ISSN 0031-0204

Transactions and Proceedingsof thePalaeontological Society of Japan
New Series

No .

162

Palaeontological Society of Japan
June 30, 1991

Co-Editors

Tsunemasa Saito and Kei Mori
Editorial Board

Kunihiro Ishizaki (Tohoku University), Yukio Isozaki (Yamaguchi University), Tomoki Kase
(National Science Museum), Itaru Koizumi (Hokkaido University), Yasumochi Matoba (Akita
University), Kei Mori (Tohoku University), Hiroshi Noda (University ofTsukuba), Tsunemasa Saito(Tohoku University), Yokichi Takayanagi (Ishinomaki Senshu University), Kazushige Tanabe(University of Tokyo), Yukimitsu Tomida (National Science Museum), Kazuhiko Uemura (National
Science Museum)

Officers for 1991-1992
President: Kiyotaka Chinzei
Honorary President: Teiichi Kobayashi
Councillors: Kiyotaka Chinzei, Takashi Hamada, Y oshikazu Hasegawa, Itaru Hayami,
Hiromichi Hirano, Hisayoshi Igo, Noriyuki Ikeya, Junji Itoigawa, Tomoki
Kase, Makoto Kato, Tatsuaki Kimura, Itaru Koizumi, Kei Mori, Hiroshi Noda,
Ikuo Obata, Kenshiro Ogasawara, Tomoo Ozawa, Tsunemasa Saito, Yokichi
Takayanagi, Kazushige Tanabe
Members of Standing Committee: Hiromichi Hirano (General Affairs), Tomoki Kase
(Finance), Tsunemasa Saito (Editor in Chief, TPPSJ), Kei Mori (Co-Editor, TPPSJ),
Noriyuki Ikeya (Planning), Hiroshi Noda (Membership; Co-Editor, Special Papers),
Kazushige Tanabe (Foreign Affairs), Itaru Hayami (Editor, "Fossils"), Juichi Yanagida(Co-Editor, Special Papers), Tatsuaki Kimura (Friends of Fossils)
Secretaries: Tatsuo Oji (General Affairs), Masanori Shimamoto (Editorial of TPPSJ), Hiroshi
Kitazato (Planning), Katsuo Sashida (Membership), Yukimitsu Tomida (Foreign
Affairs), Katsumi Abe (Editorial of "Fossils"), Takeshi Ishibashi (Editorial of Special
Papers), Tamiko Ohana (Friends of Fossils)
Auditor: Kuniteru Matsumaru
The fossil on the cover is Trilophodon sendaicus Matsumoto, an extinct elephant, which
was described from the Pliocene Tatsunokuchi Formation developed in the vicinity of
Sendai, Northeast Honshu, Japan. (lOPS coil. eat no. 87759 (A), length about 18.5 em)
All communication relating to this journal should be addressed to the

PALAEONTOLOGICAL SOCIETY OF JAPAN
c/o Business Center for Academic Societies,
Yayoi 2-4-16, Bunkyou-ku, Tokyo II3, Japan

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 162, pp. 761-766,4 Figs., June 30, 1991

917.

FOSSIL BRYOZOANS FROM THE LOWER GONDWANASISNE FORMATION, NEPAL LESSER HIMALAYAS*SUMIO SAKAGAMI
Department of Earth Sciences, Faculty of Science,
Chiba University, Yayoi-cho, Chiba 260
and

HARUTAKA SAKAI
Department of Earth Science, College of General Education,
Kyushu University, Ropponmatsu, Fukuoka 810

Abstract. A newly proposed bryozoan species, Pamirella nepalensis Sakagami andSakai, found from a limestone block which was derived from the upper part of the Sisne
Formation, Nepal Lesser Himalayas, is described. It is highly possible that the species
indicates a middle Early Permian (Artinskian) age and that it provides a datum for establishing the geological age of the formation.
Key words.

Bryozoa, Nepal Lesser Himalayas, Pamirella, PermianGroup in the upper reaches of the Badahare
river of west Central Nepal. These blocks
are considered to have been derived from theupper part of the Sisne Formation. Sakai(1983) reported some bryozoan remains of thegenera Fenestella, Polypora and Acanthocladia, but their specific identification could
not be made because of the poor state ofpreservation. They are reported to be possibly of Carboniferous to Permian age.
Additional bryozoan fossils were obtained
from an impure limestone block which wasderived from the upper part of the Sisne
Formation. They are somewhat better
preserved than the previous specimens. In
this paper, we present a brief note on thegeology of the fossil locality and describe
paleontologically one new bryozoan species.
This is the first report of fossil bryozoans
from the Nepal Lesser Himalayas.

Introduction

Some bryozoan fossil remains have hitherto
been known from the so-called "Fenestella
Shale" in the Himalayan ragion, which iswell known to represent part of the Lower
Gondwana sequence of late Carboniferous or
Carboniferous to Permian age for some students (Ganestan, 1972; Gansser, 1964; Krishnan, 1982; Jani and Das, 1973; Sakai,1983). These previously reported bryozoans,however, inel ude only fenestellids such as
Fenestella, Dogaddanella, Polypora, Protoretepora and Acanthocladia, and are usuallyin a poor state of preservation.
As already mentioned by Sakai (1983),
some blocks (floats) of shale which abundantly contain fenestellid bryozoans were collected near the boundary fault between the
Kali Gandaki Supergroup and the Tansen"Received October 31,1990; accepted April 10, 1991
761

Sumio Sakagami and Harutaka Sakai

762..-/''.
,-J . • \r- .....,.

.

.
-_ .....,.....".
r 1.
<.......
.
·"\..,...f .
;.~. .
. . . . :-:t."'-...r.L. ../\.
.. . .
. .. CD· ... ' "
~

tlfCr

Fig.3
Figure 1. Geotectonic division of the Nepal Himalayas and four main areas where the Lower
Gondwana beds are distributed. I. Central and Lesser Himalayan CrystaIIines, Tethys sediments andTertiary granite; 2. Lesser Himalayan sediments; 3. Siwalik Group. MCT: Main Central Thrust, MBT :Main Boundary Thrust.

Geological outline
The Lesser Himalayan sediments in west
Central Nepal (Figure I) are grouped into
two major divisions; the Kali Gandaki
Supergroup of late Precambrian to early
Paleozoic age and the disconformably overlying Tansen Group. The Tansen Group
comprises five formations; the Sisne,
Taltung, Amile, Bhainskati and Dumri Formations in ascending order (Figure 2). The
former three are the Gondwana rocks and thelatter two are the post Gondwana rocks.
The lower Gondwana Sisne Formation is
distributed extensively in the outer belt of theLesser Himalayas, and its eastern and westerncontinuation is disconnectedly distributed in
the frontal range near the Main Boundary
Thrust in Dharan, Sallyan and Surkhet (Figure I).
The Sisne Formation in the Tansen area ismainly composed of a glacial diamictite,
fluvial sandstone and bioturbated rhythmite
beds of thin sandstone and shale in the uppermost part (Sakai, 1983). The fossil bryozoans were discovered from a large limestone
block in the upper reaches of the Badahare
Khola (Sl of Figure 3) and from cobble-sized

shale floats in the upper stream of the Amile
Khola (S2 of Figure 3). The block andfloats must have been derived from the Sisne
Formation because their lithologies are identical to the bioturbated rhythmite and shale,
respectively, of the formation.

Fossil bryozoans and their age
Abundant bryozoan remains occur in association with some crinoid stems and a small
amount of brachiopod fragments in an impure limestone block (ca. 90 cm in length)
exhibiting a lithology of calcareous shale andlimestone interbeds. Angular, detrital
quartz grains are usually mixed with skeletal
debris in the limestone. They are considered
to have been swept up and deposited in
muddy tidal fiats during a storm (Sakai,1983).
The following three bryozoan species could
be discriminated: Pamirella nepalensis, n.
sp., Fenestella sp. indet. and Polypora sp.
indet. Although the genus Pamirella established by Gorjunova (1975) is now known torange from the Lower Carboniferous to
Lower Permian (Artinskian), Pamirella nepalensis, n. sp. is nearest to P. pulchra (Bass-917.

Bryozoans from the Sisn e Formation

763

Siwalik GroupM B T --..:.---~~~~~~---:"",,,"~__ 200Dm

Formation

Dumri

Oligocene - earlymeandering

Mioceneriver

deposits.....(/)

1500

o

~

Bhainskati
Eocene shallow mari ne & bracki sh -wat

~

'0

Amile

Formation

Cret . - Palaeocene?
deltaic deposits

fluvio -C:~_.....r~~~;;:;:;i~1
o

"
Q;

c.

Taltung

Formation~late Jurassic - early Cretaceoustrachyte lava& fluvial deposits(/)

Ritung Bioturbated Mudstone
fossil bryozoans ~

*

ro
c:

;

Sisne

Formation'0glate Carboniferous - Permianglacial diamictite & fluvial"

deposits

500oKali Gandaki Supergrouplate Precamb.- early Palaeozoic
arid shoreline deposits

Figure 2.

Statigraphic section of the Tan se n Group a nd the ho ri zo n of fossil bryozoa ns,

after Sak ai (1983).

764

Sumio Sakagami and Harutaka Sakai
Description of a new species
Genus Pamirella Gorjunova, 1975
Pamirella nepalensis Sakagami
and Sakai, n. sp.
Figures 4-1-6

Figure 3. Geological map around the fossil
localities (SI, S2). I. Dumri Formation; 2.
Bhainskati Formation; 3. Amile Formation; 4.
Taltung Formation; 5. Sisne Formation; 6. KaliGandaki Supergroup.

ler) which was originally described from theLower Permian of Bitauni in Timor Island ofIndonesia. The genera Fenestella andPolypora are both known to range from theOrdovician to Permian, especially being very
common in the Carboniferous and Permian.
Fenestella sp. and Polypora sp. are both indeterminable because of their possession ofrare and fragmentary zoaria. Thus, the present bryozoan faunule is highly possible toindicate a middle Early Permian (Artinskian)age.
In the Kumaun and Garhwal Lesser
Himalayas in India, the Blaini Formation
with glacial diamictite beds has long been
believed to represent a northern continuationof the Lower Gondwana sequence in thepeninsular India. However, recent findingsof Cambrian trilobites and archaeocyatha
from the Tal and Krol Formations, which
overlie the Blaini Formation, disclosed thatthe Blaini diamictite is not late Paleozoic butlate Precambrian in age (e.g., Singh and Rai,
1983; Joshi et al., 1989). Under these circumstances, the present finding of bryozoan
fossils of Permian age from the Sisne Formation evidently testifies that the Lower Gondwana sequence exists in the central sector of
the Himalayas.

Description.- Zoarium cylindrical, nearlystraight stem, branching mode not observed,
1.2 to 2.5 mm in diameter. Surface specimen
could not be examined but observation oftangential section near surface suggests thatzooecial apertures being not regularly arranged in any directions. Exozone very thin forthe diameter, about 0.2 to 0.3 mm in thickness. Ratio of half a diameter of zoarium to
exozone 3 : 1 to 4 : 1.
Zooecial tube straight and very long, parallel to longitudinal direction in the endozone,
and rapidly curved outwards at the inner edgeof exozone. Zooecial tubes very short in
exozone, 0.2 to 0.3 mm in length and oriented
at an angle of about 60 to 90 degrees to stem
surface. Zooecial wall very thin and nearlystraight in endozone, abruptly thickened in
exozone. Superior and inferior hemisepta
lacking. Zooecial wall laminae rather
coarse and generally parallel to the surface
except for the acanthostyle (megacanthopore)
position where the laminae are swelled out.
Diaphragm and metapore lacking. In tangential section of exozone, zooecial tube
being elongated oval, longer diameter ranging
from 0.128 to 0.192 mm. Twelve to fifteen
well-developed acanthostyles consisting of arather clear central tube with dark-colored
concentric fibrous tissue, and surrounding
zooecial tube in one row in interspaces ofzooecia. Outer diameter of acanthostyle ranging from 0.038 to 0.058 mm. In transverse
section, zooecial tube in endozone irregularly
polygonal.
Remarks.-Blake (in Boardman et al.,1983) included the following six species in thegenus Pamirella: Pamirella nitida Gorjunova (the type species), Rhombopora pulchra Bassler, R. orientalis Bassler, R. nicklesi

917.

Bryozoans from the Sisne Formation

765

Figure 4. Pamirella nepalensis Sa kagami and Sak a i, n. sp. 1, longitudin a l section , Reg. no. GKD30705, X 20. 2, enlarged part of I, x 80. 3, tangen ti a l sectio n, Reg. no . G KD-30706, X 20. 4, enl arged
part o f 3, x 80. 5, transverse secti o n, Reg. no . G KD-30 707, X 20. 6, en larged part of 5, x 40.

Ulrich, R . minor Ulrich a nd R.? asperu/aUlrich . Among them , the latter three species
were originally described from the Lower
Carboniferous o f North America , but they
seem to be quite different from th e present
new species. The present form is in generala ppeara nce not unlike the type species, P.
nitida which was described from the uppe rpart of the Ba uza rdarinsk Formation (Artin ski a n of the Lower Permian) in the so uthea stern part of Pamir, but it is di stingui shed fro m
the type spec ies in the mode ofzooecia l tubes

766

Sumio Sakagami and Harutaka Sakai

and by the smaller diameter of acanthostyle.
The present form seems to be nearest to P.
pulchra which was described from the Lower
Permian of Bitauni in Timor Island of Indonesia by Bassler (1929). The present form,
however, can be distinguished easily from P.
pulchra in having the very long, parallelzooecial tubes in endozone and the extremely
thin exozone.
Occurrence and Geological age.-Specimens ofthis new species were found in a darkgray, impure limestone block which wasderived from a horizon in the upper part of
the Sisne Formation of the Tansen Group.
The geological age is uncertain, but it isestimated to be assignable to the Artinskian(Early Permian).
Repository.- The specimens treated in thispaper are deposited in the collections ofDepartment of Earth and Planetary Sciences,
Faculty of Science, Kyushu University. Reg.
nos. GKD-30705 (holotype), GKD-30706
and GKD-30707 (paratypes). The otherthin sections, Reg. nos. GKD-30708, GKD30709, GKD-30710 and GKD-30711, areprepared.

Acknowledgements
The geological survey was done by one ofus (H. Sakai) as part of his activities in theJapan Overseas Cooperation Volunteers (JOVC) service. During the course of investigation, Dr. M.P. Sharma, Mr. B.M. Pradhan andall other staff members of Department of
Geology, Tribhuvan University, gave Sakai
every facility and valuable advice. JOCV
financially supported the field works. We

deeply appreciate the kind assistance provided.

References cited
Bassler, R.S., 1929: The Permian Bryozoa of Timor.
Paliiont. von Timor, Lief. 16, Abh. 228, p. 36-89,
pis. 225-247.
Boardman, R.S., Cheetham, A.H., Blake, D.B., Utgaard, J., Karklins, O.L., Cook, P.L., Sandberg,
P.A., Lutaud, G. and Wood, T.S., 1983:
Bryozoa. p. 1-626, figs. 1-295. In, Robison, R.
A., ed., Treatise on Invertebrate Paleontology.
Part G, Bryozoa (Revised, Volume I). Geol.
Soc. America, Boulder and Univ. Kansas Press,
Lawrence.
Ganestan, T.M., 1972: Fenestellid Bryozoa from theboulder slate sequence of Garhwal. Himalayan
Geol., vol. 2, p. 431-451.
Gansser, A., 1964: Geology of the Himalayas.
289 p. John Wiley & Sons, London.
Gorjunova, R.V., 1975: Permskie mshanki pamira.
Trudy Akad. Nauk SSSR, Paleont. Inst., vol.
149, 128 p., 29 pis.
Jain, A.K. and Das, A.K., 1973: On the discovery ofUpper Palaeozoic bryozoans from Kameng district, Arunachal Pradesh. Current. Sci., vol. 42,
p.352-354.
Joshi, A., Mathur, V.K. and Bhatt, O.K., 1989:
Discovery of redlichid trilobites from the
Arenaceous member of the Tal Formation, Garhwal Syncline, Lesser Himalaya, India. Jour.
Geol. Soc. India., vol. 33, p. 538-546.
Krishnan, M.S., 1982: Geology of India and Burma(6th ed.). 536 p. CBS Pub!. & Dist., Delhi.
Sakai, H., 1983: Geology of the Tansen Group of theLesser Himalaya in Nepal. Mem. Fac. Sci.,
Kyushu Univ., Ser. D., vo!. 25, p. 27-74.
Singh, I.B. and Rai, V., 1983: Fauna and biogenic
structures in Krol-Tal succession (Vendian-Early
Cambrian), Lesser Himalaya: Their biostratigraphic and palaeoecological significance. Jour.
Palaeont. Soc. India, vol. 28, p.67-90.

*/~ -IV, V 'Y -Ij-- e. -<-1'" '7 i;::,5j-m-r0, Sisne Formation iJ'GVIE:±l Lt..:EEK:'fiIV~EiJ'
G, ::J 'T A "/ 1r.E IV ~fl Pamirella nepalensis Sakagami and Sakai :a-~7.i1j L ~c1i: L t..:o ~G < .: IV fl fi lltrM =~ ~c cp M (7 Iv T 1 :/ 7. yilt) :a-:tIii7F-r 0 t '';If ;t G
Sisne F ormation IVtt!!.'l1t8if~:a-";lf~-r 0 t..:I!/;JIV I ~IV T -!J :a-mffli-r 0 ~ IV'C'ih 0 0 it..:, Sisne Formation fi, -{-IV:'fiffL!:il"-lt";lf;t, 1':/ n~£!,IVTiffi::J':/ I: '7 :T*IV~tj]~:!jU:,d,..tJ:-t-.: tiJ~
'C. ~ 0 0
tliLl:: ~~ • i§ #-IE>:$:n,Trans. Proc. Palaeont. Soc. Japan, N.S., No. 162, pp. 767-780,6 Figs., June 30, 1991

918.

PALEOENVIRONMENTAL TRANSITION AT 1.2 MA IN THE
OMMA FORMATION, CENTRAL HONSHU, JAPAN*
AKIHISA KITAMURA
Department of Geology and Mineralogy, Faculty of Science,
Kyoto University, Kyoto, 606

Abstract. A marked change of paleoenvironment took place at the transition from thelower to the middle part of the Omma Formation, at about 1.2 Ma. Cyclicity in litho- andbiofacies is distinctly wrought in the middle part. Each cycle in the middle part consists ofa fining-upward sequence which starts with a shell bed and ends with a muddy sandstone.
Within each cycle, molluscan associations change from those indicative of cold and shallow
waters to warm and deeper waters. This observed cyclicity has an amplitude up to 50 m inwater depth and an estimated periodicity of 28,000 years on the average and is attributed toglacio-eustatic sea-level fluctuations.
Even the molluscan composition suggests that water depth was shallower than 20-30 m
during the deposition of nearly all of the lower part, whereas cyclic changes of litho- andbiofacies as seen in the middle part are not developed in the lower part. This contrast canbe interpreted due to the increase of amplitude of glacio-eustatic sea-level changes at about
1.2 Ma. At least nine periods of influx of warm-water are detected in the middle part for atime span of 0.3 million years between 1.2 and 0.9 Ma, whereas only one is detected from thelower part spanning a time interval of about 0.16 million years. This apparent change inthe frequency of warm-water influxes may also be ascribed to the increase of amplitude ofglacio-eustatic sea-level changes.
This 1.2 Ma date of the marked transition of paleoenvironment in the Om rna Formation
seems to be synchronous with the initiation time of intensified glaciation in Europe andNorth America as recorded in oxygen isotope signatures and glacial debris in deep-sea
sediments.
Key words. Glacio-eustasy, intensification of glaciation, 1.2 Ma, Omma Formation,
Omma-Manganji Fauna.

Introduction
The Omma-Manganji Fauna is widely distributed in marine Pliocene and Pleistocene
formations along the Japan Sea coast, fromCheju (or Saishu) Island, Korea, through
Ishikawa, Toyama, Niigata, Yamagata, Akita
and Aomori Prefectures to southern Hokkaido. This fauna named by Otuka (1936,
1939a, b) has been recognized as the coldwater molluscan fauna characteristic of theJapan Sea.
'Received November 2, 1990; accepted April 10,
1991

The type section of the Omma Formationin Ishikawa Prefecture, the section studied
here, is known as one of representative localities of the Omma-Manganji Fauna. Many
works have dealt with the molluscan fauna of
the Omma Formation (e.g. Kaseno and Matsuura, 1965; Ogasawara, 1977, 1981 ; Matsuura, 1985). Ogasawara (1981, 1983, 1986)
divided the molluscan fauna, of this formation
into two faunas, "the Omma proper" and "theYounger Ommaian". The Younger Ommaian Fauna is found in the upper part of thesection and is characterized by the dominanceof extant and warm-water species. Accord767

Akihisa Kitamura

768

ing to Ogasawara (1981), the Omma proper
Fauna occurs in the rest of the Omma Formation and is characterized by the common
occurrence of extinct species and those species
which lived in shallow waters, from littoral to50-60 m depths.
Recently, Kitamura and Kondo (1990)
analyzed temporal changes in lithofacies andmolluscan fossil associations, based on
detailed field observations at the type sectionof the Omma Formation. They divided theformation into three parts, lower, middle andupper. The "Omma proper Fauna" occurs
from the lower and middle parts. The middle part of the formation exhibits at least ten
successive sedimentary cycles. Each cycle
shows a time-progressive change in molluscan
associations from the cold-water, upper sublittoral associations in the lower portion of
the cycle, to the warm-water, lower sublittoral
associations in the upper portion. They concluded that this change from cold and shallow water to warm and deep water eovironments was due to glacio-eustatic changes.
Certain records of glacio-eustatic sea-level
fluctuation can also be expected in the lower
part of the Omma Formation, as comparedwith the oxygen isotope record of deep-sea
stratigraphy (e.g., Williams et af., 1988). No
such signals have, however, been recognizedin either molluscan associations or lithofacies. This fact suggests that a paleoenvironmental transition is likely to have takenplace sometime at the boundary between thelower and middle parts of the Omma Formation. This paper intends to summarize thestratigraphic context of the Omma-Manganji
Fauna in the lower and middle parts of theOmma Formation at the type section, and to
document the transition.

Acknowledgments
This is a part of the doctoral dissertation
submitted to Kanazawa University. I am
especially indebted to Prof. Kenji Konishi ofKanazawa University for his constructive

cntlclsm and encouragement. Prof. Kiyotaka Chinzei of Kyoto University and Dr.
Yasuo Kondo of Kochi University kindly
helped with discussion and advice. My
thanks should also be extended to Dr. Takahiro Kamiya and Prof. Toshiaki Takayama of
Kanazawa University, Dr. Seiichiro Matsui of
Utsunomiya University for their assistance.
Emeritus Prof. Y oshio Kaseno of Kanazawa
University kindly allowed me to examine hiscollection of molluscan fossil specimens fromthe Omma Formation. The manuscript was
critically read by Prof. Kenji Konishi, Prof.
Kiyotaka Chinzei and Dr. Seiichiro Matsui.
Their suggestions and constructive criticisms
are acknowledged.

Stratigraphic framework and geologic age
The type locality of the Omma Formation(Mochizuki, 1930) is situated at the floor of
the River Saikawa, Kanazawa City, Ishikawa
Prefecture, Central Japan (Figure 1). The
formation overlies unconformably the Saikawa Formation (Ogasawara, 1977) and is inturn overlain unconformably by the Utatsuyam a Formation (Ichihara et af., 1950).
The marine Saikawa Formation is mainlycomposed of a massive siltstone. The nonmarine Utatsuyama Formation is represented
by an alternation of coarse-grained sandstone,
mudstone and conglomerate beds. The
Omma Formation at the type section attains
210 m in thickness (Figure I) and has anortheast-southwest strike with 10-20· dip to
the northwest.
The detailed lithostratigraphy of the Omma
Formation was not established until Takayama et af. (1988) gave a description oflithofacies of the type section. They divided
the formation into two parts; the lower partconsisting of bluish-gray, very fine- to finegrained sandstone with abundant wellpreserved marine molluscan fossils, and theupper part comprising four units, in ascending order: (1) brown fine- to medi umgrained sandstone; (2) alternation of sand-918.

Paleoenvironmental transition at 1.2 Ma

Biostratigraphy(Takayama et a1.,1988)

769'--_.....lkm

"'"
0\
00

~

...;
QI

'U

j...

t

~

i
'.;:1

£I
~

ti

}

Top of acme

§
:cl

J
I1
O.91MaReticulofenestra sp. A
O.83Ma-FAD Gephyrocapsa
parallela O.89Ma0~, . conglomeratec=:J sandstonec=:Jsiltstone~gravel~....
O.99MaLegend-~"parallel lamination~~~ cross lamination

E:J tuff~concretion-LAD Gephyrocapsar.--~':':'1_--f...,..4(large) 1.10Ma~j
Om-LAD HeJicosphaera
f:1H5~~~":'
sellii 1.19Ma-FAD Gephyrocapsa(large) 1.36Ma~shell fossils
I~v~v~l shell bed

I ...... Ilenticular shell bed~bioturbation,.0..

plant fossils
erect stump

1-10; number of sedimentary
cycles in the middle part

Figure.1. Columnar section of the Omma Formation at the type locality, showing biostratigraphic
datum horizons established by Takayama et al. (1988) and paleomagnetic data by Ohmura et al. (1989).

770

Akihisa Kitamurastone and mudstone; (3) bluish-gray finegrained sandstone; and (4) brown mediumgrained pebbly sandstone. On the basis of
the litho- and biofacies, Kitamura andKondo (1990) subdivided the lower part into
two units, and proposed a three-fold divisionof the formation (Figure I). The present
study deals particularly with the lithofacies
and moll uscan fossil associations in the lower
and middle parts.
Microbiostratigraphic and magnetostratigraphic data (Hasegawa, 1979; Takayama etal., 1988; Ohmura et al., 1989) indicate that
the Omma Formation at the type locality is ofearly Pleistocene age. According to Takayama et al. (1988), who proposed fivenannofossil biohorizons in the Omma Formation at its type section, the FAD Gephyrocapsa (large) (1.36 Ma) is located at about 10m
above the base of the formation (Figure I).
The LAD Helicosphaera sellii (1.19 Ma) and
LAD Gephyrocapsa (large) (1.10 Ma) arelocated in the upper part of Cycle I and the
middle part of Cycle 6, both in the middle
part of the formation, and two biohorizons,
the FAD Gephyrocapsa parallela (0.89 Ma)
and the top of acme Reticulofenestra sp. A(0.83 Ma), are located within the upper partof the formation (Figure I).
A paleomagnetic study of Ohmura et al.
(1989) established that the Omma Formationof the type locality is equated well with the
Matuyama Reversed Polarity Epoch. A normal polarity horizon between the bottom of
Cycle 9 and the top of the middle part is
assigned to the Jaramillo Event (0.99-0.91
Ma) (Figure I).

Cyclic changes of sediments and molluscan
fossil associations in the middle partof the Omma Formation
The middle part of the formation includes
at least 10 cyclic changes of both sedimentary
facies and molluscan fossil associations(Kitamura and Kondo; 1990). These cycles
are numbered, in ascending order, from I to

10 (Figure I). Thickness of each cycle ishighly variable ranging from 1.5 to 11.8 m
with an average of 7.0 m. The cyclicity oflithofacies and molluscan fossil associationsin the middle part of the Omma Formation
will be briefly reviewed in order to comparewith the non-cyclic nature of the lower part.
A representative cycle exhibits a finingupward lithologic sequence, starting from thebasal shell bed, through a well-sorted finegrained sandstone, and ending with a muddy
fine- to very fine-grained sandstone. The
bottom of the basal, 5 to 30 m thick, shell bed
is defined with an erosional surface. The
bed is usually packed with shells and terrigenous granules intermixed with sand.
The shells are oriented parallel to the bedding, and occur in contact with each other tobe shell-supported. The well-sorted, finegrained sandstone, 0.5 to 1 m thick, overlies
the shell bed. The sandstone appears to lackboth abiogenic and biogenic sedimentary
structures for the most part. In most cases,
the sandstone yields a large number ofarticulated shells of Felaniella usta. The
shells are dominantly oriented parallel to thebedding plane. The middle and upper portions of each cycle are composed of a muddy,
fine- to very fine-grained sandstone from 0.5
m (Cycle 4) to 8 m (Cycle 8) in thickness.
The sandstone yields molluscan fossils sporadically. Deep burrowers, such as Panopea
japonica, Barnea dilatata and Clementia
vatheleti, are preserved in the life position.
Most other bivalves are conjoined and wellpreserved, but are not in the life position.
They are mostly aligned parallel to the bedding plane.
The fossil moll uscs in the middle part of
the formation can be grouped into 11 associations by means of combined occurrences andrelative abundance of species (Kitamura andKondo, 1990). The term "association" ishere used to indicate a suite of assemblages
which are similar in species composition.
The characteristic and associated species ofeach association is shown in Table 1 along918.
Table l.

Paleoenvironmental transition at 1.2 Ma

771

Molluscan fossil associations and their main constituent species in the lower and middle partsof the Omma Formation at the type locality.

Association

Characteristic species

Associated species

a. Peronidia Assoc.

Peronidia zyonoensis
Glycymeris yessoensis
Mercenaria stimpsoni
Pseudamiantis tauyensis

Felaniella usta, Acila insignis
Turritella saishuensis saishuensis
Mizuhopecten yessoensis yokoyamae

b. Macoma sectior
Association

Macoma seclior, Acila insignis

Felaniella usta, Clinocardium Jastosum
Dosinia japonica, Panopea japonica

c. Felaniella Assoc.

Felaniella usta, Acila insignis

Peronidia zyonoensis
Clinocardium Jastosum
Turritella saishuensis saishuensis

d. ClinocardiumTurritella Assoc.

Clinocardium Jastosum
Yoldia notabilis
Turritella saishuensis saishuensis
Acila insignis, Cryptomya busoensis
Crypotonatica janthostomoides

Liocyma jiuctuosa, Ennucula tenuis
Mizuhopecten tokyoensis hokurikuensis
Cye/ocardia Jerruginea
Lucinoma annulata
Macoma tokyoensis
Antiplanes contraria
Ophiodermella ogurana
Suavodrillia dee/ivis

e. Macoma tokyoensisFelaniella Assoc.

Macoma tokyoensis, Felaniella usta

Yoldia notabilis, Panopea japonica

f. Yoldia Assoc.

Yoldia notabilis

Felaniella usta, Acila insignis
Dosinia japonica, Panopea japonica

g. Transitional
Association

Yoldia notabilis, Paphia schnelliana
Ennucula tenuis
Clinocardium Jastosum

Acila insignis, Crypotomya busoensis
Turritella saishuensis saishuensis
Cryptonatica janthostomoides
Tugurium exutum, Nassarius caelatus

h. Barnea Assoc.

Barnea dilatata

Tugurium exutum

Cye/adicama cumingi

Tugurium exutum
Paphia schnelliana
Barnea dilalataj. TuguriumPaphia I Assoc.

Tugurium exutum, Paphia schnelliana
Nassarius caelalus, Yoldia notabilis

Saccella gordon is, Limopsis crenata

k. Tugurium-

Tugurium exutum, Paphia schnelliana
Saccella gordon is, Limopsis crenata

Dentalium weinkaujji, Acila divaricata
Glycymeris rotunda
Saccella semataensis
Nemocardium samarangae

1.

Cye/adicama
Association

Paphia II Assoc.

p. A cila insignis
Association

A cila insignis, Yoldia notabilis
Sola men diaphanaq. Acila divaricataLimopsis Assoc.

Acila divaricata, Limopsis crenata

Paphia schnelliana, Phaxas attenuatus

r. Anadara-

Anadara amicula
Clinocardium Jastosum
Yoldia notabilis

Turritella saishuensis saishuensis
Acila insignis, Mya japonica
Cryptonatica janthostomoides

Clinocardium
Association

Akihisa Kitamura

772
water regime
low tidemark20-30m-B

cold water
Assoc.
h. Macamascctior Assoc.
r. AnadaraClinocardium
Assoc.

c. Felamella
Assoc.
d.C/inocardiumTurri/ella Assoc.
e. Macoma/akyoensis Felamella

f. Yaldia Assoc .

.....
d)

wann waterBa. Pcronidia

Assoc.

0.
d)-0

trawJl~~nali. Cycladicama
Assoc.

g. Transitionalj. Tugurium-

Assoc.

Paphia I Assoc.

I, q.Acila
divaricata -C;J~50-60mlimopsis Assoc

p. Aeila insignis

k. Tugurium -Assoc.

Paphia II Assoc

100-1 20m

Figure 2. Relationship between the molluscan fossil associations and environmental conditions interms of water depth and water regime.

with three associations in the lower part.
Relationships between these associations andsuch environmental conditions as water
depth, water regime and sediment are summarized in Figure 2. The environmental
characters of the associations relative to thenature of the sea water (cold-, intermediateand warm-water) and approximate water
depth of habitat are inferred from information available from the living species (Geographical distribution: Kuroda and Habe,
1952, Higo, 1973; Bathymetry: Oyama,
1952, 1973). Based on the geographical distribution along the Pacific coast shelf area,
the term "cold-water element" here refers to
those species living in the area north of 35'N
and "warm-water element" to those south of
3S'N. Species dwelling in both areas aregrouped as the "intermediate element".
In most cycles, the vertical change in molluscan associations indicates that environment had changed from the cold-water, upper
sublittoral zone through the warm-water,lower sublittoral zone to the cold-water,
upper sublittoral zone as observed typicallyin Cycle 9 shown in Figure 3. This increaseof water depth is concordant with a climaticchange from cold to warm. Based on molluscan associations, biostratigraphic as wellas paleomagnetic data, the maximum amplitude of water-depth fluctuation is estimated to
be 50 m and the periodicity 28,000 years on
the average. These characteristic temporaland cyclic changes of oceanographic conditions can be best explained by invoking
glacio-eustatic sea-level and paleotemperaturechanges (Kitamura and Kondo, 1990).

Lithofacies and molluscan fossil
associations of the lower partof the Omma Formation
Lithofacies

The 25 m-thick lower part of the Omma
Formation which was accumulated during a
0.16 m.y. time interval from 1.36 to 1.2 Ma
consists of a bluish-gray, partly brown, finegrained sandstone, except for the basal part at
Horizon I (Figure 4), where it is composed ofa silty, very fine-grained sandstone with 30%
mud content. Shells occur scatteringly
throughout most of the lower part. Some areconcentrated to form shell beds. However,those brown sandstones occurring at both

918.

Paleoenvironmental transition at 1.2 Ma

1-----==-:la~~~~;S;:::ilo~ low tide mark - 50-60m
Assoc.

\!

773

cold

50-60m -IOO-120m

Muddy finevery fine S.s.
Cycladicama Assoc.

wannlow tide mark - 50-60m

2
Yoldia Assoc.
low tide mark - 50-60m

cold

Felaniella Assoc.

omFigure 3. Stratigraphy of Cycle 9, showing distribution of the molluscan fossil associations and theirbathymetric ranges and water regimes.

Horizon 5 and 24 are apparently barren ofmolluscan fossils. Muddy tubular burrows
are often observed. There occur three whitetuff layers of between 20 and 30 em in thickness, numbered 01, 02, and 03 in upward
sequence (Hasegawa, 1979), and two 10-20
em-thick concretion-bearing layers at Horizon 7 and 14 (Figure. 4).
Seven shell beds are observed in the lower
part, and are here named SBl, SB2, SB3, SB4,
SBS, SB6 and SB7, in ascending order. The
dominant alignment of shells is parallel to thebedding plane and shells are supported bythemselves. In the lower part of the Omma
Formation, neither cyclic changes as in the
middle part nor any regular trend of verticalchange of lithofacies can be observed in sedi-ments lying between these shell beds. Theseshell beds in the lower part have their origin
apparently different from that of the basal
shell beds occurring in the middle part.
Four shell beds (SB4, 5, 6 and 7) appear to beformed by storms, because they have sedimentary features-a lenticular shape with a sharp
erosional base and the overlying massive or
laminated layer-which are typical of thestorm-generated ones (Kreisa, 1981). The
formational processes of the other three beds
are uncertain.
Faunal associations

Stratigraphic distribution of the molluscan
fossils in the lower part was described withthe methods applied for the middle part
(Kitamura and Kondo, 1990). Most bivalves

Akihisa Kitamura774

mud content
o 10 20 30 %

!
1\
/

. )-.

-

10
, . ,- :.'-

4·.1 ....

5

1\

-

.J

I

'.1

Om

!

Acila divaricatalimopsis Assoc.

2

01
1

Acila insignis
Assoc.

50-60m50-60m -lOO-120m

warm watercold water

Figure 4. Stratigraphic column of the lower part of the Omma Formation, showing mud contents,
horizons and distribution of molluscan fossil associations, accompanied with bathymetric range and water
regime of each association. For explanation of the sediments, see legend in Figure 1. 01,02 and 03: tuff
layers. SB 1- 7: shell bed.

are conjoined, except for those in the SB1, 4,
5, 6 and 7. They are not in life position.
This indicates that the shells were not transported after death for any appreciable distance from their original habitats. In theSBl, 4,5,6 and 7, shells are poorly preserved
and the abundant occurrence of fragmental
debris without any admixture of articulated
individuals suggests their transportation for aconsiderable distance from original habitats.
Therefore, they are excluded from the following discussion.
The molluscan fossils in the lower part of
the Omma Formation can be grouped into six
associations by means of associated occurrences and relative abundance of species (Figure 5). Table 1 shows the species composi-tion of these associations. Three associations (Peronidia, Clinocardium- Turritella andMacoma sectior Associations) are recognizedin the middle part. A detailed description ofthese associations has been given in Kitamura
and Kondo (1990). Three other associations, Acila insignis, Acila divaricataLimopsis and Anadara-Clinocardium Associations, are restricted to the lower part. Characteristic and subordinate species of theseassociations are described and discussed
below. Paleoenvironmental condition ofeach association is inferred from the distributional data of living species occurring in
the association.
Acila ins ignis Association

This association is composed of Acila in-918.

Paleoenvironmental transition at 1.2 Ma

775

l

~

-]

I~ =

~B ~ i...

""C

UOPR!:>OSSV.c-..p/ollUds ./pA//De"1"Pfl/U IIUI/nqlltl.
IJ~~I(IWA

II,'WURO.

.1I01I/'urpS '/f/CRJ.
wnlp.nt::JOURN.
1I,IIWZO s/ftiown.

~,,8Ufl.JWU/WS

I--

f--

~

wrrounp. ..tq'r=o.lr.J/fJOth( .:JdoWcl. _1-0"0

L..:::.::

r.JluodrI( llfU1soael- 111m .//.I""/•.:{o . . . . .

JOI"'~S ,woorw.l..-~rw.,(o'lo.( s/su:xJss:J,( u:m»doqnzIIV.L./no/8uf!l.~IIpnSIlW lIfR./o8/n.:I.
fJRJIllDO ..../d/lUVo

lPnJIod 'II//JP.JrJ.
",,/IHXf.( '/../__'urJ;~~=/':=~~_
IIPlltm7
fllld

IIIIlnuurt .uJOUprrJ.

U;y.,:K/oqnzllV.
SIIPUJIP In/o/pow mJOlpow.
S!SIDOSS~'< S/Rw,(3,(/!b1 -S[Srnn",JnJ(Of/ S{Su:lOllJ(OI

wnsolsrj wntp1r.XJUII:J.rslI/q.,ou '/P/OA.~.co. -

wnUJI],,,. wn{UOqwn.

_

L",,/uodr( 1UOfJ',(~.

'//''P/nd 1UOfJ~a.(",,/IHXf.( .,(~~
ods 1IUlt»"W_......_ ...~_1IIIj

~

-

----

I

"""1'" """"'}'Ie

IIsom:my IIW.(:KJno
s!srR.(n~ tpUllIWllpn:lSJ.

"Uf'fWOj '/p1I:)O~~SI(nJoq :J1Rl_~~ods s/sdown"(n,,um IUJ1PBUV.
/IIWl1,(0:f0,( Bw/ntmN.

BWqdB!P [QWJ'/~~-~ -~ --~ :J- =_=S!uS!SU! B/.~~s/nu:1I B/n:Jn~c./oqodoJJ'fIUB.U~/'u:KIs "fJB/~rnoG
BUB/u/~ "'tnA~N.

s/srr.mqslrlS sls[Qnl{SlrIS "1I~/f.U11.L
SIStr.H}snq B.(W0/cUo.

"Ins~~
s/su:xJuo,(r "IP/UOJ:JJO
{.lDA

-L

Ii

.- -_--..r -:~~ -1.-=I-JI- -

r.J/uodd/u IIU1O:1I1W.

.ur'."<El
J-~~:- r := -I--- :--~ -l:- l________

III I:J-.illill

OIl

o '"
"''"

-] -:- :Sn/BJI/II/nw IIU1OISOIllr.J.

s:JP/OWOISOt(lUll( r.Jf1 F1uoxt

~ 5

u

1

ruosdwns llpi'u;IO,l;Wo l ~SPOil'"•iI

IIWfJrAIP 1I110V.

'UllwnJ(l" 'P""LLo

a.

C"

-

-

SdI,nU;lI11 nnrtJ.

...

ca

~I

1IIILLllillili iii I i i II

~

'"

N

( -.1

-

e

C)rl-r-r~-'~r-~~~~~

776

Akihisa Kitamura

sign is, Yoldia notabilis and Solamen diaphana (Table I). They occur very sporadically in a silty, very fine-grained sandstone at
Horizon I (Figure 5). Most of the shells are
disarticulated and randomly oriented.
The living species in this association presently inhabit cold-water areas between 20 and
120 m deep. Takayama et al. (1988) described that the sandstone which yields thisaSSOCiatIOn abundantly contains a foraminifer, Bulimina marginata. According
to Akimoto and Hasegawa (1989), the upper
bathymetric limit of this species in the Japan
Sea is in the middle sublittoral zone (from 45
to 80-90 m depth). Thus the upper limit of
the habitat of the Acila insignis Association
may be 45 m and the bathymetric range of thisassociation is assigned to the lower sublittoralzone (Figure 2).
Acila divaricata-Limopsis Association

This association is confined to the 1.5
m-thick, fine-grained sandstone at Horizon 2(Figure 5). Characteristic species of theassociation are Acila divaricata and Limopsis
crenata, which are associated with Paphia
schnelliana and Phaxas attenuatus (Table
1). All three individuals of P. attenuatus
are found to have conjoined valves and show
a vertical, posterior-up orientation. They
seem to be preserved in life position. Other
shells are dominantly disarticulated andoccur sporadically.
According to the ecological data available
from the living species, A. divaricata and L.
crenata inhabit waters between 50-60 and
100-120 m deep and P. attenuatus from thelow tide mark to 50-60 m depth, all in warmwater areas. Therefore, this association isinterpreted to have lived in water about 50-60
m deep near the boundary between the lower
and upper sublittoral zones (Figure 2).
Anadara-Clinocardium Association

This association occurs at two horizons,
Horizon 3-SB2 and Horizon 9-23, in afine-grained sandstone (Figure 5). Characteristic species of this association inc\ ude

Anadara amicula, Clinocardium Jastosum

and Y. notabilis.

In addition, Turritella saishuensis, A. insignis, Mya japonica,
Cryptonatica janthostomoides and Myadorajaponica are found (Table I). A. amicula
forms a loosely packed shell bed (SB2) of 15
to 20 cm in thickness, in which shells, including many conjoined and lightly abraded individuals, are randomly oriented. These wellpreserved shells appear to be autochthonous
as a whole. Closely packed shells, possibly
due to wave and current actions, are, however, encountered in some part of the bed.
Mya japonica is usually found in life position, with its shells still articulated arid wellpreserved. The other shells are oriented
horizontally to the bedding plane.
Although A. amicula is an extinct species,
living species of the genus are generally
known from embayments shallower than 2030 m depth. Judging from this and otherbathymetric records of living representativesof this association, the association is considered to have lived most probably between a
low tide mark and 30 m depth in an embayment influenced by cold-water (Figure 2).
Environmental changes during thedeposition of the lower part
Among the six molluscan fossil associations recognized in the lower part of theformation, the Acila divaricata-Limopsis
Association is composed mainly of warmwater elements, and the other associations are
dominated by cold-water elements (Figure 4).
The temporal change shown by these associations indicates that the study area was essentially affected by cold water nearly throughout the deposition of the lower part, except
for a short interval at Horizon 2 when warm
water flowed into this area.
Molluscan fossils change upwards from the
Acila insignis Association (lived in the lower
sublittoral zone), through the Aclia divaricata-Limopsis Association (lived at 50-60 m
depth) to the Anadara-Clinocardium Association (lived from the low tide mark to 20-30

918.

Paleoenvironmental transition at 1.2 Ma

m depth) from Horizons I to 3 (Figure 4).
This change indicates that the water depth
decreased gradually in the study area.
In the sequence above Horizon 3, change ofwater depth can not be inferred directly fromthe molluscan associations, because the molluscan associations occurring there suggest no
bathymetric differences (Figure 4). However, the concentrated occurrence of stormgenerated shell beds in this part of thesequence indicates that water depth decreased
during the deposition of this interval. Fourstorm-generated shell beds are observed onlyin the horizon between Horizon 23 and 34(Figure 4). Kreisa (1981) discussed that theeffect of a storm at the sediment-water interface shuld be less intense in deep water thanin shallow water, and if storms are assumed tooccur randomly over a long period of time,then the number of storm deposits in strata
deposited during a given time interval would
be expected to increase with decreasing water
depth. Thus, it is interpreted that the depositional depth of the four horizons marked
by storm-generated shell beds was probably
shallower than that of the rest of the lower
sequence. In short, vertical change of molluscan associations and stratigraphical position of storm-generated shell bed suggest ashallowing-upward trend for the major partof the lower sequence, except for its basal
portion.
Transition of paleoenvironment at theboundary between the lower and middle partsof the Omma Formation

Oceanographic and climatic conditions
deduced from the sedimentological andpaleoecological data which were documented
in the preceding sections suggest that there isa remarkable difference in the pattern ofenvironmental changes between the lower andmiddle parts of the Omma Formation.
At least 10 periods of glacio-eustatic sealevel fluctuations, which have an amplitudeof up to 50 m and the estimated periodicity of
28,000 years on the average, are recognized in777

the middle part. Although, as comparedwith the middle part, the sedimentary environment during the deposition of nearly all
the lower part was shallower up to a water
depth of20-30 m under cold-water, the recordof glacio-eustatic sea-level fluctuations as seenin the middle part can not be observed in thispart. The boundary age between the lower
and middle parts is estimated to be 1.2 Ma,
based on biostratigraphic data (Takayama etal., 1988). Hence, a marked change of
paleoenvironment must have taken place atthat time.
Since oxygen isotope data base for the early
Pleistocene Epoch is relatively limited, interpretations of the isotope data in terms ofglobal eustasy are as yet not well established.
The oxygen isotope signals, however, clearlyfluctuate during the time interval coeval withthe deposition of the lower part of the Omma
Formation, between about 1.36 and 1.2 Ma(e.g., Williams et al., 1988). Thus, there canbe little doubt that climatic changes correlative with the glacial-interglacial cycles musthave occurred in the interval representing thelower part of the Omma Formation. A
period of about 0.16 m.y. during the deposition of the lower part is a time span longenough to record several sea-level fluctuations
with the periodicity of a few tens of thousand
years. Furthermore, the molluscan composition suggests that most horizons in the lower
part were deposited in depths shallower than
20-30 m (Figure 4). In such shallow-environments, changes of sea level even on theorder of 10 m should bring some variations inlithofacies as well as fossil molluscan associations. As the original record was not likely
to have been modified or lost by reworking
and bioturbation, the absence of any evidence
for a distinct glacio-eustatic sea-level fluctuation in the lower part appears to suggest thatthe amplitude of sea-level fluctuation was too
small to be detected with the kind of method
adopted in the present study. This may
imply that the amplitude of glacio-eustatic
sea-level changes increased beginning at

Akihisa Kitamura

778

molluscan fossil associations~

Biostratigraphy~(Takayama el aI., 1988)

--

•
0
..
~ :.1

~

-'8

-

(1)

:g

•

•

LAD Gepbyrocapsa(large) 1.10Ma

LAD HeJicospbaera
sellii 1.19Ma']•

FAD Gepbyrocapsa(large) 1.36Ma

Figure 6. Vertical distribution of the molluscan fossil associations and changes in marine climate andinferred sea-level during the deposition of the lower and middle parts of the Omma Formation. Biostratigraphic datums are based on Takayama et al. (1988). I: cold-water associations and cold water, 2: transitional association and transitional water, 3: warm-water associations and warm water. For explanation of
the sediments, see legend in Figure 1. Associations a-k and p-r are the same as those in Figure 2 and Table 1.

918.

Paleoenvironmental transition at 1.2 Ma

about 1.2 Ma (Figure 6).
The occurrence of the warm-water faunal
association, including the transitional association, indicates that at least nine periods ofinflux of warm water took place in the study
area between 1.2 and 0.9 Ma, whereas warm
water flowed only once between 1.36 and 1.2
Ma (Figures I, 6). This means that frequent
influxes of warm water began at 1.2 Ma.
Based on paleoecologic studies, Ogasawara(1981, 1983) pointed out that the Japan Sea
was connected with the Pacific through thepresent-day Tsushima Strait area during early
Pleistocene time and warm water flowed fromsouth through the Strait into the Japan Sea.
According to Honza (1978), the area has been
tectonically rather quiet during the Pliocene
and Pleistocene. Therefore, it is not possible
to relate the frequent influxes of warm water
to some tectonic movements around theStrait. One possible explanation for the frequent influxes of warm water is that sea levels
during the interglacial stages between 1.2 and
0.9 Ma probably stood high compared withthe previous interglacial stages, so that warm
water could invade into the Japan Sea during
every interglacial stages since 1.2 Ma.
Jansen et al. (1988) recently presented
records of climatic and oceanographic
changes in the Norwegian Sea during the last
2.8 m.y., based on sedimentologic, isotopic
and magnetostratigraphic investigations ofdeep-sea cores. According to them, glaciations were mild between 2.0 and 1.2 Ma in
Scandinavia, and "a transition toward larger
glacials took place during the period from 1.2
to 0.6 Ma", giving rise to warmer interglacials
owing to increasing influx of temperate surface waters. In the North Pacific, ice-rafted
detritus in the deep-sea sediment record indicates the initiation of cooling at about 1.2 Ma(Kent et al., 1971).
These studies suggest that oceanographic
and climatic conditions caused by glacialinterglacial changes shifted at around 1.2 Ma.
This age fits well the boundary age between
the lower and middle parts of the Omma

779

Formation. It is thought that the paleoenvironmental transition which was found at theboundary may be closely related to theintensification of glaciation in Europe andNorth America. Such a transition as recorded in the Omma Formation should be recognized in the contemporaneous marine strata
containing the Omma-Manganji Fauna elsewhere in the circum-Japan Sea region.

References
Akimoto, K. and Hasegawa, S., 1989: Bathymetric
distribution of the Recent benthic foraminifers
around Japan -As a contribution to the newpaleobathymetric scale-. Mem. Geol. Soc. Japan, no. 32, p. 229-240.
Hasegawa, S. 1979: Foraminifera of the Himi
Group, Hokuriku province, central Japan. Sci.
Rep., Tohoku Univ., 2nd Ser. (Geo!.), vol. 49, p.
89-163.
Higo, S., ed. 1973: A catalogue of molluscan
fauna of the Japanese Islands and the adjacent area. 58+397+61 p., BioI. Soc. Nagasaki
Prefecture. (in Japanese)
Honza, E., 1978: Geological development in thejunction of the Seinan (SW) Japan and Ryukyu
Arcs -preliminary concluding remarks-. In,
Honza, E., ed., Geological Survey of Japan,
Cruise Report., no. 10, p.69-73.
Ichihara, M., Ishio, G., Morishita, A., Nakagawa, T.
and Tsuda, K., 1950: Geological study of the
Toyama and Ishikawa Prefectures. No.2, Kanazawa, Isurugi and Fukumitsu provinces. Chigaku, no. 2, p. 17-27. (in Japanese)
Jansen, E., Bleil, U., Henrich, R., Kringstad, L. and
Slettemark, B., 1988: Paleoenvironmental
changes in the Norwegian sea and the northeast
Atlantic during the last 2.8 m.y.: Deep Sea
Drilling Project/Ocean Drilling Program Sites
610, 642, 643 and 644. Paleoceanography, vol.
3, p. 563-581.
Kaseno, Y. and Matsuura, N., 1965: Pliocene shells
from the Omma Formation around Kanazawa
City, Japan. Sci. Rep., Kanazawa Univ., vol.
10, p.27-62.
Kent, D., Opdyke, N.D. and Ewing, M., 1971: Climate change in the North Pacific using ice-rafted
detritus as a climatic indicator. Bull. Geol. Soc.
A mer., vol. 82, p. 2755-2766.
Kitamura, A. and Kondo, Y., 1990: Cyclic changesof sediments and molluscan fossil associations
caused by glacio-eustatic sea-level changes during
the early Pleistocene-a case study of the middle

Akihisa Kitamura

780

part of the Omma Formation at the type locality-. Jour. Geol. Soc. Japan., vol. 96, p. 19-36.
(in Japanese with English abstract)
Kreisa, R.D., 1981: Storm-generated sedimentary
structures in subtidal marine facies with examples
from the middle and upper Ordovician of southwestern Virginia. Jour. Sediment. Petrol., vol.
51, p. 823-848.
Kuroda, T. and Habe, T., 1952: Check list andbibliography of the Recent marine mollusca ofJapan. Leo. W. Stach, ed., 210 pp.
Matsuura, N., 1985: Successive changes of the marine
molluscan faunas from Pliocene to Holocene in
Hokuriku region, Central Japan. Bull. Mizunami Fossil Mus., no. 12, p.71-158. (inJapanese with English abstract)
Mochizuki, K., 1930: Neogene and later history ofKanazawa area. Jour. Geol. Soc. Japan, vol. 37,
p.278-280. (in Japanese)
Ogasawara, K., 1977: Paleontological analysis ofOmma fauna from Toyama-Ishikawa area, Hokuriku Province, Japan. Sci. Rep., Tohoku
Univ., 2nd Ser. (Geol.), vol. 47, p.43-156.
- - , 1981: Paleogeographic significance of theOmma-Manganzian fauna of the Japan Sea
borderland. Saito Ho-on Kai Mus., Res. Bull.,no. 49, p. 1-17.
Takayama, T., Kato, M., Kudo, T., Sato, T. andKameo, K., 1988: Calcareous microfossil biostratigraphy of the uppermost Cenozoic formations distributed in the coast of the Japan SeaPart 2: Hokuriku sedimentary basin-. Jour.
Japan. Assoc. Petrol. Tech., vol. 53, p.9-27. (inJapanese with English abstract)- - , 1983: Notes on the origin and migration of theOmma-Manganzian fauna. In, Kotaka, T. andOgasawara, K., eds., Origin and migration of

the Japanese Cenozoic molluscan faunas, p. 89100. Tohoku Univ. (in Japanese)- - , 1986: Notes on the origin and migration of theOmma-Manganzian Fauna, Japan. Palaeont.
Soc. Japan, Spec. Papers., no. 29, p. 227-244.
Ohmura, I., Ito, T., Masaeda, H. and Danbara, T.,
1989: Magnetostratigraphy of the Omma Formation distributed in Kanazawa City, Ishikawa
Prefecture, central Japan. In, Prof H. Matsuo
Memorial Volume, p. 111-124.
Otuka, Y., 1936: Pliocene mollusca from Manganzi
in Kotomomura, Akita Prefecture. Jour. Geol.
Soc. Japan, vol. 43, p. 726-736.
- - , 1939a: Mollusca from the Cenozoic System ofeastern Aomori Prefecture. Ibid., vol. 44, p. 2331.
- - , 1939b: Tertiary crustal deformations il1 Japan:
with short remarks on Tertiary palaeogeography.
Jubl. Publ. Commem. Prof H. Yabe's 60th
Birthday, vol. I, p.481-519.
Oyama, K., 1952: On the vertical distribution ofmarine mollusca. Venus (Japan. J. Malacol.),
vol. 17, p.27-35. (in Japanese with English
abstract)- - , 1973: Review of Matajiro Yokoyama's typemollusca from the Tertiary and Quaternary of the
Kanto area. Palaeont. Soc. Japan, Spec.
Papers, no. 17, p. 1-148.
Takayama, T., Kato, M., Kudo, T., Sato, T. andKameo, K., 1988: Calcareous microfossil biostratigraphy of the uppermost Cenozoic formations distributed in the coast of the Japan Sea
Williams, D.F., Thunell, R.C., Tappa, E., Rio, D. andRaffi, I., 1988: Chronology of the Pleistocene
oxygen isotope record: 0-1.88 million years
before present. Palaeogeogr., Palaeoclimatol.,
Palaeoecol., vol. 64, p.221-240.

Ishikawa E)II, Hokuriku ;jLIlt, Omma *~, River Sai ~)II, Kanazawa ~lR, Saikawa ~) II , Uta tsuyama gp I:lhLJ*~}fH::.t;vt0 I.2Ma ~mc-t0tl~mO')llf{L: *~~O')tl~mli, r'OO-cj:q'fBO')mw(~~ 1.2 Ma) -C'~ L llf{L L f.::.o *~~cj:l'OOI::'li, 7.kToJtilia7Jd~llfilJ (~*1Jif$ill 50 m, f
~JW;]:)tIl 28,000~) ICil]IZSl-t 0:fifl'i:"'t 1 ? ,t.-O')** I))lg L c Jl.{LElW~O')JW;]:)tIlEt:Jllf{b'J:Jil.i?
.h0 0 -15, ::E:tEH'ULElW~iJ>i? r'OOO'):fifl'i:~mli. :fifl'i::)tIlFs' (jdJ: C ~ 16 7J~Fs')0') v~ c !u c' ~Jm [. "C. 7.ke;g 30 m J: I) ~ \, 'iW~-C°;l; "" t-: c tltiE ~.h 0 0 .::. 0') J: ? tJ:~iW~-C°;l; "" t-: IC ~ iJ'iJ'b i? f, r'OO I::. Ii cj:l '00 i::'~ i?.h 0 J: ? tJ:7.kToJ tiiW7.k$llftfJO') ~c~iJ~ill~ ~<<.htJ:\"o '::'0')'::' cli. I.2Ma ~mc vc-t.htJ~.

7.kToJtilia7.k$~tfJO')1Jif$illiJ~~*Lt-:.::.

c ~:if-;~-t 0 c ~;t i?.h0 o 1fiti1rE?fdULElW~i::.:if-; ~ .h01fiti1rE0')i1rEJdi. *~~cj:l'OO (:fifl'i::)til Fs' Ii 30 7J ~Fs') -Co lij.' tJ: < c ~ 9 @-C0;l; "" t-: 0') IcM L "C. r 'OO:fifl'i:lIi'f lUi 1 @ L iJ, tJ:
iJ> "" t-:o .::. O')Ifiti1rEi1rEAO')iPJi~{L ~ 1.2 Ma tJ~0')7.kToJt1iW7.k$llftfJO')1Jif$ill~*iC!*lZSliJ~;l; 0
U!:,b.h0 0 '::'O')~~Vj:. 3 - p ,,/~~;jL7;< Y ;I;-C°7.kToJf'FffliJ~~g;{L~.h~il6t:d-:IIi'f:)tlllc­
IZ-t 0 0 -ttJ:bt>. 7.kToJf'Fffl O')~g;{L c *~~ iC~~ ~.h "C \" 0llftfJ/~ !J - '/ O')llf{L c li'$f
f8'td~1*iJ~;l;0 U!H$~.h00;jLtB?.. ~Trans. Proc. Palaeont. Soc. Japan, N.S., No. 162, pp. 781-793,7 Figs., June 30, 1991

919.

REDESCRIPTION AND MODE OF OCCURRENCE OFNIPPONOCLAVA YOKOYAMAI (SHIKAMA, 1954)(CLA VAGELLIDAE : BIVALVIA) FROM THE
PLIO-PLEISTOCENE WARM-WATER FAUNA IN JAPAN*
RYUICHI MAJIMA
Geological Insitute, Faculty of Education, Yokohama
National University, Yokohama, 240

Abstract. Nipponoclava yokoyamai (Shikama), a burrowing c1avagellid, is redescribed on the basis of 25 well-preserved specimens, newly collected from the upper Pliocene
and lower Pleistocene Ukari, Ananai and Takanabe Formations distributed along the Pacificcoast of central and southwestern Japan. This species has been known previously only fromthree imperfect specimens. It is very similar to Nipponoclava giganlea (Sowerby), but isdistinguished in having a strong contraction between the shell sheath and the anterior plate,and in having a morph with a greatly depressed oval outline in the sheath cross section. In
the Ukari Formation, N. yokoyamai occurs autochthonously in strongly bioturbated silty
sands that contain sporadically molluscan fossils indicative of upper-sublittoral, warm-watercondition.
Key words. Bivalvia, Clavagellidae,
Pleistocene, warm-water fauna.

Japan,

Nipponoclava

yokoyamai,

Plio-

1962a) or 60 (Savazzi, 1982a) valid species.
In Japan, four endemic species of clavagellids occur in Miocene to Holocene sediments.
Nipponoclava gigantea (Sowerby) is a
Holocene species distributed in southwesternJapanese waters influenced by the warm
Kuroshio Current.
Nipponoclava yokoyamai (Shikama)
occurs in the late Pliocene and early Pleistocene warm-water faunas distributed along
the Pacific coast of central and southwesternJapan. This species has been known previously only from three imperfect specimens.
Nipponoclava kanazawaensis (Omura) is
known only in the middle Miocene Sunakozaka Formation, central Japan (Omura,
1969; Ogasawara, 1976), and occurs in association with warm-water molluscs (Ogasawara, 1976).
Stirpulina ramosa (Dunker) is a late Pleis-

Introduction

Clavagellids are tube-dwelling bivalves
enclosing themselves in an adventitious calcareous envelope which is embedded in soft
sediments or attached to hard substrata.
Clavagellids first appeared in the upper
Cretaceous in eastern North America, Europe, northern Africa, and southern India(Pojeta and Sohl, 1987). They subsequently
extended their geographic range through the
Tethys seaway (Smith, 1962b) and now are
distributed In the Indo-Western Paci fic
region, from southern Japan to southern
A ustralia and to southeastern Africa, andalso in central part of the Mediterranean Sea(Smith, 1976). There are some 50 (Smith,'Received December 10, 1990; accepted April 10,
1991
781

Ryuichi Majima

782

tocene (Shikama, 1954) to Holocene species
living in southwestern Japanese waters
influenced by the Kuroshio Current.
Yokoyama (1926b) described Clavagellajaponica Yokoyama from the lower Pleistocene Shibikawa Formation of northern
Japan, but Habe (1952) considered thisspecies to be an annelid tube.
The aim of this study is to redescribe
Nipponoclava yokoyamai (Shikama) on thebasis of newly collected, 25 well-preserved
specimens, and to document its mode ofoccurrence.
This study adopts the morphological terminology for clavagellids used by Pojeta andSohl (1987) who followed Savazzi's (l982a)
suggestion and used the term crypt for all thecalcareous hard parts of clavagellids. The

word shell is limited to the bivalved juvenile
hard parts,
The specimens used in this study haverepository numbers prefixed with IGSU
(Institute of Geosciences, Shizuoka University) and UMUT (University Museum, University of Tokyo). The locality numbers
accompanying the specimens are also prefixedwith IGSU.

Collecting localities
Specimens examined in this study are collected from the upper Pliocene and lower
Pleistocene Ukari, Ananai and Takanabe
Formations on the Pacific coast of central andsouthwestern Japan (Figure 1). The molluscan fossils of the Ukari and Ananai F orma-

PACIFIC OCEANSEA OF JAPANIOOOm-32'26'N

PACIFIC OCEAN
131'33'EI

32"91'1-

133'5S'E
I

Figure 1. Map showing location of collecting localities of Nipponoclava yokoyamai, IGSU loc, nos,
52-56-8A, 52-56-8B and 52-56-8C, plotted on I: 25,000-scale topographic map of Japan, Quadrangles"Yamanashi" and "Kakegawa," Geographical Survey Institute. IGSU loc. nos. 61-54-1,61-54-4 and 6154-6, plotted on I : 25,000-scale topographic map, Quadrangles "Aki" and "Nahari." IGSU loc. no, 72-402, plotted on 1 : 25,000-scale topographic map, Quadrangles "Kawaminami" and "Takanabe."919.

Mode of occurrence of clavagellid bivalve

783

N

01

oJ
02

+

o.

oS
06

07

N=7

c
Ist~ 1U 9I I- ,[·[ I I IJ. \ I I I I I I I I 11. I I I I I I l I I I I I I I I I I I I I I .....:.!±l-- ---" .
A

!

I

N56°W

.

8OSW-=~--6-.--~~ ~~ -.--~-

2

. 'I

B

Figure 2. Mode of occurrence of fossil Nipponoclava yokoyamai in the upper Pliocene Ukari Formation. A and B, Outcrop photo (A) and sketch (8) of IGSU loc. no. 52- 56- SA. A quadrangle area
circumscribed by white dashed line of A indicates sketch area of 8. The strike of the stratum is nearly equal
to that of the outcrop surface, so that sandstone beds are seemingly horizontal on the outcrop. B- I - 9,
Nipponoclava yokoyamai (Shikama); 1, IGSU M020 ; 2, IGSU M021 (see Figure 4- 3); 3, IGSU M022 ;4, IGSU M023 (see Figure 3- 1) ; 5, IGSU M024 ; 6, IGSU M025 ; 7, IGSU M026 (see Figures 2- C - 2, 33, 6- 3) ; 8, IGSU M027 ; 9, mi ss ing during collection. C, anterior-posterior axes of Nipponoclava yokoyamai (Shikama) at IGSU loc. nos. 52 - 56- SA (1 , 2), 52- 56- S8 (3 - 5) and 52-56- 8C (6,7). Upper
hemisphere projection. Each axis is corrected from tectonic tilt (dip, 8°SW ; strike, N6rW) . All themeasurable specimens show a normal position with their siphonal opening directing upward and anterior
plate downward against the bedding plane. I, IGSU M027 (see F igure 4- 2a - 2b); 2, IGSU M026 (seeFigures 2- B- 7, 3- 3, 6- 3); 3, IGSU M029 (see Figure 3- 2) ; 4, IGSU M030 (see Figures 3-6, 6- 2) ; 5,
IGSU M031 ; 6, IGSU M033 (see Figures 3- 5, 4- la - Ib); and 7, IGSU M034.

tions at the localities listed below occur sporadically in dark gray , strong ly bioturbatedsilty sands.
IGSU loco no. 52- 56- SA. - A northeastfacing roadcut (Figures 2-A , 2- 8) at Asuka ,Kakegawa City, Shizuoka Prefecture, Pacificside of central Japan. Latitude 34 47' IS " N,longitude l3 T 59'52 " E. Ten specimens of N.
0

yokoyamai occurring In the lowerm ost partof the upper Pliocene Ukari Formation of the
Kakegawa Group were collected.
IGSU loco no. 52- 56-S 8. - A southwestfacing roadcut occurring at Asuka on the
opposite side of the road from IGSU loco no.
52- 56-SA. Four specimens of N. yokoyamai were obtained from the lowermost

784

Ryuichi Majima

part of the upper Pliocene Ukari Formationof the Kakegawa Group.
IGSU loco no. 52-56-8C. - A northeastfacing cut at Asuka on the opposite side of alow ridge from IGSU loco no. 52-56-8B.
Five specimens of N. yokoyama occurring in
the lowermost part of the upper Pliocene
Ukari Formation of the Kakegawa Group
were collected.
IGSU loco no. 61-54-1.-A cliff in a small
valley (Ikenotani valley), about 400 m upstream of the valley entrance, Tonohama, Aki
City, Kochi Prefecture, Pacific side of southwestern Japan. Latitude 32"26'49"N, longitude 133"58' II "E. One specimen of N. yokoyamai was obtained from the upper Pliocene
Ananai Formation of the Tonohama Group.
IGSU loco no. 61-54-4. - A cut on eastfacing hill slope, about 1,100 m northeast of
the Yasudagawabashi bridge, Yasuda-machi,
Aki-gun, Kochi Prefecture, Pacific side ofsouthwestern Japan. Latitude 32"26'9"N,
longitude 133"59' 49"E. Three specimens of
N. yokoyamai were collected from the upper
Pliocene Ananai Formation of the Tonohama Group.
IGSU loco no. 61-54-6.-A cliff in a small
valley (Ikenotani Valley), about 250 m upstream from the valley entrance, Tonohama,
Aki City, Kochi Prefecture, Pacific side ofsouthwestern Japan. Latitude 32"26'43"N,
longitude 133"58' II "E. One specimen of N.
yokoyamai occurring in the upper Pliocene
Ananai Formation of the Tonohama Groupwas collected.
IGSU loco no. 72-40-2. - Sand blocks
dropped from a cliff into a small valley, about
1,000 m southwest of Toriyama fishing port,
Toriyama, Kawaminami-machi, Koyu-gun,Miyazaki Prefecture, on the Pacific side ofsouthwestern Japan. Latitude 32"9'41 "N,longitude 131"32' 44"E. Two specimens of
N. yokoyamai were collected from finegrained sand blocks of the lower Pleistocene
part of the upper Pliocene and lower Pleistocene Takanabe Formation of the MiyazakiGroup.

Mode of occurrence
I have examined 19 specimens of Nipponoclava yokoyamai collected at IGSU loco nos.
52-56-8A, 52-56-8B and 52-56-8C. The
strata at these localities consist of dark gray,massive silty sands intercalated with wellsorted, fine-grained sands, of the lowermost
part of the upper Pliocene Ukari Formation.
The silty sand beds are strongly bioturbatedand molluscan fossils occur sporadically (Figure 2). Nipponoclava yokoyamai is considered to occur autochthonously, because theanterior-posterior axes of measurable. specimens dip steeply from the bedding plane(commonly more than 45 degrees: Figure 2C) and they always show the natural shellorientation of siphonal opening pointing
upward and anterior plate downward (Figure3). In the natural environment, Penicillus, aburrowing clavagellid genus like Nipponoclava, usually lies embedded vertically in asilty sand with the anterior plate lowermost
and the siphonal opening slightly above thesediment surface (Savazzi, 1982b; Purchon,
1956, 1960; Pojeta and Sohl, 1987). Nipponoclava is considered to live or have lived
in the same manner as Penicillus. Okutani
and Soyama (1987) illustrated a living
Nipponoclava gigantea (Sowerby) as oriented
vertically in the substrate with the opening of
the siphonal sheath projecting above the sediment surface. Nipponoclava yokoyamai is,therefore, considered to have lived embedded
nearly vertically in sediment with the anterior
plate lowermost and the siphonal opening
projecting above the sediments. The reason
why no fossil is oriented exactly normal to thebedding plane (Figure 2-C) is likely to be
attributed to the disturbance caused by suchbiologic agents as bioturbators, predators,
scavengers, as inferred from strong bioturbation in the fossil-bearing silty sands. Therefore, these clavagellid fossils are considered tohave been preserved essentially in situ andshow the position near to their probable life
orientation.

919.

Mode of occurrence of clavagellid bivalve

The following molluscan fossils occur inthe localities: Acila sp., Anadara suzukii(Yokoyama), Glycymeris totomiensis Makiyama, Amussiopecten praesignis (Yokoyama),
Chlamys satoi (Yokoyama), Llitraria sp.,
Phaxas attenuatlls (Dunker), Pitar sp., Paphia schnelliana (Dunker), Callista chinensis(Holten), Clementia sp., Panopea japonica
Adams, Tristichotrochus sp., Onustus exutus(Reeve), Glossaulax hagenoshitensis (Shuto),
G. hyugensis (Shuto), Cryptonatica adamsiana (Dunker), Tonna luteostoma (Kuster),
Zeuxis sp., Fusinus sp., Lophioturris
leucotropis (Adams et Reeve), and Architectonica maxima (Philippi). They indicate upper sublittoral, warm-water condition,and constitute components of the Pliocene
and early Pleistocene warm-water molluscan
faunas, collectively called the Kakegawa
fauna (Chinzei, 1986). This fauna occurs instrata distributed along the Pacific coast ofcentral and southwestern Japan.
Bivalve fossils that consist mainly of infaunal species show a high rate of articulation. Excluding Nipponoclava yokoyamai,
129 bivalve specimens occur at Locality 5256-8A (Figures 2-A, 2-B), of which 52 arearticulated. Valves of many articulated specimens are closed, whereas their shell orientation is randomly arranged. Nearly all of thearticulated bivalves, excluding N. yokoyamai,
seemingly do not occur in their life orientations. As N. yokoyamai, they are also likely
to have been reoriented by disturbance causedby the biologic agents. These bivalves havecommonly an elliptical to circular outlinethat might be more easily disturbed entirely
from their life orientation by biologic agentsthan N. yokoyamai. Gastropods are generally rare in occurrence and also show random
shell orientation.
The moll uscan fossils of the three localities
are considered to be a parautochthonous
assemblage which is composed of autochthonous specimens reworked to some degree but
not transported out of the original life habitat(Kidwell et al., 1986).

785

Systematic paleontology

Class Bivalvia Linnaeus, 1758
Subclass Anomalodesmata
Dall, 1889
Order Pholadomyoida
Newell, 1965
Superfamily Clavagellacead'Orbigny, 1844
Family Clavagellidae
d'Orbigny, 1844
Genus Nipponoclava Smith, 1976Type

species. - Aspergillum

giganteum

Sowerby, 1888, by original designation.
Recent, southwestern Japan.
Diagnosis. - Both large bivalved juvenile
shells becoming fused to elongate sheath.
Sheath circular to ovoid in transverse section
with well-developed siphonal collars at theposterior end. Enlarged anterior plate bearing many rows of tubules that may be bifurcated.
Remarks. - Nipponoclava has previously
been considered to be a subgenus of Humphyreia Gray, 1858 (Smith, 1976; Pojeta andSohl, 1987), but the latter has an angularsiphonal sheath in transverse section and nosiphonal collar and shows different life habit.
Humphyreia is usually attached to hard substrata (Smith, 1976). Because the siphonalcollar apparently functions to prevent further
sinking in a soft substrate (Savazzi, 1982a,
1982b), the presence or absence of this character is important to establish their life habits.
Nipponoclava is a genus endemic to Japanand consists of three species, Nipponoclava
gigantea (Sowerby) (Holocene), N. yokoyamai (Shikama) (Pliocene-Pleistocene), andN. kanazawaensis (Omura) (Miocene).

Nipponoclava yokoyamai (Shikama, 1954)
Figures 3, 4, 5, 6.

Aspergillllm gigantellm Pilsbry. Yokoyama, 1926a,
p. 368, pI. 42, figs. 1,2; Hatai and Nisiyama, 1952,
p.30 [not Nipponoclava gigantea (Sowerby,

786

Ry uichi Majima

919.

Mode of occurrence of c!avagellid bivalve

787

Figure 4. Nipponoclava yokoyamai (Shikama) from the uppe r Pliocene Ukari Formation , Shizuoka
Prefecture. N at ura l size. la - b, IGS U M033 , IGSU loc. no. 52- 56- SC, la, right-lateral v iew, Ib, ve ntra l
view; 2a - b, IGSU M027 , IGS U loco 52- 56- SA , 2a, dorsa l view, 2b, anterior view ; 3, IGSU M02 1, IGSU
loco no. 52 - 56- SA, a nterio r v iew; a nd 4, IG SU M035 , lGSU lac. no . 52- 56- SB, left- latera l view.

~
Figur e 3. Outcrop photos of Nippol1oclava yokoyamai (Shikama) a t lGSU loco no s. 52- 56-S A (1,3) ,52 - 56- SB (2,6) a nd 52 - 56- SC (4,5). I, la tera l view, lGSU M023 (see F igur es 2- B- 4, 4- 3) ; 2, posterolate ra l view, IGSU M029 (see Figure 2- C - 3) ; 3, latera l v iew, IGS U M026 (see Figures 2- B- 7, 2- C- 2, 6- 3) ;4, postero-latera l view, mi ss in g during co ll ecti o n ; 5, late ra l view , lGSU M033 (see Fig ure s 2- C - 6, 4- la Ib) ; a nd 6, la tera l view , IGS U M030 (see Figu re s 2- C- 4, 6- 2). ap , a nterior plate ; sc, siph o na l co ll ars;

shs, shell shea th ; ss, siph o na l shea th ; t, tubules.

788

Ryuichi Majima

Figure 5. Nipponoclava yokoyamai (Shikama) from the upper Pliocene Ananai Formation. Naturalsize. la- e, IGSU MOI7, IGSU loc. no. 6 1- 54- 4, la, dorsal view, lb, right-lateral view , Ie, anterior view;
2a - e, IGSU M018, IGS U loc. no. 6 1- 54- 4, 2a, anter ior view, 2b, ventra l or dorsal view, 2e, latera l view ;and 3a - b, IGSU MOI5 , IGSU loco no. 6 1- 54-6, 3a, dorsal view , 3b, anter ior view.
~
Figure 6. Nipponoclava yokoyamai (S hik ama) from the lower Pleistocene part of the upper Pliocene
to lower Pleistocene Takanabe Formation (la- b) and from the upper Pliocene Ukari Formation (2,3). lab, x O.78 , IGSU MOI3, IGSU loco no. 72 - 40- 2, la, left-latera l view , Ib, dorsal view; 2, IGSU M030, X
0.85 , IGSU loco no. 52- 56- 8B, ri ght-l atera l view ; and 3, X 0.85 , IGSU M026, IGSU loco no. 52 - 56- SA ,left-latera l view.

919.

Mode of occurrence of cla vagellid bivalve

789

790

Ry uichi Majima

SC~

919.

Mode of occurrence of clavagellid bivalve1888)].
Brechites (Warnea) yokoyamai Shikama, 1954, p.
63-64, pI. 3, figs. la-d; Masuda and Noda, 1976, p.
44.

Diagnosis. - Nipponoclava with a strong
contraction of crypt between shell sheath andanterior plate and with a distinct morph
being greatly laterally depressed oval outline
in cross section of sheath. Siphonal sheath
has siphonal collars numbering less than five.
Type material. - UMUT CM23537 (Ichikawa, 1983: lectotype, herein designated),from northern slope of the hill near theboundary between Yasuda-machi and Tanomachi, about 600 m northeast of the shrine atOno, Tano-machi, Aki-gun, Kochi Prefecture,
Pacific side of southwestern Japan (Hatai andNisiyama, 1952). Upper Pliocene Ananai
Formation of Tonohama Group.
Stratigraphic occurrence. - Upper Pliocene
and lower Pleistocene.
Upper Pliocene: Ukari Formation, Shizuoka Prefecture, IGSU 10c. nos. 52-56-8A(Figure 3-1, 3-3, 4-2a-3, 6-3), 52-56-8B(Figures 3-2, 3-6,4-4,6-2), and 52-56-8C(Figures3-4,3-5,4-la-lb); Ananai Formation, Kochi Prefecture, IGSU loc. nos. 6154-1,61-54-4 (Figure 5-1a-2c), and 61-546 (Figure 5-3a-3b).
Lower Pleistocene: Takanabe Formation,
Miyazaki Prefecture, IGSU loc. no. 72-40-2(Figure 6-la-lb).
Remarks. - Nipponoclava yokoyamai ischaracterized by having a strong contractionof the crypt between shell sheath and anterior
plate and by having a morph showing agreatly laterally depressed oval outline intransverse sheath section. One specimen
appears to show no contraction of the crypt(Figure 4-la-lb), but the specimen lacks thehinge part of the juvenile shells and the shell
sheath looks more slender than its true width.
Probably, this specimen has a contraction of791

the crypt. The transverse sheath section islargely variable in form from greatly laterally
depressed oval (e.g., Figures 5-1 a - 2c, 6-1 a1b) to circular (e.g., Figure 6-2).
The siphonal sheath of one specimen isslightly but abruptly bent at the posterior part
(Figure 6-la-lb). This abrupt bend of thecrypt is considered to be accidental and not astable taxonomic feature of the species. The
siphonal sheath of clavagellids is formed byperiodic shell secretion at the posterior tips ofthe siphon, and the crypt further sinks withgrowth of the siphonal sheath into the sediments (Savazzi, 1982b; Pojeta and Sohl,
1987). The crypt orientation of this specimen might have been disturbed while growing and embedded into sediment. If thecrypt was inclined by a disturbance, further
burrowing would tend to realign the crypt
vertically and result in an abruptly bending
crypt (Savazzi, 1982b).
This species is very similar to Nipponoclava
gigantea (Sowerby) (Figure 7), but the latter
never has a sheath that is greatly laterally
depressed oval in transverse section. Also,
the latter never possesses a stronger contraction of the crypt between the shell sheath andthe anterior plate than in N. yokoyamai.
Figure 7-3a-3b illustrates one specimen of N.
gigantea that most closely resembles N. yokoyamai among all the specimens of N.
gigantea 1 have seen. This specimen has acontraction of the crypt, but it is not as
distinct as in N. yokoyamai.
Nipponoclava yokoyamai and N. gigantea
probably preferred different substrata.
Nipponoclava yokoyamai had lived in silty
sands since the autochthonous specimens
occur always in silty sands. Nipponoclava
gigantea, on the other hand, now lives in agravel to sand bottom (Habe, 1977; Habeand Kosuge, 1970; H igo, 1973; Ok utani andHabe, 1975; Okutani, ed., 1986). Although~ Figure 7.
Nipponoclava gigantea (Sowerby) from off Nanbu-machi, Hidaka-gun, Wakayama Prefecture, on the Pacific side of southwestern Japan (Recent). X 0.75. la-b, IGSU M 117, I a, right-lateral view,Ib, dorsal view; 2, IGSU M118, dorsal view; and 3a-b, IGSU MOI2, 3a, dorsal view, 3b, left-lateralview. js, juvenile shell; sc, siphonal collars; shs, shell sheath; ss, siphonal sheath; t, tubules.

792

Ryuichi Majima

there is a possibility that these two species aredifferent ecophenotypic forms within a single
species living, respectively, in finer and coarser sediments, they could not justifiably be
assigned to the case of ecophenotypy withoutfinding evidence of an entirely continuous
morphological link between the two.
Nipponoclava kanazawaensis (Omura),from a sandstone bed of the middle Miocene
Sunakozaka Formation in central Japan,
differs from the present species in having asmall shell, attaining a maximum diameter of
8.7 X 11.6 mm for the si phonal sheath, and amaximum diameter of 9.0 X 9.8 mm for theshell sheath (Omura, 1969). The smallest
specimen of Nipponoclava yokoyamai (IGSU
MOI7: Figure 5-1a -Ic) measures 17.9 X 19.1mm (siphonal sheath) and 21.4x 19.1 mm(shell sheath), respectively. The largest specimen (IGSU M013: Figure 6-1a-1b) has adiameter of 22.5 X 32.6 mm at the posterior
part of the siphonal sheath. Clavagellids
predetermine the final adult size of the animal
when the anterior part of the crypt includingshell sheath and anterior plate is formed(Savazzi, 1982a, 1982b). The shell sheath
and anterior plate show no growth line except
for juvenile shells. The diameter of the crypt
is, therefore, an important character to compare the size. Further comparison of these
two species is difficult due to a poor state ofpreservation of N. kanazawaensis.
Nipponoclava yokoyamai has been known
previously only from the three imperfect typespecimens. It was originally reported by
Yokoyama (1926a), under the name of Aspergillum giganteum, based on two shell-sheathfragments from the upper Pliocene Ananai
Formation, Kochi Prefecture, on the Pacificside of southwestern Japan. Subsequently,
Shikama (1954) proposed Brechites (Warnea) yokoyamai for Yokoyama's (1926a)
specimens and one specimen in Dr. K. Sakurai's private collection which was collectedfrom the Pliocene and lower Pleistocene
Kakegawa Group, Shizuoka Prefecture, on
the Pacific side of central Japan. The detailof collecting locality of Sakurai's specimen is
unknown and the specimen consists only of
the anterior plate and shell sheath. This
study is, therefore, the first detailed description of N. yokoyamai.
Acknowledgments
I am most grateful to Dr. J. Pojeta, Jr., U.S.
Geological Survey, Reston, Dr. c.L. Powell,
II, U.S. Geological Survey, Menlo Park, and
Dr. K. Amano, Joetsu University of Education, for their thorough review of the manuscript and providing helpful com.ments.
Messrs. A. Murata and R. Uchimura, Shizuoka University, kindly assisted in collecting
clavagellid fossil specimens. This study was
funded by Grants-in-Aids for Scientific
Research from the Ministry of Education,
Science and Culture, the Government ofJapan (No. 02740394).

References cited
Chinzei, K., 1986: Faunal succession and geographic distribution of Neogene molluscan
faunas in Japan. In, Kotaka, K. and Marincovich, L., Jr., eds., Japanese Cenozoic Molluscs. - Their Origin and Migration.Palaeont. Soc, Japan, Spec. Papers, no. 29, p.
17-32.
Gray, J.E., 1858: On the families of Aspergillidae,
Gastrochaenidae, and H umphreyiadae. Proc.
Zool. Soc. London, vol. 26, p.307-318. [notseen] .
Habe, T., 1952: Pholadomyidae, Clavagellidae, Pandoridae, etc. In Kuroda, T., ed., Illustrated
catalogue of Japanese shells, No. 18. p. 121-132.
Soc. Publ. Japanese Malacological Literatures,
Kyoto.
- - and Kosuge, S., 1979: Common shells ofJapan in color. xviii+223 p. Hoikusha, Osaka.
Hatai, K. and Nisiyama, S., 1952: Check list ofJapanese Tertiary marine Mollusca. Sci. Rep.,
Tohoku Univ., 2nd Ser. (Geol), Spec. Vol., no. 3,
p.I-464.
Higo, S., 1973: A catalogue of molluscan fauna of
the Japanese Islands and the adjacent area. 397
p. BioI. Soc. Nagasaki Prefecture, Nagasaki.
Ichikawa, T., 1983: Catalogue of type and illustrated
specimens in the Department of Historical Geol-919.

Mode of occurrence of clavagellid bivalve

ogy and Paleontology of the University Museum,
University of Tokyo. Part 2. Cenozoic fossils
and Recent specimens. Univ. Mus., Univ.
Tokyo, Material Rep., no. 9, p. i + iii, 1-536.
Kidwell, S.M., Fiirsich, F.T, and Aigner, T, 1986:
Conceptual framework for the analysis andclassification of fossil concentrations. Palaios,
vol. I, no. 3, p. 228-238.
Masuda, K. and Noda, H., 1976: Check list andbibliography of the Tertiary and Quaternary
Mollusca of Japan, 1950-1974. 494 p. Saito
Ho-on Kai Mus., Sendai.
Matsukuma, A., 1986: Bivalvia. In, Okutani, T,ed., Seibutsu-Daizukan, p.274-343. Sekaibunkasha, Tokyo.
Ogasawara, K., 1976: Miocene Mollusca from
Ishikawa-Toyama area, Japan. Sci. Rep., Tohoku Univ., 2nd ser. (Geol.), vol. 46, no. 2, p. 3378.
Okutani, T. and Habe, T., 1975: Mollusca 11, Chiefly
from Japan. 294 p. Gakken, Tokyo.
- - and Soyama, S., 1987: Marine shell-bearing
mollusks. 238 p. Tokai Univ. Press, Tokyo.
Omura, K., 1969: Fossil Penicillus from Ishikawa
and Kagoshima Prefectures, Japan. Ann. Sci.,
Kanazawa Univ., Colleg. Liber. Arts, part 2, vol.
6, p.25-39.
Orbigny, A.D.D', 1843-1847: Terrains Crt!taces.
Vol. 3, Lamellibranches. 807 p. Victor Masson,
Paris. [not seen].
Pojeta, J., Jr. and Soh I, N.F., 1987: Ascaulocardium
armatum (Morton, 1833), new genus (late793

Cretaceous): The ultimate vanatlon on thebivalve paradigm. Jour. Paleont., vol. 61, no. 6,
Suppl. (Paleont. Soc. Mem. 24), p. 1-77.
Purchon, R.D., 1956: Note on the biology of Brechites penis (L.) (Lamellibranchia). Jour. Linnean Soc., vol. 43, p.43-54.
- - , 1960: A further note on the biology of Brechites penis (L.) (Lamellibranchia). Proc.
Malac. Soc. London, vol. 34, p. 19-23.
Savazzi, E., 1982a: Clavagellacea (Bivalvia) fromthe Tertiary of the Venetian region, N.E. Italy.
Acta Geo!. Polonica, vol. 32 p. 82-92.
- - , 1982b: Adaptations to tube dwelling in the
Bivalvia. Lethaia, vol. 15, p. 275-297.
Shikama, T., 1954: Clavagellid fossils from Japan.
Sci. Rep., Yokohama Nat!. Univ., sec. 11, no. 3,
p.63-65.
Smith, B.J., 1976: Revision of the Recent species ofthe family Clavagellidae (Mollusca, Bivalvia).
Jour. Malac. Soc. Australia, vol. 3, p. 187-209.
Smith, L.A., 1962a: Revision of the Clavagellacea.
Veliger, vol. 4, p.167-174.
- - , 1962b: Historical zoogeographic study of theClavagellacea. Veliger, vol. 5, p. 15-19.
Sowerby, G.B., 1888: Description of a gigantic new
species of Aspergillum from Japan. Proc. Zoo!.
Soc. London, for the year 1888, p. 290.
Yokoyama. M., 1926a: Tertiary shells from Tosa.
Jour., Fac. Sci., Imp. Univ. Tokyo, sec. 11, vol. I,
pI. 9, p. 365-360, pI. 42.
- - , 1926b: Fossil Mollusca from the oil-fields of
Akita. Ibid. p. 377-389, pIs. 44-45.

Aki ~~, Ananai /i.:p;j, Asuka ~,~, Ikenotani it/),(7);fr, Kakegawa J3:fJli, Kawaminami )11m, Koyu yc~, Sunakozaka jitYrW, Tano BUf, Tonohama Jl!f~, Toriyama JlHLU, Ukari~/(lJ,

Yasudagawabashi ~EBJIi:jJj.

B *(7),@.t~- ~~i!!:~vftJw~~iJ' GilE-r- Q Nipponoclava yokoyamai (Shikama, 1954)'7 71' l' f4: =t:lc JUIilJ) (7) ilE:±l ttRJ;\; <!: :pj:gcllJl(:: B * (7) ::t3:f1$/¥~:::. :5t;fJJ-r- Q 1: ffIlf!$ ~i;1tt,n, L rffll~~i;1t(7)~ilj~, /i.:p;j~:t-o J: LJii1ii~!i iJ' G:!*$ ~ ht-: 25 fI8lW(7)'& <f*if ~ ht-:~* ~:::.l(:, <!: --5l' -C Nipponoclava yokoyamai (Shikama) >a:':pj:~cllJl(: L t-:o *flfi..:. hi-C'
3 OO(7)~7t:@:~* L iJ':m G h -C l ' t£. iJ, -? t-:o *flfi Nipponoclava gigantea (Sowerby) <!: ~F~ v:::,.& <1JJ Q iJ;, shell sheath <!: anterior plate <!: (7) FsjiJ;sm < <LJ h Q .:. <!:, :t-o J: LJ sheath(7)iVTrnH:::.:t-o l '-C, -::>.s;ht-::ffijF9%>a:'§',-r- Q ¥£~~iJ;iftE-r- Q .:. <!: -C'I~JJiJ ~ h Q ~ilj~ (7)N. yokoyamai fi., ~i5fE(7) 1:1:li;i'ia*>a:'7F-r-,Fl. {r.E>a:'liXtEi¥J v:::' ~.7:1-, Sm l '1:.~t~%L >a:':'5t vtt-:-//v r ~jity;fiiJ' G E! 1:.i¥Jv:::.ilE:±l-r- Q o
Fsj~f&~-(-" "7 ;:1.

0Trans. Proc. Palaeont. Soc. Japan, N.S., No. 162, pp. 794-800, 8 Figs., June 30, 1991

920.

DISCOVERY OF A CORAL-RUDIST BUILDUP IN THE
MIYAKO GROUP, NORTHEAST JAPANSHIN-ICHI SANO
Geological Institute, University of Tokyo, Tokyo 113

Abstract. A coral-rudist limestone was newly discovered in the Lower Cretaceous(upper Aptian) sequence of the Miyako Group. It is small in scale but contains abundantframe-building organisms, notably autochthonous corals and rudists. Though vertical
succession was not recognized, in some parts of the limestone, large and massive corals makea rigid framework, whereas in other parts the main frame-builder is Praecaprotina yaegashii(Yehara), a caprotinid rudist, which often forms clusters but does not show dense packing.
This paper is the first concrete description of carbonate buildup in the Cretaceous of East
Asia. Existence of coral-rudist buildup indicates that the northern limit of tropicalsUbtropical realm reached north Japan in late Aptian time. The influx of abundant clastic
material may have prevented the buildup from the development of large-scale reefs, but
small-scale buildups could grow, though temporarily or episodically, on the rocky shore ina transgressive stage.
Key words. Carbonate buildup, Cretaceous, Miyako Group, Northeast Japan,
paleoecology, rudist.

and biogeographic significance. The existence provides a rare and interesting exampleof Cretaceous carbonate buildup in the continental margin of East Asia.

Introduction
Rudist reefs have been known commonly inthe platform carbonate rocks of the Caribbean, Middle East and Mediterranean regions
as well as in the limestones on several sea
mounts in the Pacific. Few examples ofrudist-dominated reef deposits, however, were
described in other regions, even if sporadic
occurrences of rudist species have been
known.
During my field survey, I discovered several
buildups of hermatypic organisms along thebase of the Early Cretaceous Miyako Groupin north Honshu, Japan. One of these buildups is, though small in scale, clearly framedby corals and rudists. The purpose of thispaper is to document the coexistence of in situ
rudists and corals and to discuss its ecologicalGeologic setting
The Miyako Group consists mainly of shallow high-energy open marine deposits that
range from the upper Aptian to lower Albian(Hanai et al., 1968). It abuts against various
basement rocks of Jurassic and Early
Cretaceous ages (andesite, granite, hemipelagic clastic rocks, etc.). Numerous wellpreserved fossils (e.g., bivalves, gastropods,
ammonites, crinoids, etc.) were describedfrom this group. Abundant hermatypiccorals, nerineaceans, rudist and orbitolinid
foraminifer, which indicate a warm environment, are noticed. Eguchi (1951) described
56 species belonging to 30 genera of corals,
most of them are hermatypic ones. Praeca-'Received September 29, 1990; revised manuscript
accepted May IS, 1991
794

920.

Aptian coral-rudist buildup in Miyako Group

.0

o
lkm
1 4 l' 56·,-'--i._'--""-----l, 1 4 l' 5 7·

JS

Figure 1. Map showing the locality of thecoral-rudist limestone. Dotted area indicates the
distribution of the Miyako Group.

o795

protina yaegashii (Yehara), belonging to thefamily Caprotinidae, is the only describedrudist species from this group (Yehara, 1920;
Yabe and Nagao, 1926).
The coral-rudist limestone described here
was discovered in the upper Aptian Tanohata
Formation exposed on both banks of Kamakano-sawa stream, near Aketo, Tanohatamura, Iwate Prefecture (Figure I). This
limestone lies on the andesite of the
Neocomian Harachiyama Formation withclinounconformity.
Observation
The coral-rudist limestone is found on bothbanks of Kamakano-sawa stream (Figure 2).
It crops out sporadically in a narrow area
(about 20 X 50 m) and is mostly covered with

501

Figure 2. Map showing the outcrops of the coral-rudist limestone in Kamakano-sawa stream.
Contour lines are drawn at intervals of about 1.5 m. Broken line indicates an approximate trace ofunconformity.

Shin-ichi Sana

796

Figure 3. Outcrop of the unconformity.
The lower part is andesite, and the upper part islimestone. The hammer shown is about 33 cm
long.

thick soil. On the south bank, the limestone
is exposed on the southern slope of a small

ridge. Because the slope has nearly the same
strike and dip with the Miyako Group of thisarea, the surface probably shows the weathered uppermost surface of the limestone. The
unconformity can be observed at two localities, where the limestone directly covers theandesite (Figure 3). The thickness of thislimestone is at least 1 m and may vary owing
to the topographic relief of the basement.
The limestone laterally merges into bioclast
grainstone, particularly southwestward. In
other directions the extension is unknown.
The superjacent strata are not exposed there,
but bioclast rudstone occurs at several meters
above. The limestone is milky white andimpure, containing numerous fragments ofandesitic rock . It is tentatively divided into
two parts by the difference of frame-builders.

cFigure 4. Sketch of the upper surface of the coral-rudi st limestone. A , B, C correspond to those in
Figure 2. Distribution of macro-organisms are plotted. Bold line indicates rudist , slim line coral , andblack spot unidentified dendroid organism. Note that most of rudist individuals are complete and oriented
nearly perpendicularly to the surface. Some indi viduals of rudist are in contact with each other, forming
cl usters.

920.

Aptian coral-rudist buildup in Miyako Group

797

Figure 5. Praecaprolina y aegashii (Yeh ara ).
Tra nsverse section o n the limesto ne surface. Scalebar is 1 cm.

Figure 6. Di stribution o f rudi st on a n uppersurface of the coral-rudi st limes to ne. Severa l in d ividuals a re visible. The mechanical pencil isa bout 14 cm in lengt h.

Some parts are dominated by coral s, whereas
in other parts the limestone contains numerous in situ individual s of rudi st as wel l ascorals. These two parts have patchy di stribution in the limestone, and do not show any
stratigraphic succession .
In the coral-dominated pa rts, the coral s are
generally of mass ive type . Their width isapproximate ly 20- 30 cm a nd attains about 50
cm at the maximum. Indi vidua ls of cora ls
are not separately identified on the s urface,
but the growth direction examined in several
specimens is always up ward . A few rudi st
individual s (several cm in diameter) are associated in this part, but their systematic
assignment is difficult due to the highly
cemented matrix . The interior of the coral

Figure 7. Occurrence of severa l individual so f rudi st and coral in the section of the upper pa n
o f the limestone. These o rgani sms grew up wa rd
o n top of other o nes and a re directl y in contact
with each other. N o te th a t sma ll indi vidu a ls ofrudi st and coral encru st large rudis t indi v idu a ls,
a nd that a rudist individu a l reta in s both the uppera nd lower va lves. Sca le bar is 5 cm.

skeleton is cemented by sparry calcite.
Betwee n the cora ls, fragment s of Lithothamnium (?), small foraminifer s, bivalves ,echin o derm s, qu a rtz grains a nd a large
amount of andesitic rock fragments arecontained in the micritic matri x.
[n other parts, individuals of organisms,
mainly rudist , are easi ly discrimin a ted fromone a nother, but the limestone is mass ive andshows no con spicuou s sedimentary structure.
Figure 4 show s the distribution of rudist andcorals on the bedding plane. Most indi vid ual s o f the rudi st and corals are not fragmented a nd often retain their origina l growth
direction . Between individu a ls o f the rudist
and cora ls, we ll-preserved skeleton of anunidentified dendoroid organism , and intact
shell s o f brachiopods a lso occur. The rudist
is po siti ve ly identified with Praecaprotina
y aegashii (Y ehara) (Figure 5). Sometimes

Shin-ichi Sano798

both the upper and lower valves are found inoriginal position. The rudist individuals arevariable in size (3 cm-12 cm in diameter).
They are crowded together and often in contact with one another, forming many clusters(Figure 6). Some individuals grew upward
on top of other ones (Figure 7). The corals
are mostly only several centimeters in width,and directly lie on rudist surface in somecases. At least several species of corals are
discriminated in this part, though only Eohydnophora cf. picteti (Koby) and Amphaslrea yabei Eguchi are identified to the species
level.
Under a microscope, calcareous alga suchas Lithothamnium (?) is seen to encrust oncorals, and vice versa. The interspace of theframe-building organisms is filled by micritic
matrix containing fragments of Lithothamnium (?), small foraminifers, corals andbivalves, as well as many grains of andesitic
rocks and epigenetic pyrite.

rigid framework on the andesitic basement.
The presence of beachrock was previously
recorded by Hanai and OJ i (1981) and encrusting bivalves and corals were reported fromthe beachrock, though it is very small in scale.
The limestone is impure and includes
coarse-grained bioclasts and rock fragments
between frame-builders. Among the framebuilders, corals are mostly massive in shapeand piles up densely. Such a massive shapeindicates a high-energy environment (James,
1983).
The newly discovered buildup is relatively
small in scale (ca. 50x20x I m), and otherbuildups observed in the basal part of the
Miyako Group are even smaller in spite ofabundant occurrence of hermatypic organisms. The probable scenario is as follows.
Such a buildup was probably only locallyformed in a transgressive stage. The influx

Transgression

Discussion
Many fossils of hermatypic organisms wererecorded from the Miyako Group, but theirdescriptions were mostly based on allochthonous specimens which occurred in sandstone
or conglomerate beds. There are few
paleoecological studies. Therefore, the presence or absence of substantial reefs has been acontroversial subject for a long time. Hanai
et al. (1968) and Tanaka (1978) presumed theexistence of barrier or patch reef. On thecontrary, Mori (1984) assumed the absence ofreef. He concluded that "corals by themselves did not form a rigid framework andwere sporadically distributed on sand".
The observed mode of occurrence of framebuilding organisms (e.g., their growth direction, direct pile and no fragmentation) indicates that this limestone abundantly contains
autochthonous and coexisting corals andrudists. This is the first concrete descriptionof carbonate buildup in the Miyako Group.
These hermatypic organisms constructed the

~

1

2

D Claslic sediments
c::::J Rudist·dominated buildup-;-:--:--....:.....

,.

-.......c-::-~~ Coral·dominated buildupoBasemenllAndesilei

Figure 8. A model for the growth and shiftof buildup in the Miyako Group. At the initialstage of transgression, a coral-dominated buildup
grew on the basement. As the transgression proceeds, it was covered by a rudist-dominated buildup under a lower energy condition, and finallyinflux of abundant clastic material prevented further buildup growth. When favorable conditions
came back, a new buildup started to grow at
different places.

920.

Aptian coral-rudist buildup in Miyako Groupof abundant clastic material may have
prevented the buildup from developing intolarge-scale reefs, and small-scale buildups
could grow only temporarily or episodicallyon the rocky shore. The site favorable forthe growth of frame-builders shifted obliquely upward along the slope during the transgression, and such a condition did not continue for long at any place (Figure 8).
The buildup of the Miyako Group represents an example considerably different fromthose of the platform carbonates in continental areas which are generally formed under amore stable and lower energy condition.
The sequential change of litho- andbiofacies of the discovered limestone from thelower to the upper part may be meaningful.
In the lower part corals are large and massive
and make a rigid framework. In the upper
part corals are small and they are no longer
main constituents. The main frame-builder
is the rudist, Praecaprotina, which sometimes
forms clusters but does not show dense packing. Even a fragile skeleton of unidentified
dendroid organism is preserved. Additionally, individuals of organisms are more easily
identified, and the framework is less rigid
than in the lower part. All these observations may suggest that the upper part was
deposited in a relatively low-energy condition. Scott (1988) considered that corals,
algae and stromatoporoids built the reefframe below normal wave base, and that
caprotinids and other rudists composed acommunity in the high-energy wave zone.
The result of my observation is somewhat
different from his interpretation.
This is the first record of rudist-dominatedbuildup in East Asia. The upper part of thisbuildup probably corresponds to "coppice"in the classification of rudist frameworks by
Kauffman and Sohl (1974). The rudist
frameworks were scarcely developed in the
North and South Temperate faunal realms(Kauffman 1973). Although Mori (1984)
suggested that the Miyako Group was deposited under warm-temperate environments,

799

such as those in the present Pacific coasts
from Kyushu to Honshu of Japan, the present
discovery indicates that the northern limit oftropical-su btropical realm reached northJapan in late Aptian time. This interpretation agrees well with the occurrence of beachrock, and also many Tethyan-type molluscs
from the Miyako Group.

Acknowledgements
I am grateful to Professor Itaru Hayami,
Associate Professor Kazushige Tanabe and
Dr. Tatsuo Oji for their guidance to this study
and critical reading of the manuscript. Professor Takashi Hamada gave me helpfuladvice on the study of the hermatypic organIsms. Associate Professor Terufumi Ohno
made useful suggestions toward an earlier
draft of this paper. I also wish to thank Dr.
Haruyoshi Maeda, Mr. Yasunari Shigeta andMr. Yoshio Yuki for their help during thefieldwork and my colleagues at the
Paleobiological Laboratory (Univ. Tokyo)
for their fruitful discussion. I also thankanonymous reviewers for the improvement of
the manuscript.

References
Eguchi, M., 1951: Mesozoic hexacorals from Japan.
Sci. Rep., Tohoku Univ., 2nd Ser. (Geol.), vol.
24, p. 1-96, pis. 1-28.
Hanai, T., Obata, I. and Hayami, I., 1968: Notes on
the Cretaceous Miyako Group. Mem. Natn.
Sci. Mus., Tokyo, no. I, p.20-28, pis. 1-4. (inJapanese with English summary).
- - and Oji, T., 1981 : Early Cretaceous beachrockfrom the Miyako Group, Northeast Japan.
Proc. Japan Acad., vol. 57, ser. B, no. 10, p. 362367.
James, N.P., 1983: Reefs. In, Scholle, P.A., Bebout,
D.G. and Moore, C.H., ed., Carbonate depositional environments. A mer. Assoc. Petrol.
Geol., Mem. 33, p. 345-462.
Kauffman, E.G., 1973: Cretaceous Bivalvia. In,
Hallam, A., ed., A tlas of Paleobiogeography, p.
353-383, 10 text-figs. Elsevier, Amsterdam.
- - and Sohl, N.F., 1974: Structure and evolutionof Antillean Cretaceous rudist frameworks.

Shin-ichi Sana

800

Verhand. NaturJ Ges., Basel, vol. 84, no. 1, p.
399-467.
Mori, K., 1984: Habitat of fossil corals from the
Miyako Group. In, Murai, T., Ok ami, K. andOishi, M., ed., Geology of a basin of the Omoto
river, p. 37-38. Board of Education ofIwaizumi
town, Iwate Pref. (in Japanese)
Scott, R.W., 1988: Evolution of Late Jurassic and
Early Cretaceous reef biotas. Palaios, vol. 3, no.
2, p. 184-193.

Tanaka, K., 1978: Miyako Group as a treasury offossils. Geological news (Geol. Surv, Japan),no. 291, p. 32-48. (in Japanese)
Yabe, H. and Nagao, T., 1926: Praecaprotina nov.
gen. from the Lower Cretaceous of Japan. Sci.
Rep., Tohoku Imp. Univ., 2nd Ser. (Geol.), vol.
9, no. 1, p.20-24, pI. 7.
Yehara, S., 1920: A pachyodont Iamellibranch fromthe Cretaceous deposits of Miyako in Rikuchu.
Jour. Geol. Soc. Tokyo, vol. 27, p.39-44.

Miyako -gil, Tanohata B3lf!l:lB, Kamakano-sawa j] ""? j] / fR, Aketo ~ p, Raga IBt
Hiraiga :ifi'Ht Harachiyama IJiUI!HU-gil~W~~~~~~d-~.=aR~N~7,~~.~:~~.B3lf!l:lBM~p~S~-gil~W~l1tmH;::, El1=.~~li«l~~ ~ :2'J~~U::~.=aRI) tJ:~:OW(~z. ~\"t':

<

J:

7,

Lko .:.

~:OW(~lt~JiitlfkJz.~ ~tr/H!H~tJ: ~ ~(50X20x 1 m) "t:~ ~o ~ Iv ~7'lt, -$-(It±:t;::~~diJ~, 5.iljtJ:'€$5j"t:lt±:t;::~.=aRiJ~;j$mz.~~o ~.=ttR~l::'lv ~7, 7'

tt.7~7W~~."t:~~0':'h~~.=aRM~~~~~~5jM~J:~t":2~~"~~t.:. I), 7 ~T 7 ~:t&MtutwMIf-1IRwMlfria~~~tJlHiJ~.~t B*t;::"f "t::&A.-"t:\, ,t.:.':' t z.
7f-i"0 ~:I:~~JiitIfkJ~fJU~iJ~7\J!~.mtJ:~~.:itz.tr.OVf, IHl'I.m~ ~ Iv J-' 7 , ~~~iJ~, ria~M~-_~~ ~h~~m~~.:itLkt~~~h~o ':'~~N~7,~tt, *~.~~*mmt.c~ ~ :2·~-'f'~.=aR~t It~f1ltt;::~tJ:-? td7Uz.~fJli L -C \"~o{;£lf1\1f-Trans. Proc. Palaeont. Soc. Japan, N.S., No. 162, pp. 801-805, I Fig., June 30, 1991

921. A NEW OCCURRENCE OF IMAGOTARIINE PINNIPEDFROM THE MIDDLE MIOCENE GOUDO FORMATIONIN HIGASHIMATSUYAMA CITY,SAITAMA, JAPAN*
NAOKIKOHNO
Natural History Museum and Institute, Chiba,
Chiba City, Chiba 280
and

YOSHIKAZU HASEGAWA
Geological Institute, Yokohama National University,
Yokohama, 240

Abstract. A pinniped tooth referable to the subfamily Imagotariinae Mitchell, 1968, is
described from the earliest Middle Miocene Goudo Formation near Higashimatsuyama City,
Saitama Prefecture. The tooth has an enlarged lingual cingulum, typical for the Late
Miocene imagotariine Imagotaria downsi Mitchell, 1968, but an enlarged lingual cingulum
with a large posterolingual protocone shelf on its crown seems also to be diagnostic for all
the genera within that subfamily. Therefore, it has been identified herein only as a left
upper second or third premolar of an indeterminate genus and species of the subfamily
Imagotariinae. This record provides additional information about the paleobiogeographic
and geochronologic distribution of imagotariine pinnipeds of the circum-North Pacific.
Key words. Carnivora, Central Japan, Goudo Formation, Imagotariinae, Middle
Miocene, Odobenidae.

suyama City, Saitama Prefecture. The present record is the first mammalian fossil to be
described from the Goudo Formation and is
one of the oldest known imagotariine fromthe North Pacific realm. The specimen wascollected by Mr. Takao Tahara on 23 September 1983, and has been stored at the Saitama
Museum of Natural History (SMNH).
Preliminary work leading to this study waspresented at the 137th Meeting of the Palaeontological Society of Japan (Kohno andHasegawa, 1988).

Introduction
The Miocene pinnipeds of the western
North Pacific are still poorly known.
Although a few materials have recently beenreported (e.g., Dubrovo, 1981; Takeyama
and Ozawa, 1984; Hirota et al., 1987),
almost all the other specimens have as yet to
be described.
In the present paper, we describe a pinniped tooth referable to the subfamily
Imagotariinae Mitchell, 1968, recovered fromthe earliest Middle Miocene Goudo Formation in the Iwadono Hills near Higashimat-

Systematic Description
In this paper, we adopted the classification"Received January 10, 1991; accepted April 15, 1991
801

Naoki Kohno and Yoshikazu Hasegawa

802ofpinnipeds arranged by Barnes (1989) with aslight permutation on its family-group systematics in consideration of the recent controversy on its higher level taxonomy among all
pinnipeds including the family Phocid ae.
Order Carnivora
Bowdich, 1821
Family Odobenidae
Allen , 1880
Subfamily Imagotariinae
Mitchell , 1968
Imagotariinae gen. et sp. indet.
Figure I a - e ; Table I

Material. - SMNH-V-e-37, left upper second or third premolar, lacking anterior andposterior roots at the base.
Locality. - A small valley at Negishi , located about 2.4 km southeast from the MusashiRanzan station of the Tobu-Tojyo Line, andabout 3.9 km west of the Higashimatsuyama
Interchange of the Kan-Etsu Expressway,
Higashimatsuyama City, Saitama Prefecture,
latitude 36°01'18" North, and longitude 139°
20' 38 " East.

Formation and Age. - The specimen was
found in a brownish, somewhat indurated ,but partially weathered conglomerate in thebasal part of the Goudo Formation (Majima,1989), which is assignable to the lowest partof Blow's planktonic foraminiferal zone N. 9
(Matsumaru et al. , 1982) and is therefore theearliest Middle Miocene in age. Inuzuka(1985 , table 2) listed, and Kohno and Hasegawa (1988) mentioned that a few desmo stylian remains belonging to the genu s
Palaeoparadoxia have been found in thesame formation at a different locality not far
from Negishi.
Description. - The crown of the tooth isshaped like a scalene triangle in occl usal
outline with a large posterolingual protocone
shelf, that is completely separated from theparacone by a sharp groove. The paracone
is situated near the midpoint of the buccal
side as a principal cusp. It is broad and low ,and a wear facet is on its occlusal tip. The
metacone is reduced to a slight spur on theposterior side of the paracone. There is asmall but distinct metastyle on the posterior
end of the crown. The crown is surrounded
by a continuous cingulum . The buccal cin-

d

a

a

,~~li,
~_~.

.

c~l

~,

_' i
. ..." /..

b

c

e

Figure 1. lm a gotariin ae gen . et sp. indet. , SMNH-V-e-37 , left p2 or P3. 2 times natural size.
a , occlusal view (stereo photograph) ; b, buccal view ; c, lingual view ; d , anterior v iew ; e, posteriorv iew.

921.
Table 1.

Middle Miocene Imagotariine from Saitama

S03

Measurements of the specimen, SMNH-V-e-37, in millimeters

Mesiodistal diameter of the crown· ........................................... 12.S
Buccolingual diameter of the crown ··········································10.2
Height of the crown at the buccal side ········································7.7
Mesiodistal diameter of the anterior root at the base ····························6.0
Buccolingual diameter of the anterior root at the base ··························5.1
Mesiodistal diameter of the posterior root at the base· .......................... ·3.S
Buccolingual diameter of the posterior root at the base ··························6.9

gulum is slightly inflated, but the lingual one
is much enlarged. The lingual cingulum isdivided into two parts, anterolingual andposterolingual, at a point slightly anterior tothe middle of the crown by a shallow notch.
The anterolingual cingulum forms a small
cingular shelf. It expands posterolinguallyand is elevated into a prominent posterolingual "cusp". This tooth is distinctly tworooted, although they are both broken off.
The anterior root is round in cross section
and the posterior one is elliptical at the base.
Discussion
The structure and proportion of the crown,
especially the well-developed lingual cingulum with the large posterolingual protocone shelf seen in the specimen SMNH-V-e-37
agree with the known upper cheek teeth ofimagotariine pinnipeds, and consequently
preclude an identification of the specimen as
a non-imagotariine having no broad basinlingual to the metacone. Such characters as
the relatively wide and low crown, the paracone bulging buccolingually, and a cingulum
moderately expanding posterolingually, seemto indicate that the specimen is a left upper
second or third premolar.
Five genera have been recognized so far
within the subfamily Imagotariinae (Barnes,
1989). Among them, the monotypic genera
Pelagiarctos Barnes, 1988 from the middle
Middle Miocene and Imagotaria Mitchell,
1968 from the late Middle to early Late
Miocene, both of California, have been

known with the large upper cheek teeth withenlarged, multiple cuspate lingual cingulum
on its crown. Prototaria primigena Takeyama and Ozawa, 1984, originally described as a primitive enaliarctine, from theearly Middle Miocene of Fukui Prefecture,
Japan was recently provisionally synonymized with the genus Neotherium and wastransferred from the Enaliarctinae to the
Imagotariinae by Barnes (1989). As can beseen from the illustration of Takeyama andOzawa (1984), the skull of Neotherium
primigenum (sensu Barnes, 1989: if the reassignment is correct) has a tooth, right upper
third premolar, with enlarged, less cuspate
lingual cingulum like that of the specimen
SMNH-V-e-37 and of the referred female
specimen (Repenning and Tedford, 1977, pI.
6) of Imagotaria downsi. The monotypic
genera Kamtschatarctos Dubrovo, 1981 from
the Middle Miocene of Kamchatka andPontolis True, 1905 from the latest Miocene ofOregon, were described on· the basis of apartial cranium and a dentary without upper
cheek teeth, and they cannot be compareddirectly with the specimen SMNH-V-e-37.
Pontolis magnus, at least, is distinct from thespecimen SMNH-V-e-37 on the basis of its
considerably larger size. Furthermore, thetwo species are separated geochronologicallyby approximately 10 million years.
Among these species, the specimen resembles most closely the cheek teeth of Neotherium primigenum in their proportions, size,and cingular cusp arrangement. However,an enlarged lingual cingulum with a large

804

Naoki Kohno and Yoshikazu Hasegawa

posterolingual protocone shelf seems to bediagnostic for all the genera within the Subfamily Imagotariinae and the development ofcusps on the lingual cingulum and conditionof root(s) also show a great variation.
Therefore, it is impossible to determine
whether this premolar pertains to the genus
Neotherium, Imagotaria or even a new genus
within the subfamily. Thus we identify itherein only as a left upper second or third
premolar of an indeterminate genus andspecies of the Subfamily Imagotariinae.
Until recently, imagotariine pinnipeds havebeen known mainly from the middle Middle
to latest Miocene of the eastern North Pacific(Repenning and Tedford, 1977). Therefore,
the specimen SMNH-V-e-37 from the early
Middle Miocene of Japan is one of the oldest
known imagotariines, not only in the western
Pacific but also anywhere in the North
Pacific. In addition, the tooth morphologyof the specimen as mentioned above is considerably primitive for the subfamily. Thus the
specimen probably belongs to the most primitive imagotariine that evolved from a certain
species within the enaliarctine pinnipeds in
Early Miocene time.
Acknowledgements

We are grateful to Takao Tahara of Sennan-gun, Osaka Prefecture, who collected anddonated the specimen described herein to the
Saitama Museum of Natural History. Our
thanks also go to Osamu Sakamoto of the
Saitama Museum of Natural History forsupporting the field work that determined thestratigraphic position of the specimen. We
are indebted to Lawrence G. Barnes of the
Natural History Museum of Los Angeles
County for his reading and criticizing themanuscript. Financial support was provided in part by a Grant-in-Aid for Scientific
Research (No. 61304010) from the Ministry of
Education, Science and Culture of the Government of Japan.

References
Barnes, L.G., 1988: A new fossil pinniped (Mammalia: Otariidae) from the Middle Miocene
Sharktooth Hill Bonebed, California. Contr.
Sci., Nat. Hist. Mus. Los Angeles County, no.
396, p. I-II.
Barnes, L.G., 1989: A new enaliarctine pinnipedfrom the Astoria Formation, Oregon, and aclassification of the Otariidae (Mammalia: Carnivora). Contr. Sci., Nat. Hist. Mus. Los Angeles County, no. 403, p. 1-26.
Dubrovo, LA., 1981: [A new subfamily of fossil
seals (Pinnipedia Kamtschatarctinae Subfam.
nov.)]. Proc. Acad. Sci. USSR., vol. 256, p.
970-974. (in Russian)
Hirota, K., Kobayashi, I., Sasagawa, I., Hori'kawa, H.,
and Kamei, T., 1987: On a skull bone of Allodesmus (Mammalia: Carnivora) found on
Sado Island, central Japan. Publ. Sado Mus.,no. 9, p. 197-209. (in Japanese with English
abstract)
Inuzuka, N., 1985: Studies and problems on theOrder Desmostylia. In, Desmostylians andtheir Paleoenvironment. Assoc. Geol. Collabor.
Japan., Monogr. 28, p. 1-12. (in Japanese withEnglish abstract)
Kohno, N. and Hasegawa, Y., 1988: [The firstoccurrence of Imagotaria (Mammalia: Otariidae) from Japan.] Palaeonl. Soc. Japan,
Abstracts with Programs, 137th Meet., p.46. (inJapanese)
Majima, R., 1989: Neogene stratigraphy along the
Arakawa River near Yorii, and of the Ogawa
Basin, Hiki Hills, and Iwadono Hills, central
Saitama Prefecture, central Japan. Geosci.
Repts., Shizuoka Univ., no. IS, p. 1-24. (inJapanese with English abstract)
Matsumaru, K., Matsuo, Y., and Kishi, R., 1982:
Miocene foraminifera from the Chichibu Basinand the South Hiki Hill, Saitama Prefecture,
Japan. Jour. Fac. Educ., Saitama Univ.,[Math. and Nat. Sci.], vol. 31, p. 39-63.
Mitchell, E.D., 1968: The Mio-Pliocene pinniped
Imagotaria. Jour. Fish. Res. Board, Canada.,
vol. 25, no. 9, p. 1843-1900.
Repenning, C.A. and Tedford, R.H., 1977: Otarioid
seals of the Neogene. U.S. Geol. Surv., Prof
Paper 992, p. 1-93.
Takeyama, K. and Ozawa, T., 1984: A new Miocene
otarioid seal from Japan. Proc. Japan A cad.,Ser. B, vol. 60, no. 3, p. 36-39.
True, F.W., 1905: Diagnosis of a new genus andspecies of fossil sea-lion from the Miocene ofOregon. Smithsonian Misc. Coli., vol. 48, no.
1577, p.47-49.

921.

Middle Miocene 1magotariine from Saitama

Saitama ~~, Higashimatsuyama *t0W, Musashi-Ranzan ftt~itW, Iwadono E)@:, Negishi tlt/¥, Goudo t$P.
~~W<*t011rm#;11):::.5};fjli' Q ,*,fl1l'*'tfTWtt$pJiiTiffiO)~EJii J: I), 1 '7 ::{!7 Y7]Ef;!I':'ji,i' Q f.!J)Jt4J~0) Sii1~:O iI>JeJl ~ :ht.:o ~~~*f:t.ii%Efl!ljiJ>fJt <, ii%EO)Jilli:Ef)lJH.:.~.lb-C Jeito) J:I, 'ii*~~":).:. c t~ c' iJ' G, -1: 1 ? 7'-f;!-0) 1 '7 ::{!7 Y7 ]Ef3H.:.ji,i' ~ f.!J)Jt4J~0), tcJ:~~n t L. < f:t.~ 3lltrSii c *IJttJi ~:h~ ~t*f-fFi'eW~IUoft ~ .:. O){<prs'O)~G~c L.-Cf:t., ':':h;l:-el.:.tmG:hQIl.&I)~~i!ll'tO)O)-":)ct~~o ~~~*f:t., .ijtmL.t.:
1 {Il!IO)Sii-e;5~t.:.lbji,fi~tIC5E-e~t~l'iI>, fp r ::z - Yo/' :r.lv 7 iJ>J: < Jeit L.-Cl'~.:. c~, 2 ii~ 1:";5 ~ t~ c'rnU&i'fJ!f!f~~*~ L. -C to I), H:I~IPJ Iliff\;: iJ , G~D Gic -C l' ~ -1: 1 ?
07'-~O)tJl7tC~:h~, **TY?A~O)Siil.:.~tJ:<~WL.-Cl'~o ':'O)':'ciJ'G, ~~~*f:t.~i!lO)f.!J)Jt4J~1:";5~;r.T Y71v(7 r 7-!ijjiJ'G, -1:1 ?7'-O)*Wtv.:.5}iI':ht.::fJJJtljo){<prs'O) 0- ":)1:";5 'cd.: 7::> ? U~;,;}:>;/c ~ 0
Ef! Il~@:~ • jjt;fr 111 ~fpc805

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 162, p. 806, June 30, 1991

SHORT NOTES

26. SIPHONOBASIS, REPLACEMENT NAME FOR CASSIOPELLA
KASE, 1984 (MOLLUSCA: GASTROPODA), NON WHITE, 1877*TOMOKI KASE
Department of Geology, National Science Museum, Tokyo 169

Kase (1984) proposed a new subgenus
Cassiopella for Cassiope [type species Cassiope (Cassiopella) ogaii Kase, 1984]. However, the recent publication of a monographof the Cassiopidae by Cleevely and Morris(1988) has brought my attention to the factthat the name is preoccupied by a genus of agastropod from North America (White, 1877,
p. 606). As the name Cassiopella becomes
unavailable, it is proposed that it be replaced
by a new name Siphonobasis. The genericname is compound from siphono, Greek,
meaning "siphon or tube", and basis, Greek,

meaning "base or bottom," in reference to thesiphon ate base of the shell.

References cited
Cleevely, R.J. and Morris, N.J., 1988: Taxonomy
and ecology of Cretaceous Cassiopidae (Mesogastropoda). Bull. Brit. Mus. (Nat. Hist.), Geol.
Ser., vol. 44, p. 233-291.
Kase, T., 1984: Early Cretaceous Marine andBrackish-water Gastropoda from Japan. 263 p.
Natn. Sci. Mus., Tokyo.
White, C.A., 1877: Paleontological Papers No.2.
Descriptions of a new species of Uniones and a
new fresh-water Gastropoda from the Tertiary
strata of Wyoming and Utah. Bull. U.S. Geol.
Geogr. Survey Territ., vol. 3, p.603-606.

'Received March 14, 1991; accepted April 15, 1991806

.-*-*-*-*-*-*-*-*--*-*-*-*-*-*-*-*-*-**
1'f • -=f ;E *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-.•••••! ©19921f.1f.~·t(MHi, 19921f. 1 }j 25 B, 26 B, 27 B ~:::.:tL1·li *~I£~$-c'lmf* ~ .td: i"" !•t~~$~ft12}j10B (&::.j9) *Wi-wl-c'i""o ~~$~O)j]¥!tJ~~~~:::.t.i:"?-r\""ii""o ~L!
! <ft i1r.:OJ 48 %~.:.'Jir~ \"0
!
0

!

••
;•

i;
i

©19921f.f7U~ (~141 @]f7U~) ft, 6 }j~~, ~llD1mO)¥f¥!If!:li~4'!lJ~"t:lmftO)T~-c'i""o

!

$~Jt:

•;•

=;= 422 MtIlD1!1f!:MtllD1m*~ 836 ~1lD1*~I£~$:ttl!~W~~~
Fax. 054 (238) 0491
)1g~1UlZ (P9~ 5801) ~t1[ 'l$ (P9~ 5810)

fi 054 (237) 1111

(fJ¥f*)•l;!

~--------------------------------------------------------------------------------------;
ji~~~~:O~(1991-1992*)

~Im

II~

110$ :&:~
I¥J~

JrI33

*~
~ij]

~;WJJ

'l$Ei''i"133¥Jt

fJ1&fE

'J'jR

~

~

~

li§
WJ$
Mtt

-Q\(;

~lE(~~:~J;fQ~*N o. 161 t:: I:t., 1989-1990:9=- M 11) Ii ~ ~ jl! ~ b:, ~ I? t::
1991-1992 :9=-""- C: tf:M~:lii: ~.n t.:.J: ? t:::jfUlI: ~ .n "i Lt.:o '- '~M • • ~I1)~.~.~L, .~~~R~.L"i~*.~.fi~.~~.m~, ~.~~.~~~, ~$.M~~R.M®~~Glj~.®~.~

G~~.iJ~~L

i?n Lit) *~o mtE~.®~.';l:r~c~;m I) L'~o*-=

E3*EnHlm.:f*A~t±

1 9 9 1 :9=- 6 )j 25 B

m

liIij

1 9 9 1 :9=- 6 )j 28 B

~

IT

ISSN

* E

B
=r ll3til

0031-0204

162-1}
2,500 fII

~

¥lJ

~

~

:lI!:Ji'(~)c:J?:lKifIJ;~2-4-16

B*~~~fn~:/?-r9~~

03-3817-5801

11iBi~IE·

B*JS~<1'kJ~~¥&15'·~~

M

m.lz:

'3~D1C~ ?!.UJ A :f* A ~ t±~t :tL 1-'-'
EH'/.'l ~ tw ~ ~?'. 1 -V :1 /' -lj- Iv ?' /' ~00 :0 nH :f* A ~ 1±
if: E rEB ~ • :f* A ~ t± (7 1 '/ .:L;;f JI~)

1 /' r~' V7EnH:f*A~t±
EnH1l7J]{Im.:f*A~t±£~p,\illj

~

*~~

~

~

{llJ ~ m;ff f* IK A T 11) § iffi IBJ 8-45m~l:iJ~mlilU:f*~~~m~*~*~ 022-288-5555 :lI!:Ji'( 3455-4415

Transactions and Proceedings of the PalaeontologicalSociety of Japan

June 30, 1991

New Series No. 162

CONTENTS
TRANSACTIONS
917. Sumio Sakagami and Harutaka Sakai: Fossil bryozoans from the Lower
Gondwana Sisne Formation, Nepal Lesser Himalayas .................... 761
918. Akihisa Kitamura: Paleoenvironmental transition at 1.2 Ma in the Omma
Formation, Central Honshu, Japan .................................... 767
919.

920.
921.

Ryuichi Majima: Redescription and mode of occurrence of Nipponoc/ava
yokoyamai (Shikama, 1954) (Clavagellidae: Bivalvia) from the PlioPleistocene warm-water fauna in Japan .................................. 781
Shin-ichi Sano: Discovery of a coral-rudist buildup in the Miyako Group,
Northeast Japan .................................................... 794
Naoki Kohno and Yoshikazu Hasegawa: A new occurrence of imagotariine
pinniped from the Middle Miocene Iwadono Formation in Higashimatsuyama
City, Saitama, Japan ................... _ ............................ 801

SHORT NOTES
26.

Tomoki Kase: Siphonobasis, replacement name for Cassiope/la Kase, 1984
(Mollusca: Gastropoda), non White, 1877 .............................. 806