Stable isotope record of Late Quaternary Sediments from northwestern Bengal Basin,Bangladesh 著者
雑誌名 号 ページ 発行年 URL
H.M. Zakir Hossain, Md.Sultan-UI Islam, Mst.Fahima Ferdousy, John S. Armstrong Altrin, Alcides N Sial, lsmail Hossain, Quazi Hasna Hossain Earth Evolution Sciences 10 3-14 2016-03-25 http://hdl.handle.net/2241/00141633
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Keywords:Carboni s o t o p e ;Oxygeni s o t o p e ;Q u a t e r a lB a s i n ;8 a n g l a d e s h n a r ys e d i m e n t ;8 -e -n "g 0 . J
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compositionsofc a r b o n a t e sa r eh i g h l ypronet oa l t e r a t i o nduringd i a g e n e s i sa n d / o rp o s t d e p o s i t i o n a lmodif i c a t i o n s(Hudso ， l !1 9 7 7 ; Hossaine ta ラ . l 2013;Fane t a ， . l2 0 1 4 ) . ・ oms t a b l e Thisstudyp r e s e n t snewi n s i g h t so b t a i n e df l !andoxygeni s o t o p er e s u l t sofLateQuaternary carbol bulk sediments analyzed w i t h i n two d r i l lc o r es e c t i o n soft h enorthwestern Bengal Basin，Bangladesh. TheUl3C 1 ' rombulksediment( e s p e c i a l l yi np e l a g i cd e ls e da sas t r a t i g r a p h i ct o o lt oe v a l u p o s i t s )i swidelyL a t ea n c i e n tshallowwaterc a r b o n a t es e t t i n g soframps and carbonate p l a t1 ' orms ( S c h o l 1 e and Arthur ，1 9 8 0 ; ちt s c he ta ラ . l1 9 9 8 ;G i s c h l e re ta ， . l 2009)，anda l s ot o Gl p r o v i d ei n f o r m a t i o n on reworkingpaleoenvironmen9 8 4 ) .S t a b l ei s o t o p estudy01 ' t a levidences( C e r l i n g1 sedimentsi nt h eBengalBasin0' 1Bangladeshi sl i m i t 9 9 4 ;Alam e d l yprovided(France-LanordandDerry 1 e ta ぅ . l1 9 9 7 ;Hossaine ta ラ . l2 0 1 3 ) .However ラt h eLate Quaternaryp a l e o c l i m a t i cv a r i a t i o ni nt h enorthwestern BengalBasini ss t i l ll a r g e l yu n c l e a r ・d uet oi n ad e q u a t e numbersoflong-sequencedsedimentaryc o r e( 1 8 41 1 1 ) 't h i ss t u d yf o c u s e s p a l e o c l i m a t i cr e c o r d s .Theaim01 ondi a g e n e t i ca l t e r a t i o n s01 'c arbonateremainedi nc o r e ' 01 't h epaleoenviron sedimentsandt h econsequences1 mental，paleotemperatureandp a l e o c l i m a t i ci n t e r p r e t a t i o nu s i n gs t a b l ei s o t o p e s . ・
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Geologicals e t t i n g TheBengalBasinofBangladeshi sl o c a t e da tat r i p l e . e .t h el n d i a np l a t et h e j u n c t i o nof1 i t h o s p h e r i cp l a t e s，i E u r a s i a np l a t eandt h eBurmeses u b p l a t e(Alame ta l 2 0 0 3 ) .I tcomprisest h r e eg e o t e c t o n i cp r o v i n c e s，such a st h es t a b l es h e l仁t h ec e n t r a l deep b a s i n( e x t e n d i n g fromt h eS y l h e tt loughi nt h en o r t h e a s ttowardst h eHat i at r o u g hi nt h es O l l t h )，andt h eC h i t t a g o n g T r i p u r af o l d b e l t(Alame ta l 2 0 0 3 ) .Theb a s i nf i l lh i s t o r ・ yoft h e s e h i c k p r o v i n c e sv a r i e dc o n s i d e r a b l y，andcomprisesat sedimentaryr e c o r d(~22 km)ofdominantlyc o n t i n e n t a lt o marine c l a s t i c sediments and s m a l l carbonate ta ラ . l2 0 1 0 ) . r o c k s(Alame ta lぺ 2003;Hossaine 'g e o t e c Thep r e s e n ts t u d ya r e al i e sont h eS t a b l eS h e l1 t o n i cp r o v i n c e(Alame ta ， . l 2003)，andi sc 10sedt oP r e cambrianl n d i a nS h i e l dP l a t J o r m( F i g .1 ) .Thea r e ai sa p a r toft h eNawabganj-Gaibandhal n t r a c r a t o n i cHigh andcomprisesat i n yl i n e a rf e a t u r et r e n d i n gNE-SW ラ . l1 9 9 7 ) .A t o t a l01 '~ 1 5 8m t h i c k d i r e c t i o n(Alame ta L a t eQuaternarysediments3 r eencounteredi nChapai Nawabganj d i s t r i c t， northwestern Bangladesh. The s t u d i e dsedimentarys e q l l e n c e sBH-l( 5 3m)andBH-2 ( 4 0m)a r ep l a c e di nt h eRajarampurandChanlaia r e a， r e s p e c t i v e l y，oft h eChapaiNawabganjdi s t r i c tn o r t h western Bengal Basin 01 'B angladesh. The Neogene ラ
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sedimentsl i ed i r e c t l yovert h eP l ・ ecambrianbasement r o c k si n s t e a dofthePermianGondwanarocksa si ti si n o t h e rp a r toft h eS t a b l eP l a t f o r m .Geomorphologically t h ea r e ai sl o c a t e dont h e lowerMahananda-Ganges f 1oodplain.I ti sac o r r i d o rofthemightyGangesRiver boundedbyPrecambrianI n d i a nP l a t f o r m L a t eJ u r a s lsR ajmahalV o l c a n i c sont h ewest s i ct oE a r l yCretaceoL andt h eu p l if t :edPleistoceneBarindTractsi nt h ee a s. t l ti sana r e a01 'g r a v i t yhighandPermianGondwanai s missingduet ou p l i f t m e n ta n d / o rn o n d e p o s i t i o n .Even P l e i s t o c e n e Barind T r a c t sediments a r ea l s oa b s e n t ・ theastward 1 1 1 0 S t probably d l l et oe r o s i o n during 1 1 0 1 journeyoft h eGangesR i v e r .From40m i nBH-2and ，d arkgrayt oy e l l o w i s hgraycarbon5 3m i nBH-lgray a t e dmlldl a y e rwiths i l t yandsandyi n t e r v a l ss t a r t e d whichc o n t a i n i n gmolluscans h e l l swithd i1 ' f e r e n tt y p e s 'o r g a n i cremainsandt h i nv e i n sofpeat .Thiscarbon01 a t e dmudl a y e rc o n t a i n smarinem i c r o f o s s i l s( f o r a m i n s t r a c o d a ) 01 'mainly Holocene age ( F e r d o l l s y i f e r a，o 2 0 1 1 )andi n d i c a t i n gt i d a lm l l d f l a t lagoon marsh low s a l i n et ob r a c k i s hwaterenvironments.Thesequencei s n o td a t e dbyanyr a d i o m e t r i cmethodsb u tt h i stypeof mangrovewoods t h i c kmudl l n i t(max.25m)withp e a t， andmarinem i c r o f o s s i l s( 1 0 7kay e a r s )a r ep r e s e n ti n t h eWestBengalp a r toftheGanges-Brahmaputrad e l t a ラ . l 2009).Radiocarbondatingoft h ea c t i v e ( S a r k a re ta Bengald e l t asedimentsfromadepth01 '25t o30m b e ' acer e c o r d sanageof8400y e a r sBP(Goodbred lows u r1 0 0 0 ) .Boreholesl o gi nt h ec o a s t a lr e g i o nof andKuehl，2 Bangladeshi n d i c a t eHolocenef i n e g r a i n e dsediments s e v e r a lt e n sofmeterst h i c ka s s o c i a t e dwithm勾orcomp a c t i o na l l i e dsubsidence(~5 mm/year)(Goodbredand Kuehl 2 0 0 0 ) . The s t r a t i g r a p h i cs u c c e s s i o n of t h e northwestern BengalBasini ssummarizedi nTable 1 .Summarized l i t h o t a c i e sl o goft h e BH-l and BH-2 a r ei l l u s t r a t e d i nF i g .2 .TheL a t eQuaternarysedimentarysequence c o n s i s t spredominantlyofc l a ywiths u b o r d i n a t esandyo rs i l t y c l a y with o c c a s i o n a l l yc o a r s e sand and c o n lTheuppermostp a r t01 'b oths e c t i o n s g l o m e r a t e / g r a v e. i sc h a r a c t e r i z e dbybrownishs i l t y c l a yt o p s o i. l ラ
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R e s u l t s The c a r b o n and oxygen i s o t o p i cc o m p o s i t i o n so f c a l c a r e o l l ss e d i m e η t si nt h eL a t eQuaternaryc o r es e c t i o n sa r eg i v e ni nT a b l e2 .The813C v a l u e sr a n g efrom .45%0POBi nRajarampurs e c t i o n( B H I )， 0 . 8 9 % 0t o1 and0 . 8 5 % 0t o0 . 5 6 % 0POBi nC h a n l a is e c t i o n(BH80v 2 ) .Sim日a r l y81 a l u e sv a r yfrom1 2 . 1 1 % 0t o5 . 5 7 % 。 POBand1 2 . 1 4 % 0t o1 2 . 9 2 % 0POBi nRajarampurand C h a n l a is e c t i o n sr e s p e c t i v e l y .The813C v a l u e sshow r e l a t i v e l yc o h e r e n tv a r i a t i o n s andf lu c t u a t e between . 45%0POBi nt h euppermost p o s i t i v ev a l u e so fn e a r l y1 BH-ls e c t i o nandn e g a t i v ev a l u e so fa b o u t0 . 9 5 % 0POB i nt h elowermostBI lls e c t i o n .C o n s e q u e n t l y，a l lsamp l e sfromt h eBH-2 d i s p l a yn e g a t i v e813C e x c u r s i o n s w i t hmaximumv a l u e sI nt h et o psample( S .No.BH)a ndminimumv a l u e sa tt h eb o t t ol11sample( S .No. 2 .1 1 3 B H 2 . 6 )( τ a b l e2 ) .Ont h eo t h e rhand t h e8 0 v a l u e s a r e1 1 1 0 s t l yi d e n t i c a lt h r o u g h o u tt h ec o r es e c t i o nBH-2 1 2 . 5 1 % 0POB)，whereast h elown e g a t i v ev a l u ei s ( a vi d e n t i f i e di nt h et o ps e c t i o no ft h ec o r eBH-l (B1 I 1 .1 =5 . 5 7 % 0POB). ぅ
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C a r b o ni s o t o p es i g n a t u r e sp r o v i d el l s e f u li n f o r m a t i o na b o u tt h ee x c h a n g e a b l es u r f a c eo c e a n i cc a r b o n r e s e r v o i r s( F a r 可u h a re ta う . l1 9 8 9 ) .V a r i a t i o ni n813C i n
marinec a r b o n a t e scanr e f l e c tc h a n g e si nt h ec a r b o n c y c l et h a tc a nb ea s s o c i a t e d¥ v i t hc h a n g e si no c e a n i c p r o d u c t i v i t yanda t m o s p h e r i cgreenhouseg a s e s( M a r 9 9 2 ) .Carboni s o t o p ev a l u e sa r er e l a t i v e l ymore s h a l l，1 s t a b l ed u r i n gp o s t d e p o s i t i o n a ld i a g e n e t i ca l t e r a t i o n ，s h i f t sc a nb e t h a n oxygen i s o t o p ev a l u e s，however s i g n i f i c a n twhereo r g a n o g e n i cc a r b o ni si n c o r p o r a t e d ( M a r s h a l l，1 9 9 2 ) . TheU13C v a ll 1e sf o rIe c e n tm a r in e 9 7 7 ) . c a r b o n a t e sr a n g ebetween0%0and4%0(Hudson，1 TheU13C c o m p o s i t i o n so ft h es t u d i e db u l ks e d i m e n t s a l ・ ec o n f i n e dt oanan ・ owr a n g eパangingf r 0 1 1 10 . 9 5 % 。 t o ω 0 . 5 6 % 0PDB whil eonesample(BI II . l )h a sp o s i t i v e a l u eupt o1 . 45%0POB( T a b l e2 ) .Thelown e g a 813C v 1C v t i v e83 a l u e si nt h es e d i m e n t sr e f l e c tt h ee f 、f e c t so f ラ . l p e d o g e n i c1 1 1 0 d i f i c a t i o no fc a r b o n a t e s( B e l l a n c ae ta 1 9 9 5 )t h a tp o s s i b l yc o n t r o ld i a g e n e s i sbym e t e o r i c¥¥la t e ra n d / o rc h a n g e si nr e l a t i v es e a I e v e l( A l l a nandMat9 8 2 ) .The11l0 r ep o s i t i v e813C v a l u e s( 1. 45 % 0 ) thews 1 o c c u r r e da t4 0 1 1 1d e p t hi nBH-I l i k e l yr e f l e c ts e a I e v e l f 1u c t u a t i o n s，i n c r e a s i n gf r e s hw a t e rc o n d i t i o n sa n d / o rs t r o n gi n f l u e n c eo fwarmerc l i m a t e s .A c a r b o n a t e d 1 1t h i c k )c o n t a i n sm o l l l l s c Ss h e l l sa n c l mud l a y e r(~5 1 c h a r o p h y t e si nt h eb o r e h o l eBH-l a r o l l n d40m d e p t h ( F e r d o u s y2 0 1 1 ) .P r e s e n c eo f m o l l u s c sandc h a r o p h y t e s 1p p e rc o r es u g g e s td e p o s i t i o na s s o c i a t e dw i t ha i nt h el f r e s h w a t e renvironment( S a n j u a ne ta ， . l2 0 1 2 )a n d / o r f 1u c t u a t i o nbetweens a l i n eandf r e s h w a t e rc o n d i t i o n s . I Iowever upperp a r toft h eBH-I i sc h a r a c t e r i z e dby f i n eg r a i n e ds a n d，s i l tands i l t y c l a y( F i g .2 ) .Thet h i c k c 1a y -01 's i l t y c l a yl a y e ri nb o t hc o r e s(~50 m)c o n t a i n s ・
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a b u n d a n tf r e s hw a t e ro r g a n i cm a t e r i a l sandp e a tr e mains( F e r d o u s y ，2 0 1 1 ) .R a s h i de ta . 1( 2 0 1 3 )n o t e dt h a t t h eh i g h e s tr e l a t i v es e a l e v e It r a n s g r e s s i o no c c u r r e di n B a n g l a d e s ha t-6000c a lBPb a s e dona b u n d a n tmar i n ed i a t o m sa n dmangrovep o l l e n s .However ，t h ep a l e o c o a s t li n es t a r t e dt or e t r e a tt o w a r d ss o u t hf 1 'omt h e c e n t r a lB a n g l a d e s hb e f o r e4870-4780c a lBP( R a s h i d e ta ， . l2 0 1 3 ) andaf r e s hw a t e rpeat-swampe n v i r o n l 3 mentwasd e v e l o p e di nt h er e g i o n .Tbep o s i t i v eU C v a l u e si nBH-] ( 4 01 1 1 )a r ec o n s i d e r e dt ob er e l a t i v e s e a l e v e lc h a n g e sw i t hr e l a t i v e l yf i ・ e s hw a t e rc o n d i t i o n s p r e v a i l e dd u r i n gs e d i m e n t a t i o na ta p p r o x i m a t e l y5000 c a lBP( R a s h i de ta ， . 12 0 1 3 ) .Theg l a c i a t i o n / d e g l a c i a t i o n o ft h eHimalayai sl i k e l yt oh a v ehadamarkede f f e c t o nt h eh i g hs e d i m e n t a t i o nr a t e sandr e l a t i v es e a l e v e l c h a n g e si nt h eB e n g a lB a s i n( 1s 1 a ma n dT o o l e y] 9 9 9 ) Hi g hhumidp e r i o dp r e v a i l e di nt h el n d i a nS u l ヲc o n t i n e n tbetween1 1， 000a n d1 0， 000y rBPwhenv a l l e yc u t t i n gbyt h er i v e r so f t h e8 e n g a lB a s i nwasp r e d o m i n a n t (VanCampo 1 9 8 6 ) .Thes t u d i e ddown-cores e d i m e n t s 1Cv r e l a t i v e l ymored e c l i n e d83 a l l l e s( u pt o0 . 9 5 % 0 )1・e f 1e c t i n gs t r e n g t h e n sh l l m i dp a l e o c l i m a t i cc o n d i t i o n s p r e v a i l e dd u r i n gd e p o s i t i o n . The i s o t o p ev a l u e sa r e s t r o n g l yc o n t r o l l e db yh i g h e rc l i m a t I cv a r i a b i l i t yd u r i n gi n t e n s i f i e d1 1 1 0l1S 0 0 np r e c i p i t a t i o n .S t r e n g t h e n e d o fS o u t hA s i a nmonsoonwasi n i t i a t e dd u r i n gL a t et o Mi c l d l eH o l o c e n e( c a .9 4k a )(Bookhagene ta ， . 12 0 0 5 ) . R e g i o n a lp r e c i p i t a t i o np r e c l o m i n a t et h ef r a c t i o n a t i o no f c a r b o ni s o t o p e sa tm o d e r a t et e m p e r a t u r eandu n d e rw e t c o n c l i t i o n s(Zhange ta l2 0 1 1 ) .O i e f e n c l o r f e ta . l( 2 0 1 0 ) r e p o r t e dt h a tt h ev a r i a t i o no fc a r b o ni s o t o p e sbetween C O:~ a n c l11l0 d e r nC3p l a n t sa n c li sn e g a t i v e l yc o r r e l a t e c l lC t op re c i p i t a t i o nr e p r e s e n t i n gt h a tmoren e g a t i v eO3 巳 e x c u r s i o nc o r r e s p o n d st omorep r e c i p i t a t i o n .T h i sr e s u l ti ss u p p o r t e db yt h es t u d yo fH a l le ta . l( 2 0 0 9 )a n c l c o n c l u c l e c lt h a tr a i n f a l ll a r g e l yc o n t r o l st h e8!3C r a t i o s o fh i g h e rp l a n t si nt h eK w a Z l l l u N a t a lS o u t hAf r i c a . J IC a l A l l a na n c lMatthews( 19 8 2 )n o t e c lt h a tt h e8 m 1 cv u e si ng r o l l n d¥ v a t e r sandr i v e rw a t e r sa r et y p i c a l l yl o w ; g e n e r a l l yr a n g eb e t w e e n-10%0a n c l-15%0f r ol11 p l a n t r e s p ir a t i o na n c lp r o d l l c t i o n 0' 1CO nt h ec a t c h m e n t 2i s o i l sF i s h e re ta. l( 2 0 0 5 )s u g g e s t e dt h a to x i d a t i o no f o r g a n i cm a t t e rc a np l a ya ni m p o r t a n tr o l et ol o w e r i n g b o t hc a r b o na n c loxygeni s o t o p ev a l u e sc l u r i n gs h o r t / l o n gt e r me x p o s u r eo ft h es e d i m e n t st om e t e o r i cwaJCi t e ri ns e a l e v e lf a l. lV e r t i c a lc l i s t r i b u t i o n so f8I nt h e 81 11a n c l8H-2c o r es e c t i o n so ft h eL a t eQ u a t e r n a r y s e d i m e n t sa r eshowni nF i g .2 .I nBI IIc o r ec h a n g e s 1 3 d r a s t i c a l l yu ps e c t i o nt op o s i t i v e8C v a l u e sr e f l e c t a n a e r o b i co x i d a t i o no f methane i na n o x i cm a r i n e < : 1n c lf r e s hw a t e rs e c l i m e n t s( N a t a l i c c h i oe ta ， . l2 0 1 2 ) . 8 u c l a ie ta . l( 2 0 0 2 )s u g g e s t e c lt h a tm e t h a n o g e n i cc a l 』 ・ ヲ
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b o n a t e sa r ec h a r a c t e r i z e dbyp o s i t i v e813C e x c u r s i o n s c l u et op r e c i p i t a t i o n介。 1 1 1aI3C e n r i c h e dc a r b o npoo . I However c l u r i n gm e t h a n o g e n e s i s，1 2 Ci sp r e f e r e n t i a l l y i n c o r p o r a t e di nmethane whil et h er e s i d u a lp o r ewat e rbecomese n r i c h e di nI J Cd u r i n gm e t h a n o g e n e s i s (Boehmee ta ， . l 1 9 9 6 ;N a t a l i c c h i oe ta ラ . l2 0 1 2 ) .The 813C o fc a r b o n a t ei sa l w a y sshowingawider a n g eo f v a r i a t i o nt h a ti smorer e l a t e c lt op l a n tp h o t o s y n t h e t i c p a t h w a y s( C e r l i n gラ1 9 8 4 ;C e l 叫n ge ta ラ . l1 9 8 9 ;Alame t a ， . l1 9 9 7 ) .The813Cv a l l l e si nt e r r e s t r i a lp l a n ta r es e n s i t i v et oc h a n g e si na t m o s p h e r i cCO2(NguyenTue ta ラ . l 2 0 0 4 ) .Thei n t e n s i f i c a t i o no fw a t e rs t r e s sa sar e s u l t o fl a r g e rCOrforcedwarmingc a l l s i n ganI n c r e a s ei n a v a i l a b l em o i s t u r ed r i v i n gg r e a t e ri s o t o p i cd i s c r i m i n a t i o nc a u s e dr a p i dd e c r e a s i n g1 3 Cv a l u e so ft e r r e s t r i a l p l a n t s(Bowene ta ， . 12 0 0 4 ) .Thee l e v a t e c la l g a lp o p u l a t i o na n c lp h o t o s y n t h e t i ca c t i v i t yi nt h es h a l l o wmal 二 1 3 g i n a lm a r i n ee n v i l ・ onmentc a ng i v ep o s i t i v e8 Cv a l u e s ( M i l l i m a nandMl Il l e r ，1 9 7 7 ;A r m s t r o n g A l t r i ne ta ラ . 1 2 0 1 1 ) . ラ
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Oxygeni s o t o p e s Theoxygeni s o t o p ec o m p o s i t i o no fc a r b o n a t er o c k s i sc o n t r o l l e db yat e m p e r a t u r ec l e p e n d e n tf r a c t i o n a t i o n o fo x y g e namongt h ep r e c i p i t a t i n gw a t e ra n dt h em i n e r a l s( e . g .c a l c i t e / d o l o m i t e )o rp r e c i p i t a t i o n / e v a p o r a t i o n 0 0 4 ) .Oxygeni s o t o p ei s r a t i o s( L e n ga n dM a r s h a l l，2 mores u s c e p t i b l et h a nc a r b o ni s o t o p ed u r i n gd i a g e n e s i s a n d / O I ・b u r i a lt e m p e r a t u r e( F i s h e re ta ， . l2 0 0 5 ) .O i a g e J ト e s i so c c u r sont h es e af l o o r ，n e a l ・ s u r f a c em e t e o r i ca n d s h a l l o wo rd e e pb u r i a le n v i r o n m e n t( S w e ia n c lT u c k e r 2 0 1 2 ) .However，t h eoxygeni s o t o p ec o m p o s i t i o no f s o i l CO2i sa l s oc o n t r o l l e db yo x y g e ni s o t o p ee x c h a n g eb e t w e e ns o i lCO2a n ds o i lw a t e ra d d i n gt ot h ep r o d u c t i o n C e r l i n g，1 9 8 4 ;8 r e e c k e re ta ラ . 1 a n c ld i f f u s i o no fCO2 ( 2 0 0 9 ) .The8 ¥ 8 0v a l u e so fb u l ks e d i m e n t sf o rc o r es e c o5 . 5 7 % 0 t i o n s8H1a n d8H2r a n g ef r o m1 2 . 1 1弘ot P08a n c l1 2 . 9 2 % 0t o1 2 . 1 4 % 0P08，r e s p e c t i v e l y( F i g . 8 10 f 2a n dT a b l e2 ) .T h i ss m a l lv a r i a t i o ni n8 o rBH-2 二 mayb et h er e s u l to fs e a w a t e rs u r f a c et e m p e r a t u r ee f f e c t，w h e r e a sl a r g ev a r i a t i o ni nBH-l i sa t t r i b u t e dt o 10 b f l u c t u a t i o n si n8 ye v a p o r a t i o n(Budda n dLand 1 9 9 0 )a n c l / o rs e a l e v e lf l u c t l l a t i o n s . Umitsu ( 1 9 8 7 1 9 9 3 )d o c u m e n t e c lt h a tas t r o n ge a r l yH o l o c e n em a r i n e i n f l u e n c et h r o u g h o u tt h es o u t h e r np a r t so ft h e8 e n g a l h i l et h en o r t h e r np a r t sw e r eu n d e rf 11 1 v i a li n 8 a s i n，w f J u e n c e s .Thep e a kr e l a t i v es e a I e v e lt r a n s g r e s s i o no c c l l r r e di n8 a n g l a d e s ha ta p p r o x i m a t e l y6000c a l8P b e i n ga tl e a s t4 . 5t o5m h i g h e rt h a nt h em o c l e r nmean ， . l2 0 1 3 ) .T h e r e a f t e rt h er e l a t i v e s e a I e v e l( R a s h i c le ta s e a I e v e ls t a r t e dt of a l l，a n dc o n s e q u e n t l y af l ・ e s h w a t e rp e a td e v e l o p e c la ta p p r o x i m a t e l y5980-5700c a l8 P . ラ
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1 8 Marinec a r b o n a t e swith8 0 v a l u erangefrom1 0t o e t a i nprimaryoxygeni s o 5 % 0canbec o n s i d e r e dt or ，1 9 9 6 ; Chakrabarti t o p es i g n a t u r e s( H a l l and V e i z e r 1 8 ラ . l2 ( 1 1 ) .Then e g a t i v e8 0 e x c u r s i o n sa r ea l s oa s e ta s o c i a t e dwithhighr a i n f a l landwets e a s o n a lc l i m a t i c c o n d i t i o n s(Dettmane ta ラ . l2 0 0 1 ) .F i s h e re ta . l(2005) notedt h a ta 1 1i n c r e a s eofoceantemperaturesof-6oC 1 8 a st h e8 0 v a l u e sd e c r e a s efrom3 . 5 % 0t o5 % 0usinga s t a n d a r dtemperaturee q u a t i o nbasedonAndersonand Arthur( 19 8 3 ) .Fort h ee q u i l i b r i u mp r e c i p i t a t i o nofc a r h eminerali s o t o p ecompositiond e c l i n e sby b o n a t e st ~0.24% f o revery1oCi n c r e a s ei ntemperature( C r a i g 1 9 6 5 ) .Theoxygeni s o t o p e sa r eknownt obemoreSllSc e p t i b l et od i a g e n e s i st h a nt h emorer o b u s tcarboni s o 1 B ラ . l2 0 ( 5 ) .Then e g a t i v e8 O canbe t o p e s( F i s h e re ta i n t e r p r e t e da sp o s t d e p o s i t i o n a l changes w i t h i nt h e rmeteoricwaterd i a g e n e s i s sedimentsduringb u r i a lo 8 1 9 6 4 ) .1 1 1a d d i t i o nt h en e g a t i v e8 0 ( K e i t handWeber 1 v a l u e sr ef 1e c thumid p a l e o c l i m a t i cc o n d i t i o n s( D e t t 1 g o s i t i v e8 0 v a l u e ss u g g e s tan mane ta l 2001)andp i n c r e a s e di ne v a p o r a t i o nr a t eduet ot h ei n c i d e n c eof a r i dc o n d i t i o n s( F i s h e re ta ラ . l 2005;Fane ta ラ . l2 ( 1 4 ) . TheBengalBasinsedimentswered e r i v e dfromt e c t o n i cu p l i f tande r o s i o noft h eHimalayanorogeny(Hos80i ， . 12 ( 1 0 ) .V a r i a t i o n si nt h e81 nt h esediments s a i ne ta r e c i p i weremainlyt h ee f f e c tofHimalayan1l10nsoonp t a t i o nt o g e t h e rg l a c i a la c t i v i t y and s e a l e v e lc h a n g e . 1987)demonstratedt h a tlowlanda r e aoft h e Umitsu( BengalBasinofBangladeshh a sexperienceddryc l i r s maticc o n d i t i o n sduringt h el a s tg l a c i a t i o n s( 1 8000y BP)andt h er e l a t i v es e a l e v e lwas100m o rlowert h a n l Strong South Asian monsoOI1 t h ep r e s e n ts e a I e v e.
wasi n i t i a t e dduring~ 1 2， 000y r sBPandr a p i d l yr i s i n g s e a I e v e lowingt oheavyr a i n f a l lt o g e t h e rd e g l a c i a t e d 1imaticcondim e l t i n gwateri nt h ea r e a .Thewarmerc t i o nwasp r e v a i l e dduringt h emiddleHolocenetimei n じ mitsu 1 9 9 3 ) .The t h eBengalBasinofBangladesh( 1 8 low8 0 v a l u e sandr a p i df 1uctuationsobservedi nt h e BH-1c o r ep o i n t e dt od i a g e n e s I sofsedimentsa sw e J Ja s ani n c r e a s ei ns e a s u r f a c et e m p e r a t u r e .Thel i t t l enega80v a l u e s( 5 . 5 7 % 0 )i nt h eup-cores e c t i o nofBH-1 t i v e81 t h a nmoren e g a t i v ev a l u e s( 1 2 . 1 1 % 0 )i nt h edown-core mightber e s u l t e dfromt h es t r o n ge v a p o r a t i o nandt h e n e l e v a t e dt h eh e a v i e ri s o t o p e si nt h ei n v e s t i g a t e da r e a ， . l2 0 1 4 ) .Themarkedp o s i t i v eC O I γ e l a t i o n( r (Fane ta =0.95，n=9 ;c r i t i c a l!v a l u ef o r99%confidencel e v e l 1 X i s0 . 7 3 5 ;Ver ・ ma 2005)between8IJC and8 O ( F i g .3 ) s u g g e s t st h a tt h eL a t eQuaternarysedimentswerea 1 二 f e c t e dp r ・i m a r i l yby meteoric d i a g e n e s i ss hi f t i n gt h e primary s i g n a lt o more n e g a t i v ev a l u e s towards t h e 9 9 2 ) .Thel i g h tcarbon bottomc o r es e c t i o n( M a r s h a l l，1 1 60)a r el i k e l yt obei n C O I ・p o r a t e di n t o ( 1 2 C )andoxygen( I ・ e p r e c i p i t a t e dc a l c i t eduringd i a g e n e t i cenvironments 1 8 l e a d i n gt on e g a t i v ee x c u r s i o n sont h e813Cand8 0v a l u e s( F i s h e re ta ， . l 2(05) 1 8 a l u eofsedimentp o r ewatercanbeL 1s e dt o The8 0 v 80 v e s t I m a t et h e81 a l u eofp r e c i p i t a t i ol 1 ラ w hichy i e l d s i n s i g h t si n t oatmosphericc i r c u l a t i o np a t t e r n sa sw e l la s t h ep a l e o e l e v a t i o nofhighlandmasses(Amundsone t ， . l1 9 9 6 ;Garzionee ta l 2000;Breeckere ta ラ . l2 ( 0 9 ) . a 80 v 80 v The81 a l u ei sl a r g e l yc o n t r o l l e dbyt h e8' a l u eof 0 0 9 ) . s o i lwaterands o i ltemperature(Breeckere ta l 2 1 8 a l u eofporewaterr a n g e sfrom Thec a l c u l a t e d8 0 v ぺ2.00%0t o1 0. 42%0(SMOW)a t200C and1 0 . 9 3 % 0t o
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9 . 3 5 % 0(SMOW)a t2 50C w h i l ea t40m d e p t hi nt h e BH-I s e c t i o ns e d i m e n ti sr e l a t i v e l y¥ v i t hmuchh i g h e r 0 0 v a l u e s十4 . 6 4 % 0a t20 Ca n d3 . 5 7 % 0a t2 5 C)( T a b l e2 ) . S h a c k l e t o n( 1 9 6 8 )a n dMeyersa n dLohmann( 19 8 5 )r e p o r t e dt h a tt h es e a w a t e rc o m p o s i t i o ni si n f e r r e dt oh a v e v a r i e db e t w e e n0 . 5 % 0a n d十0 . 5 % 0SMOW.S t r o m a t o l i t i cd o l o m i t ei nV e m p a l l eF o r m a t i o n，l n d i ai sl i k e l yt o b ep r e c i p i t a t e di ne q u i l i b r i u mw i t hm a r i n ew a t e r ss i g n i f i c a n t l yd e p l e t e di noxygeni s o t o p e sー (1 0 % 0t o1 5 % 。 SMOW)w i t hr e s p e c tt omoderns e aw a t e rにh a k r a b a r t ie ta ， . l2 0 1 1 ) .AI la na n dMatthews( 1 9 8 2 )andMars h a l l( J9 9 2 )documentedt h a tm e t e o r i cw a t e rh a sl o w e r 1O e 5H x c u r s i o nt h a nm a r i n ew a t e ra n dp o s s i b l ys h i f t e d x c u r s i o nwheret h ew a t e r sc o n t a i ni s o t o l コ ] t ol o w513Ce c a l l yl i g h tc a r b o nfroms o i l d e r i v e dCO 2 • VanG e l d e r n e ta . l( 2 0 1 3 )p r o p o s e dt h a tf r e s hw a t e rw i t hl o w8 ¥ 8 0 v a l u e so t 、7 % 0d e m o n s t r a t e sp r e s e n t d a ym e t e o r i cwa10 v a l tw a t e r01 'r e c e n tm a r i n eo r i g i nw i t h58 a l u e s t e r，s o fa b o u t0 . 8 % 0，a n db r i n ew i t ha51~0 v a l u eo f1 % 0， g 1 c l o s et ot h a to f s e a w a t e. rThe5 0v a l u e so f p o r ew a t e r s f o rt h es e d i m e n t sa r ea l ll o w e rt h a nt y p i c a ls e a w a t e r v a l u ei n f e r r i n gt h eh i g h i n f l l l e n c eo fm e t e o r i cw a t e r ラ . l 2 0 0 9 ) .However ラ d i a g e n e s i s( A r m s t r o n g A l t r i ne ta t h en eQ :a t i v e81 J :Ce x c u r s i o n st O! 2 :e t h e rw i t h n e Q : a t i v e 5 1 白 O ...... v a l l l e si nt h es t u d i e ds e d i m e n t sw O l l l db ec o n t r o l l e db y p o s t d e p o s i t i o n a lo x i d a t i o no fo r g a n i cm a t t e ri nt i n y e x p o s u r eo f t h es e d i m e n t st oo x i ca n d / o rm e t e o r i cwat e rd i a g e n e s i sa s s o c i a t e dw i t hs e a I e v e lf 1u c t u a t i o n so r t e c t o n i cu p l i f t( A l l a na n dMatthew丸 1 9 8 2 ;M a r s h a l l 1 9 9 2 ;F i s h e re ta ， . 12 0 ( 5 ) . ラ
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Thec a r b o ni s o t o p i ce v i d e n c eo ft h eL a t eQ u a t e r n a r y s e d i m e n t si nn o r t h w e s t e r nB e n g a lB a s i ni scompared ， ¥v i t ht h es t a b l ei s o t o p i cc o m p o s i t i o no fs o i1c a r b o n a t e si n Miocene S i w a l i ks l l c c e s s i o ni nw e s t e r n and c e n t r a lN e p a la n dP a k i s t a nP l e i s t o c e n ep a l a e o s o li n n o r t h w e s t e r nB a n g l a d e s h， 削l dMi d d l e L a t el lo l o c e n e w e s t e r nGanges-Brahmaputrad e l t ap l a i ns e d i m e n t si n o r d e rt ot r a c i n gt h ec o n t r i b u t i o n s0 1 、C n dC1p l a n t s 3a i nt h eHi m a l a y a nw a t e r s h e d s .Thei s o t o p i cc o m p o s i sm o s t l yc o n t l 叶l e dbyt h ep r o p o r t i o n t i o no fs o i lCO~ i o fSUtイl 1 c ep l a n tb i o m a s sL ls i n gt h eC，_ ( C a l v i nc y c l e ) I Ia t c h S l a c k )p h o t o s y n t h e t i cp a t h w a y s( S m i t h o rC1( a n dE p s t e i n1 9 7 1，C e r l i n g，1 9 8 4 ) .TheCi a n dC4 p h o t o s y n t h e t i cp a t h w a y sf r a c t i o n a t ec a r b o ni s o t o p e st o v a r i a b l ed e g r e e s，v v h i l e0 ¥ 3 Cv a l u e sf o rC3a n dC4 p l a n t s ウ 。r e r a n g i n gfrom2 2 % 0t o3 0 % 0a n d1 0 % 0t o1 4 % s p e c t i v e l y( B e n d e r ，1 9 7 1 ;F a l 可u h a re ta ラ . l 1 9 8 9 ;C e l l i n ge ta l 1 9 9 7 ) .CJ g r a s s e sa r eu s u a l l yr e s t r i c t e dt o c o o lc l i m a t i cc o n d i t i o n sa n dC.j d o m i n a t e dg r a s s l a n d a t e rs t r e s sa n d a d a p t e dr e l a t i v e l y hi g hi r r a di a n c e、 w 雪
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temperature c o n d i t i o n s( E h l e r i n g e r 1 9 7 8 ;C e r l i η ge t 1 3 a l 1 9 8 9 ;Quadee ta ， . l1 9 9 5 ) .The5 C v a l u e sofs o i1 c a r b o n a t e si nP a k i s t a nrangefrom-12%0t o-9%0POB (Quadee ta l 1 9 9 5 )，c o n s i s t e n twithC4 p l a n t sdomin a t e dv e g e t a t i o n .Sedimentsoft h eBengalBasinwere l a r g e l yd e r i v e dfrome r o s i o noftheHimalayas( F r a n c e LanordandOerry，1 9 9 4 ;Hossaine ta ， . l2 ( 1 0 ) .Miocene sedimentary r o c k si nt h eS y l h e t Basin n o r t h e a s t e r n Bangladesh a r ev e r ys i m i l a rt ot h e Miocene S u r a I Khola and Bakiya Khola sedimentary r o c k sa se v i dencedby geochemical s t u d i e s，s u g g e s t i n gas i m i l a r s o u r c e .France-LanordandOerry( 1 9 9 4 )r e p o r t e dt h a t f i n e g r a i n e dsedimentsa r ea s s o c i a t e dw i t hC4 p l a n t s whereasc o a r s e g r a i n e dsedimentsa r ea s s o c i a t e dwith C3 dominatedo r g a n i cmatter .Thisr e s u l ti sc o n s i s t e n t w i t has t u d yofo r g a n i cm a t t e rbyHossaine ta. l( 2 0 0 9 ) andconcludedt 1 la to r g a n i cm a t t e ri nt h eT e r t i a r γ S y l h e ts u c c e s s i o nn o r t h e a s t e r nBengalBasinofBangladeshwered e r i v e dfromb o t hC4andC3p l a n t s .The lJC v a l u e si nt h ep r e s e n ts t u d yr a n g ebetween0 . 9 5 % 0and 1 . 45%0 PDB，supported mainly predominance ofC4 p l a n t s . MixedC， andC4 p l a n t sa r ew e l l documented i nt h eMiddleHolocenewesternGanges-Brahmaputra d e l t ap l a i nandr e t u r nt oe x t e n s i v egrowthofC4 p l a n t s i nt h eL a t eHolocene( S a r k e re ta ， . 12(09).Aucoure ta. l ( 2 0 0 6 ) documented t h a tt h eP h r o g m i t e s l S a c c h o r u m l f m p e r o t αswampg r a s s l a n d sa r ewidespreadi nhUJ11i d r e g i o n soft h eIndo-Gangeticp l a i nandt h eBrahmaput r av a l l e y whereast h eD i c o n l h i u m l C e n c h r u s l L a s i u r u s andS ehimolDichonthiumgrasslands a r es p r e a do v e r 1 3 t h ewesternp a r toft h eb a s i n .The8 C v a l u e si ns o i l c a r b o n a t e si nt h eS u r a i Kholaand BakiyaKholaS i walik s u c c e s s i o nr a n g e from 9 . 3 % 0t o1 2 . 2 % ラ 。 w i t h ana v e r a g e1 0. 4%0(Quadee ta ， . l1 9 9 5 )，and9 . 1 % 0t o 1 1 .3%0，withanaverage1 0. 4%0( H a r r i s o ne ta ， . l1 9 9 3 )， r e s p e c t i v e l y .Thecarboni s o t o p i cp a t t e r n si nt h eS u r a i Kholaa r everys i m i l a rt oBakiyaKholas e c t i o ni nc e n t r a lNepal，b u th i g h l yd e c l i n ecarboni s o t o p i cv a l u e si n t h eL a t eQuaternarysedimentsofBangladesh( 0 . 9 5 %。 t o1 . 45%0PDB).Thepedogeniccarbonatec o n c r e t i o n s fromP l e i s t o c e n ep a l a e o s o lsequencesont h en o r t h w e s t e r ・nB angladeshhave8I:JC v a l u e srangingfrom11 .5% 。 t o2 . 5 % 0，POB(Alame ta ラ . l1 9 9 7 )，i n d i c a t i n gt h a ti n f l u enceofbothC3andC4p l a n t sr e s p i r a t i o n .C4p l a n t shave 1 3 5 Cv a l u e sofl e s st h a n1 5 % 0POB whereasC3 p l a n t s 1 3 a l u e supt o2 7 . 9 % 0POB(Meyhavemuchh i g h e r5 C v l J e r s，1 9 9 4 ) .Thesel a r g e rf r a c t i o n a t i o n sof8 C i npedog e n i cc a r b o n a t e si n d i c a t ev a r i a b l ec l i m a t i cc o n d i t i o n s t h a tf a v o rC3andC.j p l a n t s .However，t h ep h o t o s y n t h e t i ce f f i c i e n c yofC3andC4 g r a s s e si sp r i m a r i l ydepends ontemperatureandatmosphericpC0 e v e l ssucht h a t 2l r ef a v o r e dunderlowpC0 C.j-dominatedecosystemsa 2 ラ
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c o n d i t i o n swhenaccompaniedb ye l e v a t e dt e m p e r a t u r e ( C e r l i n ge ta ， . l1 9 9 7 ) .C4 g r a s s e sa r ea b u n d a n ti nt r o p i c a lands u b t r ・ o p i c a lr e g i o n s andC3g r a s s e sa r edomin a t ei nh i g hl a t i t u d eandh i g ha l t i t u d er e g i o n s( C e r l i n g e ta ラ . l1 9 8 9 ラ1 9 9 7 ) .The813Co fC3p l a n t si sh i g h l ys e n s i t i v et oh l ll11i d i t yo rp r e c i p i t a t i o na n di sm a i n l yi n f l l l e n c e db ys o i lw a t e rc o n t e n ta n d / o rp r e c i p i t a t i o n( S t e r n b e r ge ta ， . l 1 9 8 4 ;Whitee ta l 1 9 9 4 ) .A d d i t i o n a l l y ラC3 p l a n t sr e s p o n dt oc h a n g e si na t m o s p h e r i c CO2 w i t h d e c r e a s e dmaximllmn e tp h o t o s y n t h e t i cr a t e st h a ta r e r e l a t e dt ol o w e r e dCO2 l e v e l s( E hl e r i n g e re ta ヲ . l 1 9 9 1 ; C e r l i n ge ta ラ . l 1 9 9 7 )，w h i l eC4 p l a n t sa r el e s ss e n s i t i v e t oa t m o s p h e r i cCO2 l e v e l s .Changesi npC02l e v e ld u e t or a p i dc o n t i n e n t a lw e a t h e r i n ga n d旬 以 o n i c a l l ya c t i v e Himalayanr e g i o na r el i k e l yt ob el o w e r i n go fCO2 i n c o n c o m i t a n tt ot a v o r i n gt e r r e s t r i a lC4p l a n t sp h o t o s y n t h e s i st h a nC3p l a n t s( C e r li n ge ta ， . l1 9 9 7 ;P a g a n ie ta ヲ . 1 2 0 0 5 ) .Thesef e a t u r e sshowt h a tt h ed i s t r i b u t i o nofo13C i nt h en o r t h w e s t e r ns e n g a l8 a s i na r ed o m i n a n t l yc o n t r o l l e db yt h ed i s t r i b l l t i o no fC4 p l a n t s andCj p l a n t s o v e rs m a l li nt r o p i c a ls u b t r o p i c a l andt e l η p e r a t ee n v l r o n m e n t s . ラ
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C o n c l u s i o n s The s t a b l ec a r b o n and oxygen i s o t o p er e s u l t so f n i n eL a t eQ u a t e r n a r ys e d i m e n ts a m p l e so ftwoc o r e s e c t i o n sfromt h eC h a p a iNawabganj d i s t r i c t，n o r t h w e s t e r n8 e n g a l8 a s i n，8 a n g l a d e s hweres t l l d i e d .The c a r b o ni s o t o p ed a t ashowan e g a t i v ee x c u r s i o nfrom 0 . 9 5 % 0t o0 . 5 6 % 0PD8a n dap o s i t i v ee x c u r s i o na tt h e uppermost8H-Id r i l lc o r es a m p l e( 1 .45%0P D 8 ) .These n e g a t i v e813C e x c u r s i o n sa r ec o n s i d e r e dt ob et h ee f . . . 1 3 f e c to fm e t e o r i cw a t e rd i a g e n e s i sa n dt h ep o s i t i v e8 C v a l u e si n d i c a t et h ei n f l l l e n c eo fas u b a r e a le x p o s u r e h o r i z o n .The8180v a l u e sr e p r e s e n tmarkedn e g a t i v ee x c u r s i o n st h r o u g h o u tt h ec o r es e c t i ol 1s8H1and8H-2 whichr a n g efrom1 2 . 9 2 % 0t o11 .34%0PD8w i t hl o w n e g a t i v ev a l u ea tt h et o p m o s ts e c t i o n( 5 . 5 7 % 0PDs)， s u g g e s t i n gt h a tt h ep a l e o c l i m a t ewasp r o b a b l yhumid a n dg r a d u a l l ys h i f t e dt oa r i dc o n d i t i o n .Themarked p o s i t i v ec o r r e l a t i o nbetweenO13C and8180 ( 1 0 . 9 5， 1 1 =9 )i n d i c a t e st h a tt h eL a t eQ u a t e r n a r ys e d i m e n t s a r el a r g e l ya l t e r e db yl11e t e o r i cd i a g e n e s i s .Then e g a t i v e813C and81XO e x c u r s i o n sa r ep l ・ o b a b l ec o n t r o l l e d b yp o s t d e p o s i t i o n a lo x i d a t i o no fo r g a n i cl11a t t e ri nt i n y e x p o s u r eo ft h es e d il11e n t st oo x i c01 'm e t e o r i c日! a t e r d i a g e n e s i sa s s o c i a t e dw i t hs e a l e v e lc h a n g e s .However ， t h es t a b l ei s o t o p er e s u l t so ft h ep r e s e n ts t u d ys u p p o r t s f o rt h edominanceo fC4 p l a n t so v e rCJp l a n t s . ラ
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NahidNowsherf o rt h e i li n v a l u a b l ea s s i s t a n c ed u r i n g s a m p l ep r e p a r a t i o n .Thet h o r o u g hcommentso fP r of . Dr .Y o j iArakawah e l p e dt oi m p r o v et h ef i n a lv e r s i o n o ft h i sm a n u s c r i pt . ・
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2 0 0 8 .TheP a l e o g e n er e c o r do fHi m a l a y a ne r o s i o n : B e n g a lB a s i n B a n g l a d e s h . Eαr l h andP l a n e t a r y 1 4 . S c i e n c eL e l t e r s273 1 N a t a l i c c h i oラM.，B i r g e l，D .ラD e l aP i e r r e，F .，M a r t i r e，し C 1 a r iP .ラS p o t lラC .a n dPeckmann，ラ . J2 0 ]2 .P o l y p h a s i cc a r b o n a t ep r e c i p i t a t i o ni nt h es h a l l o ws u b s u r f a c e :I n s i g h t sfromm i c r o b i a l l y f o r m e da u t h i g e n i c c a r b o n a t eb e d si nu p p e rMiocenes e d i m e n t so ft h e T e r t i a r yPiedmontB a s i n(NW l t a l y ) .Pa!aeogeog，P a ! a e o c l i m a t o ! o g y ，P alaeoeco!ogy329-330， raphy 1 5 8 1 7 2 NguyenTu，T. T . ラ K u r s c h n e r う・ W.M. ラS c h o u t e nラS .and VanB e r g e nP . F .2 0 0 4 .しe a fc a r b o ni s o t o p ecomp o s i t i o no ff o s s i la n de x t a n to a k sgrownu n d e rd i ι f e r i n ga t m o s p h e r i cCO2 l e v e l s .Pa!aeogeography ， P a ! a e o c l i m a / o ! o g y ，P alaeoeco!ogy2 12，1 9 9 2 1 3 . P a g a n iラM.，2achosラ J .C .，Freeman，K . H .，T i p p l e，B .and Bohaty，S .，2 0 0 5 . Marked1 ce c l i n ei na t m o s p h e r i c c a r b o nd i o x i d ec o n c e n t r a t i o n s1 cu r i n gt h eP a l e o g e n e .Science309 ，6 0 0 6 0 3 . Q u a c l e，， . 1 C a t e r，. l .M.L . ， O jhaラT P .ラAclamラ J .a n dH a r r i s o n，T .M.， 1 9 9 5 .L a t e Miocene e n v i r o n m e n t a l c h a n g ei nN e p a la n c lt h en o r t h e r nl n d i a ns u b c o n t i n e n t :s t a b l ei s o t o p i ce v i d e n c efromp a l e o s o l s .GeoιdSocietyofAmericaBu!!etin107 1381-1397. l o g i R a s h i c l，1 ' . ， S uzuki ，S .S a t o，H .，Monsur ，M .H. a n c l Saha，S . K .，2 0 1 3 .R e l a t i v es e a I e v e lc h a n g e sd u r i n gt h eH o l o c e n ei nB a n g l a c l e s h .. ] o u r n a !ofAsian E a r f hSoences64，1 3 6 1 5 0 . S a n j u a n，， . 1 M a r t i l トC 1 0 s a s，C . ぅ S e r r a k i e lラ . J .a ndO a 1 l a r d o，H .、2 0 1 2 .S t r a t i g r a p h ya n c lb i o s t r a t i g r a p h y ( c h a r o p h y t e s )o ft h em a r i n e t e lr e s t r i a lt r a n s i t i o ni n t h eU p p e lEoceneo f t h eNEEbroB a s i n( C a t a l o n i a S p a i n ) .Geo!ogicaActa1 0，1 9 31 . S a r k a r ，A .うS e n g u p t a，S .ラM c A r t h l l r ，J .M. R a v e n s c r o f tラ P .，1 ヨ e r a，M.K.ラ Bhushan，R .，Samanta，A . and Agrawal S .，2 0 0 9 .E v o l u t i o n0 1 、o a n g e s -B r ahmapu1 1 ・ aw e s t e r nd e l t ap l a i n :c l u e sf r ・ o r ns e c l imentology a n dc a r b o ni s o t o p e s .Qu正I / e l ソ7 θ I γS c i el1c eReviews 28，2 5 6 4 2 5 8 1 S c h o l l e，P . A .a n c lA r t h u r M.A.，1 9 8 0 .Carboni s o t o p i c f l u c l u a t i o n si np e l a g i cl i m e s t o n e s :p o t e n t i a ls t r a t i g r a p h i ca n dp e t r o l e u me x p l o r a t i o nt o o . lB u l ! e t i nAmeri ωη A s s o c i a t i ol1ofPefro!eumG e o ! o g i s t s64 6 7 8 7 . S h a c k l e t o n，N .， . J 1 9 6 8 .Depth01 'p e l a g i cf D r a m i n i f e r a a n di s o t o p i cc h a n g e si nP l e i s t o c e n eo c e a n s .Nαl u r e 2 1 87 9 8 0 . Smith，B . N .a n dE p s t e i n，S .，1 9 71 .Twoc a t e g o r i e so f 1 3 C ; 1 2 Cr a t i o s1 D rh i g h e rp l a n t s .P ! a n fP h y s i o l o g y47， 3 8 0 3 8 4 SternberιLO.，DeNiro，M.， . JJ o n s o nラH . B .，1 9 8 4 .I s o ラ
