a~~~i.~~~~~·ic.'f
Transactions and Proceedingsof thePalaeontological Society of Japan
New Series

No. 70Palaeontological Society of Japan
June 30th, 1968

CONTENTS
TRANSACTIONS
Page

537.

NISIIIDA. Tamio.

On some Gastropods from Millerella zone of the Aki-

yoshi Limestone Group (Ivlolluscan Paleontology of the Akiyoshi
Limestone Group II)
538.

AOKI. Naoaki.

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

Benthonic Foraminiferal Zonation of the Kazusa Group,

Boso Peninsula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
539.

KUIHIIAHA, Kenji.

Councillors:

238

Notes on the Benthonic Foraminifera of the Tono·hama Group, Shikoku, japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

President:

233

267

Kiyoshi ASANO
Kiyoshi ASANO (Editor of Fossils), Tetsuro liANA! (Editor of Transac·

tions and Proceedings), Wataru HASHIMOTO (Treasurer), Kotora IIATAI, Koichiro ICHIKAWA, Taro KANAY A, Kametoshi KANMERA. Teiichi KOBA y ASill,
Tamio KoTAKA, Tatsuro MATSUMOTO (Editor of Special Papers), Masao
MINATO, Hiroshi OZAKI (Planning). Tokio SHIKAMA (Membership), Tsugio
SIIUTO, Fuyuji TAKA! (Chairman of Executive Councillor's Committee)
Secretaries:

Takashi HAMADA, ltaru HAYA:\11, Yasuhide IwASAKI, Yokichi TAKA·YANAGIAll Communications relating to this journal should be addressed to the
PALAEONTOLOGICAL SOCIETY OF JAPAN
Geological Institute, Faculty of Science, University of Tokyo, japan

Trans. Proc. Palacont. Soc. Japan. N. S, No. 70, pp. 233-237. June 30. 196!!

537.

ON SOME GASTROPODS FROM MILLERELLA ZONE
OF THE AKIYOSHI LIMESTONE GROUP(MOLLUSCAN PALEONTOLOGY OF THE AKIYOSHILIMESTONE GROUP-II)*
T AMIO NISHIDA
Department of Geology, Kyushu University

Shuho-cho, Mine-gun. Yamaguchi Pref.,where it is slightly lower than the Profusulinella beppensis zone of TORIY:UIA·:1958) and consists mainly of brachiopod
shells of almost single species. Cleiothyridina roysii (L'EvEII.LE). I describe inthis paper a new species of Straparollus(s. s.) and two new species of Turbonilella on the basis of newly collected specimens from the two localities (Text-fig.

Introductory Note
Since YANAGIDA (1962) described manybrachiopod species from the Uzura Limestone. which is exposed at the Uzura
Limestone Quarry, 1200 m E of Yobara,
Ofuku, l\1ine City, Yamaguchi Pref., belongs to the zone of :llillerella, the studyof the fauna of this limestone has been
progressed by many investigators, YA'\IA·
GTWA and 0TA (1963) for corals, YANA·GIDA (1963. 1965) for brachiopods, SAKA·
GAt-.11 (1964) for bryozoans and IGO (1965)
for conodonts. As primarily describedby YANAGIDA (1962, 1965), this limestone
is massive and highly fossiliferous, its
lower part being characterized by " coquinoid " or " bioclastic breccia " facies
and its upper part by " true reef" facies.
The limestone of a similar coquinoid facies is exposed in the limited area on theeastern slope of the l~yugoho, Akiyoshi,

1).

Before going further I wish to express
my sincere gratitude to Professor Tatsuro ?-.lATSt:MOTO of the Department of
Geology, Kyushu University, for his kindencouragement during the course of thiswork and critical reading of the type·script.
Further I acknowledge Dr. Juichi YA·
NAGIDA of the Department of Geology,
Kyushu University and Dr. l\lasamichi
0TA of the Akiyoshi-Dai Science ivluseum,
who offered me valuable information on
the stratigraphy and supplied me withmany specimens for the study.

* Rcceiyed July 22. 1967 read Sept. 23, 1967
at Tokyo.

233

'l'a1nio NISHIDA

2!14

t

sinus.
Remarks.-Straparollus is variable inshell form. relatively high-spired trochiform to depressed discoidal. Some species referred to this genus have whorls
out of contact except in younger stage
and some other (of subgenus Philoxene)
have foreign matters in addition to thecontigeous whorls.
Subgenus Straparollus s. s.

0

I

2

trr-rl-----t131'15'

Text-fig. 1. J\Iap showing the collecting
localities, indicated by x.

Systematic Descriptions*Superfamily Euomphalacea
DE KONINCK. 1881
Family Euom phalidac
DE KONINCK. 1881
Remarks.-EICHW AI.D (1871) in Treatise
proposed Schizostomatidae to this familyon the basis of Schizos/oma BRONN. 1834.
which is a subjective synonym of thesubgenus Straparollus (Euompha/us) ].
SOWERBY, 1814, as discussed by KNIGHT(193-1) and YocHELSON (1956).

Genus Straparollus llE MONFORT, 1810
Type-species.-Straparo/lus dionysii DEMONFORT. 1810. Lower Carboniferous of
Belgium (original designation).
Generic Diagnosi.~.-Shell trochiform
to discoidal, widely phaneromphalous
throughout all growth stages; protoconch
discoidal, followed by rounded whorls;
mature whorl rounded to subquadrilateralin cross section: aperture with a shallow• Refer plate 23 of the preceeding volume(Trans. Proc. Palaeonl. Soc. Japan, N.S., No.69).

Subgeneric JJiagnosis.-Shell trochiform
to discoidal, narrowly or widely phaneromphalous; whorls rounded. sometimes,
with rounded spiral angulation on theupper whorl surface.
Remarks.-Some species of this subgenus have three spiral ridges or angulations on the outer whorl surfaces, which
are more rounded than those of S. (Euolllphalus).
Slraparol/us (SirapG1·o/lus) otai sp. nov.

Plate 23, Figures 3-5

Materia/.-llolotype (ASM5025), paratype A. B (ASM5026, 7) collected by l'v\.
OTA from the eastern slope of the Ryugoho, Akiyoshi. Shuho-cho, !\hne-gun,
Yamaguchi Pref.
Diagnosis.-She\1 low-trochiform ; outerwhorls with three rounded spiral angulations, of which the middle one is welldefined.
Description.-Shel! moderately small,t rochiform, consisting of seven and ahalf volutions in the holotype·; whorls
rapidly increase and roughly rounded
but with distinct three spiral angulations
on its outer surface, of which the middle
one on the periphery is well defined ;periphery nearly at mid-whorl height;
spire very low-conical; spire angle 118'
in the holotype; apex, including first
three and a half volutions, well flattened;.5.17.

Ca.'lfropods from Akiyoshi

protoconch dextral in the holotype; umbilicus moderately deep: umbilical angle
73o in the paratype B: suture rather
shallow, passing around the previous

whorls at the middle angulations: growthline, passing downward the whorls witha very slight insinuation over the upper
angulation and orthocline below it.

A!easurements.Specimen
IIolotype(ASM5025)
Paratype A (ASM5026)
Paratype B (ASM5027)

Number ofwhorls7.5
7.0
5.0

Discussion.-The three spiral angulations on the outer whorls separate thisspecies from all other Slraparollus (s. s.)
except Straparollus (s. s.) savagei KNIGHT
from the Pennsylvanian of North America. Straparollus (s. s.) otai differs from
Straparol/us (s. s.) savagei in having amore strongly developed middle angulation than the upper angulation. Other
possible differences may be masked by
the incomplete preservation of the present species.
Occurrellce.-The present species occurs
in the Millerella sp. a zone of the Akiyoshi Limestone Group.
Repository.-Type-room of the Aki·
yoshi-Dai Science Museum. Yamaguchi
Pre f.
Superfamily Neritacea RAFINESQUE, 1815
Family Neritopsidae GJ{A Y, 1847

HeightDiameter

3.3
8.0+
6.1+

16.1
15.6
10.3

Umbilical
diameter
9.1

Spire
angle
118°
113"
111'

a narrow concave zone between theshoulders and a collar-like adpressedzone at the upper suture; base slightly
flattened; columellar lip arcuate, thickened and extened in the plane of theaperture; outer lip nearly straight, slightly oblique backward ; ribs or pustules
collabrally lengthened and prominent on
the shoulder and continuous downward
on the spire, appearing in two rows on
the last whorl.
/Jiscussion.-Since DE KoNINCK (1881)
established this genus and placed it to
Turbinidae, there have been much dis·cussions as to its systematic position.
ZITTEL (1885) placed this genus to Littorinidae. CosSMANN (1915) to Cyclonematidae and KNIGHT (1934) to Neritopsidae. Turbonitella is referred to Neritopsidae by its protruding spire and notresorbed inner whorls. As presently restricted, this genus ranges through theLower Carboniferous in Europe.

Subfamily Neritopsinae GRAY, 1847
Genus Tr1rbonitella DE KONJNCK, 1881
Type-species.-Turbo biserial is PHILLIPS,
1836, Lower Carboniferous Mountain
Limestone, Bolland, Yorkshire, England(subsequent designation of CossMANN,
1915).
Generic Diagnosis.-Shell trochiform,
anomphalous; spire of moderate height;
whorl profile strongly shouldered highup and gently arched below the shoulder;

Turbonitel/a yanagidai sp. nov.
Plate 23, Figures 6-9

Material.- Holotype (ASM5020), paratypes A. B. C (ASM5021-3) collected by
J. YANAGIDA from the Uzura Limestone
Quarry, 1200 m E of Yobara, Ofuku.
Mine City, Yamaguchi Pref.
Diagnosis.-Spire rather low for the
genus; spiral angle approximately 95° ;pustules opistoclinely lengthened and236

Tam.io NISHIDA

rather strongly developed and separated
by wide interspace.
Description.-Shell small, turbiniform,
anomphalous; whorls rapidly expanded,consisting of four and a half volutions;whorl profile strongly shouldered highup and gently arched below the shoulder;a narrow concave zone between shoulders
and a collar-like adpressed zone at theupper suture; spire small. conical: spire
angle 95.6' in the holotype: protoconch
simple, dextral ; base slightly flattened ;suture almost apressed ; ornamentationconsisting of growth-lines and pustules;
pustules most prominent on the shoulder,
being lengthened continuous below it on
the spire and appearing again as an alternating row on the lower surface ofthe last whorl; columellar lip arcuate,
thickened and with a shallow excavation
within its margin; parietal lip somewhat
thickened and extended in the plane Qf
the aperture: outer lip thin, nearlystraight, slightly oblique backward; shellstructure not known ; operculum not pre·served in all specimens.

Afeasurements.Specimen
Ilolotype(ASM5020)
Paratype A (ASM5021)
Paratype B (ASM5022)
Paratype C (ASM5023)

Number ofwhorls
4.5
4.5
3.5
4.5

Discussion.- The present species isclosely allied to the type-species, Tur!Jo·
nitel/a bise/iaris (PIIILLII'S). from theLower Carboniferous of Belgium. but
differs by its opistoc1inc and rather
coarsely spaced pustules and a larger
spire angle.
Occurrence.- The present species occurs in the Millerella sp. tr zone of lhe
Akiyoshi Limestone Group.
Repository.-Type-room of the J\kiyoshi-Dai Science Museum, Yamaguchi Pref.
Turhonitella ryugolwensis sp. nov.
Plate 23, Figure 10

Material.- Holotype (ASl'vf5030) collect.
eel by M. 0TA from the eastern slope of
the Ryugoho, Akiyoshi, Shuho-cho, Minegun, Yamaguchi Pref.
Diagnosis.-Spire rather high for the
genus; spire angle about 70' ; nodes pro·minent on the shoulder and opistoclinely
elongated below it and appearing as two

Height
13.5
12. l
8.2
II. 5

Spire
height
3.2
3.0
2.2
3.1

Diameter
13.1
12.3
8.0
11. 6

Apire
angle
95. 6'
96.0•
95. 7'
96.1'

rO\vs on the last whorL
Description.-Holotype small, 13.5 mm.
in height, 4.0 mm. in spire height, 11.1
mm. in diameter, trochiform, anomphalous. consisting of about four whorls;
whorl profile slightly shouldered at theupper lateral part and slightly archedbelow the shoulder; a narrow concavezone between shoulders and a collar-like
adpressed zone at the upper suture; spire
small but rather large for the genus;
spire angle about 70' ; suture almost
apressed; ornamentation consisting ofgrowth-lines and nodes: nodes prominent
on the shoulder and opistoclinely elongated below it, appearing as an alternating rows on the upper whorl face ofthe last whorl; aperture not observed;
operculum not preserved.
Discussion.- The present species is
now represented by a single specimen.
It has however. so characteristic ornamentation that the establishment of a
new species is warranted. Nodes on theouter whorls separate this species from537.

Gast1·opods from 1lkiyoshi

all other known species of this genus.
Hy other characters this species is safely refer to Turbonilella.
Occurre11ce.- The present species occurs in the Jlillerella sp. a zone of the
Akiyoshi Limestone Group.
Repository.-Type-room of the Akiyoshi-Dai Science Museum. Yamaguchi Pref.
l{eferences
H. G. (1834) : Lelheae Geognoslica,oder Abbildrwgen und Beslrreibungen dcr
fiir die Gebirgs-Formalionen bezeichnensten Versleinerungen. I. 1-96. Stuttgart.
Coss:o-!AN!';. Maurice (1915): Essais de paleoconchologie comparee. 10. 1-292, pis. 12.
Paris.
lc;o, Hisayoshi (1965): Carboniferous conodonts from Yobara, Akiyoshi Limestone,
Japan. (Studies of Asiatic conodonts. Pt.
II). Trans. Proc. Palaeont. Soc. japan,
N. S., (53), 179-193, pis. 27-28.
KNIGHT. ]. B. (1933): The gastropods of the
St. Louis, Missouri, Pennsylvanian outlier.
The Trochoturbinidae. ]. Paleont .. 7. (1),30-58, pis. 8-12.
- - (Hl34) : The gastropods of the St. Louis,
1\Iissouri, Pennsylvanian outlier. The Neritidae. Ibid, 8. (-1). 359-392, pis. 40-46.
KNIGHT,]. B.. BATTE!", R. L. and YocuELSON,
E. L. (1960): In Treatise 011 invertebrate
paleontology, Mollusca I, (Chitous, scaplroPods and gastropods). University of Kansas Press.
BRONN.

L. G. De (1881): Faunc de carcaire carbonifere de Ia Belgique, 3" partie,
Gasteropodes. Ann. Mu.~. Roy. d'Hist.
Nat. Belgique, ser, palcont .. 6, 170 pp., 21
pis.
SAKAGAi\11, Sumio (1964): Bryozoa of Akiyoshi. Pt. 2. Lower Carboniferous Bryo.
zoa from the Uzura quarry. Trans. l';oc.
Pal aeon/. Soc. jajwn. N. S .. (56). 295-308.
pis. 44-·15.
ToRJYAMA. Ryuzo (1958): Geology of Akiyoshi. Pt. 3, Fusulinids of Akiyoshi A/em.
Fac. Sci. Kyushu Unir· .. (D), 7. 1-264, pis.
1-·18.
YAMAGIWA. M. and OTA. M. (1963): Faunasand correlation of "Uzura" quarry, Akiyoshi. Southwest Japan. Pt. I, Corals. /Jull.
Akiyoshi-dai Sci. Mus .. (2). 87-93, pls. l-2.
YANAGIDA, Juichi (1962, 1965): Carboniferous brachiopods from Akiyoshi. Southwest
Japan. Mem. Fac. Sci. Kyus/111 Univ.,(D). 12, (1), 87-127. pis. 14-21; 16. (2),113-142. pls. 25-28.
- - (1963):
Upper Lower Carboniferous
brachiopods from Akiyoshi. •· Kaseki ··("Fossil"), (6), 7-8 (in Japanese).
YocHEI.SON, E. L. (1956): Permian Gastropoda of the Southwestern United States.
1. Euomphalacea, Trochonematacea, Pseudophoracea, Anomphalacea, Craspedostomatacea, and Platyceratacea. Bull. Amu.
Mus. Nat. Hist .. 110. (3), 173-276, pis 9-24.
ZrTTEI., K. A. (1885) : Handbuch der Palaeontologie. 2. Mollusca und Arthropoda, 900
pp .. 719 pis. Miinchen und Leipzig.
KQNINCI{,

Locality Guide
Uzura Limestone Quarry. 1200 m E of Yobara. Ofuku, l\Iine City, Yamaguchi Pref.
(Lat. N34'11'02", long. E 131"15'21").
"' x 7 t:11 fitfli. 111 u m~n rli b~~~iiliRW.::;J; 1200 m.
The eastern slope of the Ryugoho. Akiyoshi. Shuho-cho, Mine-gun, Yamaguchi Pref.
[Lat. E 3'1'13'42". long E 131"17'18.'].
Ill o Yil-51H%:f.Bf:k J;:fllJ f-k flb:J~$:!lt:Jt1J(Ij.

aTrans. Proc. Palaeont. Soc. Japan, N. S., No. 70, pp. 238-266, pl. 27, June 30, 1968

5~~8.

BENTHONIC FORAMIN£FERAL ZONATION OF THE
KAZUSA GROUP. BOSO PENINSULA*NAOAKI AOKIInstitute of Geology and Mineralogy, Tokyo University of Education

mm:!f:~J·

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J?;H::: t.. ~~;W!jc; J:. U:!f.]·~!<lll::: ~.:>v ·"C fiti»~Cl)j)'1f; lk'f'l/J~l- 7=, ·~ t::.. lt:fi'Rt~l:. J:. -:> 't J:~f~!lH: 17 0)11:. ~'liH:.IK 11·Hs .
.:. il..I,?Cl)uffi.!il+!t~..:Cel)fll:ftl;t;~H fc :lffH'iiih!!Q)ifljO)i~ ~ 1.:: J:. ·.:> ·c!Jl:k~tL'tv · ~. Jk
tl~h!l~'t':/f~TffliCl)ll::j]illi- :,k}Jj(/•,1 fClj.l~:d1..~ Gyroidina-Melonis 1W%li lower bathyal Q){,

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.

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continuous. They are dominated bydeeper, open sea facies and yield foraminiferal fossils in abundance throughout
the sections.
This paper gives an outline of the
Pliocene and lower Pleistocene benthonicforaminiferal assemblages from the Kazusa group, Boso Peninsula. The biostratigraphic subdivision of the group ismade with reference to the stratigraphic
distribution of these assemblages, which
are expected to furnish more accurate
information for the correlation of thestrata, the paleo-environments and geological history of the basin.

Introduction

The Boso Peninsula is situated in thecentral part of the Japanese Islands andbounds the Tokyo Bay on the easternside, protecting it from the Pacific Ocean.
For the study of Pliocene and Pleistocene
Foraminifera, the sedimentary basin of
Boso is believed to be a particularly
unique and favorable field in Japan. In
this region the marine sediments of theseages are considerably thick and mostly* Received July 20, 1967: read January 2S,
1966 at Sendai and September 2•1. !966 at
Akita.

238

538.

Benthonic Fora1nin-ife·ral Zonation

Preyious 'Vork
The foraminifera of the Boso Peninsula
were first observed by 0TUKA (1932). wholisted numerous species from the ··Pliocene Sanuki •· formation.
ASA!\0 & NAKAMURA (1937a, b) and
AsANO (1938a-e) published six monographical papers of the Tertiary and Recent
smaller foraminifera of Japan. They described and llgured several tens of species from the Pliocene and Pleistocene
rocks of the Boso Peninsula. Numerous
species were introduced as new. At thesame time, ASANO (1938f-g) reported on
the fossil foraminiferal assemblages.
Later. ASANO (1950-1952) engaged in
the descriptive works of almost all of
the known foraminiferal species fromJapan and published " lllustrated catalogue of japanese Tertiary smaller Foraminifera... tv! any of the benthonicspecies are re-figured from the Pliocene
and Pleistocene formations in Boso.
Ucmo (1950-1952) studied the sequenceof the foraminiferal assemblages of the"Pliocene" Kazusa group from the
Otaki-Mobara natural gas field. He described some new taxa from this section
and from the environs of the 1\Iinatomachi, western Boso.
TAI<AY ANAGI (1951) described the Ehrellbergina species and KuwANO (l95·1a. b)
studied the Cassidulina species from the
Pliocene formations in the western partof the Boso Peninsula.
HIRA YA~IA (1954). KOIKE (1955), and
KoMATSU & O.MOIH (1956) examined theforaminifera in some samples from thelower part of the Pliocene of the peninsula in relation to the sedimentological problems concerning the causes ofturbidites and slumping structures.
In 1957-1958. AsANO made an important contribution to the Pleistocene geochronology in the Boso Peninsula. From239

the planktonic foraminiferal analysis. heconcluded that the Pliocene-Pleistocene
boundary can be set at the middle partof the Umegase formation.
The vertical faunal variation of theplanktonic foraminifera from the ObitsuRiver section was studied by TAKA y A:>.! A(1961. 1962). AOKI (1963) worked on thebenthonic and planktonic assemblages
from the Yoro River section. In 1964,
he reported the vertical and lateral faunal variations of the planktonic assemblages in the Kazusa group.
ISHIWADA, HIGUCHI and KIKUCHI (19581965) studied successively the foraminifeni collected from the subsurface ofthe various places in this region for theforaminiferal zoning and correlation of
the subsurface columns, and they madeclear the subsurface distributions of the
Kazusa foraminiferal assemblages. lsHJ·w ADA (1958a) first established the currently accepted zonation of the group.
and recently he (ISHIWADA, 1964) attempted the paleoecological interpretations of the biofacies compared with the
Recent benthonic foraminiferal assemblages off the japanese Pacific coast.
Local Stratigraphy
The name Kazusa group was given to
the Pliocene and lower Pleistocene rocks
in the Boso Peninsula. Since 1950, detailed mapping of the group has been
carried out by several petrolem geologists
tracing a considerable number of pyroclastic layers intercalated in llne-grained
sediments as very important marker-beds
from the eastern side to the western oneof the peninsula. Thickness and lithofacies variations in vertical and lateral
directions of the strata in the important
areas of the peninsula were satisfactorily clarified. The sampling of the foraminiferal material was made on the basis

240.\laouki AOK!

of these comprehensive stratigraphic\VOrks. which are listed in the bibliography at the end of this paper. Stratigraphical descriptions and reviews ofthis region have been given elsewhereby many workers.
The Kazusa group. in the present-day
usage, is divided into the following nineformations along the Yoro River, thetype section of the group (from upper
to lower):
Kazusa Group
Kasamori formation (150m): muddy finegrained sandstone and sandy mudstone.
l\·landano formation (•LO m) : sandstone andconglomeratic sandstone.
Chonan formation (75 m) : alternation of linegrained sandstone. muddy sandstone andmudstone.
Kakinokidai formation (75 m) : massive finegrained sandy mudstone intercalated withthin sandstone layers. and muddy linegrained sandstone at the upper.
Kokumoto formation (340 m) : thick siltstone
and an alternation with sandstone.
Umegase formation (500 m) : thick sandstoneinterbedding thin layers of siltstone. withan alternation of sandstone and siltstone.
Otadai formation (500 m) : composite alternation of mud-rich and sand-rich alternations.
Kiwada formation (600 m) : siltstone, and analternation of siltstone and thin sandstonelayers. intercalated with abundant layersof pyroclastic materiaL
Kurotaki formation (280m) : tuffaceous andscoriaceous, coarse to medium-grainedsandstone, and andesitic tuffs. with conglomerate at the base and muddy sandstone at the upper.

The interval of the Kurotaki formation along the Yoro River section isdiverged and thickened to the east. attaining more than 600 m in thickness at
the eastern margin of the peninsula. andis further subdivided into three lithostratigraphic units as follows (from upper
to lower):

Ohara formation (200m): alternation of sandstone and siltstone.
Namihana formation (300m) : mudstone andmud-rich alternation of mu(h;tone and sandstone.
Katsuura formation (300m): sandstone, sandy
mudstone. and an alternation of mudstoneand sandstone, with conglomerate at lhe
lower.

In the western part of the Boso Peninsula, the Kazusa group changes inlithofacies, becoming dominantly sandstone or sandy facies, and can be divided as follows (from upper to lower) :Kazusa GroupSunami formation (150m) : mudstone, muddy
sandstone and fine-grained sandstone.
Sanuki formation (100-200 m): mudstone andsandy mudstone.
Nagahama formation (20-100 m): conglomerate and sandstone.
- - probable unconformity - lchijyuku formation (400 m): sandstone.
"Umegase formation" (100+m): alternationof sandstone and mudstone.
lligashihigasa formation (300m): sandstone
and conglomerate.
I wasaka formation ( 100-200 m) : silty linegrained sandstone.
"Takamizo formation·· (150m): mudstone.
Kurotaki formation (500 m) : tuffaceous sandstone and pyroclastics.

The supplementary works on the foraminifera and stratigraphy of the Nagahama and Sanuki formations are still
under way, and are not treated in thispaper. A stratigraphic profile of Fig. 2
illustrates the above-mentioned lithostratigraphic subdivision of the Kazusa
group in the Boso Peninsula.
Rock-samples were collected from thefollowing nine sections (routes) and some
supplemental ones in the central zone of
the Boso Peninsula. after measuring thestrata and checking their stratigraphic
positions. The locations of the sections

538.

Benthmtic Fora.m:in·iferal Zonation~-11(6) Isumi·Mobara section: Katsuura-OtakiChonan--Mobara(7) 1\atsuura-Mobara section: Katsuura-Onjyuku-Fuse-Kuniyoshi--Shin'meimacIkari yato-Sakamoto-Mobara(S) Onjyuku-lchinomiya section: Onjyuku~am ihama- Shakadani-1 wakuma- lchinomiya(9) Ea:;t Coast section: Onjyuku-Kamihana-Oharaare shown in Fig. 1.
(1) 1\Iinato-Sanuki section: Tom ira- SanukiIsone-saki(2) Takarnizo-Tamaki section: TakamizoTamaki-Tagura(3) Koito River section: Masaki-Nishi-higasa-Naewari-Nashinoki(4) Obitsu River :;cction: Sasa-gawa- -Kururi(5) Yoro River section: Awamata--Ushiku

Urawa.

Narita

.f
d'
~

~

"""'

Fig. I. Location of the examinedsections (routes) of the 1\azu~a group.
Bo:;o Peninsula.

242

Nauak·i ..10111
k

•>

~

Koku.motoU11egase.ooo ..

0Fig. 2.

5

10 leaLitho-stratigraphic subdivision of the Kazusa group, Boso Peninsula.

Foraminiferal Zoning

Both vertical and lateral variations of
the foraminiferal assemblages are considerable in the Kazusa group, and alarge number of foraminiferal species
appear in and out of the section. Until
present about 300 species have been distinguished. They are mostly of calcareous perforate forms. Then, cassidulinids,
bu!iminids, bolivinids. cibidids and num:rous shallow water species are import:>.nt constituents of the Boso faunas.
Planktonic foraminifera are also common.
Porcellaneous and arenaceous forms aremuch less frequent. represented by avery small number of species and individuals in every horizons.
The occurrence and frequency distribution of individual species were carefully examined and checked in comparison with pyroclastic key beds as wellas with lithostratigraphic divisions. Benthonic species having narrowly restrictedvertical ranges are hardly detected in
the Boso faunas. At least. no importantones are found. The specids previously
regarded as indices of the lower Plioceneof this region are round in this study toocrur in upper horizons. The stratigraphic ranges of some of these species
would extend into Recent through Pleistocene. Unlike in older formations, thebiostratigraphic subdivision by verticalranges of local occurrences of the species
is difficult to establish and is probably
useless. Therefore, frequency distributions of the dominant and characteristic
species and their assemblages are theimportant criteria for biostratigraphic
zoning and correlation.
The benthonic foraminiferal zoning of
the Kazusa group has been carried out
for the purpose of the correlation of sub·surface columns in natural gas exploration. Two or three sets of foraminiferal
zones or zonules were proposed by theprevious workers (Table 1). Some zones
were named without clear difinition of
the fossil contents and boundaries. although they are used by many workers
and by oil companies. These subdivi-Table 1. Comparison of the benthonicforaminiferal zonings prCI'iously established in the Kazusa group, Boso Peninsula.
[SHill' ADA.

Ucmo. 1951
Formation

Zone

HIGUCHI &1''"/WAUA. !9591 Kll\l'Clll.
1962

j Zonule I

ZonuleZonuleHIGUCHI. 1964
Zonule/ .
I

jPseudoeponides-Elphidium

MandanoPseudoeponides-Eiphidium

I

Kokumoto

I

I

Umegase

1-5

Cassidulina
subglobosa

Cassidulina
subglobasa

Lower Koku.
moto Faunule

15

Lower
KokumotoUz,igcrina
akitaensis
BUiwrina
aculeata

Cassidulina
subglobosa- - - - -Lower
6-H
KokumotoIU•ig"''"
akitatmsis

HiII

Bulimina
aculeata-Bul.
nipprm ica-Bolivina
robusta

17-21

22-23
Otakai

24-28

Facies -

Zon~

Zone

EIPhidi•mc/az•atum- -- ----j Nonwnclla stella
2 I
"'
1
_

1- _

Cassidulina
subglo/Josa
Lower Kokumoto FaunuleUt•igcrinl!
akttacnsts
Bulimiua/ aculeata

I

II

--W
-,,

Boli!•inah. Uvi~e1:ina

7aktlaensts. BuliminaI
aculeata
I BuliminaBolit•ina (upper)
Bolit'ina spissa
I

8

9

I

Bolivina

Bolivinav

Bulimina
aculeata

Kamihana-Katsuuraj Basal Faunulei----~ Casszdulina
5snbglobosa
Cassiduiina
6'
subcarinata

--j
1

---

__:> _ "Mandano"
I Cnbroelphulium4
clavatum

10

I
--

Co

~-

J

I

Ohara

- -

akitaensis
Buliminaaculcata

AoK1(LI11s.. p apcr )Ellipsonod~ Stlloslomella lePi· Stilostomella lePi·jsaria lepidula dula Subzonule
dula Subzonule
Bulimina
Bulimina
nipponica
nipponica
Bulimina
Bulimina
nipponica
nijlponica

Kiwada-u~·igerina1962.

----1-1

ChonanKakinokidai\\'ADA.

1964

ZonuleI

I

Kasamori

IsH!· ( AoKII KIKt:CHI, 1964

I

Bulimi1w
aculeata
Bulimina
nippon~ca
Lower Kazusa
Mixed Faunule

II

Bulimina
aculeata

Oo

~

~

~

...-5
.,...
~

2

....~

~~
:;::

....

~·

~

11

~

12

........

;;::- - - BuliminaBolivina (lower) !::)I Stilustomel/a13

ketienziensis

0

;;:::

1·1
Bulimina striata---

Gyroidinacf. orbicularis
Gyroidina-Aielonis(undivided)

Basal Kazusa
Faunule
-

-

~
,j:.
~

.. J

244

Naoaki AOKI

sions are re-examined and revised a little
from the generalized standpoint in thispaper based on the subaerial material
obtained from the whole exposed area ofthe Kazusa group in the northern partof the peninsula.
The Kazusa fauna contains several
different faunal groups which are easily
distinguishable. It is divisible into 6
groups and further subdivided into 17
or more benthonic foraminiferal assem·
blages. The zones defined by thesecharacteristic assemblages are as follows(from upper to lower) :(1) Shallow water zones
JVonirmellrz stella Zone•· Mandano ·· Zone
" Lower Kasamori" Zone
Ci/Jicides-l'seudonrmion Zone
(2) Cassidulina zones
Cassitlulina subglobosa Zone
Cassitluliua subcarina/a Zone
(3) Ul'igerina zone
Vl'igcrinu akitaensis Zone
(4) Bulimina-Boliz:iua zones
Bulimina aculeata Zone
lJulimilza-BoliL•ina Zone (upper)
Bolil'i1ra spissa Zone
Bulimina-Bolivina Zone (lower)
Stilostomclla ketienziensis Zone
Bulimina striata Zone
(5) Mixed assemblage zones
Cassidulina-lJuliurina Zone
Cassidulina-Cibicides Zone
(6) Gyroidina-.\Jelonis zones
Gyroidina cf. orbicularis Zone
Gyroidina-.\lelonis Zone (undividc<i)One half of the above-listed zones arerenamed and a few are newly proposedin this paper. The names or locally
distributed zones are not given but conventionally substituted by the lithostratigraphic (geographic) names for
simplification. The succession of the foraminiferal zones is more complete a1ong
the Yoro River section. The stratigraphic distributions of these benthonic fo-

raminiferal zones and the lateral variations of the assemblages are shown in
Fig. 3 and Table 2. The distributionsof the common and characteristic benthonic foraminiferal species are shownin Fig. 4.
Depth Variations
All of the species may be distributed
vertically and horizontally as wide as
possible in a geologic section. The distributions of the benthonic species arenaturally determined by the ecology ofthe species and the ecologic conditionsof the environments. These species may
have been assembled to form various
characteristic faunal communities according to depositional environments. The
complicated constitution with a considerable number of the species of theforaminiferal faunas is favorable forunderstanding the interrelation between
the foraminifera and their environments.
Minor environmental changes have an
immediate effect upon the frequency ofsome of the constituent species. The
faunal composition may be said to haveresulted from the total effect of various
paleo-environmental factors. Reversely,some faunal changes, vertical and lateral,
should be indicative of some change ofthe environments.
Depth of the sea is a very importantand easily distinguished factor in thefossil foraminiferal distributions, because
this factor is mutually related with otherpaleo-ecological factors of the sea. Both
distributions and faunal variations of thefossil foraminiferal assemblages in the
Kazusa group may be considered to havebeen primarily determined by the depthof the depositional sites.
The Kazusa group had been considered
to rest unconformably on the Miocene
rocks. The foraminifera from the basal

538.

Benthonic: Fora.minije?·al Zonation
.,"

.

I<

."

>

~

Ol

0

...."
....

.......
"'
0

245

::s

~

g

...!l

0

Nonionella stella
C·-clavatwa
Cassidul1na eubglobosa

Lower Kas uori

Casaidulins eubcarinata
Uvigerina akitaensis
Bulimina aculeata
Bulimina-Bolivina (upper)

1000 m500

50Fig. 3.

~
Sanuki
Nagabama

10 kiD

Benthonic foraminiferal zones of the Kazusa group. Boso Peninsula.

Table 2.

The faunal succession of the Kazusa group, lloso Peninsula.

MinatoTakamizo-Tamaki-SanukiI

Koi toRiYer--- --- - --- - ----- - - -Ssnulci
Nagabama--

ObitsuRiYer!oro River

I

Isumi
-Mobara East Coast

Nonionella
stellaKaaamori~

MandanoLower
Kasamori

Cribroelpbidium clavatum

I
I

~0

Cbonan...
Kakinokidai•• • • • • • • • • ••:1>
Caasidulina subglobosa·: ·.' . ~-·. :; ~- ·.:·{ ~~~~-~~~~-~~y~-_o__..___C_a_e_s_i_d_u_l_i_n_a_s_ub_c_ar_i_n_a_t_a_ _ _ll Kokumoto
Uvigerina ski taensis
UmegaseBulimina aculeats
Iwaasks

Cibicidee-

Peeud.ononion- - - - - - - - -lf----1

Bulimina-Bolivina (upper)
Cauidulina-Bnl111ina

Bolivina spissa_______ -·~----~'----------------+-:-B::.u::.l=111=i,;;:na-Bolivina (lower)
Stilostomella
KurotakiCaesidulina-Cibicides
ketienziensia
Cas.-Bul.

Bulimina striata

Cas.-Cib.

Gyroidina
cr. orbicularis~-----,Gyroidina

1-Melonie
Cas.-Bul. !(undivided)

Otadai

KiWadaObara
Namibsna
KateuuraNa.oak-1: AOKI

2411

---

COLD WATER ZOIIES... ~ ,... ,-<>;j

COMMON

0

al

::>

<I)

<I)

al
0

0

-

G.t.UDRYlJU, c!. ARKN.t.Rll G. & W.

~

0

PYRGO KURRHIN.t. (Schwager)s. .__NODOSA.RU LONGlSC.t.'l'A d'Orbigny

~
<I)

0

H

<I)

PRONDlCULARI.t. POLlACK& Schwager& McCulloch------LENTICULlN.t. PSEUDOI!a!!ULA'l'.t. (Aa.)----

TO'l'OMIENSIS Makiyama

-

...._

~----

PISSURINA ECHlGOENSIS (A. & I.)
SPBAEROIDINA BULLOIDES d'Orbigny.__

BULIMIBELLA ELEGANTISSIMA d 'Orb . . . . . . _BOLIVINITA QUADRILATERA (S.)
BOLIVINA ROBUSTA Brady

B.

SPISSA Cushman

B.

SUBSPINESCENS Cushman

RECTOBOLIVDiA BIPRONS {Brady)
ISLANDIELLA ISLANDICA (Njlrvang)

I.

NORCROSS! (Cushman)I.

IABSI (Aaano & Nakamura)

ORTHOMORPRlNA cf. ADVENA ( 0. & L. )STILOSTOMELLA KIITIENZIENSIS (I. )BULIMINA ACULSATA d'Orbigny

B.

MARGINATA d'Orbigny

B.

ROSTRATA Brady

Fig. 4a-c.

--

~

;

0

H

0

al

al
I

I

:0:

M

H

0

I

~

M

H

0

0

-- -

...._

- --

~-- 1 - - - - ------...._---- - ----.... __...
-- -....
.._
- -

1.-

1.-

--

-

-=

-

(a)

-

--

H

H

C>

----

-P...._VAGINULlNA BOSO Asano
PLEC'l'OPRONDICULARU GOIURAI Kuw.

..

H

...._

-

-

AMPHlCORTlNA SAGAHIENSIS (Aaano)

JAPONIOA (Aaano)

0

-

--

TOST.t. Schwager

p,

M
::>
al

Ol

·---

MARTINOT'l'IELLA c!. COMMUNIS (0.)

P.

C>
0

I

-

--

r--------'l'EXTURA.l!U c!. .t.BBREVUTA d' Orb.

SlGMOILINOPSIS SC!!WI'lBERG ERI

0

C)

0

-~

Ol

I

II

HIRATA! (Uchio)

s

C)

:0:
::>

RARE

LAGENA SPlCATA Cuah.

........

,."' "" i:i

"'I

"'I

8

SPlHOPLmTAMMlllA BlGUOHli Tal<.

N.

'""
.,...

!a
~
..."'0 ~ "'!:l,:. ~ ~...
"'00 s
"'...
§
~
~
01
"'
~ ......!
...a;£,1 ..;~ za"'::> ::> ~::> a > ... ~ ::>
...
....
~
lS ~ ....
"' ~ ~... el b... ~ ;: z... ... 5l~~llJ " ~a... "' ~ ::l ~ : ... ... ~0 ...::> ::>~ ... ~ ...z:
"'
...
"'
"'
~
s
a... "'... ~:.:..."' s ..."' ~ t:l0...~gj f;l
~
...
~
...
§
~
...
5
~
... ..."' ::>~ ~ ::>~ ...."' ....a;~ ... !";
~ "'
5l
llJ
"'
"'
"' "' "'"'~ABUNDANTSPECIESs.

W.li!M WATER ZOIIES

Generalized distributions of bcnthoni~,; Foraminifera
in the Kazus.-. group, Boso Peninsula.

...._

538.

~~

Benthonic F'O?·a.minije?·al Zonat.ion

247

---

..

COLD 'oATER ZO!r.I!SZONm\IJ.lill ii'.I.TER ZOIIES

...

..;

~
a
...... 2 s ~! b
bl ,j
~

~

s ~
<!>

0

,.... ......
ai!i' ....0 ~... ~ii: .... ~
'-'
9 &l
I

~

~

~

:::>

gj :.:"'~ ~ "' "'"':::> ~ ai
SPliXJIES
~
ui
~
~ .;
~'~ ~ "~ ~ ~> ~ ~ ...."' ~.,; "' s .. ~ :::> ... ...""
~
"'
"'
"'
"'
"' "'
"
BULIMlli.l. STJilAT.I. d' Orbigny
~

ill

-~

:::>

~

Cll

I

0

B.

SlmORN.I.TA Brady

B.

TENUATA (Cushman)-- -GLOBOBULIMINA sp.

SHIIIOENSIS Aeano---- ---- -SIPilOGE!iERlliA RAFIIANA ( P. & J. )'J'RlJ.1ARiliA BRADY! (Cusllloan)
T.

IKEBEI (Bus. & Mar.)BUCCELLA FRIGIDA(Cusbman)
B.

NIP.PONICA (Bus. & Mar. )SPISTOMINELLA NARAENSIS Kuwano

E.

P1JLC!IELLA Bus. & Mar.

E.

TAl'.J.IIA (Kuwano)

GAVELINOPSIS PRAEGERI (B.

--- ........-& E.)

G. c!. TBANSWCENS (Pb.. & Par.)ROSALINA BRADY! (Cushman)R.

WILLIAMSON I I (Parr)

VALVULIRKRIJ. SADCNICA AsanoCANCRIS .t.URICULIJilS (F. & M.)
PSEUDOEPONIDEB JAPONlCUS Ucbio
P.

NAK.I.ZATOKNSIS Uebio

AMMONIA JAPONICA (Hada)
A.

KETIENZIENSIS (Isb.izaki)

AMMONlJ. TAK.I.NABENSIS (lsbizaki)
PSEUDCROTALlJ. GUIW!llll (Forn.)
PARAROTJ.Ll.l. NIP.PONICA (Aaano)p, 7

GLOBOSA (Millett)

ELP!IIDIUM ADVENUM (Cusllloan)

E.

CRISPIJM (Linn•)

E.

P.LRVUWM, n. sp.

& vara.

CRIBROELPHIDIUM B.LRTLE'r'l'l (C.)

c.

CLAVATUM (Cushman)c.

PLliiUM (Bus. & Mar.)PROTKLPBIDIIJM K.I.SAMORIENSE ,n. sp.
KILOBEDRA ROTUlfllA (Bus. & Mar.)EPOHIDEB RKPANDUS (F. & M.)

....

---

- ....

......_---·--- - · - ·-.... -- -.... ....
-. - -------------

..__

-

---

------ - -

--

--

-

(b)

<!>

..__

-- - - - - --- -- ·--- - ----I-- - ---... - .-- - -AMPBISTEGINA sp ·

H

0

--

UVIGERlli.l. AKITAKNSIS Asano

u.

:::>

0

0

I

0

Naoa.ki AOKI

248

~~

.;.. ~ ...
.~ "'
a
~
fiJ s
.(

SPECIES~HYALIBRA B~HlCA(Sellrllter)

.;

~-~

0
:z;

lL_

~

RKFU.LGEIIS (Montfort)......

-KAZUSAENSIS ~sano & Nakamurac. liOJIIIAII~ Kuwanoc. PACIFICA Cusbaanc. PARATORrUOSA Ku~ano,...----------------·-c. SAGAMIENSIS .lsano & Nakamurac. SUBCARINATA Uebioc.

-

SUBGLOBOSA Brady"C!SSlDULlN~" BREVIS, n. ep.

''Q.••

ku,anoi Matoha---

EHREIIBERGlli~- - ----

BOS03NSIS Tal<.

......

---~·

i A.STRONOIIION \IJ'.BILICATULUII Uebio·-llONIONELLA STELLA Cusbaan & Moyer
PBEUDONONION JAPONICUM Aaano:PLORILUS LABRADORICUS (Dowson)
I!.

MAIIPUKUJIENSIS (Otuka)
1-KELO!flS PYGMUUS Aoki, n. sp.

1--

PULLEHU AP&aTURA CushmanP.

BULLOIDES (d' orbigny)

GYROIDINA KAZUSAENSIS Higuchi
G,

NlPPONICA Isbizaki

G. ef.
G.

ORBICU~ISd'orbign;y

GI!MIU Bandy...._......

'----- - --- I..--BANZAWAl~HIPPONICA Asano

--

--

I

-

-- - - - -- -!----+-=~-=-~~-~!IOI!ALINA

GLA!IRATA Cusbaan

MELONIS cf. PADAIIUM (Perconig)II.

POKPILIOIDES (Fiebtel & Moll)

HOEGLUHDlliA KLIDANS d' orbigny

r- - -

(c)

-

'

I..-

-

-

...._

-

-

--

......
-- 1--!----ORIDORSALIB UMBONATUS (Reuss)--~~-----

~ --

I

- -

-

-

'

MIIIRAEJISIS (Higuchi)

.. ..

- -

...... -C~SIDULIIIA DEPRI!SSA ~. & N.

I

01

I

I..-

-..;;,.

PLEUROSTOMELLA ~B!iliAIIS Behv ·

~

-

-

C. PSEUDOUNGFJUANUS (Cuslllaan)

c.
c.

[)

-

0

:::>

I

H

-

...

..i

ci
0
"'"' "' "'... ~oi oi ..iH "'"'<XI ~ fiJ ~ ~ci0 ~ ~ ..i~ .;0~ ..i:::> ~ ~
"'
"' "'
~

\!!I

~ ~ !; :il

CIBICIDBS ef. AKHK!U.l!IUS ( d' orb

c. ~NOI Matsunagac. PACIFICUS (Cuabaan)

~

,;

0

"' ... ..i ~0sli! ~ ..i '"',;. ....,; ~~~~......

PLU111Llll~ WUl!:LLERSTO!U'l (Bebv. )c.

W.lRH W!TI!R ZOIIESCOLD ii~'I'I!R ZOIIES

-

-

588.

Benthonic f 'oraminiferal Zona.tion

part of the group ranging from the Katsuura to the Ohara formations werepreviously reported under the name of" Lower Kazusa ~hxed Faunule." Theassemblages were interpreted as accurnu·
lated in a relatively shallow water environment under unstable or high energy
water conditions. because of the presenceof some shallow water species and thelow frequencies of the benthonic foraminiferal tests as well as of the planktonic
ones (HIGUCHI. 19&1). In other words,
this interpretation means that the lower
part of the Kazusa group represents theearly stage of the marine transgression
over the erosional surface of the Miocene
rocks. It is, therefore, necessary to determine the depth of the basal faunas of
the Kazusa group for the geologic evaluation of this " unconformity " and thepaleogeography of the group.
From the present foraminiferal study,
it is revealed that the Gyroidina-Melonis
fauna in the basal part of the Kazusa
group comprises commonly deep water
species of the bathyal depth zone. The
other constituents are not diagnostic tothe slope fauna because of their wide
depth ranges from the central shelf tothe deep, but they are characteristicallyor frequently found in the slope faunas.
The shallow water species are very low
in frequency and almost absent in the
mudstone samples.
The main constituents of the GyroidinaMelonis fauna are considered to be important and characteristic elements ofthe bathyal faunas and the majority are
representatives commonly of the middle
to \ower bathyal biofacies rather thanotherwise. It may be reasonable that
the Gyroidina- Melonis fauna of the probable bathyal zone has low frequenciesof the foraminifera. The sedimentarybasin would have been of a somewhat
deep stagnant environment. Besides, the249

mode of occurrence, characters of theassemblages and the lithofacies are consistent with this depth interpretation.
Foraminiferal analysis of the GyroidinaMelonis zones in Boso reveals that theassemblage has the closest affinity to theunderlying Miocene Kiyosumi fauna(AOKI, 1964c). This evidence indicatesa similarity of environmental conditionsof the both.
In the enstern sections studied. thefollowing vertical faunal sequence issuccessively found in ascending order:
Gyroidina-Me/onis zones!Julimina-Boli11ina zones
UL•igerina zone
Cassidulina zones
Shallow water zones

From the faunal characters of thesezones it may be concluded that thissequence indicates regressive bathymetric changes of this sedimentary basinfrom the lower bathyal to the middle or
upper shelf in depth. Therefore. it canbe said that the Kazusa group represents a series of sediments accumulated
during a long-range and gradual marine" regression:·
The foraminiferal assemblages fromthe Kurotaki formation, basal horizon of
the group in the central and westernareas, may be inferred as a mixed slope
fauna. although they consist mostly of
shelf water species. This fauna grades
laterally into the slope Bulimina faunaof the eastern sections.
The foraminiferal assemblages of thewestern sections do not show such avertical faunal trend because of thecomplicated distribution pattern of thestrata.
As the Pliocene and Pleistocene stratigraphy of the Boso Peninsula is fairly
well and rather sufficiently elucidated.
the various benthonic foraminiferal as.

Naoaki AOI<l

250~·lLI_l __I"§.,_!_lJC-6
~

~ ,

~

-· -- -- -----------

c::i____________________ ...t
<11

....l

semblages in the geologic profile indicate
the complexity of the time-space relationship in stratigraphic distribution. Fig.
3 indicates some lateral faunal variationand stratigraphic relationships among theassemblages. In general, the depth variation occurs from the west to the east
and also from the lower to the upper inthe section. so that some zones are timetransgressive in stratigraphic distributions.
The lateral faunal variation of a certain time-stratigraphic horizon can beobserved in the east-west direction by
examining samples collected from thecontemporaneous strata which are traced
by pyroclastic layers. In Fig. 5 thelateral frequency variations of a few
dominant and diagnostic species for zonation are simply shown at seven selectedhorizons indicated by marker beds. This
figure shows some general fauna I trends.
To mention an instance, the shelf assemblages which commonly comprise
Cibicides and Pseudononion are widelydistributed in the western part of thepeninsula. These two species are mostcommon in the western sections, and at
every horizon their frequencies decreasedefinitely to\vard the east. Some of theshallow water species are similarly distributed.
On the other hand. Uvigerina akitaensis. Bolit,iua rolmsla. B. spissa. Bulimina aculeata and B. striata are predominant in the mudstone of the easternsections of I3oso. Gyroidina cf. orbicularis and two species of Melonis are
frequent in the lowermost Kazusa groupin the eastern coastal area.
Cassidulina su!Jcari11ala and C. subglobosa have intermediate distribution patterns between those of the above-mentioned two groups of species. In thehorizons where U1•igerina akitae11sis,
Bolir:ina and Bulimi110 species have

538.

!Jenthonic Foniminiferal Zonation

higher frequencies, these cassidulinids
are more common in the western sec·
tions than in the eastern ones, but inthe zones dominated by Cibicides andPseudononion the frequencies of the cassidulinids increase in the opposite direction.
In summary, the Bolit1ina and Bulimina
faunas are widespread in the easternsections of the Kazusa group. According to the progressive increase and decrease of relative frequencies of theconstituent species, they are replaced.
to the west, by the Cassidu/ina assemblages and finally by the CibicidesPseudononion assemblage at the western
margin of the peninsula. This lateralfaunal variation is associated with theconvergence of the thickness of beds
and lithofacies changes (Fig. 2). This
trend is recognized in different horizons,
because the faunal assemblages might
have been influenced mainly by the depthof the past environment as in the vertical faunal sequence. The trend is inharmony with the sequence of the verti·
cal faunal variation in the Kazusa sections.
Of the cold water zones in Boso, thelateral biofacies changes due to the depth
appears to be less conspicuous and insignificant compared with those of thewarm water zones. Perhaps it suggests
vertically more uniform oceanographicalconditions of cold waters. The correla·lion of the cold water zones by the benthonic foraminifera is, therefore, easierthan that of the warm water ones.
Temperature Variations
As mentioned above, the vertical andlateral sequence of the foraminiferal assemblages is thus controlled by the depthof the Kazusa group, which reflects atectonic history and paleo-geographic

2!11changes of the basin. This variation ismodified by the temperature variation,that is. by the paleo-climatic history of
the Kazusa group.
The very distinctive faunal differentiation between the Kuroshio Current andthe Oyashio Current provinces is wellknown off the Pacific coast of the Japanese Islands, not only in the foraminiferal faunas but also in many other kindsof living organisms. As Boso is situatednear the boundary of these two waterprovinces, the both warm and cold water
currents easily invaded this basin, according to the climatic fluctuations during
the late Pliocene and early Quaternary.
These . currents alternatively brought
their respective and very different faunas
into the sedimentary basin. As in the
Recent faunas off japan (ISHIWAOA, 196·1)
the faunal differentiation due to the oscillation of water currents can be recognized even within the deep water zonesof the eastern Boso, as well as in the
shelf water faunas. from the charactersof the faunal composition and the constituent species.
Apart from minor and short-ranged
fluctuations, therefore. the gross andgeneralized changes by the relative watertemperature are self-evident in the Plio·cene and Pleistocene sections of thisregion. if the foraminiferal compositions
are examined and compared directly withthe assemblages above and below. The
fluctuations of the water temperature areclearly shown by the subdivision of the
Kazusa group presented in this paper,
although it is unable to evaluate theabsolute degree of the water temperature
variations.
The planktonic foraminiferal assemblages from the Kazusa group werepreviously reported with regard to thevertical and lateral variations of thefaunal compositions (AOKI. 1961b). Some

Naoaki J\OKI

252

of the cold and warm water horizons or
the paleo-climatological zoning of the
Boso sections were indicated. It is re·markable that these roughly defined
subdivisions of the planktonic forami·
niferal assemblages agree with the ben·thonic foraminiferal zonation of thegroup. In the paleo-climatological inter·
pretation from the complicated andsharply fluctuated frequency curves madeby the planktonic foraminiferal assemblages. the changes of the \Vater temperature causing the changes in thebenthonic assemblages are believed to
be worthy of the independent treatment.
Compared with the living foraminiferal
faunas distributed around the peninsula,
the influence of the cold water is more
prominent and the frequency of the cold
water species is generall)' higher in the
Boso Pliocene and Pleistocene microfaunas. The earliest of the cold waterzones discriminated is situated in thelower part of the Otadai formation. ReTable 3.

markable and easily distinguishable cold
water zones are as follows:(I) Bolivina spissa Zone (Upper part of the
Otadai formation)(2) U1Jigeri11a akitaensis Zone (Upper part of
the Umegase formation)(3) Two cold water horizons within the Cassidulilla subcari11ata Zone (Kokumoto formation)('t) Crib roe/ phidium cl ar•atum Zone (Chon anformation)(5) No11io11cl/a stella Zone (Upper part of the
Kasamori formation)

Table 3 shows the temperature-depth
distribution of the benthonic foraminiferal zones of the Kazusa group. The
fossil zones are listed in the order ofincreasing depth of water (from upper
to lower). Foraminiferal zones arrangedin the left column are of the warm waterr.ones, and those in the right column
indicate the corresponding zones of thecold water phase in the Kazusa group.

Temperature-depth distribution of the benthonic foraminiferal zonesof the Kazusa group, Boso Peninsula.

----------------- _____TemperatureWarm water zonsDepth
_ _ _ _ _ _ _ ___c:cl - - - - - - · - - central
Cibicides-Pseudo11ollio11 Zone
shelf

1

outer

Cassidulina subglohosa Zone
Warm water horizons of the
Cassiduli1za subcarinata Zone

Cold water zones

Nonio11ella stella Zone
Cribroeiphidium clovatum Zone
Cold water horizons of the
Cassidulina subca'rinata Zone

- - - - - - - - - - - 1 - - - - - - - - - --~upper

slope

lower

Bulimina aculeata Zone

Uvige1·ina akitaensis Zone

Bulimina-Bolivi11a Zone
Bulimi11a striata Zone

Bolivina spissa Zone
Uvige-ri11a akitael!sisBoli!Jina spissa zonulcs
in the Bulimi11a-Bolivina
Zone (East Coast)

Gy.,-oidina-Melonis Zone

588.

Benthonic Foram:i-niferal Zonation

Displaced Elements
Most of the samples treated for zoning were collected. as far as possible.
from mudstones and muddy facies within
the alternating rocks. The foraminifera
are well preserved in these rocks but
are generally absent in sandstone beds.
Only foraminiferal fossils occur in muchless abundance in sandstones containing
molluscan shells.
The material in coarse-grained sediments has not been systematically collected for this study. Jnsutlicient andsporadical data show that, in the alternating beds of mudstone and sandstone,
the foraminiferal composition of sandstone is quite different from that ofmudstone as is known well from thestudies of the distribution of the Recent
foraminifera. The sandstone interbeds
in the Bulimina-Bolivina zones containelements displaced from the shallower
places. They include: Cibicides refulgens,

Pseudononion japonicum, Elphidium advenum and vars., E. crispum, Nosalina
williamsonii, Hanzawaia nipponica, Cassidulina subglvbosa. many species of genera
Ammonia, Cassidulina, El phidi 11111, Qui nque/oculina and Discorbidae. etc.
The displaced shelf species may bemixed with the deep indigenous mudstone
fauna in various percentages. In somehorizons the faunas are composed essentially of the reworked shallow water
species or the elements of the CibicidcsPseudononion assemblage. They seem
superficially to be the indigenous "shelfassemblages." The quantity and composition of displaced elements also play
an important role in the foraminiferal
assemblages of the Boso Peninsula, andin the foraminiferal zoning such elements
should be taken into account as one of
the indicators of the environments.
The amount of displaced specimens. in

25:3

the deeper and the outer shelf facies. is
generally related to the lithofacies of thesediments. There is a marked tendency
that coarser-grained or more sandy sediments show a higher frequency of displaced specimens.
The two sandstone bodies distributed
in western Boso, the Higashi-higasa andthe lchijyu l<U formations. and theirlateral lithofacies changes show that alarge quantity of sandy material was
continuously supplied from some westernregion and transported to the east. The
sedimentological influence of this environment is recognized in the fossil assemblages in the eastern extensions of thesesandstone formations. Many shelf species. such as Cibicides, Pseudononion.
Cassidulina. etc., were commonly transported into the Bulimina-Bolivina faunas.
Concerning the transportation of theforaminiferal tests the frequency distribution of Elphidium parvulum. new species. and its varieties is another interesting matter. The species is small-sizedand occurs in mudstone facies. The highfrequency horizons of this species repeatedly appear in the interval ranging fromthe Otadai to the Kasamori formations.
Each horizon is comparatively narrowly
restricted in vertical range and can belaterally traced from section to section.
Though the occurrence of this species in
the Recent ocean has been unknown, it
is inferred that the species is probably
spread out by currents with fine-grained
detrital particles. The species may be
useful as an indicator of such environment and also for local correlation of
the strata. Some small-sized benthonicspecies seem to have similar distribution
patterns to that of E/phidium parvulum.
The currents. the distance from theshore and the submarine topography ofthe depositional sites are the other significant factors which have influence onNaoaki A.OKI

254

the distribution of foraminifera. These
environmental factors have mutual relations to the depth facies variation.
Foraminiferal Zones
The foraminiferal assemblages andzones distinguished in the Kazusa groupare briefly remarked in the following.

1. Gyroidina-Melo11is zones
The mudstones of the Katsuura, Nami·
hana and Ohara formations are poor inforaminiferal fossils. The foraminiferal
data of these three formations are stillinsufficient for biostratigraphic and paleo·
ecologic considerations of the basal partof the Kazusa group. The small popu·
lation in these horizons is due probably
to the originally meagre faunas in addi·
tion to the subaerial weathering.
Of about 200 samples examined, 55
yield foraminiferal fossils in a fairabundance represented by only a few toless than 20 benthonic species (usually
3-13 species) in each sample. Consequent·ly, the number of common constituent
species is limited, in spite of slight ver·tical variations of species association. In
most horizons the foraminiferal assemblages contain two or three species
belonging to Gyroidi11.a and Melr111is andare invariably characterized by these
species.
The interval characterized by the
Gyroidina-Melonis fauna in the lower
part of the Kazusa group can be subdivided into five units, the Gyroidi na cf.
orbicularis Zone and the lower four unnamed zonules. on the basis of the ben·thonic foraminiferal assemblages. ln theeastern coastal area a number of parallel
faults and unsuitable field conditions
make it difficult to obtain detailed strati·
graphic information. The distributionsof these four zonules are not so clear
and the subdivision is tentative at present. These zonules seem to be laterally
continuous from the lsumi-Mobara section to the eastern coast of the peninsula,and are truncated by the sea.
Zonule 1 (Lower part of the Katsuura
formation)
The foraminiferous samples were collected from the mud-rich alternations of
mudstone and sandstone at Katsuura,
eastern coast of the peninsula. Collec·
tion of the samples was limited to aparticular area and horizons. The sam·pies yield Gyroidina kazusaensis andJloeglund£na elegans, in association with
Planulina wuellerstorfii, Melonis cf. pada·num, St ilostomella spp. and a few others.
HIGUCHI (1965) reported this assemblage
from the subsurface samples of the Ku·
jyukuri-hama area at depths deeper than
1000 m. The basal part of the Katsuura
formation consists of coarse-grained sedi·ments rich in pyroclastic matter. In theoutcrop samples the foraminifera are
entirely absent.
Zonule 2 (Middle part of the Katsuura
formation)
The assemblage found in samples fromthe environs of Katsuura-machi is domi·
nated by Melonis cf. padanum and Gyroi·
dina gemma. The following species are
frequently found: Melonis pompilioides,

Oridorsalis umbonatus, Bolivinita quadri·latera. Cassidulina cf. subg/obosa andHoeglundina elegans.
Zonule 3 (Upper part of the Katsuura
formation to the lower half of the
Namihana formation)
The material from the upper part of
the Katsuura formation contains Orlho·
morphina cf. advena, Bulimina striata,

Plectofrondicularia totomiensis. Stilosto·
mella spp. and Gyroidina gemma in538.

Benthon-ic Foraminiferal ~onation

abundance. This zone is characterized
by the co-existence of two species.
Ortlwmorphina cf. advena and Plectofrondicularia lotomiensi.~.
A few samples collected from the lower
half of the Namihana formation are
scarce in foraminiferal fossils and they
contain almost the same assemblage asthat of the upper Katsuura formation.
Zonule 4 (Upper and main parts of the
Namihana formation)
The constituent species are common
with those of zonule 3. Although thedominant species vary with samples.
.Nodosaria longiscata is most abundantand ,\lelom's cf. padanum. Plectofrondi·
cularia totvmiensis. 1-locglundina elegaw;
and Melonis Pompilioides are subdominant.

Gyroidina cf. orbicularis Zone (Uppermost part of the Namihana formation to the lower or basal part of
the Kiwada formation)
It roughly corresponds to the Ohara
formation in which the foraminifera are
fairly common. It is consistently characterized by the abundance of either
Gyroidina cf. orbicularis or G. gemma.
The associated species are: Jloeglundirzaelega11s, Bulimina aculeata. Nodosaria
longi.~cata. N. los/a, Alclmzis cf. padanum,i\1. pompilioides. Stilostomella ketienziensis. !Jolit•inita quadri/atera, Bulimina
striata and Plectojrondicularia lolomienszs. The lateral faunal variation is
not considerable.
Besides the basal part of the Kazusa
group, the fossil foraminiferal assemblages in which Melonis and Gyroidina
are frequent, arc found in the central
and eastern parts of the peninsula in
the restricted horizons given below.
(1) Upper part of the Kokumoto formation(2) Uppermost horizon of the Umegase for-255

mation(3) Three or 4 horizons within the BuliminaBolivina zones of the Otadai and Kiwada
formal ions.

In these horizons Gyroidina and Melonis
are associated with the elements of the;1pper slope or outer shelf faunas inabundance, so the assemblages are different from the Gyroidina-Melonis faunaof the lowermost part of the group.

2.

l'vlixed assemblage zones

Cassidulina-Cibicides Zone
The mixed assemblages composedlargely of shelf water species with aminor amount of slope water ones arefound in pebble-bearing coarse-grainedsandstone to silly sandstone of the Kuro·taki formation in western and central
Boso. The fauna is extremely dominat·
eel by the species of Cassidulina andCibicides, such as Cassidulina subglobosa,C. fwcifica, Cibicides Pseudozmgerianus.
The characteristic common species ofthe zone are: Eh1·e11hergina bosoensis,
Elphidium crispum, Cassidulina kazusaensis, C. paratorluosa, etc.
Some of the diagnostic species are notdiscovered or are probably scarce in the
Recent sediments around Japan. and any
similar assemblage with the same associating species has not been reported.
The Kurotaki fauna seems to be superficially analogous to the Recent Cassidulina-Cibicides assemblage frequently
found on sandy submarine banks (\SHI·W ADA. 1964).
The fauna is generally associated withdeep water species although small inquantity; Bulimina aculeala. B. striata,
Stilostomella ketienziensis. Melonis pompilioides, AI. cf. padanum, Gyroidina cf.
orbicularis. etc., are not negligible ele·ments nor unusual admixture especiallyNa.oaki AOI<I

25(jin the middle and upper parts of theKurotaki formation. Moreover, the fauna
grades laterally into the Bulimina-Boli·vina or Gyroidiua-Melonis faunas in theeastern sections.
From these evidences. the large amounts of Cassidu/ina and Cibicides andother shallow water species in this fauna
can be explained that they were moreor less transported from the nearby
shelf. This prominent faunal displace·ment may be indicative of steeper sub·marine escarpments and a continuous
rapid supply of coarser material of
sediments, and at the same time some
tectonic movement of the basin.
Similar assemblages to the Kurotaki
fauna are found in the fossiliferous
sandstone beds intercalated in the Ki·
wada and Otadai formations.

Cassidulina-Bulimina Zone
The Kurotaki mixed assemblage
changes into the typical Bulimina-Boli·vina faunas of the superjacent middle
Kazusa group, with a gradual increasein frequencies of some species of Buli·mina and Bolivina and decrease of the
Cassidulina and shelf water species. Thisfaunal variation has an intimate relation
with the lithofacies which changes
from the coarse- to the fine-grained sedi·ments. The intermediate assemblage between these two zones is separated here
as the Cassidulina-Bulimina zone, whichcontains buliminid and bolivinid species
in intermediate abundance. The strati·
graphic distribution of this assemblage
may be time-transgressive in relation
with the lateral depth variation of thelower half of the Kazusa group.
3.

Bulimina-Bolivina zones

The Pliocene slope faunas characterized by buliminid and bolivinid species

range in distribution from the base of
the Kiwada formation to the middle partof the Umegase formation in the central
and eastern parts of the peninsula.
The diagnostic species of the fauna
are limited in number. The common anduseful species are four; Bulimina aculeata, Bul. striata, Bolivina spissa and Bol.
robusta. The fauna is subdivided into
several assemblages by the combination
and abundance of these index species.
Six biostratigraphic zones are definedaccording to these easily separable assemblages as mentioned below.
In addition. some local fauna occur
within this long-ranged interval, for instance. the Stiloslomella ketienzieusis assemblage (lower part of the Kiwada formation), the Uvigerina akitaensis-Holiuina
spissa assemblage (Otadai formation) and
the Gyroidiaa-.A/elonis assemblages (insome horizons of the Kiwada formation)
are found. They spread locally in shortstratigraphic ranges, and are included
tentatively in the Bulimina-Bolivina
fauna.

Bulimina striata Zone
In the lower and middle parts of theI<iwada formation of the eastern sections
between the lsumi River and the east
coast, Bulimina striata is extremely
abundant and its frequency amounts to
one-third of the fauna. Bulimina aculeata, Bolivina robus/a and B. spissa andother slope species which are common
in the surrounding deep water zones
are less frequent or aimost absent.
Bulimina-Bolivina Zone
This zone corresponds mostly to the
Otadai formation and the lower half of
the Umegase formation in the easternsections of the Boso Peninsula. The following three slope species are the common constituents: Bulimina aculeata, B.
striata and Bolivina robusta. This zone

.538.

Benthonic Foraminije1·al Zonation

is subdivided vertically into two units
by the intercalalion of the Bolit·ina spissa
Zone. The upper zone is rich in Etphidium parvulum, whereas the lower one
is more frequent in Cassidulirra subcarinata and C. subglobosa.

Bolivina spissa Zone
This is the upper part of the Otadai
formation and is particularly rich in
Bolivina spissa, which is commonly associated with Bulimilla acu/eata. Uvigerina al?itaensis, Jslantliel/a is/andica and!. norcrossi. The replacement of Bolivina
robusta with B. spissa in this zone iscaused definitely by the influence of thesubarctic Oyashio Extension. This zone
corresponds also to the low temperature
horizon interpreted from the planktonic
foraminifera assemblages. The frequencies of Globigerinila uvula and Glubigerina
quinqueloba are higher in this zone (AOKI.
1963. 1964). The faunal characteristics ofthis assemb!age are recognized extensively between the Obitsu River and theeastern coast of the peninsula.
Similar assemblages are found in the
Bulimina-Bolivina zones of the easternsections, east of the Isumi River. They
appear locally in a few horizons withcold planktonic foraminiferal assemblage
and Uvigerina akitaensis.
Stilvstomella ketienziensis Zone
This zone was originally proposed as.. Ellipsonodosaria lepidula Zonule " (lsHIWADA. 1958a). However. Stilostomellaketienziensis is more abundant and characteristic. This assemblage is found onlyin the upper horizon of the Kiwada formation in the Yoro River section.
Hnlimina aculeata Zone
This zone is represented by the middle part of the Umegase formation andis recognized between the Koito and Yoro
Rivers. In this zone 13ulimina striata

257

and Bolivina robusta disappear but only
Bulimina awleata remains characteristically. The fauna is composed of Bulimina aculeata and numerous shelf elements such as those found in the Cassidulina zones. Cassidulina subcarinata is
su bdominant.
4.

Uvigerina akitaensis Zone

The upper part of the Umegase formation corresponds to the importantUl'igerina akitaensis Zone. This zone iswell defined and the faunal featurescontinue extensively in parallel with thetime-stratigraphic markers. The faunaconsists of a relatively small number of
species. Some species found in the Bulimina-Bolivina and the Cassidulina zones
are low in frequency or absent in thiszone. The most characteristic species is
Uvigerina akitaensis. The other diagnostic species are !slandie/la islandica,!. norcrossi. !. yabei. Trifarina ikebei,
Cribroelphidium planum and Eilohedra
rotunda. Their stratigraphic distributions
are not always restricted but characteristic to this zone. They are usually morecommon in the upper part of this zone.
Distinct warm water species are absent.
Cassidulina subglobvsa, lslamliella islandica. !. yabei, Quinqueloculina sawanensis. Pseudononiun japonicum and someother species tend to be common in thewestern sections .
In association of the diagnostic foraminifera, this zone is similar to the zonuleof the same name or the UvigerinaAilgulogerina zonule widely distributedin the Japan Sea and the "subarctic''
regions of Japan. (ISlllWADA, 1964). The
Boso fauna contains relatively many
species associated with /3ulimina aculeata. species of Cassidulina and Cibicides.
etc. That is, the Ul'iger-ina akitaensis
Zone of Boso has an intermediate faunal

Ncwaki AOI<I

258

composition between the northern " Uvigerina-Angulogerina assemblages" andthe southern temperate water faunas ofjapan.
5. Cassiduliua zones
The fauna characterized by the spe·
cies of Cassidulina is found in the Ko·
kumoto and Kakinokidai formations of
the eastern half of the peninsula. Both
benthonic and planktonic foraminifera
are abundant elsewhere in these horizons.
The fauna is composed of many speciesof the shelf. and is sometimes associatedwith rare occurrences of some deep orParticularity,
blackish water species.
Cassidulina is the largest in number ofboth species and individuals.
The interval in question can be divided
into two major units, namely the upperzone which abounds in Cassidulina subg/obosa, and the lower zone in which
Cassidulina subcarinala is constantly
common in the eastern sections.
Two cyclic vertical faunal variations
are evidenced within the Cassidulina
subcarinala Zone of the Kokumoto formation. /slandiella islandica, Rulimina
aculeata, Melonis cf. padanum, Stilostomella spp .. Gyroidina nipponica, Bulimina
striata. and Uvigerina cf. akitaensis are
re:atively frequent in t~e lower half ofeach cycle. whereas Elphidium panmlum,
Cassidulina subglobosa, C. depressa vars.
and C. subcarinala are in the upper. The
former association indicates a cooler ordeeper water facies and the latter is amore typical shelf association of thetemperate waters.
This faunal variation has some affinities with the vertical variation of theplanktonic foraminiferal assemblages andwith the alternating lithofacies changes.
It is probably due to the influence of thecold water extension and not to thefluctuation of the sea depth.
If the Kakinokidai formation is included. three cyclic variations are recognized,
the last of which is separated as the
Cassidulina subglobosa Zone. This zone
corresponds to the interval ranging fromthe upper part of the Kokumoto to the
Kakinol<idai formations.
6. Shallow water zones
The upper part of the Kazusa groupis represented by the shallow water
faunas. Owing to the clear fluctuationof the water temperature and the variation of the bottom sediments, considerable vertical and lateral variations of theforaminiferal assemblages occur in thisinterval.
Unfortunately, the horizons
barren of the foraminifera due to weathering occupy Lhe larger part of thesection. Therefore, the lateral variationsof the shallow water assemblages are
uncertain. The lack of the pyroclastic
layer passing through different lithofacies is another reason for the insufficient reliability of the stratigraphicalrelation of the fossil foraminiferal assemblages.

Cibicides-Pseudononiun Zone
The Cibicides· Pseudononion assemblage
occupies the western part of the Boso
Peninsula and is typically observed in
the Kakinokidai formation of the Obitsu
and Koito RiYer sections. which corresponds to the interval of the Cassidulina
subglobosa Zone of the eastern sections.
ISHIW ADA (1958b) subdivided this assemblage into the Cibicides and the PseudoIIOni on assemblages.
The foraminiferal assemblages fromthe I wasaka formation are similar tothat of the above Cibicides-Pseudononion
Zone but have somewhat higher frequencies of the warm water species.

538.

Benthonic Foramimferal 7-onat·ion

Cribroelphidium clauatum Zone
The samples from the Chonan formation contain Cribroe/phidium davatum,
Uvigerina akitaensis, Flori/ us labradoricus
and lslandie/la islandica in higher frequencies. It is noteworthy that the mostdominant species. Cribroelphidium clavatum, shows the typical morphology, having a characteristic biumbonate test. andthat the faunal characteristics of this zone
are somewhat similar to those of the Uvi·
geri na akitaensis Zone. As previously
pointed out, it is the most distinct, coldest
water fauna found in the Boso Peninsula.
The planktonic foraminifera have also acold water assemblage (AoKJ. 1963, 196,1).
This zone extends from the Koito Riverto the eastern margin of the peninsula.
·· Lower Kasamori " Zone
The foraminifera of the lower part of
the Kasamori formation can be observed
only in the environs of !Vlobara. The
following species are common or frequent in this zone: 1~/phidium jwrvulum
vars., Cibicides aknerianus, Amphicoryna
sagamiensis, Cassidulina subcarinaia,
Gaudryina cf. arenaria, Bulimina marginata, Epistomi11ella naraensis, /Jolit•inita
quadrilatera, Lagena spicata, Cassidu/ina
sagamiensis, Nonionella stella, Elphidium
advenum vars., "Cassidulina" brevis andPararota/ia ? g/obosa.
.. l'vlandano " Zone
The foraminifera were obtained fromsome localities between the Yoro andObitsu Rivers. This assemblage is foundin conglomeratic sandstone and is easily
distinguished from those of the zones
below and above. Elphidium cri~pum,species of Cibicides, Cassidulina and
Milioidae, and Pararotalia nipponica appear commonly in this zone.

Nonionella stella Zone
The samples of the Kasamori forma-

259

tion collected from the Yoro River section and scattered localities nearby arecomparatively meagre in the number of
species, especially in the uppermost partof the zone. It belongs to the bay fauna
influenced by brackish waters. and ischaracterized by Nonionella stella, Elphidium pan•ulum vars., Bu/smina e/egan·tissima, Pseudunonion japunicum, Buccellafrigid a, Cribroe/phidi um bartletli. No influence of the warm water current isinferred in this zone.
Description of New Species

The four new species which are citedin the text as common in some horizonsof the Kazusa group are described in thefollo\ving. The type specimens are now
preserved in the author's private collection. at the Institute of Geology and Mineralogy, Tokyo University of Education.

Elphidium parvulum AoKI, 11. sp.
Pl. 27, figs. la, b

Test very small, involute and planispiral. compressed, subcircular in side
view, periphery slightly lobulate. andsides nearly parallel in peripheral view;
chambers seven to nine in the last whorl.
increasing very gradually in size as
added; sutures very slightly depressed,
fairly curved, sutural pores indistinct,
probably several slits in a suture; central portion slightly depressed, sometimes
slightly umbilicate ; wall finely perforate;
aperture several small rounded openings
at the base of the apertural face.
tvtaximum diameter of holotype 0.20mm, minimum diameter 0.16 mm, thickness 0.08 mm.
Holotype from sample jf058, river-side
exposure of the Yoro River, 0.5 km southof the Yoro-Keikoku station, Kamo-mura,Naoaki Aoia

260

Ichihara-gun, Boso; Umegase formation,
Bulimina-l3olivina Zone.
Elphidium parvulum, new species, iseasily distinguishable from the previously known species of E/phidium by its
smaller-sized and much compressed testwith strongly curved sutures.
This new species occurs abundantly in
the Bulimina-Bolivina zones of the Kazusa group. All specimens from theOtadai to Umegase formations are strictly
conspecific with the type of Elphidium
parvulum from the lower part of the
Umegase formation.
However. forms
very closely allied to this new species
are also dominantly found in the mudstones of the upper part of the Kazusa
group which ranges from the Kukumoto
formation to the Kasamori formation.
These forms show wide morphologicalvariations in the number of chambers.
inflation of chambers and the characterof sutures. Though it is believed thatthese forms are ecologically different
from the typical species and they represent two or more related species or subspecies, it is difflcult to separate one
another because of their almost gradational morphologies and the high frequencies of these small-sized specimens. In
this paper they are treated as varietiesof the present new species, Elphidium
jJ:zrvulum. Elphidium sp. A reported
from the middle Pleistocene Izumiyatsu
formation of the Shimosa group is one ofthese varieties (SUZUKI & AOKI, 1963. Ceo/.
Soc. japan, jour., v. 68, no. 804, p. 501).

Protelphidium Jwsamorie11.~e AOKI. n. sp.
Pl. 27, figs. 2a, b

Test small, compressed, planispiral andinvolute, bilaterally symmetrical, subcircular or ovate in side view, peripherysubrounded, very slightly lobulate if atall, sides almost parallel. depressed in

the umbilical regions; chambers about
10-11 in number in the final whorl, notinflated, slowly increasing in size as
added; sutures distinct, radiate andcurved, nearly flush with the surface inthe early portion, narrowly and slightly
depressed later, especially in the proximal portion; sutural pores unknown;
small areas of the umbilical regions andaround the aperture often covered withwhitish granular pustules as shown in
the figure of the holotype ; wall smooth,usually lustrous and opaque, very finely
perforate, radiate in texture ; aperture
not observable.
rvlaximum diameter of holotype 0.27mm, minimum diameter 0.22 mm, thickness 0.1:1 mm.
Holotype from sample #101, river-side
exposure of a southern tributary of the
Yoro River. at Ushiku, Nanso-machi,lchihara-gun, Boso ; Kasamori formation,
Nonionel/a stella Zone.
This new species is probably similar
to Protelphidium anglicum MURRAY (1965,
Cush. Found. Foram. Res .. Contr., v. 16,
pt. ·1. p. 149, pl. 25, f. 1-5; pl. 26, f. 1-6)
described from the Recent sediments ofEngland, but the former has a smaller testwith a somewhat larger number of Jessinflated chambers. This new species isalso different from the juvenile specimensof Prole/phidium orbiculare (BRADY) fromthe Arctic in having a more compressed
test with depressed umbonal areas.
Prote!jJhidium kasamoriense is common
in the Kasamori formation in the Yoro
River section, but hardly found in theother horizons except for occasional
doubtful specimens.

Melonis pygmaeus AOKI. n. sp.
Pl. 27, figs. ~ia, bTest minute, planispiral and involute
but somewhat asymmetrically coiled,588.

Benthonic Fora·minife·ml Zona.tion

2tH

subcircular in side view, weakly lobulate, thickness a little more than a halfof the diameter of the test. peripherybroadly rounded; chambers five or six.
commonly six in the last whorl, slightly
inflated. increasing slowly in size as
added; sutures radial, very slightly limbate and depressed a little; narrow umbilical region distinctly depressed; aperture a narrow. arched slit at the base of
the apertural face of the final chamber ;wall calcareous. rather thin, fairly coarsely perforate.
Maximum diameter of holotype 0.15
mm. minimum diameter 0.13 mm, thickness 0.11 mm.
llolotype from sample :~076. river-side
exposure of the Yoro River, NW of the
Yoro-Keikoku station. Kamo-mura. Ichihara-gun, Boso; Umegase formation,
Uvigerina akitaensis Zone.
This species is somewhat similar to ajuvenile form of Melonis pompilioides(F'!CHTEL & ~~lou.) which is sometimes
associated with this new species in the
Kazusa group, but it differs in having
a much smaller test, finer perforation.
thinner wall and inflated chambers. This
new species is probably very similar to
Melonis guada/upae PARKER (1964.]. Pal.,v. 38, no. 4. p. 633. pl. 100. f. 13-14) but
the test is about one half the size of thelatter and is less compressed. with few·er
chambers.
Melonis pygmaeus is frequent in the
Cassidulina and the Uvigerina akitaensis
Zone of the Kazusa group in Boso.

series of chambers closely coiled in theearlier stage but slightly prolonged in
the last stage, about five pairs of chambers in the final whorl, inflated slightly;
sutures distinct and slightly depressed;
wall calcareous. rather coarsely perforate; aperture terminal. comma-shaped,
at nearly a right angle to the suture of
the last chambers.
Length of holotype 0.32 mm. width
0.2lmm.
llolotype from sample ::219, river-side
exposure of the Yoro River, ca. 600 m
north of the !tabu station, !tabu, Kamomura, lchihara-gun. Boso; Chonan formation, Crihroelphidium clavatum Zone.
This new species somewhat resembles
Cassidulina subg/obosa BRADY, but thelater portion of this new species is projected from the outline of the test andthe wall is distinctly perforated. It may
be different from Cassidulinoides parkeric.na (BRADY) which has a much elongate uncoiled portion and more depressed
sutures. and also from Cassidulinoides
bradyi NORMAN which has a compressed
test. Cassidulinoides japoniws KUWANO(nom. nud., 1962. l?es. !nsf. Natur. Resources. Misc. Rep! .. no. 58-59, pl. 16. f.
5) from the Recent sediments off Bosois \'ery similar to this new species.
"Cassiduli na " brevis is occasionallyfound from the Pliocene to the Pleistocene deposits in Japan. In Boso it iscommon in the Cri/Jroe/phidium clavatum
and the Cassiduli na zones of the Kazusa
group.

"Cassidulina " brevis AOK!. n. sp.

Acknowledgements:-The author is muchindebted to the following persons: Mr.
Kunio KAGEY AMA. Drs. Takashi lVIrTSU·
NASI!l and Kiyotsura Y AZAKI of the Geological Survey of Japan, Prof. Kozo
KAWAI of the University of Tokyo, Mr.
Naomiki KOMATSU of the Teikoku Oil
Co .. lv1r. Takaichiro 01\!0R! of the JapanPl. 27, fig. 4
Cassidulinoides bradyi (Not~ MAl'>), KtKUCIII,
196<1. pl. 7, f. 27-32.

Test medium, globular. ovate in side
view, periphery slightly lobulate, biserial

Naoaki AOKI

262

Petroleum Exploration Co., Dr. Takahiro
SATO of the Hydrographic Office of Ja·pan, and .tvlr. Yoshijiro SHINADA of the
Kwanto Natural-Gas Exploration Co., forfurnishing valuable informations on thestratigraphy of the Kazusa group: Dr.
Yasufumi ISHIWADA of the Geological
Survey of japan, and Dr. Takayasu
UcHJO of the University of Tokyo, formany helpful suggestions on the biostratigraphy and the foraminifera of the
Kazusa group: Prof. \Vataru HASHIMOTO
of the Tokyo University of Education
for his kind advices and continued encouragement.

Referencl•s
AoKI, N. (1963) : Pliocene and Pleistocene
foraminifera from along the Yoro River.
Boso Peninsula-Vertical faunal change:
Tokyo Kyoiku Daigaku. Sci. Rep., Sec. C.
v. 8, no. 78, p. 203.. 227.
- - (l91Ha): Correlation of the Pliocene andPleistocene rocks in the Boso and Miura
Peninsulas (in Japanese): japan. Assn.
Petr. Tech., jour.. v. 29. no. 3, p. 100-105.
- - (1964b) : Pliocene and Pleistocene planktonie foraminifera assemblages. Hoso Peninsula (in Japanese): Geol. S1Jc. ]apa11,
jour., v. 70, no. 822. p. 170-179.
- - (1964c): Upper Miocene foraminiferafrom the Kiyosumi formation, Boso Peninsula: Pal. Soc. ]a pan, Tra11s. Proc.,
N. S .. no. 53, p. 163-169, pl. 25.
- - (1965): Pliocene and Pleistocene uvigerinid foraminifera from the Boso and Miura
Peninsulas. Saitama U11iv .. Sci. Rep., Ser.
B. v. 5, no. 1, p. ·19-63, pl. 7.
1\.sANo, K. (1938a) : On the Japanese speciesof Elphidium and its allied genera (injapanese): Geol. Soc. japa11. ]our .. v. ·15,
no. 538, p. 58!-591. pl. 14.
- - (1938!>): On the Japanese species of
Nonion and its allied genera (in Japanese): Ibid., v. 45, no. 538. p. 592-599,
pl. 15.
- - (1938c): On the Japanese species of

Bolivina and its allied genus (in Japanese): ibid., v. 45, no. 538. p. 600-607.
pl. 16.
- - (1938b): On the Japanese species ofUvigerina and its allied genera (in Japanese): Ibid., v. 45, no. 538. p. 609-616.
pl. 17.
- - (1938e): Japanese fossil Nodosariidae
with notes on the Frondiculariidae: Tohoku Univ., Sci. Rep., Ser. 2, v. 19, no. 2.
p. 179-220. pl. 24-31.
- - (1938£) : Fossil foraminifera from theBoso and Miura Peninsulas (in Japanese) :Geol. Soc. japan. jour .. v. 45, no. 437, p.
523-525.
- - (1938g): Fossil foraminifera from Boso
Peninsula (in japanese): Tohoku Univ.,
l11st. Geol. l'al .. Contr .. no. 31. p. 57-96,
pl. 6-9.
- - (1950-1952): Illustrated catalogue ofJapanese Tertiary smaller foraminifera,
Parts 1-15 with supplement no. 1, 183p.,
1040 tf.. Tokyo.
- - (1955): Some problems on the Tertiary
micro-bio-stratigraphy of japan (in Japanese): Foraminifera, no. 4, p. 3-14.
- - (1961) : The Neogene faunas of Japan(Abstract) (in Japanese): Geol. Soc.
}ajwn, jour .. v. 67, no. 790. p. 382-384.
- - (1962) : Faunal change of planktonic
f oraminifl'ra through the Neogene ofJapan: Kon. Ned. Ak. Wetensch .. Proc.,
Ser. B. v. 65, no. 1. p. 1-6.
- - & NAKAMURA, M. (!937a): On the dis·tribulion of the japanese species of Cassidulillll (in Japanese): Geol. Soc. japan.
jour .. v. 44, no. 523, p. 329-33~.
& - - (1937b): On the Japanese species of Cassidulina: japan. jour. Geo/.
Geogr., v. H no. 3-4, p. H3-153, pl. 13-14.
--. et al. (Boso Research Group) (1957) :Chronological divisions of the Cenozoic
stratal groups of the Boso Peninsula (inJapanese): Foraminifera, no. 7, p. 32-37.
- - . et a/. (Boso and Miura Research Group)(1958) : Cenozoic correlation of the Miura and Boso Peninsulas by means ofplanktonic foraminifera (in Japanese) :Foraminifera, no. 9, p. 34-39.
Geological Society of Japan (eel.) (195•1-1962):

538.

Benthonic For(oninifeml Zonation

Lexicon of stratigraphic names of Japan.
Cenozoic Erathem, Pts. I-IV (A-Z) (inJapanese). 1867 p.
Geological Survey of Japan (1960) : Geological map of Mobara gas-field. Geol. Surv.
Japan.
HATAJ, K. (1958): Boso Peninsula, Chiba
Prefecture. jub. Pub/. Comm. Prof. Fnjimoto. p. 183-201.
HIGUCHI, Y. (1964) : Microbiostratigraphicalstudies of the gas field in Chiba Prefecture. Japan (in Japanese): Tohoku Univ ..
Inst. Ceo!. l'al., Contr., no. 61, p. 1-·18.
- - (1965): On the some new species offossil foraminifera from the boring coresin the gas field in Chiba Prefecture. Japan: Pal. Soc. }aflan, Trans. Proc., N. S.,
no. 60, p. 178-181, pl. 21.
- - & KIKUCHI, Y. (196·1): Microbiostratigraphic study of the Kazusa group, special reference to its natural gas resources(in Japanese): japan. Assn. Petr. Terh.,jour .. v. 29, no. 1. p. 22-28.
- - & SAITO, II. (1965): Subsurface microbiofacies of the Kazusa group in thewestern part of Chiba gas field, Japan(in Japanese): japan. Assn. I'elr. Tech.,jour., v. 30. no. 5. p. 26!-268.
HIRAYAIIIA, j. (1954): Problems on the alternating rocks (in Japanese): Sedimenlo/ogical Research. no. 7, p. 2-5.
Huznv ARA, A. & Oc;osE. S. (1952) : The
Cenozoic strata developed in the environs
of Sanuki-mati. Kirnitu-gun, Tiha Prefecture. South Kanto. Japan (in Japanese):
Ceo/. Soc. japan, jour., v. 58, no. 683, p.
387-399.
lSHIW ADA, Y. (1958a) : One cross-section
along the coast of Kuh•ukuri (in japanese): Foraminifera. no. 8. p. ·13-48.
- - (1958b): p, 214-228, in KANEHARA, K.,
MoTOJIMA, K & lSIIIWADA, Y .. 1958.
·• Natural gas-Exploration and Resources" (in Japanese), Asakura Book Co ..
361 p.
- - (1959): Report on the exploratory clrilling, Yokoshiba R-1, Chiba Prefecture (inJapanese): Ceo/. SunJ. japan, jour., v.
10, no. 6. p. 55-66.
- - (196"1): Benthonic foraminifera off the263

Pacific coast of Japan referred to biostratigraphy of the Kazusa group: Geol.
Surv. japan, Rep .. no. 205, p. 1-45, pl. 1-8.
- - , HIGUCHI. Y. & KIKUCHI, Y. (1962): Correlation by the smaller foraminifera on
the southern Kanto gas field (in Japanese): japan. Assn. Pelr. Tech., jour., \'.
27, no. 3. p. 68-79, 1 pl.
- - & SIIINADA, Y. (1956): On the geology
and gas accumulation of the southernend of the Kujyulcuri gas field (in japa.
nese): japan. Assn. Pelr. Tech .. jour., v.
21, no. 1.. p. 13-2l.
- - & - - (1959) : Report on the exploratory drilling, Iioka R-1. Chiba Prefecture(in Japanese) : Ceo/. Surv. japan. jour ..
v. 10. no. 6, p. 86-90.
KANE HAl~ A, K, et a/. (19<19) : Natural gas
in the vicinity of Mobara, Chiba-ken (injapanese): Japan. Assn. Petr. Tech., jour ..
v. 14, no. 6. p. 2"15-274.
Kanto Natural-Gas Exploration Co. (1965):
Mobara gas-field (in japanese): japan
Petr. /nst. . .four., v. 8, no. 7, p. 540-545.
KA \\'AI, K. (Hl52) : On natural gas geologyof the western end area of the Mobara
gas Jiclc\, Chiba Pref. (in Japanese) : japan. Assn. Petr. Tech., jour .. v. 17, no. l.
p. 1-21.
- - (1960) : On the distribution of natural
gas in the southern Kanto gas producing
region (in Japanese): japan. Petr. Ins/.,
Jour., v. 3, no. 3. p. 213-218.
- - (1961): Economic geological study on
the southern Kanto gaS·I>roducing region(in Japanese): japan. Assn. l'etr. Tech ..
jour., v. 26, no. 5, p. 212-266.
- - , UCIIIO, T .. et a/. (1950): Natural gas
in the vicinity of Otaki, Chiba-ken (inJapanese): japan. Assn. Petr. Tech., jour.,v. 15, no. 4, p. 151-219.
KlKJ:Cill, Y. (1963) : Biostratigraphy (Foraminifera) of the Kazusa group on the Boso
Peninsula (in Japanese): japan. Assn.
Petr. Tech., jour .. v. 28, no. 4, p. 120-125.
- - (1964): Biostratigraphy of the Neogene
and Quaternary deposits based upon thesmaller foraminifera in the southern Kanto
region (in Japanese): Toiioku Unitl .. /nst.
Ceol. Pal., Conlr., no. 59, p. 1-36, pl. 1-8.

2G4

Naoaki AOKIKOIKE, K. (1955) : Geo-historical significanceof intraformational disturbances (in Japanese): Geol. Soc. japan, jour., v. 61. no.
723. p. 566-582.
KoMATSU, N. (1958): Geology of the central
part of the Boso Peninsula: Tokyo Univ.
of Education, unpublished master's t hcsis.
- - & OMORI. T. (1956): On one exampleof the intraformational disturbances (inJapanese):
Sedimentological Research,
no. 13, p. 1-6.
Kuw A~o. Y. (1954) : Notes on the genus
Cassidulincr and allied genera from Japan.
Description of new species of Cassidulina
from the Pliocene of southern Kwanto
region. I & II: Res. /nsf. Nat. Resources,
Misc. Rep .. no. 3·l. p. 78-81 : no. 35. p. 3336.
MATOBA, Y. (1967): Younger Cenozoic foraminiferal assemblages from the Choshi
District, Chiba Prefecture: Tohoku Uni11.,
Sci. Rep., ser. 2, v. :~8. no. 2. p. 221-263.
pl. 25-30.
MITSUCIII, T. (1937): Geological map of Japan, Scale 1 : 75,000, " Mohara •· : Geol.
Surv. Japan.
MITSUNASIII, T. (195•1) : Geology of thesouthern district of Kinadayama. Boso
Peninsula-Notes on the extension ofrock facies in time and space (in Japanese): Geol. Soc. japan, jour., v. 60, no.
710, P- 461-472.
- - (1959): The Neogene of the Boso andMiura Peninsulas-Some problem viewed
from the depositional pattern of the strata(in Japanese): Geol. Surv. japan, Hokkaido Branch, Abs/. of the lecture mig.,no. 11, p. 1-4.
- - . YASUKUNI, N. & St!INADA, Y. (1959):
Stratigraphical section of the Kazusa
group along the shores of the Rivers
Yoro and Obitsu (in Japanese): Geol.
Surv. japan. jour .. v. 10, no. 2. p. 83-98.
- - , YAZAKI, K., et al. (1961) : "FuttsuOtaki ": Geological maps of the oil andgas field of japan, no. 4, Geol. Surve.
Japan.
OMORI. T. (1957): Stratigraphical and paleontological studies of the Pliocene serie;;
developed between Obitsu and Koito

River, Chiba Prefecture (in Japanese) :Tokyo Univ. of Education, unpublishedgraduation thesis.
OTUKA, Y. (1932) : On foraminifera in thefossiliferous sands near Sanuki, Kazusa(in Japanese): Ceo/. Soc. japan, jour ..
v. 39, no. 160, p. •12-44.
SATO, T. & KoiKE, K. (1957) : A fossil submarine canyon near the southern foot of
Mt. Kano, Tiba Prefecture (in Japanese):
Ceo/. Soc. japan, jour .. v. 63. no. 737, p.
100-116.
Sl!tNAilA, Y., y ASIJKUNI. N. & MITSUNASIII.
T. (1955): On the stratigraphic relations
among the strata distributed in the middle part of the Boso Peninsula (in Japanese) : Cenozoic Nesearcii, no. 22. p. 2023.
- - . et al. (1951): Investigation of iodic
brine water in the vicinity of Kuniyoshimachi, Chiba Pref. (in Japanese) : japan.
Assn. Petr. Tech., jour.. v. 16. no. 6, p.
312-326.
TAKAYAMA, T. (1961): Chronological variation and its significance of the fossil
planktonic foraminifera assemblage fromalong the Obitsu River, Chiba Prefecture(in Japanese): Tohoku Univ., unpublished graduation thesis.
- - ( 1962) : Chronological variation of theplanktonic foraminiferal fossil assemblages along the Obitsu River route, Boso
Peninsula (Abst.) (in Japanese) : Geol.
Soc. japan, jour., v. 68, no. 802, p. 412413.
TAKAYANAGI, Y. (1951): On some E/zrel!bergina from Japan. Pal. Soc. japan, Trans.
Proc., N. S., no. 3, p. 85-93.
Ucmo. T. (l!l50): Microfossils. p. 179-190, in
KAWAI, K., el a/.. Natural gas in thevicinity of Otaki, Chiba-ken (in Japanese) :]clfJan. Assn. Petr. Tech., jour .. v. 15. no.
4. p. 151-219.
- - (1951a): Foraminiferal study of Tertiary formations ncar Otaki gas-field, Chiba
Prefecture (in japanese) : Geol. Soc.
japan, jour., v. 57. no. 664. p. 13-20.
- - (1951b): New species and genus of theforaminifera of the Cenozoic formationsin the middle part of the Boso Peninsula,

.'i88.

-Benthonic Foramin~fe1·al Zonation

Chiba-ken. Japan: Pal. Soc. japan. Trans.
Proc .. N. S .. no. 2. p. 33-42. pl. 3.
(1952): Geology of natural gas in the

Awamata
Boso
Chon an
Fuse
Higashi-higasa
lchihara
Ichijyuku
Ichinomiya
Ikariyato
Isonc-saki
IsurniItabu
Iwafunc
Iwakuma
Iwasaka
Izumiyatsu
Kakinokidai
Kamo
Kasamori
Katsuura
KazusaK6bund6
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Kokumoto

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Kurotaki
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KwantoManda noMasaki
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Nagahama
Namihana
Nan soNashinoki
Nishi-higasa
Nohichiri
NojimaObitsuOf unaOhara
Oikawa265

western part of Mobara-machi, Chiba
Prefecture (in Japanese): japan. Ass11.
Pelr. Tech .. jour .. v. 17, no. I, p. 22-37.

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266

Naoaki AoKT
Explanation of Plate 27

Fig. 1. Elphidium pannllum AoKt. n. sp., xllO, Holotype, from sample ;:058. 1 km S of YoroKeikoku Stn., Yoro River; Umegase formation, Bulimi11a-Bolivina Zone.
Fig. 2. Protelphidium kasamoriense AoKJ, n. sp., x 90. llololype, from sample ~101, Ushiku, Yoro
River; Kasamori formation. Nonionella stella Zone.
Fig. 3. Melon is pygmaeus AoKI, n. sp., x 137, Holotype, from sample ;076, south of Oritsu, NW
of Yoro-Keikoku Stn., Yoro River; Umegase formation, Uvigerina akitaensis Zone.
Fig. 4. "Cassidulina" brevis AoKI, n. sp., x 80, Holotype, from sample !!219. 0.6 km N of !tabu
Stn., Yoro River; Chonan formation, Cribroelphidium clavatum Zone.
Fig. 5. Gaudryina cf. arenaria GALLOWAY & WISSLER, x 38, from sample ::013, Tsukizaki, Yoro
River: Kokumoto formation, Cassiduli110 subgloiJOsa Zone.
Fig. 6. Gaudryia cf. arenaria GAL.LOWAY & WISSLER, x30, from sample ~150, Otadai, Yoro
River: Chonan formation. Bulimina-Bolivina Zone.
Fig. 7. Bulimina striata D'0RBIGNY, x 60, from sample ~064, near Kobundo, Oikawa, Yoro River;Otadai formation, Bolivina spissa Zone.
Fig. 8. Bulimina striata D'ORBiexv, x60, from sample ~143. Awamata, Yoro River; Kiwada formation, Buliniina-Bolivina Zone.
Fig. 9. Bulimina aculeata n'OIIIHGNY, x40, from sample ~1536, Otaki, Isumi River; Otadai formation, Bulimina-Bolivina Zone.
Fig. 10. Bulimina aculeata o'0RBIGNY, x 90. from sample ~081, south of Kazusa-Okubo Stn .. Yoro
River; Umegase formation, Uvigerina akitaensis Zone.
Fig. 11. "Cassidulina" kuwanoi MAToBA, x 125. from sample ~152, south of Oladai, Yoro River;Otadai formation, Bulimina-Bolivina Zone.
Fig. 12. Gavelinopsis praegeri (HERoN-ALLEN & EARLAr>:D), x 60, from sample #2050, ShimoMiyata, l\·1iura Peninsula; Miyata formation. middle Pleistocene.
Fig. 13. Gavelinopsis cf. translucens (PI II-EGER & PARKEH), x 130, from sample ~149, Otadai,
Yoro River; Otadai formation, Bulimina-Bolivina Zone.
Fig. 14. Cibicides cf. aknerianus (D'ORBIGNY). x 33, from sample ~008, Tsukizaki, Yoro River;
Kokumoto formation, Cassidulina subglobosa Zone.
Fig. 15. Gyroidina gemma BANDY, x47. from 8ample #2385, south or Iwafune, SE of Nam:ihana;
Namihana formation, Gyroidina-Melonis Zone.
Fig. 16. Melonis cf. padanum (PER<.:ONING), x65, from sample ~027. ncar Kazusa-Okubo Stn.,
Yoro River; Kokumoto formation, Cassidulina subcarinata Zone.
Fig. 17. Globobulimina sp., x50. from sample !!002, south of Tsukizaki, Yoro River; Kokumoto
formation, Cassidulina subcarinata Zone.
Fig. 18. Gyroidina cf. orbicularis D'0RUIG:'>IY var., x 50, from sample ~027, near Kazusa-Okubo
Stn., Yoro River: Kokumoto formation, Cassidulina subcarinata Zone.
Fig. 19. Gyroidina cf. orbicularis n'ORBIG"'Y, x 30, from sample ;1584, Isumi River: Namihana
formation, Gyroidina cf. orbicularis Zone.
Figs. 20, 22. Bolivina spissa Cu:oHMAN, x64, from sample :;064. near Kobundo, Oikawa, Yoro
River; Otadai formation, Bolivina spissa Zone.
Fig. 21. Bolivina robust a BHAI>Y, x 93, from sample ;149, Otadai, Yoro River; Otadai formation,
Bulimina-Bolivina Zone.
Fig. 23. Plcctofrondicularia japonica (AsANo), x60, from sample ~1951. Nohichiri, 4 km E of
Of una, Miura; Nojima formation, Pliocene.
Fig. 24. Plectofrondicularia goharai KuwANo, x60, from sample ~1951, Nohichiri, 4 km E of
Of una, Miura; Nojima formation, Pliocene.
Fig. 25. Plectofrondicularia tolomiensis MAKIYAMA, x 110. from sample #1951, Nohichiri, 4 km E
of Ofuna, Miura; Nojima formation, Pliocene.

AOKI :

Benthonic Foraminif era

Plate 27

Trans. Proc. Palaeont. Soc. Japan, N. S.. No. 70, pp. 267-283. pl. 28, June 30, 1968

539.

NOTES ON TIIE BENTHONIC FORAMINIFERA OF THE
TONOHAMA GROUP. SHIKOKU . .JAPAN*
KENJI KURIHARA
Institute of Geology and Mineralogy, Tokyo University of Education

the basis of benthonic foraminifera andmolluscan fossils. although it was emphasized that the Nobori foraminiferal
fauna was quite different from that of
the Pliocene Ananai formation. and had
many common species with that of the
l'v1iocene deposits of the Kar Nicobar
Islands. India. Later, however, KATTO
and OzAKI (1955) and KATTO (1960) concluded that the Nobori was Miocene inage for the occurrence of some molluscan
fossils including Periploma pulchellum
H.\TAI and NISIYAMA and shark's tooth,
Carcharodon megalodon (CHAULESWORTH).
which they regarded as characteristic
Miocene species. They also mentionedthat this conclusion did not contradict
the results of the previous study of
KATTO et a[. (1953).
Tsucm (1961). however. pointed out
the occurrence of such characteristic species of the Kakegawa molluscan fauna of
the I<akegawa group,Shizuoka Prefecture,as Amussiopecten prnesignis (YOKOYAMA)
and Venericardia panda (YOKOYAMA).
He concluded that the Nobori as well as
the Ananai was correlative with thelower or middle Kakegawa group which
is usually regarded as Pliocene in japan.

Introduction
The Tonohama group has been wellknown as the "Tonohama shell bed",
which yields abundant molluscan fossils.
This younger Neogene sediments are
distributed as isolated small patches in
the coastal region of Tosa Bay from
Ananai, Aki City. eastwards to Hane.
Muroto City. Kochi Prefecture. It was
subdivided into three formations, thatis. the Nobori, Ropponmatsu** and Ananai formations in ascending order (KAT·TO, NAKAMURA and TAKAYANAG!, 1953).
The Ananai formation has been considered to be Lower Pliocene in age
based on molluscan fossils and benthonicforaminifera (ASANO, 1937; NOMURA.
1937; KATTO et a!., 1953. and others).
However. with regard to the geologic
age of the Nobori formation, the lowest
part of the group, different opinions
have been proposed.
KATTO et a[. (1953) tentatively assigned the Nobori to lowermost Pliocene on• Received Aug. 19, 1967; read June 18. 1966.
.. The Nahari formation. Later. KATTo(l960)
changed the name to Ropponmatsu formation.

267

268

Kenji KURIHARA

iRiver~/~Toso Boy
Fig. L Geological map of the eastern coastal

Supplementary work of the molluscan
fauna of the Nobori was carried out by
AOKJ (1966). and he showed the clo:;eaffinity of the Nobori fauna with thatof the Lower Kakegawa Series of Pliocene. Accordingly the Nobori was assigned to Lower Pliocene from the molluscan fossils.
On the other hand, TAKA Y ANAGI and
SAITO (1962) described 50 species of planktonic foraminifera including Globigerina
nepenthes TODD from the type localityof the Nobori formation. They correlated
the fauna directly with the Globorotalia
menardii menardii-Globigerirza nepenthes
Zone of Venezuela and the Tortonian in
Italy. Furthermore, SAJTO (1963) correlated the Nobori fauna with that of the
Sagara group, Shizuoka Prefecture. whichis overlain by the Kakegawa group withpartial unconformity. Consequently. fromthe planktonic foraminifera the Nobori
was assigned to Upper tvliocene.
Up to now there have still remained
the two different opinions on the geologic
age of the Nobori formation based on
different l<ind of fossils. namely, the one

is Upper Miocene by means of planktonic
foraminifera and the other is Lower Pliocene on the basis of molluscan fossils.
During the stratigraphic and paleontologic investigation of the Tonohamagroup, the author obtained some newdata concerning the stratigraphic relationand the faunal characteristics of thebenthonic foraminifera of the Tonohamagroup. They are remarked and discussed
in this paper with the description offifteen species including three new species from the Nobori formation.
Stratigraphic notes
The Tonohama group which attains
about 300m in total thickness unconformably overlies the Mesozoic and Paleogene rocks, and is overlain by the
Quaternary deposits with an unconformity. The sediments are composedof two major sedimentary cycles byintercalation of non-marine deposits. andconsist of following formations as shown
below in descending order (KATTO et al..
1953).

5:39.

1'onohama Benthonic Foraminife·ra

269

/

///
/

//;
/

/

/

F.
R 0 PP ONMATSU
2NOBORI

4kmllll3

F.

!22 SHIMANTO

G.

region of Tosa Bay and sample locality.

B

c

0

E

F
Fig. 2.

G

H

J

K

L

M:TlN

Columnar sections.

1. Mudstone, 2. Muddy sandstone. 3. Fine-grained sa:1dstone, ·1. Medium-grained sandstone,

5. Coarse-grained sandstone, 6. Alternation of sandstone and conglomerate. 7. Conglomerate,
8. Lignite bed, 9. Carbonaceous matter, 10. Mollusca, 11. Lebensspu1·en.
A. Ananai, B. Shinhama, C. Kodaiji. D. Sawanoclaira. E. Kubota, F. loki. G. Tonohama, H.
Zyo, I. Ono, J. Takada. K. Notomo. L. Go, M. Ropponmatsu, N. Hane.

270

Kenji KURIJIARA

Ananai formation: 25-65 mm. Fine-grainedsandstone with abundant molluscs andforaminifers. The lower part consistsof coarse- to medium-grained sandstone
with basal conglomerate.
- - - conformity - - Ropponmatsu formation: 15-70 m. Non.marine conglomerate consisting of poorly
sorted, subangular cobbles, often boulders
at the base. Intercalated with thin Jig.
nitc and lignitic siltstone beds.
- - - disconformity - - - Nobori formation: About 140m. Massive
siltstone. In the basal part coarse- tofine-grained sandstone. alternating withsiltstone at some places. Abundant foraminifers and molluscs. Rarely foundshark's teeth, otoliths and vertebratebones.

Some stratigraphic revtstons of theprevious work (KATTO l'f a/., 1953) areproposed as shown in Fig. 1 and remarked
below.
(1) The conglomerate developed in thew·estern areas between Ananai and Tonohama which was regarded as the basal
conglomerate of the Ananai in the previous works is nothing but the westernextension of the Ropponmatsu formation.
The reason is that this conglomerate iscomposed of poorly sorted conglomerateintercalated with Hgnitic siltstone layers
and being greater in thickness comparing
with well-sorted subrounded basal conglomerate of the Ananai which is lessthan 10m in thickness and typically developed where the Ananai directly overlies the Mesozoic or Paleogene rocks.
The lithofacies of the conglomerate inquestion is quite similar to that of thetype section of the Ropponmatsu forma·tion at Ropponmatsu, and belongs to the
Ropponmatsu formation. Accordingly
the Ropponmatsu formation is distributed all over the areas where the Tonohama group is developed.
(2) The Ropponmatsu formation is con-formably overlain by the Ananai formation. This relation was formerly considered to be an unconformity. In thew·estern areas between Ananai and Tonohama the non-marine conglomerate isalways covered with the marine sandstone of the Ananai which yields molluscs and foraminifers. The former,
which has been correlated \Vith the typesection of the Ropponmatsu as mentioned
above, gradually changes upward to thelatter facies of the Ananai everywhere.
Therefore the Ropponmatsu formation is
conformably overlain by the Ananai.
This relation is well observed at loki,
Tonohama and some other localities.
(3) The stratigraphic relationship bet ween the Nobori and the Ropponmatsu
formations is a disconformity. Accord·
ing to KA TTO el a!. the Nobori wasregarded to be in fault contact with the
Ropponmatsu, and their stratigraphic
relationship was supposed to be an angular unconformity. Judging from my
own field observation, both formations
are not in fault contact, and the nonmarine conglomerate of the Ropponmatsu
seems to lie on the deep water marine
sediments of the Nobori, indicating an
unconformable relation. The unconformity is, however, not an angular unconformity but may be disconformity, because the Nobori and Ropponmatsu formations slightly dip to the west lessthan 15• at Hane and there is no perceptible difference of the geologicalstructure between them.
Discussion: According to KATTO etal. (1953), the stratigraphic relationships
among the Tonohama group were regarded that the Nobori was separated fromthe Ropponmatsu by an angular unconformity and that the Ropponmatsu wasalso separated from the Ananai by anunconformity. It was, therefore, pointed
out that there was a significant break.589.

Tonolwma Benthonic Fora'fnin.ifent.

between the Nobori and Ananai whichindicated rather long period of non-deposition.
It is known that Plio-l\liocene boundary
in Japan is placed at unconformities between the Neogene formations in manycases. The break between the Nobori
and Ananai was considered important(KATTO and OzAKI. 1955; TAKAYANAGI
and SAITO. 1962) because it might bereferrable to the unconformities of otherregions in Japan at which Plio-Miocene
boundary was placed.
KA TTO (1960)
furthermore excluded the Nobori andRopponmatsu formations from the Tonohama group. However, TsucHI (1961)
noted that three formations of the Tonohama group were appropriate to be
combined into a single sedimentary group
because of the obscurity of the unconformable relations and faunal evidenceof molluscan fossils.
As noted before it may be concluded
that the Ananai formation overlies the
Ropponmatsu with conformable relation,and the stratigraphic relation between
the Nobori and Ropponmatsu is not anangular unconformity but a disconformity. The widely distributed Ropponmatsu
and Ananai formations may indicate theTonohama group to be of rather horizontal structure than homoclinal one.
In short, there is no significant unconformity among the three formations of
the Tonohama group, and the break betw·een the Nobori and Ananai formations
is not so large as regarded in the previous studies.
Faunal remarks
Except the non-marine Ropponmatsu
formation, the Nobori and Ananai formations yield rich foraminiferal faunas,
and they were studied by AsA~O (1937)
and TAKAYANAGJ (in KATTO ei a/., 1953)

271

in detail.
The Nobori and Ananai faunas comprise two different assemblages respectively. The assemblage found from thebasal part of the Nobori is called, in thepresent paper, the sandstone member
assemblage and that from the upper ormain part of the same formation is thesiltstone member assemblage. As thefauna found in the Ananai changes laterally in this region, it is divided into two
biofacies which were called by T AKAYA·NAGI (in KATTO et al., 1953) the loki
biofacies of the west and the Senpuku
biofacies of the east. These four assemblages are remarked below. The constitution of them are shown by representative samples (Table 1).
Sandstone member assemblage of theNobori formation : This assemblage has
not been reported previously from theNobori. It is found in the basal sandstone member (20m+) of the Nobori,and characterized by the common species listed below; !lmmonia ketienziensis(ISJIIZAKI}, Cassidulina carinata CuSIII\fAN,
Bulimina marginata o'ORBIGNY, l/anzawaia nipponica AsANO, Cibicides pacijicus
CuSHMAN, and Reclobolivina raphana(PARKER and jONES). These species occur generally 5-10% in frequencies andare almost restricted to the basal member in the Nobori. They are associatedwith Stilostomella lepidu/a (SCHWAGER),
Ammonia lalwnabensis (ISIIIZAKI}, Am·phicoryna sagamiensis (ASANO). etc. which
occur in less frequencies. Some characteristic species of the Ananai fauna whichwere only reported from the Ananai formation previously are rarely found in
this assemblage, namely. Clauulina yabei
ASANO, Martinottiella bradyana tarukiensis (ASANO}. Loxostomoides amygdalaeforme iokiense (ASANO), and l'seudorolalia
yabei (ISHIZAKI). Although some predominant species of the overlying silt-

Kenji KURIHARA

272
Table 1.

Distribution of benthonic foraminifera in the Tonohama group(in percent).

Formation
Assemblage
Samplenumber

ANA N AIN 0 B 0 R I
S i Its tone Sandstone Se~fol ku I o kJ. f
10.
mem. as. mem. as.
ro.
00 r-- Cf.) I'() N(1)
I'() I'()~-I{) iD lO -t{)t{)t{) I!) t{)t{)<D<D <.D '¢

-

-

I'()
Cf.)
t{)

ro Cb 0!B

&S I{) L{)

robusta
Brizalina
62 16.1o.~3:~Stilostomella sp.A
0.4
2.:' 1,<1 0.8
0.8 7.6 1.7 ().5
proboscides
Uvigerina
0.4 0.4 7.6
rotundaEilohedra
5.0 1.1 12
kattoi
Casaidulina
sp.A
0.4 1.4 11.2
c.
orbicularis
Gyroidina
2. 3.7 0.4
w
Q~
longiscata
0.8 0.5 0.5
Nodosaria
2:1
quadrilatera
2.5
0:4
Bolivinita~ 6.2 6.6 3.2 11.4 OA
Stilostomelle lepidula
1..5 0.9
3"'nipponica
Bulimina
14.6 3:7 o.a
3.0 1.5
0.9
shiwoensis
Uvigerina
OA 42
1.5 14.5
carinate
Cassidulina
12..3
3.5
3.~
2..9
I~
o.a
q~
1~
marginate0.•.~ 1.4 0.8 2.1 &9 1.5
Bulimina
4.1~
3.8
pseudouncerianus
3.7 1.5
Cibicides
12 0.7
2.2 2.C 4.7 1.1 2.0 4.5
yabei
Clavulina
1.6
7.3 Q9yabei akiensis
c.
1.6
0.9
Martinottiella bradyana tarukiensis
8.4~~.~
Rectobolivina raphana
2. 0.5 6.9 I.S 7.4 4.7 6.e 4.7 3.3
japonica
Ammonia
9.1 1.3 I
2.1 0.5A.
ketienz~ens~s
1.4
6.4 15.~ 5.7
1.2
2.5 9.C 1.9
A.
takanabensis
1.~ 3.6 42 ~Pseudorotalis yabei
8~2.0
pacific us
Cibicides
7.3 1.6 2.5
13.3
58
manpukujiense
Florilus
4.0m~ 7.2 21 O_il
Hanzawaia
nipponica
S.!l
60 3.4 3.3 a1 14.1 10.0
Melonispompilioides
Amphicoryna
sagamiensis
Q3 'l.~ ~?.~ 3.0
Sphaeroidina bulloides
0.4 3.60.~o.~Brizalina
cf.albatrossi
3.5 7.4 11.8 9.8 17.4 14.5
OA
B.
hanzawai
Q.5
3.-1 2:4 5.7
2.5
Loxostomoides Sl!lygdalaeforme iokie1.9
2.C
0.4
2.9
Rosaline
williamsoni
nse
3.4 1.6
Ammonia
cf. beccarii
OA
3.9 ~~ ~ 0.7 2.5
Elphidiumadvenum
0:4 04 Q!ilo.:l 3.8 2..3 4.1 9.2
clava tumE.
7.4
crispum
E.
Q3 LO 0.9 ~ 2.0 ~0!4 04 04
Planktonic I Benthonic + Planktonic 642 394 35.3 21.4 9.<1 19.6 i32. 43:4 138.3 5.4 0 5.7

~

I~

i]

~

~

~

stone member assemblage occur in thisassemblage, they are very low in fre·quencies with an exception of Cll.~sidulillacarina/a which is frequent in both as·
semblages.
Siltstone member assemblages of theNobori formation : The assemblage fromthe siltstone member of the Nobori occupies almost whole part of the formation, and it corresponds to the " Nobori
fauna" reported by TAKAYANAGI. Diag.

nostic and dominant species are Brizalina
1·obusta (BRADY). UFigerina proboscidea
SCHWAGER, Bulimi IW nipponica ASANO,
Cassidulina carina/a, C. sp. A. Stilostomella lepidula. and S. sp. A. Follov,;ing
species are almost only found in thisassemblage; Plectofrondicularia totomi·
ensis MAKIYAMA. Tosaia hanzau:ai TAKA·
Stilostomella kelienziensis (ISHI·
rotunda (HUSEZIMA andtviARUIIASIII), and Cassidulina lwttoi T A·
YA:\AGI.

ZAKI). Ei/ohedra

589.

Tonohama Benthonic I•'ormninifcra

KAY ANAGI. The occurrence of the dominant and associated species are consistent through the whole section withrather uniform composition and frequencies of the species.
It is, therefore,
easily distinguished from the other as·
semblages distributed in this region.
Planktonic foraminifers are abundantly
found in each sample.
loki biofacies of the Ananai formation: The loki biofacies is developed in
the western region between Ananai andloki. It is characterized by the highfrequencies of the following species;

1/anzawaia nipponiw, EljJhidium advenum(CUSHJ\IAN). E. crisjmm (LINNE). !Jrizalina
cf. albatrossi (CUSII:'IIAN), and Reclobolivina rapJwna. The following species arealso found frequently; Rosalina wil/iamsonii (PAI(R), Loxostomoides amygdalaeforme iokiense. Brizalina hanzatrai (ASANO), Cibicides pseudoungerianus (CUSHMAN), Elphidium aaliculalum (FICIITEL
and [VIOLL) and others. OjJerculina ammonoides (GRONOVJUS) is frequently foundat loki.
Senpuku biofacies of the Ananai for·mation: In this assemblage developedat Tonohama and Ono the dominant
species of the loki biofacies also occur
in lower frequencies. The following
species are restricted only to the Senpuku biofacies in the Ananai fauna inspite of their low frequencies; !lmphi-

coryna sagamiensis, Sphaeroidina bulloides
D'0RBIGNY ,Oridorsalis umlwnatus(REUSS),
Melonis pompilioides (FICIITEL and MoLL).
Stilostomella lepidula and Bulimina nipp:mica. This assemblage is also distinguished from the loki biofacies in having
more number of specimens of planktonic
foraminifera, namely, the former usuallycontains 30-60% for total population(benthonic+planktonic). while the latter
only contains less than 6.%.

273

Discussion
The Nobori and Ananai faunas comprise many Recent species which makes
it easy to compare the two with Recent
faunas. AsANo (1936) compared the Recent benthonic foraminiferal fauna of
Toso Bay and the Ananai fauna, anddiscussed the water temperature and extinct species of the Ananai formation.
lSIIIWADA (1965) studied the frequency
distribution of the Recent benthonic foraminifera along the one traverse of
Toso Bay, and recognized neritic andbathyal faunal facies which were subdivided into two subfacies respectively.
The four assemblages of the Nobori
and Ananai formations may be comparable with the Recent fauna of Toso L3ay,
and their inferred paleo-environments areshown (Fig. 3). The Nobori fauna com·
Formation

Ananoi

Nobori~
Up~~;lf lobki>i of.

Cen1ro1 (... est) ~enpuku Sandstone memas. (lower par.!l_hi of.
Shelf
Lo~er

(e as I)

helf
Siltstone mem.
Upperas. (main part)
SloPe
Fig. 3. Inferred environments of thefour assemblages of the Nobori and Ananai[ormations.

prises shelf and slope species. The environment of the sandstone member assemblage of the lower Nobori is of central or lower shelf, while that of thesiltstone member assemblage is a deeper
water one ranging from continental edge
to upper slope. The former indicatesearly stage of the transgression and thelatter represents maximum transgression,
but regressive facies is not found in theNobori formation. The Ananai faunaconsists of shelf species. The Senpuku
biofacies of the Ananai comprises more

/{enji /(URIJIAR.4

274

Miscellaneous0

Species5063

Melon isct parkerae

5083

Bulimina
ni pponica
Uvigerina
shiwoensis

5112

Fig. 4. Lateral faunal change of the Ananai formation. Species are arranged approximately from shallow to deep water ones in ascending order. All samples are from middle
part of the Ananai formation. Sample locality is shown in Fig. 1. Dolled line is planktonic
foraminiferal content for total population.

deeper water shelf species and morenumber of planktonic foraminifera thanthose of the loki biofacies of the sameformation. The lateral faunal change of
the Ananai may indicates gradual shallowing of the environment towards thewest (Fig. ·1).
In the comparison of the Nobori faunawith that of the Ananai. the sandstone
member assemblage is more similar to
the Ananai fauna rather than the siltstone member assemblage (Table 1). The
dominant species of the Nobori sandstone
member assemblage are also common in the

two assemblages of the Ananai in rather
high frequencies, but are not present or
only rarely found in the Nobori siltstone
member assemblage. Many other species
in the Nobori sandstone member assemblage are also found in the Ananai fauna.
Comparison of the representative samples from the sandstone and siltstone
member assemblages of the Nobori and
the Senpuku biofacies of the Ananai
are shown in Fig. 5. The dominant
species in the two samples of the Nobori
sandstone member assemblage and theAnanai Senpuku biofacies are almost

539.

Tonohama Benthonic Foraminifera

Miscellaneous species
Uvigerina
proboscidea
Gyroidino
orbicularis
Meloniscf.porkerae
Sphoeroidino bulloides

AnanoiF.
Senpu kubiof.

Noboti

F.
Sand-

stone

275
Nobori

100

F.
Siltstone
mem.astt516170~~~~~~f~~~§~~~~~~~

Uvigerina
Hoeglundina shiwoensis
elegans
Stilostomello lepidula
Oridorsofis
umbanofus
Ammoniaketienjiensis
Bulimina
marginate
C ibicides pseudoungerianus
Cassidulina
carinato------1
Cossidufino
subglabosa
Clavulino
yobei
Hyolinea
bolfhicoHanzowaio
Len!iculina
Reclobolivin a

Fig. 5. Comparison of the representative samples from the three assemblages.

common with similar frequencies. Whilein the sample of the Nobori siltstone
member assemblage a larger number ofdeeper water species are contained. In
the sample of the Nobori sandstone
member assemblage the common species
with the Ananai fauna attain more than
80% in total population frequency.
Therefore. the sandstone member as·
semblage of the lower Nobori formation
is similar to the Ananai fauna particularly to the Senpuku biofacies. and dif·fers from the Nobori siltstone member
assemblage. This seems to suggest thatthe difference between the Nobori siltstone member assemblage and the Ananai fauna which does not comprise theslope assemblage such as the Nobori
siltstone member assemblage is simply
caused by different environmental con·ditions. This opinion is supported byother evidences. Some species yieldedin high frequencies in the Ananai formation of the upper Tonohama group,
such as Clavulina yabei, C. yabei akiensis

AsANO, Martinottiella bradyana larukiensis. Urizalina ha11zawai. B. cf. al/Jatrossi, Florilus japonicum (AsANO). Elphidium crispum and £. adtlenum, occur invery low frequencies (less than 1%) in
the two assemblages of the Nobori formation of the lower Tonohama group.
!\lost of these species in the Nobori
might be transported from the contemporaneous sediments of shallower placesconsidering their preservation and occurrence. The siltstone member assemblageof the Nobori has the highest frequenciesof the planktonic foraminiferal content,
and has more number of the benthonicspecies and less number of the warm tosubtropic water benthonic species thanthe other assemblages. These evidences
all indicate that the Nobori siltstone
member assemblage represents the deepest water condition in the four assemblages of the Tonohama group.
Therefore it may be concluded that
the Nobori and Ananai benthonic foraminiferal faunas are not so quite different

276

Ken.j-i KURIHARA

as stated in the previous papers, butrather belong to the same faunal group.
The different aspect of the two faunas
is mostly a reflection of the different
environmental conditions.
Geologic age of the Nobori formation

The Ananai formation, the upper partof the Tonohama group, has been considered as Pliocene from the molluscan
fossils and foraminifera (ASANO, 1937;
NOMURA, 1937, and others). On the other
hand, the Nobori molluscan fauna was
generally considered to be also correlative with the Pliocene Kakegawa fauna{TSUCill, 1961; AoKI, 1966), whereas theNobori foraminiferal fauna was assigned
to Upper Miocene in age because of thefollowing faunal evidences by TAKAYANAGI and SAITO (1962).
(1) The Nobori planktonic foraminiferal fauna is correlated with that of theUpper Miocene Globorotalia menardii
menardii-G/obigerina nepenthes Zone of
Venezuela and the Tortonian, Italy.
(2) The Nobori benthonic foraminiferal
fauna is quite different from that of theAnanai, and has some resemblances tothat of the l\liocene deposits of the Kar
Nicobar Islands.
{3) The Nobori formation contains someso called guide species which are said tooccur in the Miocene strata in Japan,that is, Porifera, Sagarites and shark's
tooth. Carclwrodon megalodon.
Among the 50 species of planktonic
foraminifera of the Nobori formation
T t\KAY ANAGI and SAITO (1962) foundthree species which disappeared within
the l\liocene Globorotalia menardii menardii-Globigerina nepenthes Zone, namely, Globigerina nepenthes. Globigerina
praebulloides BLOW and Globoquadrina
a/fispira globosa BoLLI. and they correlated the Nobori fauna with that of the

Globorotalia menardii menardii-Globigerina nepenthes Zone of Venezuela. However, the stratigraphic ranges of these
species were extended upward by suc·ceeding studies. For instance G/obigerina
nepenthes and Globigerina praebulloides
were reported from the Pliocene (JENKINS,
1964: BA!\NER and BLOW, 1967; BOLLI,
1966), and Gluboquadrina altispira globosa
was found throughout the next younger
Sj>haeroidinellojJsis seminulina Zone (BANDY, 196-i) and the Pliocene (BOLLI, 1964).
130I.LI (1964) and HUANG (1967) questioned
the identification of the Globigerina nepenthes of the Nobori formation. Moreover. some species which first appear
above the Globorotalia menardii menardii-Glubigerina nepenthes Zone or in Pliocene in other regions can be found in
the Nobori fauna such as Globorotalia
hirsuta (D'Ot{IHGNY). Globorotalia tosaensis TAKAYANAGI and SAITO. Splweroidinella dehiscens dehiscens (PARKER and]ONES) and Pu/leniatina ohliquiloculata(PAl<KER and ]ONES) (T AKAY ANAGI and
SAITO, 1962; !30LLI. 1964).
The Nobori planktonic foraminiferal
fauna is. therefore, characterized by therather peculiar association of species.
and differs from those of other regions
belonging to the Globorotalra menardii
menardii-Globigerina nepeut hes Zone.
BOLLI (196,1) and BAI'\NER and BLOW
(1967) considered the Nobori as Pliocene
in age, and :v!cTAVISH (1966) said that
the Nobori fauna was a mixed oneof the Globigerina nepenthes and the
younger Pliocene faunas, and HuANG(1967) mentioned the correlation of theNobori is a problem to be reserved forfurther study. Accordingly, the correlation of the Nobori with the Globorotalia
menardii menardii-Globigerina nepenthes
Zone seems to be incorrect.
KATTO et a/. (1953) and TAKAYANAGI
and SAITO (1962) mentioned that the539.

Tonohama Benthonic Forwmini[e1·a.

Nobori fauna comprised many common
species with those of the Miocene deposits of the Kar Nicobar Islands. India.
such as Pyrgo murrhina (SCHWAGER).
Lenticu/ina nicobarensis (SCHW AGEl<).
/Joliuini/a quadrilatera (ScHw 1\GER), Uuigerina nitidula SCJIWAGER, Uvigerinaproboscidea. Bulimina inflata SEGUEi'\ZA.
Stilo.~tomella
lepidula,
Pleuroslomellaalternans SCHWAGER, Osangularia bengalensis (SCIIWAGEH). Sphaeroidina austriacan'ORBIGNY and Melonis nicobarensis(CUSHMAN). However, these species arealso found in the Ananai fauna except
two deep water species of Pyrgo murrhina and Osangularia bengalensis which
are reported from Recent sediments.
Accordingly, all the species that arepointed out as common with the ~'liocene
foraminifera of the Kar Nicobar Islands
are also found in the Pliocene Ananai
formation or Recent sediments, and do
not indicate the Nobori to be i\liocene inage. In addition the different aspect
between the Nobori and Ananai benthonic foraminiferal faunas merely indi·cates the different environmental conditions to a large extent.
Sagarites and Carclwrodon megalodon
were reported from the Nobori formation by KATTO and OZAKI (1955) and
KATTO (1960), and considered as index
fossils of 1vliocene. The both fossils arecommonly found from the Upper l'v1iocene,
but it is known that they also occur inthe Lower Pliocene sediments. Their
restricted occurrence in the Nobori formation is mostly due to the deeper faciesof the Nobori.
In the correlation of the Nobori for·mation with the European standard orother foreign countries the planktonic
foraminifera is believed to be the mostuseful. From the planktonic foraminifera, although some different opinions werestated concerning the geologic age of277

the Nobori formation, many authors concluded that the Nobori fauna wasyounger than that of the Globorotalia
menardii me11ardii-Globigerina nepenthes
Zone as i!Oted already.
This conclusion seems to be also indicated from the benthonic foraminifera
and the stratigraphic succession as well
as molluscan fossils, because the Nobori
and the Pliocene Ananai benthonic foraminifera belong to the same faunalgroup and there are no significant unconformities among the Tonohama group.
It is most reasonable that the geologic
age of the Nobori formation is regarded
to be what is called Lower Pliocene injapan.

Remarks and descriptionof some species

The benthonic foraminifera of the
Tonohama group was studied by ASANO(1937) and TAKAYANAGI (in KATTO eta[.,1953) who reported about 300 species.
Although they were not wholly described.
AsANO (1936) described 3 new species
and subspecies from the Ananai forma·tion, and TAKA Y ANAGT (1953) described
14 new species from the Nobori andAnanai formations. In the present paper
3 new species with other unreported
species are described chiefly from theNobori formation.
Cyclommina sp.
PI 28. Fig.

Only one specimen was obtained fromthe type locality of the Nobori forma·tion. It has a large-sized test with nu·
merous chambers and flattened sides.
Diameter. 7.30 mm; thickness. 1.55 mm.

J<enji KURIJfARA

278

Spiroloculina akiensis KuRIIIARA. n. sp.
Pl. 28, Figs. 2-4

Test large, compressed. roundly ovatein side view, longer than broad, sides
flattened in some specimens, central por·tion depressed, often more so on one
side than the other : periphery broadly
rounded ; chambers consisting of about
eight or less in a megalospheric form,
only four or five chambers visible ex·
ternally due to nearly involute coilingof early chambers, inflated, rapidly increasing in size as added; sutures distinct, sometimes slightly uneven; wallchalky white. rough except the flatten
portion of the chamber; aperture rather
small. circular, with a tapering shortneck and a small bifid tooth. Length ofholotype, 1.67 mm : breadth, 1.26 mm;
thickness, 0.72 mm.
Holotype, Reg. no. 68035. from a hillside cliff, at Minamihabuki. Nishinohama.
Hane-machi, Muroto City, Kochi Prefecture, middle part of the Nobori formation, Upper Miocene or Pliocene. rare.
This form is characterized by having
a small number of chambers externallyvisible, slightly asymmetry in a cross section, and projecting short neck, which
are similar to Spiroloculina subaequalis
PARR described from the Miocene of
New Zealand. This new species, however, differs from it by having a shorterneck with a bifid tooth, and a involutechambers in early whorls. It is rarely
found at the type locality of the Nobori
formation.

Nodosaria tosta SCHWAGER
Pl. 28. Fig. 5
Nodosaria tosta SCII\L\GF.R, 1886, Novara Exp.,
Geol. Theil, p. 219. pl. 5, fig. 42; As,\NO,
1953, Tohoku Univ., Inst. Geol. Pal.. Short
Pap .. no. 5, p. 8, pl. 1, figs. 23, 24.

This species is found throughout theNobori formation (up to 8%).

Delltalina cf. spinosa n'ORBIGNY
Pl. 28, Fig. 6
Cf. Dentalina spinosa D'0RBICNY, 1846, .Foram-iniferes fossiles du bassin Tertiaire deVicnne, p. 55, pl. 2. figs. 36, 37; As.-\NO,!953. Tohoku Univ., Inst. Geol. Pal., Short
Pap., no. 5. pl. 1, figs. 33, 34.

Few specimens are obtained from theNobori formation. The figured specimenslightly differs from the typical formin having more number of costae.

Stilostomella sp. A
Pl. 28, Figs. 7, 8This small species, consisting of sevento ten chambers with a slightly elongate
last-formed chamber. shows somewhat
resemblance to Stiloslomella antillea(Cusmv!AN). It commonly occurs in thesiltstone member of the middle and upper Nobori formation (up to 8%). andalso rarely found in the sandstone member of the lower Nobori and the Ananai
formations.
Length, up to 0.70 mm:
breadth, 0.10 mm.

Parafissurina ova/is Tonn
Pl. 28, Figs. 9-11
Parafissurina ova/is Tor>o, 1957, U.S. Geol.
Surv., Prof. Pap. 28011, p. 306, pl. 76,llgs. 5, 6.
Parajissurina kiyosumiensis AoKI, 1964, Trans.
Proc. Palaeont. Soc. Ja1>an, N. S., no. 53,
p. 164, pl. 25, figs. 2a. b.

The Nobori specimens have slightly
developed keel especially at the lower
part of the test, but its development israther variable on each specimens. Para-

.589.

'l'onohama Benthonic Foraminifera

fissurina lliyosumiensis AOKI from theUpper "1\Hocene Kiyosumi formation of
the Boso Peninsula has smaller test thanthe Nobori form, but both are identical.
It is frequently found in the Nobori formation. Length, 0.68 mm; breadth, 0.62mm : thickness, 0.33 mm.
"Bulimina'' affinis n'ORBIGNY
PI 28, Fig. 12
Bulimina ajjinis D'0RBJGNY, 1839, in De Ia
Sagra, Hist. Phys. Pol. Nat. Cuba. "Foraminifercs ", p. 105, pl. 2, figs. 25. 26;
CusH~IAN and PARKF.R, 1940,
Contr.
Cushman Lab. Foram. Res., v. 16, p. 7,
pl. 2, figs. 1-4.
Globobulimina affinis PAin:En, 1958, Swedish
Deep-Sea Exped., v. 8, p. 262, pl. 2, figs.
24, 25.

The Nobori specimens characterized by
distinctly perforate wall and depressed
sutures are very similar to the figures
by CUSH~fAN and PARKER (19,10). This
species was referred to the Genus Protoglobobulimina HOFKER by BELFORD (1966).
It is rarely found in the Nobori and Ananai formations (less than 1%). Length.
up to 0.78 mm; breadth, 0.47 mm.
Trifarina s!zikokuensis KURIHARA, n. sp.
Pl. 28. Fig. 16

Angulogerina angulosa KuwANO, 1962. Misc.
Rep. Res. Inst. Natur. J{esourccs, no. 5859, pl. 14, figs. 1. 2.
Trifarina cf. angulosa AoKJ, 1965, Saitama
Univ. Sci. Rep., scr. B, v. 5, no. l, p. 59,
pl. 7, figs. 4, 5.

Test small, fusiform, triangular inapertural view, about two times as longas broad, widest at the central portion,
composed of about three whorls; chambers slightly inflated, strongly overlap-

279

ping in earlier whorls, slightly angulated
at the basal part ; sutures depressed,
nearly straight except the last whorl's
ones; wall ornamented with longitudinalcostae which show spine-like feature in
the early whorls; aperture terminal.
rounded, with a weak lip. Length ofholotype, 0.26 mm; width, 0.11 mm.
Holotype, Reg. no. 68041, from a cliff
near the top of a hill. about 300m westof Nobori. Hane-machi, Muroto City,
Kochi Prefecture. upper part of the Nobori formation, Upper Miocene or Pliocene, few.
This small species was referred to
Trifarina angulosa in japan. Trifarina
angulosa (WILLIAMSON) was originallydescribed from the Recent sediment
without designation of the type locality.
V\·ILLIAl\oJSON (1858, Rec. For. Gt. Br., p.
67. pl. 5, fig. 140) and LOEBLICH and
TAPPAN (1964. Treatise on Invert. Paleo ..
pt. C. Protista 2, p. 571, figs. 450, 1-3)
show that T. angulosa has larger size(ca. 0.60 mm), more slender form, lessoverlapping chambers, and more distinct
lip than those of the present new species.
It is also distinguished from Trifarina
angulosa pauperata (HERON-ALLEN and
EARLAND) (1932. Discovery Repts., v. 4,
p. 398, pl. 12, figs. 40-43) by less inflatedchambers. Other similar form is Trifarina trigona (SEGUENZA) (1862. Accad.
Gioenia Sci. Nat. Catania, ser. 2, v. 18.
p. 110, pl. 2, fig. 10) from the Pleistoceneof Scicily, but it has larger test than thepresent new species and is regarded to
be probably identical with T. angulosa
by CUSHMAN (19·11).
Trifarina shikokuensis is widely distributed from Miocene to Recent on the
Pacilic-side area of japan, and frequentin the Nobori and Ananai formations(up to 3,%).
Ut'igerina rutila CuSHMAN and Toon

280

J{enji KURIHARA
Pl. 28, Figs. 13. 14

Pl. 28. Figs. 17-19

Uvigerina rutila CusH~IAN and ToDD, 19,11.
Contr. Cushman Lah. Foram. Res., v.
17. p. 78. pl. 20. figs. 16-22; BooMG,\ART,1949, Smaller Foraminifera from Bodjoncgoro (Java), Diss. Univ. Utrecht, p. 119;
DRooGER, Hl53, Contr. Cushman Found.
Foram. Res., v. 4, p. 136. pl. 21, figs. 29,
30.

·• Rotalia" translucens PHLEGER and PARKER,
1951. Geol. Soc. Amer. Memoir 46, pt. 2,
p. 25, pl. 12, figs 11, 12; PH LEGER, PAR·KER and Pl~IRsON, 1953, Swedish DeepSea Expcd., v. 7, pt. 1. p. 42. pl. 9, ftgs.
22, 23; PIILEGER, 1960, Ecology and Distribution of Recent Foraminifera. pl. 13,
fig~. 13, 14.

Rare specimens only from the type
locality of the Nobori formation are
identical with CUSHMAN and TODD's
figures from the Pliocene of the Mediterranean region. The Nobori forms
have larger size than the type. This
species shows a large amount of variation in the number of costae. Nobori
specimens have numerous, narrow andweak costae. about 15 or more to achamber. Weal< and short spinose projections are sometimes found at thelower part of the earlier chambers ofthe megalospheric form.

The convexity of the dorsal side of
the Nobori form is considerably variable.
Some specimens have almost flattened
dorsal side. This species occurs throughout the Nobori formation especially inthe upper part (up to 14.%). Diameter,
up to 0.34 mm ; thickness. OJ 1 mm.

Uvigerina substriata AsANO
Pl. 28, Fig. 15
Uvigerirza substriata AsA?-lo. 1938, Jour. GeoL
Soc. Japan, v. 45, p. 614, pl. 17. figs. 21.
22; CusHMAN, 1941, Contr. Cushman Lab.
Foram. Res. v. 17, p. 77. pl. 20, figs. 14.
15: ASAJ';O, 1950, lllusl. Cat. Japan Tert.
Foram., pt. 2. p. 18, figs. 83, 84; AoKI,
1965, Saitama Univ. Sci. Rep., scr. B. v.
5, no. 1. p. 57, 1>L 7. figs. 28. 29.

This species is found in the Nobori
formation in low frequencies (less than1%)- It has been only reported fromthe Pliocene and Pleistocene of the Boso
Peninsula. Length, up to L13 mm; diameter. 0.50 mm.

Eilohedra rotunda (HUSEZIMA
and MAIWHASI)
Pl. 28, Figs. 20~22
Eponides rolundus HusEztMA and MAIWIIASI.
194-1. Misc. Rep. lnst. Natur. Resources.
v. 1. no. 3, p. 399. pl. 34, figs. 12a-c.

This very small species was describedfrom the Nishiyama formation of Niigata
Prefecture. It is similar to the Recent
and Pliocene Californian species of Eilohedra lel'icula (RESIG) (1958, I\·1icropaleontology, v. 4. p. 304, text-figs. l6a-c.).
The Californian species, however. seems
to have more broadly rounded peripheryand more inflated chambers on the ventral side than the present form. It occurs common!}" in the Nobori formation(up to 8%) and rarely found in the Ananai formation. Maximum diameter, 0.13
mm : thickness. 0.08 mm.

Quadrimorphina akiensis
KURIHARA. 11. sp.

Gaue/i no psis Ira nsluce ns (PHL EGER

Pl. 28. Figs. 23-25

and PARKER)

Test small, trochoid, biconvex, umbili-

5 ;19.

Tonohama Benthonic 1• 'o1·a.min·ije·ra

cal region depressed; periphery lobulate;edge broadly rounded; chambers inflated,
five in the last whorl. gradually increasing in size as added; sutures distinct,
slightly curved on both sides, more depressed ventrally; wall smooth, finely
perforate; aperture a low silt extending
from the umbilicus to the periphery witha elongate distinct lip. Length of holotype, 0.27 mm: width, 0.22 mm ; thickness.
0.17 mm.
Holotype. Reg. no. 680-16. from a hillside cliff. at Minamihabuki. Nishinohama,Hane-machi, ivluroto City, Kochi Prefecture, middle part of the Nobori formation, Upper r-.tiocene or Pliocene. few.
This species is similar to Quadrimorphina glabra (CusHMAN) (1927, Scripps
Inst. Oceanogr .. Tech. ser., v. 1. p. 161.
pl. 't llgs. 5, 6) described from the Pacific
Ocean. but differs from it by having
more broadly rounded periphery andmore inflated last-formed chamber.
This small species is found commonlyin the Nobori formation (up to 4,%).
Gyroidrnoides altrformis (R. E. andK. c. STEW,\RT)Pl. 28, Figs. 29-31(;yroidina soldanii var. altiformis R. E. andK.C. STEWART, 1930, Jour. Pal., v. 4, p.
67. pl. 9, figs. 2a-c.
Gyroidina allijormis KliWA:>~o, 1962, Misc. Rep.
Res. Inst. Natur. Resources, no. 58-59. pl.
18, figs. 5a, b.

This species is reported from theLower Miocene to Recent in japan. It
occasionally occurs in the Nobori formation (less than 1%).

Gyroidinoides lorul us (BELFORD)
Pl. 28, Figs. 26-28
Gyroidina lricherasensis LERoY (not BEH:-.rc-

281r>EZ), 196:1. U.S. Gcol. Surv .. Prof. Pap.
454-F. p. 37, pl. 7, figs. 1 3.
Gyroidina torulus IkLFoRD, 1966. Bur. Min.
Hesour. Aust. Rep .. no. 79, p. 168, pl. 28,
figs. 10--20, text-figs. 21. 8-9.

This species was originally describedfrom the Upper Miocene or Pliocene deposits of New Guinea. This forms havethe characteristically protruding lastchamber on the umbilical side of Gyrui·dinoide.~ lricherasen:>is (BEHl\!UllEZ) WH9.
Cushman Lab. Foram. Res., Special Publ.
no. 25, p. 254. pl. 17, figs. 55-57). but thedorsal sutures of the present species isless curved as remarked by LEROY (1964),
and peripheral edge of the last few
chambers is angled. Some Nobori specimens show gently angled peripheraledge almost through the last whorl.
It is rarely found at the type localityof the Nobori formation.
Acknowledgements
The author wishes to thank Professor
Wataru HASHIMOTO of Tokyo Universityof Education for his continuous guidanceand encouragement. Thanks are also due
to Dr. Naoaki AOKI of Tokyo Universityof Education for his kind guidance in thefield and laboratory works as well as inpreparing the manuscript. Dr. Toshio
Konu: of Tokyo University of Educationand ivlr. Sakae OHARA of Chiba University for their useful advices and reading
the manuscript.
References
AoKr, N. (1966): Molluscan Fossils from theNobori Formation Shikoku, Japan. Trans.
Proc. Palaeont. Soc. japan. N. S .. no. 62,
p. 251-259. pL 31.
AsAJ'O, K (1936): New Species of Forami·nifcra from Aki-gun, Tosa Province, Japan. jonr. Geol. Soc. japan. v. 43, no.

282

Ken:ii KURll!ARA

519, p. 942-946, pl. 51-52.
- - (1937): A comparison of the Recent Foraminifera from Tosa Hay and the Pliocene Foraminifera from Aki-gun. Provinceof Tm;a. jour. Geo/. Soc japan. v. 4·1. no520, p. 36-55 (in Japanese).
B.-\:--IDY, 0. L. (1963): Cenozoic planktonic foraminiferal zonation and basinal development in Philippines. !I mer. 1\ssoc. /'etrol.
Geol., Bull., v 47. no. 9, p. 1733-17,15.
- - (1964) : Cenozoic planktonic foraminiferal zonation. Micropa/., v. 10, no. 1, p.
1-17.
BAl':-;ER, F. T. and BLow, W. H. (1967): The
origin, evolution and taxonomy of theforaminiferal genus Pullcniatina Cushman,

1927. Micropa/., \'. 13. no. 2. p. 133-Hi2,
pl. 1-4.
BELFOIW, D. ,I. (1966): Miocene and Pliocene
Smaller Foraminifera from Papua and Xew
Guinea. Bur. Min. Resour. Ausl. Rep .. no.
79, p. 1-306, pl. 1-38.
BoLLI. H. M. (1964):
Observations on thestratigraphic distribution of some warm
water planktonic Foraminifera in theyoung 1\lioccne to Recent. Eel. Ceo/.
He/v., \'. 57, no. 2, p. 5U-552.
- - (1966): The planktonic Foraminifera in
Well Bodjonegoro-1 of Java Eel. Geol
Helv., v. 59, no. 1, p. 449-466, pl. 1.
CusHMAN, j. A. (19-11): Notes on the speciesof Uvigerina and Angulogerina described

Explanation of Plale 28
Unless localitie5 arc given. all from the type locality of the Nobori formation,a hill-side cliff, at Minamihabuki. Nishinohama, Hane-machi. Muroto City. Kochi
Prefecture. All ligured specimens from the Nobori formation.
Fig. L Cyclammina sp. x5, Reg. no. GBO:H.
Figs. 2-4. Spiroloculina akiensis KuRJJJARA. n. sp. x20. 2, 3. llnlotype, Reg. no. 680:15. 2. side
view: :l. apertural view. 4. Reg. no. 68036, horizontal section.
Fig. 5. Nodosaria lusta ScHWAGER. x·l5, Reg. no. 68037.
Fig. 6. Dentalina cf. spinosa D'ORBJGI" Y. X 35. Reg. no. 68038.
Fig::;. 7. 8. Stilostomcl/a sp. A. x55. Reg. no. 68039, a hill-side cliff. at Os6, liane-machi, l'vluroto
City. 7. apcrtural view: 8. side view.
Figs. 9-11. /'ara.fissurina ova/is ToJ>P. x 4'>. Reg. no. <18040. a diff ncar the top of a hill, about:300m west of Nobori, IIane-machi, Muroto City. 9, lL side view; 10. apertural view.
Fig. 12. "Bulimina" affinis n·ORHIC.:-fY. x 45. Reg. no. 68042.
Figs. 13, 14. UL·igcrina rulila Ct-s!l.>.L-\:"i and ToDr>. x 30. 13. l~eg. no. 68043. microspheric form.
14. Reg. no. 680H, mcgalosphcric form.
Fig. 15. Uvigerina substriata i\sA~o. xa5, Reg no. 68045.
Fig. Hi. Trijarina shikolmensis KuJHJJARA, n. sp. x 120. Holotype, Reg. no. 680•11, a cliff near
the top of a hill. about 300m west of Nobori, Hane-machi, Muroto City.
Figs. 17-19. Gaz:elitwPsis translucens (PH LEGER and PARKER). x 90, Reg. no. 68047. 17. dorsal
view : 18. edge view : 19. ventral dew.
Figs. 20-22. Eilohedra rotunda (IlusEZJ:\1A and MARilJJASJ). x 180, Reg. no. 680-18. 20. dorsal
view: 21. edge view: 22. ventral view.
Figs. 23-25. Quadrimorphina akietzsis KLIIHHARA, n. sp. x 100, Reg. no. 68046, a hill-side cliff at
Oso, Hanc-machi, Muroto Citr. 23. dorsal view; 24. edge view: 25. ventral view.
Figs. 26-28. Gyroidinoides torulus (BEJ.Folw). x50. Reg. no. 68049. 26. ventral view: 27. edgeview: 28. dorsal view.
Figs. 29-3l. Gyroidi11oides altifurmis (R. E. STEWART and K.C. STEWART). x50, Reg. no. 68050,
a river-side cliff at Nishiya, Hane-machi, Muroto City. 29. ventral view: 30 edge view: 31.
dorsal view.

KURIHARA :Tonohama Benthonic Foraminifera

Plate 28

7

3

1
4

9

11

12
13

17

14

20

15

16

21

22

23

29

18

19

24

25

30

31

53tJ.

from the Pliocene and Pleistocene. Contr.
Cushman Lab. Foram. Res., v. 17, pt. 3.
p. 70-78, pi 17-20.
HLiANG, T. (1967): Late Tertiary Planktonic
Foraminifera from Southern Taiwan. To·
ho/111 Univ Sci. Rep., ser. 2, v. 38, no. 2,
p. 165-192, pi 15-16.
ISHI\\'ADA, Y. (1964): Benthonic Foraminife.
ra off the Pacific Coast of Japan referred
to Biostratigraphy of the Kazusa group.
Rep. Geol. Surv. japan, no. 205, p. 1-45.
pl. 1-8.
]E"'KINS, D. G. (1964) : Location of the
Pliocene-Pleh;tocene boundary. Cushman
Found. Foram. Res., Contr .. v. 15, pt. 1,
p. 25-27.

KATTo, ]. (1960) : Report of geological investigation. in Report of fundamental
investigation for the establishment of the
Ashizuri-Muroto National Park. Muroto
Section. Knrhi Prefectural Government,
p. 1-20 (in japanese).
KATTO,}., NAKA~IUR.-\, ]. and TAKAYANAGI,
Y. (1953): Stratigraphical and Paleontological Studies of the Tonohama Group,
Kochi Prefecture, japan. Kochi Univ.,
Res. Rep., v. 2, no. 32, p. 1-15 (in Japanese).
KATTO, j. and OZAKI, II. (1955):
MioceneNobori formation of Kochi Prefecture,
Japan. /(ochi Univ., Res. Rep., v. 4, no.
1, p. 1-7 (in Japanese).
LERoY, L. W. (l\!6•1): Smaller Foraminifera
From the Late Tertiary of Southern Oki·

Aki
AnanaiHane
loki
Kakegawa
Kochi
Minamihabuki
MurotoNahari

1i:

~

/t.

r~

;j;j

*Jll

ta

{JI ~

l1t

.w

il'li

l~jn7'4'-

~

{ft

283

Tonolwma Benthonic Forarninifer·a

'*'

f'i
;flj

nawa. U.S. Geol. Surv., Prof. Pap. 454-F.
p. 1-58, pi 1-16.
McTAVISH. R. A (1966): Planktonic Forarn·
inifera from the Malaita Group, British
Solomon Islands. Miaopal., v. 12, no. 1,
p. 1-36, pl. 1-6.
Nor.tuRA, S. (1!137): The Molluscan Fauna
from the Pliocene of Tosa. japan. jour.
Geol. & Gcogr., v. J.1, no. 3-4, p. 67-90,
pl. 6.
SAITO, T. (1962) : Notes on Globigerirza ne·
Pe11thes Tot>D, 1957. Trans. Proc. Palaeorzt. Soc. japall, N. 5., no. 48, p. 331-3·12,
pl. 51, 52.
- - (1963): Miocene Planktonic Foraminife.
ra from Honshu, Japan. Tolwku U11iv.
Sci. Rept., ser. 2, v. 35, no. 2, p. 123-209,
pl. 53-56.
TAKAYAI'AGI, Y. (1953): New Genus andSpecies of Foraminifera found in the
Tonohama Group. Kochi Prefecture. Shi·koku, Japan. Short Papers. JGPS, no. 5,
p. 25--36, pl. 4.
TAKA Y ANAGI, Y. and SAITO, T. (1962) : Planktonic Fora111inifera from the Nobori For·znation, Shikoku, Japan. Tohoku Univ.
Sci. Rep., ser. 2. Spec. vol., no. 5, p. 67106, pl. 24-28.
Tsuclll, R. (1961): On the Late Neogene
Sediments and Molluscs in the TokaiRegion, with Notes on the Geologic His·
tory of the Pacific Coast of Southwest
Japan. japan. jour. Geol. & Geogr., v.
32, no. 3--4, p. 437-456.

Nishiya
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Osu
Ropponmatsu
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Shizuoka
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shall call a Special Meeting at the written request of more than one-third of
the members. The request shall be granted only if the written statement fully
explains the reasons for assembly and items for discussion.
Article 19. Members unable to attend the General Meeting may give an attending member
a written statement signed by himself trusting the bearer with the decisionof business matters. Only one attending member may represent one absentee.
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Addendum 1) Voting in the Council shall be by unsigned ballot.

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CONSTITUTION
of the
PALAEONTOLOGICAL SOCIETY OF JAPAN
ArticleArticleI. The Society shall be known as the Palaeontological Society of Japan.
2. The object of the Society is to promote the study and popularization of palaeon·
tology and related sciences.
Article 3. The Society, to execute Article 2, shall undertake the following business:l. Issue the Society journal and other pub! icarions.
2. Bold or sponsor scientific le6tures and meetings.
3. Popularize the science by field trips, scientific lectures and other projects.
4. Aid and encourage research work; award outstanding contributions to
the Society: carry out the objectives stated in Article 2.
Article 4. To attain the object of the Society, the Society may, by decision of the General
Meeting, establish within it re>earch committees.
Article 5. The society shall be composed of members who arc active or interested inpalaeontology or related sciences.
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l'vlembers.
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Article 8. Fellows are persons who have held Regular Membership in the Society for morethat ten years. have contributed to the science of palaeontology. have been
nominated by five Fellows and approved by the Council.
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They shall be recommended by the Council and approved by the General Meeting.
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