLER， 1967)

Plate 1， Figs. 1-7.

1967 Spathognathodus hernsteini n. sp. MOSTLER -p. 182， text-fig. 1aーc.

1968 Neospathodus lanceolatus n. sp. MOSHER -p. 930-931， p1. 115， figs. 10， 11; non fig. 7. 1971 Neospathodus herns，teurli (MOS'FLER) - SWBET' et al.， pl. 1， figs. 2， 3. 1974a Misikella hernsteini (MOSTLER) - KOZUR & MOCK， p1. 1， figs. 6， 7. 1978 Muikella hernsteini (MOSTLER) - MOSTLER et al.， p1. 1， figs. 10-19， pl. 2， figs. 5-7. 1979 Misikella hernsteini (MOSTLER) - GAZDZICKI et al.， pl. 5， figs. 3-7. 1980 Mis'ikella hernsteini (MOSTLER) - ISOZAKI & MATSUDA， pl. 1， fig. 12. 1980 Misikella hernsteini (MOSTLER) - KovAcs & KOZUR， pl. 15， figs. 4-7. 1980 M'isikella hernsteini (MOSTLER) - KRYSTIN， pl. 14， figs. 10-12. 1981 Misikella hernsteini (MOSTLER) - KOlKE， pl. 2， fig. 29. 1982 Misikella hernsteini (MOSTLER) - ISOZAKI & MATSUDA， p1. 4， fig. 8. 1982 Misikella hernsteini (MOSTLER) - MATSUDA & ISOZAKI， pl. 2， fig. 30. 1982 Misikella hernsteini (MOSTLER) - NAGAO & MATSUDA， pl. 1， figs. ~-11.

Diagnosis;-A form species of Mz.sikella， characterized by Neoφathodus-like form

and by slightly expanded basal cavity， which is rounded at the posterior end.

Desc'lψtion; In oral view unit symmetrical， showing longitudinally elongated tear四

drop form， due to laterally expanded posterior part of unit and rounded posterior mar-gin. Carina composed of 3 to 6 laterally compressed oral denticles running longitudinal-

ly in the middle of oral surface. Most specimens possessing 3 to 5 denticles， including the most robust one located at the posterior end.

In lateral view， unit looking like maple leaf. Aboral margin of unit concave ab圃

orally in the posterior part and slightly convex aborally in the anterior. Both the an-

terior and the posterior ends of aboral margin angular. Anterior margin of unit slightly

convex anteriorly， whol1y inclined steeply postero-orally at an angle over 700 with aboral

surface. Posterior margin of unit slightly concave posteriorly， inclined postero-orally at an angle around 1200 with aboral surface. Summit line uf denticles straight or convex

orally. The highest part located around mid-posterior part of unit. Denticles laterally

compressed， fused at base， inclined postero・orallyat an angle over 600 with aboral sur-

face. Inclination of denticle at the anterior end the steepest， around 750 with aboral

surface; that at the posterior end the gentlest， around 600• Denticle at the posterior

とndthicker and wider than the rest. Individual denticles showing elongated oval form

like leaf， pointed at apex. Aboral margin of unit flaring and thinning off laterally in

the posterior part of unit. Surface of unit smooth.

In aboral view， significant basal cavity， not so deep， developing in teardrop form，

with rounded posterior margin making loop. Anterior end of aboral margin sharp， pointed. Aboral surface of basal cavity smooth.

Remarks ;--MOSTLER et al. (1978) insisted that clear morphologic change from M.

Middle and Late Triassic Conodonts 介omthe Mino・TambaBelt 67

hernsteini to M. posthernsteini can be recognized especially in the form of posterior basal

cavity， namely from loop四 like，rounded posterior aboral margin of the former species to trian:gularly cornered one of the latter. Present authors stand on similar viewpoint

and regard rounded posterior aboral margin and elongated teardrop form of basal cavity

as the main criteria of this species. Specimens with cornered posterior aboral margin， even if they lack posterior concavity， are tentatively assigned to M. posthernsteini in this paper.

In addition to type specimens original1y described by MOSTLER (1967)， many speci-

mens of this species have been reported from various localities and figured by several

workers as shown in the synonym list. Almost al1 of them possess 4 to 6 denticles ex-

oept for only one specimen with 3 denticles reported by KOIKE (1981). Most of the

specimens obtained from the study three sections， however， have 3 or 4 denticles. Spec田

imens with 5 or more denticles are rather rare.

Table 1. Measurement of Misikella hernsteini (MOSTLER). 一 一ー

Specimen Sample P1. Fig. L w H N (YU) no. 一一

3012-1 HZ-41 1 0.17+ 0.06 0.15 4

-2 HZ-41 2 0.20 0.05 0.23 3

-3 HZ-41 5 0.27+ 0.05 0.21斗 4

-4 HZ-41 6 0.28+ 0.06 0.22+ 3

3013-1 HZ-42 1 3 0.19+ 0.05 0.22 4

-2 HZ-42 4 0.20 0.06 0.17 3

Misikella posthernsteini KOZUR & MOCK， 1974

Plate 1， Figs. 8-13; Plate 2， Figs. 1-7; Plate 3， Figs. 1-7.

1968 Neospathodus lanceolatus n. sp. MOSHER -p. 930-931， pl. 115， fig. 7; non figs. 10， 11. 1974 Misikella posthernsteini n. sp. KOZUR & MOCK -p. 247-249， text-figs. 1-4. 1976 Misikella posthernsteini KOZUR & MOCK - SKWARKO et al.， p. 222， text-fig. 4A-H. 1978 M'z'sikella posthernsteinz' KOZUR & MOCK - GAZDZICKI， p. 346， pl. 38， figs. 1-3， pl. 39， figs.

1-4， p 1. 40， fig. 3. 1978 Mz'sikella posthernsteini KOZUR & MOCK -MOSTLER et al.， pl. 1， figs. 20-22. 1979 Muikella posthernsteini I{oZUR & MOCK - GAZDZICKI et al.， pl. 5， figs. 1， 2. 1979 Misikella posthernsteini KOZUR & MOCK - ISHIDA， pl. 2， fig. 9. 1980 Misikella posthernsteini KOZUR & MOCK - ISOZAKI & MATSUDA， pl. 1， figs. 14， 15. 1980 Misikella posthernsteini KOZUR & MOCK - KovAcs & KOZUR， pl. 15， fig. 10. 1980 Misikella posthernsteini KOZUR & MOCK - KRYSTIN， pl. 14， fig. 7-9. 1981 Misikella posthernstez'ni KOZUR & MOCK - GAZDZICKI & GUPTA， text-fig. 1 b. 1982 Misikella posthernsteini KOZUR & MOCK - ISOZAKI & MATSUDA， pl. 4， fig. 9. 1982 Misikella posthernsteini KOZUR & MOCK -MATSUDA & ISOZAKI， pl. 2， fig. 29. 1982 Misikella posthernstei仇 KOZUR& MOCK - NAGAO & MATSUDA， pl. 1， figs. 12-15.

Diagnosis ;-A form species of Misikella characterized by broad， laterally expanded basal cavity which is triangular to heart-like in aboral vic¥v ¥vith dcep concavity in the

posterl0r margin.

68 Yukio ISOZAKI and Tetsuo恥tIATSUDA

Description; ln oral view， unit symlnetrical or slightly asymmetrical in posterior part. U nit formil1g triangular or hωrt-like slhape; its posterior part expanded laterally.

Carina running longitudinal1y in the middle of oral surface， composed of lateral1y com-

pressed 3 or 4 oral denticles. Some specimens having 5 denticles with an additional

minute denticle at the anterior end. Posterior end denticle conical， pointed at the api-cal part.

ln lateral view， aboral margin straight or concave aboral1y in the posterior part of

unit and slightly convex aborally in the anterior parも. Aboral margin angular both at

anterior and posterior ends of unit. Anterior margin of unit slightly convex anteriorIy， almost vertical or inclined postero-orally. Posterior margin of unit concave toward the

anterior， slightly inclined postero四 oral1yas a whole. Laterally compressed denticles

fused at the base， inclined postero-otally at an angle around 30-700 with aboral surface.

Denticle at the anterior end the steepest; that at the posterior end longer， thicker than the rest， inclined gently at an angle around 300 with aboral surface. Height of denticles

increasing posteriorly. Summit line almost straight or slightly convex orally. ln some

well田 preservedspecimens， many fine longitudinal striations on denticles. Surface of

other parts of unit generally smooth. Aboral margin of unit flaring and thinning off

laterally in the posterior part of unit. ln specimens with deep posterior concavity of

aboral margin， posterior surface of denticle at the posterior end possessing a significant

furrow， continued from the concavity of posterior aboral margin. Toward the apex

of the denticle at the posterior end， this furrow beconlIng shallower， disappearing in the middle of denticle.

ln aboral view， broad、basalcavity expanding laterally in the posterior part， with

V帽 formor unwinding U-form concavity in the posterior margini Both corners of the

posterior aboral margin having sharp， triangular， pointed edge. Ahoral surface of basal

cavity generally smooth. Faint concentric striations observable in some well-preserved

speclmens.

Remarks; According to the original description of this species by KOZUR & MOCK

(1974)， M. posthernste'ini is characterized by broad basal cavity expanded laterally in the

posterior part. Especially， concavity in the posterior aboral margin of unit is regarded

as one of the most characteristic feature of this species. There exists， however， con四

siderable variation in form and depth of the concavity among specimens from the

Hozukyo and lnuyama Sections. Namely， typical specimens of M. posthernsteini possess

deep concavity with V-form edge in the bottoωof depression (e.g. Piate 2， Fig. 5).

On the other hand， some other specimens have rather shal10w concavity， which shows

unwinding U四 formdepression without sharp corners. In addition， some other specimens

have almost plain posterior aboral margin. In the Hozukyo Section， typical specimens

of M. posthernstet"ni occur frequently. ln the lnuyama Section， On the contrary， most

specimens possess shallower concavity and those with V -form concavity are rare.

Specimens with almost plain posterior aboral margin are regalided as tFansitional

forms from M. hernsteini to. M. posthernsteini by MOSTLER et aZ. (1978). ln accordance

Middle and Late Triassz'c Conodonts from the Mino帽 TambaBelt 69

with their opinion， these specimens are discriminated from M. hernsteini， which has rounded posterior aboral margin， and are here classified in 1¥ダ.posthernste仇j.

KOZUR & MOCK (1974) originally defined M. posthernsteini to have only 3 oral derト

ticles. From the Hozukyo and the Inuyama Sections， however， a lot of specimens with

4 denticles and typical V-form concavity in the posterior aboral margin occur almost

always together with those with 3 denticles. In addition， specimens with 5 denticles

and significant V -form concavity are rarely found in the Hozukyo 11 Section (e.g. Plate

2， Fig. 7)， but those with 6 or more denticles (Misikella sp. A in GAZDZIClα， 1978) have

not been recognized yet. Present authors regard form of basal cavity as the most ap-

propriate criterion of distinguishing this species from M. hernsteini.

Specimen (YU)

3014-2

-3

-4

-5

-6

-7

-8

-9

-10

-11

-12

3015-3

3016-1

-2

3017-1

3018-1

-2

Table 2. Measurement of Misikella posthernstein~' KOZUR & MOCK.

Sample no. Pl. Fig. L w H

HZ-46 1 8 0.18+ 0.09 0.16+

HZ-46 9 0.22 0.09 0.15

HZ-46 1 11 0.21 0.08 0.20

HZ-46 2 1 0.24 0.11 0.20

HZ-46 2 2 0.22 0.10 0.23+

HZ-46 2 4 0.24 0.11 0.25

HZ-46 2 5 0.21 0.09 0.18

HZ-46 3 0.20 0.09+ 0.21

HZ-46 3 2 0.24 0.09+ 0.21

HZ-46 3 3 0.22 0.08 0.21

HZ-46 3 4 0.21 0.10 0.16

HZ-47 3 5 0.30 0.15 0.25

IN-26 12 0.25 0.09+ 0.17+

IN-26 13 0.20 0.17 0.18+

IN-30 3 7 0.28+ 0.14+ 0.21+

IN-24 2 6 0.28+ 0.11 + 0.18+

IN-24 3 6 0.32+ 0.17+ 0.22十

Genus PARVIGONDOLELLA KOZUR & lVlocK， 1972

Parvigondolella andrusovi KOZUR & lVlocK， 1972

Plate 4， Figs. 1-7.

1972 Parvigolldolella andrusovi n. sp. KOZUR & MOCK - p. 4-5， p1. 1， figs. 11， 12. 1972 Parvigondolella andrusovi KOZUR & MOCK - KOZUR & MOSTLEF， pl. 4， fig. 6. 1972 Parvigondolella andrusovi KOZUR & MOCK - KOZUR， pl. 7， fig. 10. 1979 Parvなondolellaandrusovi KOZUR & MOCK - GAZDZICKI et al.， pl. 5， figs. 8， 9. 1980 Parvigondolella andrusovi KOZUR & MOCK - KovAcs & KOZUR， pl. 15， fig. 3. 1980 Epigondolella bidentata MOSHER - KRYSTIN， pl. 14， figs.←6..

N

3

3

3

3

3

3

4

3

3

3

4

3

4

3

4

4

3

1982 Parvigondolella andrusovi KOZUR & MOCK - ISOZAKI & MATSUDA， pL 4， figs. 6， 7.

70 Yukio ISOZAKI and Tetsuo MATSUDA

1982 Parvigondolella andrusovi KOZUR & MOCK - NAGAO & MATSUDA， p1. 1， figs. 5， 6. non 1976 Epigondolella andrusovi (KOZUR & MOCK) - BUDUROV， pl. 5， fig. 6. non 1977 Epigondolella andrusovi (KOZUR & MOCK) - BUDUROV， p. 45-46， pl. 1， figs. 5， 6，

pl. 2， figs. 3， S， 6.

Diagnosis;-A form species of Parvigondolella， characterized by Epなondolella-like

form with only rudimentary piatform and by lacking ornamentations on oral surface， such as nodes or lateral denticles.

DesC1争tion;-Unitsymmetrical， sIightly bowed in oral view. Very faint rudimenta-

ry platform developing in posterior one third of unit. Due to very narrow platform

and lack of ornamentations， unit looking like ramiform conodont. 7 to 9 laterally com-

pressed oral denticles， pointed at their apices， fused at their basal parts. In lateral view， unit comb-like. Aboral margin straight or slightly convex aborally

in the anterI:or nalf of unit and concave ahorally in the posterior part. An.terior and

posterior ends of aboral margin rounded. Anterior margin of unit almost vertical or

steeply inclined postero四 orallyaround 800 with aboral surface. Posterior margin inclined

postero-orally at an angle of 135-1500 with aboral surface. Summit line of denticles

convex orally. The highest denticle located at anteriort"'..Jmiddle part of unit. Height

of denticles abruptly decreasing posteriorly around posterior one third of unit. Anterior

denticles standing almost vertically or steeply at an angle of 70-900 with aboral surface.

Posterior 2 or 3 denticles S'nort， wide， robust， inclined gently at an angle around 600 pos・

tero-orally. Spacings between denticles almost uniform. Surface of unit smooth.

In aboral view， narrow basal groove running along entire length of unit. Small

basal pit in elongated el1iptic form located around posterior one third of unit.

Remarks;-Specimens obtained from the study sections show great variation in the

mode of development of rudim'entary p~atform. N amely， some specimens have almost

plain lateral surface with only very faint lateral swelling， while some others have signifi-

cant but rudimentar)・ platformwithout any ornamentations. P. andrusovi is clearly

distinguished from Epなondolellabidentata MOSHER in lacking a pair of significant lateral

denticles. Specimens reported as E. andrusovi by BUDUROV (1976， 1977) are obviously identified as E. bidentata. Except for lateral denticles， however， morphologic features of P. andrusovi are quite similar to those of E. bidentata. In the study sections， especially in the Hozukyo ]1 Section， P. ，andrusovi occurs together with E. bidentata for certain

interval. Also KRYSTIN (1980) pointed out that the biostratigraphic range of this species

closely parallels with that of E. bidentata. It is suggested that P. andrusovi was phylo-

genetically derived from E. bidentata. Because of lacking well-developed platform with

oral ornamentations， which is one of the main diagnostic feature of Epigondolella， this

species is here tentatively classified in an independent genus Parむなondolella.

Although P. andrusovi apparently looks like ramiform conodonts， epigondolellid type aboral feature of this species can never be observed in ramiform conodonts such

as M. hernsteini.

n

e

m町民

Y、

p(

門

D Sample no. Pl. Fig. L w

71 Middle α:nd Late T'γiassic Conodonts jiγom the Mino-Tamba Belt

Table 3. Measurement of Parvigondolella aηdrusovi KOZUR & MOCK.

H N

3010-2 HZII-2 4 3 0.42 0.07 0.16 8 -3 HZII-2 4 4 0.32 0.11 0.15十 9 -4 HZII-2 4 7 0.46 0.12 0.27+ 11

3020-1 HZII-7 4 0.36+ 0.08 0.20+ 6 -2 HZII-7 4 2 0.32+ 0.06 0.18十 8 -3 HZII-7 4 5 0.13 0.08 0.19斗 6 -4 HZII-7 4 6 0.30+ 0.05 0.16+ 5

-5 HZII-7 4 8 0.15+ 0.05 0.21+ 5

-6 HZII-7 4 9 0.28 0.05 0.19+ 4

Appendix

Problem of Rhaetian Stage from the viewpoint of conodont biostratigraphy

In this chapter， problenl of Rhaetian Stage， present and past， is briefly summarized at first， and a proposal is made from the viewpoint of conodont biostratigraphy.

GUMBEL (1859) original1y proposed a name“rhaetische Fortnation" for the Kりssen

Beds， which occupies a position between Keuper and Lias. He also noticed that the

beds may be characterized by common occurrence of Avz'cula contorta (Rhaetavicula

contorta in present nomenclature). In his subsequent works (GUMBEL， 1861， 1864)， however， he did not give any definition， stratotype or stratigraphic boundaries for the Rhaetian to be distinguished as an independent stage. As pointed out by FABRICIUS

(1974) and MOSTLER et al. (1978)， GUMBEL seems to have regarded the Rhaetian rather as a lithofacies than as a biostratigraphic unit. Because R. contorta bearing strata were

known both from the Alpine and Germanic facies， the Rhaetian was formerly regarded as an only practical unit to correlate the two facies. However， later researchers tended

to stress biostratigraphic aspect of the Rhaetian. In addition， different interpretations for the concept of the Rhaetian among the workers have led a great confusion. Rhaetian

controversy up to 1970， including terminological problem bet，veen Rhaetian and rhae-tic， was wel1 summarized by PEARSON (1970). In any case， until early 1970s， the Rhae四

tian was regarded as an independent stage and TOZER (1967) and SILBERLING & TOZER

(1968) proposed only one ammonite zone， Choristoceras l1za1幼 iZone for the Rhaetian

which is discriminated from the underlying N orian Rlzabdoceras sueSSl~ Zone and the

overlying Hettangian Psiloceras planorbお Zone. TOZER (1971)， however， remarked “In terms of ammonoid faunas it is di伍cultto justify recognizing Rhaetian Stage".

After 1972， some drastic change was rnade in the previous biostratigraphic ranges of C. marshi and R. suessi and moreover in amnlonite zones of the uppermost Triassic.

Namely， R. suessi， previously believed to be an index fossil of the Norian， occurs from

72 Yukio ISOZAKI and Tetsuo MATSUDA

the Kossen Beds (URLICHS， 1972) and its co-existence with C. marshi for some interval was clarified (WIEDMANN et al.， 1979). In other words， R. contorta， classirc index fossil

of the Rhaetian， was found out from strata hitherto assigned to the Norian (URLICHS， 1972; WIEDMANN， 1972). On the basis of these new data， various proposals and opinions concerning the treatment of Rhaetian Stage have been presented. They are roughly

grouped into three alternatives as fol1ows (cf. Fig. 1).

GUMBEL (1859， MOJS ISOV 1 CS TOZER (1967) KOZUR (1973) 1861， 1864) et a1. (1895)

SILBERLlNG & GAZD7ICKI et FABRICIUS (1974) KOZUR (1973) MOSTLER et a 1. TOZER (1968) a 1. (1979)

TOZER (1974，1979) (1978 )

GAZOZICKI et TOLLMANN (1978) a1. (1979) KRYSTI N & WI ED国

HALLAM (1981) MANN (1979) KRYSTI N (1980)

• • ...... • Q) 。lOristoaerαe 。ωri8tocerα8 8

• 伺

I Up. L

mαr8hi Z . TTlaX'shi z. .s;;; • 0:: ' rhaetische ロ ' • .1 Rhaeti an ~- jUp・ |

u

Formatlon ' . • Choristocera8 •

lo比 ヨ

hα:ueri z. rョ• ~

' • • • Rhaetian F-・・・・・・•

(

+ω 〉ω .> ~ '

• Norian • •

=a a ω コRhαbdocer.αs Cochlocerαs .: lJpper‘

sue88も z. sues8i Z. ‘ .

r • ω • • 、句_， Pinacoceras c • F Low. . 代3 ' ~ • • metterniahi .

2 0 L4 '，... 1'.1 • ~ • .

z. 。 Sαgenites ' • . -・o!:: • Nor;an ;up. 同• •

τP:s e giebeli z. • • • ' • ' 、

ト ， ー・・骨骨'ーーー ~ • • 亡

• ~ • 可コ H会ηαυαtites Hυηαυαtite8 • • . ，... • • 玄 。olwnbianusz. aolwηbiαηus z. :附dd1e Norian :IIUp.1I •

• • • • • :

Fig. 1. Recent proposals on subdivision of the uppermost Triassic， grouped into three alternatiてes，i)， ii) and iii).

i) FABRICIUS (1974) and KRYSTIN (1974) proposed to abandon the name Rhaetian as

an independent stage comp~etely and to regard both R'. suessi Z. and C. marshi Z. sensu

TOZER (1967) as the Upper Norian (Sevat). HALLAM (1981) stands on the same view国

pOlnt.

ii) KOZUR (1973) and GA念DZICKIet al. (1979) intend to divide the R. sue‘ωZ. s民ens釦u

TOZER (1967) into three， namely Sagenites giebeli Zone， Cochloceras suessi Zone and Cho-ristoceras haueri Zone in ascending order and to iDclude the forrner two into the Norian

and the latter into the Rhaetian.

iii) WIEDMANN (1974)， TOLLMANN (1978) and MOSTLER et al. (1978) regard R. suessi Z. and C.仰 T必 Z.sensu TOZER (1967) as Rhaetian as a whole and insist to suppress the

name Upper Norian (Sevat) once and to re-define the Mi，ddle Norian in former usage

as emended Upper Norian.

Investigating on palynology of the U pper Triassic to the lowermost J urassic， SCHUURMAN (1979) also reported that strata yielding R. suessi， C. marshi or R. contorta

are di伍cultto distinguish each other from palyno】ogicalaspect， and that they are al1 represented in terms of Rhaet争ollisgermanicus Assemblage-zone. He insists that R. ger-

manicus A・z.characterizes palynologically Rhaetian Stage， standing on a viewpoint along

the iii) alternative.

一一ーーー

Middle and Late Triassic Conodonts from the M仇O圃 TambaBelt 73

The original proposal of the Rhaetian by GtiMBEL (1859， 1861， 1864) predates not only that of the Norian by MOJSISOVICS (1869) but also that of Sevat substage of the Juva-

vian (now Norian) by MOJSISOVICS et al. (1895). Because the overlap of ranges of R.

suessi and C. marshi was examined， it seems that Alpine geologists， who pay attention to the priority of the Rhaetian， favor re-definition of the Rhaetian in the manner of the iii) alternative.

Fol1owing the above-mentioned proposals， IUGS Subcommission on Trias Stra-

tigraphy held in Munchen， July， 1978， recommended as follows (in part; RICHTER-BERNBURG in WIEDMANN et al.， 1979). 1) The Rhaetian sensu GtiMBEL in chronostratigraphic concept should be by all means

maintained.

2) Based on up四 to四 datedata， Rhaetian Stage corresponds to C. marshi Z. (emended to include R. suessi Z. and C.仰 rshiZ. sensu TOZER， 1967) or Rhaet砂ollz'sgermanicus

A圃 z. Thus the name“8evat" or“Upper Norian" turns to be unneccessary. In other words， the 8ubcommission has chosen the above田 mentionediii) alternative.

As KOZUR (1973) and GAZDZICKI et al. (1979) mentioned， however， it is revealed

that only lower two thirds of R. sueωZ. sensu TOZER (1967) represents the original 8evat

by MOJSISOVICS et al. (ο1895) in t伐ermsof Pi1仰 ocerαωsnωtern炊1

neouωsl勿ycorrelated S~勾rgeniteωs ar匂-gonautωaeZone. 80， according to KOZUR (1973) and GA之D-

ZICKI et al. (1979)， there is no overlap between the Norian and the Rhaetian， both defined originally; and the boundary between them should be drawn naturally.

Recently， TOZER (1979)， KRYSTIN & WIEDMANN (in WIEDMANN et al.， 1979) and KRYSTIN (1980) emended their ammonite zones of uppermost Triassic age (Fig. 2).

TOZER (1967) KOZUR (1973) TOZER (1979) KRYSTIN & WIEDMANN anmon1te & KOZUR (1980) conodont

(1979) b;va1ve S 1 LsERLI NG & TOZER (1968) KRYSTI N (1980 )

σωz・istooe1'，αe 。101'istooe1唯 8 。IOriStooe1'α8 s barren .~ lacking(?) m(Utshi z. n奴r・shiz. mα1'shi Subz.

-1+s。5a • -p

ム …・……'jjωa --…・…

MisikelZα pos t;he:rns teini 自由

Cho1'istooe1'α8 σ10ris tooe1'S Vαnaαites ・~ l~ .... A.-z.

haueri z. 。l"iokmayiZ. S仇~e1'Benbαwni Subz. T i

.~にh. ・『Misikell.a E I ~ I he1'n8teini ，.l

句句

Rhabdooel'as Coohlooe:nαs Coohloaeros Sαgenites A.-z. +司自ゐ

令 'f lE匂<;euessi Z. 8uessi z. αmoenwn Z. l'etiaula仇clSSubz. • P. aru:1.Pusovi 。 占司凶t

. "t Cヒ ・句.、A.骨 Z. ;4。a・1悼。:1'キ悼~

Sαgenites Gnomohalor・ites Sαgeni色8Sミ。c zt

， . ー ・・・・ーー 13 ミ

giebeli Z. oOl"dillel"αnU8 quinquepunctαtus s J3i 8 Z. Subz. Epもg併 ulolell.a. . ー ・・ biden ta ta z.

H句協υαtitesoolumbianus Zone • R. LJ

Fig. 2. Uppermost Triassic amrnonite zones， conodont zones and stratigraphic distribution of representative index fossils. Correlation scheme among ammonite zones is after KRYSTIN (1980). On the basis of opinions of KRYSTIN & WIEDMANN (1979 in WIEDMANN et al.)， KRYSTIN (1980)， GAZD四

ZICKI et al. (1979)， KovAcs & KOZUR (1980)， KOZUR (1980)， !SOZAKI & MATSUDA (1980) and NAGAO & MATSUDA (1982)， stratigraphic ranges of fossils are tentatively compiled. However， they are not fixed yet， for example， co-existence of M. hernsteini and R. contorta has never been proved.

74 Yukio ISOZAKI and Tetsuo 恥1ATSUDA

Although TOZER (1974， 1979) essentially stands on the i) alternative， he dare to avoid sup-pressing the name Rhaetian at p代 sent. KRYSTIN (1980) emphasized that applying new

names to emended zones would surely invite more complicated confusion， and he recom・mended to re-define the previously well known R. suessi Z. and C. marshi Z. As R.

suessi and C. marshi co-exist during certain interval， both zones should be newly de-fined as interval zones， not as taxon岨 rangezones of the previous scheme. At the same

time， four new subzones are proposed， namely Sagenites quinquφunctatus Subzone and

S. reticulatus Subz.， belonging to emended R. suessi Z.， and Vandaites stuerzenbaumi Subz. and C. marshi Subz.， belonging to emended C. marshi Z.， in ascending order. He

also presented how these subzones correspond to the zones proposed by KOZUR (1973)

or TOZER (1979) and pointed out lacking of the very uppermost part of Triassic in North

America.

Newly proposed four subzones b勾yKRyS釘，τT百r口‘'IN& W町IEDMA釧NN(in WIEDM胤M征A閤NNetα1.， 1979均9勾)and KRyS'釘，τTIN

shi Z. by KOZUR (1973)， respectively. The present authors apply ammonite zones newly

proposed by KRYSTIN (1980) and follow his correlation scheme to other ammonite zones

proposed by KOZUR (1973) and TOZER (1979) as shown in Fig. 2. Although KRYSTIN

& WIEDMANN (in W[EDMANN et al.， 1979) and KRYSTIN (1980) insist the iii) alternative along the recommendations by the Subcommission， the present authors prefer ii) one

on the basis of conodont research as shown below.

Recently， KovAcs & KOZUR (1980) have shown range charts of the important Trias-

sic conodont species and KOZUR (1980) has emend白edhis zonation scheme 0ぱfc∞∞o∞I

for several faunaI provinces. KOZUR (1980) subdivided the uppermost Triassic into

four zones as follows on the basis of datum-planes i.e. appearance or extinction horizons

of importa1J.t species of EPigondolellaJ Parvigondolella and Misikella. Namely， E. biden-tata Zone (taxon四 rangezone of E. bidentata)， P. andrusovi Assemblage-zone (interval zone between the horizons of extinction of E. bidentata and that of P. andrusovi)， M.

hernsteini Assemblage-zone (interval zone between the horizons of extinction of P. andru田

sovi and that of M. hernsteini) and M. posth.ernsteini Assemblage-zone (interval zone

between the horizons of extinction of M. hernsteini and that of M. posthernsteini)， in as-cending order. Although correlation among conodont zones， ammonite zones and stages is diversified among the workers， the present authors apply zonal scheme of conodonts

by KOZUR (1980).

Biostratigraphic range of P. andrusovi varies considerably from place to place. How-

ever， it is suggested that P. andrusovi essentially has almost the same range as E. biden・

tata (KRYSTIN， 1980)・ Thehorizon of extinction of the two species approximately cor田

responds to the upper boundary of S. reticulatus Subz. and they never occur from V.

stuerzenbaumi Subz. or C. marshi Subz. (MOS'fLiER et al.， 1978; GA念DZICKIet al.， 1979; KRYSTIN， 1980). Biostratigraphic range of P. andrusovi examined in the Mino-Tamba

selt is also harmonic with suggestion made by KRYSTIN (1980) (ISOZAKI & MATSUDA， 1982; NAGAO & MATSUDA， 1982).

Middle and Late Triassic Conodonts from the Mino・TambaBelt 75

Various opinions have been presented on the biostratigraphic range of M. hernsteini.

MOSTLER et al. (1978) and GAZDZICKI et al. (1979) insisted that M. hernsteini occurs from

Hallstatterkalk (R. suessi Z.) but never from the overlying Zlambach Mergel (C. marshi

Z.) of Salzkammergut (e.g. Sommeraukogel， Rossmoos)， Austria. KRYSTIN (1980)， however， revealed that M. hernsteini occurs from Lower KりssenBeds at Gaissau， Adnet and the transitional beds between Hallstatterkalk and Zlambach Mergel at Sommerau-

kogel， both corresponding to V. stuerzenbaumi Subz. Since the foundation of M. posthernsteini A田 z.in C. haueri Z. sensu KOZUR (1973)，

now assigned to V. stuerzenbaumi Subz. by KOZUR & MOCK (1974)， this assemblage zone has been recognized at various places in Europe and reported also from C. 1nar:_shz' Subz.

(MOSTLER et al.， 1978; GA~DZICKI， 1978). Because strata， underlying the lowermost Lias and above the horizon of extinction of M. posthernsteini， is examined to yield

Rhaetian-type foraminifers without conodonts (GAZDZICKI， 1978)， there may exist certain interval between M. posthernsteini A-z. and P. planorbis Z.

On the basis of the above-mentioned facts， it is clarified that N orian representative

conodonts， E. abneptis， E. postera， E. bidentata and P. andrusovi occur abundantly from

S. reticulatus Subz.， and extinct completely at its upper boundary (KRYSTIN， 1980; Ko-VACS & KOZUR， 1980). These facts were examined in lnany sepaωe outcrops in cal-

careous sequences in the Alps. As mentioned by KOZUR (1973) and GAZDZICKI et al.

(1979)， drastic change is recognized， at the biohorizon between S. reticulatus Subz. and V. stuerzenbaumi Subz.， in faunal composition both of mega-and microfossils， such as bivalves， brachiopods， ostracods， holothurian sclerites， foraminifers and so on.

On the other hand， almost the sarne sequence of conodont zones as those known in the Alps were examined within continuous bedded chert sequences in the Mino-Tamba

Belt (ISOZAKI & lVIATsuDA， 1980， 1982; YAO et al.， 1980; NAGAO & MATSUDA， 1982). It was recognized that E. bidentata and M. posthernsteini co-exist in the same outcrop

and that species of Epigondolella and Parvigondolella， dorninant in the Norian， disappear together at certain horizon around the first appearance of M. posthernsteini. Thus espe-

cially from the viewpoint of conodont biostratigraphy， faunal change in the uppermost Triassic took place most clearly in terms of extinction of Epigondolella and Parvなon-

dolella.

In the areas where occurrence of ammonite is rare or unknown， correlation of marine Upper Triassic has been based on bivalve genus Monotis and some brachiopods. ln

addition， Triassic conodonts have been recently accepted as a good tool in world-wide

correlation， for they occur not only in limestone but also in chert and argillaceous rocks.

As mentioned before， IUGS Subcommission on Trias Stratigraphy recommended

that NorianfRhaetian boundary should be drawn at the lower boundary of S. quinque-

punctatus Subz. (lower boundary of R. suessi Z.)， due to priority doctrine. If the re-

commendation is accepted， however， biostratigraphic range of lVlonotis， for example，

which has long been regarded as an index of the Norian turns to extend into the Rhae-

tian. It is sure that another confusion will be brought， especially in correlation of

76 Yukio ISOZAKI and Tetsuo MATSUDA

regions poor in cephalopods， such as North四 EastUSSR (TUCHKOV， 1964)， Southwest Pacific (GRANT帽 MACKIE，1976) and ]apan (1CHlKAWA， 1950)・

1n these confused circumstances concerning definition of the Rhaetian， the present authors believe that the natural boundary indicated by biohorizons is much preferable

than that determined artificially by priority doctrine. From the viewpoint mainly of

conodont biostratigraphy， they insist that NorianJRhaetian boundary should be drawn between S. reticulatus Subz. and V. stuerzenbaumi Subz. as done by KOZUR (1973) and

GA会DZICKIet al. (1979).

References

(References cited in the preceding part of this paper are omitted.)

GAiDZIClα， A. & V.J. GUPTA， 1981: Triassic foraminifers Involutinidae from the west Carpathi-

ans and Himalayas -Its stratigraphic and palaeobiogeographic implications. Bull. Ind. Geol.

Assoc'J 14， 101-106. GRANT-MACKIE， J.A.， 1976: The Upper Triassic bivalve Monotis in the Southwest Pacific. Paci-

fic Geol.， 11， 47-56. GuMBEL， C.W.， 1859: Ueber die Gleichstellung der Gesteinsmassen in den nordδstlichen Alpen

mit ausseralpinischen Flotzshichten. Versamml. deutsch. N atu1プorsch.u. Arzte (1858)， Amt1. Ber. 34， 80-88.

" 1861:， Geognostische Beschreibung des bayerischen Alpengebirges und seines Vorlandes.

950p.， Gotha. ，1864: Ueber das Knochenbett (Bopebed) und die Pflanzen-Schichten in der rhatischen

Stufe Frankens. Sitzungsberichte kdnigl. bayer. Akad. Wiss. MunchenJ 1864， no. 1， 215-278. HALLAM， A.， 1981: The enふTriassicbivalve extinction event. Palaeogeogr. Palaeoclimat. Palaeo-

ecol.， 35， 1-44. ICHlKAWA， K.， 1950: Chronological classification of the Triassic period in Japan. Jour. Geol.

Soc. Japan， 56， 17-22. ISOZAKI， Y. & '1. 1¥在ATSUDA，1982: Middle and Late Triassic conodonts from bedded chert se-

quences in the Mino-Tamba Belt， Southwest Japan. Part 1: Epignodolella. Jour. Geosci'J

Osaka City Univ'J 25， 103-136， pls. 1-6. KOZUR， H.， 1973: Beitrage zur Stratigraphie von Perm und Trias. Geol. Palaont. Mitt. Inns-

bruek， 3， no. 3， 1-31. & R. MOCK， lo74a: Zwei neue C'onodonten圃Artenaus der Trias des Slowakischen

Karstes. Casopis Mineral. Geol.， 19， 135-139， p1. 1.

KRYSTIN， L.， 1974: Probleme der biostratigraphischen Gliederung der A1pirトMediterranen

Obertrias. In ZAPFE， H. ed.: Die Stratigraphie der alpin-mediterranen Trias. Schriftenr. Erd-

wiss. Komm. Osterr. Akad. Wiss'J 2， 137-144. MATSUDA， T. & Y. ISOZAKI， 1982: Radiolarians around the Triassic-Jurassic boundary from

the bedded chert in the Kamiaso Area， Southwest Japan. Appendix:“Anisian" radiolar-ians. In “Proceedings of the First Japanese Radiolarian Symposium" (News of Osaka Micro・paleontologistJ Spec. Vol. no. 5)， 93-101， pls. 1-3.

MOJSISOVICS， E.V.， 1869: Ueber die Gliederung der oberen Triasbildung der ostlichen Alpen.

Jahrb. kaiserl. -kδnigl. Geol. ReichsanstaltJ 9， 91-150. ， W. WAAGEN & C. DIENER， 1895: Entwurf einer Gliederung der pelagischen Sedi圃

mente des Trias-Systems. Sitzuηgsber. kaiserl. Akad. Wiss. WienJ mathm. -naturwiss. Cl'J 104， 1271-1302.

NAGAO， H. & T. MATSUDA， 1982: “Rhaetian problem" in terms of conodont biostratigraphy -

A case study in bedded chert sequence at Toganoo， in northwest Kyoto， Southwest J apan-.

Middle and Late Triassz'c Conodonts from the JYlino・TambaBelt 77

In “Proceedings of the First Japanese Radiolarian Symposium" (News of Osaka MicropaZeon-tologists， Spec. Vol.， no. 5)， 469-478， pl. 1.

PEARSON， D.A.B.， 1970: Problems of Rhaetian stratigraphy with special reference to the lower

boundary of the stage. Q. Jour. Geol. Soc. London， 126， 125-150. SCHUURMAN， W.M.L.， 1979: Aspects of Late Triassic palynology. 3. Palynology of latest Triassic

and earliest Jurassic deposits of the Northern Limestone Alps in Austria and southern Ger-

many， with special reference to palynological characterization of the Rhaetian Stage in Europe.

Rev. Palaeobot. Palynol. 27， 53-75， pls. 1-6. SKWARKO， S， R.S. NICOLL & K.S.W. CAMPBELL， 1976: The Late Triassic molIuscs， conodonts

and brachiopods of the Kuta Formation， Papua New Guinea. BMRJ. Aust. GeoZ. Geophys.J

1， 219-230. TOZER， E.T.， 1967: A standard for Triassic time. Bull. Geol. Surv. Canada. 156， 103p.

， 1971: Triassic time and ammonoids: Problems and proposals. Can. Jour. Earth

S ci.， 8， 989-1031. TUCHKOV， 1.1.， 1964: Rhaetian Stage problem and the lower boundary of the Jurassic System.

Int. Geol. Congr. Colloque du Jurassique. Luxembourg， 1962. Comptes et MemoiresJ 101-112.

URLICHS， M.， 1972: Ostracoden aus den Kossener Schichten und ihre Abhangigkeit von der 。kologie.Mitt. Ges. Geol. Bergbaustud.， 21， 661-710. pls. 1-4. WIEDMANN， J.， 1972: Ammoniten-Nuldei aus Schlammproben der nordalpinen Obertrias -ihr

stammesgeschichtliche und stratigraphische Bedeutung. Ibid.， 21， 561-622.

， 1974: Zum Problem der Definition und Abgrenzung von Obernor (Sevat) und Rhat.

In ZAPFE， H. (ed.): Die Stratigraphie der alp初回mediterranenTrias. Schriftenr. Erdwiss. Komm.

Osterr. Acad. Wiss. 2， 229-235.

Plate 1

80

Explanation of Plate r

Figs. 1， 2， 3， 5， 6 and 7 in stereoscopic pairs.

Figs. 1-7. Misikella hernsteini (MOSTLER) •.•......................................... .Page 66-67 1. YU3012-1， HZ圃 41，x 150， aboral-lateral view. 1. YU3012-2， HZ-41， X 150， aboral-lateral view. 3. YU3013-1， HZ-42， X 150， aboral圃 lateralview.

4. YU3013-2， HZ-42， X 150， lateral (a) and aboral-lateral (b) views. 5. YU3012・3，HZ-41， X 150， aboral-lateral view. 6. YU3012圃 4，HZ・41，X 150， aboral-lateral view. 7. YU3014...1， HZ-46， X 150， aboral-lateral view.

Figs. 8-13. Misikellaρosthernsteini KOZUR & MOCK........... ..................... .Page 67-69

8. YU3014-2， HZ-46， X 150， lateral (a) and aboral-lateral (b) views. 9. YU3014・3，HZ二46，X 150， aboral圃 lateralview.

10. YU3015-1， HZ-47， X 150， aboral-lateral view. 11. YU3014-4， HZ-46， X 150， aboral-lateral view. 12. YU3016-1， IN・26， X 150， aboral四 lateralview.

13. YU3017-1， IN四 30， X 150， Oral (a) and aboral (b) views.

Y. ISOZAKI & T. MATSUDA: Misikella from the Mino-Tamba Belt Plate 1

Plate 2

82

Explanation of Plate 2

Figs. 1a， 2a， 3a， 4a， 5a， 6a and 7b in stereoscopic pairs.

Figs. 1-7. Misikella posthernsteini KOZUR & MOCK ................................ .Page 67-69

1. YU3014-5， HZ-46， x 150， aboral-lateral (a) and posterior..lateral (b) views. 2. YU3014-6， HZ-46， x 150， aboral (a) and aboral-lateral (b) views. 3. YU3015-2， HZ-47， x 150， aboral四 lateral(a) and posterior-lateral (b) views.

4. YU3014-7， HZ-46， x 150， aboral-lateral (a) and posterior-lateral (b) views. 5. YU3014-8， HZ-46， x 150， aboral-lateral (a) and posterior-lateral (b) views. 6. YU3018-1， [N田 24， x 150， aboraトlatera](a)， la句raiゆ)'and oral (c) views.

7. YU3019-1， HZII-8， x150， anterior-orai (a)， oral (b) and ocal国 lateral(c)

vlews.

、

Y. ISOZAKI & T. MATSUDA: Muikella from the Mino-Tamba Belt Plate 2

lb f4b

6c

Plate 3

84

Explanatiolil of Plate 3

Figs. 1a， 2a， 3a， 4a， 5， 6 and 7 stereoscopic pairs!

Figs. 1-7. Misikella ppsthernsteini KOZUR & MOCK ................................ .Page 67-69

1. YU3014θ， HZ-46" x 150， posterior-aboral (a) and posterior (b) views. 2. YU3014-10， HZ-46， x 150， aboral-lateral (a) and posterior-lateral (b) views. 3. YU3014-11， H~-46， x 150， aboral-lateral (a) and posterior-lateral (b) views. 4. YU3014-12， HZ-46， X 150， aboral-lateral (a) and lateral (b) views. 5. YU3015-3， HZ-47， X 150， aboral view. 6. YU301s-2， IN-24， X 150， aboral view. 7. YU3017-2， lN-3P， X 150， posterior-lateral view.

、

Y. ISOZAKI & T. MATSUDA: Misikella from the Mino-Tamba Belt Plate 3

'2b

Plate 4

86

ExplanatiQn of Plate 4

Figs. 1 a， 2a， 3a and 4 in stereoscopic pairs.

Figs. 1-9. Parvなondolellaandrusovi KOZUR & MOCK ............................. .Page 69-71

1. YU3020-1， HZII-7， x 125， aboral-lateral (a) and lateral (b) views. 2. YU3020-2， HZII-7， x 125， aboral-lateral (a) and lateral (b) views. 3. YU3010-2， HZlI-1， x 125， aboral-lateral (a) and lateral (b) views. 4. YU3010-3， HZlI-1， x 150， aboral-lateral view. 5. YU3020-3， HZII-7， x 150， aboral-lateral view. 6. YU3020-4， HZII-7， x150， lateral (a) and aboral圃 lateral(h>) views.

7. YU3010-4， HZlI-1， x 75， lateral view.

8. YU3020-5， HZII-7， x 150， aboral-lateral view. 9.YU30204，Hzq-7， ×150， lateral (a)and aboral-lateral (b)views.

Y. ISOZAKI & T. MATSUDA: Parvigondolella from the Mino-Tamba Belt Plate 4

2a

6b