ELSEVIER

Sedimentary Geology 122 (1998) 151–163

Glaucony and carbonate grains as indicators of the condensed section:
Omma Formation, Japan
Akihisa Kitamura *Institute of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422, Japan
Received 15 January 1997; accepted 2 July 1997

Abstract
The fifth-order depositional sequences of the Early Pleistocene Omma Formation exposed along the Japan Sea coastof central Japan were formed by glacial-eustasy during oxygen isotope stages 50 to 28. In each depositional sequence,
two ecostratigraphic datums are always present: the appearance and disappearance datums of warm-water molluscan
species. These datums are independent of sequence stratigraphic concepts, because the establishment of them is based on
immigration events of molluscan species associated with glacio-eustatic sea-level changes. Determination of time planes
shows that the appearance datum seems to occur near the midpoint of sea-level rise on the glacial to interglacial shift
in deep-sea δ18 O records. In order to evaluate the significance of the condensed section in sequence stratigraphy andalso to facilitate its recognition, this study examines the stratigraphic relationship of the condensed section indicators,
glaucony and carbonate grains, with respect to the position of the ecostratigraphic datums in depositional sequencesof the Omma Formation. The results show that the maximum concentration of carbonate grains is a more reliablemaximum flooding surface indicator than the concentration of glaucony. The combination of indicators of condensed
section and ecostratigraphic datums represented by incursion epiboles enables the boundary between transgressive andhighstand systems tracts to be recognized in the inner shelf parts of depositional sequences. Moreover, truncation of
ecostratigraphic datums during sea-level falls demonstrates significant erosion at the sequence boundaries. Integration ofclimatic palaeoecology and sequence stratigraphy permits a level of correlational precision of the order of a few thousandsof years.  1998 Elsevier Science B.V. All rights reserved.
Keywords: Early Pleistocene; sequence stratigraphy; ecostratigraphy; condensed section; maximum flooding surface;sea-level change

1. Introduction
Both type 1 and 2 depositional sequences havetransgressive and highstand systems tracts (e.g. Vailet al., 1991). The physical boundary between themis called the maximum flooding surface. This surŁ Corresponding

author. Tel.: C81 54 2384798; Fax: C81 54
2380491; E-mail: seakita@sci.shizuoka.ac.jp

face commonly occurs within the top of, or at thebase of, a condensed section caused by very low
sedimentation rates (e.g. Vail et al., 1991; Abbott
and Carter, 1994). Stratigraphic condensation on thecontinental shelf may be characterized by concentrations of planktonic organisms, glaucony, sulphides,
phosphate, and airborne particles such as volcanic
ash and iridium (e.g. Loutit et al., 1988; Baum and
Vail, 1988). Condensed sections usually coincide0037-0738/98/$ – see front matter c 1998 Elsevier Science B.V. All rights reserved.
PII: S 0 0 3 7 - 0 7 3 8 ( 9 8 ) 0 0 1 0 3 - 1

152

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

with zones of maximum diversity and abundanceof fossils. On the other hand, condensed sectionsin epeiric settings are characterized by higher totalorganic carbon, reduced oxygen values, low concentrations of benthic foraminifera, and minimal or noburrowing, compared with rocks deposited during
more elevated sedimentation rates (Pemberton et al.,1992). Although the character of condensed sections
varies according to geologic settings, any condensed
section is interpreted as a sediment-starved interval that was caused by the trapping of terrigenous
sediments during times of relatively rapid sea-level
rise and marine flooding. Thus, the distribution of
low sedimentation rate indicators has been used torecognize the condensed section, maximum flooding
surface and the highstand and transgressive systems
tracts.
With the exception of a few studies (e.g. Saito,
1991), most studies have been based on pre-Pliocene
sedimentary sequences, where the sea-level signature
is not known independently but has to be inferredfrom the sediments under study. One of the exceptions was a depositional sequence of shelf and upper
slope facies formed in response to Late Pleistocene
to Holocene sea-level changes but the distribution ofindicators of the condensed section were not investigated in detail (Saito, 1991). Thus, the purpose ofthis paper is to examine the relationship between the
distribution of glaucony and carbonate grains as indicators of the condensed section, and true sea-levelchanges.
The Omma Formation is ideal for this purpose,
because its middle part is composed of eleven depositional sequences deposited during glacio-eustatic
sea-level changes between about 1.5 and 1.0 Ma(Kitamura and Kondo, 1990; Kitamura et al., 1994).
Moreover, each depositional sequence in the Omma
Formation contains two chronostratigraphic horizons, namely the appearance and disappearance datums of warm-water molluscan species (Kitamura,1995). Because these datums are based on the frequency variations of climatically controlled molluscan associations, their recognition is independent of
sequence stratigraphic criteria. Thus, using these twohorizons the sequence stratigraphic significance ofconcentrations of glaucony and carbonate grains canbe evaluated.

2. Depositional sequences of the Omma
Formation
The Omma Formation is exposed around
Kanazawa City on the Japan Sea coast of central
Japan (Fig. 1). The sedimentary basin is situated ina back-arc position with respect to the subducting
plate boundaries between the Pacific, Philippine andEurasia plates. Eleven cyclothems are recognized in
the middle part of the Omma Formation (Kitamura etal., 1994). These cyclothems are numbered upwards
in succession from 1 to 11 (Fig. 2). In this paper, cyclothems of the Omma Formation at the type section(Okuwa) and at Yuhidera are examined (Fig. 1).
The type locality of the formation is located in
the bed of the Saikawa River, Kanazawa City. Except for cyclothem 9, all sequences can be observed
at Okuwa (Fig. 2). The thickness of individual cyclothems exposed at this section is highly variable,
ranging from 2 m to 12 m with an average thickness of 7 m. In a representative cycle, the lithofacies
present are, in ascending order, a basal shellbed, awell-sorted fine sandstone, a muddy fine to very finesandstone and a well-sorted fine sandstone (Figs. 3
and 4; Kitamura et al., 1994).
Although cyclothems 1–4 are identified at
Yuhidera, the lower boundary of cyclothem 1 andthe upper boundary of cyclothem 4 are obscured due
to poor exposure (Fig. 3; Kitamura et al., 1997). Individual cyclothems are about 5 m thick. In cyclothem
2, the lithofacies present are, in ascending order, abasal shellbed, a fine sandstone, a muddy fine tovery fine sandstone, an intensely burrowed sandy
siltstone and a muddy fine to very fine sandstone(Fig. 3). On the other hand, lithofacies recognized in
cyclothem 3 are, in ascending order, a basal shellbed,
fine sandstone and muddy very fine sandstone.
A remarkable feature of these cyclothems is thatwithin them they show a cyclicity in the vertical
distribution of in-situ molluscan fossil associations.
The term ‘association’ used here is defined as the recurrent autochthonous relicts of former communities(Fürsich, 1984). The faunal changes within an individual cyclothem indicate that the marine conditions
changed from cold-water, upper sublittoral (low tidemark to 50–60 m deep) to warm-water, lower sublittoral (50–60 m to 100–120 m deep), followed

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

153

Fig. 1. Map of the Japan Sea and its surrounding region, and geological map and studied section of the Omma Formation around
Kanazawa City, central Japan. Modified from Imai (1959) and Tada et al. (1992).

154

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

155

Fig. 3. Correlation of depositional sequences 1 to 6 of the middle part of the Omma Formation between the Okuwa and Yuhidera sections
by ecostratigraphic datums and a volcanic ash layer.

Fig. 2. Comparison of stratigraphic distribution of warm-water species in the Omma Formation at the type section and another section
located in the bed of the Fushimi River (Fig. 1) with the oxygen isotope record from DSDP Site 607 (Ruddiman et al., 1989).
Biostratigraphic datums are after Takayama et al. (1988) and Sato and Takayama (1992); magnetostratigraphic data are from Ohmura
et al. (1989) and Kitamura et al. (1993); time scale of oxygen isotope record of DSDP Site 607 and ages of biostratigraphic datums
and magnetic polarity changes are based on chronology of Berger et al. (1994). SB D sequence boundary; 1–11, I–III D numbers ofdepositional sequences.

156

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

Fig. 4. Correlation for the Jaramillo Subchron between the oxygen isotope record of North Atlantic DSDP site 607 (Ruddiman et al.,1989) and the inferred changes in water depth and stratigraphic distribution of ecostratigraphic datums in the Omma Formation. Seelegend to Figs. 2 and 3 for explanation of symbols.

again by cold-water, upper sublittoral during the deposition of one cyclothem (Kitamura et al., 1994).
Therefore, these cyclothems are believed to haveformed during glacio-eustatic sea-level changes. In
terms of sequence stratigraphy, the cyclothems of theOmma Formation each represent one depositionalsequence at fifth-order scale (see below). Sequenceboundaries underlie the basal shellbed at the bot-

tom of the deepening-upward succession in eachsequence. The sharp erosive base of each shellbed
indicates that the lower sequence boundary coincides with a ravinement surface formed by coastal
shoreface erosion during a transgression (Bruun,1962). The basal shellbeds grade upward into lesscondensed well-sorted sandstone. Based on thesefactors, the shellbeds are interpreted as transgressive

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

lag deposits (Kidwell, 1991). Consequently, depositional sequences in the middle part of the Omma
Formation contain no lowstand systems tract sediment.
Many studies (e.g., Saito, 1991) indicate that thedepth of shoreface erosion is less than 40 m, thus therange of 0–40 m is estimated as the shallowest water
depth recorded within the depositional sequences ofthe middle part of the Omma Formation. According
to Dwyer et al. (1995), the glacial to interglacial
sea-level fluctuated on average 60 to 70 m between
2.8 and 2.3 Ma. Naish (1998) reports fluctuationsof between 25 and 90 m during oxygen iosotope
stages 100–72. Therefore, in this paper, the sea-levelchange associated with climatic cycles during thedeposition of the middle part is regarded as 60 to
90 m because the magnitude of δ18 O fluctuations
during the Early and middle Pleistocene are similar to these Pliocene eustatic estimates. Applicationof these estimates of eustatic sea-level change to
the Omma Formation depositional sequences implies that the coarser-grained sediments accumulatedon the inner shelf in water depths of 0–40 andfiner-grained sediments accumulated on the mid- andouter shelf between 60 and 100 m (Fig. 4) (Kitamura et al., 1997). This range does not contradict
significantly with the palaeobathymetric range of theconstituent molluscan fossil associations (Kitamura
et al., 1994).
The eleven depositional sequences of the middle
part of the Omma Formation correspond to fifthorder sequences equivalent to oxygen isotope stages
50 to 28 (Kitamura et al., 1994) (Fig. 2). The 75-mthick middle part of the Omma Formation at Okuwa
shows no progressive shift in facies towards deeper
or shallower deposits. In addition, if the oxygenisotope record (e.g., Ruddiman et al., 1989; Shackleton et al., 1990) is regarded as a proxy for theglacio-eustatic sea-level record, there is no significant trend in average sea-level during the depositionof the middle part (Fig. 2) (1.5–1.0 Ma). The constancy of facies in the middle part of the Omma Formation implies a balance between sedimentation andsubsidence. Using both biostratigraphic and magnetostratigraphic data (Ohmura et al., 1989; Takayama
et al., 1988; Sato and Takayama, 1992; Kitamura etal., 1993), average rates of sedimentation are estimated to be about 16 cm=ka.

157

3. Ecostratigraphic datums
The Japan Sea is a semi-enclosed marginal sea
and is connected to the East China Sea through the
Tsushima Strait, to the Pacific Ocean through the
Tsugaru Strait, and to the Sea of Okhotsk throughthe Soya and Mamiya Straits. At present, the only
current flowing into the Japan Sea is the Tsushima
Current, a branch of the warm Kuroshio Current thatenters the Japan Sea through the Tsushima Strait(Fig. 1). The current transports planktotrophic larvaeof benthic molluscs that live in the water mass influenced by the Kuroshio Current. Such warm-waterorganisms (incursion epiboles; Brett, 1995) occur
cyclically in Quaternary sediments of the Japan Sea.
Kitamura (1995) compared the stratigraphic patternof these species during the last 1.5 Ma with the
published oxygen isotope record (Ruddiman et al.,1989). The comparison suggested that warm-waterorganisms such as molluscs and diatoms expanded
their range into the Japan Sea during all interglacial
stages from 1 to 49, except for stages 3 and 23, andapparently were locally exterminated by the succeeding glacial period, implying that they were killed off
by cooling marine temperatures. These phenomena
were synchronous within one local region, 10 ð 10
km2 in area. Moreover, the molluscan fossils (timeplanes indicators) are considered to be in situ in living associations (biocoenoses), and resedimentationof fossils from underlying sediments is not a concern in the interpretation. Therefore, the appearance
and disappearance datums of warm-water molluscs
have utility as chronostratigraphic datums that canbe used to interpret depositional sequences of theOmma Formation (Kitamura, 1995). Indeed, the parallel relationship between volcanic ash layer O4
and the appearance datum of warm-water molluscs
within depositional sequence 2 demonstrates the synchroneity of the ecostratigraphic datums (Fig. 3).
However, there is a distinct difference between contemporaneous molluscan fossil associations between
Okuwa and Yuhidera. For example, at Okuwa, layer
O4 occurs at the boundary between the Tugurium–
Paphia I Association and the Tugurium–Paphia II
Association. In contrast, the O4 layer occurs within
the horizon yielding the Tugurium–Paphia II Association at Yuhidera. In addition, molluscan associations above the appearance datum of warm-water

158

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

molluscs within depositional sequence 4 are different between both sites: Okuwa contains the Barnea
Association, Yuhidera is Transitional I Association(Fig. 3). On the basis of the recent distribution ofmolluscan species (Kitamura et al., 1997), these differences indicate that the sequence at Yuhidera may
have been deposited in water a few tens of metres
deeper than that at Okuwa. The variation in lithofacies between the two sections can be explained by
the difference in inferred water depths between thetwo sites.
These ecostratigraphic datums are always present
in each of the depositional sequences in the middle part of the Omma Formation, although in somesequences the disappearance datum of warm-water
species coincides with the upper sequence boundary(Fig. 3). For example, comparison between depositional sequences 2 and 3 at Okuwa and Yuhidera
shows that the disappearance datum merges into
an upper sequence boundary towards the shoreline(Fig. 3). This implies that the upper portion is largely
truncated at the upper sequence boundary and thisportion is more complete in thicker, more basinward
sections.

4. Sea-level change and ecostratigraphic datums
Because ecostratigraphic datums within each depositional sequence in the Omma Formation are
based on biogeographic changes controlled byinterglacial–glacial cycles, these datums are independent of sequence stratigraphic concepts. Thus,
analysis of the relationship between these datums
and sequence and systems tract boundaries may help
clarify some concepts of sequence stratigraphy. In
the following section, I focus on the stratigraphic
distribution of ecostratigraphic datums and of theindicators of the condensed section such as glauconyand carbonate grains. Before doing this, however, thetemporal relationship must be established between
sea-level change and the appearance and disappearance datums of warm-water molluscs.
Since the depositional sequences in the Omma
Formation were formed by glacio-eustasy, the oxygen isotope record in deep-sea cores can be regarded
as a proxy for contemporaneous sea-level change.
The temporal position of the ecostratigraphic datumson the sea-level curve can be established by dating the datums precisely then by establishing theircorrelations with the oxygen isotope curve.
The age of the youngest appearance datum incores from the Japan Sea is shown by 14 C dating to
be about 10 ka (Oba et al., 1991, 1995). The age ofthe appearance datum within depositional sequence
10 of the Omma Formation can be dated by magnetostratigraphy. The base of the Jaramillo Subchron isplaced about 50 cm above the appearance datum ofwarm-water molluscs in this sequence (Fig. 4) (Kitamura et al., 1994). Thus, the datum age corresponds
approximately to the base of the Jaramillo Subchron.
On the basis of the benthic oxygen isotope record
from North Atlantic core V30-97 (Ruddiman and
McIntyre, 1984) and ODP site 659 (Tiedemann etal., 1994), the δ18 O value at 10 ka was about 3.5‰.
Also, according to the benthic oxygen isotope record
from ODP site 659 (Tiedemann et al., 1994), andat DSDP Site 607 (Ruddiman et al., 1989) which isquite near core V30-97, the δ18 O value at the baseof the Jaramillo Subchron was about 3.4‰ (Fig. 4).
As the appearance datum of warm-water molluscs isplaced about 50 cm below the base of the Jaramillo
Subchron, the δ18 O value at this period also can be
regarded as 3.5‰. These correlations suggest that a
δ18 O value of 3.5‰ is a threshold value for physical conditions that control the timing of initiationof inflow of the Tsushima Current. It appears thatthese physical conditions have been consistent since
1.5 Ma, because except for stages 3, 23 and 39, theδ18 O values of all interglacial stages after the oxygenisotope stage 50 became lighter than 3.5‰ in thebenthic δ18 O records from DSDP site 607 and ODP
site 659. Thus, I use this δ18 O value of the glacial–interglacial shift to estimate the ages of the appearance datums of warm-water molluscs, although thephysical conditions that control ocean currents in
the Japan Sea during the Quaternary remain poorly
understood.
According to the oxygen isotope records corresponding to deposition of the middle part of theOmma Formation, δ18 O values of 3.5‰ fall near
midpoints between interglacial and glacial peaks(Fig. 2). Also, the appearance datum of warm-watermolluscs seems to have fallen midway along glacial
to interglacial δ18 O shifts.

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

5. Relationship of ecostratigraphic datums toindicators of condensed section in siliciclastic
sequences
To document the stratigraphic distributions ofglaucony and carbonate grains in each depositionalsequence, thin sections of sandstone were made fromsamples without megafossils and trace fossils, and500 sand-size grains were identified from each thinsection. These results are shown in Figs. 5 and 6.
Cementation was not observed in any of the analyzed samples. Most of the glaucony comprises
pale green, well rounded grains. Glaucony occurs
throughout the depositional sequences and the content of glaucony in most samples ranges from 10 to
20% of the total rock (Figs. 5 and 6). A systematic
pattern within depositional sequences is not recognized in the stratigraphic distribution of glaucony.
Sand-size carbonate grains dominate samples, andoccur as both benthic and planktonic foraminifers,with a lesser contribution from fragmented grains ofechinoids and other carbonate detritus. The content
of carbonate grains in all samples is less than 10%of the total rock, except for one sample with 14%.
The abundance of carbonate grains shows a systematic change within depositional sequences; thesegenerally increase upwards (to a point identified as
the maximum flooding surface) and then decrease(Figs. 5 and 6). Typically, the stratigraphic level ofmaximum concentration of carbonate grains occurs
between the appearance and disappearance datumsof warm-water molluscs (Figs. 5 and 6). However,depositional sequences 3 and 4 at Okuwa do not havezones with upward-decreasing carbonate grains. Thisis caused by erosion of the upper part of the sequence, judging from the disappearance datum ofwarm-water species which coincides with the upper
sequence boundary in these sequences.

6. Discussion and conclusions
From the analytical results described above, thedistribution of glaucony and carbonate grains can beused to evaluate sequence stratigraphic concepts. In
this use the stratigraphic relationship between glaucony grains and ecostratigraphic datums indicatesthat the distribution of glaucony is not diagnostic of159

the condensed section or a particular systems tract ina depositional sequence (Figs. 5 and 6). Thus, in thecase of the Omma Formation, the maximum flooding surface associated with the condensed section
cannot be identified uniquely by the distribution ofglaucony alone. The sequence stratigraphic interpretation of many glaucony-bearing units is confusedby the mixing of allochthonous and autochthonous
glaucony. For example, in the lower part of the
TST, allochthonous glaucony is supplied by erosion
during shoreline retreat (Amorosi, 1995). This mixing may obscure the expected distribution of glaucony in depositional sequences of the Omma Formation. The detailed documentation in this paper suggests that fuller information on glaucony, including
spatial distribution, maturity and genetic attributes,
are required for the sequence stratigraphic interpretation of glaucony-bearing successions (Amorosi,1995).
Carbonate grains change in abundance in a regularpattern through each depositional sequence. Moreover, the temporal pattern of change of carbonate
grains within depositional sequence 2 at Okuwa issimilar to those at Yuhidera. These facts imply thatthe concentration of carbonate grains provides a criterion to help identify the maximum flooding surface
associated with the condensed section. The horizon of maximum concentration is placed above theappearance datum of the warm-water molluscs inmost depositional sequences (Figs. 5 and 6). Thus,
the horizon of maximum concentration of carbonate
grains may correspond to the part of the oxygenisotope curve representing the mid-point of the sealevel rise to the highest stand of sea-level, and thus isa good indicator of stratigraphic condensation during
rapid drowning of the shelf.
From the results described above, the distributionof carbonate grains seems to be more effective as anindicator of the condensed section than glaucony. In
all depositional sequences of the Omma Formation
except for depositional sequences 3 and 4 at Okuwa,
the maximum flooding surface can be defined at thehorizon of the maximum concentration of carbonate
grains (Figs. 5 and 6). In the case of depositional sequence 2 at both Okuwa and Yuhidera, the differencein values between the horizon of the maximum concentration and the neighbouring horizons is less than
1%. Thus, I place the maximum flooding surface

160
A. Kitamura / Sedimentary Geology 122 (1998) 151–163
Fig. 5. Glaucony, carbonate grains and sequence stratigraphic interpretation of depositional sequences 1 to 6 of the middle part of the Omma Formation in the Okuwa andYuhidera sections. See legend to Fig. 3 for explanation of symbols. SB D sequence boundaries; TS D transgressive surface; RS D ravinement surface; TST D transgressive
systems tract; HST D highstand systems tract.

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

161

Fig. 6. Distribution of glaucony and carbonate grains and sequence stratigraphic interpretation of depositional sequences 8 and 10 of the
middle part of the Omma Formation in the Okuwa section. See legend in Figs. 3 and 5 for explanation of symbols.

at a midpoint between the two horizons. Although
there is an exception (depositional sequence 4 at
Yuhidera), the maximum flooding surface is between
the appearance and disappearance datums of warmwater molluscs. This suggests that incursion epibolesof warm-water molluscs may occur in the upperparts of the transgressive systems tracts and the earlyhighstand systems tracts of depositional sequences in
the Quaternary Japan Sea basin.
In the case of depositional sequences 3 and 4
at Okuwa, the maximum flooding surface is notdefined. On the basis of ecostratigraphic datums
and carbonate grains, the upper portions of thesesequences were missing due to erosion at an upper
sequence boundary. Thus, these sequences at Okuwa
contain the transgressive systems tracts alone. Suchincomplete depositional sequences were reported byother workers (e.g., Pasley and Hazel, 1995).
Plio–Pleistocene depositional sequences derived
from the 40-ka cycle of interglacial–glacial sea-levelchange are found in Wanganui in western North Island, New Zealand (Abbott and Carter, 1994; Naish

and Kamp, 1997). In these sequences, a condensed
shellbed is recognized near the maximum flooding
surface. The shellbeds comprise a rich in-situ andnear-situm fauna of shallow infaunal and epifaunal
invertebrates and their mean thicknesses are 16 cm.
The shellbeds probably formed at 20–40 m depth in a
few thousand years (Abbott and Carter, 1994). In contrast, they are not present in the Omma Formation,although the water depth at the maximum flooding
surface was as much as 50–100 m. The developmentof a condensed shellbed requires both the absence ofa major supply of sediment and the presence of an
in-situ fauna. Molluscan species are preserved in situ
or near situm within the horizon near the maximum
flooding surface in each depositional sequence of theOmma Formation. The lack of a condensed shellbed
is therefore interpreted as a highly siliciclastic sediment supply during a transgressive phase. In fact,
the average transgressive sediment thickness of theOmma Formation (Okuwa 4.74 m, Yuhidera 2.37 m)
is thicker than that of depositional sequences at Wanganui (1.96 m). The discharge of rivers into the Japan

162

A. Kitamura / Sedimentary Geology 122 (1998) 151–163

Sea during the inflow of the Tsushima Current was
far greater than that during glacial periods (Yasuda,1982). This is because the warm Tsushima Current
would have caused heavy snowfalls on the Japan Sea
coast of the Japanese islands. At present, the annual
rainfall at Kanazawa is more than 2600 mm=yr, of
which more than half is contributed by winter snowfall. The interglacial sediment influx accompanied bysuch heavy precipitation seems to have prevented acondensed shellbed from forming.
The depositional sequences of the Omma Formation seem to be a special case, because conditions of relative sediment starvation associated withsea-level rise did not take place at the depositionsite. Regardless of the degree of change, such local and=or regional environmental changes such as
climate paralleling sea-level rise took place in all
sedimentary basins. Thus, the local and=or regional
environmental factors must be considered when theconcepts of sequence stratigraphy are applied. Climatic fluctuations associated with sea-level changes
may carry incursion epiboles that have utility as local
time markers (Martin et al., 1993; Brett, 1995). The
ecostratigraphic datums represented by such incursion epiboles are very helpful in the recognition ofsystems tracts and sequence boundaries (Martin etal., 1993; Brett, 1995). Moreover, integration of climatic palaeoecology (ecostratigraphic datums) andsequence stratigraphy permits a level of correlational
precision on the order of a few tens of thousands ofyears (Martin et al., 1993; Kitamura, 1995).

Acknowledgements
I am particularly grateful to Prof. R.M. Carter ofJames Cook University, for encouragement, and forhelp to attend the sequence stratigraphy workshop
in Townsville and the subsequent New Zealand field
trip. I acknowledge gratefully Dr. Alan Beu of theInstitute of Geological and Nuclear Sciences, New
Zealand, who critically read through the manuscript
and made constructive suggestions for revision. This
study was funded by Grants-in-Aid from the Ministry of Education, Science and Culture of Japan(No. 08454150).

References
Abbott, S.T., Carter, R.M., 1994. The sequence architectureof mid-Pleistocene (c. 1.1–0.4 Ma) cyclothems from New
Zealand: facies development during a period of orbital control
on sea level cyclicity. In: De Boer, P.L., Smith, D.G. (Eds.),
Orbital Forcing and Cyclic Sequences. Int. Assoc. Sedimentol.
Spec. Publ. 19, 367–394.
Amorosi, A., 1995. Glaucony and sequence stratigraphy: a conceptual framework of distribution in siliciclastic sequences. J.
Sediment. Res. B65, 419–452.
Baum, G.R., Vail, P.R., 1988. Sequence stratigraphy concepts
applied to Paleogene outcrops, Gulf and Atlantic basins. In:
Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea-Level
Changes: An Integrated Approach. Soc. Econ. Paleontol. Mineral., Spec. Publ. 42, 309–328.
Berger, W.H., Yasuda, M.K., Bickert, T., Wefer, G., Takayama,T., 1994. Quaternary time scale for the Ontong Java Plateau:
Milankovitch template for Ocean Drilling Program Site 806.
Geology 22, 463–467.
Brett, C., 1995. Sequence stratigraphy, biostratigraphy, andtaphonomy in shallow marine environments. Palaios 10, 597–
616.
Bruun, P., 1962. Sea level rise as a cause of shoreface erosion. Proc. Am. Soc. Civ. Eng., J. Waterways Harbors Div. 88,
117–130.
Dwyer, G.S., Cronin, T.M., Baker, P.A., Raymo, M.E., Buzas,
J.S., Correge, T., 1995. North Atlantic deepwater temperature change during late Pliocene and late Quaternary climatic
cycles. Science 270, 1347–1351.
Fürsich, F.T., 1984. Palaeoecology of Boreal invertebrate faunas
from the Upper Jurassic of central East Greenland. Palaeogeogr., Palaeoclimatol., Palaeoecol. 48, 309–364.
Imai, I., 1959. Geological map of Kanazawa District (1 : 50,000)(in Japanese with English abstract). Geological Survey ofJapan.
Kidwell, S.M., 1991. Condensed deposits in siliciclastic sequences: expected and observed features. In: Einsele, G.,
Ricken, W., Seilacher, A. (Eds.), Cycles and Events in Stratigraphy. Springer, Berlin, pp. 682–695.
Kitamura, A., 1995. Contribution of biostratigraphy to sequencestratigraphic analysis of Quaternary sediments of the Japan
Sea. Intrusion and extinction of warm-water species as time
planes (in Japanese with English abstract). Mem. Geol. Soc.
Jpn. 45, 110–117.
Kitamura, A., Kondo, Y., 1990. Cyclic change of sediments
and molluscan fossil associations caused by glacio-eustatic
sea-level changes during the early Pleistocene — a case studyof the middle part of the Omma Formation at the type locality(in Japanese with English abstract). J. Geol. Soc. Jpn. 96,
19–36.
Kitamura, A., Sakai, H., Horii, M., 1993. Sedimentary cycles
caused by glacio-eustasy with the 41,000-year orbital obliquity
in the middle part of the Omma Formation (1.3–0.9 Ma) (inJapanese with English abstract). J. Sedimentol. Soc. Jpn. 38,
67–72.

A. Kitamura / Sedimentary Geology 122 (1998) 151–163
Kitamura, A., Kondo, Y., Sakai, H., Horii, M., 1994. 41,000-year
orbital obliquity expressed as cyclic changes in lithofacies
and molluscan content, early Pleistocene Omma Formation,
Central Japan. Palaeogeogr., Palaeoclimatol., Palaeoecol. 112,
345–361.
Kitamura, A., Kimoto, K., Takayama, T., 1997. Reconstructionof the thickness of the Tsushima Current in the Japan Sea
during the Quaternary from molluscan fossils. Palaeogeogr.,
Palaeoclimatol., Palaeoecol. 135, 51–69.
Loutit, T.S., Hardenbol, J., Vail, P.R., Baum, G.R., 1988. Condensed sections: the key to age determination and correlationof continental margin sequences. In: Wilgus, C.K., Hastings,
B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van
Wagoner, J.C. (Eds.), Sea-Level Changes: An Integrated Approach. Soc. Econ. Paleontol. Mineral., Spec. Publ. 42, 183–
213.
Martin, R.E., Neff, E.D., Johnson, G.W., Krantz, D.E., 1993.
Biostratigraphic expression of Pleistocene sequence boundaries, Gulf of Mexico. Palaios 8, 155–171.
Naish, T.R., 1998. Constraints on the amplitude of late Pliocene
eustatic sea-level fluctuations: new evidence from the New
Zealand shallow-marine sediment record. Geology 25, 1139–
1142.
Naish, T.R., Kamp, P.J.J., 1997. High resolution sequence stratigraphy of 6th order (41 k.y.) Plio–Pleistocene cyclothems, Wanganui Basin, New Zealand: a case for the regressive systems
tract. Bull. Geol. Soc. Am. 109, 978–999.
Oba, T., Kato, M., Kitazato, H., Koizumi, I., Omura, A., Sakai,T., Takayama, T., 1991. Paleoenvironmental changes in theJapan Sea during the last 85,000 years. Paleoceanography 6,
499–518.
Oba, T., Murayama, M., Matsumoto, E., Nakamura, T., 1995.
AMS-14 C ages of Japan Sea cores from the Oki Ridge. Quat.
Res. 34, 289–296.
Ohmura, K., Ito, T., Masaeda, H., Danbara, T., 1989. Magnetostratigraphy of the Omma Formation distributed in
Kanazawa City, Ishikawa Prefecture, central Japan (inJapanese with English abstract). In: Prof. H. Matsuo Memorial
Volume, pp. 111–124.
Pasley, M.A., Hazel, J.E., 1995. Revised sequence stratigraphic
interpretation of the Eocene–Oligocene boundary interval,
Mississippi and Alabama, Gulf Coast Basin, U.S.A. J. Sediment. Res. B65, 160–169.
Pemberton, S.G., MacEachern, J.A., Frey, R.W., 1992. Trace
fossils facies models: environmental and allostratigraphic sig-

163

nificance. In: Walker, R.G., James, N.P. (Eds.), Facies Models
Response to Sea Level Change. Geol. Assoc. Can., pp. 47–72.
Ruddiman, W.F., McIntyre, A., 1984. Ice-age thermal response
and climatic role of the surface North Atlantic Ocean, 40º to
63ºN. Geol. Soc. Am. Bull. 95, 381–396.
Ruddiman, W.F., Raymo, M.E., Martinson, D.G., Clement, B.M.,
Backman, J., 1989. Pleistocene evolution: Northern Hemisphere ice sheets and North Atlantic Ocean. Paleoceanography
4, 353–412.
Saito, Y., 1991. Sequence stratigraphy on the shelf and upper
slope in response to the latest Pleistocene–Holocene sealevel changes off Sendai, northeast Japan. In: Macdonald,
D.I.M. (Ed.), Sedimentation, Tectonics and Eustasy: Sea-Level
Changes at Active Margins. Int. Assoc. Sedimentol., Spec.
Publ. 12, 133–150.
Sato, T., Takayama, T., 1992. A stratigraphically significant
new species of the calcareous nannofossil Reticulofenestra
asanoi. In: Ishizaki, K., Saito, T. (Eds.), Centenary of Japanese
Micropaleontology. Terra Science, Tokyo, pp. 457–460.
Shackleton, N.J., Bergeret, A., Peltier, W.R., 1990. An alternative
astronomical calibration of the lower Pleistocene timescale
based on ODP Site 677. Trans. R. Soc. Edinburgh, Earth Sci.
81, 251–261.
Tada, R., Koizumi, I., Cramp, A., Rahman, A., 1992. Correlationof dark and light layers, and the origin of their cyclicity in
the Quaternary sediments from the Japan Sea. Proc. ODP Sci.
Results 127=128 (1), 577–601.
Takayama, T., Kato, M., Kudo, T., Sato, T., Kameo, K., 1988.
Calcareous microfossil biostratigraphy of the uppermost Cenozoic formations distributed in the coast of the Japan Sea, Part
2. Hokuriku sedimentary basin (in Japanese with English abstract). J. Jpn. Assoc. Pet. Tech. 53, 9–27.
Tiedemann, R., Sarnthein, M., Shackleton, N.J., 1994. Astronomic timescale for the Pliocene Atlantic δ18 O and dust flux
records of Ocean Drilling Program site 659. Paleoceanography
9, 619–638.
Vail, P.R., Audemard, F., Bowman, S.A., Eisner, P.N., PerezCurz, C., 1991. The stratigraphic signatures of tectonics, eustasy and sedimentology — an overview. In: Einsele, G.,
Ricken, W., Seilacher, A. (Eds.), Cycles and Events in Stratigraphy. Springer, Berlin, pp. 617–659.
Yasuda, Y., 1982. Pollen analytical study of the sediment fromthe lake Mikata in Fukui Prefecture, central Japan — especially on the fluctuation of precipitation since the last glacial
age on the side of Sea of Japan. Quat. Res. 21, 255–271.