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Glaucony and carbonate grains as indicators of the condensed
section: Omma Formation, Japan
Kitamura, Akihisa
Sedimentary Geology. 122(1-4), p. 151-163
1998-12
http://hdl.handle.net/10297/534
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(c)1998 Elsevier Science B.V. All rights reserved
This document is downloaded at: 2016-03-01T09:30:20Z
Glaucony and carbonate grains asindicators of the condensed section：0mma
Formation，Japan
AkihisaKitamura＊
InstituteofGeosciences，FacultyofScience，ShizuokaUniversity，Shizuoka422，Japan
Received15January1997；accepted2July1997．Availableonline21February1999．
Abstract
The nflh−Order depositionalsequences ofthe Early Pleistocene Omma Formation
exposed along theJapan Sea coastofcentralJapan wereformed by glacial−euStaSy
during oxygenisotope stages 50 to 28．In each depositional sequence，tWO
ecostratigraphicdatumsarealwayspresent：theappearanceanddisappearancedatums
Of warm−Water mOlluscan species．These datums areindependent of sequence
Stratigraphic concepts，because the establishment ofthemis based onimmlgration
events of molluscan species associated with glacio−euStatic sea−level changes．
Determinationoftimeplanesshowsthattheappearancedatumseemstooccurnearthe
midpointofsea−levelriseontheglacialtointerglacialshiftindeep−Sea6180records．In
Ordertoevaluatetheslgni丘canceofthecondensedsectioninsequencestratigraphyand
alsotohcilitateitsrecognition，this studyexaminesthe stratigraphicrelationship of
the condensed sectionindicators，glaucony and carbonate grains，With respectto the
POSition of the ecostratigraphic datumsin depositional sequences of the Omma
Formation．Theresultsshowthatthemaximumconcentrationofcarbonategrainsisa
morereliablemaximumfl00dingsurhceindicatorthantheconcentrationofglaucony．
The combination ofindicators of condensed section and ecostratigraphic datums
represented bylnCurSion epiboles enables the boundary between transgressive and
highstand systems tracts to be recognlZedin theinner shelfparts of depositional
SequenCeS．Moreover，trunCation of ecostratigraphic datums during sea−level hlls
demonstrates slgni丘Cant erosion atthe sequence boundaries．Integration ofclimatic
Palaeoecologyandsequencestratigraphypermitsalevelofcorrelationalprecisionofthe
Orderofafewthousandsofyears．
Keywords：Early Pleistocene；sequence stratigraphy；ecostratigraphy；condensed
SeCtion；maximumfl00dingsurface；sea−levelchange
1．1ntroduction
Bothtypeland2depositionalsequenceshavetransgressiveandhighstandsystems
tracts（e．g．Ⅵlilet a1．，1991）．The physicalboundary between themis called the
maximumfl00dingsurhce．This surhcecommonlyoccurswithinthetopof，Oratthe
baseot acondensedsectioncausedbyverylowsedimentationrates（e．g．Ⅵlileta1．，
1991；Abbottand Carter，1994）．Stratigraphic condensationonthe continentalshelf
maybecharacterizedbyconcentrationsofplanktonicorganisms，glaucony，Sulphides，
phosphate，andairborneparticlessuchasvoIcanicashandiridium（e．g．Loutiteta1．，
1988；Baum and Vail，1988）．Condensed sections usually coincide with zones of
maximumdiversityandabundanceoffossils．Ontheotherhand，COndensedsectionsin
epeiricsettingsarecharacterizedbyhighertotalorganiccarbon，reducedoxygenvalues，
low concentrations ofbenthicforaminifera，and minimalor no burrowing，COmPared
withrocksdepositedduringmoreelevatedsedimentationrates（Pembertoneta1．，1992）．
AlthoughthecharacterofcondensedsectionsvariesaccordingtogeologlCSettings，any
COndensedsectionisinterpretedasasediment−StarVedintervalthatwascausedbythe
trappingofterrlgenOuS Sediments duringtimesofrelativelyrapid sea−levelrise and
marinefl00ding．Thus，the distributionoflowsedimentationrateindicatorshasbeen
usedtorecognizethecondensedsection，maXimumfl00dingsurhceandthehighstand
andtransgressivesystemstracts．
Withtheexceptionofafewstudies（e．g．Saito，1991），mOStStudieshavebeenbased
On Pre−Pliocene sedimentary sequences，Where the sea−level slgnatureis not known
independently but has to beinhrred from the sediments under study．One ofthe
exceptions was a depositional sequence of shelf and upper slope hciesformedin
response to Late Pleistocene to Holocene sea−level changes but the distribution of
indicatorsofthecondensedsectionwerenotinvestigatedindetail（Saito，1991）．Thus，
the purpose ofthispaperis to examine the relationship between the distribution of
glauconyandcarbonategrainsasindicatorsofthecondensedsection，andtruesea−level
Changes．
TheOmmaFormationisidealforthispurpose，becauseitsmiddlepartiscomposed
Of eleven depositional sequences deposited during glacio−euStatic sea−level changes
between about1．5andl．O Ma（Kitamura and Kondo，1990∴Kitamura eta1．，1994）．
Moreover，eaCh depositional sequencein the Omma Formation contains two
Chronostratigraphic horizons，namely the appearance and disappearance datums of
warm−WatermOlluscanspecies（Kitamura，1995）．Becausethesedatumsarebasedon
the frequency variations of climatically controlled molluscan associations，their
recognitionisindependent ofsequence stratigraphic criteria．Thus，uSing these two
horizons the sequence stratigraphic slgnincance of concentrations of glaucony and
Carbonategrainscanbeevaluated．
2．DepositionalsequencesoftheOmmaFormation
TheOmmaFormationisexposedaroundKanazawaCityontheJapanSeacoastof
centralJapan（Fig．1）．The sedimentarybasinissituatedinaback−arCPOSitionwith
respecttothesubductingplateboundariesbetweenthePaci丘C，PhilippineandEurasia
Plates．Elevencyclothems are recognizedinthe middlepartofthe OmmaFormation
（Kitamuraeta1．，1994）．Thesecyclothemsarenumberedupwardsinsuccessionfroml
toll（Fig．2）．Inthispaper，CyClothemsofthe OmmaFormationatthetype section
（Okuwa）andatYuhideraareexamined（Fig．1）．
The typelocality of theformationislocatedin the bed of the Saikawa River，
KanazawaCity．Exceptforcyclothem9，allsequencescanbeobservedatOkuwa（Fig．2）．
The thickness ofindividual cyclothems exposed at this sectionis highly variable，
ranglngfrom2mto12mwithanaveragethicknessof7m．Inarepresentativecycle，
thelithohcies present are，in ascending order，a basal shellbed，a Well−SOrted丘ne
sandstone，amuddy丘netoverynnesandstoneandawell−SOrtednnesandstone（Fig．3
andFig．4；Kitamuraeta1．，1994）．
Although cyclothems1−4 areidenti丘ed at Yuhidera，thelower boundary of
CyClothemlandtheupperboundaryofcyclothem4areobscuredduetopoorexposure
（Fig．3工Kitamuraeta1．，1997）．Individualcyclothemsareabout5mthick．Incyclothem
2，thelithohciespresentare，inascendingorder，abasalshellbed，anneSandstone，a
muddynnetoverynnesandstone，anintenselyburrowedsandysiltstoneandamuddy
丘ne to very nne sandstone（Fig．3）．On the other hand，lithohcies recognizedin
CyClothem3are，inascendingorder，abasalshellbed，nne Sandstone andmuddyvery
丘ne sandstone．
Aremarkablefeatureofthesecyclothemsisthatwithinthemtheyshowacyclicityin
the verticaldistribution ofin−Situ molluscanfossil associations．The term‘association−
used hereis denned as the recurrent autochthonous relicts offormer communities
（Ftlrsich，1984）．Thehunalchangeswithinanindividualcyclothemindicatethatthe
marineconditionschangedfromcold−Water，uPPerSublittoral（lowtidemarkto50−60m
deep）towarm−Water，lowersublittoral（50−60mtolO0−120mdeep），fo1lowedagainby
cold−Water，uPPerSublittoralduringthedepositionofonecyclothem（Kitamuraeta1．，
1994）．Therefore，thesecyclothemsarebelievedtohaveformedduringglacio−euStatic
Sea−levelchanges．In terms of sequence stratigraphy，the cyclothems ofthe Omma
Formationeachrepresentone depositionalsequence atnflh−Order scale（see below）．
Sequenceboundariesunderliethebasalshellbedatthebottomofthedeepening−uPWard
SuCCeSSionineachsequence．Thesharperosivebaseofeachshellbedindicatesthatthe
lower sequence boundary coincides with a ravinement surhce formed by coastal
shorehce erosion during a transgression（Bruun，1962）．The basalshellbeds grade
upwardintolesscondensedwell−SOrtedsandstone．Basedonthesehctors，theshellbeds
areinterpreted as transgressivelag deposits（Kidwell，1991）．Consequently，
depositionalsequencesinthemiddlepartoftheOmmaFormationcontainnolowstand
SyStemStraCtSediment．
Manystudies（e．g．，Saito，1991）indicatethatthedepthofshorehceerosionisless
than40m，thus the range of0−40mis estimated as the shallowest water depth
recordedwithinthedepositionalsequencesofthemiddlepartoftheOmmaFormation．
According to Dwyer et al．（1995），the glacialtointerglacialsea−levelfluctuated on
average60to70m between2．8and2．3Ma．Naish（1998）reportsfluctuations of
between25and90mduringoxygeniosotope stageslO0−72．Therefore，inthispaper，
thesea−levelchangeassociatedwithclimaticcyclesduringthedepositionofthemiddle
Partisregardedas60to90mbecausethemagnitudeof6180fluctuationsduringthe
Early and middle Pleistocene are similar to these Pliocene eustatic estimates．
Application ofthese estimates ofeustatic sea−levelchange to the Omma Formation
depositionalsequencesimpliesthatthecoarser一grainedsedimentsaccumulatedonthe
inner shelfinwaterdepthsof0−40and丘ner一grained sediments accumulatedonthe
mid−andoutershelfbetween60andlOOm（Fig．4）（Kitamuraeta1．，1997）．Thisrange
doesnotcontradict signincantlywiththepalaeobathymetricrange ofthe constituent
molluscanfossilassociations（Kitamuraeta1．，1994）．
The eleven depositional sequences of the middle part of the Omma Formation
COrreSPOnd to nflh−Order sequences equivalent to oxygenisotope stages50to 28
（Kitamuraeta1．，1994）（Fig．2）．The75−m−thickmiddlepartoftheOmmaFormationat
Okuwa showsnoprogressive shiflinhciestowards deeperor shallower deposits．In
addition，iftheoxygenisotoperecord（e．g．，Ruddimaneta1．，1989；Shackletoneta1．，
1990）is regarded as a proxyfor the glacio−euStatic sea−level record，thereis no
signincanttrendinaveragesea−levelduringthedepositionofthemiddlepart（Fig．2）
（1．5−1．OMa）．TheconstancyofhciesinthemiddlepartoftheOmmaFormationimplies
a balance between sedimentation and subsidence．Using both biostratigraphic and
magnetostratigraphic data（Ohmura et a1．，1989；Takayama et a1．，1988；Sato and
Takayama，1992；Kitamuraeta1．，1993），aVeragerateSOfsedimentationareestimated
tobe about16cm／ka．
3．Ecostratigraphicdatums
TheJapanSeaisasemi−enClosedmarginalseaandisconnectedtotheEastChina
SeathroughtheTsushimaStrait，tOthePacincOceanthroughtheTsugaruStrait，and
to the Sea ofOkhotsk through the Soya and Mamiya Straits．At present，the only
CurrentflOwinginto theJapan Seaisthe Tsushima Current，abranchofthe warm
KuroshioCurrentthatenterstheJapanSeathroughtheTsushimaStrait（Fig．1）．The
CurrenttranSPOrtSPlanktotrophiclarvaeofbenthicmolluscsthatliveinthewatermass
influencedbytheKuroshioCurrent．Suchwarm−WaterOrganisms（incursionepiboles；
Brett，1995）Occur cyclicallyin Quaternary sediments oftheJapan Sea．Kitamura
（1995）Comparedthestratigraphicpatternofthesespeciesduringthelast1．5Mawith
thepublishedoxygenisotoperecord（Ruddimaneta1．，1989）．Thecomparisonsuggested
thatwarm−WaterOrganisms suchasmolluscsand diatomsexpandedtheirrangeinto
theJapanSeaduringallinterglacialstagesfromlto49，eXCePtforstages3and23，and
apparentlywerelocallyexterminatedbythe succeeding glacialperiod，implyingthat
they were killed off by cooling marine temperatures．These phenomena were
SynChronouswithinonelocalreglOn，10×10km2inarea．Moreover，themolluscanfossils
（timeplanesindicators）areconsideredtobeinsituinlivingassociations（biocoenoses），
and resedimentation offossils from underlying sedimentsis not a concernin the
interpretation．Therefore，the appearance and disappearance datums ofwarm−Water
molluscs have utility as chronostratigraphic datums that can be used tointerpret
depositionalsequencesoftheOmmaFormation（Kitamura，1995）．Indeed，theparallel
relationshipbetweenvoIcanicashlayerO4andtheappearancedatumofwarm−Water
molluscs within depositional sequence 2 demonstrates the synchroneity of the
ecostratigraphic datums（Fig．3）．However，thereis a distinct di鮎rence between
COntemPOraneOuS mOlluscanfossil associations between Okuwa and Yuhidera．For
example，atOkuwa，layerO40ccurSattheboundarybetweentheTugurium−PaphiaI
AssociationandtheTugurium−PaphiaIIAssociation．Incontrast，theO41ayeroccurs
Within the horizon yielding the Tugurium−PaphiaII Association at Yuhidera．In
addition，mOlluscanassociationsabovetheappearance datumofwarm−WatermOlluscs
within depositionalsequence4are dif鈷rentbetweenboth sites：Okuwa contains the
BarneaAssociation，YuhideraisTransitionalIAssociation（Fig．3）．Onthebasisofthe
recent distribution of molluscan species（Kitamura et a1．，1997），these di鮎rences
indicatethatthesequenceatYuhideramayhavebeendepositedinwaterafeWtensof
metres deeper than that at Okuwa．The variationinlithohcies between the two
SeCtionscanbeexplainedbythe di鮎renceininhrredwaterdepthsbetweenthetwo
sites．
These ecostratigraphic datums are always presentin each of the depositional
SequenCeSinthemiddlepartoftheOmmaFormation，althoughinsomesequencesthe
disappearance datum of warm−Water SPeCies coincides with the upper sequence
boundary（Fig．3）．Forexample，COmParisonbetweendepositionalsequences2and3at
Okuwa and Yuhidera shows that the disappearance datum mergesinto an upper
sequenceboundarytowardstheshoreline（Fig．3）．Thisimpliesthattheupperportionis
largelytruncatedattheuppersequenceboundaryandthisportionismorecompletein
thicker，mOrebasinwardsections．
4．Sea−levelchangeandecostratigraphicdatuns
Because ecostratigraphic datumswithineachdepositionalsequenceinthe Omma
Formationarebasedonbiogeographicchangescontrolledbyinterglacia1−glacialcycles，
thesedatumsareindependentofsequencestratigraphicconcepts．Thus，analysISOfthe
relationship between these datums and sequence and systems tractboundaries may
helpclarifySomeconceptsofsequencestratigraphy．Inthefollowingsection，Ifocuson
the stratigraphic distributionofecostratigraphic datums andoftheindicatorsofthe
COndensedsectionsuchasglauconyandcarbonategrains．Beforedoingthis，however，
the temporal relationship must be established between sea−level change and the
appearanceanddisappearancedatumsofwarm−WatermOlluscs．
Since the depositional sequencesin the Omma Formation were formed by
glacio−euStaSy，theoxygenisotoperecordindeep−SeaCOreSCanberegardedasaproxy
for contemporaneous sea−levelchange．The temporalpositionofthe ecostratigraphic
datumsonthesea−levelcurvecanbeestablishedbydatingthedatumspreciselythenby
establishingtheircorrelationswiththeoxygenisotopecurve．
TheageoftheyoungestappearancedatumincoresfromtheJapanSeaisshownby
14CdatingtobeaboutlOka（Obaeta1．，1991andObaeta1．，1995）．Theageofthe
appearance datum within depositional sequencelO ofthe Omma Formation can be
datedbymagnetostratigraphy．ThebaseoftheJaramilloSubchronisplacedabout50
cm above the appearance datum ofwarm−Water mOlluscsin this sequence（Fig．4）
（Kitamuraeta1．，1994）．Thus，thedatumagecorrespondsapproximatelytothebaseof
theJaramilloSubchron．OnthebasisofthebenthicoxygenisotoperecordfromNorth
AtlanticcoreV30−97（RuddimanandMcIntyre，1984）andODPsite659（Tiedemannet
a1．，1994），the6180value atlOkawas about3．5％0．AIso，aCCOrdingtothebenthic
oxygenisotoperecordfromODPsite659（Tiedemanneta1．，1994），andatDSDPSite
607（Ruddimaneta1．，1989）whichisquitenearcoreV30−97，the6180valueatthebase
oftheJaramillo Subchron was about3．4％0（Fig．4）．Asthe appearance datum of
warm−WatermOlluscsisplacedabout50cmbelowthebaseoftheJaramilloSubchron，
the6180valueatthisperiodalsocanberegardedas3．5％0．Thesecorrelationssuggest
thata6180valueof3．5％oisathresholdvalueforphysicalconditionsthatcontrolthe
timingofinitiationofinflowoftheTsushimaCurrent．Itappearsthatthesephysical
COnditionshavebeenconsistentsince1．5Ma，becauseexceptforstages3，23and39，the
6180valuesofallinterglacialstagesaflertheoxygenisotopestage50becamelighter
than3．5％ointhebenthic6180recordsfromDSDPsite607andODPsite659．Thus，I
use this6180value of the glacial−interglacial shift to estimate the ages of the
appearance datums ofwarm−Water mOlluscs，although the physical conditions that
COntrOl ocean currentsin theJapan Sea during the Quaternary remain poorly
understood．
Accordingtothe oxygenisotope recordscorrespondingto depositionofthe middle
Part Of the Omma Formation，6180values of3．5％0hll near midpoints between
interglacialand glacialpeaks（Fig．2）．AIso，the appearance datum ofwarm−Water
molluscsseemstohavehllenmidwayalongglacialtointerglacia16180shifls．
5．Relationship ofecostratigraphic datums toindicators ofcondensed sectionin
Siliciclasticsequences
To document the stratigraphic distributions ofglaucony and carbonate grainsin
eachdepositionalsequence，thinsectionsofsandstoneweremadefromsampleswithout
megafossilsandtracefossils，and500sand−Size grainswereidentinedfromeachthin
SeCtion．TheseresultsareshowninFig．5andFig．6．
Cementationwasnotobservedinanyoftheanalyzedsamples．Mostoftheglaucony
COmPrisespalegreen，Wellroundedgrains．Glauconyoccursthroughoutthedepositional
SequenCeSandthecontentofglauconylnmOStSamPlesrangesfromlOto20％ofthe
totalrock（Fig．5andFig．6）．Asystematicpatternwithindepositionalsequencesisnot
recognlZedinthestratigraphicdistributionofglaucony．
Sand−Size carbonate grains dominate samples，and occur as both benthic and
Planktonicforaminifers，Withalessercontributionfromfragmentedgrainsofechinoids
andothercarbonatedetritus．Thecontentofcarbonategrainsinallsamplesislessthan
10％ofthe totalrock，eXCePtfor one sample with14％．The abundance ofcarbonate
grains shows a systematic change within depositional sequences；these generally
increase upwards（to apointidenti丘ed asthe maximumfl00ding surhce）andthen
decrease（Fig．5andFig．6）．Typically，thestratigraphiclevelofmaximumconcentration
Of carbonate grains occurs between the appearance and disappearance datums of
warm−WatermOlluscs（Fig．5andFig．6）．However，depositionalsequences3and4at
Okuwadonothavezoneswithupward−decreasingcarbonategrains．Thisiscausedby
erosionofthe upperpartofthe sequence，judgingfrom the disappearance datum of
Warm−Water SPeCies which coincides with the upper sequence boundaryin these
SequenCeS．
6．Discussionandconclusions
From the analytical results described above，the distribution of glaucony and
Carbonate grainscanbeusedtoevaluate sequence stratigraphicconcepts．Inthisuse
the stratigraphic relationship between glaucony grains and ecostratigraphic datums
indicatesthatthedistributionofglauconylSnOtdiagnosticofthecondensedsectionora
particularsystemstractinadepositionalsequence（Fig．5andFig．6）．Thus，inthecase
OftheOmmaFormation，themaximumfl00dingsurhceassociatedwiththecondensed
SeCtion cannot beidentined uniquely by the distribution of glaucony alone．The
SequenCeStratigraphicinterpretationofmanyglaucony−bearingunitsisconfusedbythe
mixingofallochthonousandautochthonousglaucony．Forexample，inthelowerpartof
the TST，allochthonous glauconyis supplied by erosion during shoreline retreat
仏morosi，1995）．This mixing may obscure the expected distribution ofglauconyin
depositional sequences ofthe Omma Formation．The detailed documentationin this
PaPer SuggeStS thatfullerinformation on glaucony，including spatial distribution，
maturity and genetic attributes，are required for the sequence stratigraphic
interpretationofglaucony−bearingsuccessions（Amorosi，1995）．
Carbonate grains changein abundancein a regular pattern through each
depositionalsequence．Moreover，the temporalpatternofchange ofcarbonate grains
withindepositionalsequence2atOkuwais similartothose atYuhidera．These hcts
implythattheconcentrationofcarbonategrainsprovidesacriteriontohelpidentifythe
maximumfl00ding surhce associated with the condensed section．The horizon of
maximum concentrationis placed above the appearance datum of the warm−Water
molluscsin most depositional sequences（Fig．5and Fig．6）．Thus，the horizon of
maximumconcentrationofcarbonategrainsmaycorrespondtothepartoftheoxygen
isotope curve representingthe mid−POintofthe sea−levelrise to the highest standof
Sea−level，and thusis a goodindicator of stratigraphic condensation during rapid
drowningoftheshelf．
Fromtheresultsdescribedabove，thedistributionofcarbonategrainsseemstobe
moree鮎ctiveasanindicatorofthecondensedsectionthanglauconyInalldepositional
SequenCeSOftheOmmaFormationexceptfordepositionalsequences3and4atOkuwa，
the maximum fl00ding surhce can be denned at the horizon of the maximum
concentration ofcarbonate grains（Fig．5and Fig．6）．In the case of depositional
SequenCe2atbothOkuwaandYuhidera，thedif鈷renceinvaluesbetweenthehorizonof
the maximum concentration and the neighbouring horizonsisless than1％．Thus，I
Placethemaximumfl00dingsurhceatamidpointbetweenthetwohorizons．Although
thereis anexception（depositionalsequence4atYuhidera），the maximumfl00ding
Surhceisbetweentheappearanceanddisappearancedatumsofwarm−WatermOlluscs．
Thissuggeststhatincursionepibolesofwarm−WatermOlluscsmayoccurintheupper
PartS Ofthe transgressive systems tracts and the early highstand systems tracts of
depositionalsequencesintheQuaternaryJapanSeabasin．
In the case ofdepositionalsequences3and4at Okuwa，the maximumfl00ding
Surhceisnotde丘ned．Onthebasisofecostratigraphicdatumsandcarbonate grains，
theupperportionsofthesesequencesweremissingduetoerosionatanuppersequence
boundary．Thus，these sequences at Okuwa containthe transgressive systems tracts
alone．Suchincomplete depositionalsequenceswere reportedbyotherworkers（e．g．，
PasleyandHazel，1995）．
Plio−Pleistocene depositional sequences derived from the 40−ka cycle of
interglacia1−glacialsea−levelchange arefoundinⅥbnganuiinwesternNorthIsland，
NewZealand（AbbottandCarter，1994；NaishandKamp，1997）．Inthesesequences，a
COndensed shellbedis recognized near the maximumfl00ding surhce．The shellbeds
COmPrise a richin−Situ and near−Situm huna of shallowinhunal and epihunal
invertebratesandtheirmeanthicknessesare16cm．Theshellbedsprobablyformedat
20−40mdepthina鎚wthousandyears仏bbottandCarter，1994）．Incontrast，theyare
not presentin the Omma Formation，although the water depth at the maximum
fl00dingsurhcewasasmuchas50−100m．The developmentofacondensedshellbed
requiresboththeabsenceofama］OrSuPPlyofsedimentandthepresenceofanin−Situ
huna．Molluscanspeciesarepreservedinsituornear situmwithinthe horizonnear
themaximumfl00dingsurhceineachdepositionalsequenceoftheOmmaFormation．
Thelack of a condensed shellbedis thereforeinterpreted as a highly siliciclastic
Sediment supply during a transgressive phase．In hct，the average transgressive
sedimentthicknessoftheOmmaFormation（Okuwa4．74m，Yuhidera2．37m）isthicker
thanthatofdepositionalsequencesatⅥbnganui（1．96m）．Thedischargeofriversinto
theJapanSea duringtheinflowofthe Tsushima Currentwashr greaterthanthat
during glacialperiods亀suda，1982）．Thisisbecause the warm Tsushima Current
WOuldhavecausedheavysnowhllsontheJapanSeacoastoftheJapaneseislands．At
PreSent，theannualrainhllatKanazawaismorethan2600mm／yr，Ofwhichmorethan
halfiscontributedbywintersnowhll．Theinterglacialsedimentinfluxaccompaniedby
SuChheavyprecipitationseemstohavepreventedacondensedshellbedfromforming．
The depositional sequences of the Omma Formation seem to be a special case，
becauseconditionsofrelative sedimentstarvationassociatedwithsea−levelrise didnot
takeplaceatthedepositionsite．Regardlessofthedegreeofchange，SuChlocaland／or
reglOnalenvironmentalchangessuchasclimateparallelingsea−levelrisetookplacein
allsedimentarybasins．Thus，thelocaland／orreglOnalenvironmentalhctorsmustbe
COnSidered when the concepts of sequence stratigraphy are applied．Climatic
fluctuationsassociatedwithsea−levelchangesmaycarrylnCurSionepibolesthathave
utilityaslocaltimemarkers（Martineta1．，1993；Brett，1995）．Theecostratigraphic
datumsrepresentedby suchincursionepiboles areveryhelpfulinthe recognitionof
systemstractsandsequenceboundaries（Martineta1．，1993；Brett，1995）．Moreover，
integration of climatic palaeoecology（ecostratigraphic datums）and sequence
Stratigraphy permits alevelofcorrelationalprecision on the order ofafew tens of
thousandsofyears（Martineta1．，1993工Kitamura，1995）．
Acknowledgements
I am particularly grateful to Prof．R．M．Carter ofJames Cook University，for
encouragement，and for help to attend the sequence stratigraphy workshopin
Tbwnsville and the subsequent New Zealand丘eld trip．I acknowledge gratefullyDr．
Alan Beu of theInstitute of Geological and Nuclear Sciences，New Zealand，Who
Criticallyreadthroughthemanuscriptandmadeconstructivesuggestionsforrevision．
ThisstudywasfundedbyGrants−in−AidfromtheMinistryofEducation，Scienceand
CultureofJapan（No．08454150）．
References
Abbott，S．T．，Carter，R．M．，1994．The sequence architecture of mid−Pleistocene（C．
1．1−0．4Ma）cyclothemsfromNewZealand：hciesdevelopmentduringaperiodof
orbitalcontrolonsealevelcyclicity．In：DeBoer，P．L．，Smith，D．G．（Eds．），Orbital
ForcingandCyclicSequences．Int．Assoc．Sedimentol．Spec．Publ．19，367−394．
Amorosi，A．，1995．Glaucony and sequence stratigraphy：a conceptualframework of
distributioninsiliciclasticsequences．J．Sediment．Res．B65，PP．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．，VanⅥbgoner，J．C．（Eds．），Sea−Level
Changes：AnIntegratedApproach．Soc．Econ．Paleontol．Mineral．，Spec．Publ．42，
309−328．
Berger，WH．，％suda，M．K．，Bickert，T．，We往きr，G．andTakayama，T．，1994．Quaternary
time scaleforthe OntongJavaPlateau：MilankovitchtemplateforOceanDrilling
ProgramSite806．Geology22，PP．463−467
Brett，C．，1995．Sequence stratigraphy，biostratigraphy，and taphonomyin shallow
marineenvironments．PalaioslO，PP．597−616
Bruun，P．，1962．Sealevelriseasacauseofshorehceerosion．Proc．Am．Soc．Civ．Eng．，
J．ⅥbterwaysHarborsDiv．88，PP．117−130
Dwyer，G．S．，Cronin，T．M．，Baker，P．A．，Raymo，M．E．，Buzas，J．S．andCorrege，T．，1995．
North Atlantic deepwater temperature change duringlate Pliocene andlate
Quaternaryclimaticcycles．Science270，PP．1347−1351
Ftlrsich，F．T．，1984．Palaeoecology of Borealinvertebrate hunas from the Upper
JurassicofcentralEastGreenland．Palaeogeogr．，Palaeoclimatol．，Palaeoecol．48，PP．
309−364
Imai，I．，1959．Geologicalmap ofKanazawa District（1：50，000）（inJapanese with
Englishabstract）．GeologicalSurveyofJapan．
Kidwell，S．M．，1991．Condensed depositsin siliciclastic sequences：expected and
observed鎚atures．In：Einsele，G．，Ricken，W，Seilacher，A．（Eds．），CyclesandEvents
inStratigraphy．Springer，Berlin，PP．682−695．
Kitamura，A．，1995．Contributionofbiostratigraphytosequencestratigraphicanalysis
OfQuaternarysedimentsoftheJapanSea．Intrusionandextinctionofwarm−Water
speciesastimeplanes（inJapanesewithEnglishabstract）．Mem．Geol．Soc．Jpn．45，
pp．110−117
Kitamura，A．and Kondo，Y，1990．Cyclic change ofsediments and molluscanfossil
associationscausedbyglaci0−euStaticsea−levelchangesduringtheearlyPleistocene
−aCaSeStudyofthemiddlepartoftheOmmaFormationatthetypelocality（in
JapanesewithEnglishabstract）．J．Geol．Soc．Jpn．96，PP．19−36
Kitamura，A．，Sakai，H．and Horii，M．，1993．Sedimentary cycles caused by
glaci0−euStaSyWiththe41，000−yearOrbitalobliquityinthemiddlepartoftheOmma
Formation（1．3−0．9Ma）（inJapanesewithEnglishabstract）．J．Sedimentol．Soc．Jpn．
387pp．67−72
Kitamura，A．，Kondo，Y，Sakai，H．andHorii，M．，1994．41，000−yearOrbitalobliquity
expressedascyclicchangesinlithohciesandmolluscancontent，earlyPleistocene
OmmaFormation，CentralJapan．Palaeogeogr．，Palaeoclimatol．，Palaeoecol．112，PP．
345−361
Kitamura，A．，Kimoto，K．andTakayama，T．，1997．Reconstructionofthe thicknessof
the Tsushima Currentin theJapan Sea during the Quaternaryfrom molluscan
fossils．Palaeogeogr．，Palaeoclimatol．，Palaeoecol．135，PP．51−69
Loutit，T．S．，Hardenbol，J．，Vail，P．R．，Baum，G．R．，1988．Condensedsections：thekeyto
agedeterminationandcorrelationofcontinentalmarginsequences．In：Wilgus，C．K．，
Hastings，B．S．，Kendall，C．G．St．C．，Posamentier，H．W，Ross，C．A．，VanⅥbgoner，J．C．
（Eds．），Sea−LevelChanges：AnIntegratedApproach．Soc．Econ．Paleontol．Mineral．，
Spec．Publ．42，183−213．
Martin，R．E．，Neff，E．D．，Johnson，G．W and Krantz，D．E．，1993．Biostratigraphic
expression of Pleistocene sequence boundaries，Gulf of Mexico．Palaios 8，PP．
155−171
Naish，T．R．，1998．Constraints on the amplitude oflate Pliocene eustatic sea−level
fluctuations：newevidence from the New Zealand shallow一marine sedimentrecord．
Geology25，PP．1139−1142
Naish，T．R．andKamp，P．J．J．，1997．Highresolutionsequencestratigraphyof6thorder
（41k．y．）Plio−Pleistocenecyclothems，ⅥbnganuiBasin，NewZealand：acaseforthe
regressivesystemstract．Bull．Geol．Soc．Am．109，PP．978−999
0ba，T．，Kato，M．，Kitazato，H．，Koizumi，I．，Omura，A．，Sakai，T．andTakayama，T．，
1991．PaleoenvironmentalchangesintheJapanSeaduringthelast85，000years．
Paleoceanography6，PP．499−518
0ba，T．，Murayama，M．，Matsumoto，E．and Nakamura，T．，1995．AMS−14C ages of
JapanSeacoresfromtheOkiRidge．Quat．Res．34，PP．289−296
0hmura，K．，Ito，T．，Masaeda，H．，Danbara，T．，1989．MagnetostratigraphyoftheOmma
Formation distributedinKanazawa City，IshikawaPrefecture，CentralJapan（in
JapanesewithEnglishabstract）．In：Prof．H．MatsuoMemorialⅥ）lume，PP．111−124．
Pasley，M．A．andHazel，J．E．，1995．Revisedsequencestratigraphicinterpretationofthe
Eocene−01igoceneboundaryinterval，MississippiandAlabama，GulfCoastBasin，
U．S．A．J．Sediment．Res．B65，PP．160−169
Pemberton，S．G．，MacEachern，J．A．，Frey，R．W，1992．Tracefossils hcies models：
environmental and allostratigraphic signi丘cance．In：Ⅵblker，R．G．，James，N．P．
（Eds．），FaciesModelsResponsetoSeaLevelChange．Geol．Assoc．Can．，PP．47−72．
Ruddiman，WF．andMcIntyre，A．，1984．Ice−agethermalresponseandclimaticroleof
thesurhceNorthAtlanticOcean，400to630N．Geol．Soc．Am．Bull．95，PP．381−396
Ruddiman，WF．，Raymo，M．E．，Martinson，D．G．，Clement，B．M．andBackman，J．，1989．
Pleistocene evolution：NorthernHemisphereice sheets and NorthAtlantic Ocean．
Paleoceanography4，PP．353−412
Saito，Y，1991．Sequencestratigraphyonthe shelfandupperslopeinresponsetothe
latest Pleistocene−Holocene sea−1evel changes off Sendai，nOrtheastJapan．In：
Macdonald，D．I．M．（Ed．），Sedimentation，TbctonicsandEustasy：Sea−LevelChanges
atActiveMargins．Int．Assoc．Sedimentol．，Spec．Publ．12，133−150．
Sato，T．，Takayama，T．，1992．A stratigraphically signi丘cant new species of the
calcareous nannofossilReticulo鎚nestra asanoi．In：Ishizaki∴K．，Saito，T．（Eds．），
CentenaryofJapaneseMicropaleontologyTbrraScience，Tbkyo，PP．457−460．
Shackleton，N．J．，Bergeret，A．and Peltier，WR．，1990．Analternative astronomical
calibrationofthelowerPleistocenetimescalebasedonODPSite677．Trans．R．Soc．
Edinburgh，EarthSci．81，PP．251−261
Tada，R．，Koizumi，I．，Cramp，A．，Rahman，A．，1992．Correlationofdarkandlightlayers，
andtheoriginoftheircyclicityinthe QuaternarysedimentsfromtheJapanSea．
Proc．ODPSci．Results127／128（1），577−601．
Takayama，T．，Kato，M．，Kudo，T．，Sato，T．andKameo，K．，1988．Calcareousmicrofossil
biostratigraphyoftheuppermostCenozoicformationsdistributedinthecoastofthe
JapanSea，Part2．Hokurikusedimentarybasin（inJapanesewithEnglishabstract）．
J．Jpn．Assoc．Pet．Tech．53，PP．9−27
Tiedemann，R．，Sarnthein，M．andShackleton，N．J．，1994．Astronomictimescaleforthe
PlioceneAtlantic6180and dustfluxrecordsofOceanDrillingProgram site659．
Paleoceanography9，PP．619−638
Vail，P．R．，Audemard，F．，Bowman，S．A．，Eisner，P．N．，Perez−Curz，C．，1991．The
StratigraphicslgnatureSOftectonics，euStaSyandsedimentology−anOVerView．In：
Einsele，G．，Ricken，W，Seilacher，A．（Eds．），Cycles and Eventsin Stratigraphy．
Springer，Berlin，PP．617−659．
％suda，Y，1982．PollenanalyticalstudyofthesedimentfromthelakeMikatainFukui
Prefecture，CentralJapan−eSPeCiallyonthefluctuationofprecipitationsincethe
lastglacialageonthesideofSeaofJapan．Quat．Res．21，PP．255−271
Fig．1．Map oftheJapan Sea andits surrounding region，and geologicalmap and
StudiedsectionoftheOmmaFormationaroundKanazawaCity，CentralJapan．Modined
fromImai（1959）andTadaetal．（1992）．
Fig．2．Comparisonofstratigraphic distributionofwarm−Water SPeCiesinthe Omma
Formationatthe type sectionandanother sectionlocatedinthebedofthe Fushimi
River（Fig．1）withtheoxygenisotoperecordfromDSDPSite607（Ruddimaneta1．，
1989）．Biostratigraphic datums are after Takayama et al．（1988）and Sato and
Takayama（1992）；magnetostratigraphic data are from Ohmura et al．（1989）and
Kitamuraetal．（1993）；timescaleofoxygenisotoperecordofDSDPSite607andagesof
biostratigraphic datums and magnetic polarity changes are based on chronology of
Bergeretal．（1994）．SB＝SequenCeboundary；1−11，I−III＝numbersofdepositional
SequenCeS．
Fig．3．Correlationofdepositionalsequencesl to60fthe middle partofthe Omma
FormationbetweentheOkuwaandYuhiderasectionsbyecostratigraphicdatumsanda
VOIcanicashlayer．
Fig．4．Correlationfor theJaramillo Subchronbetweenthe oxygenisotope record of
NorthAtlanticDSDPsite607（Ruddimaneta1．，1989）andthein任汀redchangesinwater
depth and stratigraphic distribution of ecostratigraphic datumsin the Omma
Formation．SeelegendtoFig．2andFig．3forexplanationofsymboIs．
Fig．5．Glaucony，Carbonate grains and sequence stratigraphicinterpretation of
depositionalsequenceslto60fthemiddlepartoftheOmmaFormationintheOkuwa
andYuhiderasections．SeelegendtoFig．3forexplanationofsymboIs．SB＝SequenCe
boundaries；TS＝tranSgreSSivesurhce；RS＝raVinementsurhce；TST＝tranSgreSSive
SyStemStraCt；HST＝highstandsystemstract．
Fig．6．Distribution of glaucony and carbonate grains and sequence stratigraphic
interpretation ofdepositional sequences8andlO ofthe middle part ofthe Omma
Formationin the Okuwa section．Seelegendin Fig．3and Fig．5for explanation of
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