Eocene shallow marine foraminifera from subsurface sections in the Yufutsu-Umaoi district, Hokkaido, Japan

32 Pages·2002·14.4 MB·English

by  Satoshi Hanagata

Paleontological Research, vol. 6. no. 2. pp. 147-178. June 28. 2002
C bs the Palaeontological Society ofJapan
Eocene shallow marine foraminifera from
subsurface sections in the Yufutsu-Umaoi district,
Hokkaido, Japan
SATOSHI HANAGATA
Japan Petroleum Exploration Co. Ltd.. NYK Tennoz building. 2-2-20. Higashishinagawa, Shinagawa-ku,
Tokyo 140-0002. Japan
(Present address: Akita Prefectural Office. 4-1-1 Sannou. Akita-shi. Akita 010-8570. Japan)
Received March 26. 2001: Revised manuscript accepted January 29. 2002
Abstract. In subsurface sections of the Yufutsu-Umaoi district, Hokkaido, northern Japan, three Eocene
benthic foraminiferal assemblage zones were defined in the Ishikari Group and the overlying Poronai
Formation. They are in ascending order: Evolutinella subamakusaensis-Haplophragmoides crassiformis
Assemblage Zone, Globocassidulina globosa-Cribroelphidium sorachiense Assemblage Zone, and Bulimina
schwageri-Angulogerina hannai Assemblage Zone. Assemblagescharacterizingeach zone indicate the littoral
to the inner sublittoral, middle sublittoral, and outer sublittoral paleobathymetric zones, respectively. A
foraminiferal fauna in the upper bathval zone was also identified based on reinterpretation ofprevious stud-
ies. It is composed of calcareous species such as Gyroidina yokoyamai and Plectofrondicularia packardii.
Abundant occurrences ofagglutinated foraminifera in shallower paleoenvironment suggest brackish and re-
lated stratified-water paleoenvironments caused by freshwater input into an embayment called the "Poronai
Sea". Such stratified conditions in coastal shallow marine areas may have formed oxygen-depleted zones as
suggested in the previous study. These data and their paleoenvironmental implications are expected to fur-
nish a basis for further consideration on geohistory of the Paleogene formations and also on the Eocene
foraminiferal fauna of the northwestern Pacific.
Key words: Eocene, foraminifera, Ishikari Group, paleoenvironment, Poronai Formation
Introduction parative taxonomic study of the Paleogene foraminiferal
faunas from Hokkaido with other regions ofthe world, and
The purpose of the present paper is to delineate the recognized some species from the Poronai Formation as an
Eocene shallow marine foraminiferal assemblages from "intermediate-water" fauna. His "intermediate-water" has
borehole sections in the Yufutsu-Umaoi district, southern a depth range of 100-1000 m (Kaiho, 1992b). This range
Ishikari Plain. Hokkaido, northern Japan; to consider almost corresponds to three bathymétrie zones in the mod-
depositional environments: and to describe paleobathy- ern northwestern Pacific coast of Japan according to the
metric distributions of benthic foraminifera. compilation of Akimoto and Hasegawa (1989). They are
Studies of the Japanese Paleogene smaller foraminifera the outer sublittoral zone (approximately 70 to 180 m),
began with the report of Yokoyama (1890). Following upper bathyal zone (180 to 550 m) and upper middle
him. studies have been conducted mainly on the fossils bathyal zone (550 to 900 m). However, correlation of
from the Ishikan Group and the overlying Poronai each paleobathymetric zone with the foraminiferal fauna
Formation in the coalfield regions of Hokkaido and from was not discussed in the report.
the Kyoragi Formation of the Hondo Group in the Deep marine foraminiferal assemblages generally in-
Amakusa Islands. Kyushu, southwestern Japan (e.g. Asano, clude elements transported from shallower marine environ-
1952. 1954. 1958, 1962: Asano and Murata. 1957: Fukuta, ments by bottom currents and/or gravity currents (Zalesny,
1962). Paleogene foraminiferal faunas at various localities 1959; Ingle, 1980). This means that the deep marine fauna
in Hokkaido were studied by Kaiho M983. 1984a, b. c) can be recognized only after the shallower marine fauna
who reported on their stratigraphie and paleogeographic has been identified. However, little is known about the
distributions. Kaiho (1992b) also conducted a com- Paleogene shallow marine foraminiferal faunas in
D
148 Satoshi Hanagata
©well location
MagaribuchiFormation
' UlsunaiFormation
K SankebetsuFormation
Of(lowerpart)
\ -
j
\I »»'Tappu+ShimokineFormation
rumoiii\
B
Ashibetsu
Studyareaof
Kita-AkebonoSK-1 MITI Umaoi UjiiéandWatanabe
(1960)
141°7'30" 141°45'
42=42' |- _|42»42'
Poronai
£- +MomijiyamaFormation -)43°
42°40' |- Numanohata SK-4D -|42°40' YufGuatssuFOiielldand ft *'"%eJd f' ^\ MainYstuubdayraireaof
Kaiho(1984a,b)
t>K-3D
3
Tomakomai Port -|42°38'
141°45'
2km PacificOcean
Figure 1. Index map showing the well sections studied. A = Dashed lines denote isopachs ofthe Poronai Formation and its equivalents
drawn in a 500-meterthickness interval (Japan Natural Gas Association and Japan Offshore Petroleum Development Association, 1992). Double
circles indicate the sites of the wells controlling the isopachs. Dark areas show surface distribution of the Poronai Formation, Momijiyama
Formation, and theirequivalents after Yamada etal. (1982). B = Location ofthe wells in the Yufutsu oil and gas field. Double circles indicate
the sites ofthe wells, and small dots indicate the bottom ofthe wells. Thick lines indicate wells used in this study.
Hokkaido. The material I examined in the present study is penetrating the Paleogene rocks, namely, the Ishikari
from marine strata (Poronai Formation) which grades from Group and the overlying Poronai Formation (Yufutsu
nonmarine coal-bearing formation (Ishikari Group), repre- Research Group ofJAPEX Sapporo et al, 1992; Fujii and
senting a transgressive phase, and thus provides an oppor- Moritani, 1998; Kurita and Yokoi, 2000). The present
tunity to study the shallow marine fauna. Moreover, study was conducted on three well sections in the Yufutsu
because paleoenvironments of the Paleogene in Hokkaido oil and gas field, Numanohata SK-3D, Numanohata SK-
and the northwestern Pacific region have not been well 4D and Kita-Akebono SK-1D. In addition, the well MITI
studied, data on paleobathymetric distribution of foramini- Umaoi, drilled in the Umaoi Hills about 25 km north ofthe
fera examined in the present study are expected to provide Yufutsu oil and gas field, was also investigated (Figure 1;
a basis for further studies in the region. MITI =Ministry ofInternational Trade andIndustry). The
Japan Petroleum Exploration Co. Ltd. (JAPEX) has been present study refers to the area including these wells as the
exploring oil and natural gas in the southern Ishikari Plain. "Yufutsu-Umaoi district".
Since the discovery ofthe Yufutsu oil and gas field, whose
reservoir is in the Cretaceous granitoids and Paleogene
conglomeratic formations, many wells have been drilled
Eocene shallow marine foraminifera 149
Geological setting mately 780 m.
Lithology of the Ishikari Group and the Poronai
The middle Eocene Ishikari Group crops out in the hilly Formation in the study well sections is similar. Its vertical
areas of the Yubari and Sorachi coal fields (Kaiho. 1983: changes are as follows in ascending order; basal conglom-
Iijima. 1996). It is composed of alternating marine and erate bed, medium to finer sandstones with siltstone beds,
nonmarine formations. Thick coal beds are present in the and finally siltstones and mudstones. The basal conglom-
nonmarine part. erate ofthe lowermost part ofthe Ishikari Group grades up-
The Poronai Formation, which overlies the Ishikari ward, intercalating with finer-grained sediments, into an
Group, outcrops in the Yubari and Ashibetsu districts alternation sequence of medium to fine sandstone beds and
(Figure 1). It is composed mainly ofmassive siltstone that olive-black to olive-gray siltstone beds. Coal beds are fre-
intercalates with acidic tuffbeds in the middle to upper part quent. The sandstone and siltstone beds of the uppermost
(Kaiho. 1983). The geologic age ofthe Poronai Formation Ishikari Group grade upward into the siltstone and
in the Yubari district was determined by calcareous mudstone ofthe Poronai Formation, which contains marine
nannofossils to be late Middle Eocene to Late Eocene in fossils such as foraminifera, ostracods, dinoflagellates, and
age (Okada and Kaiho. 1992). Broad distribution of the fragments of mollusks. The Poronai Formation consists
Poronai Formation and its equivalents in the subsurface of mainly of olive-gray or dark gray siltstone and mudstone.
the Ishikari Plain is confirmed by boreholes (Figure 1A: Tuffand sandstone beds intercalate in the upper part of the
Japan Natural Gas Association and Japan Offshore formation in Kita-Akebono SK-1D and MITI Umaoi,
Petroleum Development Association. 1992; Japanese where the formation is thicker than in the other well sec-
Association for Petroleum Technology. 1993). tions. The Upper Oligocène Minaminaganuma Formation
Many researchers have discussed the stratigraphie rela- unconformably overlies the Poronai Formation in the
tionship between the Ishikari Group and the overlying Yufutsu-Umaoi district (Kurita and Yokoi, 2000). The
Poronai Formation since Yabe (1951) proposed their Lower Oligocène Momijiyama Formation (Kaiho, 1983;
heteropic facies (synchronous) relationship (Asano. 1952, Kurita and Miwa, 1998), which overlies the Poronai
1954: Saito. 1956: Sasa, 1956: Sasa et ai, 1953; Yabe and Formation in the Yubari district, is not present in the study
Asano. 1957: Uchio. 1961, 1962), although no conclusive area.
interpretation has yet been drawn. The present study as- The upward fining of the sediments without any break
sumes a conformable contact between them in the borehole from the Ishikari Group to the lower part of the Poronai
sections studied here' This interpretation is based on tran- Formation in the Yufutsu-Umaoi district suggests a
sitional characteristics of lithology as discussed later. transgressive sequence.
Lithostratigraphv of study sections Samples and methods
Lithologie columns of the study wells are presented in All borehole samples used in the present study are ditch
Figure 2. Lithologie descriptions ofeach section are based cuttings. Borehole conditions during drilling were good,
on the wellsite survey of ditch cuttings. Numbers shown and contamination caused by the caving was negligible.
on the left of each column are drilling depths from the sur- Samples were taken every 20 m; additional samples were
face. All study wells of the Yufutsu oil and gas field are taken from the siltstones in the coal-bearing formation. In
deviated, therefore drilling length differs from true thick- the Kita-Akebono SK-1D well, samples were collected at
ness of formation. In addition, formation contacts are every 10 m for most ofthe studied interval. A total of 173
placed on the basis of wireline logs whose depths may not samples were examined.
match the drilling depths measured by the length of drill All samples were oven-dried. Subsamples of about
pipes. 100 g were soaked in boiled sodium sulfate supersaturated
Interpretations of wireline logs prove that the uppermost solution for about three hours. After removing excess so-
part of the Poronai Formation is missing because of a fault lution, soaked samples were left more than three days.
in Numanohata SK-3D. Also because of a fault, an inter- Then they were wet sieved through a 125 um-opening
val from the lowermost Poronai Formation through the screen. All specimens in the residues were picked and
upper part of the Ishikari Group is repeated in Numanohata identified under a binocular microscope.
SK-4D. Percentages of planktonic species, agglutinated species,
After correcting for well deviations and formation dips, and calcareous benthic species, and total populations were
the true thickness of the Poronai Formation in the Yufutsu determined for these samples. Diversity, species richness
oil and gas field is estimated as approximately 450 m to (number of species) as well as "Simpson's Index for
500 m. while in the vertical well MITI Umaoi. it is approxi- Diversity" (SID: Simpson, 1949) were used to analyze the
150 Satoshi Hanagata
South
LEGEND MITI Umaoi
Claystone KITR-RKEB0N0
I |
Mil Siltstone
SK-1D
IW11 Sandstone
Conglomerate rWJ
| Coal
ED]Tuft
Dv'-j intrusionrock
A pumice-bearing
containcoalymatter Li''
•
Ostracoda
^CalcareousNannofossil
NUMRNOHRTH SK-4D
^
NUMRNOHRTR
SK-3D
T± =* -
SD. O Bz«ZïhŒ-
IDO2. —r O5Z BSE
u.
Base of
foraminiferal
occurrence
.iL...
JXK
o
i>o<
Figure 2. Stratigraphie correlation based on lithostratigraphy and wireline geophysical loggings of the study wells. Well sections are
arranged at the base ofthe Poronai Formation.
Eocene shallow marine foraminifera 151
• KITR-RKEBONO
F
Li. SK-1D
S
Stratigraphie distribution
Total calcareous of selected species
ce population benthic(%) (numbersofspecimensin 100grock)
e > «100 < 10Q
z 60 40 100 40 60 20
fST 306733.0100000mmm 5JI" r -^>cutCCOcEC>ooc-eoODoO). Jm-.cCmCo0cOÉCCOD)). <-oCCocciCCuc5DonDOo" I""J-cCccCtoCOc£Q3oOODo? JLcCE3<CCCeLOoDOO —s,oCCgCCÇuc:gOOOoO0- Bio(sTsuhtbirdRsaiatvsriitgesuridaoypn)hic
k-I \ L 1"C3D 'I CD CCuoOOHCO cEDJO) forianmtienrivfaelral
-Q ,c
zo 3200m ; ^^ S 8 CCOL Buliminaschwageri-
Angulogerina hannai
Assemblage Zone
k
t"
f
r
3300m
ec ;
Globocassidulina
s
zO 3400m p > [? É Crigbrlooeblopshaid-ium
o sorachiense
—
Assemblage Zone
3500m r
i
1
1
3600m ! !
3628.0m [_ >l
Evolutinella
]
b*-r subamakusaensis -
a. 3700m r Haplophragmoides
o crassiformis
cc Assemblage Zone
CS
H
3800m
cc
cc
j
c
Barren
c/i 3900m tgggj foraminiferal
[Es» interval
WJlrr ''
Fori_egend, see Figure 2
d
Figure 3. Stratigraphie occurrences ofthe selected species in Kita-Akcbono SK ID.
152 Satoshi Hanagata
South
LEGEND
TotalpopulationofCalcareousBenthicforaminifera
Y//////A TotalpopulationofPorcellaneousforaminifera
| TotalpopulationofAgglutinatedforaminifera
PercentageofEvolutinellasubamakusaensis+Haplophragmoidescrassiformis
PercentageofGlobocassidulinaglobosa+Cribroelphidiumyabei
PercentageofBuliminaschwageri+Angulogerinahannai
For lithology, see Figure 2.
NUMHNOHflTfl SK-4D
Total Index
population species
Figure 4. Stratigraphie correlation ofthe study wellsbasedon the assemblagezonesofforaminifera. Leftcolumnsofeach well section are
cumulative (agglutinated, porcellaneousandcalcareous foraminifera) total populations in 100grocksamples. Curves inrightcolumn indicate per-
centage ofindex species against total population.
Eocene shallow marine foraminifera 153
North
MITI Umaoi Foraminiferal
Assemblage
Total Index
KITfl-HKEBONO population species
Zones
500 50%
SK-1D
Total index
population species
Bulimina
schwageri-
Angulogerina
hannai
Globocassidulina
globosa -
Cribroelphidium
sorachiense
Evolutinella
subamakusaensis
Haplophragmoides
crassiforms
Barren
foraminiferal
interval
154 Satoshi Hanagata
assemblages. ous species such as Melonis pompilioides and Pullenia
Only populations of specimens identified at species rank salisburyi than in the assemblages of the underlying E.
were used to calculate diversity; species identified as subamakusaensis-H. crassiformis Assemblage Zone.
"spp.", "sp. indet.", and "miscellaneous" were excluded. Bulimina schwageri-Angulogerina hannai Assemblage
—
Zone. Although this zone is similar to the G. globosa-C.
Biostratigraphy sorachiense Assemblage Zone, it is distinguished by larger
numbers and higher frequencies of both Bulimina
As aresult ofanalysis, 47 species belonging to 34genera schwageri andAngulogerina hannai. Assemblages ofthis
were identified from 162 samples (Appendix 1-3). Preser- zone also contain numerous agglutinated foraminifera, but
vation of most specimens was poor. have higher calcareous foraminiferal abundances and
The present study established assemblage zones based on higher species diversities compared to those ofthe previous
associations of index species based on the foraminiferal two assemblage zones.
distribution. Index species are species that are abundant
and have similar stratigraphie distribution among all Paleoenvironment
borehole sections.
Occurrences ofselected species are plotted against depth The foraminiferal fauna seen in the present material is
for Kita-Akebono SK-1D (Figure 3). This plot reveals characterized by the occurrence of abundant agglutinated
that some of the species have distinct similarities in foraminifera, especially species belonging to the Lituolidae
stratigraphie occurrences. On the basis ofthis, the follow- and Cyclamminidae. No similar fauna so dominated by
ing three associations are recognized. these agglutinated foraminifera has been reported from
1) Evolutinella subamakusaensis and Haplophragmoides anywhere else in the world. Therefore, paleoenvironmen-
crassiformis. tal implications of this peculiar fauna are considered based
2) Globocassidulina globosa and Cribroelphidium sora- on the facts of modern foraminiferal distribution. In this
chiense. section, the paleobathymetry of each assemblage zone and
3) Bulimina schwageri and Angulogerina hannai. then the additional paleoenvironmental implications are
These three associations represent zones which occur in discussed.
all the studied sections in the same stratigraphie order, and
each has aunique distribution within the section (Figure 4). Paleobathymetry
The upper part of the Poronai Formation above the As discussed by Ingle (1980) and McDougall (1980),
Bulimina schwageri-Angulogerina hannai Assemblage paleobathymetric zonations of the Eocene Pacific Ocean
Zone in Kita-Akebono SK-1D (depth 3200-3075 m) is re- are similar to the modern zonations. Paleobathymetric
ferred to here as "rare foraminiferal interval" because the zonations used in the present study follow Akimoto and
number offoraminifera in the interval is so small. As dis- Hasegawa (1989)'s compilation of bathymétrie distribu-
cussed later, boundaries between these assemblage zones tions of Recent benthic foraminifera around the Japanese
are environmentally controlled and therefore may not indi- Islands.
cate strict time horizons. Evolutinella subamakusaensis-Haplophragmoides cras-
—
Characteristics of each assemblage zone are discussed siformis Assemblage Zone. This zone is considered to
below. Boundaries between the zones are defined by have been deposited in a shallow marine environment for
changes in the abundances of the index species. the following reasons. First, it overlaps the coal-bearing
Evolutinella subamakusaensis-Haplophragmoides cras- formation of the Ishikari Group that is of paralic origin.
—
siformis Assemblage Zone. This zone is characterized by Second, it yields benthic foraminifera Cribroelphidium
abundant occurrences of the two index species. It also sorachiense and Sigmoidella pacifica, both of which sug-
characteristically includes agglutinated foraminifera such gest shallow marine (sublittoral) deposition. Most modern
as Reticulophragmium amakusaensis, Cyclammina pacifi- Cribroelphidium live in shallow marine (outer sublittoral
ca, and Recurvoidella sp. cf. R. lamella. The calcareous zone or shallower) environments, such as Cribroelphidium
foraminifer Cribroelphidium sorachiense occurs rarely in bartletti (Elphidium bartletti of Loeblich and Tappan,
this zone. Assemblages of this zone are characterized by 1953), C. clavatum (E. clavatum ofBuzas, 1966 andLagoe,
generally small populations and low diversity. 1979). Sigmoidella pacifica also lives in modern shallow
Globocassidulina globosa-Cribroelphidium sorachiense marine environments (Jones, 1994, as S. elegantissima).
—
Assemblage Zone. In addition to the two index species, Third, assemblages of this zone lack Globocassidulina and
this zone includes abundant agglutinated foraminifera such Bulimina whose modern species live at depths greater than
as Evolutinella subamakusaensis, Recurvoidella sp. cf. R. the inner sublittoral zone in the seas around the Japanese
lamella, and Budashevaella symmetrica, and more calcare- Islands (Akimoto and Hasegawa, 1989). Thus, the assem-
Eocene shallow marine foraminifera 155
—
blages of the E. subamakusaensis H. crassiformis FORAMINIFERALZONES
Assemblage Zone are considered to indicate a paleobathy- (Kaiho, 1984a, b,c)
W\A
metric range from the littoral zone to the inner sublittoral Nomonezoensis- MEGA-FOSSILZONES
zone. MJ F8 Cyclammmapaciffica (Teshima, 1954)
Assemblage-zone
Globocassidulina globosa-Cribroelphidium sorachiense
— Buliminaschwageri- Upper
Assemblage Zone. The assemblages of this zone include F7 Gyroidinayokoyamai
H Bathyal
Globocassidulina. which has its upper depth limit in the Assemblage-zone
c
middle sublittoral zone (Akimoto and Hasegawa. 1989). o g]
In addition. C. sorachiense. C. wakkanabense and — Haplophragmoides
Sigmoidella pacified, all of which indicate shallow marine Ere F6 Cycslubaemvmomlautpuascitica É.
oi- Assemblage-zone
environments, occur frequently in this —zone. Therefore, Ü. rö\
the assemblages of the G. globosa C. sorachiense ,rgHe "9" Upper
Assemblage Zone are thought to indicate the middle o F5 Buliminaschwageri- Bathyal
sublittoral zone. o H.umbilicalus B
Q. Assemblage-zone
Bidimina schwageri-Angidogerina hannai Assemblage
Zone.—The assemblages ofthis zone are similar to those of F4 H.H.usmbuibleivcoaltuutsus- A
Assemblage-zone
the Globocassidulina globosa-Cribroelphidium sorachi-
F3 H.tanaii- A0
ense Assemblage Zone except that the percentages of W\A H.subevolutusA.-z.
Bidimina andAngulogerina are higher. Since modern spe- MJ : Momijiyama Formation
cies ofBidimina andAngulogerina have upper depth limits
Figure 5. Stratigraphie relation between the megafossil zones
in the outer sublittoral (Akimoto and Hasegawa. 1989), the and foraminiferal assemblage zones.
Bidimina schwageri-Angidogerina hannai zone is consid-
ered to have been deposited in the outer sublittoral zone.
The presence of Cribroelphidium species suggests either in Consequently, the interval from the coal-bearing forma-
situ deposition or transport of shallower-water species into tion of the Ishikari Group to the Poronai Formation in the
the outer sublittoral zone, possible by marine currents. Yufutsu-Umaoi district accumulated during a single
Kaiho (1992b) reported B. schwageri and A. hannai in transgressive and regressive sequence. This is only ob-
his "intermediate-water" which ranges from depths of 100 served in the Kita-Akebono SK-1D well, since the upper-
to 1000 m. As the depth range ofthe outer sublittoral zone most part of the Poronai Formation is missing in the other
overlaps the range of Kaiho's "intermediate water," the well sections.
present study agrees with Kaiho's interpretation on B.
schwageri and A. hannai. Upper bathyal assemblages
—
Historical paleobathymetric change. Paleobathymetric As a result of the study discussed above, species compo-
interpretation of the three assemblage zones shows that the sitions from the littoral zone to the outer sublittoral zones
sedimentary environments during the deposition of the during the Eocene were described. Foraminiferal fauna of
upper pan of the Ishikari Group and the Poronai Formation the upper bathyal zone (water depth approximately 180 to
in the Yufutsu-Umaoi district changed from the littoral 550 m in northwestern Pacific coast of northern Japan),
zone to the inner sublittoral zone, then to the middle which is one rank deeper than the outer sublittoral zone, is
sublittoral zone, and finally to the outer sublittoral zone. not observed in the Yufutsu-Umaoi district. However, ex-
The successive change in paleobathymetry suggests that the istence ofstrata which show the upper bathyal environment
stratigraphie interval from the first occurrence of was reported by Teshima (1955) in the middle part of the
foraminifera to the B. schwageri-A. hannai Assemblage Poronai Formation in the Yubari district. Here, I describe
Zone was deposited during a single transgressive phase. upper bathyal foraminiferal fauna based on the correlation
This interpretation supports the observation that the Ishikari between biostratigraphy of Teshima (1955) and Kaiho
Group and the Poronai Formation are conformable in the (1984a, b). Teshima (1955) studied megafossils and di-
Yufutsu-Umaoi district. vided the Poronai Formation into the A to I megafossil
The "rare foraminiferal interval" at the depth 3190 m and zones in ascending order, stating that the megafossil assem-
SKID
shallower in Kita-Akebono well indicates that a re- blages of the B-C and H-I zones are similar to the
gressive phase followed the transgression discussed above. molluscan association found in water depth interval of 200
Evidence ofthe regression is based on the successive disap- to 300 m, offshore Otaru, Sea ofJapan. This water depth
pearances of the species. B. schwageri. A. hannai, G. in the Sea of Japan falls within the range of the upper
globosa. and C. sorachiense. Shoaling of water depth pre- bathyal zone (Akimoto and Hasegawa, 1989). According
vented distribution of these depth-controlled species. to the stratigraphie relationship between these megafossil
156 Satoshi Hanagata
Bathyal Sublittoral Bathval
AGGLUTINATED Species Inner | MiddleI Outer I Upper Cribroelphidium ishikarSipeencseies(Kaiho) InRner MidRdle OuRter UpRper
Alveolophragmium sp.Aofthepresentstudy R Cribroelphidium sorachiense (Asano) R A A C
Ammobaculites sp.AotKaiho,1984b A Cribroelphidium sorachiense (Asano)var.A R
Ammobaculkites akabiraensis Asano R R R Cribroelphidium wakkanabense (Kaiho) R C A
Ammcdlscus pahanus Hedberg R C R Dentalina sp.cf.D.kushiroensisYoshida R
Ammodiscus tenuis Brady R C C Dentalina sp.cf.D.subsoluta (Cushman) R C
Ammomarginulina sp.AotKaiho,1984b R Dentalina cocoaensis (Cushman) R C
Bathysiphon eocemca CushmanandHanna R R C C Dentalina dusenbun/l Beck R C
Bathysiphon vemoniHamlin R R R C Dentalina minuta Kaiho R
Budashevaella sp.aft.B.muttlcamerata (Voloshinova) R Elphidium mabutiiAsano' ? ? R ?
Budashevaella symmetrica (UjiieandWatanabe) R C C R Elphidium sp.AofKaiho,1984b R
Cribrostomoldas sp.cf.C.cretacea CushmanandGoudkof R R ? Epistominella exiguamultiloculala Kaiho c
Cyclammina azoensisAsano R R R R Eponldes lobatus Kaiho R c
Cyclammina orbicularis Brady R Fissurina marginata (Montagu) R R C
Cyclammina pacitica Beck R C A A Fissurina sp.AofKaiho,1984b R R
Cyclammina sp.äff.C.pusilla Brady R R R R Fursenkoina uchioiKaiho R C
Cyclammina tani Ishizaki R Glandulina laevigataovata CushmanandApplin C c C
Cyclammina sp.Aofthepresentstudy R Globobulimina ezoensis (Yokoyama) c C
Cyclammina sp.Bofthepresentstudy R Globocassidulina globosa (Hantken) A c C
Discammina sp.AotKaiho,1984b R R C R Globocassidulina sp.AofKaiho,1984b R C
Discammina sp.BofKaiho,1984b ? R R Globulina gibba (d'Orbigny) R C
Discammina sp.CofKaiho,1984b R R R Guttulina problema (d'Orbigny) C C c C
Eggerella sp.AotKaiho,1984b R Guttulina takayanagiiKaiho R R R R
Evolutinella subamakusaensls (Fukuta) A C R R Gyroidina yokoyamai (UjiieandWatanabe) A
Ghmospira gordialis JonesandParker R Heterolepa poronaiensis Kaiho R R C
Haplophragmoides crassilormisKaiho C C R R Lagena sp.cf.L.laevis (Montagu) R R R R
Haplophragmoidos sp.cf.H.dellata Sullivan R Lagena sp.cf.L.perlucida (Montagu) C
Haplophragmoides rugosussoyaensis Yasuda c C R Lagena sp.cf.Lsulcata (waiterandJacob) R
Haplophragmoides tanaii Kaiho c C Lagena striata (d'Orbigny) R R
Haplophragmoides yokoyamai Kaiho R R R Lagena sp.AofKaiho,1984b R
Haplophragmoides sp.Aofthepresentstudy R ? Lenticulina antipoda (Stäche) C
Haplophragmoides sp.Bofthepresentstudy R R R ? Lenticulina ishikariensis Kaiho C
Haplophragmoides sp.Dofthepresentstudy C R R ? Lenticulina sp.AofKaiho,1984b R R
Hyperammina elongata Brady R R Lenticulina sp.BofKaiho,1984b R
Karrerulina sp.cf.K.hokkaidoana (Takayanagi) C R Melonis affinis(Reuss) R R R
Martinottiella crassa Kaiho R Melonls elegans Kaiho R C
Martinottlella reclldelicala Kaiho R Melonis lobatus Kaiho R
Placenlammlna sp.Aofthepresentstudy R R ? Melonis sp.cf.M.multisuturalisvanBellen R
Poronaia poronaiensis (Asano) C R C R Melonis pompilioides (FrtchelandMoll) R C C C
Recurvoidella sp.cf.R.lamella (Grzybowski) A C C ? Melonis subevolutus Kaiho R R
Recurvoides sp.Aofthepresentstudy R ? Nodogeneria sp.cf.Nlepidula (Schwager) R C
Reophax minutirectus Kaiho R Nodosaria amchitkaensis (Todd)** C
Reophax multicamerarus Kaiho R C Nodosaria longiscatad'Orbigny R C
Reophax tappuensis Asano C C C C Nonion ezoensis Kaiho R C
Reliculophragmium amakusaensis (Fukuta) C C A ? Nonion subangularis Kaiho R R
Rhabdammina sp- R R Nonion takayanagii Kaiho R
Silicosigmoilina? sp- R Nonionella japonica (Yokoyama) R R
Spiroplectammina nuttaliiLalicker R Nonionella mabutiiAsano R
Trochammina sp.cf.T.asagaiensisAsano C C Oolina hexagona (Williamson) C
Trochammina squamata JonesandParker C R Oolina simplex Reuss R C
Verneuilinula takavanaoii (Kaiho) R R Oolina sp.cf.0.globosa (Montagu) R R
PORCELLANEOUS Oolina sp.AotKaiho,1984b R
Quinqueloculina seminulacompacta Serova R C C R Planulina poronaiensis Asano R
Triloculina Qibba d'Orbiqny R R R R Plectotrondicularia delicatula Kaiho R
CALCAREOUSHYALINE Plectolrondicularia packardii CushmanandSchencki C
Anomalinoides sasaiKaiho R C Plectotrondicularia smithl Kaiho c
Anomalinoides sp.AofKaiho,1984b R Plectotrondicularia vaughani Cushman R
Bolivina ouplectella Yokoyama R Praeglobobulimina pymla (d'Orbigny) R R R
Brizarina saitoi Kaiho R C Praeglobobulimina ovata (d'Orbigny) R R
Brizahna serrata Kaiho R C Praeglobobulimina pupoides (d'Orbigny) C
Bulimina schwageriYokoyama A A Procerolagena sp.cf.P.gracilllma (Sequenza) R R
Bulimina sculptilus Cushman C Pseudonodosaria conica (Neugeboren) R R R
Bulimina sp.cf.8.sculptilus Cushman R C Pseudonodosaria in/lata (Costa) R R R C
Bulimina yabei AsanoandMurata C R Pseudopolymorphim hokkaidoana Kaiho R R R R
Buliminella robertsiHoweandEllis C Pullenia eocenica CushmanandSiegfus R R C ?
Cancris torquertusCushmanandTodd R Pullenia Salisbury! R.E.andK.C.Stewart C C C
Cassidulina lobatula Kaiho R Saracenaria ujiiei Kaiho R R
Cassidulina yubariensis Kaiho R R Sigmoidella pacitica CushmanandOzawa C c C C
Cassidulinoides howeiCushman C Sigmomorphina schenckiCushmanandOzawa C C
Chilostomella sp.cf.C.cylindoroktes Reuss R Sigmomorphina sp.AofKaiho,1984b R
Cibicidos elmaensis Rau R R R Stihstomella sp.cf.S.japonica (Ishiwada) R
Cibicides complanatus Kaiho R Tritarina hannai (Beck) c C
Cibicides sp.AotKaiho,1984b R Uvigerina ombetsuensis Kaiho R
Cibicides sd.BofKaiho,1984b R Valvulineria lymani(Yokoyama) R R I
Figure6. Paleobathymetric distribution ofbenthic foraminifera. Data ofAsano (1952), Ujiié and Watanabe (1960) and Kaiho (1984a, b)
are also interpreted by the present study. R= Rare; C = Common; A = Abundant. Occurrences ofspecies shown in boldface are supposed tobe
important forpaleobathymetric interpretations. Occurrences ofspecies with * are restricted in the Utsunai Formation (Kaiho, 1984b), and with **
to the Omagari Formation (Asano, 1952; Kaiho, 1984b).
zones (B-C and H-I) and foraminiferal assemblage zones Bulimina schwageri and Angulogerina hannai (Kaiho,
indicated by Kaiho (1984a; Figure 5), it is obvious that 1984a, c) as well as numerous calcareous foraminifera such
foraminiferal assemblage zones F5 and F7 (Kaiho, 1984a, as Gyroidina yokoyamai and Plectofrondicularia packar-
c) were deposited in the upper bathyal zone. The dii. These latter two species were not encountered in the
foraminiferal assemblages ofthese zones contain abundant Yufutsu-Umaoi district and therefore must represent the