Changes in ammonoid fauna and

palaeoceanographic environment in the late Early Jurassic

Northern Hemisphere

Kentaro NAKADA

Doctoral Program in Fundamental Science

Graduate School of Science and Technology

Niigata University

Abstract

The late Early Jurassic time-interval (about 187-175 Ma) is attracted by the Early

Toarcian Oceanic Anoxic Event (OAE), regarded as a global and dramatic

paleoenvironmental change. However the paleoceanographic environments during late Early

Jurassic have been analyzed vigorously in Europe, contributions from the Asian regions are

still limited. The lack ofthese data has disturbed the discussions of global paleoceanographic

changes in this time-interval. The aims of this study are to analyze the paleoceanographic

changes in the West Panthalassa (present East Asia) during late Early Jurassic based on the

geochemical analyses of the Early Toarcian OAE in Japan, the short-term

paleoenvironmental and faunal events, and the detailed transitional patterns of the ammonoid

paleobiogeography for tracing the long-term paleoceanographic change, and to discuss the

global paleoceanographic environment affected to the change of marine biota (ammonoids)

in the Northern Hemisphere.

In this study, the revision or the establishment of ammonoid zonal schemes in the Toyora

and the Kuruma Groups and the mutual/international correlation of these zonations are

discussed before analyzing the geochemistry and paleobiogeography because of the necessity

to propose the chronological standard. Six ammonoid zones in the Toyora Group, the Lower

to Middle Jurassic epicontinental deposits distributed in southwest Japan, and three zones in

the Kuruma Group, the Lower Jurassic continental shelf sediments exposed in central Japan,

are proposed in this study and are corresponded with the zonal schemes established outside

Japan, especially with the standard ammonoid zonation discussed in the Northwest European

province.

The transitional patterns of the Japanese ammonoid faunas are analyzed by utilizing the

assemblages from the Toyora and the Kuruma Groups. The late to middle Late Pliensbachian

ammonoid assemblage from Japan is associated with the Boreal elements and shows a high

similarity with the coeval Northeast Russian ammonoid fauna. However, in latest

Pliensbachian, a turnover from the Boreal fauna to the Tethyan fauna via the Tethyan-Boreal

mixed fauna is distinguished mainly in the assemblage from the Kuruma Group. This

turnover seems to be mainly affected by the coeval regression during latest Pliensbachian to

earliest Toarcian recognized in Europe, in addition to the starting of the warming event. In

contrast, a faunal mixing of the Tethyan and the Boreal faunas recognized in the middle Early

Toarcian assemblage is perhaps reflected by the abrupt transgression distinguished in this

time-interval. Consequently, the late Early Jurassic ammonoid transitions in the Northern

Hemisphere are closely related with the changes of eustatic sea level and seawater

temperature.

The concentrations of trace elements and the anomalies of REE are analyzed for

discussing the Early Toarcian GAE in the Lower Nishinakayama Formation of the Toyora

Group. The positive excursions of the V and Co concentrations are recognized in the middle

part of the P. palms Zone, corresponded to earliest Toarcian, with a negative shift of the Ni

concentration and a positive Ce anomaly. These geochemical anomalies suggest the

oxygen-depleted marine condition biostratigraphically corresponded to the coeval minor

anoxic environment in Europe. In contrast, the major Early Toarcian GAB recognized in

Europe and North American Cordillera is not identified in the Toyora Group. Therefore, the

effect of the major Early Toarcian GAE seemed to be limited only in the West Tethys and

East Panthalassa.

Moreover, a diversity fall of ammonoid assemblage is also identified during the

oxygen-depleted redox condition in earliest Toarcian. This diversity crisis is characterized by

the extinction of East Asian endemic Harpoceratinae, and the survival of only a species of

pandemic Arieticeratinae. Consequently, the ammonoid diversity crisis in the middle part of

the P. palms Zone is perhaps reflected by the anoxic event in East Asia. Thus, the

relationships between the marine redox conditions and the faunal associations of

Hildoceratidae probably suggest the difference of the anoxic tolerances between

Harpoceratinae and Arieticeratinae.

Contents

1. Introduction

1-1. Paleoenvironmental background of late Early Jurassic

1-1-1. General climatic changes in late Early Jurassic

1-1-2. Early Toarcian Oceanic Anoxic Event

1-2. Aims of this analysis

2. Geological framework

2-1. Toyora Group

2-2. Kuruma Group

p.l

p.7

3. Ammonoid biostratigraphy and its international correlation p.17

3-1. Aims of this chapter

3-2. Re-examination of ammonite biostratigraphy in the Toyora Group

3-2-1. Characteristics of materials

3-2-2. Methods

3-2-3. Stratigraphical repetition along the Sakuraguchidani Valley

3-2-4. Results

3-2-4-1. Amaltheus stokesi Assemblage Zone

3-2-4-2. Canavaria japonica Zone

3-2-4-3. Paltarpites paltus Zone

3-2-4-4. Dactylioceras helianthoides Zone

3-2-4-5. Harpoceras inouyei Zone

3-2-4-6. Pseudogrammoceras-Phlyseogrammoceras Assemblage Zone

3-2-5. Reexamination of the PIT boundary

3-2-6. Correlation with the previous zonation in the Toyora Group

3-3. Proposal of a new ammonoid zonation in the Kuruma Group

3-3-1. Characteristics of materials and methods

3-3-2. Differences between fossil-bearing rocks

3-3-3. Results

3-3-3-1. Stokesi-Repressus Assemblage Zone

3-3-3-2. Margaritatus-aff. Talrosei Assemblage Zone

3-3-3-3. Satoi Assemblage Zone

3-4. International correlation for the new ammonite zonations

3-4-1. Northwest European province

3-4-2. Mediterranean province

3-4-3. North American Cordillera province

3-4-4. South American province

3-4-5. Northeast Russia

4. Relationship between the ammonoid paleobiogeographic and the paleoceanographic

changes

p.53

4-1. Aims of this chapter

4-2. Paleobiogeographic changes of Japanese ammonoid assemblages

4-2-1. Faunal characters of the assemblages from the Kuruma Group

4-2-2. Faunal characters of the assemblages from the Toyora Group

4-2-3. Faunal changes of Japanese ammonoid assemblages

4-3. International correlation of Japanese ammonoid assemblages

4-3-1. Stokesi Standard Subzone

4-3-2. Subnodosus-Gibbosus Standard Subzones

4-3-3. Apyrenum Standard Subzone

4-3-4. Hawskerense Standard Subzone

4-3-5. Tenuicostatum Standard Zone

4-3-6. Serpentinum and Lower to Middle Bifrons Standard Zones

4-3-7. Fallaciosum Standard Subzone and Dispansum Standard Zone

4-4. Discussion of the paleoceanographic change in the Northern Hemisphere

4-4-1. Early Jurassic paleoenvironmental changes in the Northern Hemisphere

4-4-1-1. Sea level changes

4-4-1-2. Sea surface temperature changes

4-4-2. Paleoceanographic changes on the basis of the ammonoid faunal changes

4-4-2-1. Latest Pliensbachian faunal turnover

4-4-2-2. Early Toarcian faunal mixing

5. Geochemical analyses of the Early Toarcian OAE in East Asia p.83

5-1. Aims of this chapter

5-2. Materials and analytical methods

5-3. Results

5-3-1. Trace element concentrations

5-3-2. Rare Earth Element concentrations

5-4. Discussion

5-4-1. Redox conditions during the Lower Toarcian in the Toyora Group

5-4-2. Relationships between the anoxia and the ammonoid diversity changes

5-4-3. Early Toarcian OAE in the Northern Hemisphere

6. Systematic paleontology

6-1. Genus Amaltheus

7. Conclusions

7-1. Ammonoid biostratigraphy

7-2. Ammonoid paleobiogeography

7-3. Geochemical analyses of the Early Toarcian OAE

Acknowledgements

Reference

Plates

Appendices

p.99

p.109

1

1. Introduction

1-1. Paleoenvironmental background of late Early Jurassic

The Jurassic period (199.6±0.6-145.5±4.0 Ma, Gradstein et al., 2004; Fig. 1-1)

was an important time-interval in the studies of stratigraphy because some basic

frameworks, including "law of strata identified by fossils" and the biostratigraphic

units (biozone), were proposed in the European Jurassic successions (e. g. Smith,

1816-1819). Especially, late Early Jurassic time (equivalent to Late

Pliensbachian-Toarcian time-interval in this study; 187.0-175.6±2.0 Ma, Gradstein

et al., 2004; Fig. 1-1) was also characteristic in the beginning of the break-up of

Pangaea supercontinent and recently attracted by the dramatic paleoceanographic

events, represented by the Early Toarcian Oceanic Anoxic Event (OAE).

The analyses of the paleoceanographic environments during late Early Jurassic

have been discussed mainly in Europe. In contrast, the climate changes of East

Asia in this time-interval are not discussed sufficiently. In Japan, the existence of

the Early Toarcian OAE in the epicontinental depositional environment have been

suggested only in the Toyora Group on the basis of the characteristic macro faunas,

sedimentary structures and carbon isotope profile (Tanabe, 1991; Izumi & Tanabe,

2010), although the detailed distinctions of this phenomenon have not been

analyzed in this section. Moreover, the detailed faunal transitions of the late Early

Jurassic ammonoid assemblages have not been also analyzed in East Asia. The

paleobiogeographic faunal changes of ammonoid enable to trace the long term

paleoenvironmental changes with high biostratigraphic resolution. The absence of

these data in Eats Asia has been disturbed the global paleobiogeographic

discussion of ammonoid in late Early Jurassic time.

The geochemical data of the Early Toarcian OAE, as a proxy of short-term

marine environmental change, and the paleobiogeographic faunal transitions, as a

tracer of long-term climate changes, reveal the paleoceanographic changes in East

Asia during late Early Jurassic time-interval.

.7

.-- - - - - - - - - - 1 .0

,\,

,,,,,,,,,,

\,,\,,,,,,,,,,,,,,,,,,,,

\,,,,,\,,

\

C

__._IC

Fig . 1-1 . S Jura . iod . h a ut in t I. ( 2 ).

1-1-1. G ner I _ _~ of clim t d iot i I te rly Jur ic

Through the Jurassic period, the temperatures were generally warmer than

present and rose from Triassic toward the Cretaceous. On the basi s of the oxygen

isotope analyses, a cooling during Late Pliensbachian and an abrupt warming in

earliest Toarcian were recognized in late Early Jurassic time-interval (e.g. Bailey et

3

al., 2003). On the other hand, the eustatic sea level showed the higher stand than

present and was raised from Late Permian to Late Cretaceous (e.g. Haq et aI., 1988).

In late Early Jurassic, a regression during Late Pliensbachian and a transgression in

Early Toarcian were distinguishable on the basis of the Sr isotope ratio (e.g.

McArthur et al., 2000).

The Jurassic period was also characterized by the dramatic shifts of marine and

terrestrial biota, including the explosive development of ammonoids, the prosperity

of dinosaur and appearances of bony fishes and birds. The diversification of

ammonoids in this period enabled the high-resolution ammonoid biostratigraphy

and paleobiogeography.

1-1-2. Early Toarcian Oceanic Anoxic Event

The late Early Jurassic time has been attracted to the Early Toarcian OAE, the

global paleoenvironmental change proposed by Jenkyns (1988) on the basis of the

worldwide distribution of the organic black shale (Fig. 1-2).

The Oceanic Anoxic Event is the dramatic change of marine environment

characterized by the development of the oxygen-depleted water mass and has been

mainly recognized at the Permian/Triassic boundary (around 251Ma), at Early

Aptian (Early Cretaceous, 121-120 Ma) and at the Cenomanian/Turonian boundary

(Late Cretaceous, around 93.5Ma). The Early Toarcian OAE was one of the most

large-scale paleoceanographic changes through the Jurassic period, mainly

distinguished by the carbon and the oxygen isotopic anomalies (e.g. Hesselbo et al.,

2000). This phenomenon has been analyzed in detail mainly in Europe from various

viewpoints including lithostratigraphy, biostratigraphy, sedimentology and

chemostratigraphy (e.g. Jenkyns & Clayton, 1986, 1997; Jenkyns, 1988; Palfy &

Smith, 2000; Cecca & Macchioni, 2004). Palfy & Smith (2000) considered that this

OAE was caused by the global warming in earliest Toarcian, triggered by the

coeval Karoo-Ferrar flood basalt volcanism. On the other hand, paleontological

analyses have been carried out mainly on the relationship between the OAE and the

mass-extinction events, and the diversity crises of ammonoids, coeval with the

Fig. 1-2. Distribution of arly oarci n(1988) . Paleogeographic map is modiand Dera e al. (2009a).

nkyn(2007)

arly oarcian OA, er r c g d in ur p cca & Macchi i, 2 4.

In addition, the blac -colored ediment hav be n al

pelagic succession (e.g. ori et aI., 2000).

di tin ui hed in th

1-2. im Iy i

However the paleoceanographic environments during late arly Jurassic have

been analyzed vigorously in Europe, contributions from the Asian regions are still

limited . In Japan, the existence of the Early Toarcian OA in the epicontinental

5

successions were only discussed in the Nishinakayama Formation, the middle part

of the Toyora Group exposed in southwest Japan, by Tanabe (1991) and Izumi &

Tanabe (2010). This formation is known as the most major source of the late Early

Jurassic ammonoids in Japan. Thus, the ammonoid biostratigraphy has been

discussed in this formation (e.g. Hirano, 1973b, Nakada & Matsuoka, 2009).

According to the poor exposures of the Lower Jurassic epicontinental deposits in

East Asia, this area is regarded as a suitable section for analyzing the Early

Toarcian GAE in this region because of the distinguished biostratigraphic control

in theNishinakayama Formation. Tanabe (1991) suggested that the black

mudstones in the middle part of this formation (Nb Member; Tanabe, 1991) were

deposited under the oxygen-depleted bottom conditions and enabled to correspond

to the facies of the global Early Toarcian GAE on the basis of the sedimentological

and paleontological evidence. Izumi & Tanabe (2010) distinguished an abrupt

negative shift in the carbon isotope, fluctuation and suggested the effect of the

Early Toarcian GAE. However, the detailed stratigraphic position, scale and

mechanism of this phenomenon have not been analyzed in this section. The data of

the Early Toarcian GAE in East Asia enable to contribute the global-scale

discussion of this paleoenvironmental change in the Northern Hemisphere.

In contrast, the paleobiogeographic changes of the Jurassic ammonoids have

been discussed in a global scale (e.g. Page, 2008). The transitional pattern of

ammonoid fauna is an excellent proxy for tracing the long term paleoenvironmental

changes. In Japan, the detailed transitional pattern of late Early Jurassic ammonoid

assemblages have not been analyzed, and the lack of these data have disturbed the

discussions of global ammonoid paleobiogeography in this time-interval.

Ammonoid faunas from Japan, including the assemblages from the Toyora and the

Kuruma Groups, have been compared paleobiogeographically with the faunas from

outside Japan (Sato, 1956; Hirano, 1973b). However, the transitions of a

comprehensive Japanese ammonoid fauna during late Early Jurassic and their

paleobiogeographic significances have not been discussed in previous studies.

Consequently, the aims of this study are to analyze the paleoceanographic

6

changes in the West Panthalassa (present East Asia) during late Early Jurassic

time-interval based on the geochemical analyses of the Early Toarcian GAE in

Japan, the short-term paleoenvironmental and faunal extinction events, and the

detailed transitional patterns of the ammonoid paleobiogeography for tracing the

long-term paleoceanographic change, and to discuss the global paleoceanographic

environment affected to the change of marine biota (ammonoids) in the Northern

Hemisphere.

These paleoecological analyses should be discussed on the basis of the detailed

ammonite-based chronological schemes which are compared with the European

zonation. The zonal framework of the Toyora Group has been proposed by Hirano

(1973b), and three ammonite zones were established in the Nm Member (lower part

of the Nishinakayama Formation; Hirano, 1971): the Fontanelliceras fontanellense

Zone, the Protogrammoceras nipponicum Zone and the Dactylioceras helianthoides

Zone in ascending order. However, the necessity to refine the Hirano's zonation

was pointed out by Nakada & Matsuoka (2009) based on the difficulty of the

international correlation. In contrast, the ammonoid biostratigraphy of the Kuruma

Group was analyzed by Sato (1955). Although the Teradani Formation, the upper

part of the Kuruma Group, was corresponded to the Upper Pliensbachian, the

detailed depositional age of this formation has not been discussed because of the

poor ammonoid faunal association and the unidentified ammonoid-bearing horizon

in the previous study. Therefore, the revision or the establishment of ammonoid

zonal schemes in the Toyora and the Kuruma Groups and the mutual/international

correlation of these zonations should be discussed before analyzing the

geochemistry and paleobiogeography.

7

2. Geological framework

2-1. Toyora Group

The Toyora Group is the Lower to Middle Jurassic epicontinental sediments

exposed around the Tabe Basin in the western part of Yamaguchi Prefecture,

southwest Japan (Fig. 2-1). The distribution of the group is divided into the

northern district (Ishimachi district) and the southern district (Tabe district) by the

Kikugawa (Tabe) Fault. The Toyora Group exposed in the northern district yields

numerous ammonoid fossils (e.g. Matsumoto & Ono, 1947; Hirano, 1971, 1973a, b),

with bivalves, gastropods and echinoids (e.g. Hayami, 1958, 1959, 1960a, b, 1961,

1962). In contrast, the latter, where the lithofacies are similar to the former and

abundant plant fossils are obtained, are rare in marine biota (Hirano, 1971;

Kawamura, 2010). The study area includes the majority part of the north district,

3.5 km northwest-southeast (NW-SE) and 4.5 km northeast-southwest

(NE-SW)(Fig.2-1).

The lithostratigraphic classification of the Toyora Group follows Hirano's

study (1971). A geological map and a generalized geological column of the study

area are presented in Figs. 2-2 and 2-3, respectively. The group is divided into

three formations (in ascending order): the Higashinagano Formation, the

Nishinakayama Formation and the Utano Formation (Figs. 2-2, 2-3). Each

formation is subdivided into two to four members. The lithostratigraphic

denominations of these members are revised based on the International

Stratigraphic Guide (Salvador, 1994).

The Higashinagano Formation consists of mainly sandstone with conglomerate

and siltstone. It is subdivided into four members (in ascending order; Fig. 2-3); the

Chuzankei Conglomerate Member (basal conglomerate), the Higashinakayama

Sandstone Member (massive arkose medium to coarse sandstone), the Kido

Sandstone Member (bedded medium to fine sandstone with sandy siltstone and thin

coal beds) and the Koyagawa Sandy Mudstone Member (sandy siltstone). Some

ammonite specimens were obtained from the base of the Kido Sandstone Member

··· 1······

.i.'

:r"..'

r__------"--...., '.;.

".

Shira 0

)5 (

-,

'....~

Sea of Japan

o

.......

r

raz

2 m

~.:' \

.........'

o

o

Kuru a Gro

is io soGro is

oyora Group

. S di areaFi . 2-5.

9

(Hirano, 1971), and many bivalves and gastropods from this formation were

described by Hayami (1958, 1959, 1960a, b, 1961, 1962). The Higashinagano

Formation generally shows a fining upward sequence. The Chuzankei

Conglomerate Member covers the basement, the Permian Toyohigashi Group which

is composed of metamorphic sedimentary rock (merange), at an unconformity,

although the Higashinakayama Sandstone Member overlies the basement directly in

the Higashinagano area because the basal conglomerate pinches out to the north

(Fig. 2-2).

The Nishinakayama Formation, mainly analyzed in this study, is composed of

(in ascending order) the Sakuraguchidani Mudstone Member and the Ishimachi

Sandstone and Mudstone Member (Fig. 2-3). The Sakuraguchidani Mudstone

Member is mainly composed of silty clay and clay, often with parallel lamination

or bioturbation, and is characterized by abundant occurrence of ammonoid fossils.

Some thin sandstone (fine to medium .grain) and acidic tuff beds are alternated with

these black mudstones (Fig. 2-3). This member is well exposed along the

Sakuraguchidani Valley (Fig. 2-2). The Ishimachi Sandstone and Mudstone

Member is mainly consisted of black bioturbated siltstones with numerous

intercalates of fine to medium grained thin sandstones (Fig. 2-3). Ammonoid

fossils were obtained from three mudstone beds and a tuffaceous sandstone horizon

of this member exposed along the Sakuraguchidani Valley.

The Utano Formation consists mainly of alternating beds of sandstone and

sandy siltstone. This formation is subdivided into the Eragawa Sandy Mudstone

Member (well-laminated sandy siltstone), the Andadani Sandstone and Mudstone

Member (mudstone with many intercalates of sandstone), the Kodani Sandy

Mudstone Member (massive sandy siltstone), and the Kamiokaeda Sandstone and

Mudstone Member (sandstone with many intercalates of mudstone), in ascending

order (Fig. 2-3). The Utano Formation is generally composed of a coarsening

upward sequence and is overlain by the Cretaceous Kanmon Group, the

epicontinental sediment which is composed of coarse-grained clastic rocks, at an

angular unconformity.

,

131.03434.084N

,,

,,,

! 0 500 1,000 (m)

LEGE D -/

Higa hinag no F. nmon Group conformityKoy a a Sa m nt unconformity

c=J Kido M. Quartz porphyry Faultc=J Higa hina ayama M. Rhyolite Con al d fault" Chuzan ei Porphylit Inferred fault

It ~ Anticfin

/" Strike and dip Syncfin

Fig. 2-2 . Geological map of the study area in the Toyora Group .

11

t1y II

with

mo t part i compo

60­125m

60 m+

60­120m

60­150m

50­120m

oz ~ ~ I-__I- -t4:e4:zIen4:

"I

?

alenian

Sinemurian

Callo ian

Pre-Jurassic

(!)

0 Toarcian «CJ) a:CJ) aco >- rL- a::J., I- ~

IenZ

Pli ns-bac ian

D udstoneSandstoneAmmonoid fossils

o Calcareous nodule

D Sandy silt toneConglomerate

( Bivalve fossils-=- Coal beds

Fig. 2-3. Generalized geolog'cal column of the Toyora Group in the study area.

12

In the study area, the Toyora Group generally strikes NE-SW and dips

northwestward at 30-40° (Fig. 2-2). A NE-SW striking fault occurs near the Koya

River, and three NW-SE striking faults occur to offset the NE-SW striking fault. In

addition, two fold structures are observed: an anticline in the Ishimachi area and a

syncline across the Utano River (Fig. 2-2).

2-2. Kuruma Group

The Kuruma Group, the Early Jurassic continental shelf sediments, is exposed

around the northeastern part of the circum-Hida terrane in the eastern part of

Toyama Prefecture, the western part of Niigata Prefecture and the northern part of

Nagano Prefecture, central Japan (Fig. 2-1). The distribution of this group is

divided into the main area and the eastern area (Kumazaki & Kojima, 1998)(Fig.

2-1), and lithostratigraphy has been analyzed separately by Kobayashi et aI. (1957),

Chihara et aI. (1979), Takizawa (1984), Shiraishi (1992) and Kumazaki & Kojima

(1998)(Fig. 2-4). The ammonoid biostratigraphy in this study is analyzed along the

Daira River and the Teradani Valley, located at the western part of the main area in

Toyama Prefecture (Figs. 2-1, 2-5), because this section yields abundant Early

Jurassic ammonoid fossils (Sato, 1955; Kobayashi et aI., 1957).

The Kuruma Group exposed in the main area was divided into seven formations

by Kobayashi et al. (1957) in ascending order: the Jogodani, the Kitamatadani, the

Negoya, the Teradani, the Shinatani, the Otakidani and the Mizukamidani

Formations (Fig. 2-4). Thereafter, the Mizukamidani Formation was included into

the Tetori Group, the Middle Jurassic to Early Cretaceous continental shelf

sediments distributed in central Japan, by Takizawa (1984). This group is mainly

composed of sandstones, mudstones and conglomerates with numerous fossils, for

example, ammonoids, bivalves, gastropods, belemnites and plants, and is

characterized by alternation of the marine and non-marine sediments (Kobayashi et

aI., 1957). The Kuruma Group covers serpentinite melange and olistostrome of the

circum-Hida terrane and is mainly overlain by the Tetori Group, including the

Mizukamidani Formation, the Kurobishiyama Formation and the Siritakayama

Kobayashi at at (1957) Takizawa (1984) Shiraishi (1992) Kumazaki & Kojima (1996)main area main area eastern area main area eastern area

Mizukami- Km3Km2

danl F.Km1 ...... ..... -- ..... ---- -- ...... ",. ~ .... ......

Otakidani F. Otakidani F. Otakidani F.

Shinatani F.Ks2

Shinatani F. Shinatani F.Ks1

Teradani F. Teradani F. Teradani F.

Kn2

Negoya F. Negoya F. Negoya F.

Kn1

?Kk3 Yoshina ...

Kitamata- Yoshina- Kitamata-zawa F.

Kk2 Kitamata-dani F. dani F. zawa F. dant F.

Odokoro-Kk1 Odokoro- gawa F.

Kj.2gawa F.

Jogodani F. Jogodani F. Gamahara- Jogodani F. Gamahara-Kj1 zawa F. zawa F.

Fig. 2...4. Different views on the stratigraphic sequence of the Kuruma Group.

37.7073 ° 2

FO

. 2-5. I a &:! "' ;~In" .oJIlUr"-AI";.u ro es a d fa . locatrues

15

Formation, at an unconformity (Kobayashi et aI., 1957; Takizawa, 1984; Kumazaki

& Kojima, 1996).

In this study, the lithostratigraphic classification of the Kuruma Group follows

Kobayashi et al. (1957) and Takizawa (1984). Individual columnar sections of the

Kuruma Group in study area are presented in Fig. 2-6. The Kuruma Group

distributed in the study area are divided into four formations (Fig. 2-6), the Negoya

Formation (alternating medium to fine grained sandstone and mudstone with some

conglomerate or fine grained tuff intercalations), the Teradani Formation (sandy

siltstone with some fine grained sandstone beds), the Shinatani Formation (fine

grained sandstones with numerous sandy siltstones and some conglomerates) and

the Otakidani Formation (black mudstone with thin sandstone and conglomerate

intercalations) in ascending order. These formations exhibit lateral changes in

lithofacies, and the Teradani Formation pinches out to the west (Fig. 2-6). In the

study area, the Kuruma Group generally strikes W-E and dips northward at 25-50°.

A W-E striking fault occurs along the Daira River, and many NW-SE striking faults

occur to offset the W-E striking fault (Kobayashi et aI., 1957; Kumazaki & Kojima,

1996).

Ammonoid fossils have been obtained from the Teradani Formation (Sato,

1955) and the Otakidani Formation (Kobayashi et al., 1957). Most of the ammonoid

specimens analyzed in this study were yielded in the former formation. The

Teradani Formation is successively exposed along the Teradani Valley, the type

area of this formation, which mainly composed of black sandy mudstone without

sedimentary structure and bioturbation (Fig. 2-6). On the other hand, this formation

distributed along the Daira River is composed of alternating sandy mudstone and

fine to medium grained sandstone and is divided into some tectonic blocks by many

faults (Kobayashi et al., 1957; Kumazaki & Kojima, 1996). Abundant marine biota,

including ammonoids, bivalves, gastropods and echinoids, and plants are obtained

from this formation in this study.

Daira River 1

1

Te adani Vall y

congkHllerale

I'lIl 'Fft1i ft2

- - - - _.. '

-,: 100m,,IIIII1III

--I,: Daira Ri er 2II,I Daira RO r 3: Daira i rL ----------------------------

u.:cco~~

co(5

u.:cco"0coL-

~ca

:;::coEL-

au,co~aC)Q)

Z

u.:cco.....,coc

..c(f)

~(':tinr,~ co po de ee .... lIrT1 .....~rr 'esa e saFig. 2-6. Individual columnar sectio s of e ruto the fossil locality numbers in Fi s. 3 , 3-5.

17

3. Ammonoid biostratigraphy and its international correlation

3-1. Aims of this chapter

The ammonoid biostratigraphy in the Toyora Group has been discussed by

Matsumoto & Ono (1947), Hirano (1973b), Tanabe (1991) and Nakada & Matsuoka

(2009). The zonal framework of the Toyora Group was mainly established by

Hirano (1973b) and three ammonite zones were mentioned in the Nm Member

(lower part of the Nishinakayama Formation; Hirano, 1971). On the other hand,

Nakada & Matsuoka (2009) drew the Pliensbachian/Toarcian (P/T) boundary in the

Nishinakayama Formation and pointed out the necessity of refining the Hirano's

zonation.

In the Kuruma Group, although the Teradani Formation was compared roughly

to the Upper Pliensbachian based on the·· occurrences of Amaltheus sp. and

Canavaria sp. ex gr. C. geyeriana (HAAS) by Sato (1955), the detailed ammonoid

biostratigraphy has not been analyzed in the Kuruma Group because of their poor

faunal association. The occurrence of abundant ammonoid materials in this study

enables to propose the ammonoid zonal framework in the Teradani Formation.

This study aims to revise the ammonite zonal scheme of the Toyora Group, to

establish an ammonoid zonal scheme in the Kuruma Group and to correlate these

new frameworks with the zonations established outside Japan.

3-2. Re-examination of ammonite biostratigraphy in the Toyora Group

3-2-1. Characteristics of materials

Ammonoid biostratigraphic work of the Toyora Group was mainly carried out

along the Sakuraguchidani Valley, one of the tributary streams of the Koya River

(Fig. 2-2), because of the outcrop condition and abundance of ammonoid fossils. In

addition, in previous studies, ammonoid biostratigraphical analyses have been

mainly carried out along this route. A total of 304 ammonoid specimens (276

specimens from 48 horizons of the Sakuraguchidani Mudstone Member and 28

specimens from four horizons of the Ishimachi Sandstone and Mudstone Member)

18

obtained along the Sakuraguchidani Valley are utilized in this study, in addition to

a specimen from the Kido Sandstone Member described by Hirano (1971)(Fig. 3 in

Plate 4). Twenty two identified genera and 32 identified species are shown in

Appendices 3-1, 3-2, 3-3, 3-4 and Plates 1-4 and 8. Almost all of the specimens

from the Sakuraguchidani Mudstone Member were embedded and compressed

horizontally to the bedding plane but the ornaments were well preserved.

The faunal characteristics of the ammonoid assemblages change with

stratigraphic levels in the Sakuraguchidani Mudstone Member. The lower part of

the member is not as abundant in ammonoid fossils. The fauna from the middle part

is characterized by the abundance of Harpoceratinae, especially Protogrammoceras

nipponicum (MATSUMOTO)(Figs. 1-3 in Plate 2). In the upper part, the diversity

reaches its maximum level, and this assemblage is identified by the abundance of

"Cleviceras" chrysanthemum (YOKOYAMA)(Figs. 1-3 in Plate 3) and Dactylioceras

helianthoides (YOKOYAMA)(Figs. 1-3 in Plate 1). Except for the Eoderocerataceae

genera (Dactylioceras, Peronoceras and Amaltheus), the fauna from the upper part

of this member consists mostly of high-diversity Hildoceratoidea genera. These

specimens indicate successive ages from Late Pliensbachian to Early Toarcian

(Hirano, 1973b). On the other hand, most of the materials from the Ishimachi

Sandstone and Mudstone Member were obtained from bed 53-4 which consists of

tuffaceous fine grained sandstone. This assemblage is mainly associated with

Grammoceratinae (genera Grammoceras and Pseudogrammoceras) and the genus

Osperlioceras with some Phylloceratina (Plate 8; Appendices 3-4).

3-2-2. Methods

This study shows the necessity of recognizing ammonoid-bearing levels in

detail for establishing a new zonation, which can be compared to higher-resolution

biostratigraphic frameworks proposed outside Japan. The mudstones of the

Sakuraguchidani Mudstone Member exposed along the Sakuraguchidani Valley

were subdivided into a few meters thick layers on the basis of the following

indices: particle size, laminated or bioturbated, fissility, fragments of fossil woods

19

and calcareous nodules. A detailed route map and corresponding lithological

columnar sections of the valley are shown in Fig. 3-1.

Biostratigraphical analysis was based on the range charts of the

Sakuraguchidani Valley. The valley branches into the North Valley and the South

Valley. The analyses were carried out separately (Figs. 3-2, 3-3).

3-2-3. Stratigraphical repetition along the Sakuraguchidani Valley

As mentioned above, the previous ammonoid biostratigraphical analysis has

been mainly carried out along the Sakuraguchidani Valley (Fig. 2-2). This route has

been considered to have no repetition of strata but this analysis proposes a new

interpretation (Figs. 3-1, 3-2, 3-3). Around the fork of the North and the South

Valleys, a specimen of the genus Dactylioceras, the index taxa of the Lower

Toarcian, was obtained from bed 14-1 in the North Valley (D. helianthoides; Figs.

1-3 in Plate 1), corresponding with the lowest occurrence of this species. Therefore,

this horizon was regarded as the lower Toarcian by Nakada & Matsuoka (2009). In

contrast, a specimen of Amaltheus margaritatus MONTFORT was found in bed 36-1

along the South Valley (Figs. 3-1, 3-3) in our additional examination after the

working by Nakada & Matsuoka (2009). This species has been obtained from the

Margaritatus Standard Zone to the Apyrenum Standard Subzone, the Upper

Pliensbachian except for the uppermost part of the Northwest European zonation

(e.g. Meister, 1988). Based on the lithological correlation between these two

sections, the latter is obtained from a horizon stratigraphically slightly higher than

the former. This biostratigraphical disagreement suggests the repetition of strata by

an inferred fault that exists between these beds (Figs. 3-1, 3-2, 3-3). The

occurrence of Petranoceras sp. aff. P. rinaldinii VENTURI (Fig. 9 in Plate 2) from

bed 10-6 supports this tectonic interpretation because P. rinaldinii was described in

the Mirabile Zone (Lowermost Toarcian) of central Italy (Faraoni et aI., 1994). The

ammonoid biostratigraphy should be discussed separately above bed 17-5 and

below bed 14-1 along the North Valley, as well as above bed 36-1 and below bed

10-6 along the South Valley.

(a)

II

10 m

-: HlGllSH1NAC3ANO...... I I

n t c l lTCW"'t Fa

ISH I KAY. Fo on WSAKURAGUCHIDA I ~

ud 0 e em r

.......

............'CD. heliclzlIlthcfides

// " .:···············C__··~

ISouth Vall yl

..'

............

! I

.../ ..

21

3-2-4. Results

Four ammonoid zones in the Sakuraguchidani Mudstone Member in the Toyora

Group are proposed in this analysis as follows, in ascending order (Figs. 3-1, 3-2,

3-3): the Canavaria japonica Zone, the Paltarpites paltus Zone, the Dactylioceras

helianthoides Zone and the Harpoceras inouyei Zone. In addition, two ammonoid

assemblage zones are also established in this study as follows: the Amaltheus

stokesi Assemblage Zone In the Higashinagano Formation and the

Pseudogrammoceras-Phlyseogrammoceas Assemblage Zone in the Ishimachi

Sandstone and Mudstone Member (Figs. 3-1, 3-2).

3-2-4-1. Amaltheus stokesi Assemblage Zone

This zone is represented by Amaltheus stokesi (SOWERBY)(Fig. 4 in Plate 4),

widely distributed in the Northwest European, the North American Cordillera and

the Russian provinces and regarded as one of the typical Boreal elements in this

period (e.g. Meister, 1989).

This interval is characterized by two specimens (GK. G. 11293 and GK. G.

11292) described by Hirano (1971) as Amaltheus sp. cf. A. stokesi (SOWERBY) and

Arieticeras sp. aff. A. apertum MONESTIER. According to Hirano (1971), they

obtained from almost same horizon of the Kido Sandstone Member, the

Higashinagano Formation, exposed along the Chuzankei Valley (Fig. 2-2). The

occurrences of these two species are limited in this zone.

3-2-4-2. Canavaria japonica Zone

This zone is represented by Canavaria japonica (MATSUMOTO)(Fig. 8 in Plate

1). The base of this zone has not been observed along this route by the inferred

fault. In this study, the lowermost part of this zone is characterized by the

Occurrence of A. margaritatus (Figs. 9-10 in Plate 1), one of the most important

index taxa of Late Pliensbachian, from bed. 36-1 along the South Valley, and this

zone is not recognized along the North Valley because of the absence of outcrops.

In addition to the genus Amaltheus, this interval is characterized by the abundance

o

?

o

a.:

Fg. 3-2. Columnar section and biostratigraphic succession of ammonoid along the North Valleyof t e Sakuraguchidani Valley. The numbers beside the columnar section correspond to thenumber of the outcrop in Fig. 3-1. Thin broken lines: re-examined zonal boundaries . Thickbro en line: prensbachianIToarcian (PIT) boundary. The previous ammonite zonation followsHirano (1973b) and Tanabe (1991). The legend of the columnar section is as in Fig. 3-1.

23

of the index species from bed 36-2 immediately above the Amaltheus bed along the

South Valley. The genus Canavaria is common in the Mediterranean province, and

A. margaritatus is dominant in the Northwest European province in the Upper

Pliensbachian. Moreover, both of these two genera are limited to this zone.

3-2-4-3. Paltarpites paltus Zone

This zone is represented by Paltarpites paltus (BUCKMAN)(Fig. 8 in Plate 2),

also described in the Northwest European province (Howarth, 1957) and North

American Cordillera (Frebold, 1970). The base of the P. paltus Zone is defined by

the first occurrence of the index species and is drawn at bed 41-1 along the South

Valley (Fig. 3-3). In contrast, this zonal boundary seems to be drawn below bed

17-5 along the North Valley based on the stratigraphic correlation between the

North and the South Valleys of the Sakuraguchidani Valley (Figs. 3-1,3-2,3-3).

This interval is stratigraphically divided into two parts depending on the faunal

characters. The lower part is represented by low-diversity Hildoceratidae with rare

Lytoceratina. More precisely, the occurrence of ammonoid fossils is generally rare

in the lower part of the P. paltus Zone except for some diverse fauna including P.

paltus (Fig. 8 in Plate 2), Paltarpites toyoranus (MATSUMOTO)(Fig. 7 in Plate 2),

Fontanelliceras fontanellense (GEMELLARO)(Figs. 6-7 in Plate 1), Lytoceras sp.,

Lioceratoides aradasi (FUCINI)(Fig. 10 in Plate 2), and Lioceratoides yokoyamai

(MATSUMOTO) from bed 41-1 along the South Valley, and the occurrence of F.

fontanellense (Figs. 6-7 in Plate 1), which is a pandemic taxon distributed mainly

in Europe and ranges from the middle to the top of the lower part of this zone, from

bed 18-1a along the North Valley. Almost all taxa are common in the Mediterranean

province, except for the genus Tiltoniceras, and are limited to the lower part of the

P. paltus Zone except for L. yokoyamai, which extends into the H. inouyei Zone.

The upper part of theP. paltus Zone is characterized by high-diversity endemic

species of Harpoceratinae with some Lytoceratina and Phylloceratina. This part

almost corresponds to the range of P. nipponicum (Figs. 1-3 in Plate 1), the most

dominant species in the upper part of the P. paltus Zone. The lower half of this

oQ.c:3:J

enCD~

»33o:Joa:-oen~,

en

P.

,.,.tptpNt.I

I

~

La

roro

nt8\dense

-10.

o

N

HIGASHINAGANOKOYAGAW

c: r~;:;:

I I I ... =ren 0

en@~

(1)

CJ)

fI)

Q)

5

'<

c

0 '(ii ' fI)

Q)

o

0"-t\ - ,..... (0=r '(1)(,.)

I(,.)

to

25

upper part is composed of alternating sandstone and mudstone and is poor m

ammonoid fossils. Only two specimens of P. nipponicum are obtained from bed

18-1c, corresponding to the first occurrence of this species. In contrast, the abrupt

diversification of Harpoceratinae is recognized in bed 19-1b, corresponding to the

upper half of the upper part, along the North Valley. The fauna from this bed is

characterized by the abundance of P. nipponicum and the appearance of many

Harpoceratinae species, including Protogrammoceras yabei HIRANO (Fig. 5 in

Plate 2):> Fuciniceras nakayamense (MATSUMOTO)(Fig. 6 in Plate 2):> Fuciniceras

primordium (MATSUMOTO):> Polyplectus okadai (YOKOYAMA)(Fig. 6 in Plate 3):> and

"Cleviceras" chrysanthemum (Figs. 1-3 in Plate 3):> with Lytoceras sp. In addition

to the North Valley, L. yokoyamai, P. nipponicum (Figs. 1-3 in Plate 2) and

Calliphylloceras sp. from bed 48-2:> and "Cleviceras" chrysanthemum from bed

48-3 are recognized in the upper part of the P. paltus Zone along the South Valley.

Almost all species obtained from this interval extend into the superj acent D.

helianthoides Zone except for P. nipponicum and F primordium.

3-2-4-4. Dactylioceras helianthoides Zone

This zone is represented by D. helianthoides (Figs. 1-3 in Plate 1):> also

described in Germany and Spain (Schmidt-Effing, 1972). The base of the D.

helianthoides Zone is marked by the first occurrence of the index species and is

drawn at bed 19-5b along the North Valley and bed 48-4 along the South Valley.

This interval is characterized by the abundance of D. helianthoides (Figs. 1-3

in Plate 1) and high-diversity Harpoceratinae, and contains a large number of

"Cleviceras" chrysanthemum (Figs. 1-3 in Plate 3):> F nakayamense (Fig. 6 in Plate

2) and the index species, with some specimens of L. yokoyamai, P. okadai (Fig. 6 in

Plate 3), Protogrammoceras onoi HIRANO (Fig. 4 in Plate 2), P.yabei (Fig. 5 in

Plate 2), Lioceratoides matsumotoi HIRANO, Hildaites sp. (Fig. 7 in Plate 3),

Calliphylloceras sp. and Lytoceras sp. All these species extend into the superjacent

H. inouyei Zone, with the exception of the genus Protogrammoceras, which

disappears at bed 21-1 within this zone. The uppermost part of the D. helianthoides

26

Zone along the South Valley has not been observed because the distribution of the

outcrops along this route is limited at bed 48-9.

3-2-4-5. Harpoceras inouyei Zone

This zone is represented by Harpoceras inouyei (YOKOYAMA)(Fig. 4 in Plate 3),

the endemic species of the Toyora Group, and almost corresponds to the range of

the index species (Fig. 3-2). The base of the H. inouyei Zone is defined by the first

occurrence of the index species and is drawn at bed 23-1 along the North Valley,

synchronous with that of Cleviceras sp. cf. C. exaratum (YOUNG & BIRD)(Fig. 5 in

Plate 3). The upper boundary of this zone is difficult to define because of the

absence of proper index taxa, for example the genus Hildoceras.

This interval is characterized by diverse genera of Harpoceratinae and

Dactylioceratidae, which includes the genera Cleviceras, Harpoceras,

Lioceratoides, Polyplectus, Fuciniceras, Dactylioceras and Peronoceras, with

some Calliphylloceras and Lytoceras. The fauna of this interval is dominated by

"Cleviceras" chrysanthemum (Figs. 1-3 in Plate 3) and Peronoceras subfibulatum

(YOKOYAMA)(Fig. 5 in Plate 1) which appears at bed 25-3 in the H. inouyei Zone.

Lioceratoides yokoyamai, Calliphylloceras sp., Lytoceras sp., L. matsumotoi and P.

subfibulatum (Fig. 5 in Plate 1) disappear gradually from the middle (bed 26-4) to

upper part (bed 28-4) of this zone. The fauna obtained from the uppermost part of

the H. inouyei Zone at bed 29-3 along the North Valley consists of D. helianthoides

(Figs. 1-3 in Plate 1), P. okadai (Fig. 6 in Plate 3),F. nakayamense (Fig. 6 in Plate

2), "Cleviceras" chrysanthemum (Figs. 1-3 in Plate 3), C. sp. cf. C. exaratum (Fig.

5 in Plate 3), and H. inouyei (Fig. 2 in Plate 3).

3-2-4-6. Pseudogrammoceras-Phlyseogrammoceras Assemblage Zone

This zone IS represented by the genera Pseudogrammoceras and

Phlyseogrammoceras (Figs. 10-19 in Plate 8) which are especially dominant in

central Europe (Guex, 1975).

This interval is characterized by the occurrence of Harpoceratinae (genus

27

Osperlioceras), Grammoceratinae (genera Grammoceras, Pseudogrammoceras and

Phlyseogrammoceras) and Phylloceratina (genus Calliphylloceras). A total of eight

species are recognized as follows; Osperlioceras sp. A (Figs. 1-4 in Plate 8),

Osperlioceras sp. B (Figs. 5-7 in Plate 8), Pseudogrammoceras sp. A (Figs. 10-12

in Plate 8), Pseudogrammoceras sp. B (Figs. 13-14 in Plate 8), Grammoceras sp.

(Figs. 8-9 in Plate 8), Phlyseogrammoceras sp. (Fig. 19 in Plate 8), Dactylioceras

sp. (Figs. 20-21 in Plate 8) and Calliphylloceras sp. (Figs. 22-23 in Plate 8).

Almost all species are obtained from bed 53-4 only, except for Osperlioceras sp. A

which are recognized from beds 53-2, 53-3, 53-4 and 56-2 (Fig. 3-2).

3-2-5. Reexamination of the PIT boundary

The ammonoid zonation in the Toyora Group has been documented mainly in

the Sakuraguchidani Mudstone Member by Hirano (1973b), who established three

ammonite zones, in ascending order: the Fontanelliceras fontanellense Zone, the

Protogrammoceras nipponicum Zone and the Dactylioceras helianthoides Zone.

Nakada & Matsuoka (2009) recently reviewed the PIT boundary by adopting the

European index, the first occurrence of the genus Dactylioceras. It was drawn by

the first occurrence of D. helianthoides (Figs. 1-3 in Plate 1) within the F.

fontanellense Zone of Hirano (1973b). However, this index species was identified

as the subgenus Dactylioceras (Orthodactylites), and the first occurrence of this

species seemed to be correlated to a horizon within the Clevelandicum Standard

Subzone, the second subzone of the Toarcian stage, by Schmidt-Effing (1972). In

contrast, Paltarpites paltus (BUCKMAN)(Fig. 8 in Plate 2) obtained from this group

characterizes the first subzone of the Toarcian and has been utilized as an index

species of the PIT boundary in France (Gabilly, 1976; Elmi et aI., 1997).

Consequently, the first occurrence of P. paltus is the most suitable candidate for

indicating this stage boundary in the Toyora Group. Nakada & Matsuoka (2009)

pointed out problems of the previous studies as follows: the disagreement between

the zonal boundaries of Hirano (1973b) and the PIT boundary of Nakada &

Matsuoka (2009) and the zonal nomenclature of the D. helianthoides Zone. This

28

biostratigraphic study should be discussed for taking these Issues into

consideration.

The PIT boundary must be revised to consider this stratigraphic repetition. It is

marked at bed 41-1 in the South Valley above the fault by the first occurrence of P.

paltus and is revised to a higher stratigraphic level than that of Nakada & Matsuoka

(2009)(Figs. 3-1, 3-2, 3-3). In contrast, the interval below the fault is compared to

the Lower Toarcian based on the occurrence of some indicators such as P. paltus,

Dactylioceras and Petranoceras, and consequently has no stage boundary.

3-2-6. Correlation with the previous zonation in the Toyora Group

As mentioned above, three ammonite zones- the F. fontanellense Zone, the P.

nipponicum Zone and the D. helianthoides Zone- were established by Hirano

(1973b) in the Toyora Group. According to Hirano (1973b), the lower boundary of

the F. fontanellense Zone was marked by the appearance of Amaltheus, Arieticeras,

Canavaria and/or Dactylioceras, and the base of the P. nipponicum Zone was

probably defined by the first occurrence of the index species, drawn immediately

below the first occurrence of P. nipponicum in the range chart (Hirano, 1973b;

Table 1). The upper limit of the P. nipponicum Zone, equal to the basement of the D.

helianthoides Zone, was described immediately above the last occurrence of the

genera Protogrammoceras and Fuciniceras and was drawn immediately above the

last occurrence of P. yabei (Hirano, 1973b; Table 1). The indicator of this boundary

was revised by Tanabe (1991) to the last occurrence of the genus

Protogrammoceras, because the range of F. nakayamense (Fig. 6 in Plate 2)

extended to the higher stratigraphic level. The upper boundary of the D.

helianthoides Zone was drawn just below the Ishimachi Sandstone and Mudstone

Member (Na Member in Hirano, 1973b), characterized by the last occurrence of P.

subfibulatum in Table 1 (Hirano, 1973b).

Results of the correlation of the ammonite zonal scheme established in this

study with the previous ammonite biostratigraphic analyses in the Toyora Group

are presented in Figs. 4-2 and 4-3. The C. j aponica Zone and the lower part of the P.

29

paltus Zone nearly correspond with the F. fontanellense Zone by Hirano (1973 b),

and the upper part of the P. paltus Zone is compared with the lower half of the P.

nipponicum Zone by Hirano (1973b). The D. helianthoides Zone established in this

study corresponds to the upper half of the P. nipponicum Zone and lowermost part

of the D. helianthoides Zone proposed by Hirano (1973b). The H. inouyei Zone in

this study is nearly corresponds to the D. helianthoides Zone proposed by Hirano

(1973b).

The new zonal framework is established to take international correlation into

account. Therefore, the zonation is more suitable internationally compared to

previous studies (Hirano, 1973b; Tanabe, 1991), especially in the Toarcian.

Moreover, the definitions of the D. helianthoides Zone in this study differ from the

previous study, while these zonal names are the same. The D. helianthoides Zone in

this study is proposed to solve the problem about biostratigraphical nomenclature

of the previous D. helianthoides Zone as pointed out by Nakada & Matsuoka

(2009).

3-3. Proposal of a new ammonoid zonation in the Kuruma Group

3-3-1. Characteristics of materials and methods

Ammonoid biostratigraphic work of the Kuruma Group was carried out along

the Daira River and the Teradani Valley, one of the tributary streams of the Daira

River (Fig. 2-5), because the Teradani Formation is well distributed along these

routes (see Fig. 2 in Kumazaki & Kojima, 1996). A total of 90 ammonoid

specimens obtained along these routes are utilized in this study. Identified eight

genera and 16 species are shown in Appendix 3-5 and Plates 4-7. Although 36

materials are recognized from four beds exposed along the Teradani Valley and

eight beds along the Daira River (Figs. 2-6, 3-4, 3-5, Appendix 3-5), the others are

found from the floated rocks which are provided from Daira 6 and 7 sections (Fig.

3-4; Appendix 3-5). Almost all of the specimens were compressed horizontally to

the median section, but some well preserved specimens were not affected the

compaction (Figs. 3-4 in Plate 5).

Daira River 7

mu

CI)

.2~

"2ci.en

E c

c~

~ ·coE ~ Emacia r

- ~ • • - • . <{ ._ •••••• -.- •• _------ ----------------+--------1

5

-~F

Da ira River 6

.................111111~---

co

+JroE~

oLL

cro'Uro~

~

u,ro~

o0)Q)Z

Fig. 3-4. Detailed colum a ec s a rnrnonoio s a e locaJitJes a e Fi . 2-5.

31

In this study, ammonoid fossils are obtained from the lower and the upper parts

of the Teradani Formation (Figs. 2-6, 3-5). The fauna from the lower part is

characterized by the occurrence of Harpoceratinae, including the genera Canavaria

and Emaciaticeras, and the genus Amaltheus, which is compared to the fauna

described by Sato (1955). Moreover, these genera indicate the Late Pliensbachian

(Sato, 1955). In contrast, the assemblage from the upper part of this formation is

associated with Fuciniceras nakayamense (MATSUMOTO), Protogrammoceras sp.

and Dactylioceras sp. This faunal association has a high similarity with that from

the Toyora Group. On the basis of the faunal characters, this assemblage enables to

compare chronologically to the Early Toarcian, although more detailed correlations

are difficult because of the impossibility of specific identification. In this study,

the ammonoid biostratigraphy of the Teradani Formation is discussed by using the

fauna from the lower part of this formation.

3-3-2. Relationship between fossil-bearing rocks and included ammonite taxa

Biostratigraphical analysis was based on the range charts of the Daira River

and the Teradani Valley (Figs. 3-4, 3-5). As mentioned above, most of the fossil

specimens are obtained from the floated rocks provided from Daira 6 and 7 sections

(Fig. 3-4; Appendix 3-5). The relationships between the ammonite-bearing clastic

rocks and the included taxa are distinguishable in the floated collections from

Daira 6 section.

The specimens identified as the genus Amaltheus are mainly obtained from

well-sorted mudstone with abundant pyrite. In Daira 6 section, the lowermost part

of the Teradani Formation, characterized by the occurrence of A. cf. stokesi (Fig. 6

in Plate 4) from bed DRFO101, is composed of black mudstone with sandy siltstone

and fine-grained sandstone (Fig. 3-4). In contrast, most of the specimens of the

genera Canavaria or Emaciaticeras (both are included in Arieticeratinae) are found

from the poorly-sorted sandy mudstone or tuffceous fine-grained sandstone blocks

with the fragments of plant fossils. This kind of sandy mudstone is mainly

recognizable in the upper part of Daira 6 section, including bed DRFO102 which

·~s:en

Margaritatu

Stokesi

Gibbo us

Subnodos u

..-Stokes,:..Re ressus

Margaritatuaft. Talrosei

J:Qf............ ... 3(I)

a. a.en enc CI) OJ

E mOJ a. C

CU 0g g en ECU -:.:::: E OJ ECU o E C «cCI) CU m OJ

~a 8>

C>OJQ) - ro

.~ 0 c:

.S a.. ~roo ~

u.. OJ

8-~

ro:::c

~cu"'Sc~Q.(I)Q)

1::W__.I.Of .Q:L . ~ . . . ..., . ..,.. .. Haw k r n.. ·tD~02··'~. . . 'Co' .,... . 3 Em ci ti r............... ... .. .c: .. « ci 'Ci) ci __ . - c

Q. . en c en ro~ a. CU Q> OJ Apyrenum :c;:) en ' t::: E ~ I--- - - -+- - - ----l U

..., >CUQ>c ro.TQEOj... 0 ~ ' - 0 .0

c: CU (I) E enCU c:: ~' t::: CU o E~O (1)«CU ~c:: ~

t3 ~-J

Fig, 3-5 . Columnar sections and biostratigraphic succession of ammonoids along the TeradaniValley. The localities are shown in Fig. 2-5 .

33

yielded to a specimen of Canavaria nov sp. A (Fig. 3-4). Thus, the floated

collections from Daira 6 section enable to divide into two groups, the genus

Amaltheus group and the Arieticeratinae group, on the basis of the lithofacies of

the fossil-bearing rocks. The biostratigraphic disagreement between the genera

Canavaria or Emaciaticeras and almost all species of the genus Amaltheus in

Europe (e.g. Page, 2003) supports this faunal division. Moreover, a specimen

identified as A. margaritatus is almost co-occurred with the genus Canavaria in

Daira 7 section (Fig. 3-4). According to this biostratigraphic data and the

phylogeny of the genus Amaltheus proposed in Europe and Russia (Meister, 1988;

Dagis, 1976), the genus Amaltheus group seems to be subdivided

biostratigraphically into two groups (in ascending order) as follows; A. repressus-A.

stokesi group and A. margaritatus-A. aff. talrosei group.

The ammonoid biostratigraphy in the Kuruma Group is discussed on the basis

of these lithostratigraphic and biostratigraphic evidence (Fig. 3-4).

3-3-3. Results

Three ammonoid assemblage zones in the Teradani Formation of the Kuruma

Group are proposed in this analysis as follows, in ascending order (Figs. 3-4, 3-5):

the Stokesi-Repressus Assemblage Zone, the Margaritatus-aff. Talrosei Assemblage

Zone and the Canavaria-Emaciaticeras Assemblage Zone.

3-3-3-1. Stokesi-Repressus Assemblage Zone

This zone is represented by Amaltheus stokesi (SOWERBY)(Figs. 1-2, 4-5 in

Plate 4), also recognized in the Northwest European, the North American

Cordillera, the Russian and the East Asian (Toyora Group) provinces, and

Amaltheus repressus DAGIS (Figs. 6-7 in Plate 4), described only in Northeast

Russia by previous studies (Dagis, 1976). The co-occurrence of A. stokesi and A.

repressus has been also recognized in Northeast Russia (Dagis, 1976).

This interval is identified by the occurrences of these two species. Amaltheus

cf. stokesi (Fig. 6 in Plate 4) was obtained from bed DRFO101 of the Daira River 6

34

section (Fig. 3-4), and A. repressus (Fig. 6 in Plate 4) was obtained from bed

DRF0201 of the Daira River 7 (Fig. 3-4). These two species were also found into

the floated rocks provided from these two sections (Appendix 3-5).

3-3-3-2. Margaritatus-aff. Talrosei Assemblage Zone

This zone is represented by Amaltheus margaritatus MONTFORT (Figs. 7-15 in

Plate 4) widely distributed in high latitudinal areas of the Northern Hemisphere and

Amaltheus sp. aff. A. talrosei REPIN (Fig. 1 in Plate 5), the similar species was

previously recognized only in Northeast Russian (Repin, 1968). These two species

were co-occurred within the Russian provinces reported by Repin (1988).

In the Daira River 7 section, a specimen of Canavaria sp. cf. Canavaria nov sp.

B was obtained from bed DRF0202b just below the occurrence of A. margaritatus

(Fig. 3-4). Canavaria nov sp. B (Fig. 7 in Plate 6) is characterized by the quite

rigid ribbing which has a high similarity with that of the genus Arieticeras,

co-occurred with A. margaritatus in central Europe (e.g. Meister, 1989). Therefore,

this interval is identified by the occurrences of A. margaritatus, A. aff. talrosei and

Canavaria nov sp. B (Fig. 3-4). Many specimens of these species were also found

in the floats from the Daira River 6 and 7 sections.

35

only floated rocks provided from the Daira River 6 and 7 sections (Fig. 3-4). As

mentioned above, these taxa were perhaps obtained from the stratigraphically

higher horizons than those of the genus Amaltheus based on the lithofacies of the

fossil-bearing rocks. In addition, Canavaria naxensis (GEMMELLARO), Canavaria

haugi (GEMMELLARO), Canavaria prognatum FUCINI and the genus Emaciaticeras

have been recognized only in the Elisa Subzone (Upper Emaciatum Zone) of the

Mediterranean province (Braga, 1983), equivalent to the Hawskerense Standard

Subzone (Upper Spinatum Standard Zone) of the Northwest European province

(Page, 2003), although the range of A. margaritatus was limited in the Apyrenum

Subzone, the Upper Spinatum Standard Zone, and the Margaritatus Standard Zone

(Meister, 1988). Therefore, this zone is located above the Margaritatus-aff.

Talrosei Assemblage Zone (Fig. 3-4).

3-4. International correlation for the new ammonite zonations

Ammonoid biostratigraphical analyses from Late Pliensbachian to Toarcian

have been discussed in Europe since the mid-19th century (e.g. d'Orbigny, 1842;

Oppel, 1856-1858). The zonal schemes of this time-interval have been developed

mainly in the Northwest European province and are subdivided into a sequence of

zones, subzones and horizons (Dean et aI., 1961; Gabilly et aI., 1971, 1974;

Howarth, 1973, 1978, 1980, 1992; Gabilly, 1976; Dommergues, 1979; Cope et aI.,

1980; Dommergues & Meister, 1987; Elmi et aI., 1991, 1994, 1997; Page, 2003). In

addition, the zonal frameworks of this period were also documented in the

Mediterranean province (Donovan, 1958; Braga et aI., 1982; Braga, 1983; Guex,

1973; Elmi et aI., 1974, 1991, 1994; Macchioni, 2002), the North American

Cordillera province (Smith et aI., 1988; Jakobs et aI., 1994), the South American

province (e. g. Hillebrandt, 1981, 1987) and the Northeast Russian province (e. g.

Dagis, 1968; Polubotko & Repin, 1974; Repin, 1988; Kalacheva, 1988), and these

zonations were correlated with the Northwest European zones (e.g. Dommergues et

aI., 1997a; Page, 2003-; Smith et aI., 1988; Fig. 3-6). These interprovincial

correlations, especially at subzone and horizon level, are usually difficult because

Romn'-""lZl

F

F

....

t-- - - t-- - - - - - - --t-- - - -+-- - - --+-- - - ---+ - - - - - - - - -

....Q)

~o

.....J

Q)

C. t-- - - t-- - - - - - - --t-- - - -+-- - - --t ... - - - - - - - - - - - - - - - - - - -c.:;)

c:

e

0 1--+--__-+-_~::;::..--__l--__4---__r--~I- 1---- --1

Fig. 3-6. Correia 'provi ceot e ort

37

of the faunal provincialism. In this section, the ammonite zonal schemes of the

Toyora and the Kuruma Groups proposed in this study are compared to these

zonations established outside Japan on the basis of a review of the ammonite zonal

schemes established in each province.

3-4-1. Northwest European province

Representative countries included In this province are Britain, France,

Germany and northern Spain (Page, 2003). The detailed ammonite zonal scheme

established in England has been regarded as the standard zonation of this period.

The general framework of zone and subzone in this province was documented by

Dean et al. (1961) and the details have been discussed by Gabilly et al. (1971,

1974), Howarth (1973, 1978, 1980, 1992), Gabilly (1976), Dommergues (1979),

Cope et al. (1980), Dommergues & Meister (1987), Elmi et al. (1991, 1994, 1997)

and Page (2002, 2003).

The PIT boundary has been traditionally defined by the first occurrence of the

genus Dactylioceras because of their pandemic and abundant occurrence (e. g. Dean

et al., 1961). Moreover, several definitions have been submitted, for example, the

first occurrence of Protogrammoceras paltum (BUCKMAN) in England (Howarth,

1973) and the occurrence of Paltarpites paltus (BUCKMAN) in addition to the genus

Dactylioceras in France (Gabilly, 1976; Elmi et al., 1997). As mentioned above,

the base of the P. paltus Zone corresponds to this boundary in the Toyora Group.

The zonal scheme of Late Pliensbachian has been documented on the basis of

the evolutionary lineage of Amaltheidae. The Late Pliensbachian was divided into

two zones (in ascending order): the Margaritatus Zone and the Spinatum Zone. The

Margaritatus Zone, introduced by Oppel (1856), was represented by A.

margaritatus and was subdividedinto three subzones on the basis of the lineage of

the genus Amaltheus (in ascending order): the Stokesi Subzone, the Subnodosus

Subzone and the Gibbosus Subzone. Some horizons were documented in each

sUbzone on the basis of lineage of the genus Protogrammoceras. The base of the

lowest subzone, the Stokesi Subzone, was clearly defined by the first occurrence of

38

the index species, Amaltheus stokesi (SOWERBy)(Dean et al., 1961). The base of the

middle and the upper zones were also marked by the first occurrence of each index

species, Amaltheus subnodosus (YOUNG & BIRD) and Amaltheus gibbosus

(SCHLOTHEIM). The Spinatum Zone was represented by Pleuroceras spinatum

(BRUGUIERE) and was subdivided into two subzoneson the basis of the lineage of

the genus Pleuroceras (in ascending order): the Apyrenum Subzone and the

Hawskerense Subzone. The base of the lower subzone was defined by the first

occurrence of Pleuroceras solare (PHILLIPS) and that of the upper zone was drawn

immediately above the last occurrence of P. solare.

In the Toyora Group, the A. stokesi Assemblage Zone is correlated to the

Stokesi Standard Subzone, the lowermost Margaritatus Standard Zone, based on the

occurrence of the index species, A. stokesi (Fig. 3-6). In the Nishinakayama

Formation, the base of the C. japonica Zone observed along the Sakuraguchidani

Valley in this study seems to be comparable with Late Pliensbachian. In this study,

the lowermost ammonite horizon of this zone is characterized by the occurrence of

A. margaritatus (Fig. 4-6) obtained from bed 36-1 along the South Valley. These

specimens (SA36-1-1, Fig. 9 in Plate 1; SA36-1-2, Fig. 10 in Plate 1) have a very

strong keel and the ribs projected on the keel. Although this species has been

recognized from the Subnodosus Standard Subzone to the Apyrenum Standard

Subzone (Meister, 1988), these characters are limited to the late type obtained from

the Apyrenum Standard Subzone (e.g. Fig. 3 in Plate 4; Meister, 1988). Thus, this

horizon corresponds to the Apyrenum Standard Subzone (Fig. 3-6). This

correlation suggests that the C. japonica Zone is compared to the Spinatum

Standard Zone of the Northwest European province. However, the biostratigraphic

correlation of the base of this zone is impossible along the Sakuraguchidani Valley

because the lowermost part of this zone is lacked by the inferred fault (Figs. 3-1,

3-2, 3-3). In addition, the absence of any other Amaltheidae specimens from the

Toyora Group in this study makes further detailed comparisons of these zones in

this section difficult.

In the Teradani Formation of the Kuruma Group, the Stokesi-Repressus

39

Assemblage Zone enables to compare with the Stokesi Subzone of the standard

zonation and the A. stokesi Assemblage Zone in the middle part of the

Higashinagano Formation of the Toyora Group proposed in this study (Fig. 3-6),

based on the occurrence of A. stokesi. As mentioned above, the Margaritatus-aff.

Talrosei Assemblage Zone is mainly represented by A. margaritatus. This index

species corresponded from the Subnodosus Standard Subzone to the Apyrenum

Standard Subzone is characterized by the chronological changes of surface

ornaments (Meister, 1988) as follows; the early type from the Subnodosus and

Gibbosus Standard Subzones has a low keel with fine crenulations and the weak

ribbing, and the late type from the Apyrenum Standard Subzone is characterized by

the individual keel with well prorsiradiated serrations and the connection of the

ribs and the keel. Based on these morphological characters of A. margaritatus from

the Margaritatus-aff. Talrosei Assemblage Zone, this interval is correlated from the

Subnodosus to the Apyrenum Subzones of the standard zonation (Fig. 3-6). The

Canavaria-Emaciaticeras Assemblage Zone is associated with the genera

Canavaria and Emaciaticeras, typical in the Mediterranean assemblage (Braga,

1983). Based on the correlation of the Northwest European and the Mediterranean

zonations, this zone is corresponded to the Hawskerense Standard Subzone (Fig.

3-6).

The Early Toarcian zonation of northwest Europe has mainly been established

on the basis of the evolutionary lineages of Dactylioceratidae and Hildoceratidae

and has been divided into three zones (in ascending order): the Tenuicostatum Zone,

the Serpentinum Zone, and the Bifrons Zone. The Tenuicostatum Zone was

represented by Dactylioceras tenuicostatum (YOUNG & BIRD)(Dean et al., 1961)

and was subdivided into four subzones (in ascending order): the Paltum Subzone,

the Clevelandicum Subzone, the Tenuicostatum Subzone and the Semicelatum

Subzone, which were discussed by the lineage of Dactylioceratidae except for the

lowest subzone (Howarth, 1973). The Serpentinum Zone, represented by

Harpoceras serpentinum (SCHLOTHEIM), was subdivided into two subzones based

on the lineage of Harpoceratinae (in ascending order): the Exaratum Subzone and

40

the Falciferum Subzone. The base of the Exaratum Subzone, represented by

Cleviceras exaratum (YOUNG & BIRD), was defined by the first occurrence of the

genus Eleganticeras (Howarth, 1992; Elmi et al., 1997). Howarth (1992) drew this

base by the first occurrence of Eleganticeras elegantulum (YOUNG & BIRD) in

Yorkshire coast (England), and described a sequence of E. elegantulum followed by

the first occurrence of C. exaratum and H. serpentinum, an early type of the genus

Harpoceras, which was approximately 3 m thick. The upper subzone, the

Falciferum Subzone, was represented by Harpoceras falciferum (SOWERBY) and

the base was defined by the first occurrence of the index species (Dean et al., 1961).

The Bifrons Zone, represented by Hildoceras bifrons (BRUGUIERE), was

documented on the basis of the evolutionary lineage of Dactylioceratidae and was

subdivided into three subzones (in ascending order): the Commune Subzone, the

Fibulatum Subzone and the Crassum Subzone. The bases of these subzones were

defined by the first occurrences of each index species, Dactylioceras commune

(SOWERBY), Peronoceras fibulatum (J. DE C. SOWERBY) and Catacoeloceras

crassum (YOUNG & BIRD).

In this study, a zonal boundary, the base of the P. paltus Zone, is proposed

above the PIT boundary in the Toyora Group. The base of the D. helianthoides

Zone, drawn at the first occurrence of D. helianthoides, seems to be correlated to a

horizon within the Clevelandicum Standard Subzone (Fig. 3-6), because the first

occurrence of this species was drawn immediately below the first occurrence of

Dactylioceras tenuicostatum (YOUNG & BIRD), the index species of the base of the

Tenuicostatum Standard Subzone (Fig. 31; Schmidt-Effing, 1972). The base of the

H. inouyei Zone, defined by the first occurrence of H. inouyei (Fig. 4 in Plate 3), is

equivalent to the first occurrence of Cleviceras sp. cf. C. exaratum. The first

Occurrence of the index 'species also corresponds to that of the genus Harpoceras in

the Toyora Group (Fig. 3-6). This relationship between C. exaratum and the genus

Harpoceras is very similar to the sequence of Harpoceratinae horizons into the

Exaratum Standard Subzone in the Northwest European province (Howarth, 1992).

The minor difference between the first occurrence of E. elegantulum and those of C.

41

exaratum and early Harpoceras may be disregarded. Therefore, the base of the H.

inouyei Zone corresponds to the base of the Exaratum Standard Subzone (Fig. 3-6).

As mentioned above, the upper boundary of the H. inouyei Zone is difficult to

define because of the absence of suitable index taxa. The international correlation

of the uppermost part of the H. inouyei Zone, represented by the occurrence of D.

helianthoides (Figs. 1-3 in Plate 1), P. okadai (Fig. 6 in Plate 3), F. nakayamense

(Fig. 6 in Plate 2), C. sp. cf. C. exaratum and H. inouyei (Fig. 2 in Plate 3), is also

complicated by the endemism of the Toyora assemblage that lacks the

biostratigraphic index species of the European province. Hirano (1973b) pointed

out the morphological similarity between P. subfibulatum (Fig. 5 in Plate 1) and P.

fibulatum, the index species of the Fibulatum Standard Subzone, and therefore,

proposed that the upper boundary of his D. helianthoides Zone which was equal to

the upper limit of the H. inouyei Zone of this study seems to be correlated to a

horizon within the subzone (Fig. 3-6). In addition, the biostratigraphic key genera,

which are indicated to be above the Fibulatum Standard Subzone, were absent in

this section. These characters suggest that the uppermost part of the H. inouyei

Zone is approximately correlated within the Fibulatum Standard Subzone by

following Hirano (1973b)(Fig. 3-6).

The Late Toarcian ammonoid zonal scheme of this province has been discussed

on the basis of the evolutionary lineages of Grammoceratinae, Phymatoceratinae

and Hammatoceratinae and has been divided into five zones (in ascending order):

the Variabilis Zone, the Thouarsense Zone, the Dispansum Zone, the Pseudoradiosa

Zone and the Aalensis Zone. The Variabilis Zone was represented by Haugia

variabilts (D'ORBIGNY)(Dean et al., 1961) and was subdivided into three subzones

(in ascending order): the Variabilis Subzone, the Illustris Subzone, and the Vitiosa

Subzone, which were discussed by the lineage of the genus Haugia (Gabilly et al.,

1971; Gabilly, 1976). The Thouarsense Zone, represented by Grammoceras

thouarsense (D'ORBIGNY), was subdivided into four subzones based on the lineage

of Grammoceratinae (in ascending order): the Bingmanni Subzone, the Striatulum

Subzone, the Fascigerum Subzone and the Fallciosum Subzone. The Dispansum

42

Zone was represented by Phlyseogrammoceras dispansum (LYCETT) and was

subdivided into two subzones (in ascending order): the Insigne Subzone and the

Gruneria Subzone. The Pseudoradiosa Zone, represented by Dumortieria

pseudoradiosa (BRANCO), was documented on the basis of the evolutionary lineage

of the genus Dumortieria, Grammoceratinae, and was subdivided into two subzones

(in ascending order): the Levesquei Subzone and the Pseudoradiosa Subzone. The

Aalensis Zone, represented by Pleydellia aalensis (ZIETEN), was subdivided into

two subzones based on the lineage of the genus Pleydellia, Grammoceratinae (in

ascending order): the Mactra Subzone and the Fluitans Subzone.

In the Ishimachi Sandstone and Mudstone Member of the Toyora Group, the

assemblage of the Pseudogrammoceras-Phlyseogrammoceras Assemblage Zone

contains the genera Grammoceras and Phlyseogrammoceras (Fig. 3-2, Appendix

3-4). The former has been mainly obtained from the Fallciosum Standard Subzone

(Gabilly, 1976), and the latter is characterized by the limited range in the

Dispansum Standard Zone (Rulleau, 2007). These biostratigraphical characters

suggest that the Pseudogrammoceras-Phlyseogralnmoceras Assemblage Zone

enables to compare from the Fallciosum Standard Subzone of the Thouarsense

Standard Zone to the Dispansum Standard Zone of the Northwest European zonal

scheme (Fig. 3-6).

3-4-2. Mediterranean province

Representative countries included in this province are Austria, Italy, southern

Spain and North Africa (Page, 2003). Ammonite zonal schemes employed in this

province are commonly different from those of Northwest Europe owing to the

faunal provincialism. The provincial zonations were mentioned by Donovan (1958),

Guex (1973), Elmi et al. (1974, 1991, 1994, 1997), Braga et al. (1982), Braga

(1983), Meister (1987), Dommergues et al. (1997a, b) and Meister et al. (1994).

However, the biostratigraphic correlations between the Northwest European and

the Mediterranean provinces that have been tabulated by Dommergues et al.

(1997b), Elmi et al. (1997), Macchioni (2002) and Page (2003), and the intra-zonal

43

comparison, especially at the horizonal level, still has many problems (Page,

2003).

Although a rework due to the regression around the PIT boundary has been

identified in the Northwest European province (Page, 2003), these phenomena are

not recognized in the Mediterranean province. Therefore, almost all candidates of

Global Stratotype Section and Point (GSSP) are selected from this province by the

International Commission on Stratigraphy (ICS). In this province, this boundary

has been defined by the first occurrence of the subgenus Dactylioceras

(Eodactylites) , including D. (E.) polymorphum, D. (E.) mirabile, D. (E.) simplex

and D. (E.) pseudocommune (Guex, 1973; Macchioni, 2002). Because this

subgenus has not been reported in the Toyora Group, the PIT boundary drawn in

this area is difficult to compare in detail with that of the Mediterranean province.

Late Pliensbachian fauna in the Mediterranean province are characterized by

the abundance of Hildoceratidae genera (Fuciniceras, Protogrammoceras,

Arieticeras, Emaciaticeras and so on), with some rare Amaltheidae specimens (e.g.

Elmi et al., 1974). Therefore, the zonations of this province have been discussed on

the basis of evolutionary lineages of Hildoceratidae. The zonal scheme of Late

Pliensbachian in this province has been divided into three zones (in ascending

order): the Lavinianum Zone, the Algovianum Zone and the Emaciatum Zone (Fig.

3-6). The presence of faunal differentiations makes interprovincial correlation

difficult at the intra-zonal level (Page, 2003). The lower zone, the Lavinianum(

Zone represented by Fuciniceras lavinianum (MENEGHINI), was compared with the

lower part of the Margaritatus Zone of the Northwest European zonation. Detailed

subdivision of this zone was different in the interprovincial area. The Algovianum

Zone, represented by Arieticeras algovianum (OPPEL), was subdivided into five

subzones (in ascending order): the Rogazzonii Subzone, the Bertrandi Subzone, the

Accuratum Subzone, the Meneghinii Subzone and the Levidorsatum Subzone. This

zone corresponds with the lower part of the Margaritatus Standard Zone to the

lower part of the Spinatum Standard Zone. The upper zone, the Emaciatum Zone

represented by Emaciaticeras emaciatum (CATULLO), was subdivided into the

44

Solare Subzone and the Elisa Subzone, in ascending order, and correlated with the

upper part of the Spinatum Standard Zone.

The zonal scheme of Early Toarcian was divided into three zones (in ascending

order): the Polymorphum Zone, the Levisoni Zone and the Bifrons Zone (Fig. 3-6).

The closest correlation between the Mediterranean and the Northwest European

provinces is enabled only within the Bifrons Zone (Page, 2003). The Polymorphum

Zone, represented by Dactylioceras polymorphum FUCINI, was mentioned by the

evolutionary lineage of Dactylioceratidae, especially the subgenus Eodactylites,

and was subdivided into the Mirabile Subzone and the Semicelatum Subzone, in

ascending order. This zone corresponds to the Tenuicostatum Zone of the

Northwest European zonation. The Levisoni Zone, the middle zone represented by

Harpoceras levisoni (SIMPSON), was mainly discussed on the basis of the

evolutionary lineage of Hildoceratidae. The base was defined by the first

occurrence of the index species. This zone was subdivided into two subzones (in

ascending order): the Levisoni Subzone and the Falciferum Subzone, and compared

to the Serpentinum Zone of the standard zonation. The Bifrons Zone, the upper

zone represented by H. bifrons, was subdivided into the Sublevisoni Subzone and

the Bifrons Subzone, in ascending order, and correlated with the Bifrons Zone of

the standard zonation.

The zonation of Late Toarcian was divided into five zones (in ascending

order): the Gradata Zone, the Bonarellii Zone, the Speciosum Zone, the Meneghini

Zone and the Aalensis Zone (Fig. 3-6). The zonal scheme of this period has been

discussed on the basis of the evolutionary lineages of Harpoceratinae,

Mercaticeratinae, Grammoceratinae, Phymatoceratinae, Hammatoceratinae and

Dactylioceratidae. The closest correlation between the Mediterranean province and

the Northwest European province (especially central Europe) enables only within

the Aalensis Zone (Page, 2003). The Gradata Zone was represented by Brodieia

gradata (MERLA) and was subdivided into the Gemma Subzone and the

Alticarinatus Subzone, in ascending order. This zone corresponds to the Variabilis

Zone of the Northwest European zonation. The Bonarellii Zone, represented by

45

Hammatoceras bonarellii PARISCH & VIALE, was mainly discussed on the basis of

the evolutionary lineage of the genus Pseudogrammoceras. This zone was

subdivided into two subzones (in ascending order): the Mediterraneum Subzone

and the Fallaciosum Subzone, and compared to the Thouarsense Zone of the

standard zonation. The Speciosum Zone, represented by Hammatoceras speciosum

JAMENSCH, was subdivided into the Speciosum Subzone and the Reynesi Subzone,

in ascending order, and correlated to the Dispansum Standard Zone. The Meneghini

Zone was represented by Dumortieria menegnihi HAUG, subzones were not

proposed. The Aalensis Zone of this province is the same as that of the Northwest

European province including the subdivision of the subzones (see above).

In general, the Toyora faunas, especially in Early Toarcian, shared many

similarities with the Mediterranean fauna (Hirano, 1973b). The faunal composition

characterized by the dominance of the high-diversity Harpoceratinae genera is

typical in the Mediterranean province, although the genus Cleviceras is more

common in the Northwest European province (Howarth, 1992; Page, 2008). In

contrast, correlation between these two zonations is difficult because of the

absence of the biostratigraphic key species of the Mediterranean zones from the

Toyora Group. On the basis of the correlation between the Northwest European and

the Mediterranean zonal schemes, the zonation of the SakuraguchidaniMudstone

Member, the Toyora Group, is compared to the Mediterranean zonal scheme, as

shown in Fig. 3-6. The A. stokesi Assemblage Zone is roughly corresponded to the

lower part of the Lavinianum Zone. The base of the C. japonica Zone seems to be

compared to the base of the Meneghinii Subzone, and the base of the P. paltus Zone

is corresponded to the base of the Polymorphum Zone (PIT boundary). The D.

helianthoides Zone is perhaps correlated to the Semicelatum Subzone of the

Mediterranean zonation. In the H. inouyei Zone, the base is correlated to the

Levisoni Zone, and the upper boundary is roughly compared to the middle part of

the Bifrons Subzone. The Pseudogralnlnoceras-Phlyseogrammoceras Assemblage

Zone enables to correspond to the upper part of the Fallaciosum Subzone and the

Speciosum Zone of the Mediterranean province.

46

The interval below the inferred fault along the North Valley contains several

ammonoid specimens as follows: P. sp. aff. P. rinaldinii (Fig. 9 in Plate 2), P.

paltus (Fig. 8 in Plate 2) and Fontanelliceras sp. from bed 10-6, and Lytoceras sp.

and D. helianthoides (Fig. 1 in Plate 1) from bed 14-1. In addition to the

occurrence of P. paltus, the occurrence of the genus Petranoceras, described in the

Mirabile Zone (lowermost Toarcian) of central Italy (Faraoni et al., 1994), and the

genus Fontanelliceras, characteristic taxa from the uppermost Pliensbachian to the

lowermost Toarcian, suggest that bed 10-6 is comparable to the P. paltus Zone. In

contrast, bed 14-1 is corresponded to the D. helianthoides Zone based on the

occurrence of the index species.

As mentioned above, the assemblages of the Teradani Formation, the Kuruma

Group, are mainly associated with the genus Amaltheus, except for that of the

Canavaria-Emaciaticeras Assemblage Zone. Therefore, correlation of the

Stokesi-Repressus and the Margaritatus-aff. Talrosei Assemblage Zones with the

Mediterranean zonal scheme is difficult because of the faunal disagreement. On the

basis of the correlation between the Northwest European and the Mediterranean

zonal schemes, these two assemblage zones are compared to the Mediterranean

zonal scheme, as shown in Fig. 3-6. The Stokesi-Repressus Assemblage Zone is

compared to the lower part of the Lavinianum Zone, and the Margaritatus-aff.

Talrosei Assemblage Zone is corresponded to the upper part of the Lavinianum

Zone, Algovianum Zone and the Solare Subzone. In contrast, the fauna of the

Canavaria-Emaciaticeras Assemblage Zone includes the affinitive species of C.

naxensis, C. haugi and C. prognatum, in addition to the occurrence of the genus

Emaciaticeras from this zone. On the basis of the ranges of these species and the

genus in the Mediterranean province, the Canavaria-Emaciaticeras Assemblage

Zone enables to compare to the Elisa Subzone (Upper Emaciatum Zone) of the

Mediterranean zonation (Fig. 3-6).

3-4-3. North American Cordillera province

In North America, the ammonoid biostratigraphy has been studied in Cordillera,

47

western North America. The assemblages from this area contain some endemic taxa

known from the circum-Pacific area, for example Dactylioceras kanense McLEARN

and Peronoceras pacificum HILLEBRANDT, and lack some European genera

including Nodicoeloceras, Hildoceras and Haugia. These characters necessitate the

establishment of regional zonal frameworks in this province. The ammonoid zonal

schemes were mentioned by Smith et al. (1988) and Jakobs et al. (1994), mainly

discussed in the Queen Charlotte Islands.

, The Upper Pliensbachian was divided into the Kunae Zone and the

Charlottense Zone in ascending order. The former, represented by Fanninoceras

kunae McLEARN, was corresponded to the Margaritatus Standard Zone, and the

latter, represented by Fanninoceras charlottense McLEARN, was compared to the

Spinatum Standard Zone.

The Toarcian was divided into five zones, the Kanense Zone, the Planulata

Zone, the Crassicosta Zone, the Hillebrandti Zone and the Yakounensis Zone in

ascending order. The Kanense Zone was represented by Dactylioceras kanense

McLEARN, and the base was defined by the first occurrence of the index species.

This zone was correlated to the Tenuicostatum and the Serpentinum Zones of the

Northwest European zonation (Fig. 3-6). The Planulata Zone, represented by

Rarenodia planulata VENTURI, was almost compared with the Bifrons Standard

Zone (Fig. 3-6), and the base was defined by the first occurrence of index species.

The Crassicosta Zone was represented by Phymatoceras crassicosta MERLA, and

the base was defined by the index species. This base was corresponded to the

lowermost Variabilis Zone of the standard zonation, and the upper boundary

equivalent to the base of the Thouarsense Standard Zone (Fig. 3-6). The

Hillebrandti Zone, represented by Phymatoceras hillebrandt JAKOBS, was

compared to the Thouarsense Zone of the standard zonation (Fig. 3-6). The base of

this zone was defined by the first occurrences of the genus Grammoceras,

Podagrosites latescens (SIMPSON) and the index species. The Yakounensis Zone

Was represented by Yakounia yakounensis JAKOBS & SMITH, and the base was

marked by the first occurrences of Yakounia silvae JAKOBS & SMITH,Pleydellia

48

maudensis JAKOBS & SMITH, Hammatoceras speciosum JANENSCH and Pleydellia

spp. This zone was compared to the Dispansum, the Pseudoradiosa and the Aalensis

Zones of the standard zonation (Fig. 3-6).

The North American Cordillera fauna is characterized by the high endemism,

for example the occurrence of the endemic genus Fanninoceras. Thus, the

zonations proposed in the Toyora and the Kuruma Groups are difficult to compare

to the North American zonal scheme directly because of the absence of the

biostratigraphic key species of the North American zones from these groups

without some exceptions, for example the occurrence of "Cleviceras" sp. cf. C.

chrysanthemum (YOKOYAMA) and Cleviceras sp. cf. C. exaratum (YOUNG & BIRD)

from the North American Cordillera province. On the basis of the correlation

between the Northwest European and the North American Cordillera zonal schemes

(Smith et aI., 1988; Jakobs et aI., 1994), the zonations of the Toyora and the

Kuruma Groups are compared to the North American Cordillera zonal scheme, as

shown in Fig. 3-6. The A. stokesi Assemblage Zone of the Toyora Group and the

Stokesi-Repressus Assemblage Zone of the Kuruma Group are correlated to the

lower part of the Kunae Zone, and the C. japonica Zone (Toyora Group) is almost

corresponded to the Charlottense Zone. In the Kuruma Group, the lower part of the

Margaritatus-aff. Talrosei Assemblage Zone is equivalent to the upper part of the

Kunae Zone, and the upper part of the Margaritatus-aff. Talrosei Assemblage Zone

and the Canavaria-Emaciaticeras Assemblage Zone are corresponded to the

Charlottense Zone of the North American Cordillera zonation. The P. paltus, the D.

helianthoides and the lower part of the H. inouyei Zones of the Toyora Group are

compared to the Kanense Zone, and the upper part of the H. inouyei Zone is coeval

with the lower part of the Planulata Zone in North American Cordillera. The

Pseudogrammoceras-Phlyseogrammoceras Assemblage Zone is roughly correlated

to the upper part of the Hillebrandti Zone and the lower part of the Yakounensis

Zone.

49

3-4-4. South American province

Ammonoid assemblages from the South American province also contain some

endemic species of circum-Pacific and lack some European species like the North

American Cordillera province. Hillebrandt (1987) proposed the regional ammonoid

zonal schemes in the Northern Atacama and the Northeast Antofagasta regions of

Northern Chile. The Upper Pliensbachian was subdivided into the Fannini and the

Disciforme Zones in ascending order, and the Toarcian was subdivided into 10

zones, the Tenuicostatum Standard Zone, the Hoelderi Zone, the Largaense Zone,

the Pacificum Zone, the Chlensis Zone, the Toroense Zone, the Copiapense Zone,

the Tenuicostatum Zone, the "Lotharingica" Zone and the "Fluitans" Zone in

ascending order. Although this zonation was well compared with the North

American Cordillera zonal scheme on the basis of the abundant common species

(Jakobs et aI., 1994; Hillebrandt et aI., 1992), the correlations of this zonal scheme

to the Toyora and the Kuruma zonations are difficult because the faunal

disagreement.

According to the comparisons among the North American Cordillera, the South

American and the standard zonations (Smith et aI., 1988; Jakobs et aI., 1994), the

zonal schemes of the Toyora and the Kuruma Groups are indirectly corresponded to

the South American zonation, as shown in Fig. 3-6. During Late Pliensbachian, the

A. stokesi, the Stokesi-Repressus and the lower part of the Margaritatus-aff.

Talrosei Assemblage Zones are correlated to the Fannini Zone, and the C. japonica

Zone, the upper part of the Margaritatus-aff. Talrosei Assemblage Zone and the

Canavaria-Emaciaticeras Assemblage Zone are compared to the Disciforme Zone

of the South American zonation. In the Toarcian of the Toyora Group, the P. paltus

and the D. helianthoides Zones are almost equal to the Tenuicostatum Standard

Zone of the South American zonal scheme, and the H. inouyei Zone is roughly

corresponded to the Hoelderi, the Largaense and the lower part of the Pacificum

Zones in South American province. The Pseudogrammoceras-Phlyseogrammoceras

Assemblage Zone seems to be compared to the upper part of the Copiapense Zone

and the lower part of the Tenuicostatum Zone represented by Phlyseogrammoceras

50

tenuicostatum (JAWORSKI).

3-4-5. Northeast Russia

In the Russian province, the ammonoid biostratigraphy from the Upper

Pliensbachian to the Toarcian have been mainly analyzed in five areas; the Russian

Platform, the Mediterranian Geosynclinal Belt, the Siberian Platform, the

Northeast Russia, and the Far East Russia. The regional ammonoid zonal schemes

were proposed by Dagis & Dagis (1965), Polbotko & Repin (1966, 1974) and Dagis

(1968, 1976) in the Omolon and the Korkadon Basin, the Northeast Russia, the

most maj or ammonoid source of the Russian province during this period.

The zonation of the Upper Pliensbachian was divided into three zones, the

Stokesi Zone, the Tarlosei Zone, and the Viligaensis Zone in ascending order. The

Late Pliensbachian assemblage from this province is characterized by the

co-occurrence of the Northwest European and the Russian endemic species of the

genus Amaltheus, the typical Boreal taxa in this period. Dagis (1976) discussed the

systematic evolution of the Russian endemic species and the biostratigraphic

correlation of the ranges of these species. The regional zonal scheme of the Upper

Pliensbachian was established on the basis of the evolutionary lineage of the genus

Amaltheus and was compared to the standard zonation. The Stokesi Zone,

represented by A. stokesi, was applied the Stokesi Subzone of the Northwest

European zonation. This zone was corresponded to the range of the index species,

and the fauna was associated with A. stokesi, Amaltheus bifurcus (HOWARTH) and

Amaltheus repressus DAGIS (Dagis, 1976; Repin, 1988). The Tarlosei Zone was

represented by Amaltheus tarlosei REPIN, the endemic species of the Russian

provinces. The fauna of this zone was associated with A. margaritatus, Amaltheus

subbifurcus REPIN, Amaltheus brodnaensis ventrocalvus REPIN, A. talrosei,

Amaltheus striatus asiaticus REPIN, Amaltheus bulunensis REPIN, Amaltheus

evolutus BUCKMAN, Amaltheus sensibilis DAGIS and Amaltheus conspectus DAGIS

(Dagis, 1976; Repin, 1988). This zone was corresponded to the Subnodosus Zone

and the lower part of the Gibbosus Subzones of the standard zonation. The

51

Viligaensis Zone was also represented by the Russian endemic species, Amaltheus

viligaensis (TUCHKOV), and was correlated to the upper part of the Gibbosus

Standard Subzone and the Spinatum Standard Zone. The assemblage of this zone

includes A. talrosei, Amaltheus brodnaensis brodnaensis REPIN, Amaltheus

borealis DAGIS, Amaltheus complanatus DAGIS, Amaltheus extremus REPIN and

Arieticeras (?) sp. aff. A. algovianum (OPPEL) in addition to the index species

(Dagis, 1976; Repin, 1988).

In the Kuruma Group, the Stokesi-Repressus Assemblage Zone is corresponded

to the Stokesi Zone of the Northeast Russian zonation on the basis of the

occurrence of the A. stokesi and A. repressus (Fig. 3-6). The Margaritatus-aff.

Talrosei Assemblage Zone is compared to the Talrosei Zone and the lower part of

the Viligaensis Zone because of the occurrence of A. margaritatus and A. aff.

talrosei from this assemblage zone (Fig. 3-6). The Canavaria-Emaciaticeras

Assemblage Zones is difficult to correlate directly to the Northeast Russian zones

because of the faunal disagreement. On the basis of the comparisons among the

Northeast Russian, the Mediterranean and the standard zonations in this study, this

assemblage zone is indirectly compared to the upper part of the Viligaensis Zone of

the Northeast Russian Zonation, as shown in Fig. 3-6.

In the Toyora Group, the A. stokesi Assemblage Zone is correlated to the

Russian Stokesi Zone because of the occurrence of A. stokesi from the Toyora

Group (Fig. 3-6). The base of the C. japonica Zone of the Toyora Group enables to

compare to the lower part of the Viligaensis Zone of the Northeast Russian

zonation because of the occurrence of A. margaritatus with the Apyrenum-type

surface ornaments (see above in detail)(Fig. 3-6).

The zonation of the Toarcian in Northeast Russia was subdivided into six zones,

the Propinquum Zone, the Falciferum Standard Zone, the Athleticum Zone, the

Monestieri Zone, the Polare Zone and the Rozenikrantzi Zone in ascending order.

The Propinquum Zone, represented by Tiltoniceras propinquum (WHITEAVES), was

subdivided into two beds. The lower bed was characterized by the occurrence of

Kedonoceras (=Orthodactylites) asperum DAGIS with Kedonoceras comptum DAGIS,

52

T. propinquum and Tiltoniceras costatum BUCKMAN, and the upper bed was

distinguished by Arctomercaticeras costatum REPIN associated with

Arctomercaticeras tenue REPIN and T. propinquum. The PIT boundary was drawn at

the base of the lower bed defined by the first occurrence of the subgenus

Orthodactylites, the genus Dactylioceras. The PIT boundary seems to be correlated

to the base of the Clevelandicum Subzone of the Northwest European zonation (Fig.

3-6), thus the Propinquum Zone is corresponded to the Clevelandicum, the

Tenuicostatum and the Semicelatum Subzones of the Tenuicostatum Zone proposed

in the Northwest European province (Fig. 3-6). Moreover, this boundary is

compared to the base of the D. helianthoides Zone proposed in the Toyora Group

(Fig. 3-6), because the base of this zone is also marked by the first occurrence of

the subgenus Dactylioceras (Orthodactylites), D. (0.) helianthoides. The

Falciferum Standard Zone was applied to the Falciferum Zone (=the Serpentinum

Zone) of the Northwest European zonal scheme. Thus, the base of the falciferum

Standard Zone in Northeast Russia enables to correlate to the base of the H. inouyei

Zone in the Toyora Group (Fig. 3-6). The Athleticum Zone, represented by

Dactylioceras athleticum (SIMPSON), was compared to the lower part of the Bifrons

Standard Zone (Fig. 3-6). The Monestieri Zone, represented by Zugodactylites

monestieri DAGIS, was corresponded to the middle to upper part of the Bifrons

Standard Zone, the Polare Zone, represented by Porpoceras polare (FREBOLD), was

correlated to the Uppermost Bifrons Zone, and the Rozenikrantzi Zone,

distinguished by Pseudolioceras rozenikrantzi (SIM:PSON), was compared to all over

the Upper Toarcian (Fig. 3-6). The upper boundary of the H. inouyei zone proposed

in the Toyora Group is roughly compared to the Monestieri Zone in Northeast

Russia, and the Pseudogrammoceras-Phlyseogrammoceras Assemblage Zone seems

to be corresponded to the upper part of the Rozenikrantzi Zone (Fig. 3-6).

4. Relationship between the ammonoid

paleoceanographic changes

53

paleobiogeographic and the

4-1. Aims of this chapter

The paleobiogeographic changes of marine biota enable to trace the long term

paleoceanographic changes, for example, global ocean circulation, sea water

temperature and sea level change. In Early Jurassic period, the paleobiogeography

of marine biota has been discussed in many taxa, including ammonoids (e.g.

Hallam, 1975; Macchioni & Cecca, 2002; Page, 2008), bivalves (e. g. Hallam, 1977,

1983; Liu et aI., 1998; Damborenea, 2002) and ostracods (Arias, 2006, 2007, 2008).

Above all, ammonoid is one of the most distinguished index taxa because of their

high biostratigraphic resolution.

The paleobiogeographic changes of the Jurassic ammonoid have been

discussed in a global scale. Arkell (1956) analyzed the worldwide Jurassic

ammonoid paleobiogeography by using the terms realm and province, and

recognized three realms as follows; the Boreal Realm (high latitudinal realm in the

Northern Hemisphere), the Tethyan Realm (low latitudinal realm) and the Pacific

Realm (endemic realm in the Eastern Pacific). Hallam (1975) decided the

boundaries between the Boreal and the Tethyan Realms globally on Pliensbachian,

Bathonian, Callovian and Tithonian. Page (2008) discussed the ammonoid

paleobiogeography through Jurassic period based on the recognition of marine

paleobiogeographic units (realm, subrealm, province and subprovince) proposed by

Westermann (2000a, b). In the Northern Hemisphere, four provinces including the

Arctic, the Subboreal, the Athabascan and the West Pacific provinces were

recognized in the Boreal Reahn, and four provinces, the Submediterranean, the

Mediterranean, the Ethiopian and the Andean provinces, were distinguished in the

Tethyan Realm during Late Pliensbachian and Toarcian. The East Pacific Realm

was also decided on the Athabascan and the Andean provinces by the occurrence of

endemic taxa in the East Pacific. Although these Early Jurassic ammonoid

paleobiogeographic studies have been analyzed mainly in Europe, North American

54

Cordillera and East Asia (Japan), it has not been discussed in West and Central

Asia because of the absence of ammonoid paleobiogeographic data. The lack of

these data has disturbed the discussions of ammonoid paleobiogeography in all

over the Northern Hemisphere. In contrast, the late Early Toarcian ammonoid

assemblage from Northern Tibet was recently described by Yin et al. (2006).

In Japan, the Early Jurassic ammonoid assemblages have been compared

individually with the European, the North American Cordillera, the West Asian and

the Madagascar faunas. Sato (1956) indicated that the assemblage from the

Teradani Formation, the Kuruma Group, was characterized by the mixing of a

Boreal taxon, the genus Amaltheus, and a Tethyan taxon, the genus Canavaria,

during Late Pliensbachian, although the fauna from the Nishinakayama Formation,

the Toyora Group, was' associated only with the Tethyan genera. Hirano (1973 b)

compared the faunas from the Toyora Group with that from outside Japan and

pointed out the faunal similarity between the Toyora and the Mediterranean or the

central European assemblages, associated with the Tethyan elements, during Late

Pliensbachian. According to Hirano (1973b), the Toyora assemblage showed high

similarity with the Alta Brianza, the Pyrenee and the Eastern Paris Basin faunas

during Early Toarcian, in addition to the high similarity between the Toyora and the

Eastern Caucasus faunas during Late Toarcian. However, a comprehensive and

detailed transitional pattern of late Early Jurassic ammonoid assemblages from

Japan has not been analyzed in previous studies. The global and the detailed

ammonoid paleobiogeography should be discussed by utilizing the more detailed

faunal association data of Japanese Early Jurassic ammonoid assemblages revealed

in this study. Therefore, the aims of this study are to analyze a comprehensive and

detailed chronological changes of the late Early Jurassic ammonoid faunal

compositions from Japan by using the assemblages from the Toyora and the

Kuruma Groups, to indicate the paleobiogeographical positions of each assemblage

by comparing with faunas from outside Japan, for example, the Northwest

European, the Mediterranean, the North Tibetan, the Iranian, the Southeast Asian,

the Northeast Russian and the Far East Russian provinces and to discuss the

55

paleoceanographic changes which affected the paleobiogeographic changes of late

Early Jurassic ammonoid assemblages in the Northern Hemisphere.

4-2. Paleobiogeographic changes of Japanese ammonoid assemblages

The paleobiogeographic changes of Japanese ammonoid assemblages are

discussed on the basis of Fig. 4-1, the ranges of each ammonite taxon obtained

from the Toyora and the Kuruma Groups are illustrated in the family or the

subfamily level.

4-2-1. Faunal characters of the assemblages from the Kuruma Group

As mentioned above, the ammonoid assemblage from the Stokesi-Repressus

and the Lower to Middle Margaritatus-aff. Talrosei Assemblage Zones of the

Kuruma Group, corresponded to the Margaritatus Standard Zone, is associated with

the genus Amaltheus (Fig. 4-1). The family Amaltheidae including the genera

Amaltheus, Amauroceras and Pleuroceras is dominant in the assemblages from

high latitudinal areas of the Northern Hemisphere, such as the Northwest European

and the Northeast Russian provinces. Dommergues et al. (1987) designated the

family Amaltheidae as a distinctive index taxon of the Boreal fauna. Thus, the

dominance of the genus Amaltheus in this assemblage indicates a high similarity

with the Boreal fauna of this period. In addition, the faunal specific composition of

this assemblage is characteristic in the mixing of Pan-Boreal species, A. stokesi and

A. margaritatus, and Russian endemic species, A. repressus and A. aff. talrosei.

The ammonoid assemblage from the upper part of the Margaritatus-aff.

Talrosei Assemblage Zone, corresponded to the Apyrenum Subzone of the standard

zonation, is mainly composed of the genus Canavaria, Canavaria nov sp. B, with a

few specimens of the genus Amaltheus, A. margaritatus (Fig. 4-1). The subfamily

Arieticeratinae (family Hildoceratidae), including the genus Canavaria and

Emaciaticeras, is typical in low latitudinal areas, for example, the Mediterranean

province (Braga, 1983), and has been regarded as one of the major Tethyan faunal

composition (e.g. Hallam, 1975). Therefore, this faunal association suggests that

l ,evesat.lei

So 5

Fig. 4-1 . Ranges of ach ammonit family or ub mily obt in from th Toyor nd h Kurum rouduring late Early Jura ic time (La e PH n b chi n-To rcian). Ammonoidzon I ch m in th orthwEuropean province folio Page (2003). u rieal g r from Gr d t in t I. (2004).

thi a embla e i charact nz d by th mrxm

fauna.

f th n th I thy' n

The assemblage from the anavarra- maciatic ra A mblag n ,

correlated to the Hawskerense ubzone of the standard nati n, i character ized

by a high di ersity of the subfamily Arieticeratinae associated with f u P C I of

the genus Canavaria Canavaria nov sp. A, C. aff. naxensis, aff. pro natum and

C. aff. haugi) and a species of the genus Emaciaticeras maciaticeras nov

sp. (Fig. 4-1. his assemblage is characterized by the dominance of the ethyan

index taxa.

57

The other ammonoid assemblage is obtained from the uppermost part of the

Teradani Formation exposed along the Teradani Valley (Figs. 3-4, 4-1), associated

with the subfamily Harpoceratinae, including Fuciniceras nakayamense and

Protogrammoceras sp., and the family Dactylioceratidae (Dactylioceras sp.). This

faunal association suggests the high similarity between this assemblage and that

from the Tethyan Realm. Although this assemblage enables to be roughly

corresponded to Early Toarcian on the basis of the existence of the genus

Dactylioceras, more detailed biostratigraphic correlations are disturbed by the poor

occurrence of the ammonoid specimens.

4-2-2. Faunal characters of the assemblages from the Toyora Group

The ammonoid specimens corresponded to the Stokesi Assemblage Zone were

obtained from the Higashinagano Formation, the Toyora Group. As mentioned

above, two materials were described as A. cf. stokesi and Arieticeras aff. apertum

by Hirano (1973b). These specimens suggest that the fauna from this assemblage

zone is characterized by the mixing of the Boreal and the Tethyan taxa (Fig. 4-1).

From the lower part of the C. japonica Zone correlated to the Apyrenum

Standard Subzone, two specimens of A. margaritatus are obtained along the South

Valley of the Sakuraguchidani Valley (Fig. 3-3). Therefore, this assemblage is

composed of the Boreal fauna (Fig. 4-1). In contrast, the assemblage from the

upper part of the C. japonica Zone, correlated to the Hawskerense Subzone of the

standard zonation, is associated with Canavaria japonica, the subfamily

Arieticeratinae (Figs. 3-3, 4-1). This faunal composition shows a high similarity

with that in the Tethyan Realm.

The ammonoid assemblages from the P. paltus and the D. helianthoides Zones,

biostratigraphically corresponded to the Tenuicostatum Standard Zone, is

dominated by a high-diversity of the subfamily Harpoceratinae (family

Hildoceratidae), such as the genera Protogrammoceras, Fuciniceras, Lioceratoides,

Paltarpites and Petranoceras, with some Arieticeratinae (F. fontanellense) in the

lower part of the P. paltus Zone and abundant Dactylioceratidae (D. helianthoides)

58

during the D. helianthoides Zone (Fig. 4-1). In addition to the subfamily

Arieticeratinae, some genera of the subfamily Harpoceratinae including all of these

taxa mentioned above are also dominant in the low latitudinal assemblages, for

example in the Submediterranean faunal province, thus this subfamily has been

regarded as the index taxa of the Tethyan Realm (e.g. Macchioni & Cecca, 2002;

Page, 2008). On the other hand, the family Dactylioceratidae has been regarded as

the pandemic paleobiogeographic character (e.g. Macchioni & Cecca, 2002).

Therefore, the faunal association indicates that this assemblage is the

Tethyan-derived fauna.

The ammonite assemblage from the H. inouyei Zone is dominated by some

Harpoceratinae genera, such as Harpoceras, Cleviceras, Polyplectus, Hildaites and

Lioceratoides, with some Dactylioceratidae (D. helianthoides, P. subfibulatum)(Fig.

4-1). During the early to middle Early Toarcian (Tenuicostatum and Serpentinum

Standard Zones), the ammonoid assemblages from the Boreal Realm, for example,

the Northwest European and the Northeast Russian provinces, are characterized by

the occurrence of the phylogeny of Cleviceras, constituted by the genera

Tiltoniceras, Eleganticeras and Cleviceras (Howarth, 1992). Some specimens of C.

cf. exaratum, also described previously in the Northwest European and the North

American provinces, are obtained from the H. inouyei Zone. In contrast, the other

genera of Harpoceratinae, such as Harpoceras, Polyplectus, Hildaites and

Lioceratoides, are mainly distributed in the Tethyan Realm. Thus, the assemblage

from the H. inouyei Zone is characteristic in the mixing of the Boreal and the

Tethyan faunas.

The Late Toarcian ammonoid assemblage fro In the Ishimachi Sandstone and

Mudstone Member, corresponded to the Fallaciosum Subzone (Thouarsense Zone)

and the Dispansum Zone of the standard zonation, is mainly composed of

Harpoceratinae (genus Osperlioceras) and Grammoceratinae (genera Grammoceras,

Pseudogrammoceras and Phlyseogrammoceras) with a few Dactylioceratidae and

Phylloceratina (Fig. 4-1). These taxa were mainly distributed in low and middle

latitudinal areas of the Northern Hemisphere during Late Toarcian. In contrast, the

59

fauna from the Boreal Realm including the Northwest European province and North

Alaska have been characterized by the occurrence of the genus Pseudolioceras in

the subfamily Harpoceratinae (e.g. Page, 2008). Consequently, the Late Toarcian

ammonoid fauna from the Toyora Group is associated only with the Tethyan index

taxa.

4-2-3. Faunal changes of Japanese ammonoid assemblages

On the basis of the paleobiogeographic faunal characters, seven ammonoid

assemblages are identified in East Asia (Japan) during late Early Jurassic time

(Late Pliensbachian-Toarcian).

In the Margaritatus Standard Zone, the first ammonoid assemblage associated

with the Boreal fauna is recognized from the Kuruma Group (Fig. 4-1). However,

this Boreal faunal composition is completely replaced by the Tethyan elements in

the third assemblage corresponded to the Hawskerense Standard Subzone, through

the second assemblage characterized by the mixing of the Boreal and the Tethyan

index taxa during the Apyrenum Standard Zone. The same faunal transition is also

detectable in almost coeval assemblage from the Toyora Group. Consequently, a

turnover from the Boreal fauna to the Tethyan fauna is recognizable in the Japanese

ammonite assemblages during the Apyrenum Standard Zone (Fig. 4-1). This

bio-event occurs in the Japanese assemblages is biostratigraphically earlier than

the timing of corresponded faunal change previously identified in the Northwest

European assemblages. The faunal replacement from the Boreal to the Tethyan

faunas, chronologically corresponded to Pliensbachian/Toarcian boundary, has

been mainly recognized in the Northwest European province (e.g. Dean et aI.,

1961; Macchioni & Cecca, 2002) and is characterized by the extinction of the

family Amaltheidae in whorl the Boreal Realm.

The Tethyan-derived faunal composition continues during the Tenuicostatum

Standard Zone (fourth assemblage obtained from the Toyora Group). However, the

faunal composition of the fifth assemblage corresponded to the Serpentinum and

the Lower-Middle Bifrons Standard Zones (Commune-Fibulatum Subzones) is

60

distinguished by the dominance of Tethyan Harpoceratinae with a few Boreal

elements, the genus Cleviceras. Therefore, a mixing of the Tethyan and the Boreal

faunal elements is recognized in East Asia during middle to late Early Toarcian

(Fig. 4-1). In contrast, the sixth ammonoid assemblage obtained from the middle

Upper Toarcian of the Toyora Group is composed of the Tethyan index taxa (Fig.

4-1), thus the faunal mixing seem to be limited in middle to late Early Toarcian.

During the Stokesi Standard Zone, the ammonoid assemblage from the Toyora

Group is characterized by the mixing of Boreal and the Tethyan faunal elements.

This faunal association differs from the Boreal-dominated faunal composition of

the coeval assemblage from the Kuruma Group (Fig. 4-1). This faunal disagreement

between the Kuruma and the Toyora assemblages during this time-interval seems to

reflect the latitudinal interval between these two localities.

4-3. International correlation of Japanese ammonoid assemblages

Faunal compositions of 13 faunal elements in seven time-intervals during Late

Pliensbachian to Toarcian and their geographic distribution in the Northern

Hemisphere are shown in Figs. 4-2, 4-3, 4-4, 4-5, 4-6, 4-7 and 4-8. The pie charts

are illustrated on the basis of the number of the specimens, fossil-bearing horizons

or associated species in each faunal element, distinguishable from the color of the

numbers shown at the center of these circles (to see Fig. 4-2 for the legend of the

colors). The paleogeographic map in late Early Jurassic time utilized in this

analysis is modified from the reconstructions of Damborenea (2002), Golonka

(2007) and Dera et al. (2010).

4-3-1. Stokesi Standard Subzone

As mentioned above, the Boreal fauna has been characterized by the

dominance of Amaltheidae during late Pliensbachian. In the Stokesi Standard

Subzone, the typical Boreal assemblages, such as Northeast Russia, Far East Russia,

Northern Caucasus, Brooks-Mackenzie Basin (North Alaska) and Western Scotland,

are composed of only Amaltheidae (Fig. 4-2). In addition, the fauna from Northeast

Fig. 4-2. Fau al com

Tul, B.C . (Sp)

1. ,1988:. 1992)

.)

62

Russia is characteristic in the dominant Russian-endemic species of the genus

Amaltheus, represent 93 % of the faunal composition.

The Tethyan assemblages distributed in latitude 300N or less is mainly

associated by Harpoceratinae and Arieticeratinae. In the Submediterranean faunal

province including Apennines (Italy), Subbetic (Southern Spain), Lusitania Basin

(Portugal), Bakony Basin (Hungary) and High-Atlas (Morocco), the assemblages

are dominated by Mediterranean Harpoceratinae, representing 42-92 % of the

faunal composition, with abundant Phylloceratina and Lytoceratina accounted for

94 % in maximum (Fig. 4-2). In the North American Cordillera province except for

Tulsequah (Northern British Columbia), it is difficult for the ammonoid

assemblages from this province to discuss the faunal correlation in subzonal level

because of the low biostratigraphic resolution of the North American regional

zonal scheme.Although the fauna from southern part of North American Cordillera,

such as Oregon (USA), Spatsizi (Northern British Columbia) and the Queen

Charlotte Islands, look to be characterized by the abundant occurrence of

Arieticeratinae, these faunal compositions seems to be mainly reflected by that of

the Subnodosus-Gibbosus Standard Subzones, because of the dominance of the

Tethyan elements, Harpoceratinae, in the Tulsequah fauna during the Ha wskerense

Standard Subzone. Moreover, the mixing of the Boreal and the Tethyan faunas are

recognizable in the assemblages from the Causses Basin (France) and Tulsequah

(Northern British Columbia), located around latitude 30oN.

The fauna from the Kuruma Group in the Stokesi Standard Subzone is

dominated by the Northwest European species of the genus Amaltheus,

representing 75 % of the faunal composition, with some Russian endemic

Amaltheus species (Fig. 4-2). This association indicates high faunal similarity

between the Kuruma and the Northeast Russian assemblages. In contrast, the

mixing of Amaltheidae and Arieticeratinae recognized in the fauna from the Toyora

Group is also distinguishable in the Tulsequah fauna. Thus, the assemblage from

the Toyora Group is somewhat similar with that from Northern British Columbia

during this time-interval.

63

4-3-2. Subnodosus-Gibbosus Standard Subzones

As well as the Stokesi Standard Subzone, the Boreal fauna during the

Subnodosus-Gibbosus Standard Subzones IS identified by the dominant

Amaltheidae, recognized in Scotland, England, Northeast Russia, Siberian Platform

(Russia) and Northern Caucasus assemblages (Fig. 4-3). The Russian endemic

species of the genus Amaltheus are mainly distinguishable in the Northeast Russian

and the Siberian Platform assemblages, representing about 55 % of the faunal

composition. The assemblage from the Kuruma Group in this time-interval is

dominated by the Northwest European species of the genus Amaltheus with some

Russian endemic Amaltheus (eight percents of the faunal composition), thus, is

similar with the Northeast Russia and the Siberian Platform assemblages (Fig. 4-3).

In contrast, the Tethyan fauna of the Subnodosus-Gibbosus Standard Subzone

IS generally characterized by the dominance of Arieticeratinae (representing

46-94 % of the composition) which is recognizable in the assemblages from

Apennines, Subbetic, the Bakony Basin, Jebel Zaghouan (Tunisia), Oregon,

Spatsizi and Eastern Caucasus. In addition to Arieticeratinae, the abundant

occurrences of Harpoceratinae are characteristic in High-Atlas, Lycia Allochton

(Turkey), the Queen Charlotte Islands and Vietnam assemblages (Fig. 4-3). The

dominance of Phylloceratina and Lytoceratina in the Bakony Basin, the Lusitania

Basin and Lycia Allochton, representing 27-58 % of the faunal composition,

enables to except for this paleobiogeographic discussion because of the pandemic

distribution of these suborders. The assemblages from North American Cordillera

are characteristic in also the genus Fanninoceras (6-37 % of the faunal

composition), the endemic genus of Harpoceratinae in Cordillera. According to the

distribution of the mixing fauna of the Boreal and the Tethyan elements

distinguished in the Causses Basin, the Lusitania Basin, Tulsequah and Far East

Russia, the boundary between the Boreal and the Tethyan Realms enables to be

drawn around latitude 300N as well as the Stokesi Standard Zone, except for the

remarkable distribution of the Far East Russian fauna (Fig. 4-3).

J

B kony B(Geczy &

1 8)

c;

Fig. -3. Faunal coSubzo e . Legend ofSpatsizi in 8ri . Colu

65

4-3-3. Apyrenum Standard Subzone

In the Apyrenum Standard Subzone, the assemblages from the Boreal Realm

are characterized by the dominance of Amaltheidae including the genus

Pleuroceras, the Russian endemic species of the genus Amaltheus and A.

margaritatus, in addition to the genus Tiltoniceras which is mainly distributed in

high latitudinal areas of the Northern Hemisphere. The typical Boreal fauna

recognized in Northeast Russia, Western Scotland, England and the Causses Basin

are composed of almost only Amaltheidae (Fig. 4-4), especially the Northeast

Russian fauna is dominated by the Russian endemic species of the genus Amaltheus

(97 % of the faunal composition).

The Tethyan faunas in this time-interval are mainly composed of

Harpoceratinae (distinguished in High-Atlas, Subbetic and the Queen Charlotte

Islands) or Arieticeratinae (recognizable in Oregon)(Fig. 4-4). The assemblage of

Far East Russia, biostratigraphically compared to this time-interval by Repin

(1988), is probably corresponded to the Hawskerense Standard Subzone on the

basis of their faunal association including the genus Paltarpites and C. japonica.

The assemblages from the Bakony Basin and Apennines, paleogeographically

located at the eastern edge of the Western Tethys, are dominated by Phylloceratina

and Lytoceratina (representing about 75 % of the faunal composition) with some

Hildoceratidae (Harpoceratinae and Arieticeratinae) and a few Amaltheidae. The

mixing of the Boreal and the Tethyan faunas is distinguishable in the assemblages

from Subbetic, the Queen Charlotte Islands, Spatsizi and Tulsequah. In North

American Cordillera except for Oregon, the Boreal elements are mainly associated

with the genus Tiltoniceras and the Northwest European Amaltheidae, however the

former taxon is absent in the coeval European faunas. During the Apyrenum

Standard Subzone, the boundary between the Boreal and the Tethyan Realms IS

removed southward and is drawn around latitude 300N (Fig. 4-4).

The fauna from the Kuruma Group in the Apyrenum Standard Subzone is

characterized by the dominant Arieticeratinae, representing 83 % of the faunal

composition, with some Northwest European species of the genus Amaltheus (Fig.

Or on (Or)(Iml y. 1968:

Smith l I. 1 8),

in (l u) /

~I

1. .2007) /I

I/

0

<> /

Fig. 4-4. Faunal coSubzone. Legend of e u er( orth American Cordillera). SEast (Russia) are com 0 0

67

4-4). Although this faunal association indicates the mixing of the Boreal and the

Tethyan faunas, no similar composition, characterized by the dominance of

Arieticeratinae with some Amaltheidae, are recognizable in the Northern

Hemisphere. In contrast, the assemblage from the Toyora Group in this

time-interval is composed of only the Northwest European species of the genus

Amaltheus, and show a high similarity with those of the Boreal fauna. However,

this assemblage does not seem to be reflected by the original faunal composition

sufficiently, because of the small amount of the specimens.

4-3-4. Hawskerense Standard Subzone

The genus Pleuroceras, the Russian endemic species of the genus Amaltheus

and the genus Tiltoniceras are regarded as the Boreal faunal elements during the

Hawskerense Standard Subzones. In the Northwest European province, the Boreal

faunas are characterized by the dominance of the genus Pleuroceras (representing

more than 86 % of the faunal composition), recognizable in Western Scotland,

England and the Causses Basin (Fig. 4-5). In contrast, the fauna from Northeast

Russia is dominated by the Russian endemic species of the genus Amaltheus. A

specimen of Amaltheus viligaensis TUCHKOV, one of a typical endemic species of

the Russian province in this time-interval, was also reported in the Queen Charlotte

Islands (Smith et al., 1988).

In the Tethyan Realm, the ammonoid assemblages are mainly composed of

Harpoceratinae, Arieticeratinae and Phylloceratina/Lytoceratina in this subzone.

The assemblages from the Submediterranean faunal province are generally

characterized by the dominant Arieticeratinae (36-84 % of the faunal composition),

especially in Subbetic, Apennines and High-Atlas (Fig. 4-5). This trend is also

recognized in Japanese assemblages, representing 94 % in the Kuruma Group and

100 % inthe Toyora Group. This means that the faunal composition of the Japanese

assemblages show a high similarity with that of the Submediterranean faunal

province, especially the High-Atlas fauna. In contrast, the faunas from Jebel

Zaghouan (Tunisia), Lycian Allochton (Turkey) and Far East Russia are dominated

68

by Harpoceratinae, representing 45-97 % of the faunal compositions.

The faunas from the Lusitania and the Bakony Basins are associated with

dominant Harpoceratinae, Arieticeratinae and Phylloceratina/Lytoceratina with rare

Boreal elements, such as the genera Pleuroceras and Tiltoniceras (Fig. 4-5). In the

North American Cordillera province, including the Queen Charlotte Islands,

Tulsequah and Spatsizi, the fauna is characterized by the mixing of the Tethyan

elements and the genus Tiltoniceras. These mixed faunas are distributed around

latitude 30 oN .

Engl nd (En)(Howarth . 1992

Simm et 1. .2010),Braa - c nz

B in (Br)(Paul on. 1991)

... )

Fig. 4-6. Faunal cornoosmonsZone. Lege d of e

S ard

70

The assemblage from the Toyora Group in the Tenuicostatum Standard Zone is

composed of the dominant Harpoceratinae (67 % of the faunal composition) with

Arieticeratinae (genus Fontanellicerasv, Dactylioceratidae (genus Dactylioceras)

and Lytoceratina (Fig. 4-6). This faunal association is similar with the

Submediterranean faunas. Especially, the diversified generic composition of

Harpoceratinae from the Toyora Group including the genera Paltarpites,

Protogrammoceras, Fuciniceras, Lioceratoides and Petranoceras has a high

similarity with that from Apennines in this time-interval.

4-3-6. Serpentinum and Lower to Middle Bifrons Standard Zones

As well as the Tenuicostatum Standard Zone, the pandemic distribution of the

genus Dactylioceras is also distinguishable in the Serpentinum and the Lower to

Middle Bifrons Zone (including the Commune and the Fibulatum Standard

Subzones).

The Boreal Realm fauna during the Serpentinum Zone is characterized by the

dominance of the genera Eleganticeras and Cleviceras. The phylogeny of

Cleviceras constituted by the genera Tiltoniceras, Eleganticeras and Cleviceras

was proposed by Howarth (1992) and has been regarded as a Boreal element from

latest Pliensbachian to middle Early Toarcian (e.g. Page, 2008). In addition, the

Boreal fauna from the Bifrons Standard Zone and the Upper Toarcian are identified

by the occurrence of the genus Pseudolioceras (Harpoceratinae)(e.g. Page, 2008).

The Boreal type assemblages of this time-interval are mainly recognized in the

Russian province, such as Northeast and Far East Russia (Fig. 4-7).

The Tethyan Realm during this time-interval is characterized by the dominant

occurrence of some Harpoceratinae genera, for example, Harpoceras, Hildaites,

Hildoceras and Ovaticeras (e.g. Macchioni & Cecca, 2002; Page, 2008). These

genera account for 56 % of the faunal composition and are co-occurred with some

characteristic taxa containing the subfamily Mercaticeratinae (Hildoceratidae) in

the Mediterranean province, including Apennines and Algeria (Fig. 4-7). The

Tethyan-derived fauna are also recognized in West and Southeast Asia (Iran,

a d

( 0 )ort

.C. )

in (C )S)

w. Scotl nd (Sc)(Howarth . 1992;

Simm at at., 2010)•

Fig. 4-7. Faunal compositio of e" a etementsMiddle Bifrons S andard Zo es. Lege doe n l u." h.c~r

72

Vietnam and Kalimantan).

The assemblage from the Toyora Group is associated with the dominant

Mediterranean Harpoceratinae, representing 57 % of the faunal composition, with

some Arctic Harpoceratinae (C. cf. exaratum), Dactylioceratidae (genera

Dactylioceras and Peronoceras) and Phylloceratina/Lytoceratina. This faunal

composition, characterized by the mixing of the Tethyan and the Boreal faunas,

shows a high similarity with that of the Northwest European province, especially

the Causses Basin fauna (Fig. 4-7). These mixed faunas are also distributed in

North American Cordillera and Northern Caucasus. In contrast, the assemblage

from Northern Tibet, paleogeographically near the Toyora Group, is dominated by

Arctic Harpoceratinae, such as the genus Cleviceras (Yin et al., 2006).

4-3-7. Fallaciosum Standard Subzone and Dispansum Standard Zone

As mentioned above, the Boreal ammonite fauna during Late Toarcian IS

distinguished by the dominance of the genus Pseudolioceras (e.g. Page, 2008). The

typical Boreal fauna recognized in the Brook-Mackenzie Basin, Northern Alaska, is

characterized by the occurrence of Pseudolioceras lectum (SIMPSON) and was

roughly corresponded to the Thouasense Standard Zone (Poulton, 1991).

In contrast, the Tethyan faunas in the Fallaciosum Standard Subzone

(Thouasense Standard Zone) and the Dispansum Zone are characteristic in the

dominance of Hildoceratidae including Harpoceratinae, Grammoceratinae and

Paroniceratinae, except for the genus Pseudolioceras (e.g. Page, 2008). The

Northwest European, the West Asian, the Northern Caucasian and the Southeast

Asian (Roti; Indonesia) faunas are dominated by the subfamily Grammoceratinae.

The assemblages from the southern part of the Northeast European province, such

as the Causses and Lusitania Basins, are composed of the various taxa including

Harpoceratinae, Grammoceratinae, Paroniceratinae and Hammatoceratidae (Fig.

4-8). The fauna from North American Cordillera, recognizable in the Queen

Charlotte Islands, is distinguished by the dominant Phymatoceratidae, representing

72 % of the faunal composition, with some Tethyan elements.

welatemnann.

Toyor G. ( 0)(Th' y)

••En I nd (En)

(Simm at al.. 2010)

e a S ar

74

The assemblage from the Toyora Group is characterized by the abundance of

the genus Osperlioceras (Harpoceratinae) and Grammoceratinae (including the

genera Grammoceras, Pseudogrammoceras and Phlyseogrammoceras)(see chapter

3 and Fig. 4-8). The generic composition of this assemblage shows a high

similarity with that of the assemblage from the Causses Basin, located in the

Submediterranean faunal province of the Tethyan Reahn.

4-4. Discussion of the paleoceanographic change in the Northern Hemisphere

4-4-1. Early Jurassic paleoenvironmental changes in the Northern Hemisphere

Among the various paleoceanographic elements, the fluctuations of sea level

and seawater temperature are attracted for considering the origin of the late Early

Jurassic ammonoid paleobiogeographic changes in the Northern Hemisphere. The

faunal changes of Japanese ammonoid assemblages analyzed in this study are

illustrated in Fig. 4-9, with the paleobiogeographic faunal changes of the European

ammonoid assemblages (Macchioni, 2002), the strontium isotope fluctuation

(87 Sr/86 Sr) analyzed in Yorkshire, England (Jones et al., 1994; McArthur et al.,

2000), the oxygen isotope excursion ( D 180 ) in Yorkshire (McArthur et aI., 2000;

Bailey et al., 2003), Dotterhausen and Aselfingen (both in Germany; Bailey et al.,

2003) and the seawater temperature fluctuations calculated by the composite D180

data (Dera et al., 2009a).

4-4-1-1. Sea level changes

The sea level changes during the Jurassic period have been analyzed in

utilizing various techniques by Hallam (1978, 1988, 2001), Vail & Todd (1981),

Haq et al. (1988), Sulyk (1991), Li & Grant-Mackie (1993), Legaretta & Uliana

(1996), de Graciansky et al. (1998) and Hardenbol et al. (1998). Hallam (1978,

1988) proposed the shallowing and deepening cycles in Europe by using the

combination of facies analyses. The sea level curves through the Jurassic time were

illustrated in the North Sea by Exxon team on the basis of the seismic stratigraphic

analysis (Vail & Todd, 1981) and sequence stratigraphic analysis (Haq et aI., 1988).

9 Ea Ju a ic

87Sr Sr 8 180 ( POS)(0

•0

0 0 0 0

~ ~ ~ ~~ ::! jj

0 ., ·2 -J0 (II 0 tit

Ter dani F.,Kuruma Group

(This study )

Mactra

FluitansAalensis

P udo dio

c:ro

Northwe t European Provine(Page , 2003)

roo~

182?

c:.~ Spin tums:oCO.c G' u(/)c:

.~a.. rg S

186 Q)-ro S...J

ILFig. 4-9. Relatio ip a eta E

180

(M) St. Zone Subzone

178

176

76

According to Haq et al. (1988), the sea level during Early Jurassic was generally

rising from Hettangian to Toarcian. Similar eustatic carves have been also

proposed in East Greenland (Sulyk, 1991), Southern Tibet (Li & Grant-Mackie,

1993) and west-central Argentina (Legaretta & Uliana, 1996). In contrast, the

second order transgressive-regressive cycles during late Early Jurassic time (Late

Pliensbachian and Toarcian) were revealed both in the Northwest European and the

Mediterranean provinces by de Graciansky et al. (1998). According to de

Graciansky et al. (1998), two regressions (Lower Pliensbachian-lower part of the

Margaritatus Standard Zone and Upper Toarcian-Aalenian) and a transgression

(middle to upper part of the Margaritatus Standard Zone-Bifrons Standard Zone)

were recognized in the Northwest European province, and two regressions (middle

to upper part of the Margaritatus Standard Zone-lower part of the Tenuicostatum

Standard Zone and Upper Toarcian-Aalenian) and two transgressions (Lower

Pliensbachian-lower part of the Margaritatus Standard Zone and upper part of the

Tenuicostatum Standard Zone-Bifrons Standard Zone) were distinguished in the

Mediterranean province.

On the other hand, the Sr isotope fluctuation has been considered to reflect the

eustatic sea level changes during late Early Jurassic (Hallam, 1997; Cope, 1998),

because the Sr isotope ratio is controlled by the amount of the detrital fluxes which

are relevant to the erosion of continents. Jones et al. (1994) analyzed the Sr isotope

ratio in the Lower Jurassic succession exposed in Yorkshire, England, for the first

time (Fig. 4-9), and recognized a negative excursion from Hettangian to

Pliensbachian and a positive shift in Toarcian. McArthur et al. (2000) showed the

high-resolution Sr isotope fluctuation of belemnites obtained from the same section

of Jones et al. (1994)(Fig. 4-9). Cohen et al. (2004) suggested that the abrupt

positive shift of the Sr isotope ratio in the Exaratum Standard Subzone, analyzed

by McArthur et al. (2000), was reflected in the global warming which has been

considered as the trigger of the Early Toarcian OAE and enhanced the chemical

weathering of continents.

77

4-4-1-2. Sea surface temperature changes

Oxygen isotope excursions (D 180 ) have been considered as an important

paleoenvironmental proxy for reflecting the seawater temperature. The numerous

data of D 180 have been analyzed in the European Lower Jurassic successions by

using the various taxa including belemnite, bivalve, planktonic foraminifera and so

on. Especially, the D 180 data from the Lower Toarcian have been attracted for

discussing the causes of the Early Toarcian OAE (Jenkyns & Clayton, 1986;

McArthur et aI., 2000; Bailey et aI., 2003; Rosales et aI., 2004; Gomez et aI., 2008;

Dera et aI., 2009b).

The D 180 profiles of belemnite have been regarded as the index of sea surface

temperature and have been examined in several regions in Europe, such as

Yorkshire (McArthur et aI., 2000; Bailey et aI., 2003), the Paris Basin (Dera et aI.,

2009b), the Southern German Basin (Bailey et aI., 2003) and Northern Spain

(Rosales et aI., 2004; Gomez et aI., 2008). According to the D 180 records of

belemnite in Yorkshire and the Southern German Basin analyzed by McArthur et al.

(2000) and Bailey et aI. (2003)(Fig. 4-9), a prominent negative shift was

distinguishable from the Apyrenum Standard Subzone to the Exaratum Standard

Subzones, in addition to two gentle positive excursions recognized in the

Subnodosus Standard Subzone and the Serpentinum Standard Zone. On the basis of

these geochemical fluctuations, the presence of a cooling during Late

Pliensbachian (Margaritatus Standard Zone) and an abrupt warming during Early

Toarcian (Tenuicostatum Standard Zone and Exaratum Standard Subzone) have

been distinguished in Europe (e.g. Bailey et aI., 2003; Dera et al., 2009b). This

strong positive excursion suggesting the abrupt warming event is stratigraphically

corresponded to the strong positive shift of the Sr isotope ratio which mentioned

above (Fig. 4-9). The profile of the sea surface temperature calculated by the

composite D 180 data of belemnite is illustrated in Fig. 4-9.

78

4-4-2. Paleoceanographic changes on the basis of the ammonoid faunal changes

4-4-2-1. Latest Pliensbachian faunal turnover

As mentioned above, a turnover from the Boreal to the Tethyan faunas in the

Apyrenum Standard Subzone is recognizable in the late Early Jurassic ammonoid

assemblages from Japan (Figs. 4-1, 4-9). This turnover is biostratigraphically

coeval with the beginning of the warming mainly distinguished from the

Tenuicostatum Standard Zone to the Exaratum Standard Subzone in Europe (Fig.

4-9). The fluctuation of seawater temperature enables to regard as one of the

important factors which affect the paleobiogeographic faunal changes of

ammonoids. These Tethyan-dominated faunal compositions of the Japanese

assemblages are quite different with the association of the Northwest European

fauna, characterized by the abundant occurrence of Amaltheidae, in the

Hawskerense Standard Subzone. The Northwest European province was perhaps

paleolatitudinally correspondent to Japan in late Early Jurassic time on the basis of

the paleogeographic continental distribution (e.g. Golonka, 2007). Therefore, the

dramatic faunal change of Japanese assemblages in the Apyrenum Standard

Subzone is chronologically discordant for the comparable faunal turnover,

characterized by the extinction of Amaltheidae and corresponded to the

Pliensbachian/Toarcian boundary, in the almost equal latitudinal regions in the

western Tethys, such as the Causses Basin and England (Figs. 4-4, 4-5, 4-9). The

additional paleoceanographic factors are required for accounting this disagreement

of faunal compositions between the Japanese and the Northwest European

assemblages during latest Pliensbachian.

The recognition of the Tethyan-derived fauna in Japanese assemblages is

synchronous with the eustatic low stand of sea level during latest Pliensbachian

(Spinatum Standard Zone) to earliest Toarcian (Tenuicostatum Standard Zone) on

the basis of the Sr isotope ratio in Yorkshire (Fig. 4-9). On the basis of the

high-resolution ammonoid biostratigraphy, the presence of reworking and the

condensation of ammonoids have been distinguished in England and Digne area

(South France) by de Graciansky et al. (1998) and Guex et al. (2001). Macchioni

(A) arga -t tu tan..ard 0 (

~-

Fig. 4-10. Schema ic repre enta 'on 0 e s eaStandard Subzone.

rnrn,nnJ"l.at"t· tau as ,.n~ r;'+~h S S a (B)

80

(2002) suggested that this phenomenon was caused by the regression recognized in

latest Pliensbachian-earliest Toarcian. The uppermost Pliensbachian-lowermost

Toarcian succession in the Northwest European province are mainly composed of

the shallow marine sediments, such as mudstone, sandstone, limestone and

ironstone (Guex et al., 2001; Simms et al., 2010).

The uppermost Pliensbachian-lowermost Toarcian Far East Russian and North

Alaskan successions are also composed of the shallow marine clastic deposits

(mudstone and sandstone)(Poulton et al., 1992; Sey et al., 1992). The coeval South

Alaskan successions are lacked by the unconformity (Poulton et al., 1992).

According to Golonka (2007), these sediments were deposited in the shallow

marine, distributed between the North American and the Eurasian continents and

divided the Anui Ocean (Zonenshain et al., 1990; Senger & Natalin, 1996; Golonka

et al., 2003) from the Panthalassa. In the Margaritatus Standard Zone, the Boreal

elements, such as Amaltheidae, were diffuse from the high to the middle latitudinal

areas through this seaway, decided Paleo-Bering Strait in this study (Fig. 4-10).

However, the shallowing of this seaway affected by the regression during latest

Pliensbachian and earliest Toarcian perhaps disturbed the spreading of the Boreal

faunal elements from the Anui Ocean to the Panthalassa (Fig. 4-10). Consequently,

the disappearance of Amaltheidae and the domination of the Tethyan elements

recognized in the latest Pliensbachian ammonoid assemblages from Japan reflected

the shallowing of Paleo-Bering Strait caused of the global regression.

4-4-2-2. Early Toarcian faunal mixing

The mixing of the Boreal and the Tethyan faunas of the Toyora assemblage is

distinguishable in the Exaratum Standard Subzone and the Lower to Middle Bifrons

Standard Zone. During this time-interval, the eustatic sea level had been rose in

high stand (McArthur et al., 2000), almost equal to that of the Margaritatus

Standard Zone (see Fig. 4-9). This transgression allowed the spreading of the Early

Toarcian Boreal elements (phylogeny of Cleviceras) to the Panthalassa through

Paleo-Bering Strait (Fig. 4-11). In addition, the slight and coeval cooling was

(C) nu·co t m ~~I"~~r Zo ( )

Fig. 4-11. Sc ernatic represeSerpentinum and the Ea y

. (C) nuicostatum S e a (0)

82

proposed on the basis of a small positive excursion of the 5 180 fluctuation in

Europe (Fig. 4-9). Thus, the faunal mixing of Japanese assemblage in this

time-interval is affected by the global transgression and the cooling. In the

Exaratum Standard Subzone, the faunal mixing in the European ammonoid

assemblages reduced the provincialisms In the European ammonoid

paleobiogeography (Dera et al., 2010). This faunal equation also seemed to be

affected by the coeval and abrupt transgression.

83

5. Geochemical analyses of the Early Toarcian OAE in East Asia

5-1. Aims of this chapter

Deposition of organic black shales in the Lower Toarcian has been recognized

in the Northwest European province. Jenkyns & Clayton (1986) analyzed the stable

carbon isotope record of bulk carbonate ( 8 13Ccarb) through the Lower Toarcian

succession and showed a positive shift of 013Ccarb at the black shale horizon. On the

basis of this fluctuation into the black shale, corresponded biostratigraphically in

the Falciferum Zone (= the Serpentinum Zone in this study), the sedimentation of

the black shale was considered as the Early Toarcian Oceanic Anoxic Event (OAE).

Jenkyns (1988) suggested that this phenomenon was the global environmental

change because of the 'worldwide distribution of the black shale, including the

Northwest European province, the Mediterranean province, the North American

Cordillera province, the South American province, the East Asian (Japan) province,

Madagascar and Australia (Fig. 1-2). This event has been studied in detail in

Europe from various viewpoints as follows; (i13C (e.g. Jenkyns & Clayton, 1986,

1997~ Jenkyns, 1988~ Hesselbo et al., 2000, 2007~ Schmid-Rohl et al., 2002~ Cohen

et al., 2004~ Gomez et al., 2008~ Hermoso et al., 2009), (i180 (e.g. McArthur et al.,

2000~ Bailey et al., 2003~ Rosales et al., 2004; Gomez et al., 2008; Dera et al.,

2009b), Os isotope (Cohen et al., 2004), major/trace elements (Bellanca et al.,

1999; McArthur et al., 2000; Bailey et al., 2003), trace fossil contents (Parisi et al.,

1996) and distribution of clay minerals (e.g. Dera et al., 2009a). Moreover, this

phenomenon is recorded not only in continental shelf sediments but also pelagic

successions. Hori et al. (2000) showed the positive excursions of V/Ah03 ratios in

the Toarcian black chart succession exposed in the Katsuyama Section, central

Japan, suggesting the effect of the Early Toarcian OAE. The pelagic black

mudstone were recognized in Slovenia by Gorican et al. (2003), also considered to

deposit under the Toarcian OAE.

In contrast, the relationship between the Early Toarcian OAE and the mass

extinction event in epicontinental marine environments have been also discussed in

84

various taxa including ammonoids, bivalves, rhynchonellid brachiopods,

ostracodes, belemnites and dinoflagellates (Raup & Sepkoski, 1984, 1986; Hallam,

1996; Hallam & Wignall, 1997; Aberhan & Fursich, 1997, 2000; Harries & Little,

1999; Fursich et al., 2001; Macchioni & Cecca, 2002; Cecca & Macchioni, 2004;

Dera et al., 2010). This extinction has been regarded as the global bio-event on the

basis of data from northern Siberia (Zakharov, 1994) and the Andean Basin

(Aberhan & Fursich, 1997, 2000). Moreover, this event also has been recognized in

pelagic environment with the extinctions of radiolarians and calcareous

nannofossils (Hori, 1997; Gorican et al., 2003). Especially in ammonoids, two

mass extinction events were recognized in both the Northwest European and the

Mediterranean provinces around the Upper Pliensbachian-Lower Toarcian (seven

ammonoid zones, about 4.7My) by Macchioni & Cecca (2002) and Cecca &

Macchioni (2004). The first bioevent took place at the Pliensbachian/Toarcian

boundary which is connected with the extinction of Boreal type ammonoids and sea

level fall, while the second mass extinction took place at the uppermost part of the

Semicelatum Subzone of the standard zonation which corresponds to the beginning

of the Early Toarcian GAE. This extinction is characterized by the diversity fall

and the increasing value of extinction. In addition, the diversity of endemic species

significantly fell at this horizon.

In Japan, the existence of the Toarcian GAE was discussed in the

Nishinakayama Formation of the Toyora Group by Tanabe (1991) and Izumi &

Tanabe (2010). The middle part of the Nishinakayama Formation, composed of

laminated, bituminous black mudstones with sedimentary pyrite, is characterized

by the macrofauna which consists of nekton and pseudoplanktonic bivalves. On the

basis of these faunal compositions, Tanabe (1991) suggested the existence of the

Early Toarcian GAE in the Toyora Group. In addition, Izumi & Tanabe (2010)

showed the effect of the Toarcian OAE in the middle to the upper part of the Lower

Nishinakayama Formation on the basis ofthe negative carbon isotope excursion of

organisms ( 0 13Corg) and the low trace fossil content. However, contributions about

the Toarcian GAE from the Asian regions are still limited, although the Toarcian

85

GAE and the related mass extinction have been regarded as the global event. The

aims of this study are to determine the paleochemical environment of the East

Asian province during Early Toarcian by the trace element and the rare earth

element (REE) analyses, and to discuss the effect of the OAE, including the

extinction of marine macro biota, in the western Panthalassa.

5-2. Materials and analytical methods

Twenty-eight samples of mudstones from the Sakuraguchidani Valley were

analyzed as whorl rock in terms of trace element and REE geochemistry. Almost all

of these specimens were collected from the North Valley of the Sakuraguchidani

Valley except for a material from bed 41-1 exposed along the South Valley (Fig.

5-1).

Major and trace element concentrations were measured by X-ray fluorescence

(XRF) spectrometry, using a Rigaku RIX 3000 system at the Faculty of Science,

Niigata University. Glass disks were prepared by fusing rock powder sample (0.5

g) with lithium tetraborate (LbB407 , 5.0 g) for major element analysis, and rock

powder sample (1. 8 g) with lithium tetraborate (2.88 g) and lithium metaborare

(LiB02, 0.72 g) for trace element analysis. Detailed analytical procedures have

been described by Takahashi & Shuto (1997).

REE and Li, Sc, Co, Zn, Ga, Cs, Hf, Ta, Th and U abundances were determined

by using an inductively coupled plasma-mass spectrometer (ICP-MS; Agilent

7500a) at the Faculty of Science, Niigata University. Whorl rock powder (0.1 g)

was dissolved in an HF -HN03 mixture on a hotplate, followed by fusion with

Na2C03 (0.5 g) at 1,050°C. The solution was neutralized with HN03+HCl and

diluted by a factor of 20,000 with a mixture of HF -HN03-HCl. A single solution of

USGS reference material (BHYO-2) was utilized as an external calibration

standard, using reference values of Eggins et al. (1997). Sensitivity variation

during the analytical runs was corrected by using four internal standards (In, Re,

Bi). External standardization was performed for individual elements in unknown

samples by interpolation of results for replicate analyses of BHVO-2 after 5-6

86

unknown samples. Analytical quality was examined by comparing the results of

this analysis for USGS reference materials, JG-1a and W-2a with literature values.

The data of this study are consistent with literature values within 5 % deviation for

all elements, although results for other than REE are not shown.

5-3. Results

Geochemical data for the black mudstone samples from the Sakuraguchidani

Valley, including V/Ah03, U/Ah03, Ba/Ah03, Ni/Ah03, Zr/Ah03, Cr/Ah03,

Co/Ah03, Th/U, Ce/Ce* and Eu/Eu*, are shown in Figs. 5-1, 5-2, 5-3 and

Appendix 5-1. The fluctuations of 8 13Corg and Lamina Preservation Index (LPI)

shown in Figs. 5-1 and 5-2 were also analyzed in the North Valley of the

Sakuraguchidani Valley by Izumi & Tanabe (2010). The ammonite zonal scheme of

the Toyora Group in Figs. 5-1 and 5-2 are proposed in this study (see chapter 3).

5-3-1. Trace element concentrations

The results of various trace element fluctuations illustrated in Figs. 5-1 and 5-2

are normalized by Ah03 because these elemental concentrations are affected by the

amount of the detrital flux. Al concentration is regarded as a good proxy for

analyzing the fluctuation of the flux (e.g. Bellanca et aI., 1999).

Overall, U, Zr and Cr concentrations are relatively uniform through the

Sakuraguchidani Mudstone Member (Figs. 5-1, 5-2). Th/U fluctuation mostly

follows the same pattern except for three small positive shifts at beds 19-5b, 21-1

and 24-4 and three small negative shifts at beds 19-1b, 20-3b and 28-1 (Fig. 5-2).

Concentrations of V, Ba, Ni and Co strongly increase during the lower part of

the Sakuraguchidani Mudstone Member, almost all of these shifts are corresponded

to the P. paltus Zone (Figs. 5-1, 5-2). Synchronous shifts to higher values for V and

Co are recognized at bed 18-1 c, which is associated with a small shift in Ni (Figs.

5-1, 5-2). The V concentration increases slightly during the upper part of the H.

inouyei Zone with two small positive shifts at beds 26-1 and 28-1 (Fig. 5-1). The

Co fluctuation also has some small positive peaks, for example, at beds 25-5 and

VIA120 3

Fig. 5-1 . Co u arin parallel colu s. ecolumnar ion is as i

U/A1203 UA1203 Zr/A1203

Cr/A120J Co /AI20J Th/U CeJCe Eu/Eu·

p

o...J

o...J

89

27-1 (Fig. 5-2). In contrast, the Ni concentration shows an abrupt increase at bed

17-3, immediately before the positive excursions of V and Co, with four small

positive shifts at beds 18-1c, 26-2,27-1 and 28-1, and with a negative shift at bed

18-1b associated with an increase of Ba concentration (Fig. 5-1). In addition to the

positive excursion at bed 18-1 b, the fluctuation of Ba also has two abrupt positive

shifts at beds 19-1b and 20-3b (Fig. 5-1).

5-3-2. Rare Earth Element concentrations

The North American Shale Composite (NASC)-normalized REE patterns using

values from McLennan (1989) are illustrated in Fig. 5-3. These fluctuations show

some minor variations in the REE patterns, for example a change in Eu data. I

attracted attention in Ce and Eu, considered as geochemical tracers of the GAE (e. g.

Hori et al., 2000), and analyzed the Ce and the Eu anomalies. These are calculated

as Ce/Ce*= Ceu/((Lan+Prn/2) and Eu/Eu*= Eun/((Smn+Gdn/2) after Hori et al.

(2000), and are shown in Fig. 5-2.

However the Ce/Ce* has little variation (Ce/Ce*=O. 853-0.923), some positive

shifts are recognized through the Sakuraguchidani Mudstone Member. During the P.

paltus and the D. helianthoides Zones, the Ce/Ce* value is relatively low except for

two positive Ce anomalies at beds 18-1band 20-3b (Fig. 5-2). In contrast, the

Ce/Ce* become high in the lower part of the H. inouyei Zone with some positive

anomalies at bed 25-3, 25-8 and 26-2, and decrease in the upper part of the H.

inouyei Zone.

Overall, the Eu/Eu* is uniform and increases from lower to the upper part of

the Sakuraguchidani Mudstone Member, except for a small positive anomaly at bed

18-1c and a negative anomaly at bed 26-1 (Fig. 5-2).

5-4. Discussion

5-4-1. Redox conditions during the Lower Toarcian in the Toyora Group

The geochemical data from the Sakuraguchidani Valley, the Toyora Group,

provide insights about stratigraphical changes of redox conditions during Early

01

1 1-1

1 -10

17

- 1 1 20 1 -1b 2en

18 1c 2

- 1 1 251 1 2 1-1

0

E00

s:1en

coG)

E

0

G)oecac~

.c

ww0::

0.1ro

.....J(1)

oL-

a.. "CZ E

(J)

:::JW

.0t- o o

J:L-

W Et-

.0>-

:::J......J

Fig. 5-3. orth American Shale Composit (NASC)-normarized REE patterns of black mud tone fromthe Sakuraguchidani udstone Member, exposed along the Sakuraguchidani Valley, in the ToyoraGroup. The ASC data are after cLennan (1989). The numbers of p cim n corre pond to thenumber of the outcrop in Fig. 3-1 and the number beside the columnar section in Fig. 5-2. The legendof the columnar section is as in Fig. 3-1.

91

Toarcian in the East Asian province.

As mentioned above, the concentrations of V and Co are strongly increase in

beds 18-1 c which is corresponded to the middle part of the P. paltus Zone,

associated with an abrupt negative shift of the Ni concentration and a positive

anomaly of Ce at bed 18-1b (Figs. 5-1,5-2). These elements have been recognized

as redox tracers of marine environments.

Under reducing sea water condition, V is reduced to V (III) by free H2S which

is generated by bacterial sulfate reduction and is precipitated as the solid oxide

V203 (Breit & Wanty, 1991; Wanty & Goldhaber, 1992; Hetzel et aI., 2009). In

addition, the V (III) is taken up by geoporphyrins and concentrated into the

sediments under the anoxic environment, although Ni ions are taken into the

porphyrins under the oxic condition (Moldowan et aI., 1986; Hatch & Leventhal,

1992). These excursions are stratigraphically corresponded to a negative shift of

the 013Corg and the low value of LPI analyzed by Izumi & Tanabe (201 O)(Fig. 5-1).

As a result, the positive peak of the V concentration at bed 18-1 c and the negative

excursion of the Ni fluctuation at bed 18-1b suggest that these beds were deposited

under the sulfide-bearing strongly anoxic paleoenvironment, just after the oxic

condition characterized by a positive shift of the Ni concentration at bed 17-3 (Fig.

5-1). The positive shift of the Co concentration at bed 18-1 c supports this

hypothesis (Fig. 5-2), because this element is precipitated as CoS under the

reduced condition with free hydrogen sulfide (Heggie & Lewis, 1984; Gendron et

aI., 1986). Moreover, the positive Ce anomaly at bed 18-1 b also suggests an anoxic

environment because of the enrichment of Ce (III) into the reducing water mass

(Liu et aI., 1988)(Fig. 5-2).

These geochemical peaks are also associated with a positive shift of the Ba

concentration (Fig. 5-1). Barium enrichment has been regarded as the indicator of

the high biogenic flux, which suggests the high productivity on the surface water

(Schmitz, 1987; Dymond et aI., 1992). Therefore, the anoxic marine condition

identified at beds 18-1band 18-1c seems to be affected by the high productivity on

the photic zone.

92

A strong negative excursion of the o13Corg fluctuation was also recognized

around bed 19-1 a by Izumi & Tanabe (2010), associated with the low LPI values

(Fig. 5-1). However, no distinct excursions of the redox elements at this bed

suggest that this negative shift of the o13Corg does not reflect the redox condition of

this period.

During the D. helianthoides and the H. inouyei Zones, the various excursions

of the redox elements are recognized in some beds. A small positive shift of the

concentration of V is identified at bed 20-3b corresponded to the upper part of the

D. helianthoides Zone, with the anomalies of Ba, Ni, Ce and 013 Corg (Figs. 5-1, 5-2).

Around the middle part of the H. inouyei Zone including beds 25-8, 26-1 and 26-2,

small excursions of V, Ni, Co and 013 Corg are recognized with the positive Ce

anomalies and a negative Eu anomaly (Figs. 5-1, 5-2). Moreover, the

concentrations of V and U slightly increases at bed 28-1 corresponded to the upper

part of the H. inouyei Zone (Fig. 5-1). These small shifts of the redox elements

seem to be affected by the dysoxic environments, although the o13 Corgfluctuation

increases gradually during overall these two zones (Figs. 5-1, 5-2). As a result, the

anoxic condition occurred in the P. paltus Zone was generally recovered through

the D. helianthoides and the H. inouyei Zones with some short term

oxygen-depleted marine environments.

5-4-2. Relationships between the anoxia and the ammonoid diversity changes

As mentioned above, the various epicontinental taxa, including ammonoid,

bivalve, ostracode, and so on, were affected by the Early Toarcian GAE in Europe.

Especially, the relationship between the diversity crises of ammonoid and the Early

Toarcian GAE has been discussed in both the Northwest European and the

Mediterranean provinces (Macchioni & Cecca, 2002~ Cecca & Macchioni, 2004).

The mass extinction recognized at the uppermost part of the Semicelatum Subzone

of the standard zonation was corresponded to the beginning of the Early Toarcian

GAE and was considered to be affected by this Early Toarcian paleoenvironmental

change.

93

The biodiversity fluctuation in ammonoid also has been analyzed in the Toyora

Group, southwest Japan by Nakada & Matsuoka (2008). The evolutionary trends of

diversity, origination and extinction are discussed at specific and generic levels in

the Nishinakayama Formation exposed along the Sakuraguchidani Valley. Nakada

& Matsuoka (2008) recognized a strong diversity fall at beds 18-1a, 18-1band

18-1c in the lower part of the P. paltus Zone, followed by an immediate

diversification at bed 19-1 b, a small diversity fall at bed 23-1 corresponded to the

base of the H. inouyei Zone, and a gradual diversity fall from bed 26-3 to bed 29-3,

compared to the upper part of the H. inouyei Zone (Figs. 5-2, 5-4). These events

mainly reflect the diversity fall of Harpoceratinae and that of endemic species.

The distinct diversity crisis recognized at beds 18-1 a, 18-1band 18-1 c in the P.

paltus Zone is stratigraphically corresponded to the most maj or anoxic event

characterized by the geochemical shifts of the V, Ni and Co concentrations, Ce/Ce*

and o13 Corg fluctuation (Fig. 5-4). This relationship suggests that the anoxic marine

condition in the P. paltus Zone caused the East Asian ammonoid assemblage to the

diversity crisis. In addition, this diversity crisis is characterized by the extinction

of the subfamily Harpoceratinae, and the survival of only a species of pandemic

Arieticeratinae. The ammonite assemblage from bed 41-1, corresponded just below

the horizons with geochemical anomalies and faunal extinction, is mainly

associated with moderately diversified Harpoceratinae, P. paltus (Fig. 8 in Plate 2),

P toyoranus (Fig. 7 in Plate 2), L. yokoyamai and L. aradasi (Fig. 10 in Plate 2),

with a few Arieticeratinae (F. fontanellense) and Lytoceratina (Lytoceras sp.)(see

Fig. 3-3). The specific composition of Harpoceratinae shows a high endemism of

the East Asian province. All of these endemic Harpoceratinae species are

disappeared in bed 18-1 by affecting the dramatic shift of the marine redox

condition, and only a pandemic species of the subfamily Arieticeratinae, F.

fontanellense (Figs. 6-7 in Plate 1) is recognizable during this oxygen-depleted

time-interval. The end of the anoxic marine condition is accompanied by the

dramatic recovery of the ammonoid diversity, especially the endemic

Harpoceratinae species. Seven endemic species of the subfamily Harpoceratinae

c:cu

0F"- rum

CU0I-

-"-cuW

VlA120J

80 7.'0 alo 9~O

NilA120 3

1.0 15 20 25 0 5" 0

4,

95

are obtained from bed 19-1, correlated to the uppermost part of the P. paltus Zone,

including P. nipponicum (Figs. 1-3 in Plate 2), P. yabei (Fig. 5 in Plate 2), F.

nakayamense (Fig. 6 in Plate 2), P. okadai (Fig. 6 in Plate 3) and "Cleviceras"

chrysanthemum (Figs. 1-3 in Plate 3). These relationships between the marine

redox conditions and the faunal associations of Hildoceratidae (including

Harpoceratinae and Arieticeratinae) probably suggest differences of anoxic

tolerances between these subfamilies.

The diversity falls of ammonoid assemblage in the upper part of the H. inouyei

Zone also seems to be related to the oxygen-depleted marine environment,

distinguished geochemically by a gradual increase of the V concentrations with

SOlne excursions of the Ni and Co concentrations (Fig. 5-4). Therefore, SOITIe minor

diversity fall affected by the dysoxic environments are accompanied during the

recovery of ammonoid diversity from the extinction in the lower part of the P.

paltus Zone.

5-4-3. Early Toarcian OAE in the Northern Hemisphere

Since the geochemical analysis of Jenkyns & Clayton (1986), the Early

Toarcian OAE has been mainly discussed on the basis of the 013C fluctuation in

Europe. Jenkyns & Clayton (1986, 1997) displayed the Ol3 C fluctuation in England

and recognized a positive shift in the Serpentinum Standard Zone following the

negative stage during the Spinatum and the Tenuicostatum Standard Zones. In the

Northwest European province, Hesselbo et al. (2000) analyzed the high-resolution

o13Ccarb, ol3Corg and 013Cwood through the Lower Whitby Mudstone exposed in

Yorkshire Coast, England, and identified an abrupt negative excursion in each of

these fluctuations, biostratigraphically corresponded to the uppermost part of the

Tenuicostatum Standard Zone (Semicelatum Subzone) and the Lower Serpentinum

Standard Zone (lower to middle part of the Exaratum Subzone)(Fig. 5-4). Cohen et

al. (2004) identified the anoxic condition during the uppermost Tenuicostatum

Zone and the Exaratum Subzone in England on the basis of the Ol3 Corg and the Os

isotope profiles, in addition to a negative excursion of the o13 Corg fluctuation in the

96

lower part of the Tenuicostatum Standard Zone (Fig. 5-4). Hermoso et al. (2009)

analyzed the 813Ccarb fluctuation in the southern Paris Basin and recognized that the

negative shift of carbon isotope occurs in four steps during the upper part of the

Tenuicostatum Standard Zone, in addition to a gentle negative excursion of that in

the lower part of the Tenuicostatum Standard Zone. In northern Spain, Gomez et al.

(2009) also recognized a negative excursion of the 813Ccarb fluctuation analyzed in

northern Spain during the upper part of the Semicelatum Subzone and the lower

part of the Elegantulum Zone (Fig. 5-4). As a result, the anoxic marine condition in

the Northwest European province was identified from the uppermost Tenuicostatum

Standard Zone to the Exaratum Standard Subzone of the Serpentinum Standard

Zone.

The negative shifts of 013 C have been also recognized in the Mediterranean

province. According to Hesselbo et al. (2007), negative shifts of the () 13Ccarb and

813Cwood fluctuations analyzed in Peniche, Portugal, were identified in the

lowermost Polymorphum Zone, almost equivalent to the Paltum Subzone of the

standard zonation, and the Lower Levisoni Zone, corresponded to the Exaratum

Standard Subzone (Fig. 5-4). In northern Italy, Bellanca et al. (1999) identified the

oxygen-depleted zone on the basis of the fluctuations of 813Ccarb and the some

redox element concentrations. Based on these analyses, the anoxic event in the

Mediterranean province has been confirmed from the uppermost Polymorphum

Zone to the lower part of the Levisoni Zone. The ammonoid diversity crisis mainly

identified in the Mediterranean province (e. g. Cecca & Macchioni, 2004) was

biostratigraphically corresponded to the Early Toarcian GAE (Fig. 5-4) and

therefore considered to be affected by this marine environmental change.

In the North American Cordillera province, the 813Corg profile was analyzed

along Yakoun River in the Queen Charlotte Islands by Caruthers et al. (2010). The

813Corg fluctuation of Caruthers et al. (2010) shows a dramatic negative excursion

that averages -30.94%0 with increasing of Total Organic Carbon value. These

geochemical anomalies are probably corresponded to the upper part of the Kanense

Zone of the North American Cordillera zonation. Although the detailed

97

biostratigraphic correlation of these curves with the European geochemical results

is disturbed by the poor occurrence of ammonoid fossils in the Yakoun River

succession, the negative shift of 0"c., is almost coeval with the Early Toarcian

GAE distinguished in Europe. The effect of the Early Toarcian OAE seemed to

have reached the coastal areas of North American Cordillera via the Viking

Corridor, a seaway from northwest Europe to the Anui Ocean, or the Hispanic

Corridor, which pass through the Central America. On the other hand, the al3 Core;

curve of North American Cordillera is stable in the lowermost Toarcian, and no

shifts are recognizable in this interval.

The Early Toarcian OAE has been also discussed in the Northern Tibet and the

pelagic area. Chen et al. (2005) displayed the a13Core; and the atomic C/N ratio

profiles, and recognized a negative shift of the a13Core; fluctuation. In the pelagic

area, this event has been identified in East Asia (the Katsuyama Section, central

Japan; Hori et al., 2000) and Slovenia (Gorican et al., 2003) on the basis of the

positive excursions of V/Ah03 ratios and the occurrence of the pelagic black

sediments. However, the detailed biostratigraphic correlation between these events

and the Early Toarcian OAE recognized in European epicontinental successions

and the Toyora Group are difficult because of the low-resolution of the

biostratigraphic age controls in the Northern Tibet and the pelagic successions.

The East Asian Toarcian OAE in this study is recognized in the middle part of

the P. paltus Zone (Fig. 5-4). This event is compared to the Paltum Subzone, the

lowermost subzone of the Toarcian Stage, in the standard zonation. This result

suggests that the OAE in East Asia is corresponded to the oxygen-depleted

condition identified by the al3Ccarb and the al3Core; negative shifts in both of the

Northwest European and the Mediterranean provinces (Cohen et al., 2004;

Hesselbo et al., 2007)(Fig. 5-4). Therefore, the anoxic event recognized in the

lowermost part of the Tenuicostatum Zone enables to regard as a global

paleoenvironmental change in the Tethys and the West Panthalassa. The oxygen

depleted conditions identified in Northern Tibet and the pelagic successions (Chen

et al., 2005; Hori et al., 2000; Gorican et al., 2003) seeln to be corresponded to this

98

earliest Toarcian dysoxic event. In contrast, the maj or Early Toarcian OAE from

the lowermost part of the Tenuicostatum Zone to the Exaratum Subzone,

recognized in Europe and North American Cordillera, is not identified clearly in

the Toyora Group. This means that the anoxic condition in this period was

developed only in the limited area, the western Tethys and the East Panthalassa.

99

6. Systematic paleontology

3-1. Genus Amaltheus

Remark: Almost all of the materials utilized in this analysis are crushed

horizontally to the bedding plane and the preservation is not so well.

Class Cephalopoda CUVIER, 1798

Sub-class Ammonoidea ZITTEL, 1884

Order Psiloceratida HOUSA, 1965

Amended by Dommergues (2002)

Superfamily Eoderoceratoidea NEUMAYR, 1875

Family Liparoceratidae HYATT, 1867

Amended by Dommergues & Meister (1999)

Subfamily Amaltheinae HYATT, 1867

Genus Amaltheus MONTFORT, 1808

Type species: Amaltheus margaritatus MONTFORT, 1808

Remark: The whorl section is compressed and subelliptical. Surface ornaments

are varied; some species have smooth whorl flank, and others are characterized by

the spiny or strong ribbing. Most of species have a crenulated keel.

Amaltheus stokesi (SOWERBY, 1818)

Plate 4, figs. 1-5

1818. Ammonites Stokesi SOWERBY, pI. 190.

1955. Amaltheus cf. nudus (QUENSTEDT). - IMLAY, pI. 10, fig. 5.

1958. Amaltheus stokesi (SOWERBY). - HOWARTH, pI. 1, figs. 5, 7, 12-14; pI. 2, figs.

1, 3, 10; text-figs. 4, 5.

1964. Amaltheus stokesi (SOWERBY). - FREBOLD, pI. 6, figs. 6, 13.

1967. Amaltheus stokesi (SOWERBY). - FREBOLD, et aI., pI. 1, figs. 1,7.

1971. Amaltheus cf. stokesi (SOWERBY). - HIRANO, pI. 17, fig. 11.

100

1974. Amaltheus (Amaltheus) stokesi (SOWERBY). - REPIN, pI. 1, figs. 5, 9.

1988. Amaltheus (Amaltheus) stokesi (SOWERBY). - KRYMHOLTS et aI., pI. 2, fig. 1.

1991. Amaltheus stokesi (SOWERBY). - POULTON, pI. 8, figs. 2, 7, 8.

1992. Amaltheus (Amaltheus) stokesi (SOWERBY). - In: WESTERMANN, pI. 17, figs.

1,3,6.

1992. Amaltheus stokesi (SOWERBY). - In: WESTERMANN, pI. 3, fig. 11; pI. 5, fig. 9;

pI. 6, fig. 4 (cf.).

1994. Amaltheus cf. stokesi (SOWERBY). - PALFY & HART, pI. 1, fig. 12.

1994. Amaltheus stokesi (SOWERBY). - JAKOBS & PALFY, pI. 1, fig. 9.

1996. Amaltheus stokesi (SOWERBY). - SMITH& TIPPER, pI. 19, fig. 1; pI. 20, fig. 3.

1997. Amaltheus stokesi (SOWERBY). - JOHANNSON et aI., pI. 2, fig. 13.

1998. Amaltheus stokesi (SOWERBY). - GECZY& MEISTER, pI. 6, fig. 10.

? 2002. Amaltheus stokesi (SOWERBY). - RAKUS & GUEX, pI. 27, fig. 8.

2003. Amaltheus stokesi (SOWERBY). - MEISTER & FRIEBE, pI. 16, figs. 9, 14.

2006. Amaltheus stokesi (SOWERBY). - FAURE, p. 43, fig. 8.

2006. Amaltheus stokesi (SOWERBY). - TOPCHISHVILI et aI., pI. 11, fig. 4.

2007. Amaltheus stokesi (SOWERBY). - RULLEAU et aI., pI. 34, fig. 5; pI. 35, fig. 1.

2007. Amaltheus stokesi (SOWERBY). - MOUTERDE et aI., pI. 1, figs. 9, 14.

Material: Four specimens, DRF0101, DRF0148, DRF0141 and DRF0209, from

the Kuruma Group, and a specimen, GK. G. 11293, from the Toyora Group.

Diagnosis: A species of the genus Amaltheus with one-to-one connection

between the each ribs and serrations of the crenulated keel.

Dimensions (mm):

No. D Wh U U/D Wh/D

DRFOI0l 47.7 23.0 11.2 0.235 0.482

DRF0148 29.2 14.2 6.0 0.206 0.486

DRF0141 35.2 15.6 9.1 0.259 0.443

GK. G. 11293 41.4+ 20.5 8.2 0.198 0.495

101

Description: The whorls are moderately to quite involute and enlarged rapidly,

therefore the umbilici are narrow (Fig. 6-1). Detailed characters of the whorl

section are unknown because of the compression. The venter bears a broad and

elevated keel with coarse crenulation. The radial and sometime irregular ribs are

somewhat strong in inner two-third of the whorl flank and become slightly weak

toward the venter. They are strongly projected forward at the ventrolateral part and

pass onto the keel as crenulation.

Discussion: This species is mainly distinguished from Amaltheus margaritatus

MONTFOR'!, one of the most typical species of this genus, by the connecting pattern

between the ribs and the crenulations and characters of the keel. The former

species has a round keel, and the ribs are connected with each serration of the

crenulation of keel. On the other hand, a keel of the later species is more individual,

and the crenulation becomes finer than former. In addition, the ribs of the latter

species are not connected with each serration of the crenulation one by one.

Amaltheus sensibilis DAGIS and Amaltheus subbifurcus REPIN, both are

obtained from the Northeast Russian province, are distinguished from the present

species by the larger umbilicus and stronger projection of the ribs at the

ventrolateral part.

The present species lS quite similar with Amaltheus bifurcus HOWARTH.

However, A. bifurcus lS characterized by the more coarse ribbing with a not

developed keel.

A specimen, DRFO143 (Fig. 6 in Plate 4) obtained from the Kuruma Group, has

some affinities with the present species, for example, the connection of some ribs

with the serration of the crenulated keel. However, this specimen is small with not

so well preservation. In this description, the specimen is treated as Amaltheus sp.

cf. A. stokesi (SOWERBY).

Age and distribution: Amaltheus stokesi is an index species of the base of the

Upper Pliensbachian. Therefore, this species characterizes the Stokesi Subzone of

the Margaritatus Zone, Upper Pliensbachian.

The present species has been recognized in the Northwest European province,

25~----------------------------------------.,

..-.EE"'-"....., 20.cC).-.c

-CG.~-:cE

::::>

5

Legend

• 0 Ama/theus stokes!• 0 Ama/theus magaritatusA ~ Ama/theus repressus• o Ama/theus aft. ta/rosei

16 specimens

•

Umbilical width

o 10 20 30

Diameter (mm)

40 50 60

Fig. 6-1. Variation in whorl height and umbilical width of the genus Amaltheus from Japan.

103

the Mediterranean province (Morocco in North Africa), East Asia (Japan), North

American Cordillera (British Columbia and Alaska), Caucasus {Georgia) and

Russia (the Northeast and the Far East provinces).

Amaltheus margaritatus MONTFORT, 1808, form margaritatus MONTFORT, 1808

Plate 1, figs. 9-10; Plate 4, figs. 7-16

1808. Amaltheus margaritatus MONTFORT, p. 90 (fig.), 91.

1812 . Ammonites acutus J. SOWERBY, pI. 17, fig. 1.

1845. Ammonites sedgwickii J. BUCKMAN, p. 40 (nomen nudum).

1852. Ammonites foliaceus GIEBEL, p. 540.

1885 Ammonites amaltheus nudus QUENSTEDT, pI. 41, figs. 1-2.

1885 Ammonites amaltheus compressus QUENSTEDT, pI. 41, fig. 17; pI. 42, fig. 8.

1955. Amaltheus sp. indet. SATO, pI. 18, figs. 1, 2.

1958 Amaltheus margaritatus de MONTFORT, 1808. - HOWARTH, text-fig. 8

(neotype), 9 (lectotype).

1964. Amaltheus stokesi (SOWERBY). - FREBOLD, pI. 6, fig. 7.

1974. Amaltheus margaritatus de MONTFORT. - ELMI et aI., pI. 1, fig. 1.

1976. Amaltheus margaritatus de MONTFORT. - POURMOTAMED & MOTAMED, p. 106,

fig.3.

1988. Amaltheus (Amaltheus) margaritatus de MONTFORT. - KRYMHOLTS et aI., pI. 2,

fig. 5.

1991. Amaltheus stokesi (SOWERBY). - POULTON, pI. 8, fig. 1.

1998. Amaltheus margaritatus de MONTFORT. - GECZY & MEISTER, p. 103 with

synonymy.

1997. Amaltheus stokesi (SOWERBY). - JOHANNSON et aI., pI. 2, fig. 12.

2002. Amaltheus margaritatus de MONTFORT. - FAURE, pI. 7~ fig. 16.

2006. Amaltheus margaritatus de MONTFORT. - TOPCHISHVILI et aI., pI. 11, figs. 1,

2.

2006-2007. Amaltheus margaritatus de MONTFORT. - FAURE, p. 43, figs. 1, 3, 4.

104

2007. Amaltheus margaritatus de MONTFORT. - RULLEAU et aI., pI. 35, figs. 3-5.

2007. Amaltheus margaritatus de MONTFORT. - MOUTERDE et aI., pI. 2, figs. 1, 8.)

2008. Amaltheus margaritatus de MONTFORT forme margaritatus de MONTFORT. -

DOMMERGUES et aI., pI. 10, fig. 4.

Material: Nine specimens, DRF0147, DRF0142, DRF0207, DRF0208,

FMM2007, FMM2008, FMM2009, MM2791 (T5303-1a in Sato, 1955) and

MM2792 (T5303-1 in Sato, 1955), from the Kuruma Group, and three specimens,

SA36-1-1,SA32-1-2 and THM0001, from the Toyora Group.

Dimensions (mm):

No. D Wh D DID Wh/D

DRF0147 33.0 16.6 6.8 0.206 0.503

DRF0142 24.7 11.0 5.5 0.223 0.445

DRF0207 40.2 19.2 9.2 0.229 0.478

FMM2007 41.3 18.1 11.2 0.271 0.438

FMM2008 36.4 13.6 11.4 0.313 0.374

MM2792 35.9 16.6 10.2 0.284 0.462

MM2791 25.2 12.4 5.5 0.218 0.492

SA36-1~1 .33.5 17.4 10.7 0.319 0.519

THMOOOI 41.7 18.6 11.0 0.264 0.446

Description: The whorls are moderately involute and enlarged rapidly, and the

umbilicus are slightly narrow (Fig. 6-1). Detailed characters of the whorl section

are unknown because of the compression. The venter bears an individual and

elevated keel with fine crenulation. The present species from Japan is characterized

by the lateral ribs. On the inner whorl, the radial and slightly sigmoidal ribs started

from umbilical edge are well developed on middle of the flank and are tending to

disappear near the venter, but not completely fade out. They are strongly projected

forward at the upper part of the flank until the keel, but each serration of the

crenulation of the keel are not connected with the ribs. A specimen, DRFO147 (Fig.

7 in Plate 4), has some longitudinal striae on the whorl flank. On the other hand,

105

the ribs become weak and fade out on the outer whorl.

Discussion: On the basis of the recognizable characters of surface ornament

and keel. all of our materials identified as the present species are similar to the

classic Amaltheus from Europe. The present species is distinguished from

Amaltheus stokesi (SOWERBY) by characters of the ribbing and the keel, as

mentioned above.

The specimens identified as the present species from Japan are similar to

Amaltheus margaritatus MONTFORT from the Northeast Russian province described

by Dagis (1976). However, the Northeast Russian specimens have the little more

evolute whorls and the more sick keels.

The present species is similar to Amaltheus conspectus DAGIS but is

distinguished by the more involute whorl and the connection between the serration

of the crenulated keel and the ribs recognized in the latter species.

The present species is also similar with Amaltheus talrosei REPIN, probably

one of the varieties of A. margaritatus. However, A. talrosei is distinguished from

the present species by the more evolute whorl and stronger projection of the ribs at

the ventrolateral part.

The specimens obtained from the Nishinakayama Formation of the Toyora

Group (SA36-1-1, Fig. 9 in Plate 1; SA36-1-2, Fig. 10 in Plate 1) and some

materials from the Teradani Formation (e.g. DRF0207, Fig. 12 in Plate 4) are

characterized by an elevated and individual keel with well prorsiradiated serrations

and the connection of the ribs and the keel, occasionally some ribs and the

serrations of the crenulation. These characters are limited to' the specimens

obtained from the Apyrenum Subzone of the Northwest European province (e.g.

Fig. 3 in Plate 4; Meister, 1988). The Japonica Zone established by Nakada &

Matsuoka (in press) in the Toyora Group was compared to the Apyrenum Standard

Subzone based on these morphological characters.

A specimen, DRF0210 (Fig. 2 in Plate 5) obtained from the Kuruma Group, is

similar to the present species in the characters of the ribbing but is only a large

fragment without the ventral part. Therefore, this specimen is described as

106

Amaltheus sp. in this study.

Age and distribution: This species ranges from the Subnodosus Subzone of the

Margaritatus Zone to the Apyrenum Subzone of the Spinatum Zone in the

Northwest European zonation, compared to the Upper Pliensbachian.

Amaltheus margaritatus was mainly distributed in high latitudinal area of the

Northern Hemisphere, equal to the Boreal Realm in Late Pliensbachian, as follows;

the Northwest European province, East Asia (Japan), North American Cordillera

(British Columbia and Alaska) and Russia (the Northeast and the Far East

provinces). In addition, this species is also recognized in the Mediterranean

province (Algeria and Morocco in North Africa) and Caucasus (Georgia).

Amaltheus repressus DAGIS, 1976

Plate 4, figs. 17-18

1976. Amaltheus (Proamaltheus) repressus DAGIS, pl. 11, figs. 1-5.

/Material: Two specimens, DRF0125 and DRF0202, from the Kuruma Group.

Diagnosis: A species of the genus Amaltheus with constrictions.

Dimensions (mm):

No.

DRF0202

D

27.1

Wh U

12.4 6.8

UID Wh/D

0.251 0.458

Description: The whorls are moderately involute and enlarged rapidly,

therefore the umbilicus are slightly narrow (Fig. 6-1). Details of the whorl section

are unknown. The venter has a slightly weak and crenulated keel, and the

crenulations are very fine and well prorsiradiated. However surface ornaments on

the whorl flank are generally weak, the present species is characterized by the

presence of constrictions. On the small whorl, a specimen of DRF0202 (Fig. 17 in

Plate 4), the radial and irregular ribs started from umbilical edge are well

developed in the inner half of whorl and become weak rapidly for the venter. They

are strongly projected forward at the ventrolateral part and connected with the keel.

107

A slightly sigmoidal constriction IS developed on the whorl flank and is also

strongly projected at the ventrolateral part. On the outer whorl examined In a

specimen DRFO125 (Fig. 18 in Plate 4)~ the ribs become very weak and two

constrictions per 45° of a whorl are developed near the aperture.

Discussion: In previous study, the Russian endemic species of the genus

Amaltheus was only recognized in Alaska of North America by Imlay (195'5)~

Amaltheus viligaensis (TUCHKOV)~ without the Russian province. Therefore, the

occurrences of the present species and Amaltheus sp. aff. A. talrosei REPIN as

mentioned below are the first records of the Russian endemic Amaltheus from Asia.

The present species is similar to Amaltheus margaritatus MONTFORT and

Amaltheus conspectus DAGIS in surface ornaments. However, the former IS

distinguished from the latter two species by the presence of constrictions.

Age and distribution: Amaltheus repressus co-occurred with Amaltheus stokesi

(SOWERBY) in the Northeast Russian province and correlated with the Stokesi

Standard Subzone of the Margaritatus Standard Zone, earliest Late Pliensbachian

(Dagis, 1976).

The present species was distributed in the Northeast Russian province and East

Asia (Japan).

Amaltheus sp. aff. A. talrosei REPIN, 1968

Plate 5, figs. 1a-b

DID Wh/D

0.407 0.328

D

19.6

Wh

15.8

Material: Only a specimen, DRFOI49~ from the Kuruma Group.

Dimensions (mm):

No. D

DRF0149 48.2

Description: The whorl is moderately evolute, and therefore the umbilicus is

slightly large (Fig. 3-1). Details of the whorl section are unknown because of the

compression. However the ventral part is not well preserved, a broad and

crenulated keel is partly recognized in the outer whorl (Fig. 1b in Plate 5)~ and the

108

serrations of the crenulation are coarse and well prorsiradiated. The rursiradiate

and irregular ribs started from umbilical edge are strong near the inner flank and

are tending to disappear from middle to outer flank. They are strongly projected

forward at the ventrolateral part, and some of them pass through onto the

crenulated keel.

Discussion: The present specimen is quite similar to Amaltheus talrosei REPIN,

described only in the Northeast Russian province by Repin (1968) and Dagis

(1976), in the evolute coiling, well prorsiradiated serration of the crenulated keel

and the connection of the ribs and the serration of the keel. However, the former

has more rigid and irregular ribbing than the latter. Consequently, the present

specimen is identified as Amaltheus sp. aff. A. talrosei REPIN in this description.

The present specimen is also similar to Amaltheus margaritatus MONTFORT and

Amaltheus viligaensis (TUCHKOV) in characters of the ribbing but is distinguished

by the more evolute whorl and the stronger projection of the ribs at the

ventrolateral part.

Age and distribution: In Russian, A. talrosei was obtained from the Viligaensis

Zone, equivalent to the Spinatum Zone of the Northwest European zonation (Dagis,

1976; Krymholts et al., 1988). However, the base of the Viligaensis Zone is

compared into the ~ Margaritatus Standard Zone because of the occurrence of

Arieticeras sp. aff. A. algovianum (OPPEL), ranges into the Subnodosus-Apyrenum

Standard Zone, from the Viligaensis Zone (Fig. 3-6). In addition to the zonal

correlation, the present specimen is co-occurred with Amaltheus margaritatus

MONTFORT from the Kuruma Group. Consequently, the range of the present species

is corresponded to the upper part of the Margaritatus Zone of the Northwest

European zonal shame (Fig. 3-6).

The present specimen was distributed in East Asia (Japan).

109

7. Conclusions

7-1. Ammonoid biostratigraphy

The ammonoid zonal scheme of the Toyora Group is revised in this study, and

six zones are proposed (in ascending order) as follows; the A. stokesi Assemblage

Zone, the Canavaria japonica Zone, the Paltarpites paltus Zone, the Dactylioceras

helianthoides Zone, the Harpoceras inouyei Zone and the Pseudogrammoceras­

Phlyseogrammoceras Assemblage Zone.

In contrast, three ammonoid zones are established in the Teradani Formation,

the Kuruma Group, as follows; the Stokesi-Repressus Assemblage Zone, the

Margaritatus-aff. Talrosei Assemblage Zone and the Canavaria-Emaciaticeras

Assemblage Zone in ascending-order.

These zonations are corresponded to the zonal schemes of outside Japan,

especially the Northwest European standard zonation (Fig. 3-6). The A. stokesi

Assemblage Zone and the Stokesi-Repressus Assemblage Zone are compared to the

Stokesi Standard Subzone of the Margaritatus Standard Zone (Late Pliensbachian).

The Margaritatus-aff. Talrosei Assemblage Zone IS correlated to the

Subnodosus-Gibbosus Standard Subzones (Margaritatus Standard Zone) and the

Apyrenum Standard Subzone (Spinatum Standard Zone, Late Pliensbachian). The

Canavaria-Emaciaticeras Assemblage Zone is corresponded to the Hawskerense

Standard Subzone of the Spinatum Standard Zone. The base of the C. japonica

Zone is roughly correlated to the Apyrenum Standard Subzone. The base of the P.

paltus Zone is equivalent to the Pliensbachian/Toarcian boundary. The base of the

D. helianthoides Zone is compared to the base of the Paltum Standard Subzone

(Tenuicostatum Standard Zone, Early Toarcian). The base of the H. inouyei Zone is

corresponded to the Exaratum Standard Subzone of the Serpentinum Standard Zone,

and the upper limit seems to be corresponded to the Fibulatum Standard Subzone

(Bifrons Standard Zone, Early Toarcian).

110

7-2. Ammonoid paleobiogeography

The transitional patterns during late Early Jurassic time-interval (Late

Pliensbachian-Toarcian) and their paleobiogeographic correlation of a

comprehensive Japanese ammonoid fauna are analyzed by utilizing the ammonoid

assemblages from the Toyora and the Kuruma Groups.

During the Stokesi Standard Zone, the assemblage from the Kuruma Group,

characterized by the Russian endemic species of the genus Amaltheus, shows the

high similarity with the Northeast Russian fauna, although the coeval assemblage

from the Toyora Group is associated with the Boreal and the Tethyan elements.

This faunal disagreement reflects the paleolatitudinal interval between these

groups. The assemblage of the Subnodosus-Gibbosus Standard Subzone from the

Kuruma Group is continuously characteristic in the Boreal-derived fauna. The

faunal association of the Apyrenum Standard Subzone from the Kuruma Group, the

mixing of the Tethyan and the Boreal elements, is not recognized in the Northern

Hemisphere. The faunas from the Hawskerense Standard Subzone and the

Tenuicostatum Standard Zone, dominated by Arieticeratinae and Harpoceratinae,

are similar with those of the Mediterranean province. The fauna in the

Serpentinum-Lower to Middle Bifrons Standard Zones from the Toyora Group is

characterized by the mixing of the Tethyan and the Boreal faunas and shows the

high similarity with the Northwest European fauna. The generic faunal association

of the Fallaciosum Standard Subzone and the Dispansum Standard Zone is similar

with that from the Causses Basin in the Northwest European province.

As a result, a turnover from the Boreal fauna composed of the genus Amaltheus

(Amaltheidae) to the Tethyan fauna dominated by Arieticeratinae is distinguished

mainly in the Kuruma Group during the Apyrenum Standard Subzone (Fig. 4-1).

This faunal change is chronologically discordant for the comparable faunal

turnover in the almost equal paleolatudinal areas of the Northwest European

province, which is corresponded to the PIT boundary. The turnover recognized in

the latest Pliensbachian ammonoid fauna from Japan seems to be mainly affected

by the regression during latest Pliensbachian (Spinatum Standard Zone) to earliest

111

Toarcian (Tenuicostatum Standard Zone), in addition to the starting of the warming

event (Fig. 4-9).

In contrast, a faunal mixing of the Boreal and the Tethyan faunas is recognized

in the assemblage from the Toyora Group during the Exaratum Standard Subzone

(Fig. 4-1). This bio-event enables to correspond to the coeval faunal conformity in

the Northwest European and the Mediterranean provinces. The faunal mixing in the

middle Early Toarcian ammonoid assemblage is perhaps reflected by the abrupt

transgression during Early Toarcian, with the slight cooling event (Fig. 4-9).

7-3. Geochemical analyses of the Early Toarcian OAE

The concentrations of trace elements and the anomalies of REE are analyzed in

the Sakuraguchidani Mudstone Member exposed along the Sakuraguchidani Valley,

the Toyora Group. The positive excursions of V/Ah03, Ba/Ab03 and Co/Ah03 are

recognized in bed 18-1c, the middle part of the P. paltus Zone (earliest Toarcian),

with a negative shift of NilAh03 and a positive Ce anomaly (Figs. 5-1, 5-2). These

geochemical anomalies suggest the oxygen-depleted paleoceanographic conditions,

biostratigraphically corresponded to the coeval minor anoxic environment in the

Northwest European province (Fig. 5-4). The major Early Toarcian OAE from the

uppermost Tenuicostatum Standard Zone to the Exaratum Standard Subzone

recognized in Europe and North American Cordillera is not identified in the Toyora

Group. Thus, the anoxic water mass affected by this event was developed only in

the West Tethys and East Panthalassa.

Moreover, a diversity fall of ammonoid assemblage is also identified in bed

18-1. This diversity crisis is characterized by the extinction of Harpoceratinae, and

the survival of only a species of pandemic Arieticeratinae, Fontanelliceras

fontanellense. Consequently, the ammonoid diversity crisis in the middle part of

the P. paltus Zone is perhaps reflected by the anoxic event in East Asia. Moreover,

the relationships between the marine redox conditions and the faunal associations

of Hildoceratidae probably suggest the difference of anoxic tolerances between

Harpoceratinae and Arieticeratinae.

112

In addition to the faunal transitions affected by the changes of eustatic sea

level and seawater temperature, an ammonoid bioevent reflected by the marine

redox condition can be identified during earliest Toarcian (Tenuicostatum Standard

Zone).

113

Acknowledgements

I gratefully thank Prof. Atsushi Matsuoka (Niigata University) for his general

guidance for this study. I would like to thank Dr. Christian Meister (Natural

History Museum of the City of Geneva) for their kind guidance on the

classification and identification of ammonoids with many valuable comments about

ammonoid taxonomy, biostratigraphy and paleobiogeography. I also thank Mr.

Ken-ichi Miyakita (Niigata City), Mr. Kaku Nagata (Niigata City), Mr. Kazunobu

Terabe (Arabian Oil Company), Mr. Hideo Ishida (Mine City), Mr. Yoshihiko Kubo

(Nagano City) and Mr. Takahiro Aoki (Nagano City) for offering many ammonoid

specrmens.

I am grateful to Prof. Jean Guex (University of Lausanne), Prof. Jiarun Yin

(China University of Geosciences, Beijing), Dr. Naoki Watanabe (Niigata

University), Prof. Kazushige Tanabe (the University of Tokyo), Prof. Hiromichi

Hirano (Waseda University), Dr. Yasuhiro Iba (National Museum of Nature and

Science), Dr. Alain Morard (University of Fribourg) and Dr. Tadashi Sato (Fukada

Geological Institute) for their valuable comments. I also thank Prof. Jun-ichi

Tazawa, Dr. Isao Niikawa, Dr. Toshiyuki Kurihara, Dr. Naoto Ishida, Mr. Takashi

Nikaido and the other members of the Historical Earth Science Seminar in Niigata

University for their helpful suggestions. I wish to thank Dr. Takenori Sasaki (the

University Museum, the University of Tokyo), Prof. Hiroyoshi Sano (Kyushu

University), Dr. Akihiro Misaki (Kitakyushu Museum of Natural History and

Human History) and Mr. Yosuke Ibaraki (Fossa Magna Museum) for their kind

assistance in observation of specimens. Mr. Koshiro Takanasi (Niigata University)

is thanked for their guidance for the geochemical analyses. I thank Mr. Takayoshi

Fukutomi (Shimonoseki City), Mr. Keisuke Kawano (the Firefly Museum of Toyota

Town), Ms. Junko Masahara (Shimonoseki City) and Tenkyoji Youth Hostel for

their kind helps during my field work. The Asahi Townhouse is thanked for their

cooperation in the field. I express my gratitude to these persons.

114

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135

Plate 1

Dactylioceras helianthoides (YOKOYAMA)

la-b. SA14-l-l, North Valley, locality 14 *la: Rubber cast, 1b: external mould

2. SA27-3-l, North Valley, locality 27

3. SA27-3-2, North Valley, locality 27

Dactylioceras sp. aff. D. helianthoides (YOKOYAMA)

4. SA2B-1-4, North Valley, locality 28 *Rubber cast

Peronoceras subfibulatum (YOKOYAMA)

5. SA26-5-3, North Valley, locality 26

Fontanelliceras fontanellense (GEMMELLARO)

6. SA18-lh-l, North Valley, locality 18

7. SA18-la-3,North Valley, locality 18

Canavaria japonica (MATSUMOTO)

8. SA36-2-3, South Valley, locality 36

Amaltheus margaritatus MONTFORT

9. SA36-l-l, South Valley, locality 36

10. SA36-l-2, South Valley, locality 36

The locality numbers correspond to that of Fig. 3-1. Scale bars are equal to 1 em.

137

Plate 2

Protogrammoceras nipponicum (MATSUMOTO)

1. KTI9-1b-l, North Valley, locality 19

2. SAI9-1c-2, North Valley, locality 19

3. SA18-1c-1, North Valley, locality 18

Protogrammoceras onoi HIRANO

4. SA19-1b-2, North Valley, locality 1.9

Protogrammoceras yabei HIRANO

5. HI48-8-1, South Valley, locality 48

Fuciniceras nakayamense (MATSUMOTO)

6. SA19-1b-20, North Valley, locality 19

Paltarpites toyoranus (MATSUlVIOTO)

7. SA41-1-3, South Valley, locality 41

Paltarpites paltus (BUCKMAN)

8. SA41-1-2, South Valley, locality 41

Petranoceras sp. aff. P. rinaldinii VENTURI

9. SAI0-6-2, South Valley, locality 10

Lioceratoides aradasi (FUCINI)

10. KT41-1-2, South Valley, locality 41

The locality numbers correspond to that of Fig. 3-1. Scale bars are equal to 1 em.

139

Plate 3

"Cleviceras" chrysanthemum (YOKOYAMA)

1. SA19-1b-30, North Valley, locality 19

2. SA20-3b-3, North Valley, locality 20

3. SA26-4-4, North Valley, locality 26

Harpoceras inouyei (YOKOYAMA)

4, SA23 -1- 7, North Valley, locality 23

Cleviceras sp. cf. C. exaratum (YOUNG & BIRD)

5. SA23-1-3, North Valley, locality 23

Polyplectus okadai (YOKOYAMA)

6. SA20-3b-6, North Valley, locality 20

Hi/daites sp.

7. SA23-5-1, North Valley, locality 23

The locality numbers correspond to that of Fig. 3-1. Scale bars are equal to 1 em.

141

Plate 4

Amaltheus stokesi (SOWERBY)

1. DFFO101, Daira River 6 section, floated rock

2. DRFO148, Daira River 6 section, floated rock

3. GK. G. 11293, loco 50 in Hirano (1971), Chuzankei Valley *Rubber cast

4a-b. DRF0209, Daira River 6 section, floated rock

5. DRE0141, Daira River 6 section, floated rock

Amaltheus sp. cf. A. stokesi (SOWERBY)

6. DRF0143, Daira River 6 section, horizon: DRF0101

Amaltheus margaritatus MONTFORT

7. DRFO147, Daira River 6 section, floated rock

8. FMM2007, Daira River 6 section, floated rock

9. FMM2008, Daira River 6 section, floated rock

10. FMM2009, Daira River 6 section, floated rock

11. DRFO142, Daira River 6 section, floated rock

12. DRF0207, Daira River 7 section, floated rock "Apyrenum-type

13. MM2791 (T5303-1a in Sato, 1955), locality: unknown *Rubber cast

14. MM2792 (T5303-1 in Sato, 1955), locality: unknown *Rubber cast

15. DRF020 8, Daira River 7 section, floated rock *Rubber cast

16. THM0001, Toyora Group, locality: unknown

Amaltheus repressus DAGIS

17. DRF0202, Daira River 7 section, horizon: DRF0201

18. DRF0125, Daira River 6 section, floated rock

The numbers of section correspond to that of Fig. 2-5. The horizon numbers

correlate to Figs. 2-6 and 4-4. Scale bars are equal to 1 em.

143

Plate 5

Amaltheus sp. aff. A. talrosei (REPIN)

la-b. DRFOl49, Daira River 6 section, floated rock

Amaltheus sp.

2. DRF0210, Daira River 7 section, floated rock

Emaciaticeras nov sp .

.3a-Q~ DRFOl02, Daira River 6 section, floated rock

4a-b. DRFOl03, Daira River 6 section, floated rock

Juraphyll ites planulata FUCINI

5. TDFOIOl, Teradani Valley, horizon: TDFOI

The numbers of section correspond to that of Fig. 2-5. The horizon numbers

correlate to Figs. 2-6, 4-4 and 4-5. Scale bars are equal to 1 em.

I 4

145

Plate 6

Canavaria nov sp. A

1. TDF0210, Teradani Valley, horizon: TDF02

2. DRFO124, Daira River 6 section, floated rock

3. DRF0150, Daira River 6 section, floated rock

4. DRFOI23, Daira River 6 section, floated rock

5. I2RFO 121, Daira River 6 section, floated rock

Canavaria sp. aff. C. haugi (GEMMELLARO)

6. DRFO111, Daira River 6 section, floated rock

Canavaria nov sp. B

7. DRFO134, Daira River 6 section, floated rock

Canavaria sp. aff. C. naxensis (GEMMELLARO)

8. DRFOI04, Daira River 6 section, floated rock

Canavaria sp. aff. C. prognatum FUCINI

9. DRF020 1, Daira River 7 section, floated rock

Canavaria sp.

lOa-b. DRFO128, Daira River 6 section, floated rock

11a-b. DRFO129, Daira River 6 section, floated rock

12a-b. DRFO110, Daira River 6 section, floated rock

13a-c. TDF0206, Teradani Valley, horizon: TDF02

The numbers of section correspond to that of Fig. 2-5. The horizon numbers

correlate to Figs. 2-6, 4-4 and 4-5. Scale bars are equal to 1 em.

14

147

Plate 7

Lytoceras sp. cf. L. siemensi (DEKMAN)

1. TDF0302, Teradani Valley, horizon: TDF03

The horizon number corresponds to that of Figs. 2-5, Figs. 2-6 and 4-5. Scale bars

are equal to 10 em.

Pia 7

(scale bar =10em)

Plate 8

149

150

Dactylioceras sp. juv

20. SA53-4-15, North Valley, locality 53

21. SA53-4-17, North Valley, locality 53

Calliphylloceras sp.

22. SA53-4-18, North Valley, locality 53

23. SA53-4-1, North Valley, locality 53

The locality numbers correspond to that of Fig. 3-1. Scale bars are equal to 1 em.

Plate 8

6

75

3

4

1

89

10 11 12

15

14

18 1923

1-16,18-19,22-2317,20-21

20 21 22(scale bar =1cm)

2120

Sakuraguchidani Mudstone Member, Nishinakayama Formation

17 18 191410~. Outcrop No.Species I-----.-----.-----,.--=:....----,-----~---=-------=~--------,-----:----I

~ Fontanellicerasfontanellense~ (GEMELLARO)Q)o.~

~

SA10-S-1 SA18-1a-1SA18-1a-2SA18-1a-3SA18-1a-4SA18-1a-5SA18-1b-1

Petranoceras art: rinaldiniiVENTURI

SA1Q..6..2

Pallarpitespallus (BUCKMAN) SA10-6-6

Protogrammocerus nipponicllm(MATSUMOTO)

SA18-1c-1 SA19-1a-1 SA19-1b-11 SA19-1b-23SA18-1c-2 SA19-1a-3 SA19-1b-15 SA19-1b-25

SA19-1a-4 SA19-1b-16 SA19-1b-35SA19-1b-3 SA19-1b-17 SA19·1b-36SA19-1b-8 SA19-1b-18 SA19-1b-37SA19-1b-9 SA19-1b-19 SA19-1c-1

SA19-1c-2SA19-1c-3SA19-1c-4SA19-5a-1SA19-5a-2KT19-1b-1

KT19-1b-3KT19-1b-4KT19-1b-6KT19-1b-8

SA20-3b-7

SA20-3b-1 SA21-1-4

SA19-1b-26 KT19-1b-7

SA19-1b-1 SA19-1h-32 KT19-1b-2SA19-1b-29 SA19-1b-34SA19-1b-27

SA19·1b-2

SA19-1b-5

SA19·1b-10 SA19-1b-33SA19-1b-20 KT19-1c-1

Cll Q) Protogranrmo. cr. nippotlicllnl

~ ~ Protogramn,oceras )!abei

~ ~ ~ HIRANO8 g ~ Protogrammoceras cr. yabei

:si! ~ Protogrttmmoceras anoi HIRANO!:'! :r: 0:E e- hF;:;:u='cl;':':·nT:ie":':er='as::"'p:"":rT:im:"":o:":"rd:n"ill:::":m-::----I---+----l----+----+-----------------------4---+---1

~ (MATSUMOTO)Fuclniceras nakayamense

(MATSUMOTO)Lioceratoldesmafsllmotoi

HIRANOSA19-5b-1

TtltOl,iceras sp. SA17-5-1

"Cleviceras" chrysanthemum(MATSUMOTO)

SA19-1c-S SA19-1b-30SA19-1b-21

SA20-3b-3 SA21-1-1SA20-3a-3 SA21-1-3

"Co" afr. Chrl!SQllthemllm SA19-1b-28PolyplectllS okadai

(yOKOYAMA)SA19-1a-2SA19-1b-31

SA20-3b-2SA20-3b-6SA20-3b-8

Eoderoce- Dactyliocerasheliallthoidesrataceae NOKOYAMA)

SA14-1-1 SA19-5b-3 SA19-5b-5SA19-5b-4

SA20-3a-1SA20-3a-2

LJ'toceras sp. SA14-1-4 SA19-1b-4 SA19-1b-24SA19-1b-7 SA19-1b-38

Ammonitesp. SA10-S-3 SA14-1-2 SA17-4-1 SA18-8-1SA10-6-4 SA14-1-3

SA14-1-5

SA19-1b-6 SA19-5b-2SA19-1b-22 KT19-1b-5SA19-1c-6

SA20-3b-1 SA21-1-2

Appendix 3-1. Occurrence list of ammonoid fossils from the Sakuraguchidani Mudstone Member along the North Valley of the SakuraguchidaniValley, part 1. The inventory numbers of specimens are presented by each outcrop. The outcrop numbers correspond to those of Fig. 3-1.

~. Sakuraguchidani Mudstone Member. Nishinakayama FormationSpecies 23 24 25 26 27 28 29

FuciniCl!rosnaka)'amense SA23-1-1 SA24-1-2 SA26-4-9 SA27-4-1 SA29-3-8(MATSUMOTO) SA23-3-4

Lioceratoidesyokoyamai SA25-6-1 SA26-4-10(MATSUMOTO)

Liocerotoides matsumotoi SA26-1-4 SA27-5-2HIRANO SA27-5-10

"Ciesicems It chfJ'sllIfthtmum SA23-2-1 SA24-1-1 SA25-2-2 SA26-1-1 SA26-S-7 SA27-2-2 SA28-1-3 SA29-3-1(I) (MATSUMOTO) SA23-2-3 SA25-3-2 SA26-1-2 SA26-S-2 SA27-S-4 SA28-4-1 SA29-3-2co (I) co

SA26-4-4 SA26-S-4 SA27-S-8 SA28-4-7 SA29-3-3CI> IV .5:2 ;g ~ SA26-4-6 SA27-5-90tti ~ s SA26-4-7 SA27-5-1S~ § 0 "e. "cr. cJlrysonthemume- SA27-5-17 SA29-3-9 SA29-3-110 :2 IV32 I I Clnicerascr. exaralum SA23-1-3 SA28-4-2 SA29-3-4I (yOUNG & BIRD) SA28-4-4 SA29-3-7

Harpoceras ino'J'e; SA23-1-7 SA26-5-8 SA29-3-6(YOKOYAMA) SA23-3-3

Harpoceras sp. SA23-2-2 SA27-5-16

Polypleclus okadai SA24-S-1 SA29-3-5(YOKOYAMA)

* Hi/daltes sp. SA23-5-1

Dactylioceras helianthoides SA23-1-S SA26-1-3 SA27-3-1 SA29-3-10(YOKOYAMA) SA23-1-6 SA26-4-5 SA27-3-2

co SA23-2-S SA27-5-S

-8 SA23-3-1 SA27-5-11:§ SA23-3-2 SA27-S-12~ Dactylioceras afT. heliandloidts SA28-1-4se DactJ'/ioceras sp, SA26-1-6 SA28-4-8-8 Peronocems subflbulatum SA25-3-1 SA26-1-5 SA27-2-1 SA28-4-50w (YOKOYAMA) SA26-3-1 SA27-4-2

SA26-5-3 SA27-5"()SA26-7-1 SA27-5-7

Calliph).lloceras sp. SA26-4-1

Lywcefassp. SA26-7-2

Ammonite sp, SA23-1-2 SA25-2-1 SA26-5-S SA26-7-3 SA26-4-3 SA27-5-1 SA27-5-14 SA28-1-1 SA28-4-6 SA29-4-1SA23-1-4 SA26-5-6 SA26-7-4 SA26-4-8 SA27-5-3 SA28-1-2 SA28-4-9SA23-2-4 SA26-S-9 SA26-4-2 SA27-5-13 SA28-4-3

Appendix 3-2. Occurrence list of ammonoid fossils from the Sakuraguchidani Mudstone Member along the North Valley of the Sakuraguchidani Valley.part 2. The inventory numbers of specimens are presented by each outcrop. The outcrop numberscorrespond to those of Fig. 3-1. *: Hildoceratinae.

o. Sakuraguchidani Mudstone Memberl Nishinakayama FormationSpecies 36 40 41 43 48

Q,) Fonlanefliceras!ontalleUense SA41-1-11as (GEMELLARO).;;~ Call1lvarla japollica SA36-2-1~ (MATSUMOTO) SA36-2-2

:;:: SA36-2-3(l)'C SA36-2-4-c

SA36-2-5Paltarpitespallus (BUCKMAN) SA41·1·2 SA41-1-19Paltarpites tOJ'oranus SA41-1-3 KT41-1-1

(MATSUMOTO)PrologramnlOceras nipponicum SA48-2-5

(MATSUMOTO)

ProtograRlmoceras )labe; HIRANO HI48-8b-1Profogrammoceras sp. SA48-2·3

m Fudniceras nakaJYlmellse SA48-8b-4 SA48-8c-1Q,) m (MATSUMOTO) SA48·9-1 KT48-8a-3:2 "0

(l) Lioceratoides matsumoto;0 1= KT48-8c-2'@ e as

s .!: HIRANO

~1ii LioceratoidesJ'Okoyamai0~

SA41-1-8 SA48-2-1 KT48-8c-1:g :2 (MATSUMOTO) SA48-8a-4I I 0

~ Lioceratoides aradasi(FUCINI) KT41-1-2J:

Liocerato;des sp, SA41-1-10 SA41-1-12"Cfeviceras" chfJ'santhemuII' SA48-3-1

(MATSUMOTO) SA48-8a-8Clev;ceras sp. SA48-8a-10Polyplectus okadai SA48-6-1

(YOKOYAMA)

Amoftheus margorltatus HI36-1-1MONTFORT HI36-1-2

Eoderoce- Dactylioceras he/ianthoides SA48-4-1 SA48-8a-9 KT48-8a-1ratoidea (yOKOYAMA) SA48-4-2 SA48-8b-3 KT48-8a-2

SA48-8a-2 SA48-8c-5 KT48-8a-4

DacfJ'lioceras sp. KT4B-8a-5

CalfiphJ'lfoceras sp. SA48-2-4 SA48·8a-1 SA48·8b-1SA48-2-6 SA48-8a-7 SA48-8b-2

~'toceras sp, SA41-1-18 SA48-8a-6Ammonite sp. SA40-4-1 SA41-1-1 SA41-1-6 SA41-1-13 SA41-1-16 SA41-1-21 SA43-2-1 SA43-4-1 SA43-4-4 SA48-2-2 SA48-8c-2

SA41-1-4 SA41-1-7 SA41·1-14 SA41-1-17 KT41-1-3 SA43-2-2 SA43+2 SA48-8a-3 SA48-8C-3SA41-1-5 SA41-1-9 SA41-1-15 SA41-1-20 KT41-1-4 SA43-3-1 SA43+3 SA48-8a-5 SA48-8c-4

Appendix 3-3. Occurrence list of ammonoid fossilsfromthe Sakuraguchidani Mudstone Memberalongthe South Valley of the Sakuraguchidani Valley.The inventory numbers of specimens are presented by eachoutcrop. The outcrop numbers correspond to thoseof Fig.3-1.

o. Ishimachi Sandstone and Mudstone Member. Nishinakayama F.Species 53-2 53-3 53-4

Osperlioceras sp, A SA53-2-1 SA53-3-1 SA53-4-4al SA53-4.7c: SA53-4.8e SA53-4·9I Osperlioceras sp, B SA53-4.2iv SA53-4·3J: SA53-4-5

Grommoceras sp. SA53-4·11SA53-4·14

as ID-2l as PseudograntnJoceras sp.A SA53-4·10.:2:§ m SA53·4·12e B SA53-4-19S 00 30! al30! :fJ: c:

Pseudogrontmoceras sp. B SA53-4·20~ SA53-4·21S0EEe(!)

SA53-4.13 SA53-4-22Pseudogrammoceros sp,juvSA53-4.16 SA53-4·23

Phlyseogramntoceras sp, SA53-4-6

Dact}'/ioceras sp,juv SA53-4-15SA53-4.17

Eoderoce·ratoldea

Calliph}'lloceras sp, SA53-4·1SA53-4.18

Appendix 3-4.Occurrence list of ammonoid fossils fromthe Ishimachi Sandstone and Mudstone Member along the North Valley of the SakuraguchidaniValley. The inventory numbers of specimens are presented by each horizon. The outcrop numbers correspond to those of Fig.3-1.

~'Teradanl Formation Kuruma GrOUD

SpeciesDaira River 6 section Daira River 7 section Teradani Vallev Locality

DRFOf01 DRF0102 floated collecriol'l DRF0201 DRF0202a DRF0202b DRF0202c DRF0203 DRF0204 floated couecnon TDF01 TDF02 TDF03 TDF04 unknown

Canavaria novsp.A DRF0150 DRF0108 DRF0120 020301 020401 DRF0203 TDF0210DRF0110 DRF0121 020302 020402 TDF0211DRF0131 DRF0122

DRF0123DRF0124

Canavarta novsp.B DRF0134 DRF0144 020101 DRF0211DRF0135 DRF0146 DRF0213DRF0136DRF0137DRF0138DRF0104 DRF0132 DRF0204

DRF0133C. aff. haugl DRF0111C. aff. oroanatum DRF0201

020202 DRF0205 TDF0202Canavarta sp. DRF0206 TDF0203

TDF0204TDF0205TDF0206TDF0207TnF:O?QR

Emaciattceras sp. DRF0102 DRF0212DRF0103

Arieticeratinae gen.et sp. DRF0106 DRF0109 020201

indet DRF0107 DRF0112DRF0126 DRF0129DRF0127 DRF0130DRF0128

Amaitheus stokest DRF0101 DRF0148 DRF0209DRF0141

A. cf. stokes! DRF0143 DRF0207DRF0147 FMM2Q07 0202a02 DRF0208 T5303·1

A.margarttatus DRF0142 FMM2008 T5303·1aFMM2009

A.reoressus DRF0125 DRF0202A. aff. talroset DRF0149Amaitneu» sp. DRF0210Juraphyllites planulata DRF0214 TDF0101Lytoceras cf. siemenst. TDF0302

DRF0113 DRF0139 0202a01DRF0114 DRF0140

Ammonite sp, DRF0115 DRF0118DRF0116 DRF0119DRF0117

Appendix 3-5.Occurrence list of ammonoid fossils fromthe Teradani Formation, the Kuruma Group. The inventory numbers of specimens are presentedby each section and horizon. The horizon numbers correspond to those of Figs. 3-4 and 3-5.

sample No. 10-6 14-1 41·1 17-3 18·1a 18-1b 18·1c 19-1a 19-1b 19-5b 20-3b 21·1 23·3 24-2 24-4 25-2 25-3 25·5 25-8 26-1 26-2 26-4 26-7 27-1 27·3 27-5 28-1 29·2{malor elementsl

5102 60.58 61.58 61.34 59.75 61.41 62.79 53.04 59.35 60.59 57.97 60.80 54.75 58.27 56.08 61.78 56.38 57.58 60.34 55.95 57.63 61.50 56.65 60.59 57.60 59.32 60.62 55.34 54.94TI02 0.74 0.70 0.70 0.72 0.71 0.76 0.89 0.73 0.73 0.68 0.74 0.64 0.69 0.68 0.76 0.68 0.69 0.74 0.67 0.70 0.74 0.67 0.72 0.67 0.73 0.75 0.65 0.70

AI203 17.25 16.70 17.18 15.96 17.03 17.36 17.33 17.42 15.39 16.88 16.19 15.10 15.86 15.58 17.54 15.81 16.22 17.22 15.96 16.13 17.49 15.69 16.78 15.61 16.09 17.24 15.21 15.94FeO· 5.54 5.98 5.38 5.35 5.32 4.17 6.62 5.72 5.87 5.01 4.47 4.93 4.77 4.94 4.96 4.99 4.98 5.56 4.94 4.76 4.98 4.67 4.95 5.01 4.87 5.01 4.64 4.58MnO 0.02 0.03 0.02 0.05 0.02 0.02 0.04 0.03 0.03 0.04 0.01 0.05 0.04 0.05 0.02 0.04 0.04 0.03 0.05 0.04 0.02 0.05 0.03 0.04 0.03 0.03 0.05 0.04MgO 2.43 2.47 1.86 2.38 1.97 1.66 2.98 2.,26 2.50 2.31 2.06 2.03 2.20 2.20 2.01 2.25 2.28 2.40 2.27 2.25 2.15 2.21 2.34 2.39 2.54 2.45 2.18 2.15CaO 0.36 0.32 0.18 1.58 0.24 0.23 0.36 0.26 0.26 3.25 0.25 5.53 2.87 4.23 0.25 3.93 3.96 0.79 4.96 3.92 0.41 4.36 1.66 4.27 2.12 1.89 5.67 5.14Na20 2.49 2.50 2.50 2.29 2.04 2.05 1.67 1.84 1.97 2.21 1.76 1.92 2.24 2.19 2.42 2.12 2.14 2.35 2.15 2.24 2.32 2.11 2.21 2.04 2.06 2.18 1.97 1.92K20 2.80 2.53 2.72 2.43 2.93 3.13 2.71 3.22 2.30 2.84 2.76 2.49 2.48 2.48 2.84 2.55 2.68 2.83 2.63 2.66 2.82 2.55 2.76 2.53 2.51 2.81 2.45 2.70P205 0.13 0.12 0.15 0.14 0.16 0.15 0.16 0.16 0.15 0.14 0.14 0.14 0.15 0.15 0.15 0.15 0.16 0.16 0.15 0.16 0.16 0.15 0.16 0.15 0.16 0.16 0.17 0.16

H20tiLOI+Fe203-FeO' 6.56 7.10 7.47 6.94 7.78 7.11 10.67 8.13 7.63 7.54 7.96 9.76 7.76 8.84 6.87 8.45 8.08 6.95 8.88 7.71 7.14 8.85 6.46 8.10 7.23 6.40 9.68 9.90Total 98.89 100.04 99.51 97.60 99.59 99.42 96.46 99.12 97.42 98.88 97.15 97.34 97.33 97.43 99.60 97.34 98.81 99.38 98.62 98.21 99.72 97.95 98.66 98.42 97.65 99.56 98.01 98.18

(trace elementsl

Nb 9.821 9.629 9.794 9.897 11.32 11.408 9.859 12.231 11.059 10.062 11.762 9.911 10.5 9.933 11.359 9.507 11.05 10.926 10.465 10.16 10.66 10.375 10.055 9.613 10.651 10.301 9.376 11.026NI 56.2 62.2 51 63.5 33.6 24.5 52.1 41.1 36.3 39.7 34.7 38.7 36.7 34.7 40.7 42.5 39.9 43.9 35.8 35.8 34 33.6 40.1 44.8 35.8 44.1 45.5 41.2Pb 16.903 21.356 20.894 23.885 25.136 22.309 40.599 28.443 30.179 21.129 27.283 28.24 26.173 27.227 19.07 27.638 17.721 20.257 16.339 16.776 17.812 27.069 18.891 19.564 28.897 17.392 22.387 24.141Rb 118.34 111.22 123.1 112.76 131.82 140.64 126.19 147.79 110.04 128.5 134.92 112.08 113.82 113.13 130.4 116.64 121.88 127.1 118.8 118.08 128.23 118.17 126.81 118.48 117.88 127.52 111.8 122.61Sr 156.56 157.2 148.84 228.49 121.49 123.48 133.19 107.05 136.99 317 116.67 376.06 279.88 361.56 144.88 313.04 306.3 171.31 381.07 326.9 164.88 367.49 221.26 348.83 247.74 236.43 443.94 437.17Th 11.22 10.61 13.35 12.06 11.48 13.78 9.36 11.06 10.76 10.89 12.02 9.22 11.08 10.20 12.90 10.69 10.16 12,18 10.80 10.12 11.87 10.06 12.39 10.03 11.06 10.64 9.78 10.24Y 22.613 26.419 38.278 38.083 32.843 29.4 28.602 27.244 29.798 25.418 28.9 26.439 28.819 28.372 23.994 27.467 28.948 28.851 29.09 31.122 24.582 26.122 27.946 29.418 26.142 29.798 31.088 28.574Zr 181.68 176.94 160.56 168.97 163.98 171.81 156.36 169.17 168.56 164.86 159.48 147.28 181.64 152.53 173.52 152.29 180.58 167.72 180.21 168.41 165.78 154.92 162.55 158.93 153.47 185.61 149.1 156.49Sa 581 528.7 484.4 503.8 590.7 884.4 671.8 593 723.1 819.8 729.5 593.3 678.8 569.1 678.8 580.5 5n.4 569.2 559.8 565 589.9 570.6 807.2 534.7 576.5 627.6 573.7 694.4Cr 95.2 84.1 75.2 n,8 78.8 83.3 93.1 84.9 78.9 80.8 81.5 74.3 76.8 79.5 82 n,7 79.6 81.8 77.9 85.1 85.8 81.6 84.2 81.3 88.2 91.7 81.2 86.5V 127.43 114.06 111.34 104.29 113.44 117.6 166.28 117.67 100.69 114.51 115.96 99.18 109.28 102.75 111.17 102.79 106.66 110.48 106.09 116.2 121.61 108,86 116.56 116.03 124.29 132.4 132.82 125.1

Co 20.31 23.20 17,6947 22.70 15.04 13.36 27.22 17.01 19.41 16.62 15.68 20.17 19,55 16.69 19;66 19.96 16.99 23.04 17.27 19.13 14.45 17.52 18,11 21.21 15.21 16,25 15.85 16.22Th 12.20 11.60 12.3167 12.31 14.24 14.10 13.94 14.65 12.29 14.06 12.86 14.02 14.66 14.14 13.96 13.82 13.92 13.64 14.09 13.40 13.74 14.14 13.14 13.00 13.77 13.04 13.14 14.33U 2.80279 3.24378 3.17074 2.79196 3.30991 3.37115 3.20764 3.1561 2.92916 2.76661 3.20001 2.87518 3.10039 3.12033 2.83296 2.94707 3.03522 2.90145 3.00158 2.9509 2.90163 3.03036 3.07402 2.7905 3.10768 2.86791 3.33876 3.42735

I'lIre earth elementsLa 0.99104 0.88541 0.98396 1.19736 1.12712 1.13143 1.24023 1.13947 1.03652 1.06678 1.11484 1.01206 1.14605 1.00785 0.97263 0.99721 1.08096 1.03702 1,08021 1.02803 0.93814 1.03748 1.08787 1.03406 1.06139 1.0546 1.08217 1.05271Ct 0.85081 0.78449 0.86901 1.02661 0.96197 0.94522 1.0939 0.96072 0.909 0.90924 0.96239 0.90207 0.99803 0.91242 0.82529 0.87101 0.948 0.93907 0.942 0.94078 0.8248 0.93381 0.92103 0.90249 0.93112 0.93117 0.95851 0.91044

Pr 0.94902 0.87641 1.03118 1.16968 1.10937 1.07016 1.19837 1.07334 1.03778 0.99637 1.04631 0.98999 1.13957 1.01643 0.85846 0.97808 1.027211 1.02893 1.02645 1.0097 0,90694 1.01964 1.04943 0.9941 1.03847 1.04099 1.08592 1.0119

Nd 0.81296 0.80049 1.00856 1.10208 0.99428 0.96156 1.10463 0.96398 0.98179 0.88539 0.93671 0.89721 1.04987 0.93328 0.n654 0.90082 0.94334 0.93802 0.92522 0.94096 0.81316 0.92142 0.93474 0.91104 0.94494 0.92407 1.00395 0.896438m 0.86744 0.91325 1.34181 1.37854 1.15158 1,01356 1.23099 1.01113 1.179n 0.94478 1.09984 1.04523 1.20694 1.1169 0.80221 1.06638 1.07915 1.08597 1,03378 1.10062 0.86247 1.10889 1.07206 1.06988 1.11961 1.08063 1.21956 1.04771

Eu 0.80452 0.85286 1.47953 1.29271 0.98636 0.90745 1.07461 1.00749 1.12341 0.8346 0.96294 0.98312 1.06032 0.98066 0.74017 1.02439 1.03261 0.99998 0.99628 0.99398 0.73906 0.99107 1.04678 1.06393 1.01677 1.06121 1.15668 1.08431

Gd 0.n138 0.88079 1.48831 1.41686 1.05816 0.94255 1.08816 0.93246 1.1291 0.90859 1.04844 1.01611 1.14638 1.02753 0.76452 1.04486 1.06106 1.01942 1.0231 1.06227 0.85914 1.00622 1.03788 1.07161 1.04637 1.00937 1.17886 1.02564Tb 0.71541 0.87092 1.4066 1.34273 0.98148 0.87134 1.0676 0.86138 1.08982 0.8301 1.02137 0.94989 1.08228 0.97402 0.70044 0.98143 0.96563 0.94817 0.99256 1.0089 0.76947 0.93206 0.94881 0.95568 1.003 0.98272 1.11412 0.98806

Dv 0.63869 0,7687 1.15643 1.09824 0.89989 0.79302 0.91753 0.75707 0.9357 0.74088 0,91352 0.81362 0.91803 0.83025 0.62976 0.81097 0.79852 0.82291 0.8568 0.89927 0.66907 0.79599 0.80544 0.82901 0.84275 0.832 0.93295 0.87446

Ho 0.7698 0.90789 1.31743 1.22267 1.03239 0.92766 1.09888 0.88204 1.06316 0.87108 1.07556 0.92381 1.04613 0.96911 0.78862 0.95233 0.94314 0.93696 0.98867 1.00466 0.83262 0.91844 0.9485 0.96916 0.95885 0.91964 1.06119 1.01623

Er 0.70054 0.82743 1.06626 1.03853 0.94003 0.89198 1.00318 0.78811 0.93631 0.n676 0.93682 0.82948 0.92661 0.8349 0.71985 0.83198 0.83527 0.83694 0.86084 0.89355 0.73688 0.80623 0.83439 0.84807 0.85538 0.87096 0.92669 0.91887

Tm 0.79694 0.92139 1.02227 1.0n69 0.94936 0.81781 1.12063 0.81831 0.95484 0.83001 1.01666 0.83169 0.98485 0.87198 0.1766 0.87356 0.90117 0.88971 0,92132 0.93778 0.8238 0.87881 0.86133 0.83856 0.90999 0.90678 0.94071 0.9365

Yb 0.60234 0.96867 1.05887 1.02902 0.93616 0.92486 1.15686 0.82951 0.96541 0.84834 1.03921 0.8874 0.99848 0.93123 0.8181 0.89382 0.87387 0.91631 0..92648 0.90969 0.82818 0.87833 0.88903 0.86809 0.92284 0.927n 0.96879 0.99024Lu 0.82443 0.97516 1.06569 1.03663 0.94639 0.9189 1.1763 0.82887 0.95619 0.82427 1.02939 0.8796 0.99496 0.91447 0.80837 0.89069 0.86761 0.88004 0.91811 0.88948 0.79607 0.86803 0.90019 0.85835 0.89467 0.92538 0.95526 0.96751

Appendix 5-1.Analytical results of majorelements, traceelements and rareearth elements in mudstone samples fromthe Toyora Group.Sample numbers correspond to the horizon numbers in Figs. 5-1, 5-2 and 5-3.