meh - 産業技術総合研究所...50m 0 (m) ʼφ 4φ-φ-4 4゛ s ゝ kamitoyo section kt-7...
TRANSCRIPT
183-lntegratedStrati11raphyofthelゝ /liocene5;(?(nlence,lゝ /liocenefromJapan
(WGkaderMasakiTakahash沁-lmi1:masak返)lg・1j・gojp)
/zzzEgrαなj∫なα哨iz‘αρ/zyθ/’治εルfiθa?zze謂αΓ加e∫ε9zzEzzce加治ε7・αzlαgzμ゛ααΓεα
/VθΓ治eαsljαραzz
MasakiTakahashilntc5gratedbio,andchlonostratigraphyResealchGI‘oup,lnstituteofGeo5;cience,AISTsiteC-7.
1-1-IHigashi,Tsukuba,lbarak□()5-8567,Japan;msk.ta1こlltlashi@11汝.go.jpYukioYanaがsawa
lrltc5gratedbio-andchronostlatigraphyRc5seafchGroup,lnstituteofGeo如ence.AISTsite(:ンフ.1↓1Rllashi,ljukuba,lbafaki305-8567,Japan;y・yanagisawa@11i・;t.gojp
HirokiHayashilnstituteofGe2010gyandl)ale(mtology丿ohokuun沁ersity.
Aoba,.4J‘llmaki,Aoba-ku,Sendaj,Japan;nn@mail.(:clohoku.ac.jpHidekilwano
KyotoFissiorl-TrackCo.Ltd.;44-4Min21rni-Tajiricho,Kita-ku,Kyoto603-8832,Japan;kyot()-ft@mbJew油.ne.jpToshinoriokada
Hiruzenlnstittltefor(11eologyandChl` alology;161-ISaiJkayama703-8242,Japan;hiruzen@oran卯.ocn.nejp
Summary
lntegTatedstratigraPhicstudyalongtheMiocenemarinesequenceintheTanaguraarea,Nor-theastJaPanjsbrienyintroduced.
Radiometric芒萍werel・e(;entlydcうtenTlinedontwovolcaniclasticl’ocks(Kt-1andKt-フ)inter-t)(iidde(lintheloRz(:5standupPermostPartoftheMioceneKubotaForm21tioninthe’I’al’1aguraarea.(:)btainedK-Arage(10,6士0,2Ma)andf`issiontrackage(10√7士0,2Ma)oftheKt-1TuffshowgoodagTeementwitheachother,whichsuggeststh21tthescagesl ePIでsenttheeruptionageoftheKt-1
pyrodastics.ThefissiontrackageoftheKt` フPumicetuffwas&lerminedon100zirconl;I’ains(10,6土0,3Ma),which(;()incideswiththeradiometric昭esoftheKt-1Tuff.
Highsedim(うntaccumulationrate(25,5cm/1000aor:!55m/Ma)issuggestedbasedonK-Arandfissiontrackl;eochronology.Pre;vi()usly5tablishedmi(;I-ofossilbiostratigraPhyarew(う11consis-tentwiththegeochr()nology・
Keywords:M沁cenc≒lntegratedstrat址raphy,}C嶋lag(≒fissiontrack211gらbiostratigraphy,calcareousnannofossn,
planktonicforalninifera,radiol函a,diatom
1.1ntroduction
Biostratigraphyisoneofthemostcommonandusefultoolsforagedeta` minationofmarinesediments,althoughitindicatesonlystratigraphicrelations.lfweneednumericalagesofstratabasedonyieldedmicrof;()ssns,wecanestimatetheageusingatimescale,whichis(氾nstrllctedbyacombi-nationofmEt即et()-biostratigraPhyandgeomagneticPolaritytimescale(GPTS).The51‘ef()I’e,thereha-bilityofthetimescaledependsonthea(;(;uracyoftheGPTSandvalidityofcorrelationbetweenmahnemagneticanomalyP旅em(GPTS)andmagne杖)stratigraphy。
RecentlyBerggreneta1.(1995)constructedagx)logictimescalebasedonCande&Kent
(四95)’sGPTS,11hhoughBaksiG993),Wd(1995)andTakahashi&Danhara(1997)havel:)ointedoutseriousproblemsontheGPTS.Thc51‘ef()rejtisbasedontheradiometricdatingwiththemagneto,
(力viouslyeffectivet()illtegratethechl7onologyand/orbk)stl・姐graPhy.SomeNeogenemarine
seqllellcesherbeddiltablevolcaniclastic121yersinJapan,whichisagoodoPportunityforcollstruct`姐gatimescale(Takahashi&Oda,1997),
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - n e x t p a g e 一 一 , - - - - - - - - - - - 一 一 - 一 一 , - - , - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - > >
Fig.ISml)kl()cationonage()logicalmapoftheNUocenemarinest5(luenceintheTanaguraarea,NOI ‘ thealstJapan
(mo(lifiedfroml;himamotoetlll・,1998).
OdinG.S.(Ed.),PhanerozoicTimeScalらBuILLiai!Elnform.IUGSSubcomJeocllr()no1J6,0ffsetParis,2000
㎜ Quatemaryvolcano
Neo9ene
!事゛`か
1
々
〆
‘ ? β
S
き。III.Ij
T
●
●●
●’●
1●
● ● ●● ● ●● ● ●● ●‥ |● ● 。r‥‥
ΦΦ・
● ● ● ●
● ● ● ●
● ● ● ●
. ● ● ●● ● ●
.:.●●●:::...::::::●●::::::.::::::` ●●●●●●難
参 ・ 。 J T
LEGEND
[lii]Niko9iFm.
【IIlmΞHIKubotaFm[2≡∃keytuff
[ΣΞご]AkasakaFm.
[Σ□]Pre-Neo9ene
140°241E
● S
● ●
● ●● ●
● ●
● ●● ●
● ●
● ●
● ●● ●
++
● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ● ●● ● ● ●.yl..々
●
●
●
●
●●
●
●
●●
●
●
●
●
ΦΦΦ
HU l
●●
●
●●
●
●●
+i++
● ●● ●
● ●
● ●
● ●● ●
● ●
● ●
● ● ●● ● ●● ● ●● ● ●●●`:
E 晨● `● ● ●● ● ●● ● ●● ● 1●●..il
●::3● ●● ●●
●
●●
●
●● ● ●● ● ●● ● ●叫 ● ●
r ● ゜● ● ●●●..111111
17 lol i 11 ll
EE--。。+++++
1++++++++++++++i
+ ++ +
● ● ●
● ● ●
● ● ●
● ●
● ●
● ●
● ●● ●
● ●
● ●● ●
● ●
● ●
照Φ
・
●●●●●|●::::::lEEE’●
M’ヨヨ●
● ● ●● ● ●● ● ●●●:。:4●
Hへ●
19
●
Φ
・
香春
Φ・ΦΦΦΦΦ
Φ・ΦΦΦ参Φ
Φ・ΦΦΦ春香
参ΦΦ参・
一
φ
Φ
‥・ΦΦ
・Φ一
言……‥‥.…1111
・ΦΦΦIアー9
0
●●●●●●●●●●
:こ=:
●
●
●●
●
●
●
r●●●●●
:jj
●●● ●● ●● ●● ●● 負
l ゛● ●● ●● ●● ●● ●● ●
●●●
劣
碁 ● ● ●● ● ● ●● ● ● ●● ● ● ●j ● ● ●
●
●● ●
● ●
● ●
● ●
●
1000
j
kada
+ ++ふ +|ra+ぶ 十十 十十 十十 十十 十十 十十 十十 十十 十庵 +
+++
+
+ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ +++.
++++++++++++十十十十十十十十
+ ++ ++ ++ ++ ++ ++ ++ +十 十十 十十 十十 十十 十
+++++++十十十十十十十
‥‥`+++++++++
計19尹0外H
H1
..一■’lにに‥‥‥l‥″‥‥‥a:”はll++
蟻
十十十十十十十十十十十
難
白
++++++
452yl +++ ’!’;E17°01N
に
※
征
治
一
回
鰍
熱
牡
-1111111111131に3aaにaallaにZlll・
ヅフか?+++
…ゞ………y2000m
● ●
Q ● ●● ● ●● ● ぶ● ● ●● ● ●い ●
● ●
●
●
●
●
l:::・メ1
臨MEH
ぷ:;:::
y::r:::3
● ●
● ●
● ●
● ●
● ●● ●
● ●
● ●
● ●
冷 ●
・参・
一以yl
:::ミy::●カ●
●
涵巨眼Ei
●
・
・
:::ご:zj
●●
●
● ●
居 E●●●●●●
lll滋丈:に:::‡‡‡
20AMiocenemarinesequenceiswellexposedintheTanaguraarea,NortheastJapan(FigJ).
ThissequcnceisdividedintotheAkasakaandKubotaFormations.TheKubotaFormationyieldsrl励1‘ofossilsdolllinantly.AitaGS)88)andTaketani&Aka(1991)inve・;tigatedthePlanl(t()nicly()rami-111feralandradiol訂ianbiostratigraPhyofthef ormation,resPectively.Shimamotoetal.(1998)alsoreportedbiostratigraPhicstudyl7esultsofPlanktonicforaminifera,calcalcousnannofossilandradiola-ria.R・:・centlyHayashieta1ぺ2000)rev汝dtheplanktonicforall″1岫feralbio・;tratigraPhy.Diatombios-t心組raphywas丘rstl` ePortedbyY皿agis21waeta1ぺ::!000).
Therearesevensetsofvolcanidastic121yersintheKubotaFormation,asreportedbyShima-motoeta1.(1998)jnwhichwedatedtwovolcanidastiく:;1ayers(尺1-7and瓦z’7).lnthisPaPer,weshowbriefintroductionofthegeology,1itho-andbiostratigraphyandK-Arandfissiontrackagesobtained.ThestratigraphicrelationsbetwecnsomeimPortantmicl ofossilbiohorizonsandradiometricagesoftwopyl‘odasticrocksarealsod返ctlssed.
2.Geologyandstl`atigraphy
TheTanaguraareaissituatedonthesouthernPartofNortheastJapan(F址.1),wheretheMiocenem肛inesequencciswellexPosed.ThissequenceunconformablyoverliesthePre“Neogene
graniticandmcうtamorPhicrocksalongtheeastemmargin,andiscoveredbyaPHoceneconglomerateoftheN張ogiFormationhorizontally.TheMiocenesedimeりntaryrocksaregentlytiltednorthw(iりsterly,buttheysteePlyincnneeasterlyalongthewestemmarがnalthru・;tfault(ShilllamotoetllL,1998).
TheMiocenesequenceismorethan500minthkknessanddividedintothefollowingtwoformations.TheAkasakaFomlationiscomposedofconglom‘こrate,medium-tocoarse“gTainedsands-toneandsntstone.Cross-bed(hngs;tructureisoftenobservedthroughoutthisf ormation.MJjnemo1-柚scsareyielded,whichindicatesashallowsedimentaryenvironment.Benthic柘raminifersarerePortedfromtheAkasakaFormation,whichsuggestsaninnersublittoralzoneenvironment
(shallowerthan50m).
lncontrast,fine-grainedsandstoneandsiltstonewithfrequentintercalationofthinvolcani-clasticlayersdominatetheKubotaFormation,whichconformablycoverstheAkasakaFormation.Shimamotoet11L(195j)8)rePortedthebie;tratigraPhyofthePlanktonicforarllinifera,calcareousnan-1^ 10170ssilandl‘a(1101aria.TheyconcludedthatmostoftheKubotaFormationwascorrelativetozoneN,16ofthePlanktonicfo17amjiniferalzoneofBlowGS)69)orCN6toCNフofcalcareousnannofossilzonesofokada&Buk叩(1980).
RecentlyHayashietal.(2000)re-investigatedtheplanktonicforaminiferalbiostratigraPhy,andrecognizedakeysPeciesofyV・E?∂g/∂か∂‘7Majr加aαcど)μα四∫む,whosefirstoccuITence(FO)definesthelowerlimitofzoneN.16jnthelowestpaltoftheKubotaFormation(Fig.2).
CalcareousnannofossilkeysPeciesofC沢加附記rc∂α治心,whoseFOdefinesthebaseofCN6,andCとzr加心記7イα/yc❹心,whoseFOdefinesthebaseofCNフ,werealsorePorted(Fig.2).
Radiolariacontinuouslyoccun` edfromthemiddlepartoftheKubotaFormation.ShimamotoetaL(1998)condldedthatthemiddleFu‘toftheKubotal:;ormationwascorr(jativetothe句c・/z4aaz-z2θz77α澗αg/7‘2cθz71陥2ZoneofMotoyama&Mal°uyama(1998).
DiatombiostratigTaPhyoftheKubotaFon‘nationwaばecentlyestablishedbyYanaがsawaetaL(200(球ThestratigraphkJintervalfromtheKt-1tothemiddleoftheKt-4BandKt-4Ctufi’levelsiscoalativetothe7’加友・出回沢7y功とiZon球NPD5C)ofYanagisawa&Akiba(1998),becauseoftheoccurrenceofboth£)四面μ/卯吋∫∫加∂だa?ffand£)飢面£z/叩∫なvμなぶ忿andtheabsenceof£)四面❹∂一
戸∫む必朋∂?/7と7and£)と?几だczl/∂ρ∫a/7心~必朋∂伊/zj7.’rhequiterareoccu】Tenceof£)ど甜fc£1/∂ρ∫む/z心応虜ffl;tllggeststhatthelowerPartoftheKubotaFormationisyoungerthantheacmeandlastcommonoccurrence1)iohorizonsofZ:)./z乙4jr6’・ゴぷ(Dj55.8:10,IMa),thatis,theupperpartofthe7こy功友Zone.AfewoccuITencesofsomeimPortantdiatomkeysPaiesalsosu百翌stthattheupPerl:)artoftheKubotaFormation(ar()undtheKt-6Tuff`1eve1)alsocanbecon‘elatetotheでr丿功どZone(NPD5C).
… … … . . . … - 一 一 , - , - . - … … 一 一 , ・ 一 一 - , - n e x t 2 >>
I ig.2T’h(11;tratigraphicdistributionsofl;・うlectedplanktoni(;k)raanifera田ayashietal.1000λcalcareaJsnannofossil
(Shimamotoetal・、1998)、adi()・ria侈himamotoetal.J998)anddiatom・;I)e(ごies(Yanagisawaet;IL、2000)ofthelくLubotaFormationJtrat址raphicl)(吋tiorlsofda❻tuff7s(Kt-landKt-フ)afeals(nndicated.
OdinGふ(Ed.),PhaneozoicTimeScalらBu1LLiai・Elnfom,IUGSSubcom.Ge,(,(;hronol.,16,()ffsetParis,2000
50m
0
(m)
’ φ
4 φ
- φ
- 4
4
♂S♂ゝ●●
KamitoyoSection
Kt-7
Kt-6
一一KM14一
一 K M 1 3
PlanktonicForaminifera(Hayashietal・,2000,modified)
NishikawaSection
Kt-7
- K M 1 0
.「ゝ1ylQて
⊇ 麟
veryfinesandstone
darkgreyclaystronealtematjonofclaystone&coarsetuff
massivefine・mediumsandstone
greyclayeytuffwjththinfinetuff
alternationofbiolite-bearingwhilesandytuff(1・10cm)&dark9reyhetuff(1-3cm)
massiveclayeytuff
thin-beddedclayeytuffquartzgrain
pumiceousdarkbrownsijtysandstone
massjvedarkgreyveryfinesandstone
9reyclayeytutf!
E11ternationofgreyclayeytuff&biotite-bearingcoarsetu町light9reyclayeytuff皿‘bearingverycoarse
dark9reyclayeytutfbiotite-bearingverycoarsetuffdarkgreyveryfinesandslone
Kt-6AKt・6
Kt・5
Kt-4D
Kt-4C
Kt-4B
Kt-4A
KI-4
Kt-3
Kt-2
Kt-ICKt-IBKt-IA
laEs∽
1’□
…………NK45
,NK44…
NK38 ・・- - -・a - -a
N K 3 7 =
N K 3 5 ‾
.NK33
一 一 一 一 一 一 N K 2 5 一 一
,-NK24
NK22
1
- - - - - - - N K 1 9
’NK15
‥NK12
NK7
RmyNMIF5mUgE
政男にl゛‘゛にミ`ミmaeQQSQ
男にIQ迎’`Q`)心’包b心`‘き9`SQ
- - ・ K M 1 2 ‥ ‥ ‥ ‥
51 019 1 1011 0111 lijil 1 l l 1 1 19111 9011 31 1 l ll 1 1 1 111 i l 1 1 1 1 l ll 1 1 111j 11111 1 151 l
21
ヅ ・ ・ : -● ミ
ltJIIをiIIII
W
I ・ I l i l
l ● ● | | |
J . . . し 習 y i = & a ¥ ■ や - i . . ‥ . . Q . . . . . L . .・ ・ i l l 1
1 ・ ・ l i l
5 04111J1511 lol 15 411 15000 o5 111 111 91 15111 11 iJ 11 ll 111111 114 N11jr
9 0111111jlill oll 151111 01501 5 111 1111 411111 lll iJ 11 ll 111 111 oll 471115111 j
忽匂にISQQQI心http://www9 1 411164j4 jl 11 0011 0150 tlliilll 11 o J1114 11 011 ll 421111119111 一
: i ’ , ; : : : :犬 ● - ● 犬 ● 犬1 1 ● ● I I I I: l : ● : : : :し よ . j . . . し _ ニ . よ . パ … … 1
●lll-1111
:ト
Φ5(aS’ioi)
一回』mnEs』UnmUa
Z
Calcareousnannofossl(Shimamotoetal・,1998)
KM14
KMI
a;:ls‰NK43KM4/NK42/KM3‘NK4
mm jlE」oLβoaコ)一
哨`‘Qふ”lqQ‘心ミQりQQQ
哨コQ瓶心lqSE哨3£`、IQQQQ
nm2 1 l z 1 li 112 o 5o 11 11171 5o ll I I 4
l o5 11J411 1 1 111 ol l 211 4 1 1 1 11 1 11105 01501 5 li 4 ll 19 21 o5 1 jll ol 1
R mE n11 11911 JI l 1 jl4 1291 1 2
l 11 111 ll 110111111 liJ lij 1 o9 lil 5 l o5 1 105 1 11211 11 1 5 0111 iii l i 1 434 ol l ll 4g
NK44
--二止
四
l
KNNN
NK35NK34
NK32
NK31
NK24
NK23
NK22
NK21
9876543210‘
11111111119
KKKKKKKKKKK
NNNNNNNNNNN
NK7NK6NK5NK4
NK9..NK2‥
NKI’
‘ tll
I I
I ・
l i
・ ‘ ^ “ l -
| ・
l ・
|||’ ‘ 「|
2Ej2ゴご21¬==デ=●= ¬ ¬: : :
t ’ ‘
|
R
W
W
O
j
’
W
W
I
W
U
W
5
0
M
l 1 11110tl l 194111 iil 5 11141tl 5http://www... 5 11 4 11 1115 305 1 1 1 l l 5 11tl 5 ll 111t 4 59011 li 111 114116tl 5111 4
Mnh U j mW y jj
nm zj 51111 3112 1 l ol 1 1 1 5011 l l 3
m U n J9 jl j l oil II l 4
111-¶
-IIrl
一II中
‾ ‾ ‾ 「 ‾ ‾ ‾ ・ ‾ ” ‾ r ’ ‾
. . . j . . . . I . ■ ■ ■ 1 . .
lmNni
mHmm
WaN一mmmZnm2ml
SZU
taZQ
NK26 -
N K 2 5 -
i i i i i : : : : : : I: : : : : ; ; : : : : 1
ヤ 1 犬 φ → や 二i : : : | : : ; ; ; ; l; 1 : ; ; : : ; ; : ; ‘`r…7TTT‥y……,…4-一一,:,一一,F-一一で.
i ; ; ; : i ; : : : ; ;| ・ l l l r l 1 1 ● |j l j l F F り F ・ 4 1 F l i
:÷
FOΛ/.∂coslaer7s/・s
10.9Ma
□ 呵 ふ 7 晶 ぐ
「¬FOD.内びgかesy
0.6±0.2Ma0.7t0.2Ma
(K-A「」(FT)
し‘|().6±0.3Ma(FT)
FOC.c∂/ycぴ/us10.7Ma
Radiolaria(ShimamotoetEII・,1998)
K M 1 4 … … … … …
卵 3 … … … … …
KM12………ijk4i
KM11‥‥‥‥‥‥‥
NK44
KM10‥‥‥‥‥‥
KM9‥‥‥‥‥‥‥aMa7こ…… l
乞……lテャT
2 1 5554111111151 1490 11 ll 5 35JI 5 11 lil l 11111 1 1 1 1 1 1111 111 iil 4111411T’-一一………
w
m
N
D
m
l
十
-
卜
…
…
…
9WM9
lQal`包司一昨`吻QQtxQ……………
心Q’、’`Qa久司哨q巴Q゛XQト’-レーー::’-
SコSQQミーQq’`りQtxQ十:二………
NK40‥NK39・、、
N K 3 8 -
NK34
NK33,
NK32
NK31
NK30NK29
NK28
NK26
unm mnD
5W W
EコミsSEI心だxuコ山
SIEヾ司哨6QuQ之りこ哨……………
9 3i 11110 ol 01111111 111111511 41 11151 il 1 21 ll 3114111 111 11 1 l ll 1 tlli 1111 411 j l 1 l 11 I l i……………
4-&i-i
・.
t・∵:
| ・
: :’ ` ’ r ’ ゛ r ’1 1
● ・
I I I
I I 1^ t ^ T ゛ ゛ ’ r ’
● I I
I l t
. k . . . 1 ■ ■ ■ ● . . . J . . . . ・ . . .
1 1 1 1 ・
_ I . . _ . L - ・ = 1 . _ _ J _ _ _ . L _ _ .
NK3.....;
ごy……↑
NK18NK17NK16NK15
NK14
NK13
NK12NK11NK10NK9NK8’
NK7-NK6-NK5‘NK4
j . . . d .
NK21
II一一II
ikiI
91KN
----111111111-IIIIII
-11-II-IIII
II111111-I-I-I
NK22
NK24・一一レートj… ÷ ・
: : : i :l l l l l● - ● 八I ・ I l l: : : l :ト ト T T ト
4
・ 還 ■ a ■ r ■ ■ - 「 ・ ・ ’ ¶ ゛ ” ・ ” ” r ” ’ ・ ” ’ ・ ” ‥ ● ’
I r l ・ I I l l l l’ 1 ’ ゛ ’ T ^ ^ ` ・ ’ ^ ^ ` r … r ‥ 1 ” ” I ゛ T ^ ^ ` I … ’ . ’
l ● I ● ● ● l l ● ●
I F I I ● 1 1 1 1 1
1 ・ I l l l l l ・
I I I l l I I I
I I I l l ● ● l i l
・ | ・ l l ・ ・ l l l
卜 1 1 1 ● ・ ・ l l
φ | 中 ・ ■ ・ l l l ・
● 1 1 ・ l ・ ・ I ・ ・
● | を ● I I ● I ● ●
● 1 ● ■ ● ● l l 1 ●
・ i l l l l l ・ ・ ・
i i 4 1 1 1 1 ・ ・ ・
- 1 ‥ . 二 _ . . 1 . . . . L . . . L . . . J . ‥ - L - . _ L ‥ λ . . 1
1 1 1 1 1 ・ ・ ● l j
● I ● 1 4 1 ● * ● |
1 1 ● I ■ i ・ ● ・ |・ r ` ・ ・ 1 ・ ゛ ゛ 1 ` ” ’ n ’ ゛ ” I ” ‾ ’ 1 ’ ‾ - ・ 晶 晶 - 晶 r ’ 1 ■ n ¶ 「 | ‾
llIdrd
-rIIIi
---1-
:
:
てIIIIf-I
IIli一-II
一
-TI
I
. | . . . . 1 . . . j . -
l i l
P ` ・ ・ r - ■ ■ ● ■ -
lm1 ll lEnmE m
m
〇ma
11
li ijl S 11
KamitoyoSection
50m
0
22
aj-Q。
Kt-
Diatom(YilnagisawaetE11・,2000)
Biohorizons&theirestimatedages(E3er99renetal・,1995)
mHnlMmwH
j
EH NWni
Mw
u
w
m
E
R
Mhttp://www.aQS碧’‘りQ
心QQQにQEI々哨qQ15Q’、ミQQ
Tan919-
‥ ‥ ‥ T a n 9 - 6 8 ‥ ‥ ‥ ‥
Ξ ” T a n 9 - 6 7 … … …
-
`
一
一
-II`-II--IIIIISI11-
一 一 ‥ y ・ ‥ ・ i
l :… - ト … り
i
-
l
ir
i
`一
NishikawaSection
Kt-6AKt-6
Kt-5
4
0
4
0
4
8
1 i
i
mUml」OL30aコv一
Kt-4A
Kt-4
Kt-2
Tan9・63Tan942Tan9-61Tan940Tan9・59
j
-
-
-
I
J
I
-
-
丿
-
I
I
I
丿
-
1
-
1
1
1
F
一
■
一
一
一
一
一
り
I
一
一
゛
一
一
`
一
一
一
゛
`
一
`
一
`
一
゛
一
一
f
一
y
y
一
l
l
一
`
一
一
一
゛
一
`
一
`
一
゛
一
W
一
y
y
一
一
一
W
一
`
f
一
`
■
I
I
I
I
l
f
I
I
1
-
-
-
一
1
}
l
y
一
一
■ 晶 還 ■ ■ 1 ■ a ■ ■ ■ J . .
゛ “ ` ” r ’ ” T ’
. . . . . k - . . . . J . .
--‘……………11 o1 7 oj4 1 1 l o 11 114j11111911
112481
=-’…………LI-
OdjnG.S.(Ed.)、PhanaozoicTimeScale、BljlLLiaisJIlform.IUGSSubcom.Geo(ご11ronol)6、OffsetPalis、2000
‥ ‥ ‥ ‥ T a n 9 ‘ 0 1 … … … ; - 一 一 -
L . .Kt-IA
Kt-1
一一一一一一Tan9-(33一一
‥ 一 一 ‥ T a n g - 0 2 ‥
頁:謡圖丿彗|飛台こ 丿 丿 丿 こ コ ニ ニ ニ こ ニ ニ l こ i i ニ ニ i l t i .
. . . . . j ㎜ ■ ■ 弔 u . 1 - 習 - w ■ - t ミ ・- a ■ 還 a ¶ - ・ ● ・ ・ ● . - - - ■ 一 叫 w - -
‾Tan9-1 ilデ三]ノノドノノテ
1
1
W
W
f
l
l
l
1
1
1
■
y
l
l
y
■
皿
皿
I
I
■
■
l
一
一
一
一
■
f
l
i
y
l
四
I
l
n
l
l
l
J
「
`
J
I
一
I
J
I
I
l
l
l
I
I
J
I
l
l
-
-
-
-
i
-
-
-
丿
-
-
-
一
-
-
’
-
-
一
-
-
一
-
肖
J
-
I I I I
l w ¶ ・ r - ■ ¶ 警 警 警 ? ・ ¶ r ・ 警 警 ¶ ¶ y
l l l ・
l l l ト
| ・ | |
1 1 1 1
| | |
¶ ¶ 警 ■ 警 - J 還 r 警 r ? ■ 1 ■ ・ ・ ■ ■ - ・ .
● ・ i
一 一 ・ 一 一
ニ。。-。・-。
i『ljlIIIIII.jlll・
☆☆・--=
・
宍
符
号
回
謡
二
一
`
… … … T a n g - 4 1 -
Tan9-2S
23
3.Rad沁metricages
Morethantwentyvolcani(;1astictufflayers肛einterbeddedintheKubotaFormation,althoughonlytheKt-1TuffcontainssufficientmineralsforconventionalK-yxJ4dating.TheKt-1Tuffisbiotite-I ichco21rse-grainedl:tlf fasshowninFig.2.Takahashktaけ2001)madeadetailedcolumnarsectionoftheKt-ITuff,andcoUectedsample・;(about5kl;)fromitsmiddlePart(Fig.2)。
Coarse-§;rainedtuff5;EtmPleswerecrushedandsievedintothe48-80meshsizefTI・21ctionsforK-Aldatinlyょ・xfterultrasonicrinsing,themagneticfractionofthesaTlplewassep四回蚤dusinganiso,dynamicseParator.FreshbiotitefractionsxverePurifiedusingaheavyliquidtechnique.QuantitativeamUysisofargonandPotassiumwasPerformedatHiruzcnlnstittltcforGeologyandGeochl“:)nolo-
gy,tlsingtheanalyticalPro(;el(1ureass111ggestedbyltayaetaL(1991),The2sultsare・listedinTablelandtheweigllted-meanagewith1.u以氾rtaintyiM111;ocalculated.
Tablel.lくンν・XI-biotiteageoftheKt-ITuffinthelowestpartoftheKtlbotaFo皿ation.T’heK-Ar昭esヽ xzclrecalc山
tedwiththeSOGconvention21川eca)y(;onstants侈te呼r&Jag(・rj977).
Sample
(「111neral」
Kt-1
(biotite)
Potassium
(wt.%)-
4.56710.091
Radio9enicar9on40
(10’8ccSTP/9)
189.7土2.4
185.5±2.4
K-Arage
(Ma)
10.6710.25
10.4410.25
weりhtedmeanl0.5610.18
Table2Fi!;siontrackdataofzil・consfromtheKt,landKt-7TumintheKubotaFormation.
Sampe
code
Kt-1(EDI)
Kt-1(ED2)
No.of Spontaneous
(垂錫)
(扨{5cm’2〉
30
30
Kt-7(EDI)100
lnduced
p / ( 頂 菰
(106cm’2)
2.40(3289)3.09
1,56(1136)4.33
crystalsps
P(X2)
(%)
Dosimeter
p d ( / V の
(104cm’2)
「
NonRadiogenicAr(%)
10.6±0.3
19.9
20.6
U - A g e
(;ontent(=tl(y)
(ppm)(Ma)
OdinG.S.(Ed.)、Phanel‘ozoicTimeScalQButljai・Elnfom.IUGSSubcom.G(・()(;hronol・、16j)171;etParis、2000
(1)pand/Varetheciensityandtotalnumberoffissiontrackscc,11nted,respectively.
(2)Analysesweremadebythe(・xtel・naldetectormethod(Gleadow,1981)usinggeometryfactorsof0,5for2π/4π(ED1)andlforS!π/2π(ED2).
(3)Ageswer(・calculatedusingadosim(・t(・rglas・;SRM612andagaallrationfEtorsC(ED1)=352=t3(lwano&Dan-hara,1997)andこ(ED2)=372±5(Danharaetal。1991).
㈲/:)(χ2)isthel)1’obabintyofobtaininμheχ2-valueforv(陶reesoffreedom(wherev=numb2rofcrystals-1).(5)risacor2lationcoefFficientbetw(lenpsand匪(6)SampleswereirradiatedintheTRIGAMARKHnuclearrea(1()ratStJaul’suniversit)z(RikkyoDaigaku),Japan.
(4232)07.909
(3149)267.909
(2430)0.85431010.8±0.3
(2430)0.89844010.610.4
weightedmean10.710.2
1.59(4286)2.14(5779)28.130(2498)0.902210
24
SufficientzircongTainswereconcentratedbysieving,PanningバmdstandardmagneticandheavyliquidseParatingtechniques.ThesePajratedzirconswerered,euhedralandveryhomogeilleous,and,dlcうrefデorらregardedas(:り5;5;ential.Fissiontrackdatingwascarriedoutusingthec5xternaldc5tectormethod,whichisaPpliedtoboth泊terrla1(pohshed)surfacesandextemalsurfacesofjrcongrains
(EDlandED2methods,resP(iうctively:GleadoNv,1981).TwosetsofdatawereobtainedindePende-ntlyind廿fel` entsystems(observers).Ageswere(JctllatedfollowingthezetaaPProach(Hurford,1990).TheexPerimenta1Proceduresand町stemc£111brationsweredet訟edelsewhere(seeDanharaet111・,1991;lwano&Danhara,1997).Thaesultsar(・listedinTable2。
Onlythefis三.ontrackdatingwasappliedfortheKt-フpyl’o(:;lastics,becausethetuffdoesnotcontainbiotitenorsumcienthomblendemineralsforK-Ar(lating.Wemeasuredfissiontrack百啓oftheKt-7Tuffonmorethan100zircongr21㎞lsthroughEDlmcthod.Thefissiontrackagewascalcu-1atedfrom100grains,whichwereregardedas(う5;sentialbasedonthecarefulobservationthroughm沁1°ol;coPe.TheresultsarelistedonTable2・
4.Discussion
WeobtainedtheK-Art)iotiteagc5sof10,67土0,25Maand10,44土0,25Maforthe幻-j,and10,56士0,18Maasw(:り毎hted-meana§;(:り(Table1).As;f` orf7issiontrackages,|:11eresultilrltages
(10,8士0,3Maand10,6士0,4Ma)ar(・consistentwitheachoth(2r,butthedatafromintemalzircon
・;l.Hfaces(EDnf` ailedtotheZ2-te・;tatthe5%1evel(Table2).DanharaetaL(1991)(うxplaine(lthatthemainsourceofthenon-PoissonvariationinEDldatacouldbeattributedtotheh婁価箆ogeneityofura-niumcontentsaboveandbelowtheobservcdintcmalsurfacesusingagestandardswithnocontami-nationofdetritallgrains,Takahashietal.(2001)concludedthatthemainreasonfortheresultofthe
x2-testisnotthecontaminationofde❼talgrainsbutthehetero即neityofm‘aniumcontents;insidethe
grain.lnfact,theED2datapassedthe万一test.ThcうI elyore,weadoPtedaweう塘11ted-meanvalueof10√7士O,2Maforthef7issiontrackageoftheKt-1Pyrodastic・;(’rable2).ThisagewellcoillcideswiththeK-Arageofthesametuff・Con坦三quently,wecanconcludethattheobtainedagesarel‘eiliableandindicatetheeruptionageoftheKt-1pyrodastics。
0nlyfissiontrack昭ewasobtainedforthe尺1-7Pumicetuf’HayerintheupPerpartoftheKubotaFormation.Thefissiontrackageof10,6士0,3Maindic包皿salmostequaltoboththeK-AraswellasfissiontrackageoftheKt-1Pyr()dastics;jntcit)eddedabout200mbelowtheKt-フTuff.ThusthehighsedimentaccumulationratefortheKubotaFormationissuggestedbychronostl` atigTaPhybasedonK-Arand/orfissiontrackages。
11{うcentlyHaya如etal,(2()00)recognized旭昭/と)Z7・フ・7μ乙❹心aαc∂皿7四臨fromalmostthesamehorizonasthedatedKt-1Tun’(Fig.2).TheFOof7VJ・:ヽ乙7J芯凹斑definc・sthelowe・stlimitofzoncN.16,whichisestimatedas10,9Ma(Bcrggrenetal.,1995)or11,0(Montilnarietal.1997,zonclN.1c),wnlcnlsestlmateclas八J,ソMa(,bcrggreneta払1ソソ匈or11,UりVlontananetal.1ソソ/,P・613).Thel` (5fore,theageoftheKt-1Tuf’f(10,6-10,7Ma)is1:)沁stratil;I’aPhicallyconstrainedtobe10,9Maoryounger.ThusthestratigraPhicl` elationbetweenthePlanktonicforamini弛ralbiostratigTa-
Phyandobtainedradiome❼cagesisveryconsistent(Fig.3).
Asforthecalcareousrlannofossilbiostratigraphy,someimPortantbiohorizonswererecogni“5;1111Tlamotoet11L(1998).TheFOofa加7yr・アノイと)❹泣ら(jefiningaCN5b/CN6boundary,zedbyl;hilrnamotoet21L(1998).TheFOof(:フ乙・rj回心・’
estimatedaO1,y10,9Ma(Beilyラ毒芸net;1L,1995)J/;lsrcうc()gnizedatthemiddlelevelt){うtweentheKt-3飢dKt-4tu汀horizolls,about30mabovetheljCt-1.TheFOof(:フ面z7乙7之rcαか観4/z4s,defh‘1ingthebaseofCN7whoseagewasestimatedas10,7Ma(or11,2MaMontanarietal・,p.613),wa5;1゛epor-tedattheuPperPartoftheKubotaFormation汀heotherimPortantbiollorizonofth{う唵stoccul‘rence
(LO)ofoccり/隔心加叩ε必が四百estimatedan1,0-10,8MaDslocatedattheuPpermostpartoftheKubotaFormation,about10mbelowtheKt-フpyroclastics(10,6±0,3Ma).ThusthccstimatedagesofeachbiohorizonalmostcoincidewiththeradiometricageoftheKt’1andKt‘7tufflayers.ThesechronostratigraPhicaswellasbiostratigraPhicag(5-estimatesstronglysuggestthatabout200“mthicklTlarinesedimentsoftheKubotaFormationmaybedePositedduringaveryshorttimeinterva1(theuncertaintyofthaadiometricages;ca.0,4Ma),indicatingahighsedimentationrate(>25,5(j‘n/100011に5j5m/Ma).
OdinG.S.(Ed.),Phanel` ozoicTimeScalらBull.Liais.lrlform.IUGSSubcomJeochlonol.,16,○治etParis,2000
25
Magneticpolarity/ChronI C 4 A r l C 5 n l C 5 「 |I I ■ | ㎜ ㎜ ■ ||
Calcareousnannofossil CN8a
CN71CN6NN5b S5
Planktonicforaminifera N.16 N.15 N.14eつ:Z
A g e ( M a ) j , I l 0 , 1 1 1 , 1 §
KamitoyoSectionNishikawa
●●●●●●●●●●●●
□
\
Kt-7
● ● ● ● ● ● ● ● ■ ¬ ・ I
L w U I り ・ り 1 ″ リ μ t が a S j ″ し u a ・ : r 、‾ ( 1 1 . 0 - 1 0 . 8 M a ) 。 ]
j l j ・ ■ ■ 1
j●●帰●●●●●・●●●●●●●●●●●●●●●●●●●●●●●●●●●●●偏偏偏●●■■■■■
♂ % ♂ % ♂ ゝ ♂ l g t 7 E 7 こ て て r で r l . . . λ . 、 ・ . 、 . ; . i f 四 ・ ゝ ` | 、 = 1 、
♂ ・ ♂ % ♂ ゝ ♂ む / ~ l i 箆 ご こ 「 ` ` ″ l ` 」 . ` 」 ` ゛ ・ ヽ 」 ” I ° ぃ リ 7 ‾ 7 r ‾ T T ‾ 7 :`
‥ に
♪| ; a 畠 温 - ミ●●●●●●●●●●●●●
. ・ ・ . ・ ● ● ●
診鄙Iニ∇レm
£ N 6ー j ・SS,SI ’i ・ ‘S・ ’ZiZi
ご ば 雪
CO
IKt-5.□コKI-4D2
Kt-4C
Kt-4B
KI,4A
KI・4
50mKt-3
Kt・2
Kt-lcKI-IBKI-IAKt-1
0
l 笙 陽 二 J 『 コ i N P D 5 c ?
圖 ‥圓 づ 尚
ド ザ ]
]プ]●●E]lj]
|……1、
CN6
V:洋i哨
ヤ
\jE]皆J∇..、,ンN16レ
へJ
\.;
几
PD5- - 再 J r x . ノ U l f v . d し U さ l a じ り a j a ‾ T T T て T T T . , ・ 、 ・ 軍
M n o M c n l : ‘ : ‘ ヌ ・ 、ゝ f ゝ r ・ r l f
心 _ _ _ l / ↓ 4 4 ハ e . ハ n ● ● 。 / 1 / A 。 ゝ ・ ・ t 乙 乙 - J l ・ ・ Z ,
m ‾ 二 三 元 已 回 二 ご ‾⑤
-F否否万万司fine-mediumsandstoneF万石で石lcoarsesandstoner7て7てltuff
FO:firstoccurrenceln・|きeヤnββHrr凸nr、凸
■ ■ ● ● ● ● ● ● ■
■ ● ● ● ● ● ● ● ● ■
■ ● ■ ● ● ● ● ■ ■
■ ● ■ ● ■ ● ● ● ■ ■
■ ■ ● ■ ■ ● ● ● ■
■ ■ ■ ■ ■ ● ● ● ■ ■
■ ■ ■ ■ ● ● ● ● ■
● ● ● ● ・ 蒔 ● 帰 ● ・
● ● ● ・ ● ● ● ● ・
1・「
Fig.3Stmtigraphicrelationshipbetx4’(・enthedatedt1Jffsandbiostrtaigmphkzones(illckldingsomeimportantbiohori-
zons).Theobtainedageilsofthe幻-jand尺1-7Tuffsandthenumcう雨alageofeachb沁horiz()n、estimatedonthebasis
ofthel3erggrenet11L(1995)’stim(5scale、afe出oindicated.
OdinG.S.(Ed.),PhanerozoicTim(・5;calらBu1LLiai!Jnform.IUGSSubcom.Geo(;11rono1・,16,()ffsetPil心,2000
5.Conclusion
26
K-Arand/orfissiontrackdatingwereappliedfortheKt-landKt-7Tuffs,in回箆beddedinthelowestPartanduPPermostPartoftheMioceneKubotaFormationintheTanaguraarea,Nol・theastJaPan。
TheK-Arbiotitellges(10,6士0,2Ma)andfTissiontrackalg6(10,7士0,2Ma)oftheKt-1
Pyrodasticscoincidewitheachother,suggestingthel°(うliabilityoftheagesobtained.ThefissiontrackageoftheKt-フpumicetuff(10,6士0,3Ma)弛111mostequaltotheKJUa.ndf`i∬iontrackagesoftheKt-1Tuffl
Theseradiometric啓発sshowgoodagTeementwiththel)17eviouslyestabHshedcalcaJ°eousand5;iliceoえlsmicl` ofossnbiostratigraPhy・
AcknowledgmentsThisworkhasbeenrealizedundertheaeがsoftheworkinggTouplntegratedStratigraPhyof
theMioceneSequence:MiocenefromJaPan,whichisundertheauspicesoftheSubcolllmissiononGeochronology(S.0.G.),lntemationa1CommissiononStratigraPhyofthel.U.G.S.lnthiscontext,山elong-standingconal:)orationwithProf.G.S.0dinofthePierreetMarieCurieuniversity(Paris)hasbeencうspeciallyhelpful.
References(*inJaPanesewithEnglishabstract.**inJaPanese)
Aita,Y.,1988.Neogeneplanktonicforal㎡niferafromtheKubotaForTnation,Tanaguraarea,NortheastHonshu,Japan.
BuII.FukushimaMuseum,(2)13-27.*
Baksi,A.K.,1993.AgeomagneticpolaritytimescalefortheperiodO-17Ma,basedon40Ar-39Arplateauagesfor
selectedfieldrevel・sals.Geophys.R(う・Lett.,20:1607-1610.
BerggrenJV.A・,Kent,D.V・,Swisher,C.C・III&Aubry,M.-P.,1995.ArevisedCenozoicgeochronologyandchro-
nostratigraphyjnBerggren,XV.A・,etal・,eds・,Geochronology,timescalesandglobalstratigraphiccorrelation,
SEPX/ISpecia1Pub.,54:129-212.
Blow,XV.H.,1969.LateMiocenetoRecentplanktonicforaminiferalbiostratigraphy.lnBrうnnimann,P.andRenz,H.
H.,eds.,Pro(氾(5dil唱softheF汀stlrltemationalConkrenceonPlanktonicMicrofossils,Geneva1967,1:199-422,
E.J.Brill,Leiden.
Cande,S,C.&Kent,D.V.,1992.Anewgeomalgneticp()1aritytimescalefortheLateCretaceousandCenozoic.Jour.
Geophys.Res.,97:13917-13951.
Cande,S.C.&Kent,D.V.,1995.RevisedcalibrationofthegeomagneticpolaritytimescalefortheLateCretaceous
andCenozoic.Jour.Geophys,Res.,100:6093-6095.
DaJlhara,T..Kasuya,M,&Yamashita,T・,1991.Fission-trackagecalibrationusingintemalandextemalsurfacesof
zircon.Jour.Geo1.Soc.Japan,97:977-985.
Gleadow,A.J.XV.,1981.Fission-trackdatingmethod:what訂etherealaltemative?Nucl.TrackDetection,2:105-
117.
Hayashi,H.,Yalllaguchi,T.&Takahashi,M。2000.Planktonicforarlliiferalbiostra唯raphyoftheMioceneKub()ta
Formationinthe}ligashitana卯ra町ea,FukushimaPr(うfecture.Abstr.2000AnnuaIMeet.,Paleontol.So(;.Japan,
31.**
Hurford,A.J.,1990.StJldardjzationoffissiontmckdatingcalibraUon:RecommendationbytheFissionTrackWork-ingGroupofth(・I.U.G.S,SubcomlnissiononGeoctlmnololly.(こhem.Gc・()いlsotopeGeosci.Sect.),8():171-178.
1taya,T・,Nagao,K.jnoue,K・,Honjou,Y。0kada,T.&Ogata,A・,1991.Argonisotopeanalysisbyanewlydevelo-
pedmassspectrome❼csystemforK-Ardatin11.Mineri1□our.,1j5:S203-221.1wano,H.&Danhara,T.,1997.Zetacil五brationoffis;sion-trackdaUngsystemusinghi1111-res()lutionmonitoraJ!dcom-
p姐sonofreportedzetavalue・J7issionTrackNewsLetters,(10),11-20.*Motoyama,I.&Maruyama,TJ998.N{logenediatomandradiolarianbiochro叩logyforthemi(l(11e-to-tli帥1atittldesof
theNo岫westPacil゛1cregion:Cal改ationtotheCandeandKe❹sgeomagneticpolaritytimescales(CK92and
CK95)Jour.Geo1.Soc.Japan,104:171-183.*
Okada.H.&Bukry,D.,1980.5;tlpplementarymod汀icationandintrc3ductionofcodenumb(,rstothelow心titude(;occo-1ithbios;tratigraPhiczonati()n(Bukry,197E3,1975).Maf.M虹opaleont()1.,5:2321-325.
Shimamoto・M。Hayashi,H.,Suzuki,N.,Tanaka,Y.&Saito,T.,1998.Lithostratigraphyandmkl・ofossilb沁chrono-
1ogyofNeogenesedimentsintheeastemTanaguraafea,FtlkushimaPre5fecture,NortheastJapan.Jour.Geol.Soc.
jl叩an,104:296-312.*
O函G.S.(Ed.),PhanerozoicTimdcale・,BuILLiai・Elnfo回.IUGSISt]bcollL(3e()(;11ronol.,16,0ffsetPaJis,2000
27
5;teiger,R.H.,&Jager,E.,1977.Subcommisionongeochronology:conventionontheuseofdecayconstantsingeo-
andcosmochronology.EarthPlanet.Sci.Lett.,36:359-362.
Takahashi,M.&Danhara,T.,1997.RssiontrackageofMioceneKn-3TuffincentralJapan:Towardsbetterage-
controlonmagne杖)-biostratigraphictimescakJour.Geomag.Geoelectr.,49:89-99.’rakahashi,M.&Oda,M。1997.Geology,tectonics,andintc5gratedstratigraphypotentialofJapan.lnMontanari,A.et
aL,eds・,MioceneStntigraphy:Anlnt昭ratedApproach,(15y187-202,1EElse,・ier.
Takahashi,M。Hayashi,H.,Tanaka,Y.&Okada,T.,2000.1ntegratedstratigraphyofthelowerl)artoftheMiocene
Kafasuyamasequence,centralJapan.Japan.Assoc.Petrol.Technol.,65;571-583.’rakahashiM.,HayashiH.,DanharaT.,lwanoH.&OkadaT.,2001.K-ArandfissiontrackagesoftheKt-ITu汀in
theMiocenemarinesequenceintheTanaguraafea,NortheastJapan.Japan.Assoc.Petrol.Techno1.,66:inpress.
Taketani,Y.&Aita,Y.,1991.Miocenea(1101ariafromtheKubotaFormation,Tanaguraafea,NonheastHonshu,
Japan,BullJukushimalVluseum,(5)31-51.*Xvei,W。1995.Revisedagecalibrationpointsforthegeomagneticpolaritytimescale.Geophys.R(うs.Lett.,22:957-
960.
Yanagisawa,Y.&Akiba,F.,1998.RefinedNeo卯nediatombiostr21tigraphyforthenorthwestPacificaroundJapan,
withanintr()ductionofcodenumbel’1;fol’s(うlecteddiatombiohorizor11;.Jour.Geol.SG;.Japanj04:395414.
Yallagisawa,Y.,Yamaguchi,T.&Hayashi,H.,2000.Diatombiostr21tigraPhyoftheMioceneKubotaFormationin
the}-I址ash姐naguraafea,FukushimaPrefecture.Abs;tr.2000AnnuaIMeet.,Paleontol.Soc.Jap2lnJ9.**