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Abstract Volume6th Swiss Geoscience MeetingLugano, 21st – 23rd November 2008
Apply!Geosciences
6th Swiss Geoscience Meeting 2008 - Lugano6th Swiss Geoscience Meeting 2008 - Lugano
Institute of Earth Sciences
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13. Global change – lessons from the geological pastHelmut Weissert, Peter O. Baumgartner
13.1 Adatte,T.:Impacts,volcanism,sea-levelandclimatefluctuations:towardsamulti-causalscenarioforthePhanerozoicextinctions,alessonfromthepast?
13.2 BaumgartnerP.O.&TschudinP.:Eutrophicationofmarginalseasbyriverinput:TheMiddleJurassicWesternTethyscomparedtotheModernCaribbean
13.3 DessaugesA.,LeuenbergerM.,NicolussiK.,SchlüchterC.:Glacialgeologyandpaleoclimate:StableisotopeanalysisinHolocenetreeringsMontMinéglacier(VS)
13.4 ErbaE.,BottiniC.,CasellatoC.E.,DeBernardiB.,TiraboschiD.:Ageologicalperspectiveoncalcareousnannoplanktonevolution:bioticresponsetoglobalchangeandenvironmentalperturbations?
13.5 FöllmiK.B.,GodetA.,BodinS.,LinderP.,deKaenelE.,AdatteT.,SteinM.:TheriseandfalloftheUrgonianempire
13.6 GiorgioniM.,WeissertH.,BernasconiS.:OceanicandclimaticChangesduringtheAlbian-Cenomanian:theWorldattheEndofPangea
13.7 GiraultF.E.,WellerA.F.,ThiersteinH.R.:Neogeneglobalcoolinganditsimpactondiatomsizeevolution
13.8 GodefroidF.,KindlerP.,SamankassouE.:Confirmationofanexceptionalsea-levelhighstandat+20mduringMIS11(400’000kaBP)fromBahamiansedimentaryrocks:acrediblescenarioforfutureglobalwarming?
13.9 HermannE.,HochuliP.A.,BucherH.,BrühwilerT.,GoudemandN.,GhazalaR.:EvidenceformajorclimaticchangeattheSmithian-Spathianboundaryfromlowpalaeolatitudinalrecords
13.10 JaccardS.,GalbraithE.,HaugG.,SigmanD.:ReducedoxygenconcentrationsintheabyssalNorthPacificduringthelastglacialperiod–implicationsforoceaniccarbonstorage
13.11 KellerC.E.,GiorgioniM.,GarciaT.I.,BernasconiS.M.,HochuliP.A.,WeissertH.:Cretaceouscarboncycleandclimate:TheBarremian-EarlyAptianC-cycleperturbation
13.12 MehayS.,KellerC.E.,BernasconiS.M.,WeissertH.,ErbaE.: The initiationofOAE1arevealedbyahighresolutionbiomarkercarbonisotoperecord
13.13 RichozS.,VanDeSchootbruggeB.,PüttmannW.,HeunischC.,QuanT.M.,FiebigJ.,ProssJ.:Evidenceofsulfidicmari-neenvironmentaftertheTriassic-Jurassicmass-extinctionevent
13.14 WestermannS.,MateraV.,FietN.,AdatteT.,FöllmiK.B.:PaleoredoxchangesassociatedwiththeEarlyAptianOceanicAnoxicEvent
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Impacts, volcanism, sea-level and climate fluctuations: towards a multi-causal scenario for the Phanerozoic extinctions, a lesson from the Past
Adatte Thierry
Institut de Géologie et Paléeontologie, Anthropôle, Université de Lausanne, 1015 Lausanne, Suisse
Mass extinctions in the Phanerozoic are closely related with severe climate changes and sea-level fluctuations. The consist-ent association of large magmatic provinces (LIPs and CFBPs) with all but one (end-Ordovician) of the five major Phanerozoic mass extinctions suggests that volcanism played a major role. Faunal and geochemical evidence from the end-Permian, end-Devonian, end-Cretaceous and Triassic/Jurassic transition suggests that the biotic stress was due to a lethal combination of tectonically induced hydrothermal and volcanic processes, leading to eutrophication in the oceans, global warming, sea level transgression and ocean anoxia. It must be concluded that major magmatic events and their long-term environmental conse-quences are major contributors, though not the sole causes of mass extinctions. Sudden mass extinctions, such as at the K/T boundary, may require the coincidence of major volcanism and a very large impact. Mass extinction is therefore the cul-mination of many factors which contributed to high-stress environmental conditions, including longterm perturbations (volcan-ism, e.g. Deccan traps for the end-Cretaceous, cooling, sea-level fluctuations) and short terms events (impacts). No single kill mechanism can really be identified. Whether studies into Earths oceans and climate change are conducted in the present or the past, they remain of fundamental importance in predicting the future. A grasp of how climate has behaved and evolved in the past allows us to put into context what we see today and better understand what could lye ahead tomorrow. The mass extinction events that punctuate Earth’s history are still enigmatic and therefore understanding their various causal mecha-nisms can provide us with a powerful tool in accessing future climate scenarios.
13.2
Eutrophication of marginal seas by river input: The Middle Jurassic Western Tethys compared to the Modern Caribbean
BaumgartnerPeterO.*&TschudinPascal*
* Institut de Géologie et Paléontologie, University of Lausanne. Anthropole, CH-1015 Lausanne, Switzerland. ([email protected])
TheCaribbean-GulfofMexicomarginalsea(15-30°N)isdiscussedhereintermsofapotentialcirculationmodelfortheMiddleJurassicWesternTethys.Bothseasshareasimilarsize,latitude,lieWofalargeoceanandarecharacterizedbyasystemofcomplicatedsub-basins,shelvesandislands.HighnutrientinputintheCaribbeanresultsfromdirectriverinput(Mississippi,Orinoco)andindirecttransferofnutrient-richfreshwatertransportedbyoceancurrents–thesubjectdiscussedhereindetail.
TheAmazonandOrinocoRiversshedtogetherapproximately8000km3yr-1freshwaterintothetropicalAtlanticOceanandtheCaribbeanSea.Thiscorrespondsto20%oftheglobalcontinentalrunoffatarateof≈0.2Sv.Undisturbedriversystemscarry≈20µgofdissolvedPand>40µgoftotaldissolvedNperLofwater[3]resultinginaminimalfluxof1.6*1011gyr-1Pand>3.2*1011gyr-1N.Particulatetransportmaybeamultipleoftheabovevalues.TakingaC/Pratioof500-1000inCaribbeanmarineorganismsimpliesthatthiswater-massiscapableoffixing80-160Tgoforganiccarbonand(assumingaK/Siratioof1) >0.32Tg of Si annually. TheAmazonandOrinoco river inputs form largeplumes that are carried into theSouthernCaribbeanbytheNorthBrazilCurrent(NBC≈20Sv).IntheSouthernCaribbeansurfacewatersalinity,temperatureandnu-trientavailabilityvaryseasonallywiththevariationoffreshwaterinputfromtheriversandthepositionoftheIntertropicalConvergenceZone(ITCZ)thatdeterminestheoceaniccurrentpattern.DuringsummerandfallNBCrings(around400kminoveralldiameter,average≈9Sv)separatefromthemaincurrent,translatenorthwestwardtowardtheCaribbeanSea,stallaround14-18°Nanddecaysheddingimportantamountsofnutrientladen,lowsalinitywaterintotheareaoftheWindwardAntilles.
Whilethephysicaloceanographyofthesystemisnowwelldescribed,itsimpactonCaribbeanecosystemsispoorlydocumen-ted.Thereare reportsof increasingandrapiddemiseofcoral reefs in theWindwardAntilles fromareasdevoidof localpollution,butnorelationshipwithdecliningAmazonandOrinocowaterqualityhasbeenestablished.Wesuspectthatthe
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st rapidlyincreasingdeforestationofthelast20-30yearsinthecatchmentareasofthetwolargeS-Americanriversmayhaveincreasedthenutrientloadoftheirwaters,duetoincreasederosionoforganictopsoils.TheareamostaffectedbysuchachangemustbetheSE-Caribbean,wherethefreshwaterpulsesaremostevident.
TheMiddleJurassic(ormoreexactlytheToarciantomiddleOxfordian)isatimeintervalofimportantfluctuationsof∂13CwithlonglastinghighsintheAalenian-earlyBajocianandtheMiddleCalloviantoMiddleOxfordianintervals.Thesefluc-tuationshavebeeninterpretedintermsofhighC
orgcyclingandlowC
carbproductionduringpositivepeaktimes.Whilethe
N-TethyanmarginisswampedbydetritalmaterialwashedofftheEurasiancontinent,southernTethyansedimentsofthistimearecharacterizedbymeso-toeutrophicbiogenicfacies:greenradiolaritesinbasinsandmonotonous,grey,microbial,oftensiliceouslimestonesonplatformssuchastheHighKarstandthePelagonian.BothpelagicandshelfareasofS-Tethyswerebeyondthereachofdetritalinput,butexperiencedincreasednutrientlevelsthroughoutmostoftheMiddleJurassic.
RadiolariteoccurrencesinTethyanbasinshavebeenexplainedbyupwellingeitherinaperi-equatorialoceanbasinor inmonsoonalcirculationsystem.However,themoreelaboratereconstructionsofhemiddleJurassicTethysshowacomplicatedsystemofpoorlyinterconnectedoceanicbasinswithoftendeeplysubmergedmarginsseparatedbysubmergedshelvesonmicro-continents.Toproduceupwellinginalltheserelativelynarrowbasins,especiallytheAlpineTethys,seemsverydiffi-cult.Anequatorialcurrentsystemcannotbemaderesponsibleeither,becausepalaeolatitudesofthemidJurasssicTethyanbasinsarebetween20°and40°N.Anotherfactspeaksclearlyagainstanequatorialcurrentsystem:TheJurassicCentralAtlanticisdevoidofbiosiliceoussediments.Thepresenceofpelagiccarbonates(abovetheCCD)throughouttheJurassicmustbeinterpretedastheconsequenceofsurfacewatersthataremoreoligotrophicthanthoseoftheadjacentTethysandPaleo-Pacific.TheJurassicAtlanticwasa“mediterranean”oceanbasinsuchastheModernRedSea.Importantbottlenecks(Paleo-Gibraltar,S-Florida-Bahamas)existthroughthemiddleandlateJurassicandmusthavepreventedavoluminous(10-20Sv)waterexchangebetweentheAtlanticanditsneighbouringbasins.
WhilethemidJurassicglobalsettingisrightformeso-toeutrophic(lowCcarb
.)sedimentation,weneedamechanismtocon-tinuouslysupplynutrientstotheWesternTethys.InanalogywiththeCaribbean-GulfofMexicowecanimaginethattheTethyanN-EquatorialCurrentstrucktheArabianPlatform,wasdeviatedtotheNandmayhaveenteredtheJurassicEasternMediterranean.Onitsway,itinteractedwithfreshwaterplumesoflargeriversdrainingtropicalN-Africa.Whilethesuspen-dedloadsedimentedinthedeepEasternMediterranean,freshwaterplumesrichindissolvednutrientswerecarriedintotheentireS-Tethyanrealmprovidingaconstantnutrientinput.Thisinputallowedforhighaccumulationratesofbiosiliceoussediments,causeddeepwateranoxiaduringpeakintervalsandmicrobialcarbonatesonplatforms.
ModernanthropogenicchangesintheAmazon–Orinoco-CaribbeansystemmayrepresentaturningpointfromCcarb
richtoC
carbpoorsedimentation.GolbalChangecanbealessonfortheinterpretationofthePast.
13.3Glacial geology and paleoclimate: Stable isotope analysis in Holocene tree rings Mont Miné glacier (VS)
DessaugesAude*,LeuenbergerMarkus**,NicolussiKurt***&SchlüchterChristian*
* Institute of geological sciences, University of Bern, Baltzerstrasse 3, CH-3012 Bern ([email protected])** Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern*** Tree-ring Group / Institute of Geography, University of Innsbruck, Innrain 52, A-6020 Innsbruck
Thegoalofthisstudyistoreconstructregional-scaleclimatevariabilityintheVald’HérensinValais.Theperiodwearein-vestigating is theHolocene. It isknown that theearlyHoloceneclimatewasunstableandcharacterizedbya cool eventaround8.2kaBP(BeforePresent).ThisworkwasmotivatedbytherecentfoundofPinus cembraandLarix deciduatreesduringthesummer2006atthefrontofthetongueoftheMontMinéglacier,foundthankstothepresent-daymeltingoftheglacier.Wefirstreconstructedtheenvironmentcharacteristicsandpropertieswherethetreeswerefoundandwheretheylivedwithaglacialgeomorphologicalmapandwithageoradarinvestigation.ThereconstructionoftheMontMinéglaciermovementshelpedtoshowthedifferentphasesofadvancesandretreatsoftheglacierwithtime.Thisanalysisoftree’slocalenviron-mentwasthencompletedbyatemporalclimateanalysismadeaccessiblewiththeoxygenandcarbontracersmeasuredoncelluloseextractedfromringsofthefoundtrees.Dendrochronology(Nicolussi2006)showsthattheyoriginatfromtheear-lyHolocene.
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astDuringtheinvestigatedperiodourresultsshowsignificantchangesinthevalueofδ18O,indicatingthattheclimatealready
wasunstablewithwarmerandcolderperiods.Wesuggestthatthesesignatuesindicatethatbetweentheyears6450and6180BCtheMontMinéglacierwassmallerthantoday.ClimaticconditionsduringtheHolocenewerewarmenoughtoallowtothevegetationtogrowatanaltitudethatiscurrentlyrecoveredbytheglacier.ThehypotheticaladvanceoftheMontMinéglacierthatfollowedseemstobecontemporaneouswiththe«8.2event».Wespeculatethatbeforethisdatetheglacierwassmaller.Duringthewarmerperiodtheglaciercouldmostlikelynotadvance.Itisevenpossiblethattheicewasmeltingduringthiswarmerperiod.Theδ18Ovaluesreachaminimum,whichindicatesthatacooleventoccurredandimpliedthedeathofthetrees.
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A geological perspective on calcareous nannoplankton evolution: biotic response to global change and environmental perturbations?
ErbaElisabetta,BottiniCinzia,CasellatoCristinaEmanuela,DeBernardiBianca&TiraboschiDaniele
Dipartimento di Scienze della Terra, Via Mangiagalli 34. 20133 Milano ([email protected])
Recentenvironmental changesandclimate instabilitiesposeurgentquestions regardingbiotaability tokeeppacewithconcurrentexcessCO
2,globalwarmingandoceanacidification.Majorconcernsareaddressedtothepossibilityofnearfu-
tureextinctionscausingabiodiversitylossandrevealingabiotafailureinsustainingrapidandprogressiveenvironmentalchangesacceleratedbyanthropogenic impacts.However, the findingsofneworganisms in various ecosystems raise thepossibilitythatglobalchangemightstimulatebiotaspeciationand/orinnovation:novellifeformsmightrepresenttempo-raryadaptationtoenvironmentalstressormightberealnewspeciesevolvedinresponsetoglobalchange.
Theocean,theoldestandlargestecosystemonEarth,bestrecordedglobalchangesinclimateandoceanicphysical,chemi-calandtrophicparameters.Withintheoceanicbiosphere,calcareousphytoplanktonplaysaspecialroleas:(1)iscommonandwidespreadandconsistsofcosmopolitanandendemictaxa;(2)hasa220My-longevolutionaryhistory;(3)isonethemosteffectivecalciteproducersoftheplanetsincetheJurassic;(4)isrelevantforboththeinorganicandorganiccarboncycle;(5)isextremelysensitivetoenvironmentalvariations;(6)maydirectsclimatechangebyalteringalbedoandabsorpti-on/emissionofatm-CO
2atlargescale.
The Phanerozic geological record of global changeunambiguously indicates that the Earth system already experiencedconditionsof(super)greenhouseand(super)icehouse.Diversitypulsesofcalcareousnannoplanktonaregrosslycoevalwithmajoreventssuchasclimateandsea-levelchanges,largemagmaticepisodesandvariationsinoceanstructureandcompo-sition,suggestingthatevolutionarypatternsareintimatelylinkedtoenvironmentalmodifications.
Ourstudyaimsatreconstructionofbothtempoandmodeofnannoplanktonevolutionandthecausal/casualroleofenvi-ronmentalpressure.Weexploredtime-intervalsof(1)evolutionaryaccelerationinabsenceofcoevalenvironmentalchange,duringaperiodofpresumedclimaticstability(Tithonian,latestJurassic),and(2)globalchangemarkedbycalcareousphy-toplanktonadaptation/evolution(EarlyAptianOceanicAnoxicEvent1a;PETM).Foreachcasehistorycalcareousnannofos-silshavebeeninvestigatedinsectionsfromdifferentoceansinordertodiscriminateamonglocal,regionalorglobalcauses,andtoverifypossiblediachroneityincalcareousphytoplanktonevolutionand/orinresponsetoglobalchanges.Calcareousnannofossil species richness, first and last occurrences and abundance (relative and absolute) have been achieved.Morphometricanalysesofselectedtaxahavebeenperformedtoseparatemalformation,under-calcification,over-calcifica-tion,andrealultrastructurechanges.
Threespeciationmodelswereproposed:phyleticgradualism,punctuatedequilibriumandpunctuatedgradualism.Phyleticgradualismholdsthatnewspeciesarisefromslowandsteadytransformationofpopulationsprovidinggradationalfossilserieslinkingseparatephylogeneticspecies.Punctuatedequilibriumexplainstheappearanceofnewspeciesbyrapidspe-ciationoccurringinsmallperipheralisolatedpopulations,followedbymigrationtootherareaswherethefossilsequenceusuallyshowsaseriesofsharpmorphologicalbreaks.Punctuatedgradualismimplieslong-lastingevolutionarystasisinter-ruptedbyrapid,gradualphyletictransformationwithoutlineagesplitting.
TheJurassic-Paleogenecase-historiesinvestigatedprovideexamplesofallevolutionarypatternsincalcareousnannoplank-ton.Preliminaryresultssuggest:(1)potentiallydifferentspeciationstylesofcoccolithsversusnannoliths;(2)thatpunctua-tedgradualismprevailsinintra-genericspeciation,whereaspunctuatedequilibriumdominatesinter-genericspeciation;(3)thatmostnewmorphotypes associatedwith extreme, global change represent ephemeral adaptations rather than truespecies.Althoughclimateandenvironmentalchangeshavebeeninstrumentalfordirectingnannoplanktonevolution,epi-
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st sodesofmajorinnovationoccurredduringtimesofecosystemstabilitysuggestingverysuccessfuldiversificationandadap-tationstosteadyconditions.Contrarytogeneralmodels,extremeeventssuchasOAE1aandPETMdidnotcauseextinctionsamongcalcareousnannoplankton.
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The rise and fall of the Urgonian empire
FöllmiKarlB.*,GodetAlexis**,BodinStéphane***,LinderPascal****,deKaenelEric*****,AdatteThierry*,SteinMelody*
* Institut de Géologie et Paléontologie, Université de Lausanne, CH-1015 Lausanne** Neftex Petroleum Consultants Ltd., Oxfordshire, GB-OX14 4RY*** School of Earth, Atmospheric and Environmental Sciences, University of Manchester, GB-M13 9PL**** Institut de Géologie, Université de Neuchâtel, CH-2009 Neuchâtel***** DeKaenel Paleo-Research, CH-2000 Neuchâtel,
Urgonian-typeshallow-watercarbonatesoflateearlyCretaceousageexhibitatypicalfaciescharacterizedbythepresenceoflargebenthicforaminifera,greencalcareousalgae,calcareoussponges,chaetetids,stromatoporoids,andtheco-occurrenceofcoralsandrudists.Urgoniancarbonatesoccuronaglobalscaleinshallow-watersoftropicalandsubtropicalregionsandrepresentaphotozoan,oligotrophiccommunityofcarbonateproducers,whichwasuniquefortheCretaceous-atimeofotherwisefrequenteutrophicepisodes,whichtranslatedintooceanicanoxiceventsandplatform-drowningepisodes.TheonsetanddemiseoftheUrgonianregimeiscontroversiallydated,whichisforalargepartrelatedtodifferentcalibra-tionschemesforlargebenthicforaminiferausedbydifferentresearchgroups.Wepresentnewammoniteandnannofossil-baseddatafromthehelveticAlpsandthewesternSwissJura,whichsuggestthattheonsetoftheUrgoniandidnotoccurbeforethelateBarremian,afteralongperiodoferosion,condensationandphosphogenesisrelatedtothedrowningoftheHauteriviancarbonateplatform,forwhichitsonsetisrelatedtotheFaraonianoxicepisode.ThedemiseoftheUrgonianplatformappearssynchronousonaworld-widescaleandisdatedasmiddleearlyAptian,justbeforetheunfoldingoftheSellianoxicepisode.TheexacttimingoftheUrgonianperiodallowsustotietheevolutionofUrgonianplatformsandespeciallytheirdemisetoenvironmentalandpaleoceanographicchangeinaway,whichresemblestheactualdevelopmentofso-called"deadzones"inshallow-waterareasandtheprogressivelossofreefsonaworld-widescale.
13.6
Oceanic and climatic Changes during the Albian- Cenomanian: the World at the End of Pangea
GiorgioniMartino*,WeissertHelmut*,BernasconiStefano*
*ETH Zürich, Geologisches Institut, Universitätstrasse 16, CH-8090 Zürich ([email protected])
Themid-Cretaceous is renown forbeingaperiod inEarth'shistorywhen theglobal conditionsdiffereddrastically fromthoseoftoday.Therewereexceptionallyhightemperatures,anabsenceofpermanentpolaricesheets,veryhighsealevelandstronggreenhouseeffect.ThebehaviorofEarth’sclimatesystemanditsrulingfactorsinsuchwarmconditionsarestillpoorlyunderstoodandrepresentatantalizingtopicinEarthandclimatesciences.NewpaleotemperatureandCO
2estimatesrevealthattheperiodfromtheAlbiantotheTuronianwasthewarmestoftheall
Cretaceousandthatthiswarmingcannotbeexplainedbyenhancedgreenhouseeffectonly.Quantitativemodelsshowarelationshipbetweenthethermalmaximumandamajorre-arrangementofoceaniccirculationduetotheopeningoftheEquatorialAtlanticGateway(EAG)thatbroughtthedefinitivebreak-upofthesuper-continentPangea.DuringtheAlbiandeep-watersedimentsintheWesternTethysarecharacterizedbymoreorlessalternatingvaricoloredfa-ciestestifyingtoveryunstableconditionsatthebottomoftheocean,punctuatedbythreeorganicmatterrichintervals,identifiedasminorOceanicAnoxicEvents(OAE1b,OAE1c,OAE1d).IntheuppermostAlbian,aftertheendoftheOAE1d,thissedimentationpatternisreplacedbymorehomogeneousfaciesthatspantheCenomanianintervaluntilthelastmajorCretaceousOceanicAnoxicEvent(OAE2).Thisworkprovidesstratigraphical,sedimentological,andgeochemicaldataofAlbian-CenomaniansectionsfromLusitanianBasin (Portugal) and Southern Alps (Northern Italy). During the Albian-Cenomanian these areaswere part of theNorth
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astAtlanticandtheWesternTethyanrealmsrespectivelyandtheymusthavebeenparticularlysusceptibletothechangesindu-
cedbytheopeningoftheEAG.Wepresentcorrelationbetweenthetworegionsandpossibleevidencesofthemajorclimatechangesthattookplaceatthattime.TheaimistotestwhetherthesechangescanberelatedtotheopeningoftheEAG,supportingthepredictionofthemodels,orotherfactorsplayedasignificantroleonthemid-Cretaceousoceanic-climaticsystem.
REFERENCESBellanca,A.etal.1996:Orbitallyinducedlimestone/marlstonerhythmsintheAlbian-CenomanianCismonsection(Venatian
region, northern Italy): sedimentology, calcareous and siliceous plankton distribution, elemental and isotopegeochemistry.PalaeogeographyPalaeoclimatologyPalaeoecology,vol.126,pp.227-260,
BersezioR.1992:LaSuccessioneApriano-AlbianadelBacinoLombardo(Alpimeridionali).GiornalediGeologia,serie3a,vol.54/1,pp.125-146,Bologna
Bice, K. L. &Norris R.D. 2002: Possible atmospheric CO2 extremes of theMiddle Cretaceous (late Albian-Turonian).
Paleoceanography,vol.17,n.4Bice,K. L. et al. 2006:Amultipleproxyandmodel studyofCretaceousupperocean temperaturesandatmosphericCO
2
concentrations.Paleoceanography,vol21,PA2002,doi:1029/2005Pa001203,2006Petrizzo,M.R.etal.2008:LateAlbianpaleoceanographyofthewesternsubtropicalNorthAtlantic.Paleoceanography,vol.
23,PA1213,doi:10.1029/2007PA001517Poulsen, C. J. et al. 2001: Response of themid-Cretaceous global oceanic circulation to tectonic and CO
2 forcings.
Paleoceanography,vol16,n.6,pp.576-592,DecemberPoulsen,C.J.etal.2003:DidtheriftingoftheAtlanticOceancausetheCretaceousthermalmaximum?Geology,vol.31,n.
2,pp.115-118Reichelt, K. 2005: LateAptian-Albian of theVocontianBasin (SE-France) andAlbian ofNE-Texas: Biostratigraphic and
paleoceanographic implicationsbyplanktic foraminifera faunas.DissertationderGeowissenschaftlichenFakultätderEberhard-Karls-UniversitätTübingen.
Rey, J. et al. 2003: Les séquences dedépot dans leCrétacé inférieur duBassin Lusitanien.Comunicacoes do InstitutoGeológicoeMineiro,90,15-42
Wilson,P.A.&NorrisR.D.2001:Warmtropicaloceansurfaceandglobalanoxiaduringthemid-Cretaceousperiod.Nature,vol.412,26July
13.�
Neogene global cooling and its impact on diatom size evolution
GiraultFranceE.1,WellerAndrewF.1,2&ThiersteinHansR.3
1Geological Institute, ETH, CH-8092, Zurich, Switzerland([email protected])2Present address: Geosoft Australia Pty Ltd, 14/100 Railway Road, Subiaco WA 6008, Australia3Geological Institute, ETH Zurich and University Zurich, Universitätstrasse 6, CH-8092 Zurich, Switzerland
Amajorcharacteristicamongskeletonizedphytoplanktonintheoceanisthattheydependontheavailabilityofbio-limitingnutrientsinthephoticzone.Competition(inter-andintra-group)forthesebio-limitingnutrientstogetherwithpresentandpastchangesinoceanicconditionsarepotentialdominantdriversoftheadaptationandresultingevolutionofthesemicro-organisms.OvertheCenozoicandparticularlysincetheNeogene,diatomshavebecomethemostefficientgroupfornutri-entuptake,byfaroutcompetitingthecoccolithophoresinnutrient-richareasandassumingdominanceintheoceaniccy-clingofdissolvedsilica.
Hereweexploretheutilityofaquantitativemeasure,meantestsizesofcentricdiatomsandtheirvariability,tocharacteri-zethemacro-ecologicalpatternsintoday’soceansandtheevolutionaryresponseofthisgroupinthepast.Sizeandmorpho-logicalcharacteristicsofthecentricdiatomfrustules(diameter>20µm)werecollectedusingrecentlydevelopedautomatedlightmicroscopyandimageanalysistechniquesforastatisticallyrepresentativenumberofspecimens(i.e.250-700)persam-ple.Wepresentinitialresultsofthesesizeanalysesbycomparingourmacro-ecologicalcalibrationin46Holocenecore-topsamplesfromtropicaltopolarenvironmentswiththemacro-evolutionarypatternsobservedinDSDP/ODPsites fromtheSouthernOcean,theEquatorialandtheNorthPacificoverthepast20millionyearsatatemporalsamplingresolutionof0.3-2m.y.
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st AlthoughourHolocenesamplesetshowslargevariabilityinenvironmentalconditions,changesinthemeansizeofcentricdiatomassemblagesarerathersmall.Incontrast,duringtheNeogenemeansizesofcentricdiatomsshowlargevariabilitythroughtimewithregionalshiftsoccurringduringwell-knownclimaticandoceanicevents(i.e.onsetofnorthernhemis-phereglaciation).ThesepatternsimplyanevolutionarytrendpossiblyrelatedtoNeogeneglobalcoolingandrelatedreorga-nizationsofwatermassesandtheirdissolvedsilicapools.Sincediatomsaretheprimarycompetitorsofcoccolithophoresfornutrientsamongtheskeletonizedphytoplankton,theirevolutionaryemergencetodominancewouldimplycoevalconse-quencesfortheevolutionofthecoccolithophores.
13.8
Confirmation of an exceptional sea-level highstand at +20 m during MIS 11 (�00’000 ka BP) from Bahamian sedimentary rocks: a credible scenario for future global warming?
GodefroidFabienne*,KindlerPascal*,SamankassouElias*
*Section of Earth Sciences, University of Geneva, Maraîchers 13, CH-1205 Geneva, Switzerland ([email protected])
ThediscoveryofelevatedmarineandlacustrinedepositsnearGlassWindow(NorthEleuthera,Bahamas)validatesthecon-troversialsea-levelhighstandatabout+20mduringMarineIsotopeStage(MIS)11.Consideredasthelongestinterglacialofthepasthalfmillionyears,MIS11isanexcellentcandidateforprovidingacrediblescenarioforafuture,human-induced,globalwarming.
Twostratigraphicsections(GW1andGW2)includingfivecarbonateunitswereloggednearGlassWindowinNorthEleutheraIsland.Sedimentological,petrographicandgeochronological(amino-acidracemizationdating)analyseswereperformed.
Onbothsections,whichformhighcliffsabout18and22mhigh,Unit1consistsofcross-stratifiedbiopeloidallimestoneshowingalategenerationoffibrousrimcementofmarineorigin.Thislatecementationentirelyaffectsthisfirstunit.TheboundarybetweenUnits1and2isrepresentedbyaplanarerosionalsurface.Unit2displayswell-definedplanarbeddingatbothsites,whereasfaintcross-stratificationsarealsovisibleatGW1.Itconsistsoflaminatedbiopeloidalgrainstonecontai-ningHalimedafragmentsandroundedlithoclastsderivedfromUnit1,andisfurthercharacterizedbyanearlygenerationofisopachousfibrouscement.TheupperpartofUnit2showsonethicklaminatedcrustincludingnumerousspherulitesofcyanobacterialorigin,andiscappedbyareddishpaleosol.ThetopoftheGW2sectionisrepresentedbyanoolitic/peloidalgrainstone(Unit3),whereastheupperpartofGW1includesonebioclastic(Unit4)andoneoolitic(Unit5)unit,separatedbyapaleosol.
Thevaluesofalloisoleucine/isoleucine(A/I)ratiosaverageat0.740,0.737,0.652,0.467,and0.371forUnits1to5,respective-ly.
Basedontheseanalyses,Units1,3,4and5canbeidentifiedaseolianitesdatingfromMIS11(A/I=0.740),MIS9(A/I=0.652),MIS7(A/I=0.467)andMIS5e(A/I=0.371),respectively.Exposedbetween+12and+14.5m,thebasalpartofUnit2canbeinterpretedassubtidalandbeachdeposits,whereasitsupperpart,at+15m,likelycorrespondstolacustrine(pond)sedi-ments,bothdatingfromMIS11(A/I=0.737).Thepresenceofspherulitesofcyanobacterialoriginshowsthatthethicklami-natedcrustatthetopofUnit2wasformedatthesurface,andnotwithinasoilprofile.ConsideringthesubsidenceaffectingEleutheraIsland(1m/100kyr),thebeachandponddepositsofUnit2andthemarinecementspresentinUnit1indicatethatsealevelreachedanelevationofabout+20mduringMIS11, implyingthecollapseofboththeGreenlandandtheWest-Antarcticice-sheets,andthepartialmeltingoftheEast-Antarcticice-sheet.
TheEarth’sorbitalparameterswereaboutthesameduringMIS11thantoday(i.e.MIS1).Climaticconditionsandclimateevolutionduringthesetwointerglacialscan, therefore,becompared.Theprominentmeltingofpolar ice-sheetsandtheassociatedsea-levelfluctuationat+20moccurredattheendofMIS11,andwereprobablylinkedtoitsexceptionalduration(20-35’000yrs).Stage1beganonly12’000yearsagoand,thus,theprospectofa20mriseinsealevelappearsratherremoteintime.However,thepresent-day,human-inducedincreaseinatmosphericgreenhousegasesmaydrasticallyacceleratethedisintegrationofpolarice-sheets,triggeringacatastrophicelevationofsealevelinthenextdecadesorcenturies.TheMIS11stratigraphicrecordfromtheBahamasshowsthatthisispossible.
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Evidence for major climatic change at the Smithian-Spathian boundary from low palaeolatitudinal records
HermannElke*,HochuliPeterA.*,**,BucherHugo*,**,BrühwilerThomas*,GoudemandNicolas*&GhazalaRoohi***
*Paläontologisches Institut und Museum, Karl Schmid-Strasse 4, CH-8006 Zürich ([email protected])**Geologisches Institut, Universitätsstrasse 16,CH-8050 Zürich ***Pakistan Museum of Natural History, Garden Avenue, PK-44000 Islamabad
The delayed recovery ofmarine and terrestrial ecosystems after the end-Permian extinction event is still up for debate.FocusingontheSmithian-Spathianboundary,palaeoecologicalchangesarereflectedbyasignificantglobalfaunalturnoverasindicatedbyammonoids(Brayardetal.2006)andconodonts(Orchard2007)aswellasachangeinthepalynologicalasso-ciationsoftheBorealrealm.There,theSmithian-Spathiantransitionismarkedbyaconspicuouschangefromsporedomi-natedassemblagesintheSmithiantogymnospermdominatedassemblagesintheSpathian(Galfettietal.2007a).Here,wepresentthecompositionoftheEarlyTriassicmicroflorasofNammal,SaltRange,Pakistan.Ammonoidsandcono-dontsprovidethehighresolutionagecontrolofthestudiedsection(Brühwileretal.2007).The lateSmithianpalynologicalassemblagesarecharacterizedbyageneraldominanceofhygrophyticelements.SlightlybelowtheSmithian-Spathianboundary,betweentheAnasibiritesbedsandtheGlyptophicerasbeds,thecompositionchangesdramaticallywithadrasticallyincreasingproportionofxerophyticelements.Thiseventcoincideswiththeonsetofaposi-tive shift in the δ13C record marking the Smithian-Spathian boundary (Galfetti et al. 2007b). Preliminary results fromsouthernTibetalso indicatea similar trend fromhygrophyte-dominated toxerophyte-dominatedassemblagesacross theboundary.Thus,thereisevidencefortheSmithian-Spathianboundaryclimaticeventfromhighaswellasfromlowpalaeolatitudes,demonstratingitsglobalsignificance.
REFERENCESBrayard,A., Bucher,H., Escarguel,G., Fluteau, F., Bourquin, S.,Galfetti, T. 2006: TheEarlyTriassic ammonoid recovery:
Paleoclimaticsignificanceofdiversitygradients,Palaeogeography,Palaeoclimatology,Palaeoecology,239,374-395.Brühwiler,T.,Bucher,H.,Goudemand,N.,Brayard,A.2007:Smithian(EarlyTriassic)AmmonoidsuccessionsoftheTethys:
Newpreliminiaryresults fromTibet, India,PakistanandOman,NewMexicoMuseumofNaturalHistoryandScienceBulletin,41,25-26.
Galfetti, T.,Hochuli, P.A., Brayard,A., Bucher,H.,Weissert,H.,Virgan, J.O., 2007a: Smithian/Spathianboundary event:Evidenceforglobalclimaticchangeinthewakeoftheend-Permianbioticcrisis,Geology,35,291-294.
Galfetti,T.,Bucher,H.,Ovtcharova,M.,Schaltegger,U.,Brayard,A.,Brühwiler,T.,Goudemand,N.,Weissert,H.,Hochuli,P.A.,Cordey,F.,Goudun,K.2007b:TimingoftheEarlyTriassiccarboncycleperturbationsinferredfromnewU-Pbagesandammonoidbiochronozones,EarthandPlanetaryScienceLetters,258,593-604.
Orchard,M.J. 2007: Conodont diversity and evolution through the latest Permian and Early Triassic upheavals,Palaeogeography,Palaeoclimatology,Palaeoecology,252,93-117.
13.10
Reduced oxygen concentrations in the abyssal North Pacific during the last glacial period – implications for oceanic carbon storage
JaccardSamuel*,GalbraithEric**,HaugGerald*,SigmanDaniel**
*D-ERDW, ETHZ, Universitätstr. 16, CH-8092 Zurich ([email protected]).**Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
ThedeepNorthPacificrepresentsanend-memberofthemoderncirculationregime.Itisfarfromsitesofdeep-waterrenew-al, and so is enriched inCO
2 anddissolvednutrientsdue to theaccumulationof theproductsof remineralisedorganic
matteralongthepathofglobaldeep-watercirculation.Forthesamereasons,deepNorthPacificwatersshowadepletionindissolvedoxygen.
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st Reconstructionsofδ13CdistributionfortheglacialPacificOceanshowthatdeepwaterbelow2000-2500mwasdepletedinδ13Cwhencomparedwithmid-depthandupperoceanwaters.Below2000m,thedeepwaterswereenrichedinnutrientsandmetabolicCO
2,whilenutrientconcentrationsintheintermediatedepthPacificwereapparentlylower.PartitionofCO
2in
favorofthedeepoceanwouldhavecontributedtodecreaseatmosphericρCO2duringcoldperiods.
Thishypothesishasbeentestedbystudyingthesedimentarydistributionofredox-sesitivetracemetals(Mo&U)intwosedi-mentcoresspanningtheabyssalsubarcticPacific.Thefundamentalcontrolonsedimentredoxstateisthebalancebetweenthefluxoforganicmattertotheseafloorandthefluxofoxidantstothesedimentfromoverlyingseawater.Thus,variationsinsedimentaryredoxstatearelinkedtochangesinthemagnitudeofbiologicalexportandtheroleofoceancirculation.Comparisonofredox-sensitivetracemetalsabundancewithreconstructionofbiogenicfluxtothesedimentwillyieldinfe-rencesaboutrelativechangesofoxygenconcentrationsatthewater-sedimentinterface.
SedimentsdepositedduringthelasticeageareenrichedinauthigenicUwhencomparedtotheHoloceneHere,theexportproductionproxiesBa/Alandbiogenicopal indicatethatthelocalfluxofbiogenicdetritustotheseafloorwasgenerallyreducedduringthe lastglacialperiod.Giventhisevidence, theenhancedUaccumulationmusthavebeenaresponsetosubstantiallylowerbottomwaterO
2and,byinference,theglacialNorthPacificcontainedahigherconcentrationofrespired
carbonthantoday.AlthoughtheabsenceofMoenrichmentsarguesthatanoxiadidnotdevelopinthevicinityofourcoresites,oxygenconcentrationsmayhavedroppedfarbelowtheircurrentconcentrationsduringthelasticeage.IfthiselevatedrespiredcarbonburdenisrepresentativeofthedeepglacialIndo-PacificOcean,itcouldrepresenttheprimaryreservoirofglacialCO
2sequestration.Itresults,thatasignificantfractionofCO
2hasbeensequesteredintothedeepoceanduringgla-
cialperiodsleadingtoalargereductionofatmosphericρCO2,thatiswidelydocumentedinAntarcticicecores.
13.11
Cretaceous carbon cycle and climate: The Barremian-Early Aptian C-cycle perturbation
KellerChristinaE.*,GiorgioniMartino*,GarciaThereseI.*,BernasconiStefanoM.*,HochuliPeter**,WeissertHelmut*
*Geological Institute, ETH Zürich, Universitätsstr. 16, CH-8092 Zürich ([email protected])**Palaeontological Institute, University of Zürich, Karl Schmid-Strasse 4, CH-8006 Zürich
LateEarlyCretaceousmarinesedimentsfeatureafascinatingsuccessionofrepeatedgreenhousepulsesinterruptedbyepi-sodesofcoolclimate,whichisindicatedbytheseveralimportantpositivecarbonisotopeanomaliesdocumentedinthese-dimentaryrecord.TheOntong-JavavolcanismisthoughttobethetriggerofthemajorpositivecarbonisotopeexcursionintheAptian(Larson&Erba1999).However,thisvolcanicactivitypredatestheisotopeexcursionconsiderably(Tejadaetal.2002).Thisledtothehypothesisthatthe“Aptiangreenhousepulse”alreadybeganintheBarremian(Weissert&Erba2004;Coccionietal.2004)withafirstCO
2pulseinitiatingclimatewarmingandafirstperturbationoftheglobalcarboncycle.Thisisevidencedby
deposition of black shales and a positive carbon isotope excursion during themid-Barremian (mid-Barremian event ofCoccionietal.2004).AcceleratedorganiccarbonburialcausedadecreaseoftheatmosphericCO
2levelsandinducedacoo-
lingevent,whichisthoughttohaveresultedinarenewedcarbonate-dominatedsedimentationintheLateBarremian/EarlyAptianoceans.
Inthisstudy,acompositeLateHauterivian-EarlyAptianTethyanrecordispresentedcombiningcarbonatecarbonisotopevalueswithmagnetostratigraphicandbiostratigraphicdata.FromtheLateHauteriviantotheearlyEarlyAptian,thecarbo-natecarbonisotopevaluesfluctuateessentiallybetween1.6‰and2.4‰.ThemostpositivevaluesarereachedduringtheearlyAptianpre-OAE1aexcursionwithcarbonatecarbonisotopevaluesofupto3‰.
Thedifferentsectionsfeatureextremelyvariablethicknesses,whichseemstobeduetofrequentsedimentaryhiati,apatternthatiswell-knownfromBarremian-Aptiansuccessionsandisinterpretedtoresultfromincreasedcurrentintensities.Thedistributionpatternofblackshalescombinedwiththecarbonisotopesallowstoassigntheblackshalestotheknownover-regionaleventssuchastheFaraoniEventintheLateHauterivianortheOAE1aintheEarlyAptian.
ThestudiedsectionshighlightthevariabilityandcomplexityofsedimentarydepositsatvariouspositionsinthedifferentbasinsatthesouthernmarginoftheTethyanOceanandallowavariedinsightintotheocean-atmosphericevolutionoftheEarlyCretaceous.
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REFERENCESCoccioni, R.,Galeotti, S.,Marsili,A.& Sprovieri,M. 2004: TheMid-Barremian event (MBE): Theprelude to theOAE1a.
GeophysicalResearchAbstracts,6,05130.Larson,R.L.&Erba, E. 1999:Onsetof themid-Cretaceousgreenhouse in theBarremian-Aptian: Igneous events and the
biological,sedimentary,andgeochemicalresponses.Paleoceanography,14(6),663-678.Tejada,M.L.G.,Mahoney,J.J.,Neal,C.R.,Duncan,R.A.&Petterson,M.G.2002:Basementgeochemistryandgeochronologyof
centralMalaita,Solomonislands,withimplicationsfortheoriginandevolutionoftheOntongJavaPlateau.JournalofPetrology,43,449-484.
Weissert,H.&Erba,E.2004:Volcanism,CO2andpalaeoclimate:aLateJurassic-EarlyCretaceouscarbonandoxygenisotope
record.JournaloftheGeologicalSociety,161,695-702.
13.12
The initiation of OAE1a revealed by a high resolution biomarker carbon isotope record
MehaySabine*,KellerChristinaE.*,BernasconiStefanoM.*,WeissertHelmut*,ErbaElisabetta**
* Department of Earth Science, Geological institute, ETH, 8092 Zürich, Switzerland ([email protected])** Department of Earth Sciences, University of Milan, Via Mangiagalli 34, Milan, 20133, Italy
Oceanicanoxicevents(OAEs)aretimeenvelopesintheCretaceouswhenoceanconditionsfavouredtheepisodicdepositionoforganic-richsedimentsonaglobalscale.ThefirstCretaceousoceanicanoxicevent (OAE1a,EarlyAptian,≈120millionyearsago)ismarkedbyanenigmaticnegativecarbonisotope(δ13C)spikeofupto3‰inmarinecarbonatesandof4to5‰intheorganiccarbonatitsbase(Schlanger&Jenkyns,1976;Menegattietal.,1998).Thiscarbon-cycleperturbationisbelievedtoreflectamassivereleaseof13Cdepletedcarbonintotheoceanandtheatmosphere.BecausetheEarlyAptianisknownasaperiodofgreenhouseconditions,thislightcarbonhasbeenproposedtoderivefromthedissociationofmethanehydrates(Dickens,2003).TheaimofourstudyistoelucidatetheinitiationofOAE1ainanattempttoanticipatethepossibleevolu-tionsofbothatmosphericandoceanicecosystemsonEarth,underwarmerclimatethantoday.
Becauseexchangesbetweenoceanandatmospherepoolsarefasterthantheresolutionofthecarbonisotoperecordsavaila-blesofarfortheOAE1aandbulkδ13Ccombineseffectsofawholeecosystem,ahigherresolutioncarbonisotopestudyonspecificbiomarkersisessential.Bulkandbiomarkersδ13Cwerethereforemeasuredatsamplingintervalsof2000to6000yearsonsamplesfromtheCismoncore(SouthernAlps,Italy),showingoneofthebeststratigraphicresolutionfortheOAE1aintervalatlowlatitudes(Lietal.,2008).
ThenewcarbonisotoperecordshowsastepwiseinitiationofOAE1awhichwasdividedintofiveintervals,covering≈70kyr.TheysuccessivelydescribeamassiveoutgassingofmantleCO
2,atemperaturerise,anincreaseincarbon-isotopefractionati-
onandpartialmethanehydratesdissolution.ThisevidencesthatthenegativecarbonisotopespikerecordedattheonsetofOAE1awasprobablycausedbyacombinationofdifferentprocessesaffectingthecarbon-cycleandprimarilytriggeredbyanintensevolcanicactivity,linkedtotheOntong-JavaPlateaulargeigneousprovince.
REFERENCESDickens,G. R. 2003: Rethinking the global carbon cyclewith a large, dynamic andmicrobiallymediated gashydrate
capacitor,EarthPlanet.Sci.Lett.,213,169-183.Li,Y.-X.etal.2008:TowardanorbitalchronologyfortheearlyAptianOceanicAnoxicEvent(OAE1a,≈120Ma),EarthPlanet.
Sci.Lett.,doi:10.1016/j.epsl.2008.03.055.Menegatti,A. et al.1998:High-resolutionδ13C stratigraphy through the earlyAptian “Livello Selli” of theAlpineTethys,
Paleoceanography,13,530-545.Schlanger,S.O.&Jenkyns,H.C.1976:Cretaceousanoxicevents:Causesandconsequences,Geol.Mijnbouw,55,179-184.
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Evidence of sulfidic marine environment after the Triassic-Jurassic mass-extinction event
Richoz,Sylvain1,2,VanDeSchootbrugge,Bas1,PüttmannWilhelm3,HeunischCarmen4,QuanTracyM.5,FiebigJens1&ProssJoerg1,
(1) Institute of Geosciences, Goethe University Frankfurt, Altenhoeferallee 1, Frankfurt, 60438, Germany, [email protected] , [email protected], [email protected]. (2) Institute of Paleontology, University Vienna, Athenstrasse 14, 1090 Vienna, Austria, [email protected].(3) Institute for Atmosphere and Environment, Goethe University Frankfurt, Altenhoeferallee 1, Frankfurt, 60438, Germany, [email protected].(4) State Authority for Mining, Energie and Geology, Geocenter Hannover, Stilleweg 2, Hannover, 30655, [email protected](5) Institute of Marine and Coastal Sciences, Rutgers University, 72 Dudley Road, New Brunswick, NJ 08901, [email protected].
TheTriassic-Jurassicboundary(T-J;201Ma)marksoneofthesocalledBigFivemass-extinctioneventsthatmayhaveledtotheextinctionofmorethan80%ofallmarineinvertebrates.TheextinctionofmarineandterrestrialbiotaisincreasinglylinkedtotheoutgassingoflargevolumesofCO
2andSO
2duringtheemplacementoftheCentralAtlanticMagmaticProvince,
howevertheexactkillmechanismsandthelong-termeffectsofthislargeigneousprovinceremaintobeelucidated.Here,we presentmulti-disciplinary data, including organic geochemical, isotope (C, N) andmicrofossil data, from 3 cores inLuxemburg(Rosswinkel),andnorthern(Mariental)andsouthernGermany(Mingolsheim)thatprovideevidenceforprolon-gedenvironmentalinstabilityduringtheearliestJurassic.Organicgeochemicalanalysesshowelevatedquantitiesofthebi-omarkerisorenierataneinthelowermostHettangianfollowingamajoroverturnofterrestrialvegetation(fernspike)asdo-cumentedbypalynologicalanalyses.Isorenieratanederivesfromthebrownstrainsofphotosyntheticgreensulphurbacteria(Chlorobiaceae)thatrequirebothlightandfreehydrogensulfideinthewatercolumn.Thepresenceofabundantaryliso-prenoids(isorenierataneanditsdiageneticproducts)inLuxemburgandNGermanysuggeststhatmarginalmarinebasinsinNWEuropebecamesalinitystratifiedanddevelopedintensePhoticZoneEuxinia(PZE)afterthemassextinctionevent.Thisexcludeseuxiniaaskillmechanism.NitrogenandcarbonisotopedatafromorganicmattersupportthedevelopmentofshallowmarineanoxiainNWEurope.Ourobservationsareconsistentwiththelong-termeffectsofCO
2releaseandgreen-
housewarming.RepeatedandprolongedPZE in theTethysOceanmayhavecontributed to the slowrecoveryof shallowmarineecosystemsaftertheTriassic-Jurassicboundary.
13.1�
Paleoredox changes associated with the Early Aptian Oceanic Anoxic Event
WestermannStéphane*,MateraVirginie**,FietNicolas***,AdatteThierry*&FöllmiKarlB.*
*Institut de géologie et de paléontologie, Université de Lausanne, Antrople, CH-1015, LAUSANNE,**Institut de géologie et d’hydrogéologie, Université de Neuchâtel, Emile-Argand 11, CH-2007 NEUCHATEL, *** AREVA, 33 rue La Fayette,F-75442 PARIS, France(Email : [email protected])
TheCretaceousischaracterizedbyshortperiodsduringwhichwidespreadoceanicanoxicconditionsdeveloped,documen-tedbytheextensivedepositionoforganiccarbon–richsediments(SchlangerandJenkyns,1976).TheearlyAptianOAE,label-ledOAE1a,correspondstooneofthemoststudiedanoxiceventwithintheCretaceous.Thiseventischaracterizedbyapo-sitiveexcursioninδ13C,precededbyapronouncednegativespike,whichwasinterpretedastheresultofapulseofmethanereleasefromclathratesfromtheoceantotheatmosphere(WeissertandErba,2004).Inourstudy,weaimatimprovingourunderstandingofpalaeoceanographicchangeleadingtothiseventandtesttheproposedmodelsbyinvestigatingphospho-rus(P)andredox-sensitivetrace-metals(TM)contentsinsectionsthroughlowerAptiansedimentsalongabasin-shelftransectinthewesternTethys.Wecomplementourgeochemicalanalysisbytheanalysesoforganicmattercontents.Weselectedthreerepresentativesections:GorgoaCerbara(centralItaly)intheUmbriaMarchebasin,Glaisel’Ermitage(SEFrance)locatedintheVocontiantroughandCassis/LaBédoule(SEFrance)locatedalongtheProvencalplatform.
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astThegeneraltrendinPaccumulationshowsanincreaseattheonsetoftheearlyAptianeventfollowedbyarapiddecrease.
Thissuggestsanincreaseinnutrientinput,whereasthereturntolowervaluesthroughthefirstpartoftheanoxiceventmayberelatedtoaweakenedcapacitytoretainPinthesedimentaryreservoirduetobottomwateroxygendepletion.ThisgeneralpatterniscontrastedbythedataofGorgoaCerbarawhichalsoshowP-enrichmentsatthetopoftheLivelloSelli.Wecomparedtheseenrichmentstothetotalorganiccarbon(TOC)values.TheshaleswiththemaximumTOCvaluesalsocorrespondtothosewiththehighestPcontent.WealsocalculatedC
org:P
totratiosandobservedthatthehighestvaluescorre-
spondstothetopoftheSelli level.Thisis interpretedasareflectionofthedecreasedcapacityofstoringandpreservingphosphorusinoxygen-depletedsediments.TMexhibitcomparablevariationsinthebasinalsettings.InthesectionofGorgoaCerbara,thedataforU,V,Mo,Co,Asshowalowbackgroundlevel,constrastedbydifferentmaximainconcentrationsnearthetopoftheSellilevel.Conversely,inthesectionofGlaisel’ErmitageandCassis/LaBédoule,nosignificantenrichmentshavebeenobservedinsedimentsequivalenttotheSellilevel.ThedifferentbehaviouroftheTMinthestudiedsectionsmayberelatedtothepalaeogeographicsettingofthestudiedsections.Thesedataseemtoindicateanoxicconditionsinthebasin.Inshallower-waterenvironments,condi-tionsmayhavebeenlessreducing.Moreover,inGorgoaCerbara,threedistinctenrichmentshavebeenobserved.Thisseemstoindicatefluctuationsintheintensityofwatercolumnanoxiaduringtheshiftinδ13C.OurresultsshowthattheexpressionoftheOAE1aisdifferentfollowingthepalaeogeographicsetting.TheevolutionofthePtrendsuggestsanincreaseinnutrientinputattheonsetoftheanoxicevent,justafterthenegativespikeinδ13C.TMandhighC:Pvaluesmayindicateanoxiaconditionsinthedeepenvironmentcharacterizedbyseveralanoxicphaseswithinter-mittentreturntolessoxygen-depletedconditions.
REFERENCESchlanger,S.O.,Jenkyns,H.C.,1976.Cretaceousoceanicanoxicevents:causesandconsequences.GeologieenMijnbouw,55,
179–184.Weissert,H.,Erba,E.,2004.Volcanism,CO
2andpalaeoclimate;aLateJurassic–EarlyCretaceouscarbonandoxygenisotope
record.JournaloftheGeologicalSocietyofLondon161(4),695–702.
