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I..ANI)FOR5・ISANDMANGROVEHABITATINT11ESATUNLOXVLAND, SOUTIIEllNTHAILAND MasatomoUMITSU゛,PaiboonPRAMOJANEE大・,AkioOHIRA角・大, KumikoKAVVASE゛andJingFANG゛ ゛DepartmentofGeo琴巾尚垂聯自警匹oyauniversity9・IAPAN ゛゛SchoolofMarineandCoastalResourceManagementTechnology, iValailakuniversitv,THAILAND ~゛SchoolofEduc・ltion,M珍azakiuniversity lntroduction Them。grovev雨雲tatedshorelineshad widelydevelopedinthesouthwesl:empaftof theMalayPenisula.lnthelatterhalfofthe twentiethcentury,mostmangovevegetation insouthemThailand,however,was(lestroyed byhumana(;tivities(Aksomkaoeand Paphavatist,1993),andwdlprel;erved mangrovefol`estscanbeseenonlyinafew limitedareas。 Thisstudyaimsatexllminingthelandforms andsedimentsofanestuarinelowlandin l’elationtothemangrovehabitat,andalso discul;sestheefTectofthefilturesealevelrise causedbythe11reenhouse{1111ecttothe mangrovedistributionofthestudyarea。 ThestudyareaistheSatunlowlandinthe southw6tempartoftheThajlandwherethe rnangoveve筝tatlonlspl゛‘:;servedlna rdativelybettercondition. Regionalsettings TheSatunlowlandlocatesinthe southwel;tti npartof゛IS4alaype111stlla,andis sulToundedbyrelativelylowmountainsand hinswithheightofseveralhundredmeters. Thelowland,about25kmfromnorthto southand10-lj5knln・omeasttowest,faces totheStral小tofN,1111acca,andsomeisolated limestonehinscanbeseeninthelowland。 Theheightofthelowlandisabout20min thenorth,5-8minthecentralpart,lower than2-3minthesouthempart,respectively・ Mostl;otlthempartofthelowlandislower thanhi小tidelevel,andis皿)veredwith mangovevel芦itation.Tidalran誤()f`thisarea basedonour()bservlltionsinDecember1996 andinSeptember1997wasapproximately2 to3meters. FigJMapshowingtheSatunlowland. Nlethods Geomorpholoがcalandgological investiptionhavebeendoneinlate1996and middle1997.Aほldfomlclassifical:ionmap wasdrawnusing1:40,000scaleaerialphotos. Toclarifythelandformsandge()k)gical 121jaturesoftheregjon,theauthorsdidneld research皿d(;ollectedsomel;anlplesusinga handauga’.Somesampleswere∞hctedfor -155-

I..ANI)FOR5 ......I..ANI)FOR5・ISANDMANGROVEHABITATINT11ESATUNLOXVLAND,SOUTIIEllNTHAILAND MasatomoUMITSU゛,PaiboonPRAMOJANEE大

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I..ANI)FOR5・ISANDMANGROVEHABITATINT11ESATUNLOXVLAND,SOUTIIEllNTHAILAND

MasatomoUMITSU゛,PaiboonPRAMOJANEE大・,AkioOHIRA角・大,KumikoKAVVASE゛andJingFANG゛

゛DepartmentofGeo琴巾尚垂聯自警匹oyauniversity9・IAPAN゛゛SchoolofMarineandCoastalResourceManagementTechnology,

iValailakuniversitv,THAILAND~゙ SchoolofEduc・ltion,M珍azakiuniversity

lntroduction

Them。grovev雨雲tatedshorelineshad

widelydevelopedinthesouthwesl:empaftof

theMalayPenisula.lnthelatterhalfofthe

twentiethcentury,mostmangovevegetation

insouthemThailand,however,was(lestroyed

byhumana(;tivities(Aksomkaoeand

Paphavatist,1993),andwdlprel;erved

mangrovefol`estscanbeseenonlyinafew

limitedareas。

Thisstudyaimsatexllminingthelandforms

andsedimentsofanestuarinelowlandin

l’elationtothemangrovehabitat,andalso

discul;sestheefTectofthefilturesealevelrise

causedbythe11reenhouse{1111ecttothe

mangrovedistributionofthestudyarea。

ThestudyareaistheSatunlowlandinthe

southw6tempartoftheThajlandwherethe

rnangoveve筝tatlonlspl ‘゙:;servedlna

rdativelybettercondition.

Regionalsettings

TheSatunlowlandlocatesinthe

southwel;tti‘npartof゙ IS4alaype111stlla,andis

sulToundedbyrelativelylowmountainsandhinswithheightofseveralhundredmeters.

Thelowland,about25kmfromnorthto

southand10-lj5knln・omeasttowest,faces

totheStral小tofN,1111acca,andsomeisolated

limestonehinscanbeseeninthelowland。

Theheightofthelowlandisabout20min

thenorth,5-8minthecentralpart,lower

than2-3minthesouthempart,respectively・

Mostl;otlthempartofthelowlandislower

thanhi小tidelevel,andis皿)veredwith

mangovevel芦itation.Tidalran誤()f` thisarea

basedonour()bservlltionsinDecember1996

andinSeptember1997wasapproximately2

to3meters.

FigJMapshowingtheSatunlowland.

Nlethods

Geomorpholoがcalandgological

investiptionhavebeendoneinlate1996and

middle1997.Aほldfomlclassifical:ionmap

wasdrawnusing1:40,000scaleaerialphotos.

Toclarifythelandformsandge()k)gical

121jaturesoftheregjon,theauthorsdidneld

research皿d(;ollectedsomel;anlplesusinga

handauga’.Somesampleswere∞hctedfor

- 1 5 5 -

radiocarbondatingalldforbothchemicajand

paleontologicalanalyses.TheboringsitesinthelowlandareinandaroundSatunurban

area,andinseveralspotsalongtheroad

number4183toFerryport,

LandformsoftheSatunlowland

Theelevationofg’aterpartofsouthem

Satunlowlandisbetweenthenleantidelevel

andhi小ti(lelevel,andthereがoniscovered

withtidewaterduring

l:heh肺tie.Thi,;1・(,gion1台台轟面映(:lasatidal

plain.IUversastheKhlongThaChin(ChinRiver),KhlongPhrao(PhraoRiver),Khlong

l3slBang(Ban1BangRiver)nowinthesouthempartofthelowland,andmanytidal

cl‘eeksdeveloponthetidalplain.Amongthe

tidal(;1-eeks,therearesomelargcreeksasthe

KhlongTaMiang(TaMiajngCreek)witha

widthofseveralhundredmeters.Themouth

oftheseriversformsalargee5;tuary,andit

extendstotheinlandapproximately2,5and

withthenlaximumwidthis2.0km.Tidalnats

developalongthemouthoftheel;ttlaryinthe

levelbetweenrlleantideandlowtide.

Mangrovefol‘estsdeveloponthegeaterpart

oftheuppertidalplain,butmuddysediments

areexposedinthetidalnat.

0ntheotherha.nd,thedensityofl;treamnetworkislowinthenorthemhalfofthe

lowland。

Riverscannotbeseeninthecentraland

northemlowlandexcepttheKhlongW皿gPra

(Wa.n11PraRiver)anditり)ranchesandKhlongBamBag(BamBangll,iver).Thesel`ivers

(nssectthesurface()f゙ thelowland,andform

nalTowvalleyplains.Relativehei小ts

betweenthe陶成lceofthelowlandandthe

vaneyplainsare3-5meters。

Sincethee21stemmountainsandsmallhills

inthe(;entrallowlandareconsistedof

limestone,theslopesofthemountainsand

hinssu汀oundedbythelowlandarevery

l;teep.Lowandgentleslopesandrelatively

natsurfaceswiththeh面映tofabout20-30m

developalongthefootofmountainsandhills

inthew6temmarljnofthelowland.The

mrfacesedimentsofthere画onafeoxidizedin

deepreddishbrown()()1()r、anditis

remarkablydUfflrentfiomthesedimentsof

thelowland.

I)kistocenesediments

uppersedimentsofnorthemhalfofthe

lowlandisremarkablyd汀ferentfyomthoseof

thesouthemh毒曇Theboundaryofthetwo

男旱onsisalmostalongtheeast-westline

acl’()sstheSatunurbanarea。

lnnorthempart(:)f` thelowland,thel;urface

sedimentsconsistofthegaywhiteand

occsiona11’e(ldishmottledsiltys飢dorsa,ndy

silt.Thissedimentsarel’elativelyhafdand

compact,alsoseenintheoutcropsnearthe

airportwhichlocates2kmnorthofSatun

urbanarea。Thel;url:11cesedimentsofthearea

aroundBanThaChinwhichlocatesnorthof

theKhaoWangMan(Mt.WajngMa,n)arethe

same.Sincethesedimentsafenotdeeply

weatheredincomparisonwiththereddishweatheredsedimentsinthesu汀oundingrφon

ofthelowland,itseemstobefk)rmedinthelatePleisl:()cene。

Thesul-IF11ceofthisPlei山)cenesediments

l)ecomeslowerandisc()veredwithrecent

muddysedimentstowardstheso山:hempart

()fthelowland.The(lepthsofthePleil;tocene

srfaceare0.5-1。0minandaroundthe(:;entral

partofSatunurbanarea,2minthe釦u幽emmarginofSatunurbanareawhichlocates10

kmfromthecoast,andabout5matthesite

about5kmn’omthecoast.Thel;urfllceis

lowerthan7mintheregionnearthecoast。

ltisclearthatthe5;ulfaceofthis

Pleil;1:ocenesedimentsbecomedeepertowards

thesouth,anditfbrmsalow筝ntlel;urfllcein

thenorthempartofthelowland.Asthe

gradientofthisPleist()cenesu吋a£eisl;teeperthanthetidalplainofthelsouthemlowland,

thePleis;1:()cenel;urfaceisconsideredtobe

fk)rmedinthelatePleistoceneorthelast

glacialperiodunderthelowersealevel.

Holocenesedimentsandtheirage

ThesedimentswhichcoverthePleistocene

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Mostofthesedimentsinthesouthempart

oftheSatuncoastallowlandconsistofmuddy

sedimentswithpeatlayerintheupper卜1.5

m.Themuddysedimentsaregreengayor

blueぎaycolor,anditsu留eststhatthe

sedlmentsaremanneongln。

Apeatlayerinthemuddysedimentsatthe

siteof961130-4canbeseeninthedepthof

3.10-330m,A筝ofthepeatis6640±90

yrBP(NUTA-5161).Thisshowsthatthe

l)eatlayerwaslFormedintheculminationoftheHolocenetrajnsgression.Ageofthepeaty

materialintheupperpartofthemuddy

sedimentsnearBanKaianBatualthesiteof!;)61201-lis5710±100yrBP(NUTA-5159).

Thisalsoshowstheal尹ofth(5culminationof

theHolocenetransgression。

ConcentrationofwoodylFyallmentscanbe

seenatthedepthsof5.06-5.78mand6」8-

6,94mofthesiteat970922-1,3kmfromthe

coastline.Sedimentsinbetweenandoverthe

woodyl:hgmentsaresandorsandymud.

A聊邑ofthewoodfragmentsare950±130

yrBPatthetophorizonand1270±200yrBPatthebottomhorizon,resp警謐vely.These

al尹5;sugl尹stthatthewoodyf` ragmentsarenot

thet)a5;alpeatbutthecon(こ(うntrationofdrifted

m2 -

961130-1

- - -

Peatymud

W -

Silt- - -

・ 一 一 一 一 一 一

;Sandysilt

Marineclay

%1201-3

-

Silt

W - 〃 〃 ・ - - 〃 - J I I - 〃 -

Siltyclay

リIS4-

Woodfragments

970922-1

Peat-Peatymud- - - W - - 皿 - -

M t x j

970923-1

Marinemud

Sandysilt

woodlfi’agmentsalongsandspitorbarwhich

extendedfi・omthewest.

Landfi)rmsandMangrovehabitat

Asmentionedabove,thelandlFormsofthe

Satunlowlajldarenotasimplegomorphicl;tlrfacebuttheml‘facesofPleistoceneand

lateHolocene.ltisfairlyhardtodistingμish

theboundafyoftwos;ul・facesinthefield,but

itispossibletotracetheboundaryfiomthe

detailanalysisofaerialphotos.These

boundariescanbeseennotonlyalongthe

KhlongWangPrabutalsoalongtheKhlong

ThaChin(ThaChinRiver)andtheKhlong

KhanChin(KhanChinRiver).Thesel’iversdissectedthePleil;tocenel;tlrfacevery

shallowlyandlデk:)rmednarrowvalleyl)lains。

UppersoftsedimentsonthePleil;tocene

sedimentsnearthecentralpartofSatunurban

areaareverythinandrnainlyconsistofsandy

sediments.Thisl;t111Fststhatmangrove

,reli,tationhaven’tc,)veredtheregionsince

themiddleHolocenewhenthemarinearea

e)cpandedaccordingtothepostjacial

trarls;gresslon‥

Mangrovevegetationd(うvelopsnorthof

KhaoWangMan(Mt.WangMan)which

l,:)cateseastofSatunurbanarea.The

%11304970922-2961201-2970923-2

- 一 一

Mud

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664()±90

PLEIST(:X2ENE

Mud

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Peaty

m u d

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〃 〃 〃 - ・ 〃 〃 〃 - ・ 〃 〃 -- W 〃 〃 - 〃 - - l 〃 -

手.3Geological(;rosssectionoftheSatunlowland斤omsouthtonorth.

-158-

0 lkm

1‘4uddyPeat

PLEIST(XこENE

Marinemud

CoarseSand

〃 〃 〃 〃

IFりeistocenel;urfllce,however,(ievelopsjust

northofthel)resentmaJlgoveforest.This

rll,:濯lsthatthen71angr(:)veforest❼ヲ` theareain

themiddleHolocenee7q)andedalmosttothesouthemendofthePleistocenel;ulfllce。

Mangrovevegtationneaftheeasternpart

ofSatunurbanareainthemiddleHolocene

a15;oexpaJldedtothel;outhemendofthe

l)leistoceneliul‘face,Thepresentmangrove

limitoftheareaisalsoverydosetothe

southemPleistocenelimit.ltisaboutlkm

southfi・omthePleistocenestldace。

SouthemmostpartLoftheSatunurbanarea,

however,isnotcoveredwithma.ngrove

R)rests,andtheareaissubm琴声dbynood

tideinthetimeofhi小tide.Thismeansthat

thep妻皿ntlimitofthe111angrovehabitatin

theareaisnotthenaturalconditionbutthe

conditioncontrolledbythehumaJlactivity・

Furtllermore,thedistancebetweenthe

sollthemendofthePleisl:(:)cenesl血ceand

thenortllemendofthepresentMangrovefol’estsalongtheKhlongPharao(thePhafao

River),justeastofSatunurbanareaisonlylkm.ThislsuglgeststhemiddleHolocene

l‘11angrovelimitwasnotarn’omthepresent

mangrovelimit。

Thereisnodetailrecordofthemiddle

HolocenesealevelintheSatun鸚皐on.Evenif

thesealevelinthemiddleHolocenewas

hi小ertha,nthepl‘esentsealevel,thelimitof

mangrovevegiitalionatthattimewasnotso

dほerent斤omthatofthepresent,becausethe

southemlimitofthePleistocenel;urfhceis

veryclosetothepresentmangrov{31imit.

Concludingl‘{lmarks

Landforms()ftheSatunlowland(;onsistof

Pleil;toceneaJldlateHolocenelsurfllces.The

Holocenesurfactl(;onsistofthelateHolocene

sedimentswhichdepositedinandafterthe

Holocenetransgession.Southempartofthe

lowlandisclassinedasatidalplain,andthe

levelofthetidalplainisbetweenhi小tideandlowtide.Presentinangrovev響蓼tation

developsonthetida11)lain.lnthemiddleor

lateHolocene,nlangoveforestdeveloped

alongtheexl)andedinletoftheSatunbayand

southemlimitofthePkistocenesurface.

DistancebetweenthenorthernlimitofmangroveforestinthemiddleHoloceneand

thatofthepresentoneislessthan2kmin

rnaxlmum。ICPP(1995)estimatesthesealevelrise

unti12100ADtobeabout50cmasthemean

valueandaboutlmasthenlaximumvalue.Thesevaluesaren’thi小erthaJlthemiddle

HolocenesealevelintheMalaypeninsula

参蓼()nr(・portedbyl;insakl(1992).Andsince

幽ePleilsll(:)c{311esurface()nheSatunlowlandisrelativelysteeperandhi小erthanthe

Holocenelsul’face,southemmostpartofthe

Pleil;tocenesurfllcewinnotbecoveredbythe

expandedinletcausedbythesealevelrise,

Thel-efbre,evenifitisassumedthatthesea

leve11-{iachestotheestimatedvaluein2100

ADunderthepredictedsea-levelrise‘こaused

bythegeenhouseeffect,nlanぎoveR)rest

willnotexpandfurthernorthofthelimitof

l:heMiddleHolocenemangroveforest.

Acknowledgment

Wewouldliketoexpressourthanksto

ProflT、Kawana、Mr.K.lchikawa、Mr.J.

TsuchiyaandMr.T.Takaifortheirfield

assistanceofaugringWealsoexpressour

l:hankstoDr.CharlchalTanavud(Princeof

Son福轟un沁・i・rsty、’Trhail飢d)forhiskindhelptoourl゙ elserch.

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Urnitsu,M.(1997)DevcうI()pmentandEnvironmentalChangesoftheJapaneseD,:・ltas.REKIHAKUlntel・1・lationaISymposium:Terl・{:5striaIEnv汁onmentalChangesandNaturalDisElsters(luringtheLa・;t10,000Years.(国立歴史民俗博物館)

海津正倫(1997)沖積低地の古環境変遷と人間活動.タンデトロン加速器年代測定装置の 学 際 利 用 と そ の 地 球 環 境 解 析 へ の 応 用 . 名 古 屋 大 学 年 代 測 定 試 料 研 究 セ ン タ ー シンポジウム.(名古屋大学)

海津正倫(1997)完新世における環境変化と熱帯デルタの地形変化.地球惑星科学関連学 会 合 同 大 会 シ ン ポ ジ ウム , 地 球 規 模 変 動 に 対 す る 熱 帯 海 岸 環 境 の 応 答 と 対 応 戦 略 .(名古屋大学)

海津正倫( ‘ 1罷賜)デルタ海岸の地形変化.IGCPシンポジウム「最近地質時代の地球環境」.(神戸大学)

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