Antarctica's Contribution to Eustasy During the Past Glacial/Intergiaciai Cycie

CoastalChange on the TimeSea/e pl' Oecades to Millennia

Antarctica's contribution to eustasy during the past glacial/intergiaciai cycie

John B. Anderson

DepartmentOf Geologyand GeophysicsRice Llniirersity, HOOSten, TexaS, 77251, U,S,A, e-mail:tohnaOrice.edu

Knowledgeof Antarctica'scontribution to eustasyduring the past glacial/interglacialcycle has recently improved as a resultof onshoreand marinegeological surveys. Marine geological stud es haveyielded compelling evidence that all three componentsof the Antarctic cryosphere,the EastAntarctic Ice Sheet EAIS!,West Antarctic Ice Sheet WAIS!, and Antarc- tic Peninsulaice sheet,advanced across the continentalshelf during the last glacialcycle. There is also new evidenceto suggestthat the EAISretreated from the continentashelf prior to 24,000yrs BP,possibly during OxygenIsotope Stage 3. The WAIS retreated from the shelf after the I GM Oxygen Isotope Stage 2!. Retreat of the Antarctic Peninsulaice sheet from the shelfwas completeby the mid-Holocene.

Marinegeological surveys conducted during the past five yearshave focused on the individua drainagesystems of the West Antarctic ce sheet. These studies have shown that the retreat of the WAIS was diachronous around the continent, with differentglacial drainage systems behaving more or lessindependently during recession,Some drainage systems, suchas those of the westernRoss Sea, retreated slowly and continuouslyfrom the shelf,whereas other segments,such asthe PineIsland Bay drainage system, t'etreated rapidly. Collapse of someWAIS drainage systems, such as the PineIsland Baysystem, could havecaused eustatic rises of severaldecimeters over a fewcenturies. There were still significantvolumes of ice left on the Antarctic continental shelf after 9000 years to have contributed to the observed sea-levelnse of the late Holocene.There is someevidence for rapidphases of retreatduring this time interval,

Thecomplex retreat history of the Antarctic Ice Sheetsindicates an episodic nature to sea-levelrise with potentially rapid phasesof retreatthat could havesignificantly altered coastal systems, Thereis no evidencefor widespreaddeglacial episodesthat would have caused the kinds of meter-scalerapid risesinvoked by some researchers.

CoastaiChange on the TimeScare of Decadesto Mi lennia

Relative variation curves in sea-level during the last 7000 years in Brazil: A review

RodolfoJosh Angulo and MariaCristina de Souza

Departamentode Geoogia, univerSidade Federal dO Parana, Caixa Postal 19001, 81 93 1-990 Curitiba-PR, BRASIL e-mail Angulo!.angulotgao logla.uf pr.br e-mail de Souza!:cristinaegeologla.ufpribr

In the last three decades hundreds of paleosea-levelindicators from the Brazilian coast were dated and several paleosea-levelcurves, for the last 7,000 years,were published for different sectorsaf the coastline Figs. 1 and 2!. Thesecurves presentsignificant differences and contradictions, which are; i! the existenceor not of 3-4 rn oscillations between 4100- 3800 years B.P.and between 3000-2700 years B.P. Suguio et al. 1985, Angulo & Lessa1997, Martin et al. 1998, Lessa& Angulo1998!; ii! the existenceor not of a sea-levelrise in the lasttwo thousandyears along the coastof RioGrande do Sul State, and Tomazelli& Villwock 1989 apud Tomazelli 1990, Tomazelli 1990, Angulo & Giannini 1996!, iii! the maxi- rnum altitude attained by the post-glacial marine transgressionon the State of Parana Martin et al. 1988, Angulo 1992, Angulo & Suguio 1995!,

Thereare still other aspectsthat have not yet been discussed,such as a! when did the sea reach a level similar to the current one for the first time during the Holocene,and b! what was the maximum altitude of the post-glacial marine transgression PMT! in the country? Previousstudies suggested different times when sea-leveleventually reached the present mean sea-levelafter the PMT,and that would span between 7100 and 6600 years B.P.Holoceno Suguio et al 1985!. It is also proposedthat the maximum sea-levelat the end of the PMTwould have occurred around 5100 years B.P.,and that it would have reachedaltitudes that vary from 4.8 x 0 5 m to lessthan 2.5 m. These differences in age and elevation are explainedby the shifting of a geoidal depressionnow located close to Cananeia, Sao Paulo State Martin et al. 1985!.

A critical analysiso the literature suggests that elevations of sea-level maximum higher than 4 m are probably overestimated. This s mainly due to the fact that there are more than one hundred vermets samplesdated in the Brazilian coast, and only three indicate paleo-sea-levelshigher than 4 m Fig. 3!. The majority of the samples were obtained on cliffs exposedto strong wave action, in which case the ecological zone of the vermets can be displaced 1 rn upwards Laborel 7986!. In two places, "in situ" oyster shells would suggest a sea-level maximum of 4,8 m. However, Delibrias & Laborel 969! consider that this elevation would also be overestimated since the reference level used was the mean sea-level insteadof the ecological zone of the oysterswhich in some situations can be 3 m higher than that level. It would then be necessaryto know the characteristicsof the place where the oysters were collected to define the precise paleo-sea-level. Finally,higher than 4 m estimatesof the sea-levelmaximum come from shellfragments found on paleo-beachdeposits or the elevation of the paleo-beachesterraces. In these cases it is well known that wave run-up can form sedimentary depositsseveral meters above mean sea-level, Theanalysis of the data usedto producethe curvesreveal that, besidesthe scarcityof the data, the consideredmargins of errorare frequently extremely small for the type of indicatorused. Thus, the curvesare not too precisedue to the qual- ity of the data utilizedin their construction.As for the time when sea-levelfirst reachedthe presentone, the published dataindicate only that this happenedabout 7000 yearsA.P. The data are not sufficientlyprecise for an adequateidentifi- cationof the proposedregional differences. For example, wood fragmentsdeposited in clay-sandysediments attributed to mangroves,which would more likely indicate a lowestpossible paleo-sea-level, isused to determinemean sea-levei with a margin of error of only 0.3 m to 0,4 m. Consideringthe maximumsea-level altitude after the PMT,the publisheddata, in mostcases, does not allowfor a deter- minationwith an accuracy of less than 1 meter.Moreover, they do not have enough precision to identify possible signifi- cantdifferences in altitude at severalsections of the Brazliancoast as previously proposed. The data only indicate altitudes around 2.5 to 4.0 m in the penod between 5000 and 5400 years B.P.

References Angulo,R.J., 1992, Geoiogia daPianicie Costeira doEstado do Parana. Unpublished Ph.D. Thesis, Geoscience Institute, Universityof SaoPaulo, Brazil, 334 p, Angulo,R.J. and Giannini, P.C. F., 1996. VariaCao donivel relativo domar nos ultimos dois rnil anos na regiao suldo Biasil: umadiscussao, aofetim Paranaense de GeocienciasCuri tiba. 44:67-75. Angulo,R.J.and Lessa, G.C., 1997. The Brazilian sea-level curves: a critical review with emphasis onthe curves from Paranaguland Cananeia regions. Mar. Geol., 140 l41-166. AnguloR.J, and Suguio K.,1995. Re-evaluation ofthe Holocene sea-level maxima forthe state ofParanh, Brazil. Paleo- geog.,Paieoclim., Paleontology, 113;385-393.

31 Delibirias,C. and Laborel,J. 1969. Recentvariations of the sea-levelalong the Braziliancaast. Quaternana. 14:45-49. LaborelJ, 1986.Vermetid gastropods assea-evel indicators. In:Van de Plassche, O.ed, Sea-level research: a manual for the collection and evaluation of data. Norwich. Geo Books, p,281-310. Lessa,G.C, and Angulo, R,J., 1998. Oscillations or not oscillations:that is thequestion - Reply,Mar Geol.,150:189-196. Martin,L.; Bittencourt, A. C. da S P.;Dominguez, J. M. L.;Flexor, J. M.; Suguia,K. 1998.Oscillations or not oscillations, thatis the question: Comment on Angulo, R. J. and Lessa, G. C, The Brazilian sea-level curves: a criticalreview with empha- sison the curvesfrom the Paranaguhand Cananeiaregions. Mar. Geol., 140:141-166. Marine Geology. Amsterdam, 150:179-187, Martin,I; Flexar,J.M.; Blitzkow, D. andSuguio, K. 1985.Geoid change indications along the braziliancoast during the last 7,000 years.In lnt. CoralReef Congress, 5. Tahiti,1985, Proc... Tahiti, v.3, p,85-90. Martin,L.; Suguio, K.; Flexor, J.M. and Azevedo, A.E,G.. 1988. Mapa Geol6gico do QuaternarioCosteiro das Estados do Paranhe Santa Catarina. Serie Geal6gica DNPM, no. 28, 40 p. Suguio,K; Martin, L.; Bittencourt, A.C.S.P., Dorningues, J.M.L.; Flexor, J,M. and Azevedo, A.E.G., 1985 Flutuaqoes donlvel relativodo mardurante o QuaternkrioSuperior ao longo do litoral brasileiroe suasimplicaCoes na sedimentaqaocosteira. Rev. 8ras, Geoc., 15:273-286. Tomazelli,L.J. 1990.Contribuiqao ao estudodos sistemas deposiaonais holocenicos do nordesteda provlncia costeira do RioGrande da Sul,corn enfase na sistemae6lico. Unpublished Ph.D. Thesis, Geoscience Institute, Federal University of Rio Grande do Sul, Porto Alegre, Brazil, 270p.

Fig.t. Location map

32 F>g.2. The Braziliansea level curvesfor the last 7000 years after Suguio et al., 1985 and Villwock and Tomazel- li, 1989, in Tomazelli, 1990!. See Figure 1 for location.

33 Fig. 3. Elevationof the publishedpaleo-sea level indicatorsin Brazilderived from vermetidradiocarbon dates. Shaded areas indicate the time for the proposed secondary oscillations proposed by other authors seeSuguio et al. 1985!.The line is a 4th order polynomialbest fit. Angulo5 Lessa1997!

34 CoastalChange on the TimeScale of Oecadesto fvfrllennia

A review of Holocene sea-level curves from the southwest Atlantic Ocean

R. Angulo", F. I. Isla>, E. J. Schnack3and M. C. de Souza' 1 aepartamentodeGeologia, Llnmersidade Federal do Parana, Caixa Postal 19001, 81931-990 Cuiitiba-PR, BRASIL e-mailiAngulO!; angulOrtigeOIOgia.ufpr.br e-mail de SO~ Zai:CriStina@geOIOgia ufprbr ZCentrode Geologia de Costas, universidad Nacional de Marde P ata,ARGENTINA e-mail:fislatamdp.edu.ar 3LabOratOriOdeOCeanOgraffa COStera, FaCultad deCienciaS Naturales y MuSeO de LaPlata, C.C 49, 1900La Piata, ARGENTINA CgrreSpOndenCe tOthiS address! [email protected]

Upper Pleistocenemarine terracesfrom northern Argentina and sauthern Brazil suggest that the southwestern coast of the AtlantiCOcean haSbeen approximately stable since the last interglaCial Sangamnanian.

Different se-levelcurves have been proposed showing a fluctuation for the last 7,000 years, From the camparison of these curves,some questions arise: a!Which was the maximum height of the Holocene transgression? b!When did the maximum sea-level stand occur? c! Were there fluctuations be ow present mean sea-level MSL!? a! Height of maximum MSL Many authors have proposed different maxima for the MSL Suguio et al,, 1985; Martin et al.,1988; Isla, 1989; Caval- otto et al., 1993; Agklirre and Whatley, 1995; Angulo and Lessa, 1997!. A critical analysisof the literature suggeststhat elevationsof maximum sea-levelhigher than 4 m are probably overestimated. In southern Brazil some maxima are based an in siru vermetids and oyster shells. Values based upon vermetids probably are overestimated because the majority of the sampleswere obtained on cliffs exposed to strong wave action, in which casethe ecological zone of the vermets can be displaced 1 m upwards Laborel, 1986!. Maximum levels based on oyster shells can be overestimated becausethe ref- erencelevel used was the mean sea-levelinstead of the ecological zone of the oysters which in some situations can be 3 m higher than that level.

Most estimations of these maxima in northern Argentina and some of southern Brazil are based on reworked mollusk shels andtherefore indicating the level reachedduring storms. Extra-tropicalstorm surgesoriginating in the South Atlantic are frequent and are a strong morphodynamic factor on the whole coast. Becauseit is reasonableto assumethey have been acting during the last few thousand years, dating on storm deposits should be avoided in order to estimate MSL. Furthermore,a cleanup processof the existing database is necessaryto provide safer data for MSL estimation and construction of sea-levelcurves. In addition, further examinatian of chronalagical evidence should prove useful in order to understandthe slight differences in the age af the maximum sea-levelstand.

The Braziliansea-level curve composed from radiocarbon-dated vermetids Fig, 1! is significantly lower that other curves basedon different materials mollusk shells, wood fragments, peats, carbonate algae, corals!. Out of more than one hundred vermetid samplesonly three indicate paleo sea-levelshigher than 4 m and this are probably over estimated. On the other hand, trying to discard those datings related to storm ridges and considering only those datings belonging to estuarine environments estuariesand coastal lagoons!, a MSL curve "out of storms" for northern Argentina has been proposed Fig. 1; Isla and Espinosa, 1998!. b! Age of maximum MSL In the last 10 years, it has been clear that the so-called "mid-Holocene transgression" MHT! was older in northern Argentina than in southern Brazil see Isla, 1989!. The maxima for the brazilian MHT was 5000 to 5400 years B. P.;instead in Argentina it was older than 6000 years B.P.

Comparingthe vermetid Braziliancurve with the Argentine MSLcurve "out of storms" there is still a lag about 500-1000 yearS SeeFig. 1!; Argentine data older than Brazilian. BuenOSAireS sediments and SOilSare dOminated by a high cOntent in calciumcarbonate caliche!. Surface water and groundwaterhave a highercontent in CO3 and HC03 pH is usually between 7.8 ta 9!. Mollusk shells are therefore subject to incorporate much reworked carbon. There is no reservoireffect CarriedOut, but SOmepreliminary radiOCarbandateS perfarmed On Shellson living Tage/uSplebeiuS fram the Quequcsn Grandeestuary indicate an age of 230 years Figini, 1997!. On the other hand, surface water and groundwater an the southern Braziliancoastal zone have not such CO3 and HC03 content pH is usually between 4.0 to 7.2!. This reservoir-effectdifference could explain the lag on the timing of maximum MSLbetween both regions.

35 c! Fluctuationsbelow presentMSL Althoughtwolower-than-present sea-levelstands were proposed inBrazil about 4100-3800 yearsB P. and between 3000-2700yearsB.P. Sugu oet al. 1985 and Martin etal. 'I998!, According toAngulo andLessa 997! and Lessa and Angulo998! dates donot support theexistence ofsuch oscillations. Noevidence hasbeen found inthis sense inArgenti- na

Acknowledgernents R.J. Angulo isa Scientistofthe Brazilian Research Council CNPq!;F IslaI. isCareer Scientist ofthe National Research Coun- cilof Argentina; E.J.Schnack isa Career Scientist ofthe Buenos Aires Province Science Commission

References Aguirre,M.L.y Whatley,R.C., 1995. Late Quaternary marginal marine deposits andpalaeoenvironments fromnorth- easternBuenos Aires Province: a review. Quaternary Science Reviews 14, 223-254. Angulo,R.J.and Lessa, G.C., 1997. The Brazilian sea-level curves:a critical review with emphasis onthe curves from Paranaguaand Cananisia regions, Mar. Geol., 140.'141-166, Cavalotto,J.L.,Parker, G.and Violante, R.A., 1995. Relative sea-level changes inthe Rio de la Plata during the Holocene. InOrtlieb, L. ed.! Late Quaternary coastal records ofrapid change: application topresent and future conditions. 2nd. AnnualMeeting, Abstracts, 19-20 Antofagasta, Chile, November 12-18. Figini,A,J., 1997. Comparaci6n deedades C-14 en muestras deorigen man'no y terrestre. EfectoReservorio. Unpublised report,LATYR, UN! P, La Plata, Argentina, 6 pp. Isla,F.l., 1989. The Southern Hemisphere sea-level fluctuation. Quat. Sc. Reviews, 8'359-368. Isla,F.l. y Espinosa,M.A, 1998. Modelo sedimentario decolmatacidn depequenos estuarios dominados porlimos, ProvinciadeBuenos Aires. V/I Reunidn Argentina deSedimentologia, Salta,AAS, 12 al 16 de octubre de1998, Actas, 24- 36. Laborel,J.,1986. Vermetid gastropods assea-level indicators. InVan de Plassche, O. de,! Sea-level research; a manual for the collectionand evaluation of data.Geobooks, Norwich, 281-310. Lessa,G.C.and Angulo, R J.,1998. Oscillations ornot oscillations: thatisthe question- Reply, Mar. Geol., 150:189-196. Martin,L.,Bittencourt, A.C.,Domingues, J.M.L.,Flexor, J.M.and Suguio, K.,1998. The Brazilian sea-level curves: a criticalreview with emphasis onthe curves from the Paranaguh andCananeia regions. Mar. Geol.: 150:179-187. Suguio,K.,Martin, L.,Bittencourt, A.C.,Domingues, J.M.L.,Flexor, J.M.and Azevedo, A.E.G.,1985, Fluctuacoes donivel relativodomar durante o Quaternlrio Superior aolongo do litoral brasileiro e suas implicacoes nasedirnentacao costeira. Rev. Bras. Geoc., 15:273-286.

24 O C7 co 3

E -8000-6000-4000 years BP Fig,l. Comparisonbetween the vermeti brazilian curve and the argentine MSLcurve out of storms After Angulo and Lessa, 1997; 'sla and Espinosa, 1998!.

36 CoastalChange crn the TimeSCate Of DeCadeS te IVtrltennia

Factorscontrolling the formation of intercalatedpeat beds in the Holocenesequence of the coastal lowlands of the southern North Sea

Cecile Baeteman

BelgianGeological Survey, Jennerstraat 13, 1MOBrussel, BELGIUM e-mail:cecilebaeterrianthotrnait.coin

Introduction Peatbeds intercalated in tidal mud deposits are very typical in the Holocene sequence of coastal lowlands along the southernNorth Sea. AlthoLtgh their formationis usuallyattributed to sea-levelfluctuations, their formationremains ques- tionable.Despite the uncertainorigin of their formation,intercalated peat bedsare very often regardedas stratigraphical units or indicators of sea-level tendencies.

In orderto revealthe factorscontrolling the formation of the intercalatedpeat beds,detailed stratigraphical and sedi- mentologicalwork on the basisof a denseboring grid!, supportedby 14Cdatings, was carriedout in the landwardpor- tion of the Belgian coastal plairi, in particular in a major paaeavalley containing a complete sequence of Holocene deposits!and its tributaries where it is assumedthat maximum preservation of the various facies occurs, lt is most likely that the palaeovalleywas formed by river action during the Weichsefiansea-level fall and lowstand. The presenceof basal peat on top of the Pleistocenedeposits, in particular in the deeper parts of the palaeovalley,indicates that the rnorpholo- gy of the valley already existed before the sea-levelstarted to rise in the Holocene. The stratigraphica and chronological resultsof the landward portion were compared with the central and seaward portion of the plain.

Discussion The palaeOValleyfillS ShOWa high VariabilityOf the SedimentarySuCCeSSian. DifferenCeS Of the enCOunteredfaCieS mud, sand,peat and gyttja! are expressedacross and along each palaeovalleyfill itself, between the different palaeovalleys,and between the various sub-regions. However, intercalated peat beds are completely absent in the period prior to ca. 7300 cal BPbecause sea-level rise was too rapid ca. 7m/ka!, so that the active sedimentation surface of the flats did not silt up until supratidal levels lasting a sufficient long period, thus enab ing a freshwater lens to form in the subsoil, with conse- quent initiation of a freshwater marsh. For that period, only vegetation horizons are occurring. As from 7300 cal BP.on, intertidal and supratidal flats, freshwater swamps and freshwater-filled depressionsexisted next to each other, even over very short distances,resulting in a rapid alternation of mud, peat and gyttja in the vertical sedimentarysequence.

Intercalatedpeat beds originate when the active sedimentary surface builds up high enough that it is permanently situated abovethe level of the highest astronomical tide HAT! resulting in the formation of a freshwater marsh in which peat can accumulateprovided that the sediment surface remainssaturated throughout its formation. However,the initiation of peat in a freshwatermarsh requiresthe installation of a freshwater lens in the subsurfacefor a sufficiently long duration, oth- erwiseonly humic vegetation horizons will be a lowed to exist due to the dense salt-marsh vegetation introducing a lot of organic matter into near-surfacedeposits.

Unlike autochtonous peat, gytt!a is formed by plant remnants which have been physically moved from a somewhat dis- tant source,most likely the vegetation lining influent rivulets. The formation of gyttja must be attributed to ponding and sluggishdrainage in the topographic depressionswhere water is backed up in the drainage channels of the palaeovalleys. The latter had no significant slope and acted as a drain for the outcropping Pleistocenehinterland. E3yttjaformation also denotes inadequatesediment supply, so that the sedimentary surface could not accrete upwards in pace with the water level.Consequently, the initiation of peat on gyttja implies a lowering of the water level with respect to the sedimentary surface,most likely caused by an improvement of the drainage. This is in contrast with the initiation of peat on the salt marsh where vertical accretion of sediment is the determining factor. Consequently, changes between gyttja and peat reflect temporary changes in the local hydrology within the drainage channels in the palaeovaleys.

Thecomparison of the facies changesand their chronology within the palaeovalleysand between the different areas clear- ly demonstratesthat a general synchroneity or regular distribution pattern does not exist at particular levels throughout the entire area, at least not until ca 5500 cal BP,and not until a level of about 0 rn period and elevation at which the plain was almost completely filled!. Throughout the whole period before 5500 cal BP,the area was characterisedby a vari- ety of facies ranging from tidal-channel sand, intertidal mud and sand, peat and gyttja; all occurring next to each other.

Theobserved facies changes and their chronology suggest that the changes are directly related to the position of the active sedimentarysurface with respect to the level of the water. The sedimentary surface is determined by the sediment supply which, in turn, is governed by the sediment source, while the water level depends on the tidal and groundwater level, both of which are induced by the level of the sea.

37 Thetidal flat is dissected bya veryextensive network of tidalchannels and creeks

38 With a decreasingrate of relativesea-level rise as from about 5500cal BP,the creationof new accommodationspace pro- gressivelyreduces, and the vertical sediment accretion in the channel and on the flats slows down. This results in a reductionin the frequencyof channelshifting and explains why the periodsof peatgrowth lastedlonger, and why the lat- eralextension became more and moregeneralised as the filling of the tidal basinproceeded.

Thispurely sedimento ogical mechanism, acting only underconditions of a rapidrelative sea-level rise and a generalland- ward migration of the channel network, is at the origin of the alternation of peat beds, gyttja and tidal sediments, It also explainswhy the intercalatedpeat bedsare not synchronousand do not exhibita regularpattern in termsof leveland spatial distribution.

Thus,a singlepeat bed shouldnot to be usedas markerbed in the stratigraphy,nor as stratigraphicunit. Nor doesthe alternationof mud and peat reflectpositive or negativesea-level tendencies, since sea-level fluctuations pay no part in their formation.

Conclusion Thestudy of the Holocenesequence of a mainpa aeovalleyand itstributaries has shown the complexityof the fill and facies distribution, laterally as well as vertically. The filling of the palaeovalleyand the ultimate formation of the coastal plainwere controlled by a deceleratedrelative sea-level rise, the palaeotopographyand accommodationspace, sediment supply and the configuration of the tidal flat, especiallythe distal and proximate position of the tdal channel in relation to a particularsite. The positionof the channelsand creekssignificantly determined the developmentof the different depositionalenvironments during the fill. Changesin the rate of reative sea-levelrise seemsto be the only regionalfac- tor, All other controlling factors act locally and their identification requires an integration of local site-basedstudies in the context of the large-scalecoastal behaviour of the entire tidal basin, It should be mentioned that possible crustal move- rnentsthroughout the Holocenehave not beenconsidered and muststill be investigatedwithin this context.

Theinfill of the palaeovalleysdid not occurcontinuously, nor gradually,but in successivesteps. Changes between different depositionalenvironments mutually, and betweenpeat growth and tida depositionoccurred rapidly, and this also appliesto the spatia distributionand the verticalsuccession. The changes and the successivesteps were not synchronous, not evenover short distances, but depended on the localfactors mentioned above Thefacies sequence is muchmore sen- sitiveto changein sedimentsupply than is generallyassumed. The facies changes, in particularbetween mud and peat, is determinedby sedimentologicalcontrol under the conditionsof a rapidrelative sea-level rise and a landwardmigration of the channel network associatedwith a surpassingsediment supply. Periodsof peat growth lasted longer and the lateral extensionbecame more and morewidespread as decelerationof the relativesea-level rise continued and the filling of the tidal basin proceeded, associatedwith the progradation of the shoreface.

Becauseof the irregular pattern of peat growth in time and space resulting from the combined action of the loca! factors whichgovern their formation,peat bedsshould no longerbe usedto differentiatestratigraphical units in the coastalsed- imentarysequence.

CoastafChange on the 7imeScale of Decadesto lV!i!Jennta

Retreat of the Rio Grande Do SUI Coastal Zone, Brazil

R. Baitelli'z L. E. S. B. Almeida' E. E. Toldo, Jr,' C. E. Barros' L. R. Martins' and J. L. Nicolodi'

Centrode Estudosde GeologiaCosteea e Dceanica CECO. Instituto de Geociencias- IG, Univecsidade Federal do RioGrande do Sul UFRGS,Av., BentOGonCalves 9900, 91509-900, Porto AIegre RS,BRAZIL e-mail Baitelli!. [email protected] e-mail Almeida!: almeida!if.ufrgs.bc e-mail TOldO!: tnldOOvortex.ufrgs.br e-mail Barros!: ennesOif,ufcgs.br e-mail ivlartinsl ImartinsOif.ufrgs bt e-mail Nicolodi!! !I nicolodi@zipmailcorn br

Departamentode Geodesialnstituto de Geociencias- IG, Universidade Federal do RioGrande do Su - UFRGS,Av BentoGonCalves 9500, 91S09-900, PortoAlegre RS,BRAZIL

Introduction In this work retreat and progradation refer to a change in shoreline position, whereas erosion and accretion refer to vol- Umetricchanges in the subaerialbeach Wood et al. 1988,Oertel et al. 1989,In: Pilkey& Thieler1992!. As usedin this paper,erosion refers to anyform of shorelineretreat, consistent with commonUsage Pilkey and Thieler,1992!.

Onall typesof sandyor unconsolidatecoasts, beach erosion can be consideredto be controlledby a dynamicequilibrium involvingthree major components, amount and type of sedimentsupply, physical energy along the coastand rate of sea- levelchange Davis, 1997!.

Whendealing with shorelinesand beaches, it is crucialto distinguishbetween erosion and the erosionproblem. Many kilo- metersof undevelopedU.S. shoreline are eroding and, asa rule,such locations are not consideredto be a socialproblem. It is onlywhen humanactivity interferes with or getsin the way of shorelineerosion that is becomesa problem Pilkey& Thieler, 1992!.

This paper reports on changes in shoreline position in the state of the Rio Grande do Sul, where the rapid erosion is well documented,the accretiona areas is not known and the processesresponsible for these conditions are not well understood, by comparing the beach line determined by GPSsurvey in 1997 with the beach Inc determined from aerial photos taken in 1975.

PhysicalSetting TThestudy area is a sandycoastline composed mainly of unconsolidate Quaternary sediments Villwock, 1986!. The coastal plain of Rio Grande do Sul covers a large area of 33,000kmz, consists mostly of sandy deposits interrupted by small StreamS,haS eleVatianS Up tO 6m, and COntainSan great number of ponds and lakeSand twO large lagOOnS.ThiS COaStal plain extendsfrom a headland of granite rocks at Cabo Polonio in Uruguay to the basaltsof the Serra Geral Formation at Torres beach.

The RioGrande do Sul coastal line is a 630km long beach, which runs roughly NE-SW Fig. 1!. The continuity of the beach is interrupt by four inlets, which represent a shallow embayment that receivesfreshwater and high suspended sediment concentration,mostly from the Lagoados Patos Lagoon Hartrnan, 1988!, whose a meandischarge is 4,800mB/s. The supply of sandysediments to the coast is not important becausethe rivers deposit their sedirrient load into the estuariesand lagoons.Hard structureshave been built at three locations, Chui inlet South limit!, Lagoa dos Patos inlet, Mampituba inlet North limit!, in an effort to fix three inlets.

Thecoastal line trends ESSE,has a mean tidal amplitude of 0.45m, and is exposed to a dominant wave approach from the passageof frontalsystems and from passingextratropical cyclones. Prevailing winds are northeast along virtually the entire coast.These wind conditions are particularly persistent during summer, In the summer and autumn the storms frequency are of east and southeast, and in the winter the storms frequency are from the south and southeast, Tozzi 8 calliari, 1997!, Exceptfor the passageof cold fronts, the coast experiencesmedium to high wave energy conditions; mean annu- al significant wave height is 1.50m and the mean wave period is 9 seconds Wainer, 1963; Motta, 1969; Almeida et al., 1997!. Swell and sea conditions occur along all coast with periods up to 9 and 5 secondsrespectively, swell is from SEand the sea is from the E.

Storm surgeshave been recorded at numerous locations in the study area over the past few decadesduring the passage of coldfronts. Almeida et al. 997!, observeda stormevent at Tramandaibeach, which produceda maximumwater level of 1,5m in Apri 07, 1997.

41 The subaerialbeach at the North littoral, betweenTorres beach and Quintaobeach Fig. 1!, hasa smoothslope between 1:30and 1:40and an averagewidth of 60m,which immediately flattens to about 1:60!in the subtidalzone. The sedimentsacross the beachand the surf zoneconsist mostly of well-sortedfine sand meansize 0.2mrn, as analyzedby Martins967!, Alvarezet al. 983!, Tomazelli& Villwock 'I 992!, Toldoet al. 993!, Weschenfelderet al. 997!. From the Conceicaolighthouse southward, Calliari & Klein993!, reportfine quartz sand with graveland bioclastic sand, Siegle 996!, also noted the dominanceof fine sandin this areaas well as somemedium sand and heavyminerals in sections of the beachbetween the Conceicaolighthouse to the Herrnenegildobeach Martinsda Silva1976, Villwock 1978, Tomaze lli 1978!. The mast betweenthe Imbeand Tramandaibeaches is characterizedby intermediateto dissipativestates Todo et al., 1993!,from Conceicao lighthouse to SaoJose do Nortethe beachesare also intermediate to dissipativewith a morereflec- tivestage during periods of low waveheights Alvarez et al, 1981,Barleta & Calliari,1997!. The mast between Cassino beachand Chui beach,has different morphodynamic states: intermediate to dissipativeNorth of the Albardaolighthouse, and intermediate-reflectiveat Southof this lighthouse Calliari & Klein1993, Tozzi 1995!.

Methods Measurementsthe positionof the coastalline were made from 26 to 28 November1997, between Torres beach and Chu beachusing two GPS,GARMIN model GPS 100 Personal Surveyors, with an accuracy of 10mfor the navigatormode and 3m for the static mode. The GPSwas installed in a vehicle that was driven approximately 20m of distance from the waterline with a mediumspeed of 50km/h,and an otherGPS, in the staticmode, was positioned at placespreviously establishedon the coastabout 100kmapart, in orderto coverthe readingsand to increasethe precisionof data.The sam- plingrate for bothof the GPSinstruments was 5 seconds,which allowed past-processing to show the coastlineposition with anaccuracy of 3m.In this work, the space of 18kinbetween the Mostardaslighthouse and Barra da Lagoado Peixe, was not measured Fig. 2!. Thebeach line establishedby GPSin 1997,was comparedwith the beachline reproducedfrom the armychart collection makein 1978year at a scaleI:50,000, based on aerophotogrametricstudy in 1975year. Changes in beachline were establishedon a scale1:1,300,000 using the IDRISIsoftware.

Results and Discussion TheRio Grande do SulState includes 630km of opencoast with Quaternarydeposits that arealmost exclusively uncon- solidatedand the shorelineranges from severelyeroding to prograding Fig,2!. Shorelinecomparisons between 1975 and 1997 show both the retreating and progradating areas along the coast between Torresbeach and Chui beach. There are 528km of erodingbeaches, 50km of progradingbeaches and 52km of beachwith- outsignificant variations. The coast near the hard structures built c oseto Chuiinlet and Lagoa dos Patos inlet has a bal- ancebetween sediment supply and removal with variationsof the coastline smaller that 20mbetween 1975 and 1997, Thiswork does not consider,however, the shorelinebetween Torres and Mampituba inlet nor the 18kmnear the Lagoa do Peixeinlet. As shownby Figure2 themajority of RioGrande do Sulcoast is retreatingat a highrate. The landward translationof the coastlirieexceeds 100m in 378kmwhereas nowhere has shoreline progradation exceeded 40m during thepast 22 years Fig. 2!. Evidencesof beach erosion in theRio Grande do Sul coastal zone have been documented by Alvarezet al. 981, 1983!,Barletta 8 Calliari997!, Calliari& Klein993!, Calliariet al. 996!, Siegle996!, Toldoet al. 993!, Tomazelli& Villwock989, 1992!,Tornazelli et al. 996! and Tozzi& Calliari997!. Thesetrends of erodingbeaches are an example of thecomplex interaction between the ratesof sea-levelchange, wave processesand storm impacts. to understandthe historical shoreline evolution along the Rio Grande do Sul coast. The vari- ationsrates of sea-levelfor this areaare in the orderof +0,62mm/yearasestablished from the tidegauge of Puntadel Este UruguayRepublic Fig. 1!, from 1901, Laborde in: Isla, 1997!. Toldo 989!, in geologicaland hydrodynamic stud- iesof theLagoa dos Patos, inferred a recentelevation of themedium water level in +1mfor thelast 300 years, using growth ratesof spits. Fourother factors wave refraction,storms, bulkheads and humanactivity, need to be consideredqualitatively even throughtheir magnitudes are not known. The first factor was analyzed by Siegle 996!, whoobserved that occurrence of energyconcentration induced by wave refraction in the places with high erosion rates ! 80m!,between Conceicao lighthouseand the Chui beach. The second factor are the effects caused by catastrophic storms, generated during the passageof coldfronts which raise the medium level of thesea up to 1.5mon the coast Alrneida et al.,1997!. Waves associatedwith extratropicalstorms cause the mostvisible and obvious shoreline erosion, but oftenstorm-caused erosion is substantiallyrepaired by pos-storm onshore and longshore sediment transport in theRio Grande do Sul coast. Calliari et al. 996!, Tozzi& Calliari997!, describethe shorelineretreat under storm conditions in the RioGrande do Sulcoast. Thethird and fourth process are the influenceof bulkheadsabout the front dunes,and the impactsof populationoccu- pation,mainly at theNorth area between Torres and Pinhal beach Fig, 1!, where population in the Summer reaches more than2 million.As discussed by Willians et al.997!, the vastmajority of coastalareas around the worldwhich are under increasingstress from natural processes in recent years received the effectof populationgrow. Thesefour processes,responsible for short and long period of erosion, demonstrate the complexity of its interactions when trying to explain coastal erosion in Rio Grande do Sul and rank them in relative importance. Besidesthese processes, the presenceof accretional areas, in the absenceof new sand from the mainland is also a problem. The existence of theseaccretional and erosional areas shows that the rates of shoreline erosion along Rio Grande do Sul coast cannot be viewedindependently of the laige-scaleprocesses of erosion, deposition and sediment redistribution that occur along the whole coastespecially in the shoreface,as observedby List et al. 997!, in studies from 100 years of historical bathymetric data of the Louisianabarrier island coast, and McBride & Byrnes 997!, when analyzing the importance of the coastal sedimentbudget on the coastal change. List 997!, concluded that historical shoreface map comparisons have led to resultsthat were not anticipated from an examination of shoreline changesalone, and also that longshore transport seems to play a major role in the rapid erosion. This longshore transport occurs both along the shoreline through well-documented littoral processes along the Louisiana coast, and also apparently at shoreface depths by processes that are poorly understood.

Regardlessof its causesthe results of this study are important for the management of the coastal zone in Rio Grande do Sul.Coastal restoration programs can utilize this information to: identify areas in greatest need for protection and restoration, help determine the type of coastal protection needed, and evaluate project performance hard or soft structures! by comparingpost-project rates of shoreline change with long-term historical trends, i,e,, have a well established baseline control data set McBride and Byrnes, 1997!.

Final Comments Thereare some generalizationsthat can be made along with their respective rationales, about this study that has documented the accretional areas and erosion problem about many kilometers of Rio Grande do Sul shoreline.

The Rio Grandedo Sul State shoreline is experiencing severeeroding conditions. Over the period of 22 years, the primary factorsdriving erosionalong of coastal zone are the combined effects of wave energy, sea-levelchange and sediment supply with recent and local impact from human intervention.

Coastalerosion contributes to improved understanding of the historical shoreline evo ution along the Rio Grande do Sul Stateas well as the accretional areas. These conditions suggests that for the understanding of the coastal sedimentary dynamicsis necessaryto understand the large-scaleprocess of erosion, deposition and sediment redistribution on shoreline and on shoreface.

Thedata obtained from of the methodology used in this wok provides a mechanism for estimating the coastal sediment budget,that in beginningconstituted in the most influentialfactor affectingthe RioGrande do Sulcoastal change. Acknowledgements Thiswork is the result of researchsponsored by OEA/CECOProject. We are gratefu to Tec.Cesar D. C. Goncalves,Luiz G. Rauppand Jose C. Nunes,for their technicalsupport. The authorswish to thank Prof.Paul E. Potterfor his thorough review, constructive comments and suggestions.

References Almeida,LE.S,B.; Rosauro, N.M,L& Toldo JrE,E., 1997. Anhlise Preliminar das Mares na Barra do Rio Tramandai,RS, XII SirnposioBrasileiro de RecursosHidricos, Vitoria, ES,Resumos, p. 560-566.

Alvarez,J.A; Gre, J.C.R.;& ToldoJr., E.E.1981. Estudosda Praiaa Nordestedo Molhe de Rio Grande,Pesquisas, 14: 131-147.

Alvarez,J.A; Gre, J.C.R;& Toldo Jr., E.E. 1983. EstudosOceanogrkficos e sedimentologicos preliminares da piaia de Tra- mandai-RS, Pesquisas, 15: 66-85.

Barletta,R.C., & Calliari, L.J,, 1997. CaracterizacaoMorfodinhmica de PraiasCompreendidas entre o Farol da Conceicao e SaoJose do Norte, RS.Resumos, p. 24-26, Anais da Semana Nacional de Oceanografia, UNIVALI,Itajai, SC, Brasil. Calliari,LJ., & Klein,A.H.F., 1993. CaracteristicasMorfodinkrnicas e Sedimentologicasdas PraiasOceanicas entre Rio Grandee Chui, RS.Pesquisas 20!, 48-56, UFRGS,Porto Alegre, RS,Brasil. Calliari,L.J.; Tozzi, H.A.M.; & K ein, A.H.F.,1996. Erosaoassociada a maresmeteorologicas na costasul-riograndense COMEMIR/OSNLR!,Anais, 34o Congresso Brasileirode Geologia, Salvador.SBG. 4:682-684.

Davis,Jr., R.A., 1997. Regional Coastal Morphodynarnics Along the United States Gulf of Mexico. Journal of Coastal Research, 13!, 595-604. Hartman,C; & Sano,E.E. 1988. Contribuicao ao estudoda hidrodinBmicae evolucaodas massas de aguana Lagunados Patos,atraves de imagens MSS/Landsat,no periodo de 1979 a 1983. RevistaBrasileira de Geofisica, 4:215-228.

Isla,Fl., 1997. Boletin Informativo Regional no 12. OSNLRUniversidad Nacional de Mar del Plata,Argentina.

43 Coasta!Change on the TimeScale of Oecatteste littittennta

List, J,H.; Jaffe, B.E; Sallenger,A HJr., & Hansen, M.E., 1997. Bathymetric Comparisons Adjacents to the Louisiana Bar- rier Islands:Processes of Large-scaleChange. Journal of CoastalResearch, 13!:670-678. McBride,R.A. & Byrnes,M.R. 1997, RegionalVariations in ShoreResponse along BarrierIsland System of the Mississipi RiverDelta Plain: Historical Change and FuturePrediction. Journal of CoastalResearch, 13!:628-655. Martinsda Silva,M.A., 1976.Mineralogia das Areias de Praiaentre RioGrande e Chui,Rio Grande do Sul. Cursode Pos- Graduacaoem Geociencias,UFRGS. Dissertacaa de Mestrado. 93p. Martins,L.R. 1967. Aspectos texturais e deposicionaisdos sedirnentos praiais e eolicosda planiciecosteira do RioGrande do Sul. PublicacaoEspecial da Escolade Geologia, UFRGS,Porto Alegre, 13:1-102. Matta, V. F.1969. Relatorio Diagnostico Sobre a Melhoriae o Aprofundamentoda Acessopela Barrado RioGrande. Rela- torio Tecnico.Porto Alegre, Instituto de PesquisasHidraulicas, UFRGS. 144p. Pilkey,O. H. Jr., & Thieler,E, R. 1992. Erosionof the UnitedStates Shoreline. Quaternary Coasts of the United States: Marineand LacustrineSystems. IGCP Project ¹274, SEPM,Special Publicaton 48. Siegle,E., 1996.Dtstribuicao dos SedimentosLitoraneos entre a Farolda Conceicaoe Faroldo Chui, RS,e FataresCondi- ciortantes.Curso de Graduacaoem Oceanologia,Fundacao Universidade do RioCirande. Trabalho de Graduacao,91p. ToldoJr., E.E.1989. Os Efeitosdo TransporteSedimentar sabre a Distribuicaados Tarnanhosde Graoe Marfadinamica Lagunar,Porto Alegre. 143 p. Dissertacaade Mestradaem Geaciencias, Instituto de Geociencias, Universidade Federal do Rio Grande do Sui.

ToldoJr, E.E.; Dillenburg, S.R.; Almeida, L.E.S.B.; Tabalara, J.L.; Martins, R.R.; & Cunha,L,O,B.P1993. Parkmetras Morfod- inamicas da Praia de lmbe, RS.Pesqu sas, 20!:27-32, UFRGS,Porto Alegre, RS,Brasil.

Tamazelli, L.J., 1978, Minerais Pesadosda Plataforma Continental do Rio Grande do Sul. Acta Geologica Leopoldensia, 5!:103-160.

Tamazelli,L.J., 1990. Contribuicao ao estudo dos sistemasdeposicionais holocenicos do nordeste da provincia costeira do Rio Grande do Sul corn enfase no sisternaeolico. Porto Alegre. 270 p. Tesede Doutorado em Geociencias,Instituto de Geociencias,Universidade Federal do Rio Grande do Sul.

Tamazelli,L.J., & Viilwock, J.A., 1989. ProcessosErosivos na Costa do Rio Grande do Sul, Brasil: Evidenciasde uma Provav- el TendenciaConternporanea de Elevacaodo NivelReiativo do IVlar.Resumos, I Congressoda AssociacaoBrasileira de Estudos do Quaterrtdria, Rio de Janeiro, ABEQUA, p. 16.

Tornazelli,L.J. & Villwock, J.A. 1992. ConsideracoesSobre o Ambiente Praiale a deriva litoranea de sedimentos ao Longo do Litoral Norte do Rio Grande da Sul. Pesquisas,19!:3-12. Tomazelli,L.J.; Villwock, J,A.; Dillenburg, S.R.; Bachi, F.A.; & Dehnhardt,B,A., 1996. Erosaa Costeira na RiaGrande do Sul, Anais, 34a Congressa Brasileirode Gealogia, Salvador,BA. SBG.4:685-687.

Tozzi, H.A.M& Calliari, L.J., 1997. Influencias das TempestadesExtratrapicais sobre o estoque de Sedimentos das Praias entre RioGrande e Chui,RS, Resumos, p. 85-87,Anais da SemanaNacional de Oceanografia,UN!VALI, Itajai, SC, Brasil

Tazzi, H.A.M., 1995. Morfodinamica da Praia do Cassino, Rio Grande, RS.Curso de Gradua«aoem Oceanologia, Funda- cao Universidadedo Rio Grande. Trabalho de Graduacao, 52p.

Villwack, J.A.; Tomazelli,L.J.; Hofmeister, T.; Juchem, PL.; Dehnhardt, E.A.; & Loss,E,L., 'l978, Anllise Texturale Mineralog- icadas Areias Negras da Costado RioGrande do Sul.Anais, XXX Congresso Brasileira de Geologia,Recife, PE, 2:913-926.

Villwock, J.A.; Tomazelli, L.J.; Loss, E.L.;Dehnhardt, E.A.; Horn Fo, N,OBachi, F.A.,& Dehnhardt, B.A. 1986. Geology of the Rio Grande do Sul Coastal Province,In; RABASSA,J., ed.!, Quaternary of South America and Antarctic Peninsula.Rot- terdam: A,A, Balkerna Publishers,4, 11p.

Wainer, I.J., 1963. Analise e Previsao das Alturas de Onda em Tramandai. Relatorio Tecnico. Porto Alegre, lnstituto de Pesquisas Hidraulicas, UFRGS.

Weschenfelder,J. 1996. Variabilidade Morfodinamica das Praias Oceanicasentre Imbe e Arroio do Sal, Estado do Rio Grande do Sul, Brasil. Dissertacaode Mestrado em Geocencias, Instituto de Geociencias,Universidade Federal do Rio Grande do Sui, 132 p.

Williams, S.J.;Stone, G W., & Burruss, A.E., 1997. A perspective on the LouisianaWetland loss and coastal erosion problem, Jounal of Coastal Research, 13!:593-594.

44 Fig. 1. Study area showing the principal locations.

CoastalChange on the TimeScafe of Oecadesto Millennia

Heavyrftetal enrichments in an 'Endangered' coast, south west coast of India: A baseline study

K. Balakrishna',B. R. Manjunatha2,R. Shankarz and T. R. Mahalingam3

OCeanOgraphyand ChrnateStudieS, PhySICa! ResearCh labaratOry, Navrangpura,Ahmedabad 380 009, INDIA email: kbalaeeprl.ernetin

Dept of MarineGeology, Mangalore University, Mangalagangotri 574 199,INDIA e-mail:rshankarOmnglr.ernet.in 3lndiraGandi Centre for AtomicResearch, Kalpakkam 603 102, IN ~ IA email:trmOlgcar.ernet.in

Riversare the channelised routes through which continental materials like weathered products and anthropogenic materialsare transported to the coast.Remova! of both suspendedand dissolvedmaterials takes place during the mixing of riverwater with seawater dueto gradientsin pH, salinityand other physico-chemicalparameters like dissolvedoxygen, Eh,turbidity and humicacids About 92'/o of the river-bornesediments 3.5 billion tons/yr!are trappedin estuariesand connecteddrainage basins like lagoons, tidal flats, marshesand adjacent continental shelvesdue to flocculation, aggluti- nationand fecal pelletisation processes. This is the prime reasonfor the accumulationof contaminantslike heavymetals, radionuclides,and organic contaminants in densely populated and industrialised coastal belts of the world

Nearshoreregions serve as a sink or filter for continental detritus, but they are not a permanent sink for base metals. Due to the rapidaccumulation of organicmatter in thesesediments, diagenetic processes result in the depletionof dissolved oxygenproducing anoxic conditions, under which redox sensitive metals are easily rernobilisedfrom the sedimentary col- umn and added through the pore water to the overlying water. Remobilisedmetals may again undergo adsorption and precipitationand thus be incorporatedinto the particulatephase under oxic conditions.The direction of bottom currents influencesthe transportof remobilisedelements either landward or seaward.In general,because of the seawarddecrease of terrigenousinflux and the existenceof oxicconditions in the openocean, base metals are enrichedin open oceansed- imentswhen compared to nearshore sediments.

Astwo thirdsof the world populationlives in and aroundcoastal areas, it is imperativeto monitor pollutionin the aquatic system.Baseline data for the various organic and inorganic constituents in the environment air, water and land! and their pediodicmonitoring are needed to evaluate the impact of industries on the environment. Baselinestudies will not only help in evaluating the impact from upcoming industries on the environment but also in understanding natural processesoperating in the area.

India'svast coastline is densely populated and characterisedby a number of industries like chemical and fertiliser plants, oil refineries,nuclear power plants, ports etc. The study area forms a part of Karnataka State which has a coastline of about300 km alongthe southwest coastof India, borderedby the WesternGhats on the eastand the ArabianSea on the west. Thiscoastlne is punctuatedby a numberof naturalas well as man-madefeatures; man-made features include ports / harbours, fertiliser plant, etc. A number of industries have recently come up and few others are in the processof beingset up in the coastalzone like the MangaloreChemicals and Fertilisers,Mangalore Refineries and Petrochemicals, Cogentrix thermal power plant, Nuclear Power Plant, Naval Base etc.Therefore coastal environment of Karnataka is presentlysitting under an industrial hotspot .

Keepingthis in background, the present study is taken up in this area along a small tropical river-estuary-coastalsystem Kaliriver; Iat 74'54'N, long 74'29'E and 14' 48'N, 74'01'E! draining into the Arabian Sea.This study acts as a baseline datawhich investigates the anthropogeniccontnbution of tracemetals in the river-estuaryand coastalsediments. ln this study, enrichment factor and geoaccurnulation index have been used to assessheavy metal pollution in the area of investigationfor Mn,Fe, Co, Ni, Pb, Zn, Cu and Mo. Enrichmentfactor EF= Metal/Al pl ! / Metal/Al ,,g,,h,l,!! has beencalculated for these elements both in suspended and river-bed sediments that were co lected during pre-monsoon, monsoonand post-monsoon seasons. The composition of global average shale has been taken as the background value as no similar data are available for the study area. The average composition of normal shallow water shale used in this studyrepresents the crustal composition and is basedon the averageof 277shale samples. Geoaccumulation index Ig! is another measureof quantifying metal accumulation in polluted sediments. Becauseit is a simple measure of knowing the levelof heavy metal pollution in aquatic environments, it is widely used.

Geoaccumulation index is expressed as: lgeo logz An/Bnx 1,5! where:An = concentration of element A in a sample Bn = background value i.e. average shale! of element A, and 1.5 = factor that takes care of possiblevariations in background data due to lithologic effects

47 Geoaccumulationindex«an be classified into seven grades, of whichl>6 indicatesa 100-fold enrichment of an element abovethe background. It isdistinct from EF because ofthe factor of 1,5provided inthe equation which takes care of possiblevariations inthe background data due to lithologiceffects. In addition, EF does not take into account the nature and genesisof the matrixwhich plays a crucialrole in metalcontamination, Manganeseand Pb show EFs of in differentseasons for SPMand bottom sediments from the riverine and estuarine environments.The occurrence of Mn depositsin the catchmentmust have contributed to the highenrichment of Mn. TheI forMn is uniformly zero in all the environments ofthe Kali system proving that there is no anthropogenic factor behindMn enrichment.Lead is enrichedin the estuarineand coastalocean SPM of post-monsoonand monsoonseasons andin theestuarine bottom sediments of the pre-monsoon season. The I> for Pbin pre-monsoonestuarine sediments isalso 2. The principal source of Pbcould be the atmosphere which reacts with particulates leading tothe enrichment of Pb in SPM and bottom sediments. Ironin themonsoon season ismainly enriched in theriverine SPM; but the EF gradually decreases in the estuary and the coastalocean. A similarpattern is observed for bottomsediments. Iron in theriverine sediments has an EFof 2. Thisis supplementedbythe high lzvalues observed forthe sediments. Dueto the predominance ofchemical weathering inthe catchment,the rocks are transformed into laterites which are rich in Feand Al. With passage of time, they are eroded and transportedasparticulate load or asbed-load in theKali river. Cobalt shows an EF of about2 inthe riverine and estuar- inebottom sediments whereas enrichment in SPMis uniformin all thethree environments. Cobalt shows an Igppof 2 for riverinesediments of themonsoon and post-monsoon seasons whereas Ni shows an lz~ of 2 inthe pre-monsoonseason. Thishigher-than-normal enrichment could mainly be due to naturalprocesses asCo and Ni are known to beassociated with Feand Mn dioxidephases during chemicalweathering. Copper,Zn and Mo show moderate to minimal enrichment inthe riverine, estuarine and coastal environments inthe three seasons.Their I< valuesdonot exceed 1 which iswell within the safe limits from the point of view of pollution. Thisstudy has suggested that there is no pollution of SPMand bottom sediments in the area investigated due to anthro- pogenicactivities asof date of sample collection. However, theenrichment inMn, Pb, Fe and Co in SPM and bottom sediments could be due to natural materials/ processes.

48 Coas atChange on the TimeScate of Oecadesto Mii ennia

Rapidsea-level changes anci coastal evolution on the Pacificmargin of Canada

J. Vaughn Barrie and Kim W. Conway

GeologicalSurvey ol CanadaPO. Box 6000 Sidney. Bruish Columbia VBL 4B2, CANADA e-mail Barrie!: barrieiispgc.nrcan. gcca e-toailIconway!: conwayOpgc nrcan.gc.ca Glaciationreached its maximumextent sometime after 21,000 '4C yr B.P.off the northernPacific margin of Canada withice moving into Dixon entrance from southeastern Alaska and the BritishColumbia mainland, joined by local ice from thenorthern Queen Charlotte Islands. Glacial retreat began sometime after 15,000 '4C yr B.P.and ice had completely left themarine areas by 13,500to 13,300'4C yr B.P.A coreobtained at the presentday water depth of 37 m containscold waterforaminifera Cassidulina reniforme! in iceproximal laminated fine-grained sediments which date to 14,570'4C yr B,P. Barrie and Conway,1999!. Another coretaken from a nearshoresand deposit has been dated to between12,710 and12,880 '4C yr B.P.in 77 m ofwater, The indication is that a rapidregression occurred on the continentalshelf between approximately14,600 and 12,500'4C yr B.P.,contemporary with deglaciation,due almostentirely to rapidisostatic rebound.Sea level had reached a maximumlowering of over150 m andremained low untilapproximately 12,400 '4C yrB.P., after which a rapidtransgression occurred Josenhans et al., 1997!.As the seatransgressed the continentalshelf westof theBritish Columbia mainland, sea-level reached a maximumof 200 rn abovepresent n Kitimattrough on the mainlandat 'I0,500i4C yr B.P. C ague, 1985!. ContempOraneous shelf tilt exiStedacross the northern Pacific margin of Canadaranging from 200 m ofsubmergence at the fjord head near Kitirnat on the BritishColumbia mainland to greater than100 m ofemergence on the westernedge of the QueenCharlotte Islands at approximately10,500 l4C yr B.P.This regressive/transgressivecyclelasted only 5,200 to 5,500'4C years, a resultof thedevelopment and collapse of a glacioiso- staticforebulge.

Sediinentsupply, wave and tidal currentenergy were the primaryfactors that controlledcoastal response to theselate Quaternaryrelative sea-level changes. Plate tectonics, on the other hand, playeda secondaryrole in coastalevolution. Duringdeglacial regression of the shelf and transgressionof mainlandBritish Columbia sediment supply was abundant. Thisresulted in extensiveg acialoutwash and glaciomarinedeposition except where wave and current energies where high,such as Dixon Entrance and the westerncoast of the QueenCharlotte Islands. In theseareas early intrusion of the highenergy Pacific waters resulted in the transferof sedimentto the selfbreak.During the earlyHolocene transgression of theshelf, sediment supply was primarily restricted to the erosionof the previouslydeposited deglacial deposits, resulting in the formationof drown wave-cutterraces and spit platformsas sea-levelrose in steps.The rapid rate of sea-level rise cm/yr!was such to alsodrown and preservefetch-protected paleolacustrine and estijarineenvironments. Sediment supplywas reduced as sea-levelsincreased, except for the northeastern coastline of the Queen Charlotte Islandswhere glacialand outwash deposits still form much of the coastline.Here, Holocene sea-level changes still impactthe coastal zoneand transfer sediment offshore, As much as 12 rn of coastalerosion occurred during the recentEl Nino,when sea- levelsreached 40 cm abovenormal during the peakin February1988.

References Barrie,J V.and Conway, K.W. 1999. Late Quaternary glaciation and postglacial stratigraphy of the northernPacific magin of Canada, QuaternaryResearch, 51, 113-123.

Clague,J.i. 1985.Deglaciation of the PrinceRupert - Kitimatarea, British Columbia. Canadian Journal of EarthSciences, 22. 256-265.

Josenhans,H.W., Fedje, DPienitz, R.,and Southon,J, 1997.Early humans and rapidlychanging Holocene sea-levels in the Queen Charlotte Islands-HecateStrait, British Columbia, Canada. Science, 277, 71-74.