10 14 july 2017 utrecht, the netherlands abstracts...welcome and key-note: oliver plümper...

10 – 14 July 2017

Utrecht, the Netherlands

Abstracts

MondayJuly 10

TuesdayJuly 11

WednesdayJuly 12

ThursdayJuly 13

FridayJuly 14

SundayJuly 9

SaturdayJuly 15

08:00

11:00

10:00

09:00

12:00

15:00

14:00

13:00

16:00

19:00

18:00

17:00

21:00

20:00

23:00

22:00

Lunchde Vagant

PostersSessions 4, 5, 6

de VagantKey-note: Ben GilbertKoningsberger Pangea

Session 5:Sediment

magnetization –acquisition and

preservationKoningsberger Pangea

Session 3:Environmental

magnetismKoningsberger Pangea

Session 4:Determining

geomagnetic fieldbehavior from

terrestrial and extra-terrestrial materials

Koningsberger Pangea

Session 6:Advanced approaches

to rock magneticcharacterization and

data analysisKoningsberger Pangea

Session 2:Sources and

significance of crustalmagnetic anomalies


Drinksde Vagant

Welcome and Key-note:Oliver Plümper

Janskerkhof 2/3

RegistrationJanskerkhof 2/3

Guided city tour

Opening receptionJan de Winter

Session 1: Fundamental rock

magnetismKoningsberger Pangea

Farewell dinnerand party

Botanical GardensFort Hoofddijk

Lunchde Vagant

Closing remarksCelebration Cor


Night canoeingde Rijnstroom

Tours of the FortConference dinner

Fort Hoofddijk

Pre-registration andbicycle pick-up

Star Lodge

Lunchde Vagant

LunchRhijnauwen

PostersSessions 1, 2, 3

de Vagant

Pre-registration andbicycle pick-up

Star Lodge

Bicycle drop offStar Lodge

ICRM17International Conference on Rock Magnetism 2017

FundamentalRockMagnetism

Orals:TuesdayJuly11-08:30-12:00KoningsbergergebouwPangea

Posters:WednesdayJuly12-15:30-18:00

deVagant

Convenors:RichardHarrison&AnnHirt

start end talk+Q&A Presenter abstracttitle08:30 09:15 30+15 KarlFabian Micromagneticenergybarriersandthephysicsof

thermoviscousmagnetization09:15 10:00 30+15 TrevorAlmeida DirectvisualizationofCRMandTRMofpseudo-

single-domainmagnetiteparticles10:00 10:30 30 coffeebreak 10:30 11:15 30+15 AndrewRoberts Whatispseudo-singledomainmagnetic

behavior?11:15 12:00 30+15 RamonEgli Distinguishingmagnetofossilsfromothersingle-

domainmagnetitecrystals:FirstinsightsfromthePaleocene-Eoceneboundary

1


Posters

presenter(sortedbylastname)

abstracttitle

RobertsBlukis In-fieldimagingofthe'cloudyzone'ofTazewellIIICDiron-nickelmeteoriteusingX-rayholography

LennartdeGroot MicromagneticTomography-itspotentialandpitfallsKatarzynaDudzisz OriginofinversefabricintheEarlyTriassicrocks,SpitsbergenChloëJansen MicromagneticTomography-resultsfromavolcanicsample

MikeJackson TitanomagnetiteCurietemperatures:Effectsofvacancies,chemical/cationorderingandthermalhistory

DiliaraKuzina PetromagnetismofPermian-TriassicsequenceatKuznetskBasin,RussiaAlexanderMichels PaleomagneticStudyoftheLekaOphioliteComplexincentralNorwayFatimahAbdulghafur(AbuduwufuPatiman)

Evaluationofaginginnaturalvolcanicglass:magneticpropertyvariationsduringartificialagingexperiments

AlejandroRodriguez-Trejo

RockmagneticpropertiescharacterizationofMayanpotteryforthePre-Classic,ClassicandPost-Classicperiods,southeasternMexico.

PierreRochette DifferentapproachesoftheSD-SPthresholdatroomtemperatureChristeanneNicoleSantos

UnderstandingtheRoleofNon-SingleDomainRemanencesinPaleointensityExperiments

CourtneySprain ImportanceoftitanohematiteindetritalremanentmagnetizationsofstrataspanningtheCretaceous-Paleogeneboundary,HellCreekregion,Montana

GeertjeterMaat Micromagneticmodellingofmicrostructuresinmagnetite

HuapeiWang RockmagneticthermalalterationsfailedtobedetectedbypTRMchecksduringThellier-seriespaleointensityexperiments

WynWilliams ThermalstabilityofPalaeomagneticRecorders

2


FundamentalrockmagnetismOral(invited)-TuesdayJuly11-08:30-09:15

DirectvisualizationofCRMandTRMofpseudo-single-domainmagnetite

particlesPresenter:

TrevorP.Almeida([email protected])

Authors: TrevorP.Almeida,UniversityofGlasgowAdrianR.Muxworthy,ImperialCollegeLondonWynWilliams,UniversityofEdinburghLesleisNagy,UniversityofEdinburghPádraigOConbhu’,UniversityofEdinburghTakeshiKasama,TechnicalUniversityofDenmarkThomasHansen,TechnicalUniversityofDenmarkAndrasKovacs,ForschungszentrumJülichRafalDunin-Borkowski,ForschungszentrumJülich

In order to reliably interpret palaeomagnetic measurements, the mechanisms of chemical remanentmagnetization (CRM) and thermoremanentmagnetization (TRM)must be fully understood. Currently,mostmodelsofCRMandTRMprocessesonlyexistforthesmallest,uniformlymagnetizedgrains,termedsingledomain(SD).However,themagneticsignalfromrocksisoftendominatedbyslightlylargergrainscontainingnon-uniformmagnetizationstates,termedpseudo-SD(PSD)grains.Magnetite (Fe3O4) is the most magnetic naturally occurring mineral on Earth, carrying the dominantmagneticsignatureinrocksandprovidingacriticaltoolinpalaeomagnetism.TheoxidationofFe3O4tootherironoxides,suchasmaghemite(ël-Fe2O3)andhematite(ë±-Fe2O3),isofparticularinterestasitinfluencesthepreservationofremanenceoftheEarth'smagneticfieldbyFe3O4.Further,TRMinFe3O4grains is acquired in the direction of the ambient geomagnetic field as they cool below their Curietemperature of ~ 580 °C. The latest transmission electron microscopy (TEM) techniques like electronholographyandenvironmentalTEM(ETEM)allowsfortheimagingofmagnetizationinnano-scalemineralsduringinsituheatingundervacuumandcontrolledatmospheres.Inthepresentstudy,syntheticFe3O4particlesinthePSDsizerange(~200nm)wereheatedinsituinanETEMunderanO2atmosphere.CloseexaminationofFe3O4particlesafterinsituheatingrevealedsurfacedegradation,whilstelectronenergy-lossspectroscopyconfirmedtheiroxidation.TheeffectofCRMwasvisualizedusingelectronholography, intheformofreconstructedmagnetic inductionmaps,wheretheoxidizedgrainsexhibitedalossofoverallremanenceandchangeinremanentdirection.ThethermomagneticbehaviourofFe3O4particlesinthePSDsizerangeisalsoinvestigatedusingoff-axiselectronholography.Magneticinductionmaps,whicharerecordedduringinsituheatinguptoabovetheTC, reveal thePSDnatureof severalFe3O4grainsbyvisualizing theirvortexdomainstates.ThevortexstatesinsmallFe3O4grainsareshowntorotateclosetoitsunblockingtemperature,ratherthanremainingthermallystableasseeninthevortexstatesoflargerFe3O4grains.Inaddition,stepwisedemagnetizationofalargeFe3O4particleuponheatingtoabovetheCurietemperature,performedinasimilarfashiontobulkthermaldemagnetizationmeasurements,revealedthatitsvortexstateremainsstableunderheatingclosetoitsunblockingtemperatureandisrecovereduponcoolingwiththesameorreversedvorticity.

3


FundamentalrockmagnetismPoster-WednesdayJuly12-15:30-18:00

In-fieldimagingofthe'cloudyzone'ofTazewellIIICDiron-nickelmeteorite

usingX-rayholographyPresenter:

RobertsBlukis([email protected])

Authors: RobertsBlukis,UniversityofCambridge,Cambridge,UKRichardJ.Harrison,UniversityofCambridge,Cambridge,UKBastianPfau,Max-BronInstitut,Berlin,GermanyChristianGünther,TechnischeUniversitÌlt,Berlin,Germany

Iron-nickelcontainingmeteoritesareauniquesourceofpaleomagneticinformationfromtheearlydaysoftheSolarsystem.Themostreliablepaleomagneticinformationisextractedfromthe'cloudyzone'regionofmeteoriticiron-nickelalloys.The'cloudyzone'formsbyaspinodaldecompositionofanickelrichalloyformingafineintergrowthon~150-30nmscaleconsistingofislandsofnickelrichtetrataeniteembeddedinanironrichmatrix.Duetothehighcoercivity(~2.2T)oftetrataenite,thecloudyzoneformsaverystablemagnetic structure. However, due to the close proximity of tetrataenite islands there are going to beinevitableinteractionsbetweenthem.Duetothehighcoercivityoftetrataenite,itishardtostudyhowthecloudyzonerespondstoanappliedfield.X-rayholographyallowstostudymagnetisationofasampleunderhighappliedmagneticfieldsastheX-raysandthesensorarenotaffectedbystrayfields.ThecloudyzoneoftheTazewellIIICDmeteoritewasstudiedusingsoftX-RayholographyattheBESSYIIfacilityinBerlin.UsingtheexperimentalsetupattheU52-SGMbeamlineasamplecanbeimagedwithaspatialresolutiondown to~30nmwithanapplied fieldofup to1.07T. In thisworkwepresent the resultsof theX-rayholographyexperimentincludingtwohysteresismeasurementswiththemagneticfieldbeingappliedbothin-planeandout-of-plane relative to the sample surface.A change inmagnetisation stateof individualtetrataeniteislandsinresponsetoafieldwasobserved.

4



MicromagneticTomography-itspotentialandpitfalls

Presenter:

LennartdeGroot([email protected])

Authors: LennartdeGroot,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,NLAnnemariekeBéguin,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,NLKarlFabian,NGU,Trondheim,NorwayPimReith,Mesa+Institutefornanotechnology,UniversityofTwente,Enschede,NLAnkurRastogi,Mesa+Institutefornanotechnology,UniversityofTwente,Enschede,NLAukeBarnhoorn,FacultyofCivilEngineeringandGeosciences,TUDelft,NLHansHilgenkamp,Mesa+Institutefornanotechnology,UniversityofTwente,Enschede,NL

Methodstoderivepaleodirectionsorpaleointensitiesfromrockscurrentlyrelyonmeasurementsofbulksamples(typically~10cc).Theprocessofrecordingandstoringmagnetizationsasfunctionoftemperature,however,differsforgrainsofvarioussizesandchemicalcompositions.Mostrocks,bytheirmerenature,consist of assemblages of grains varying in size, shape, and chemistry. When dealing with lavas, thisdiffering magnetic behavior often hampers paleointensity experiments; while occasionally a reliablepaleodirection isobscured. Ifwewouldbeable to isolate thecontributionofeachmagneticgrain inasampletothebulkmagneticmomentofthatsample,awealthofopportunitiesforhighlydetailedmagneticanalysiswouldbeopened,possiblyleadingtoanentirelynewapproachinretrievingpaleomagneticsignalsfromcomplexmineralogies.Herewetakethefirstpracticalstepstowardsthisgoalbydevelopinganewtechnique:'micromagnetictomography'.Firstly,thedistributionandvolumeoftheremanencecarryinggrainsinthesamplemustbeassessed;thisisdoneusingaMicroCTscannercapableofdetectinggrains~1micron.Secondly,themagneticstrayfieldperpendiculartothesurfaceofathinsampleismeasuredusingahigh-resolutionDCSQUIDmicroscope.Amathematical inversion of these measurements yields the isolated direction and magnitude of themagneticmoment of individual grains in the sample. As themeasured strength of themagnetic fielddecreaseswiththethirdpowerasfunctionofdistancetotheexertinggrain(asaresultofdecayinthreedimensions),grainsinthetop30-40micronsofoursyntheticsamplewitharelatively lowdispersionofgrainsinamatrixcanbeassessedreliably.Wewilldiscussthepotentialofournewinversionscheme,andcurrentchallengesweneedtoovercomeforboththescanningSQUIDandMicroCTtechniquesbeforewecananalyse'real'volcanicsampleswithourtechnique.

5



OriginofinversefabricintheEarlyTriassicrocks,Spitsbergen

Presenter:

KatarzynaDudzisz([email protected])

Authors: KatarzynaDudzisz,InstituteofGeophysics,PolishAcademyofSciences,KsieciaJanusza64,01-452Warsaw,Poland;CentreforPolarStudies,LeadingNationalResearchCentre,Bedzinska60,41-200Sosnowiec,PolandAnnHirt,InstituteofGeophysics,ETH-Zurich,Sonneggstrasse5,8092Zurich,SwitzerlandRafalSzaniawski,InstituteofGeophysics,PolishAcademyofSciences,KsieciaJanusza64,01-452Warsaw,PolandMartinChadima,AGICO,Inc,Jecna29a,CZ-62100Brno,CzechRepublic;InstituteofGeologyoftheCAS,v.v.i.,Rozvojová269,CZ-16500,Prague6-Lysolaje,CzechRepublicKrzysztofMichalski,InstituteofGeophysics,PolishAcademyofSciences,KsieciaJanusza64,01-452Warsaw,Poland

MagneticfabricstudieshavebeencarriedoutonEarlyTriassicsedimentsfromtheWestSpitsbergenFoldandThrustBeltanditsforelandintheSassendalenvalley,situatedinCentralSpitsbergen.Theaimwastorecognizemagneticmineralogyofthesedimentswithintheinvestigatedareasanddeterminetheoriginofmagnetic fabric. Magnetic mineralogy was defined using hysteresis, backfield IRM and thermaldemagnetizationofcompositethree-axisIRMcurves.Thelow-field,in-phaseandout-of-phase,anisotropyofmagnetic susceptibility (AMS)wereused todetermine themagnetic fabric,whereas isolationof theferro- and paramagnetic subfabrics was performed using high-field torque magnetometry at roomtemperatureand77K.Themeanmagneticsusceptibilityisbetween10and400*10-6SI.Theferromagneticmineralogyisdominatedbythelow-coercivityfraction,withsomesmallcontributionofhighercoercivitymaterial.Thein-phaseAMSanalysisshowsthataninversefabricispresentin4ofthestudiedsites;twofromthesouthernmostpartofthefold-and-thrustbeltandanothertwofromSassendalen. Incontrast,out-of-phaseAMSindicatesnormalfabriconlyatsitesfromSassendalenwhichsuggestsamineralogicalorigin for thedifference in fabric.Hysteresis studies indicate thatparamagneticmineralsdominate theinducedmagnetization in these rocks. Similarly, the torquemeasurements imply that the susceptibilityanisotropyisdominatedbyparamagneticminerals(~95)forbothnormalandinversemagneticfabrics.At77K,theparamagneticcontributionislargerthanatroomtemperature,thusthep77valuewascalculatedto identify minerals, which carry magnetic fabric. There are no pronounced difference between themagnetic mineralogy in sites from the fold belt and Sassendalen. Magnetite was found to be mainferromagneticcarrier,althoughparamagneticmineralsareresponsiblepredominantly for themagneticfabric;theferromagneticcontributiontomagneticfabricisnegligible.Theincreaseindegreeofanisotropyisabout8.3-9.4,whichisclosetovaluesobservedforsideriteidentifiedinthesamples.Moreover,thereisa variation in the type of magnetic fabric with stratigraphic position in Sassendalen. The most likelyexplanation is that the normal and inverse fabrics reflect variation in the content of iron-bearingcarbonates,mainlysiderite,duetosedimentarycycles.

6



Distinguishingmagnetofossilsfromothersingle-domainmagnetitecrystals:

FirstinsightsfromthePaleocene-EoceneboundaryPresenter:

RamonEgli([email protected])

Authors: RamonEgli,CentralInstituteforMeteorologyandGeodynamics,Austria,ViennaClaireCarvallo,IMPMC,UniversitéPierreetMarieCurie,Paris,FrancePeterLippert,UniversityofUtah,UnitedStatesMichaelWinklhover,OldenburgUniversity,Oldenburg,Germany

Thecombinationofmagneticcharacterizationtechniques,suchasfirst-orderreversalcurves(FORC)[1],andelectronmicroscopeobservationsonmagneticextracts, ledtothediscoverthatmagnetofossilsarewidespreadandcanbepreservedovergeologicaltimescalesinsediment[2].Nevertheless,themagneticsignatureofmagnetofossilsisnon-unique,sinceitissharedbyisolatedsingledomain(SD)particleswithnomagnetostatic interactions.TheimpossibilitytodistinguishbetweenSDparticlesthatareisolatedorarrangedinlinearchainsledtoconflictinginterpretationsofthesourceofultrafinemagnetiteinsedimentsfromthePaleocene-Eoceneboundary[3,4].ThefactthatmagnetosomshavebeenidentifiedwithelectronmicroscopyinmagneticextractsdoesnotexcludeothercontributionstotheobservedSDsignature,whichmightevenbedominantifmagneticextractionisstronglyselectivetowardsmagnetofossils(e.g.becauseof their largermagneticmoment). If non-biogenic SDparticlesoccuras inclusions in silicates, selectivechemical extraction can be used to separate their contribution from that of magnetofossils [5]. Thisprocedure, however, fails if all SDparticles are exposed to chemical dissolution.Herewepresent twopossiblenewapproachestotheproblem:(1) forwardmicromagneticmodelingofmagnetosomechainsand (2) inversemodeling of FORCmeasurements. The first approach helps constrainingmagnetofossilsignatures, whereby a good agreement with most magnetofossil-bearing sediments is obtained. Thesecond approach enables to extract the mean squareness of the hysteresis loops of individual SDremanence carriers (isolated or in chains), which depends on particle volume and on the switchingmechanism. A difference is expected between isolated particles switching by coherent rotation andmagnetosomechains,whoseswitchingmechanismcontainsafanningcomponent.Bothapproachespointto significant differences between sediments from the Paleocene-Eocene boundary and othermagnetofossil-bearingsediments.[1]Eglietal.,Geochem.Geophys.Geosys.11(2010).[2]Robertsetal.,J.Geophys.Res.117(2012).[3]LippertandZachos,Paleoceanography22(2007).[4]Wangetal.,PNAS110,(2013).[5]Ludwigetal.,GlobalPlanet.Change110(2013).

7



Micromagneticenergybarriersandthephysicsofthermoviscous

magnetizationPresenter:

KarlFabian([email protected])

Authors: KarlFabian,GeologicalSurveyofNorway,LeivEirikssonsvei39,7491Trondheim,NorwayValeraP.Shcherbakov,GeophysicalObservatory'Borok',YaroslavskajaOblast,RussiaWynWilliams,DepartmentofGeosciences,UniversityofEdinburgh,Edinburgh,UK

Thermoviscousmagnetization(TVRM)ofmultidomainparticlesistheprimaryremanencemechanisminigneousrocks.Whilecoolinginanexternalfield,asingleparticleacquiresitsremanentmagnetizationbythermalblockingofoneamongstaplethoraofpossiblemagnetizationstates.TheTVRMofanensembleofparticlesisthendeterminedbythestatisticalevaluationofmanyindividualblockingprocesses.HerethemathematicalbackgroundforcalculatingtheTVRMincomplexmultidomainensemblesisdescribed.Thefirststep isamethodtocalculateenergybarriers inmicromagneticmodels.Becauseoptimaltransitionpathsbetweenphysicaldomainstatesaregeodeticsoftheenergysurface,amodifiednudged-elastic-bandtechniquecanbeusedfortheircalculation.ThisisnowimplementedinMERRILL.Morsetheoryprovidesameanstoestimatethenumberofpossibletransitionpathsandpredictshugenumbersinrealisticsystems.ThethermallyactivatedtransitionsbetweenlocalenergyminimaformacontinuoushomogeneousMarkovprocess. If all energy barriers are known, this process can be evaluatedwhich provides the statisticalremanenceevolutionof anensembleofparticles.While it still is amajorproject touse thedescribedtechniques toobtainestimatesof TVRM in real particle ensembles, theyprovideallmathematical andcomputationalmeanstodoso.

8



TitanomagnetiteCurietemperatures:Effectsofvacancies,chemical/cation

orderingandthermalhistoryPresenter:

MikeJackson([email protected])

Authors: MikeJackson,UniversityofMinnesotaJulieBowles,UniversityofWisconsin-MilwaukeeSophie-CharlotteLappe,RWTHAachenUniversityPeatSolheid,UniversityofMinnesota

Intermediate-compositiontitanomagnetites(TM30-TM50)haveCurietemperatures(Tc)thatdependnotonly on composition but also quite strongly on thermal history, withincreases�o�f��1�0�0�°�C��o�r��m�o�r�e��i�n��T�c��p�r�o�d�u�c�e�d��b�y��m�o�d�e�r�a�t�e�-�t�e�m�p�e�r�a�t�u�r�e��(�3�0�0�-�4�0�0�°��C�)��a�n�n�e�a�l�i�n�g��i�n��t�h�e��l�a�b��o�r��i�n��s�l�o�w��n�a�t�u�r�a�l��c�o�o�l�i�n�g�,��a�n�d��e�q�u�a�l�l�y��l�a�r�g�e��d�e�c�r�e�a�s�e�s��p�r�o�d�u�c�e�d��b�y��m�o�r�e��r�a�p�i�d��c�o�o�l�i�n�g��(�'�q�u�e�n�c�h�i�n�g�'�)��f�r�o�m��h�i�g�h�e�r� �t�e�m�p�e�r�a�t�u�r�e�s� �[�e�.�g�.�,� �B�o�w�l�e�s� �e�t� �a�l� �2�0�1�3�,� �N�a�t�u�r�e� �C�o�m�m�u�n�i�c�a�t�i�o�n�s�]�.� �T�h�e� �p�h�e�n�o�m�e�n�o�n� �i�s� �r�o�b�u�s�t�l�y� �d�e�f�i�n�e�d� �a�n�d� �r�e�p�e�a�t�a�b�l�e�,� �b�u�t� �t�h�e� �u�n�d�e�r�l�y�i�n�g� �m�e�c�h�a�n�i�s�m��r�e�m�a�i�n�s� �e�n�i�g�m�a�t�i�c�,� �a�l�t�h�o�u�g�h� �i�t� �p�r�e�s�u�m�a�b�l�y� �i�n�v�o�l�v�e�s� �s�o�m�e� �r�e�a�r�r�a�n�g�e�m�e�n�t� �o�f� �m�e�t�a�l� �c�a�t�i�o�n�s� �w�i�t�h�i�n� �t�h�e� �s�p�i�n�e�l� �l�a�t�t�i�c�e�.� �W�e� �h�a�v�e� �p�e�r�f�o�r�m�e�d� �h�i�g�h�-�a�n�d� �l�o�w�-�t�e�m�p�e�r�a�t�u�r�e��m�e�a�s�u�r�e�m�e�n�t�s�,��i�n�c�l�u�d�i�n�g��h�y�s�t�e�r�e�s�i�s�,��f�r�e�q�u�e�n�c�y�-�d�e�p�e�n�d�e�n�t��A�C��s�u�s�c�e�p�t�i�b�i�l�i�t�y��(�k�(�f�,�T�)�)��a�n�d��M�a�s�s�b�a�u�e�r��s�p�e�c�t�r�o�s�c�o�p�y�,��a�s��w�e�l�l��a�s��X�M�C�D�,��t�o��h�e�l�p��s�h�e�d��l�i�g�h�t��o�n��t�h�e��n�a�n�o�s�c�a�l�e��m�e�c�h�a�n�i�s�m�s��r�e�s�p�o�n�s�i�b�l�e��f�o�r��t�h�e��o�b�s�e�r�v�e�d��c�h�a�n�g�e�s��i�n��T�c�.��F�a�b�i�a�n� �e�t� �a�l� �[�2�0�1�5�,� �G�J�I�]� �h�a�v�e� �s�h�o�w�n� �f�o�r� �f�e�r�r�i�m�a�g�n�e�t�i�c� �c�o�m�p�o�s�i�t�i�o�n�s� �i�n� �t�h�e� �h�e�m�a�t�i�t�e�-�i�l�m�e�n�i�t�e� �s�y�s�t�e�m� �t�h�a�t� �h�i�g�h�-�T� �h�y�s�t�e�r�e�s�i�s� �m�e�a�s�u�r�e�m�e�n�t�s� �e�x�h�i�b�i�t� �a� �p�e�a�k� �i�n� �h�i�g�h�-�f�i�e�l�d� �s�l�o�p�e� �k�h�f�(�T�)� �a�t� �t�h�e� �C�u�r�i�e� �t�e�m�p�e�r�a�t�u�r�e�,� �a�n�d� �t�h�a�t� �t�h�e� �m�a�g�n�i�t�u�d�e� �(�a�r�e�a�)� �o�f� �t�h�i�s� �p�e�a�k� �i�s� �a� �s�t�r�o�n�g� �f�u�n�c�t�i�o�n� �o�f� �o�r�d�e�r�i�n�g� �d�e�g�r�e�e�.� �O�u�r� �d�a�t�a� �f�o�r� �s�y�n�t�h�e�t�i�c� �t�i�t�a�n�o�m�a�g�n�e�t�i�t�e�s��i�n��q�u�e�n�c�h�e�d��a�n�d��a�n�n�e�a�l�e�d��s�t�a�t�e�s��s�h�o�w��a��s�i�m�i�l�a�r��s�t�r�o�n�g��r�e�l�a�t�i�o�n�s�h�i�p�,��a�l�t�h�o�u�g�h��i�t��i�s��i�n�v�e�r�s�e��(�t�h�e��k�h�f�(�T�)��p�e�a�k��m�a�g�n�i�t�u�d�e��d�e�c�r�e�a�s�e�s��w�i�t�h��i�n�c�r�e�a�s�i�n�g��T�c�)�.��C�h�u�r�c�h��e�t��a�l��[�2�0�1�1�,��G�3�]��h�a�v�e��p�r�o�p�o�s�e�d��t�h�a�t��a��s�h�a�r�p��c�h�a�n�g�e��i�n��l�o�w�-�T��m�a�g�n�e�t�i�c��b�e�h�a�v�i�o�r��o�f��i�n�t�e�r�m�e�d�i�a�t�e��t�i�t�a�n�o�m�a�g�n�e�t�i�t�e�s��i�s��a��'�p�i�n�n�i�n�g��t�r�a�n�s�i�t�i�o�n�'��r�e�l�a�t�e�d��t�o��r�e�d�i�s�t�r�i�b�u�t�i�o�n��a�n�d��l�o�c�a�l�i�z�a�t�i�o�n��o�f��f�e�r�r�o�u�s��i�o�n�s��w�i�t�h�i�n��t�h�e��o�c�t�a�h�e�d�r�a�l��s�i�t

9



MicromagneticTomography-resultsfromavolcanicsample

Presenter: ChloëJansen([email protected])Authors: ChloëJansen,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,NL

KarlFabian,NGU,Trondheim,NorwayAnnemariekeBéguin,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,NLIoanLascu,Nanopaleomagnetismgroup,dept.ofEarthScience,CambridgeUniversity,UKRichardHarrison,Nanopaleomagnetismgroup,dept.ofEarthScience,CambridgeUniversity,UKAukeBarnhoorn,FacultyofCivilEngineeringandGeosciences,TUDelft,NLLennartdeGroot,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,NL

Methodstoderivepaleodirectionsorpaleointensitiesfromrockscurrentlyrelyonmeasurementsofbulksamples(typically~10cc).Theprocessofrecordingandstoringmagnetizationsasfunctionoftemperature,however,differsforgrainsofvarioussizesandchemicalcompositions.Mostrocks,bytheirmerenature,consistofassemblagesofgrainsvaryinginsize,shape,andchemistry.Unravelingthebehaviorofindividualgrainsisaholygrailinfundamentalrockmagnetism.

Recently,weshowedthat it ispossibletoobtainplausiblemagneticmoments for individualgrains inasyntheticsamplebyamicromagnetictomography(MMT)technique(c.f.abstractofdeGrootetal.).Thistechnique uses a least-squares inversion to obtain these magnetic moments based on the physicallocationsanddimensionsofthegrainsobtainedfromaMicroCTscannerandamagneticfluxdensitymapofthesurfaceofthesamplemeasuredwithaScanningSQUIDMicroscope(SSM).Thesampleusedforthisproofofconcept,however,wasoptimizedforsuccess:ithadalowdispersionofthegrains,andthegrainswere largeenoughsotheywereeasilydetectedbytheMicroCTscanner.Natural lavasaremuchmorecomplexthanthesyntheticsampleanalyzedsofar.Thedispersionofthemagneticmarkersisoneorderofmagnitudehigher,thegrainsdiffermoreincompositionandsize,andmanysmall(submicron)magneticmarkersmaybepresentthatgoundetectedbytheMicroCTscanner.Furthermore,theSSMset-uprequiresthesampletobesubmergedinliquidhelium(4K)togetherwiththeSQUIDsensor,hencethesampleisanalyzedbelowitsVerweytransitionandnotinitsnaturalmagneticstate.

HerewepresentthefirstMMTresultsobtainedfromasamplefromthe1907-flowatHawaii.Thephysicalproperties of the remanence bearing grains were obtained with a MicroCT scanner of the TechnicalUniversityinDelft.Toanalyzethemagneticfluxatthesurfaceofthesampleatroomtemperature,henceavoidingtheVerweytransitionthatisinherenttotheSSM,weturnedtotheMagneticTunnelingJunction(MTJ) technique. TheMTJ scanner of theNanopaleomagnetism group in Cambridge operates at roomtemperature,andsamplepreparationandscanningaremucheasiercomparedtotheSSMscanner.Theresolution,stepsizeandscanheight(distancefromthesensortothesurfaceofthesample),however,allarelessdesirablecomparedtotheSSM.WewereabletosuccessfullyobtainMicroCTandMTJscansfromthesampleandisolateplausiblemagneticmomentsforindividualgrainsinthetop70µmofthesample.WewilldiscussthepotentialoftheMMTtechniqueappliedtonaturalsamplesandcomparetheMTJandSSMmethodsintermsofworkflowandqualityoftheresults.

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PetromagnetismofPermian-TriassicsequenceatKuznetskBasin,Russia

Presenter:

DiliaraKuzina([email protected])

Authors: DiliaraKuzina,KazanFederalUniversity,InstituteofGeologyandPetroleumTechnologiesIlmirGilmetdinov,KazanFederalUniversity,InstituteofGeologyandPetroleumTechnologiesRadmirAupov,KazanFederalUniversity,InstituteofGeologyandPetroleumTechnologiesVladimirSilantev,KazanFederalUniversity,InstituteofGeologyandPetroleumTechnologiesDanisNurgaliev,KazanFederalUniversity,InstituteofGeologyandPetroleumTechnologies

Theproblemofcatastrophicextinctionsofbiotaisoneofthemostimportantandexceedinglydebatingproblems, which attracts the attention of the broad science community as well. There are a lot ofhypothesis describing the causes of Permian - Triassic (P-T) extinction, but none of them have beencommonlyacceptedyet.Magnetic,andfurtherpaleomagnetic,investigationswillclarifyourunderstandingofprobablycauseofPermian-TriassicextinctionandparticulartheroleofSiberiantraps.Themainaimistofindthespecificpositionoftheboundarybetweentwoepochs.Fullsetofmagneticinvestigationswerecarried out on the samples. Measurements of magnetic susceptibility (MS), natural remanentmagnetization(NRM),hysteresisparametersandinducedmagnetizationversustemperaturewerecarriedoutfordeterminationmagneticmineralogy.Differentialthermomagneticanalysiswascarriedoutinspecialequipment'CurieExpressBalance'thatwascreatedinthePaleomagneticLaboratoryoftheKazanFederalUniversity.Thisprocessincludedthemeasurementofthesampleinducedmagnetizationasafunctionoftemperature.Therateofheatingwas100°C/min.Themeasurementsweremadeinaconstantmagneticfield-400mT.Wehavegotthermomagneticcurvesofthefirstandsecondheatingupto800°C.HysteresisparametersweredeterminedusingaJ-coercivityspectrometer,alsobuiltinthePaleomagneticLaboratoryofKazanUniversity,andprovidingforeachsampleamodifiedhysteresisloop,backfieldcurve,acquisitioncurveof isothermalremanentmagnetization.Eachmeasurementsetwasobtained inasinglerunfromzero field up to 1.5 T and back to -1.5 T. Magnetic susceptibility was measured in Multi-functionKappabridgeMFKA1-FA(AGICO)onfrequency976Hz,NRMmeasuredwasmeasuredinCryogenic(SQUID)magnetometer2GEnterprises.Accordingtotheobtaineddata,thesequenceisdividedintotwoparts:thelowerone-withlowvaluesofthemagneticsusceptibilityandNRMandtheupperonewithhighervalues.Acknowledgements: The work was carried out according to the Russian Government's Program ofCompetitiveGrowthofKazanFederalUniversityandsupportedbythegrantsofStatePrograminthefieldofscientificresearchandRussianFoundationforBasicResearch(projectno.16-04-01062).

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PaleomagneticStudyoftheLekaOphioliteComplexincentralNorway

Presenter:

AlexanderMichels([email protected])

Authors: AlexanderMichels,NorwegianUniversityofScienceandTechnologySuzanneMcEnroe,NorwegianUniversityofScienceandTechnology

TheLekaOphioliteComplex(LOC)isacompleteandwell-exposedophiolitelocatedincentralNorwayontheislandofLeka.ThecomplexhasaU-Pbzirconageof497±2MafromacrosscuttingtrondhjemitegivingalowerlimitfortheageofformationfortheLOCinthemiddletolateCambrian.Thepurposeofthisstudywas toconstrain the timingofemplacementandageof serpentinizationof theultramafics.TheLOC iscomprisedoffivemajorrockunits(1)harzburgite(2)ultramaficcumulateswithasequenceofwebsterite-wehrlite and dunite with some crosscutting layers of chromite (3) metagabbros which are cut by (4)metabasaltic dykes that gradually becomes (5) pillow basalts with bedded chert forming the ancientoceanicfloor.Samplesweretakenfrom86siteseitherasorientedblocks,ororienteddrillcores.Measurementsweremade on 567 samples and include natural remanent magnetization (NRM), magnetic hysteresisparameters, temperature-dependent susceptibilityandmagnetic susceptibility.NRMvalues range fromlessthan0.01to34A/mwithameanNRMof2.58A/mandsusceptibilityvaluesrangesfrom1*10-4to0.22(SI)withanaveragemagneticsusceptibilityof2.9*10-2(SI).Samplesweredemagnetizedusingboththermal and alternating field techniques. High-temperature magnetic moment measurements, andtemperature-dependent susceptibility confirm a dominant Curie temperature of approximately 580°C,indicatinganendmembermagnetiteasthetypicaloxide,acompositionexpectedfrommagnetiteformedbyserpentization.Thisisalsoseeninthethermaldemagnetizationthatmagnetiteistheprimarycarrierfor themagnetic remanence.Anotherpotential carrier is chromite found in someof thedunitic rocks,thoughpreliminarytestssuggestthechromitetobeparamagneticatroomtemperature.ThechromiteisofinterestasthesampleswithhighconcentrationshaveanaverageNRMdirectionthatisdifferentfromtheotherdunitesamplesbyapproximately28degrees.Thechromitesampleshaveastablemeandirectionthat is resistant toAFdemagnetization andmay retain aprimary TRM.Most chromites showa rimofmagnetitethatmaypredatetheserpentinization.PreliminarycalculationsshowthepaleopolefortheLOCcoincides with the present day field. This could suggest that the LOC has been overprinted recently.Howeverexaminingthedipofthepaleohorizontalindicatedbythepillowbasalts,andtreatingtheLOCasone block, the LOC can be rotated back to horizontal. This paleomagnetic pole plots closer to otherpaleomagnetic poles for Baltica at 430 Ma, at time period, which correlates to the beginning of theCaledonian orogeny. At this time the LOC underwent heating that would overprinted the primarymagnetization.

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Evaluationofaginginnaturalvolcanicglass:magneticpropertyvariations

duringartificialagingexperimentsPresenter:

FatimahAbdulghafur(AbuduwufuPatiman)([email protected])

Authors: FatimahAbdulghafur,UniversityofWisconsin-Milwaukee,USAJulieA.Bowles,UniversityofWisconsin-Milwaukee,USA

The recorded geomagnetic field intensity is a functionofmagneticmineralogy, grain size, andmineralconcentrationaswellasmaterialstabilityinnatureandduringlaboratoryexperiments.Fresh,unhydratedvolcanicglassesare recognizedasanearly idealnaturalmaterial foruse inpaleointensityexperimentsbecausetheycontaintherequisitesingledomaintopseudo-single-domainmagneticparticles.Althoughalterations of magnetic mineralogy can be monitored during the experiments, it is unclear how themagneticmineralogyandhencemagnetizationmightchangewithageasthemetastableglassstructurerelaxesand/ortheglassbecomeshydrated.Bulkmagneticpropertiesasafunctionofageshownocleartrend,evenoverhundredsofmillionsofyears.Thismaybeduetothefactthateveninfresh,unhydratedglass, therewill be differences inmagnetic properties due to variation in cooling rate or composition.Therefore,inordertobetterunderstandhowamagneticmineralogyassemblageevolveswithtime,weconductedartificialagingexperimentsonfresh,unhydratedrhyolitic(SouthDeadmanCreek,California,650-yr) and basaltic (Axial Seamount, 2011) end-member glasses. Glass relaxation or devitrification isextremely slowat room temperature, but elevated temperatures accelerate theprocess in away thatrelaxationtimedecreaseswithincreasingtemperature.Wearethereforeannealingsamplesat200,300and400°Cforperiodsof15,30,60,120,and240days.Here,wepresentsomepreliminaryresults forsamplesannealedupto60days.Isothermalremanentmagnetizationacquisitionismonitoredtoassesschangesinthecoercivityspectrumandsaturationremanentmagnetization.Preliminaryresultsshowthatinbasalticglassthereareatleasttwodifferentcoercivitypopulationscenteredabout30mTand125mT.Nocleartrendincoercivityalterationisobservedafter30daysforallthreetemperatures.Asimilarresultisobservedintherhyoliticsamples.

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Whatispseudo-singledomainmagneticbehavior?

Presenter:

AndrewP.Roberts([email protected])

Authors: AndrewP.RobertsTrevorP.AlmeidaNathanS.ChurchRichardJ.HarrisonDavidHeslopAdrianR.MuxworthyWynWilliamsXiangZhao

Theterm'pseudo-singledomain'(PSD)hasbeenusedtodescribethetransitionalstateinrockmagnetismthat spans the particle size range between the single domain (SD) andmulti-domain (MD) states. TheparticlesizerangeforthestableSDstateinthemostcommonlyoccurringterrestrialmagneticmineral,magnetite,issonarrow(~20-100nm)thatitiswidelyconsideredthatmuchofthepaleomagneticrecordof interest is carried by 'PSD' rather than stable SD particles. The PSD concept has, thus, become thedominant explanation for the magnetization associated with a major fraction of particles that recordpaleomagnetic signals throughout geological time. We argue that a particular set of interpretationsconcerning the origin of 'PSD' behavior has arisen in paleomagnetism and rockmagnetism that is notsupportedbythephysicsoftherelevantprocesses,bythree-dimensionalmicromagneticmodeling,orbyparallel research inmaterials scienceandsolid-statephysics.Wealsoarguethat featuresattributedto'PSD'behaviorcanbeexplainedbynucleationofamagneticsinglevortexstate immediatelyabovethemaximumstableSD(flower)transitionsize.Withincreasingparticlesize,multiplevorticescannucleate,alongwithdomainwalls,whichproduceagradualtransitionintotheMDstate.Thus,whiletheterm'PSD'describes a well-known transitional state, it fails to describe adequately the physics of the relevantprocesses.Werecommendthatuseofthistermshouldbeabandonedinfavourofthevortexstate,whichspansarangeofbehaviorsassociatedwithmagneticvortices.

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DifferentapproachesoftheSD-SPthresholdatroomtemperature

Presenter:

PierreRochette([email protected])

Authors: P.RochetteF.Demory

Frequency dependence of susceptibility at room temperature (fd%) is a classicmethod to detect andquantifythepresenceofgrainsattheSPandSDthreshold.Whenusingdifferentfrequenciesinthe1to15kHzrangeanddifferentinstrumentsfd%valuesappearnotwellcorrelated.Comparingfd%fromdifferentprotocolsisthereforedelicate.Wewillalsopresentaseldomusedtechnique:theIRMdecaymeasuredusingtheVSMon500susing1sstep.Thismaybeequivalent toa frequencydependenceon the~1Hz range.The relative timedecaycoefficient of various samples with high fd% (obsidian, impact glass, martianmeteorites) apears veryweaklycorrelationwithfd%.Thiscoefficientishighonlywhenfd%ishigh,butcanalsobelowwhenfd%ishigh.IntermsofpredictingtheviscouscontributiontoNRMthistechniquemaybemorerelevantthanfd%andmuchmorerapidthanstandardviscosityexperiments.

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RockmagneticpropertiescharacterizationofMayanpotteryforthePreClassic,ClassicandPost-Classicperiods,southeasternMexico.

Presenter:

AlejandroRodriguez-Trejo([email protected])

Authors: LuisM.Alva.Valdivia,InstitutodeGeofísica-UNAMSocorroJimenez-Alvarez,UniversidadAutonomadeYucatanRosalbaNieto-Calleja,InstitutoNacionaldeAntropologiaeHistoriaMarcosN.Pool.Cab,UniversidadAutonomadeYucatanRafaelCobos-Palma,UniversidadAutonomadeYucatanRubenNuñez,UniversidadAutonomadeYucatanJoelPalka,UniversidadAutonomadeYucatanIlianaAncona-Aragon,UniversidadAutonomadeYucatanHéctorHernándezÍlvarez,UniversidadAutonomadeYucatanCharlesGolden,IllinoisStateUniversity

We present magnetic properties, obtained from 220 ceramic specimens of the Maya zone (Yucatan,ChiapasandQuintanaRoo,Mexico).ThesamplesbelongtodifferentmaterialsfromthePre-Classic,ClassicandPost-Classicperiods, from1000aCto1600dC,whichhave17periodsofoccupationduringthe las2600yearsinthedifferentareas.Magneticproperties,suchassusceptibilityvs.temperature,hysteresisloop,FORC,IRM,dIRM,UNMIX,thermalandalternatingfielddemagnetizationwereperformed.Theresultsshowtitanomagnetiteasthemagneticmineralthatcarriesthemagnetization.ThesampleswereselectedaccordingtogroupingsintheDayplot(magneticdomain),consideringtheirlocationandtheoccupationperiod.Atrendwasobservedinbetweendifferentgroups,estimatingpossiblecoincidencesonthesourcesoftherawmaterialsused,aswellastheirchangesovertime.Thecoercivitywascharacterizedaccordingtotheirprovenanceandperiodoftime.TherockmagneticspropertieswereusedtoselectspecimenstoperformthepaloeintensitydeterminationbytheThellier-Thelliermethod.Thiswill improvethesecularvariationcurveofthesoutheasternpartofMexico.Ourresults,allowtoestablishthemagneticpropertiesoftherawmaterialsusedintheregionduringthisperiod,aswellastheirrelationshipandevolutionovertime, which shows a change in themanufacture, selection and exchange of natural materials for themanufactureofceramicsinthearea.



UnderstandingtheRoleofNon-SingleDomainRemanencesinPaleointensity

ExperimentsPresenter:

ChristeanneNicoleSantos([email protected])

Authors: ChristeanneNicoleSantos,ScrippsInstitutionofOceanography,LaJolla,CA92093-0220LisaTauxe,ScrippsInstitutionofOceanography,LaJolla,CA92093-0220

The optimization of laboratory and analytical techniques for paleointensity determination has been alongstandingdebateinthepaleomagneticcommunity.Themanycomplexitiesandambiguitiesbothinthefield and in the laboratory have fostered a multiplicity of approaches to the problem of intensityestimation.Inthisstudy,wefocusonthreekeycomponentsofestimationtechniques:theeffectofcoolingrateonTRMacquisitionrelativetomagneticdomainstate,experimentalnoiseanditseffectonaccuracy,andastatisticalanalysisofintensityatthespecimenlevel(totalTRMvs.lineofbest-fit).TheIZZI-variantoftheThellierintensityestimationmethod(Yuetal.,2004)wasimplementedonspecimensfromlavaflowscollectedfromvarious localitiesaroundtheworld(McMurdo,Socorro Island,Hawaii, JanMayen,CostaRica,SnakeRiverPlain,andSpitsbergen).AlloftheseflowshadbeensubjectedtotheIZZIexperimentpriortothisstudyandsamplesweredividedintotwogroups:ideallylinear('straight')andnon-ideallycurved('curved')araiplotsusingthecurvaturecriterionofPaterson(2011)whichisthoughttoseparatesingledomain behavior (straight) from multi-domain behavior (curved). For the current experiment, sisterspecimensweremadefromthesetwogroupsofsamplesandgivenanew,laboratorycontrolled,totalTRMandsubjectedtoasubsequentIZZIexperimenttoempiricallydemonstrateanydomainstate-dependentcomplicationsthatcanariseexperimentally.Coolingrate:ThecoolingrateeffectonTRMacquisitioninmagneticparticlesispredictedbysingledomaintheory(e.g.,Halgedahletal.,1980)wherebythemagnetizationincreaseswithdecreasingcoolingrate.Incontrast,Yu(2011)summarizedevidencefortheoppositeeffectinmulti-domainremanencesandnoeffectin pseudo-single domain remanences. This effect can be quite large and has been almost completelyignoredinroutine(non-archaeological)studies.Coolingratecorrections,whichcanbequitelarge,shouldbeimplemented in Thellier and Thellier-type experiments to minimize under- or over-estimation ofpaleointensitywhenthenaturalcoolingrateisunknownordiffersfromthelaboratorycontrolledcoolingrate.However,theunderlyingfactorsofthiseffecthavenotbeendeterminedconclusivelyintheliterature.WegaveallspecimensatotalTRMintwocoolingrates('fast',orlessthan45minutesand'slow',orabout10hours)andcomparedthetwoTRMs.Ourdatademonstrateasystematicbiasofthiscoolingrateeffectof some 6% in the 'straight' category of specimens, and an almost negligible effect on the 'curved'specimens,which suggests a domain-state dependenceof cooling rate correctionon thermal intensityexperiments,essentiallyconfirmingresultsreportedbyYu(2004)andothers.ExperimentalNoiseandStatisticalAnalysis:Patersonetal.(2012)modeledabaselineinaccuracyof6-7%for paleointensity of ideal specimens in the presence of experimental noise. It was suggested thatquantifyingaccuracyof intensityestimationsshouldentailusingdeviationsgreater thanthis threshold.However,ourdatashowstandarddeviationsaslowas~2%forthe'straight'specimensandasignificantlyhighervalueof~7%forthe'curved'specimens.Furthermore,theslopesofthetheseAraidiagramswerecalculatedwithbothalineofbest-fitthrougheachspecimenandfromthetotalTRM.Comparisonofthetwomethodsshowedsignificantlylessscatterfromthemedianvaluewhenanalyzedwiththeformerandnobiasintherecoveredintensityestimate.The'curved'specimensgavenotonlyhigherscatterbutalsowereslightlybiasedtohighervalues.Thissuggeststhatextremelyaccurateintensitiescanbesuccessfullyreproducedwithidealsamples,whilenon-idealbehaviorresultsinmorescatterandbiasintheestimatedintensity. Taking all of these conclusions into consideration underscores the importance of using

17


experimentaltechniquesthatrevealnon-idealbehavior(suchastheIZZImethod)andthedangerofusingmethodsthatdonot.ReferencesCited:Halgedahl,S.L.,Day,R.,andFuller,M.,Theeffectofcoolingrateonthe intensityofweak-fieldTRM insingle-domainmagnetite,J.Geophys.Res.,85,3690-3698,1980.Paterson, G. A. (2011), A simple test for the presence of multidomain behavior during paleointensityexperiments,J.Geophys.Res.,116,B10104,doi:10.1029/2011JB008369.Paterson,G.A.,A.J.Biggin,Y.Yamamoto,andY.Pan(2012),TowardstherobustselectionofThellier-typepaleointensity data: The influence of experimental noise, Geochem. Geophys. Geosyst., 13, Q05Z43,doi:10.1029/2012GC004046.Yu,Y.,Tauxe,L.,Genevey,A.,Towardsanoptimalgeomagneticfieldintensitydeterminationtechnique,Geochem.,Geophys.,Geosyst.,5,Q02H07,10.1029/2003GC000630,2004.

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ImportanceoftitanohematiteindetritalremanentmagnetizationsofstrataspanningtheCretaceous-Paleogeneboundary,HellCreekregion,Montana

Presenter:

CourtneySprain([email protected])

Authors: CourtneyJ.Sprain,UniversityofCalifornia,Berkeley/UniversityofLiverpoolJoshuaM.Feinberg,UniversityofMinnesota/InstituteforRockMagnetismPaulR.Renne,UniversityofCalifornia,Berkeley/BerkeleyGeochronologyCenterMikeJackson,UniversityofMinnesota/InstituteforRockMagnetism

Intermediatecompositiontitanohematite(Fe2-yTiyO3,0.5<y<0.7)isoftendescribedasoccurringrarelyinnatureandisseldomthefocusofpaleomagneticstudy.Itsformationislimitedtogeologicenvironmentsassociatedwithrapidlycooledintermediatecalc-alkalinevolcanicrocksanditismostcommonlyidentifiedbyitsuniqueself-reversingproperty.Ithasbeenidentifiedonlyinahandfulofpaleomagneticstudiesandasidefromrockmagneticstudiesonitsself-reversingmechanism,itisoftenviewedasbeingofnegligibleimportancetopaleomagneticstudies.Despitethesebeliefs,intermediatecompositiontitanohematitehasbeenidentifiedasthedominantferrimagneticmineralinavastarrayoflateMesozoictoearlyCenozoicclasticdepositsacrosscentralNorthAmerica.ThismineralhasalsobeenidentifiedinMesozoicandMiddleCenozoic uranium-bearing sandstones and Late Cretaceous placer deposits across the United States.Intermediate titanohematite, unlike its end-members, is ferrimagnetic and displays similar unblockingtemperatures and coercivities to titanomagnetite. With detrital remanent magnetizations maskingintermediate titanohematite's self-reversing property, this mineral is easily misidentified astitanomagnetite in sedimentary deposits and requires extensive rock magnetic analysis for properidentification. Past studies reliedonnon-magnetic techniques, includingX-Raydiffraction andelectronmicroprobe analysis, to identify this mineral. While these techniques are excellent at identifying thepresenceofthismineral,theyfailtoassessitsimportanceasacarrierofremanence.To facilitate the identificationof intermediatecomposition titanohematite insedimentary rocks, in thisstudywecharacterize thismineralusinghigh-temperaturesusceptibilityexperiments, low-temperaturemagnetometryexperiments,andanewly-developedtechniquebasedonitsself-reversingpropertythatuniquelyidentifiesthismineralwhilesimultaneouslyassessinghowmuchremanenceisheldbythisphase.ThisstudywasconductedonfluvialsedimentsthatspantheCretaceous-PaleogeneboundaryfromtheHellCreek region, NE Montana. Our results show that the dominant ferrimagnetic mineral by mass istitanohematite with compositions ranging from y = 0.53-0.63. However, the dominant carrier ofremanence is probably titanomagnetite(maghemite). Our results show that Néel/Curie temperaturedetermination,low-temperaturemagnetometry,andXRDandEPMAanalysisareeffectivetechniquesforrecognizingthepresenceofintermediatetitanohematite.Theself-reversaltest,developedinthisstudy,uniquely identifies this mineral, while also commenting on its importance as a carrier of remanence.However, further development is needed to make this tool capable of identifying a greater range ofcompositions.ComparingourresultstootherrockmagneticandpaleomagneticstudiesonLateCretaceousandPaleogeneageclasticdepositsacrosscentralNorthAmerica,itcanbeseenthatthesesedimentssharesimilar magnetic properties. This outcome suggests that intermediate titanohematite may be a moreimportantcarrierofnaturalmagneticremanencethanpreviouslyrecognized,andfurtherisimportanttorecognize (particularly asmild reheating~200°Cmay result in a reverse thermoremanentoverprint) inordertoavoidspuriouspaleomagneticinterpretation.Whileearlierliteraturesuggeststhatintermediatecompositiontitanohematiteisrareinnature,reanalysisusingspecializedrockmagnetictechniquesmayrevealittobemoreabundantintherockrecord,particularlyaroundsedimentarybasinsadjacenttocalc-alkalinevolcaniccenters,thanpreviouslyperceived.

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Micromagneticmodellingofmicrostructuresinmagnetite

Presenter:

GeertjeterMaat([email protected])

Authors: GeertjeterMaatNathanChurchKarlFabianSuzanneMcEnroe

Micromagneticmodellingisausefultoolinunderstandingthebehaviourofmagneticgrainsondifferentscalesundervaryingconditions.Itgivesinsightinthedomainstateandtheinteractionbetweenparticlesandtheinfluencesoftheshape,sizeandspacing.ThesamplesusedformicromagneticmodelscomefromtheStardalurvolcano in Iceland,whichyieldsa largepositiveanomaly (27000nTabovebackground).Qvaluesare~22onaverage,whichindicatestheanomalyisdominatedbyremanence.TheaverageNRMintensity is61A/m,15timesstrongerthansimilar Icelandicbasalts(Kristjansson,2002).High-andlow-temperaturemagneticmeasurements suggest themain carrier of themagnetization in these rocks ismagnetite. The magnetite contains extensive oxy-exsolution microstructures from the micron tonanometer scale, which leads to the complex morphologies of grains modelled here. Here, withmicromagneticmodellingwetesttheinfluenceofthesemorphologiesonenhancingthemagnetisationinthesegrains.Thegeometryofmagnetitethatissubdividedbytheparamagneticilmenitelamellaeischaracterisedusingaslice-and-viewprocedureonadualbeamFIB-SEM.ThetruegeometryoftheparticlesaremodelledusingMERRILLmicromagneticssoftwaretocalculatemagnetisationstructures.Therealistic3Dmorphologiesofcloselyspacedparticlesaremodelledingroupsof2-3particles,andthewidthofthelamellaeisvariedfrom20-100nm.This isdone inordertotesttheroleof interactions instabilisingdomain,ormagnetisationstates. The variation in thicknessof the lamellae subdividing themagnetite grainsmay result in grainsbehavingmorePSDtoSDifnointeractionacrossthelamellaeoccurs.ThiswouldleadtoastrongerandmorestableNRM.Tomimicstraininthesamplesthematerialpropertiesaremodified.Byincreasingtheanisotropy in theparticleswecanstudytheeffects relatedtomagnetostrictionwhich is relatedto theexsolutioninterface.Usingthetruegeometryoftheoxy-exsolvedgrainsallowsforafullevaluationoftheeffectofshape,size,spacingandstrainonthemagneticpropertiesoftheparticles.Bychangingthesevariableswetestifthereisanincreaseinremanencecarryingcapacity,andstudywhethermodificationofthegeometrybyoxy-exsolutionenhances themagnetization,or thatother factorsare involved.Betterunderstandingof theprocessesthatyieldstrongNRMisanimportantkeytofurtherourknowledgeonremanencedominatedanomalies.

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RockmagneticthermalalterationsfailedtobedetectedbypTRMchecks

duringThellier-seriespaleointensityexperimentsPresenter:

HuapeiWang([email protected])

Authors: HuapeiWang,PlanetaryScienceInstitute,ChinaUniversityofGeosciences,Wuhan,Hubei430074,P.R.ChinaDennisV.Kent,EarthandPlanetarySciences,RutgersUniversity,Piscataway,NJ08854,U.S.A.andLamont-DohertyEarthObservatory,ColumbiaUniversity,Palisades,NY10964,U.S.A.

Partial thermal remanentmagnetization (pTRM) check isoften taken for grantedas thermal alterationindicatorforThellier-seriespaleointensityexperiments.Inthisstudy,weuserockmagneticpropertiestomonitorthermalalterationofGalapagoslavasfromsiteGAXthatwerepreviouslyusedformultidomain(MD)correctedpaleointensities[WangandKent,2013,G-cubed].Themainmagnetizationcarriersarefinemagnetitegrainsrangingfromsingledomain(SD)-liketoMD-likebehaviors.High-fieldthermomagneticexperiments show mostly reversible heating and cooling curves, which suggest little thermochemicalalterationduetomagneticmineralogicalchanges.Wecomparedtwo~30mgfreshsubsamples,oneofanSD-like lavathathadpasseda500°CpTRMcheckbutwasrejectedbytheMDcorrectedpaleointensitylinearitycriteria,andanMD-likeone thathad failedpTRMcheckbutyieldedaqualifiedMDcorrectedpaleointensityestimate.Weheatedthefreshsamplesstepwisein50°Cintervalsupto600°Candaftereachstep, wemeasured their hysteresis parameters, first-order reversal curves (FORC) and high-resolutionFORC.OurresultsshowthattherockmagneticpropertiesoftheMD-likesamplewereverystableatallheatingstepswhereasfortheSD-likesample,FORCdiagramsshowthatitchangesfromtheoriginalnon-interactingpseudo-SDtointeractingSDaround500°C,whichindicatesthermaldomainstatusalterations.However,theseresultsareoppositetowhatwouldhavebeeninferredfrompTRMchecks.Thisdiscrepancyisbecausemostofthemagneticgrainsinsamplethermallyalteratthefirsttimewhenreachinganewhightemperature.GivingsampleapTRMatalowertemperaturewillonlymagnetizethemagneticgrainsthathaveblockingtemperaturelowerthanthat.Grainswithblockingtemperaturesinbetweenthecurrenthightemperature and the previous low temperaturewill not carry usefulmagnetization signals to identifythermal alteration.On theotherhand, for theMD-like sample, itsMDeffects contribute to thepTRMchecks,causingfalsealarmsevenifitdidnotalter.WeconcludethatpTRMchecksshouldnotbereliedupon to indicate thermal alteration for Thellier paleointensity experiments. Instead, appropriate rockmagneticpropertiesaremorefaithfulmonitors.

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ThermalstabilityofPalaeomagneticRecorders

Presenter:

WynWilliams([email protected])

Authors: WynWilliams,UniversityofEdinburghLesleisNagy,UniversityofEdinburghAdrianMuxworthy,ImperialCollegeKarlFabian,GeologicalSurveyofNorwayJayShah,ImperialCollegeTrevorAlmeida,UniversityofGlasgow

Palaeomagneticrecordingsofthegeomagneticfieldhave,formorethanhalfacentury,providedarichsourceofscientificdataaboutthegeologicalevolutionoftheEarth.ThetheoreticalbasisthatunderpinsourunderstandingofrockmagneticrecordingscomesfromNéel'stheoryofthermo-magneticstabilityinsmalluniformlymagnetised,singledomain(SD)particles.NéeldemonstratedthatforSDgrains,signalsrecordedneartheCurietemperatureandsubsequentlycooledtoroomtemperaturecanremainstableformanybillionsofyears.Over the last twodecadesnumericalmicromagneticmodellinghasallowedus togainamoredetailedunderstandingofmagneticdomainstructuresandtheirvariationwithgrainmorphology,temperatureandmineralogy.ThesestudieshavedemonstratedthattrulyuniformSDgrainsexistonlyinaverynarrowrangeofgrainssizes,andthemajorityofremanencecarriersinpaleomagneticsamplesarelikelytoresideinnon-uniformlymagnetised pseudo-single domain (PSD) grains. Hitherto the assumption has been that therecording stability of PSD grainswas significantly less than SD, although no theoretical basis for theseassumptionshasbeenprovided.InthispresentationwewillexaminedomainstructureandinparticularthermalstabilityofSDandPSDgrainsasafunctionoftemperatureandgrainsizeformagnetiteandironparticles.WewilldemonstratethatevenforgrainsintheSDsizerange,deviationfromperfectlyuniformdomainstructurecanprovideincreasedmagneticstability.Forlarger,PSDgrainsdominatedbyvortexdomainstructures,weobservestructure-coherentrotationofthevortexdomainsanalogoustocoherentrotationobservedinSDdomains.Moresignificantly,itwillbeshownthatPSDgrainshavesignificantlyhighermagneticstabilitythantheirSDcounterpartsforequidimensionalcuboctaheralmagnetitegrains.TheoriginofstablepaleomagenticremanencesisthereforemorelikelytoresideinPSDgrainsthanSDmagnetitegrains,andthegrainsizerangefor'ideal'magneticrecordersismuchlargerthanpreviouslythought.Theseinitialresultssuggestthatsimulationsofthermomagneticprocessesinassemblagesofparticlesmaysoonprovideamuchbetterconstraintoftheaccuracyofpalaeomagneticobservations.

22


SourcesandSignificanceofCrustalMagneticAnomalies

Orals:TuesdayJuly11–13:00-16:30

KoningsbergergebouwPangea

Posters:WednesdayJuly12-15:30-18:00deVagant

Convenors:SuzanneMcEnroe&LaurieBrown

start end talk+Q&A Presenter abstracttitle

13:00 13:30 20+10 SuzanneMcEnroe Remanentmagneticanomaliesandconsequencesofexsolutionofanduncompensatedspinsatinterfacesinmagneticminerals

13:30 14:00 20+10 CarmenGaina AreviewofglobalmarinemagneticanomaliesatEocenetime

14:00 14:15 10+5 PierreRochette Measuringremanenceundervariablepressureandtemperatureusingacryogenicmagnetometer

14:15 14:30 15 plenarydiscussion 14:30 15:00 30 coffeebreak 15:00 15:30 20+10 DavidClark Methodsfordeterminingremanentandtotal

magnetizationsofanomalysources15:30 16:00 20+10 HirokuniOda Superconductingmagnetometerasatoolfor

mappingmagneticanomalies16:00 16:15 10+5 LaurieBrown Paleomagnetism,RockMagnetism,andMagnetic

Anomaliesofthe920MaTellnesOreBody,SouthNorway

16:15 16:30 15 plenarydiscussion

23


Posters


abstracttitle

HodelFlorent IdentificationofCr-magnetite,magnetiteandferritchromiteinNeoproterozoicserpentinites

ZeudiaPastore MODELLINGOFHIGHRESOLUTIONMAGNETICMICROSCOPYDATA:ANAPPLICATIONTOASERPENTINECARBONATEMAGNETITESAMPLEFROMMODUM,NORWAY

24


SourcesandsignificanceofcrustalmagneticanomaliesOral-TuesdayJuly11-16:00-16:15

Paleomagnetism,RockMagnetism,andMagneticAnomaliesofthe920Ma

TellnesOreBody,SouthNorwayPresenter:

LaurieBrown([email protected])

Authors: LaurieBrown,UniversityofMassachusetts,Amherst,MA,USASuzanneMcEnroe,NorwegianUniversityofScience&Technology,Trondheim,NorwayPeterRobinson,NorwegianGeologicalSurvey,Trondheim,Norway

The Tellnes ore body, a wide dike-like ilmenite-rich norite, intrudes the Ana-Sira anorthosite in theRogaland IgneousProvince in southernmostNorway.Theorebodyappears tobeoneof theyoungestbodiesinthecomplexwithaU-Pbzirconageof920+/-3Macomparedtothe~930Maageforassociatedanorthosites.Currently,TitaniaA/SisactivelyminingatTellnes,extractingtitaniumfromtheubiquitousilmenite,compositionally29%ofthenorite,foruseinthepigmentindustry.TwelvesitesfromtheorebodyitselfarecurrentlybeingstudiedfortheirpaleomagneticsignatureforcomparisonwiththesurroundingAna-Sira anorthosite, other anorthosites in the complex, and the nearby Bjerkreim-Sokndal layeredintrusion.Reflected-lightstudiesof theoxides (McEnroeetal,2001)showthatthecoarse ilmenitehasextensive µm to nm-size exsolution of hematite and commonly, largeMDmagnetite grains with raremicrostructures.Meansusceptibilityvaluesrangefrom0.003(SI)forsampleswithoutmagnetitetoover0.100(SI)forsampleswithbothmagnetiteandhemo-ilmenite.NRMvaluesarealllarge,from5A/mtoover30A/m,andwithsteepnegativeinclinationsandwesterlydeclinations.ResultinghighQvalues(3-26)indicatethebroadnegativeanomalyseenovertheTellnesbodyandthesurroundingAna-Siraanorthositeis dominated by NRM directions relatively close to anti-parallel to the present field. Demagnetizationstudiesindicatethathemo-ilmeniteisthecarrierofthestrong,stableremanence.Upondemagnetizationsamples retain steepnegativedirections similar to those found in the surroundinganorthosites (-80.1,325.9for13sitesfromtheEgersund-Ognabody)andthenearbyBjerkreim-Sokndal layeredintrusion(-73.5,303.4,60sites).YoungerdoleriticdikesoftheEgersundDikeSwarm,datedat616+/-3Ma,cuttheTellnes body. Paleomagnetic directions from three dikes cross-cutting the ore body have magneticdirections with steep positive inclinations and northeasterly to southeasterly declinations, similar topublished directions for Egersund dikes in other parts of the province. The dikes have very low NRMintensities(~1.0A/m),andintransmitted-andreflected-lightshowalterationsofsilicatesandoxides.Thesimilarityindirectionsbetweenthenoriteandtheolderanorthositesimplieseitherthemagneticfieldwasstableoversome10millionyearsorthatthislarge,deep-seatedigneouscomplexcooledslowlyandalltheremanencewasacquiredataboutthesametime.

25


SourcesandsignificanceofcrustalmagneticanomaliesOral(invited)-TuesdayJuly11-15:00-15:30

Methodsfordeterminingremanentandtotalmagnetizationsofanomaly

sourcesPresenter:

DavidClark([email protected])

Authors: DavidA.ClarkAssumingwithoutevidencethatmagneticsourcesaremagnetisedparalleltothegeomagneticfieldcanseriouslymisleadinterpretationandcanresultindrillholesmissingtheirtargets.Ireviewmethodsthatareavailable forestimating,directlyor indirectly, thenatural remanentmagnetisation (NRM)andtotalmagnetisation of magnetic sources, noting the strengths and weaknesses of each approach. Thesemethodsare:(i)magneticpropertymeasurementsofsamples,(ii)boreholemagneticmeasurements,(iii)inference of properties from petrographic/petrological information, supplemented by palaeomagneticdatabases,(iv)constrainedmodelling/inversionofmagneticsources,(v)directinversionsofmeasuredorcalculatedvectorandgradienttensordataforsimplesources,(vi)retrospectiveinferenceofmagnetisationofamineddepositbycomparingmagneticdataacquiredpre-andpost-mining,(vii)combinedanalysisofmagneticandgravityanomaliesusingPoisson'stheorem,(viii)usingacontrolledmagneticsourcetoprobethesusceptibilitydistributionofthesubsurface,(ix)Helbig-typeanalysisofgriddedvectorcomponents,gradienttensorelements,andtensorinvariants,(x)methodsbasedonreductiontothepoleandrelatedtransforms, and (xi) remote in situ determination of NRMdirection, totalmagnetisation direction andKoenigsberger ratio by deploying dual vector magnetometers or a single combinedgradiometer/magnetometertomonitorlocalperturbationofnaturalgeomagneticvariations,operatinginbasestationmodewithinamagneticanomalyofinterest.Characterising the total and remanent magnetisations of sources is important for several reasons.Knowledge of totalmagnetisation is often critical for accurate determination of source geometry andposition. Knowledge of magnetic properties such as magnetisation intensity and Koenigsberger ratioconstrains the likely magnetic mineralogy (composition and grain size) of a source, which gives anindication of its geological nature. Determining the direction of a stable ancient remanence gives anindicationoftheageofmagnetisation,whichprovidesusefulinformationaboutthegeologicalhistoryofthesourceanditsenvirons.

26


SourcesandsignificanceofcrustalmagneticanomaliesPoster-WednesdayJuly12-15:30-18:00

IdentificationofCr-magnetite,magnetiteandferritchromitein

NeoproterozoicserpentinitesPresenter:

HodelFlorent([email protected])

Authors: Hodel,F.,GéosciencesEnvironnementToulouse,OMP,Univ.ToulouseIII,CNRS,IRD,31400Toulouse,France/InstitutodeAstronomia,GeofísicaeCiénciasAtmosféricas,Univ.deSãoPaulo,05508-900SãoPaulo,BrazilMacouin,M.,GéosciencesEnvironnementToulouse,OMP,Univ.ToulouseIII,CNRS,IRD,Toulouse,FranceTrindade,R.,InstitutodeAstronomia,GeofísicaeCiénciasAtmosféricas,Univ.deSãoPaulo,SãoPaulo,BrazilCarlut,J.,InstitutdePhysiqueduGlobedeParis,Univ.ParisDiderot,UMR7154CNRS,Paris,FranceRousse,S.,GéosciencesEnvironnementToulouse,OMP,Univ.ToulouseIII,CNRS,IRD,Toulouse,FranceMeira,V.T.,DepartamentodeGeologiaeRecursosNaturais,Univ.DeCampinas,13083-872Campinas,BrazilDantas,E.L.,InstitutodeGeoci�ncias,Univ.deBras’lia,70910-900Brasília,BrazilPaix‹o,M.A.P.,InstitutoFederaldeEduca�ao,CienciaeTecnologiadeGoias,72811-580Luzinia,Brazil

MagnetiteisacommonserpentinizationproductwhileCr-magnetiteandferritchromiteareby-productsofCr-spinelalteration.TheoccurrenceofmagnetiteandCr-magnetitecouldprovide insightsonprocessesthataffecttheseafloor.Asironoxidescarrytheoceaniclithospheremagnetization,understandingtheirformationcouldhelpwithmagneticdatainterpretation.Ifpresentseafloorandmid-ridgehydrothermalprocessescouldbeassessedwithoceaniccampaigns,remnantsofpastoceanic lithospherecanonlybefoundwithinophioliticunits.Inordertoassessmagneticmineralogyofsomepartsoftheancientoceaniclithosphere,weinvestigate,here,throughpetrography,mineralchemistryandrockmagnetism,twomajorNeoproterozoicophioliticunits(800-700Ma)fromMorocco(BouAzzer,Anti-Atlas)andBrazil (SerradoQuatipuruandSerradoTapa,AraguaiaBelt).TheBou-Azzer serpentinesdisplayunique centimetric,massive andalmostpuremagnetite veins. Suchmineralizationsarerarelyobservedinserpentinites.Theyresultfromtheironleachingintheserpentinitesand subsequent ironprecipitation asmassive veins in an abyssal black smoker environment.Magneticmeasurementsrevealalowermagnetitecontentinhydrothermalizedserpentiniteshostingthemagnetiteveins,withlowestvalues(downto0.58wt.%)forbleachedserpentinitesconstitutingthewallrockofveins.Fresh serpentinites are characterized by relatively small sized magnetite grains, mainly pseudo-singledomain magnetites. Hysteresis parameters and first order reversal curves (FORC) diagram denote amagneticgrainssizethat increaseswiththealteration.Thiswell-markedtendency isalsorevealedbyashiftoftheisothermalremanentmagnetization(IRM)componentstowardlowercoercivitiesforalteredserpentinites. This grain size increase is associatedwith the emergence of a newmagnetic phase, Cr-magnetite,resultingfromthehydrothermalalteration.TheCr-magnetiteisevidencedbythermomagneticmeasurementswithTcaround540°C.ThisultimateCr-spinelalterationproductisassociatedwithanotherCr-spinel alterationmineral, the ferritchromite, also identifiable on thermomagnetic curves by a rapidincreaseofthemagnetitesusceptibilityat130°Cduetoitstransformationduringheating.TheSerradoQuatipuruandtheSerradoTapaophiolitesinBrazildisplayadifferentmagneticmineralogy.Fromthermomagneticcurvesaswellasmicroprobesanalysis,magnetiteisabundantwhileCr-magnetiteisalmostabsentandferritchromiteslightlyrepresented.Inbothophiolites,serpentinizationtemperatures

27


rangebetween200 °C and350°C, but tectonic setting andhydrothermalprocesses aredifferent. Suchdifferencesresultinvariousmagnetite/Cr-magnetiteratio,anddifferentconcentrationsofmagnetitethatcouldinducestrongmagnetiteanomalies.Thermomagneticcurvesallowustoproposeaproxy,theCrM/Mratio,whichprovidesaquantificationoftheCr-magnetitecontributionwithrespecttothepuremagnetiteone. Similarly, the correlation slope between susceptibility increase due to the ferritchromitetransformationaround130°Candsubsequentdecreaseofthelikelyproducedmaghemite,givesinsightonthe ferritchomite composition as evidenced by microprobe analysis. Susceptibility as a function oftemperaturecurvesarethereforeusefultodiscriminatebetweenmagnetiteandCr-magnetiteaswellasdetectingdifferentcompositionsofferritchromite.

28



AreviewofglobalmarinemagneticanomaliesatEocenetime

Presenter:

CarmenGaina([email protected])

Authors: CarmenGaina,UIO,Oslo,NorwayInmanyoceanicbasins,thelithosphereformedatmid-Eocenetimedocumentschangesinthetectonicplatemotions.AdramaticchangeintheopeningoftheNortheastAtlanticoceanobservedaroundchron21o(47.9Ma)seemstohavebeentriggeredbychangesinbothabsoluteandrelativeplatemotions(Gainaetal.,2009;Gainaetal.,2017).IntheIndianOcean,rigorousplatecircuitanalysishasalsoshownalargebutgradualslowdownontheCentralIndianRidgeandSEIndianRidgestartingshortlyafterchron23o(51.9Ma)��t�h�a�t��c�o�n�t�i�n�u�e�d��u�n�t�i�l��c�h�r�o�n��2�1�y��(�4�5�.�3��M�a�)��(�C�a�n�d�e��e�t��a�l�.�,��2�0�1�0�)�.��C�h�a�n�g�e�s��i�n��e�a�r�l�y��C�e�n�o�z�o�i�c��s�p�r�e�a�d�i�n�g��d�i�r�e�c�t�i�o�n�s��b�e�t�w�e�e�n��t�h�e��P�a�c�i�f�i�c��a�n�d��a�d�j�a�c�e�n�t��t�e�c�t�o�n�i�c��p�l�a�t�e�s��w�e�r�e��r�e�c�o�r�d�e�d��b�y��n�u�m�e�r�o�u�s��f�r�a�c�t�u�r�e��z�o�n�e��i�n��t�h�e� �P�a�c�i�f�i�c� �o�c�e�a�n�,� �a�n�d� �t�h�e� �â�¬ S�b�e�n�d�â�¬_� �i�n� �t�h�e� �E�m�p�e�r�o�r�-�H�a�w�a�i�i�a�n� �h�o�t�s�p�o�t� �t�r�a�c�k� �t�h�a�t� �d�e�v�e�l�o�p�e�d� �i�n� �t�h�e� �e�a�r�l�y� �t�o� �m�i�d�-�E�o�c�e�n�e� �(�S�h�a�r�p� �a�n�d� �C�l�a�g�u�e�,� �2�0�0�6�;��T�o�r�s�v�i�k��e�t��a�l�.�,��2�0�1�7�)��s�h�o�w�i�n�g��a��c�h�a�n�g�e��i�n��e�i�t�h�e�r��t�h�e��P�a�c�i�f�i�c��a�b�s�o�l�u�t�e��p�l�a�t�e��m�o�t�i�o�n�,��c�h�a�n�g�e�s��i�n��m�a�n�t�l�e��c�o�n�v�e�c�t�i�o�n�,� �o�r� �t�h�e��p�l�u�m�e��c�o�n�d�u�i�t�.� �I�n��t�h�e��s�a�m�e��t�i�m�e�,� �a� �s�t�u�d�y��o�f� �g�l�o�b�a�l� �p�l�a�t�e��m�o�t�i�o�n�s� �a�n�d��d�i�s�t�r�i�b�u�t�i�o�n��f�o�r� �t�h�e��l�a�s�t��1�5�0��M�a��h�a�s��s�h�o�w�n��t�h�a�t��E�a�r�l�y��C�e�n�o�z�o�i�c��g�l�o�b�a�l��l�i�t�h�o�s�p�h�e�r�i�c��n�e�t��r�o�t�a�t�i�o�n��e�x�p�e�r�i�e�n�c�e�d��a��d�r�a�m�a�t�i�c��i�n�c�r�e�a�s�e��a�r�o�u�n�d��6�0��M�a��f�o�l�l�o�w�e�d��b�y��a��s�u�d�d�e�n��d�e�c�r�e�a�s�e��a�t��5�0��M�a�,��p�o�i�n�t�i�n�g��t�o��a��s�e�r�i�o�u�s��d�e�c�o�u�p�l�i�n�g��b�e�t�w�e�e�n��m�a�n�t�l�e��a�n�d��l�i�t�h�o�s�p�h�e�r�e��(�T�o�r�s�v�i�k��e�t��a�l�.�,��2�0�1�0�)�.��T�h�i�s��s�t�u�d�y��r�e�v�i�e�w�s��t�h�e��m�a�g�n�e�t�i�c��a�n�o�m�a�l�i�e�s��o�f��m�i�d�-�E�o�c�e�n�e��a�g�e��i�n��o�c�e�a�n�i�c��a�r�e�a�s��t�h�a�t��e�x�p�e�r�i�e�n�c�e�d��t�e�c�t�o�n�i�c��e�v�e�n�t�s��w�h�i�c�h��i�n�f�l�u�e�n�c�e�d��t�h�e��d�i�r�e�c�t�i�o�n��o�r��s�p�r�e�a�d�i�n�g��r�a�t�e�s��o�f��o�c�e�a�n�i�c��c�r�u�s�t��f�o�r�m�a�t�i�o�n�.��W�h�e�n��a�v�a�i�l�a�b�l�e�,��w�e��l�o�o�k��a�t��o�t�h�e�r��g�e�o�p�h�y�s�i�c�a�l��d�a�t�a�,��l�i�k�e��s�e�i�s�m�i�c��r�e�f�l�e�c�t�i�o�n�,��f�o�r��c�o�n�s�t�r�a�i�n�i�n�g��t�h�e��s�t�r�u�c�t�u�r�e��o�f��o�c�e�a�n�i�c��l�i�t�h�o�s�p�h�e�r�e��a�t� �t�i�m�e�s� �o�f� �c�h�a�n�g�e�s�.� �F�i�n�a�l�l�y�,� �r�e�g�i�o�n�a�l� �a�n�d� �g�l�o�b�a�l� �t�e�c�t�o�n�i�c� �m�o�d�e�l�s� �w�i�l�l� �b�e� �a�n�a�l�y�z�e�d� �a�n�d� �d�i�s�c�u�s�s�e�d� �t�o� �t�e�s�t� �w�h�e�t�h�e�r��a��d�r�a�m�a�t�i�c��d�e�c�o�u�p�l�i�n�g��b�e�t�w�e�e�n��l�i�t�h�o�s�p�h�e�r�e��a�n�d��m�a�n�t�l�e��c�o�u�l�d��h�a�v�e��t�r�i�g�g�e�r�e�d��p�r�o�f�o�u�n�d��c�h�a�n�g�e�s��i�n��g�l�o�b�a�l��o�c�e�a�n�i�c��b�a�s�i�n�s�.��

29



Remanentmagneticanomaliesandconsequencesofexsolutionofand

uncompensatedspinsatinterfacesinmagneticmineralsPresenter:

SuzanneA.McEnroe([email protected])

Authors: SuzanneA.McEnroe,NorwegianUniversityofScienceandTechnology,SemSælandsveg1,N-7491Trondheim,NorwayPeterRobinson,GeologicalSurveyofNorway,Postboks6315Sluppen,7491,Trondheim,NorwayNathanChurch,NorwegianUniversityofScienceandTechnologyKarlFabian,GeologicalSurveyofNorway,Trondheim,NorwayGeertjeterMatt,NorwegianUniversityofScienceaTechnologyAlexanderMichels,NorwegianUniversityofScienceandTechnologyZeudiaPastore,NorwegianUniversityofScienceandTechnologyRichardHarrison,NorwegianUniversityofScienceandTechnologyandDeptEarthScience,Univ.ofCambridgeUKLaurieBrown,UniversityofMassachusetts-Amherst,USA

Magneticanomaliesaremappedtodayovermanylengthscales,fromtheplanetarytothemicroscopic.Anomalies incrustalrocksreflectthemagneticminerals,whichtovariousdegreesrespondtochangingplanetarymagneticfields.Anomaliesareinfluencedbythegeometryofgeologicalbodiesandthemagneticpropertiesoftherocks,includingtheratiosofremanentversusinducedmagnetizationsandtherelativevector orientations of the two. Here we highlight how phase separation (exsolution) and resultantinterfacesinmagneticmineralsaffectthenatureofmagneticanomaliesatmanyscales.Rockscontainingmainlyrhombohedraloxideswithexsolutionlamellaeofhematiteinilmenite,orilmeniteinhematite,havehighQvaluesandtypicallyhaveremanent-dominatedanomalies.Alargecomponentoftheirmagnetizationsiscarriedattheinterfacesofthelamellae.Whenmagnetiteisaco-existingoxide,theQvaluesmaybelower,duetotheadditionofalargerinducedcomponent,butcommonlyQvaluesare>2,thusretainingthestrongerinfluenceoftheremanentcomponent.Rockswithoxidesinvolvingilmeniteandmagnetite are characterized by two related exsolution systems. Typically, oxidation-exsolution ofilmenite frommulti-domainmagnetite produces induced anomalies commonlywithQ values 10. Thisstrongremanenceeffect,presumablyrelatedtophase interfaces,hasyettobefullyunderstood. Bothrhombohedralandcubicoxideexsolutionlamellaearecommoninsilicatesinintrusiveandmetamorphicrocks, notably in pyroxenes and feldspars. Microstructures created by phase separation, includingoxidation/reductionexsolution,canhaveprofoundeffectsonanomaliesoverrocks,eitheratthesurfaceor at depth, by changing the intensity, the temperature stability (paramagnetic tomagnetic) and thecoercivityofthemagneticphases.Rocks fromwell characterized localities from around the world are presented andmineral propertiesexploredinrelationshiptothebulkmagneticresponseofrockbodies.Studiesonsyntheticferri-ilmenitesamples have complemented our understanding of the magnetic behavior of rocks over a widetemperaturerange.

30



Superconductingmagnetometerasatoolformappingmagneticanomalies

Presenter:

HirokuniOda([email protected])

Authors: HirokuniOda,GeologicalSurveyofJapan/AISTSuperconducting magnetometers or superconducting quantum interference device (SQUID)magnetometersusemagnetic sensorsallowingmagneticanomalymappingwithhigher sensitivity thanmostoftheothermagneticsensorssuchasfluxgatesensors,protonprecessionsensors,etc.However,theneed for the sensors to be cooled down with liquid He or nirogen has prevented the use in severeenvironmentslikeunderwaterorspace.Ontheotherhand,thankstothesensitivityofthemagnetometers,thesystemcanbedeveloped to formvectorcomponentmagnetometers,gradiaometersand/orarrayswitharelativelyshortbaselines.Inthepresentation,(i)IwouldliketointroducesuccessfulapplicationsofSQUIDmagnetometers inmagneticmappingof archeology andgeophysics. Further, (ii) Iwould like tointroducescanningSQUIDmicroscope(SSM)usedfornon-destructivedetectionofelectriccircuitsfailures,studyofsuperconductingmaterialsandbiomagneticapplications.Then,(iii)SSMforgeologicalsamplesdevelopedinGSJ/AISTwillbepresentedfollowedbysuccessfulapplicationsofscanningSQUIDmicroscopyin paleomagnetism and rock magnetism. The applications include sub-millimeter scalemagnetostratigraphyappliedtoferromanganesecrust,magneticmappingoffaultgaugesamples,etc.(iv)AnothertopicismappingofmagneticfieldproducedbysinglemineralgrainswithNRMusinganSSMandcalculation of magnetic dipole moments (i.e. intensities and directions), which is important forpaleomagnetists. (v) Further, magnetic mapping of rock magnetic properties (ARM, IRM etc.) will bediscussedtogetherwiththe2Dinversion.Startingfromtheinversionofrockmagneticpropertiesisagoodidea, because inversion of ARM or IRM with basically unidirectional magnetization should be easiercomparedwithNRM,whichcanbecomplexwithmultiplemagnetizationeventstypicalforpaleomagneticsamples.Finally, (vi)magneticmappingofprismsampleswithSSMwillbepresentedtogetherwiththemeasurementsusingpass-throughsuperconductingmagnetometersonlong-coreoru-channelsamples.

31


SourcesandsignificanceofcrustalmagneticanomaliesPoster-WednesdayJuly12-15:30-18:00

MODELLINGOFHIGHRESOLUTIONMAGNETICMICROSCOPYDATA:ANAPPLICATIONTOASERPENTINECARBONATEMAGNETITESAMPLEFROM

MODUM,NORWAYPresenter:

ZeudiaPastore([email protected])

Authors: ZeudiaPastore,NorwegianUniversityofScienceandTechnology(NTNU)NathanChurch,NorwegianUniversityofScienceandTechnology(NTNU)SuzanneMcEnroe,NorwegianUniversityofScienceandTechnology(NTNU)

Scanningmagneticmicroscopyisahighlysensitiveandhigh-resolutiontechniqueformappingtheNRMmagneticfieldoveraplanarsurfaceofarocksample.Thetechniqueoffersaspatialresolutiondowntotensofmicrometersand thuscanbeused to investigatediscretemagneticmineralgrainsormagnetictexturesandstructures.ThescanningdeviceusedinthisstudyisequippedwithamagnetictunneljunctionsensorandHelmholtzcoilsaroundthesamplespaceenablingthemeasurementoftheremanencefieldinfield-free conditions, or alternatively of the induced magnetization in a controlled magnetic field.Measurementsareperformedatroomtemperature.Wepresentascase-studyathinsectionmagneticscanofaserpentinecarbonatemagnetitesamplefromModum, in southern Norway. Across the selected thin section is a 2 to 6millimeterswidemagnetitesurroundedbyserpentineandcarbonate.Themagnetiteispredictedtoexhibitmultidomainbehaviorandinanappliedfieldwouldcontributetoinducedanomalies.Twoscansweremadeoverthethinsection:oneameasureoftheverticalcomponentBzoftheNRMmagneticfield,theothertheverticalcomponentBzofthemagneticfieldwhileapplyinganinducingfieldof40µTintheplaneofthesample,paralleltothetrendofthemagnetitegrains.Wepresentthepreliminaryresultsobtainedapplyingaforwardmodellingapproachonthemagneticanomalymapsacquiredoverthethinsection.Modellingconsistsofuniformly-magnetizedpolygonalbodieswhosegeometryisconstrainedbythethicknessofthethinsectionandbytheshapeofthemagnetitegrains.WeusedtheinducedfieldanomaliestocharacterizetheextentoftheindividualpolygonsinsidethemagnetiteandthenwemodelledtheNRMdirectionineachpolygontofittheNRMmagnetic field.Modellinghelps indetermining theNRMdirectionsand intensitiesofdiscretemagnetic sources inside themagnetiteand thusprovidesapowerful tool fordetailedstudyof the linkbetweenthemagneticpetrologyandthemagneticanomalies.

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SourcesandsignificanceofcrustalmagneticanomaliesOral-TuesdayJuly11-14:00-14:15

Measuringremanenceundervariablepressureandtemperatureusinga

cryogenicmagnetometerPresenter:

PierreRochette([email protected])

Authors: P.RochetteN.LaunayN.BezaevaF.DemoryJ.Gattacceca

We present two applications at variable temperature of a nonmagnetic pressure cell withmaximumpressure 1.6 GPa that can be loaded into the 2Gmagnetometer. By cooling the cell to 250 K with asaturatedhematitesampleandallowingittowarmupinthecryowehavepreciselydeterminedin[1]thepressuredependenceoftheMorintransition:25±2K/GPa.Morintransitionoccursatroomtemperatureat1.5GPa.IntheMarscrustcaselargeimpactscancycleasignificantportionofthecrustthroughoutthetransition.In[2]wehaveacquiredTRMunderpressureontitanomagnetitewithCuriepointsinthe290-310Krange.WehavethenthermallydemagnetizedthisTRM,allowingtoestimatetheCuriepointpressuredependenceat15-20K/GPa.TRMintensityalsoincreasesunderpressure.BotheffectscauseasignificantenhancementofdeepcrustalmagnetizationintheEarthcase,ifextrapolatedtopuremagnetite.[1] Bezaeva et al. (2015)The effect of hydrostatic pressure up to 1.61 GPa on theMorin transition ofhematite-bearingrocks:Implicationsforplanetarycrustalmagnetization.GRL42,10188-10196.[2]Launay et al. (2017). Thermoremanence acquisition anddemagnetization for titanomagnetite underlithosphericpressures.GRLaccepted.

33


EnvironmentalMagnetism

Orals:WednesdayJuly12–08:30-12:00KoningsbergergebouwPangea

Posters:WednesdayJuly12-15:30-18:00

deVagant

Convenors:FabioFlorindo&YongxinPan

start end talk+Q&A Presenter abstracttitle

08:30 09:15 30+15 KennethKodama High-ResolutionRockMagneticCyclostratigraphyandtheDurationoftheShuramC-isotopeExcursion

09:15 10:00 30+15 AndrewRoberts Newmeasurementprotocolsforhysteresisreversalcurvesandidentificationofmagneticmineralcomponentsinenvironmentalmagnetism

10:00 10:30 30 coffeebreak 10:30 11:15 30+15 BarbaraMaher Magnetiteiseverywhere.11:15 11:30 10+5 EricFont Themagnetic,mineralogicalandgeochemical

signatureoftheDeccanvolcanismintheglobalsedimentaryrecord

11:30 11:45 10+5 JoyMuraszko ClimatevariabilityintheSWIberianMargin:newinsightsfromFORC-PCA.

11:45 12:00 10+5 TilovonDobeneck CyclicmagnetitedissolutioninabyssalNorthwestPacificsediments-evidenceformassiveglacialcarbontrapping

34


Posters


abstracttitle

ElenaDegtyareva Usingpetromagneticdataforsectionallayeringofmonotonoussedimentarysequence

ChristineFranke "Magneticfingerprinting"offluvialsuspendedparticlesinthecontextoffertilesoilerosion:exampleoftheCancheRiverwatershed(Nord-Pas-de-Calais,France)

ChristineFranke EnvironmentalmagnetismasatracerofurbanmetallicpollutioninSeineRiversediments(Paris,France)

RobertGHatfield CharacterizingthemagneticvariabilityoftheNordicBasalticProvince:Particle-sizespecificmagneticinsightsfrom72corescollectedbeforetheadventofthefieldofenvironmentalmagnetism.

DianaJordanova ExploringthedifferencesinmechanismsofsoilmagneticmemoryinrecentChernozemsandpaleosols

DianaJordanova RockmagneticpropertiesofremainsfromNeolithic'burnthousehorizon'(Mursalevosite,SWBulgaria)-influenceoffiringtemperature.

LuigiJovane AntarcticaicesheetevolutionduringupperEocene-middleMiocenethroughenvironmentalandrockmagneticstudies:examplefromasedimentarycorefromtheRossSea(DSDPLeg28)

MyriamKARS Non-steadystatemagneticmineraldiagenesisinaverydeepmethaniczoneinIzureararcmarinesediments

FranceLagroix EnvironmentalMagneticRecordoftheHarletz(NWBulgaria)LoessSequence

WeiLin/YongxinPan Magnetotacticbacteriainaquaticenvironments:implicationsforsedimentarymagnetismandglobalironcycling

PeterCLippert IronintheFire:UsingControlledHeatingExperiments,High-ResolutionFORCs,andLow-TemperatureRemanenceExperimentstoRevealFire'sMagneticFingerprint

SuzhenLiu EnvironmentalinterpretationofgreigitelayersintheCentralParatethys:evidenceforprimarypaleomagneticsignals

MelinaMacouin Spatialisationofurbanairborneparticulatematterpollutionusingmagneticproperties:casestudyofParis(France)

GrasianeLuzMathias MagneticsignaturesrelatedtoNorthBrazilianCurrentinthemarginoffNEBrazil:Insightsaboutcross-shelftransport

EllenPlatzman EnvironmentalMagneticRecordofHoloceneClimateVariabilityfromLakeMalawi,EastAfrica

BrendanT.Reilly DeconvolvingglaciomarinesedimentaryprocessinPetermannFjord,NorthwestGreenland,usingparticlesizespecificmagneticmeasurements

DanielRodelli BiogenicmagnetiteasanindicatorofchemicalstratificationinthesedimentcolumnofMamanguáRía(Paraty,Brazil)

SoniaROUSSE Spatialisationofmetalliccontaminationusingmagneticpropertiesinacarbonatedcontext(JebelRessas,Tunisia)

SarahP.Slotznick ProbingSequentialChemicalExtractionsforIronMineralogyusingMagneticMethods

AlekseyV.Smirnov ROCKMAGNETICINVESTIGATIONOFTHEMICHIGANBASINSOILSANDSEDIMENTSOVERLYINGTHEOIL-BEARINGSILURIANPINNACLEREEFS

35


PriyeshuSrivastava RockmagneticcharacteristicsofDeccanboles:Implicationsforpaleoenvironment

AlexisUrbalejo CharacterizingMagneticPropertiesinBelizeCoralsLuigiVigliotti MagneticpropertiesofmunicipalsolidwasteincinerationashesJoonasWasiljeff FirstglimpseontheenvironmentalmagneticrecordoflateEocenetolate

OligoceneagedUlantatalSequence,Nei-Mongol,ChinaAldoWinkler FifteenyearsofmagneticmonitoringofPMatINGV(Rome,Italy):key

results,perspectivesandoutreachactivities

36


EnvironmentalmagnetismPoster-WednesdayJuly12-15:30-18:00

Usingpetromagneticdataforsectionallayeringofmonotonoussedimentary

sequencePresenter:

ElenaDegtyareva([email protected])

Authors: ElenaDegtyareva,InstituteofPhysicsoftheEarthRAS,Moscow,RussiaStanislavaAkimova,InstitutdePhysiqueduGlobedeParis,France/InstituteofPhysicsoftheEarthRAS,Moscow,Russia

Theaimofthisstudyistoinvestigatethepaleoclimaticfeaturesbystudyingthepaleomagneticdata.Toimplementthisweproposetheusethemethodofunmixingpaleomagneticrecordofsedimentaryrocksontheferromagneticcomponentsbyanalyzingthespectraofsamplescoercivity(Kosarevaetal,2015),thermomagneticanalysis,aswellasthestudysusceptibilityofdifferentmagneticcomponents,basedonthehysteresisloopshape.Theobjectofthestudyisa5-mthicksequenceoftakyrdeposits,representedas a superposition of annual varvs, located in Danatinsky corridor area (foothills of Kopetdag,Turkmenistan). The stratigraphic sequence has been deposited for the past ~5000 years. Gratestratification on a thick layers (approximately 1mma year) andwell known conditions of its currentlysedinentationmaketakyrdepositsaperspectiveobjectforinvestigatethepaleoclimateonpaleomagneticdata.Wewill present the preliminary results frompaleomagneticmeasurements of the samples. Groups ofmagnetic components are obtained according to the analysis of magnetization and remanentmagnetizationcurves.Thesecurvesweretreatedinaspecialprogram,thatusewavelettransformationformagnetizationspectrumtoidentifythemagneticcomponents.Inallsamplesoftheselectedseriesclearlyobserved the BS component (biogenic soft), which is about 60% of the total samples magnetization.Component H (magnetic hard) is observed in all series of samples, and is about 15% of the totalmagnetization. We have identified the contribution of paramagnetic, superparamagnetic andferromagnetic susceptibility components to the common signal through the sequence. The analysis ofthesecomponentsrevealedthechangesinthematerialinfluxandformationofauthigenicmineralsthatcan indicateclimaticconditions.Wemadeasuppositionof thesedimentationconditionsbasedon thestudying of the magnetic components susceptibility variations. We also traced the correlation ofpaleomagneticsamplescharacteristicswithavarvchronologyofthesequence.Finally,wewillshowthepotential of using the petromagnetic data and paleomagnetic methods for detail paleoclimaticreconstructions.

37


EnvironmentalmagnetismOral-WednesdayJuly12-11:15-11:30

Themagnetic,mineralogicalandgeochemicalsignatureoftheDeccan

volcanismintheglobalsedimentaryrecordPresenter:

EricFont([email protected])

Authors: EricFont,IDL-FCUL,InstitutoDomLu’s,FaculdadedeCi�nciasdaUniversidadedeLisboa,CampoGrande,Lisbon,Portugal

ThecontributionoftheDeccanTrapsvolcanismintheCretaceous-Palaeogene(KPg)crisisisstillamatterofdebate.ThemainlimitationisthelackofmassextinctionproxieswithintheDeccanlavaflows,makinghardthecorrelationoftheDeccan-inducedclimatechangeswiththemassextinctionrecordedintheglobalmarinerecord.Analternativeistoinvestigatethemagneticandmineralassemblagesofremotemarinesection. Ironoxidesareverysensitivetochanges inredoxconditions,andthuscanbepossiblyusedasmarkers of paleoenvironmental changes driven by Deccan volcanism. This is the case in the Basque-Cantabricbasin(Bidart,Zumaya)andthewesternmarginoftheTethys(Gubbio),whereanintervaloflowmagnetic susceptibility (MS) containing akagenéite, a Cl-bearing oxyhydroxide described in acidic andhyper-chlorinated environments; features in the last 50 cm just below the KPgboundary. The lowMSinterval originated from the loss of detrital magnetite and magnetosomes, features consistent withreductive iron oxide dissolution possibly linked to environmental acidification. These magnetic andmineralogical benchmarks correlated with mercury anomalies in Bidart, reinforcing the link with theDeccaneruptions.TheseinsightsprovidenewandpromisingcluestoidentifythesignatureoftheDeccan-inducedpaleoclimaticandpaleoenvironmentalchangesintheglobalsedimentaryrecordandreinforcethetemporallinkbetweentheDeccaneruptionandtheKPgmassextinction.Keywords:Deccan,KPgmassextinction,acidification, ironoxidedissolution,magnetosome,akaganéite,mercury.PublicationsupportedbyFCT-projectUID/GEO/50019/2013-InstitutoDomLuiz

38



"Magneticfingerprinting"offluvialsuspendedparticlesinthecontextoffertilesoilerosion:exampleoftheCancheRiverwatershed(Nord-Pas-de-

Calais,France)Presenter:

ChristineFranke([email protected])

Authors: ChristineFranke,MINESParisTech,PSLResearchUniversity,CentredeGéosciences,35rueSaint-Honoré,77305FontainebleauCedex,France)EdouardPatault,LGCgE,IMTLille-Douai,DépartementGénieCivil&Environnemental,764boulevardLahure,59508DouaiCedex,FranceClaireAlary,LGCgE,IMTLille-Douai,DépartementGénieCivil&Environnemental,764boulevardLahure,59508DouaiCedex,FranceFranceLagroix,IPGP,ÉquipedePaléomagnétisme,1rueJussieu,75238ParisCedex05,FranceArnaudGauthier,LGCgE,IMTLille-Douai,DépartementGénieCivil&Environnemental,764boulevardLahure,59508DouaiCedex,FranceNor-EdineAbriak,LGCgE,IMTLille-Douai,DépartementGénieCivil&Environnemental,764boulevardLahure,59508DouaiCedex,France

IntheNorthofFrance,wherelanduseismainlydominatedbyagriculturalactivity,erosionbywaterrun-offresultsinheavylossoffertilesoilandleadstothegradualdisappearanceanddepletionofthisnon-renewableresourceathumantimescales.Additionally,watererosioncansignificantlydamagetheaquatichabitatandcanberesponsiblefortheinputofnutrients,bacteria,pesticidesorheavymetalsintosurfacewater. This study combines environmental magnetic characterisation (RT hysteresis parameters, LTremanence cycles) with other sediment-physical (grain size analyses, XRD, color spectroscopy) andgeochemicalanalyses(ICP)onsuspendedparticulatematter.Theobjectiveistodevelopeffectivetoolstotraceerosionbywaterrun-off.In 2015 and 2016, spatio-temporal sampling campaigns of suspended particulate matter (SPM) wereconducted at key positions along the Canche River and its tributaries using bottle sediment traps. RThysteresis curves of the recovered dry bulk SPMwere obtained using at the AGM 2900 of the LSCE.MagneticconcentrationoftheSPMevaluatedbyMrsorMsvaluesaretypicalofvaluesforagriculturalsoils in the region.However,magneticconcentrationandtotal iron fromgeochemicalanalysesarenotalways correlated. S-ratio data indicate that during low water conditions ('natural fluvial backgroundsignal')theCancheRiverSPMisdominatedbyasoftferrimagneticmineralassemblagewhileduringhighwaterstages(localrainevents)themagneticmineralassemblageisdominatedbyhighcoercivityphases.Increasedsoilerosion,especiallyviawaterrun-off,isexpectedduringrainevents.Theobservedtemporal(seasonal)variationsinthemagneticmineralassemblagewouldbeexpectediftheagriculturalsoilswereenriched in goethite and/or hematitewith respect to ferrimagnetic pedogenicminerals. Additional LTremanence experiments are being conducted on selected samples using the MPMS housed at IPGPproviding greater insight into the mineralogy of the magnetic phases of the SPM and surroundingagriculturalsoils.Wealsoattempttodeterminewhethermagneticgrainsizevariesbetweenlowandhighwaterconditionsandhowitcomparestosedimentarygrainsizevariations.

39



EnvironmentalmagnetismasatracerofurbanmetallicpollutioninSeine

Riversediments(Paris,France)Presenter:

ChristineFranke([email protected])

Authors: ChristineFranke,(1)MINESParisTech,PSLResearchUniversity,CentredeGéosciences,35rueStHonoré,77305FontainebleauCedex,FranceAudeIsambert,(2)InstitutdePhysiqueduGlobedeParis,UniversitéParisDiderot,SorbonneParisCité,UMR7154CNRS,1rueJussieu,75238ParisCedex05,FranceMélinaMacouin,(3)GéosciencesEnvironnementToulouse,UMR5563CNRSUR234IRD,UniversitéPaulSabatier,Toulouse,FranceSoniaRousse,(3)GéosciencesEnvironnementToulouse,UMR5563CNRSUR234IRD,UniversitéPaulSabatier,Toulouse,FranceAurélioPhilip,(1,2)MINESParisTech,PSLResearchUniversity,CentredeGéosciences,35rueStHonoré,77305FontainebleauCedex,France&InstitutdePhysiqueduGlobedeParis,UniversitéParisDiderot,SorbonneParisCité,UMR7154CNRS,1rueJussieu,75238ParisCedex05,FranceSybilleHenrydeVilleneuve,(2,3)InstitutdePhysiqueduGlobedeParis,UniversitéParisDiderot,SorbonneParisCité,UMR7154CNRS,1rueJussieu,75238ParisCedex05,&GéosciencesEnvironnementToulouse,UMR5563CNRSUR234IRD,UniversitéPaulSabatier,Toulouse,FranceYuyinWu,(2)InstitutdePhysiqueduGlobedeParis,UniversitéParisDiderot,SorbonneParisCité,UMR7154CNRS,1rueJussieu,75238ParisCedex05,France

Thepresenceofferruginousparticlesisoftenassociatedwithhighconcentrationsofheavymetals.Inurbanenvironment,environmentalmagnetismhasbeendemonstatedasan interestingtooltodeterminethespatialdistributionofmetalpollutioninsoils,sediments,dust,plants,amongothers.Thus,thenatureofurban fluvial sedimentsmayberelated to itsmultiplenaturaloranthropogenic inputsources (detrital,erosion, re-suspension, authigenic, run-off, traffic, industry,wastewater treatment, etc.; Frankeet al.,(2009).In the frameworkof theÇParis2030Èproject, twodistinctenvironmentsweresampled in2015-2016alongtheSeineRiverintheParisianagglomeration:theaquaticenvironmentrepresentedbyfluvialbankandriverbedsedimentsand theatmosphericenvironment,by regardingmagneticparticles trapped inadjacenttreebarks(Platanushispanica).About60sedimentsamplesand~200barksampleshavebeencollectedandanalyzed todetermine theirmagneticproperties (frequency-dependent susceptibility,RThysteresisparameters,IRM)andtoestimatethepresenceandspatialconcentrationofsuperparamagnetictomulti-domainparticlesforeachsampletype.RecentlyKayvantash(2016)characterizedtheferruginousparticlesof thesuspendedfractionalongtheSeineRiverprofileusingenvironmentalmagnetism.Additionally;Kayvantashetal.(2017)highlightedthelinkbetweenthehydrodynamicsofa(rural)SeineRiverbend,theoverallsuspendedsedimentloadandthemagneticfraction.Inthisstudy,theupstreamtodownstreamresultsoftheSeinesedimentsshowthatthemagneto-mineralogyismainlydominatedbymagnetite.However,thegrainsizedistribution(domainsize)differswithrespecttothetypeofsample(bed loadandriverbanksediments,suspendedparticlematter,etc)andthussuggestschangesinthecompositionmix(andthusofthesources)ofthemagneticparticles. For example, airborne particles from traffic combustion are typically spherule shaped (ofdifferentpossibledomainsize),whereasdetritalandscoriaparticlesbothhaverather irregularhabitus(althoughtheirtraceelementcompositionisratherdifferent)andmayrangefrommicro-tonanometersize.Thustheimportancetocombinethemagneticanalyseswithelectronmicroscopytechniques(SEM,

40


TEM) and geochemical analyses (ICP, XRF) to better distinguish and characterize the different particleclassesbeforebeingabletoadvancefurtherinthequantificationoftheirspecificcontributiontothebulkmagneticsignal.Franke,C.,Kissel,C.,Robin,E.,Bonté,P.,Lagroix,F.(2009).MagneticparticlecharacterizationintheSeineriver system: Implications for the determination of natural versus anthropogenic input. Geochemistry,Geophysics,Geosystems,10(8).Zayvantash,D., (2016).Characterizationof ferruginousparticles in theSeineRiverusingenvironmentalmagnetism,Ph.D.thesis,MINESParisTech/LSCE,France.Kayvantash, D., Cojan, I., Kissel, C., Franke, C., (2017).Magnetic fingerprint of the sediment load in ameanderbendsectionoftheSeineRiver(France),Geomorphology,286,14-26.

41



CharacterizingthemagneticvariabilityoftheNordicBasalticProvince:

Particle-sizespecificmagneticinsightsfrom72corescollectedbeforetheadventofthefieldofenvironmentalmagnetism.

Presenter:

RobertGHatfield([email protected])

Authors: BenjaminH.Wheeler,OregonStateUniversity.RobertG.Hatfield,OregonStateUniversity.JosephS.Stoner,OregonStateUniversity.

MarinesedimentsintheNorthernpartoftheNorthAtlanticOcean(NNA)arerichinferrimagneticmineralsthatareerodedfromsurroundingterrestriallandmassesand(re)distributedbysurfaceandoceancurrents.Downcorevariationsinbulk(wholesample)magneticpropertiesobtainedfromcorescollectedfromtheNNA often correlate to independent properties, e.g. Heinrich Events or Greenland Ice cores, and arefrequentlyinterpretedtoreflectvariabilityinsedimenttransportprocessesi.e.theincidenceoficerafteddebris(IRD)orfluctuationsinthestrengthofoceancurrents,ratherthanaschangesinsedimentsource.The'NordicBasalticProvince'(NBP),stretchingbetweenGreenland,Iceland,andNorway,isanimportantsubmarinesourceofmagneticmineralstotheNNAassedimentsfromthisregionareentrainedinoverflowwaters that form slope hugging contour currents and sediment drifts. Magnetic properties of NBPsediments have been considered relatively homogeneous, although little evidence exists for thisassumptioneverbeingtested,andasaresultspatialvariabilityacrosstheNBPthatmightcontributetovariationsinNNAsedimentsremainspoorlyconstrained.ToinvestigateNBPvariabilitywesampledcoretopmaterial(top2cm)from72pistoncoresrecoveredfromtheGreenlandandNorwegianSeasby theUSCGCEdisto in1963 (hereinafter referred toas theEdistoarray).Wefirstmademeasurementsofbulkmagneticsusceptibilityandbulkhysteresisparametersbeforerepeating these measurements on five sediment fractions (~ 63, 32-63, 10-32, 2-10, and ~ 2 µm)constitutingthebulksediment.BulkmagneticpropertiesvaryconsiderablyacrosstheEdistoarray.HighestbulksusceptibilityisfoundproximaltothelandmassesofJanMayenandIcelandandalongtheGreenland-Scotland sill. Coarsest bulkmagnetic grain sizes are found close toGreenland,Norway, and the FaroeIslandswhilefinestbulkmagneticgrainsizesarefoundacrosstheIcelandPlateausouthofJanMayenandin the deeper basin of the Norwegian Sea. When disaggregated into their constituent size fractionsmagnetic properties reveal strong particle size dependence. Across the entire array clays possessdisproportionatelylowsusceptibilities(thesameistrueforotherinfieldandremanentmagnetizations),the finestmagnetic grain sizes, and is the only fraction to possess array-wide spatial homogeneity. Incontrast,thesiltfractions,particularlythe10-32µmsortable-siltsizefraction,containsdisproportionatelyhighsusceptibilities(andMs,Mrs),coarsermagneticgrainsizes,andgreaterspatialheterogeneitythantheclayfraction.Theseobservationshaveimportantimplicationswhenconsideringbulkmagneticproperties.Forexample,thesilt-sizesedimentscontributeuptothreetimesmoretobulksusceptibility,Mr,andMrsvaluesthantheirphysicalabundancemightsuggest,whiletheclayfractionuniversallydepletesparameterssensitivetomagneticconcentrationandfinesmagneticgrain-size.TheseobservationscanpotentiallyhelpreconcileandexplainthecorrelationsbetweenmarinesedimentrecordsandGreenlandicecores,butalsocautionagainstassumptionsofhomogeneouspropertiesacrosssourceregions.

42



Exploringthedifferencesinmechanismsofsoilmagneticmemoryinrecent

ChernozemsandpaleosolsPresenter:

DianaJordanova([email protected])

Authors: DianaJordanova,NIGGG-BAS,Acad.G.Bonchevstr.,block3,1113Sofia,BulgariaNeliJordanova,NIGGG-BAS,Acad.G.Bonchevstr.,block3,1113Sofia,Bulgaria

Thephenomenaofpedogenicmagneticenhancementofwelldrained(aerated)soils iswellknownandwidely used in paleoenvironmental reconstructions based on studies of terrestrial loess-paleosolsequences. Still disputable is the exact mechanism of formation of the strongly magnetic magnetite(maghemite) responsible for this enhanced magnetic signal. However, little attention is paid on therelationshipbetweenthesoilformationmechanismandtheobservedmagneticsignaturealongdepthofthesoil (paleosol).Theeffectsof twocontrasting (and/orcompeting)soil formationmechanisms- top-down(classicalinsoilgenesisstudies)andup-building(accretionary)onthepossibleformationpathwaysandtimeevolutionofthestronglymagneticpedogenicfractioninsoilsdevelopedonloessdepositsareconsidered. Magnetic characteristics along depth of recent Chernozems and selected loess-paleosolcoupletsfromoutcropsinNEBulgariaareconsideredinlightofthetwopossiblesoilformationscenarios.Incaseofclassicaltop-downsoilformationmechanism,astablelandsurfacewithnegligibledustadditionsduringpedogenesisisestablished.Inthiscase,asoilisgraduallydevelopingindepthwithinthealreadyaccumulatedloessparentmaterial.However,themostintenseweatheringandliberationofferrousFe,necessaryprecursorfortheformationofpedogenicFeoxidesoccuratthedeepeningweatheringfront.This implies that theyoungestpedogenicoxideswillbe formedat thebottomof theprofile,while the'oldest'pedogenicfractionwillprevailinthetopmostsoilhorizons.Intermsofmagneticsignature,itwouldresultinenhancedSPferrimagneticfractionindeepersoillevelsanddominanceofSD-likebehaviorintheuppermost(humic)horizonsifwesupposethatthepedogenicstronglymagneticgrainsgrowwithtime.Examplesofsuchtypeofmagneticbehaviorwillbepresented.Inthesecondscenario,widelyapplicabletothefamousChineseloess-paleosolsequences,pedogenesisanddustdepositionareactingsimultaneouslyanddeterminetheaccretionalcharacterofthe(paleo)soils(atleastfortheHoloceneera).Evenissuchacase,dependingontherelativeimportanceofpedogenesisintensityversusdustaccumulation,stillsometop-downphasesinthesoildevelopmentcoulddesupposed.Thecombinationofthetwomodesofsoilformation will result inmore complex variation ofmagnetic parameters along the solum. It could besupposedthatup-buildingpedogenesiswillresultinnormal(sedimentarylike)depth-agedependenceforthe pedogenicmagnetic grains. Alongwith it, both SP and SD-like fractionswould have similar depthdistribution. Examples of magnetic behavior along paleosols possibly formed through subsequentpaleoenvironmentalconditionsfavoringupbuildingandtop-downsoilformationmechanismswillbegivenanddiscussed.

43



RockmagneticpropertiesofremainsfromNeolithic'burnthousehorizon'(Mursalevosite,SWBulgaria)-influenceoffiringtemperature.

Presenter: DianaJordanova([email protected])Authors: NeliJordanova,NIGGG-BAS,Sofia,Bulgaria

DianaJordanova,NIGGG-BAS,Sofia,BulgariaMariaKostadinova-Avramova,NIGGG-BAS,Sofia,BulgariaDejanLesigyarski,NIGGG-BAS,Sofia,Bulgaria

Neolithicsettlements(ca.6-5thmillenniumBC)foundinvastareasontheBalkansareallcharacterizedbymassiveaccumulationofburnedclayrubbleindicativeofstrongfireswhichoftenencompassallancienthouses.Thishasledarchaeologiststocallthephenomenon'burnthousehorizon'butitsexplanationisstillamatterofdebate.Oneofthemostdiscussedhypothesessuggestsdeliberatehouseburningwithritualpurposesbecausemanyexperimentalarchaeologytestsimplythatadditionalhugeamountoffuelmusthavebeenaddedduringhouseburninginordertoreachthemassivebrick-likelookwithvitrificationsignsfoundinarchaeologicalsites.BurntclaysamplesfromalargeNeolithicsettlementMursalevo(SWBulgaria)weregatheredforrockmagneticinvestigationsanddeterminationofmaximumfiringtemperature.Theresults obtained show that burnt claymost often contains amixture ofmagnetite-likemineral of lowcoercivity and a high-coercivitymineral, identified as hematite.Hematite's contribution ismost clearlyexpressedinmagneticpropertiesoforange-redcoloredsamplesshowingwasp-waistedhysteresisloops,whilebrowncoloredclayisdominatedbymagnetite/maghemite.Purple-coloredvitrifiedclaymaterialischaracterizedbythepresenceoftwocoercivitycomponentswhichhowevershowhighercoercivitiesthanthecorrespondingcomponentsofotherburntclaymaterials.Hysteresisloopsforvitrifiedclayareeithernormal(magnetite-like)orpot-belliedandsaturationmagnetizationisthestrongestamongallsamples.Itissupposedthatpurplecolorisduetotheformationofhigh-temperaturehematite,resemblingpigmentaryfine-grained phase often reported to exhibit such specific color. At the same time, percent frequencydependentmagneticsusceptibility isthehighestfororange-redburntclay(10-12%)andthe lowest- inpurplecoloredsamples(1-4%),suggestingthatthemostimportantshareofultra-finestronglymagneticmagnetite/maghemite is characteristic for well oxidized burnt clay. Ancient firing temperatures wereestimated applying the laboratory step-wise re-firing followedby room-temperaturemeasurements ofmagnetic susceptibility, as suggested by Rassmussen et al. (2012). The estimates obtained show thatNeolithichouseswereburnttoquitehightemperaturesvaryingbetween720-1140degreesC.Relatedtothe clay color, brown coloredmaterials were fired to the lowest temperatures, while purple vitrifiedmaterialsreachedtemperaturesabove1000degreesC.

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AntarcticaicesheetevolutionduringupperEocene-middleMiocenethroughenvironmentalandrockmagneticstudies:examplefromasedimentarycore

fromtheRossSea(DSDPLeg28)Presenter:

LuigiJovane([email protected])

Authors: Jovane,L.1Rodelli,D.1

Earth'sclimatesawamajorshiftfromgreenhousetoicehouseconditionsduringCenozoic,thatculminatedwiththepermanentonsetofcontinentscaleAntarcticicesheetatca.34Ma.GlobaltemperaturesduringtheOligocene,aswellasthesizeoftheAntarcticicesheet,fluctuatedonshort(~500Kyr)andlong(2-3Myr) timescales, terminatedwith amajor increase in size of the Antarctic ice sheet at theOligocene-Miocene transition.Thecausesof such fluctuationsare stillnot fullyunderstood,butareknown tobeinfluencedbyorbitalparametervariations.Orbitalparametervariationplayedanevenmore importantroleduring the lowerMiocene,whereglobalclimatestarted tobecontrolledbyeccentricityvariationsratherthanobliquity,inamuchsimilarwayofwhathappenedinthelast800thousandyears.ThisshiftisassumedtobeoneofthefactorsthatcontributedtotheonsetoftheMiddleMioceneClimaticOptimum(MMCO).Inthispaper,wepresentacompletepaleomagneticstudyofcoresfromtheRossSea(DSDPleg28,site274),thatrepresentstheperiodbetweentheupperEoceneandmiddleMiocene,thereforeabletoregisterthevariationsof the ice sheetcharacteristics since its formation.Themagnetostratigraphic recordwasused toprovidemuchmore reliableandhigher resolutionage constraint than thepreviouslyavailablebiostratigraphy(byshipboardscientificparty)fortheenvironmentalmagneticstudy.TheinfluenceoftheoscillationsintheAntarcticicesheetproducedmarkeddifferencesinthemagneticmineralassemblagesalong the stratigraphic section, with periods of warmer and cooler climate recognizable as a generalincreaseofbiogenicmagnetiteanddecreaseofbiogenicmagnetite,respectively.Fertilizationofthewater,thatultimatelycontrolstheproductionofbiogenicmagnetite,wasprobablycarriedduringmassdiscargeofsedimentfromtheretreatingicesheet,insteadofdusttransportedwindasmorecommonlythecase.

45



Non-steadystatemagneticmineraldiagenesisinaverydeepmethaniczone

inIzureararcmarinesedimentsPresenter:

MyriamKARS([email protected])

Authors: MyriamKARS,CenterforAdvancedMarineCoreResearch,KochiUniversity,JapanRobertJ.MUSGRAVE,GeologicalSurveyofNewSouthWales,AustraliaandSchoolofGeosciences,TheUniversityofSydney,AustraliaKazutoKODAMA,CenterforAdvancedMarineCoreResearch,KochiUniversity(nowatDoshishaUniversity,Japan)Ann-SophieJONAS,InstituteofGeosciences,Christian-AlbrechtsUniversity,Germany

MagneticmineraldiagenesisisanimportantprocessinsedimentsthatisresponsibleforthepartialortotaldestructionofthepastEarth'smagneticfieldrecord,aswellasforironandsulfurcycling.Arockmagneticstudyon114mudstonesampleshasbeencarriedoutatIODPExpedition350SiteU1437intheIzuBoninreararcinordertoinvestigatethemagneticmineraldiagenesisindeeplyburiedsedimentsfrom~775to1002metersbelowseafloor(mbsf)withburialtemperaturerangingfrom~65to83°C.Thesitepresentsnon-steadystategeochemicalconditionswithanunusualdeepmethaniczone(below850mbsf)becauseof a release of sulfate below the shallow sulfate reduction zone (~27-83mbsf). Remanence and rockmagneticmeasurements,includinglowtemperaturemagneticmeasurementsandFORCdiagrams,werecarriedoutinordertoinvestigatetheconcentration,grainsizeandcompositionofthemagneticmineralassemblage.Fourmagneticzonesaredefinedbasedontheirgascontentandmagneticproperties:Zone1(~775-850mbsf),Zone2dividedinsubzones2A(~850-870mbsf)and2B(~870-936mbsf),Zone3(~936-949mbsf)andZone4(~949-1002mbsf).Adrasticdecreaseofthemagneticsusceptibilityandremanenceisobservedat~850mbsf(passagefromZone1toZone2),asaresultofadecreaseinferrimagneticironoxideconcentration.Reductionof(titano)-magnetitewhichisthemainmagneticcarrieridentifiedoccursatthisdepth.InZones2and4,decreasingvaluesofthemagneticpropertiesandlowermagneticmineralcontentscoincidewithastrongerreleaseofmethane(downto~1000mbsf).Inthisoveralllowmagneticintensity interval, a localmaximum (Zone3)occurspresenting similaritieswithZone1. Thisdiageneticzonation characterized by typical magnetic properties and mineralogy is supported by geochemicalanalysesandphysicalproperties,andcanbeexplainedbyapetroleumsystem-likesetting.

46


EnvironmentalmagnetismOral(invited)-WednesdayJuly12-08:30-09:15

High-ResolutionRockMagneticCyclostratigraphyandtheDurationofthe

ShuramC-isotopeExcursionPresenter:

KennnethP.Kodama([email protected])

Authors: DanielMinguezYong-xiangLiZhengGong

Using rockmagnetic cyclostratigraphywewere able to identify astronomically-forced climate cycles inthreegloballydistributedoccurrencesoftheShuramC-isotopeexcursion,DeathValleyCA,SouthAustralia,andSouthChina.TheShuramexcursionmayrecordtheoxidationoftheworldoceanintheEdiacaran,justbeforetheCambrianexplosionofmetazoans.Paleomagnetismsuccessfullyyieldedamagnetostratigraphyattwooftheselocalities,theJohnnieFormationinDeathValleyCAandtheWonokaFormationinSouthAustralia.TherockmagneticcyclostratigraphyindicatedadurationfortheShuramexcursionof8.2±1.2Myrand8.0±0.5Myr,respectively,basedontheidentificationofastronomically-forcedclimatecyclesintherockmagnetictimeseries.InSouthChina,rockmagneticcyclostratigraphyalsoallowedidentificationof Milankovitch cycles and a duration for the Shuram excursion of 9.1±1.0 Myr in the DoushantuoFormation, but the paleomagnetism of the detrital magnetite in the rocks was remagnetized in theCretaceous, thusnomagnetostratigraphycouldbedeveloped.AtDeathValleyandSouthAustraliaourresults indicate that the nadir of the Shuram C-isotope excursion occurs at a reversed to normalgeomagneticfieldpolaritytransition,thusstronglysupportingsynchroneityoftheexcursiongloballyand,withsimilardurationsworldwide,aprimaryoriginfortheexcursion.

47



EnvironmentalMagneticRecordoftheHarletz(NWBulgaria)LoessSequencePresenter:

FranceLagroix([email protected])

Authors: FranceLagroix,InstitutdePhysiqueduGlobedeParis,SorbonneParisCité,UMRCNRS7154,Paris,FranceDianaJordanova,NIGGG,BulgarianAcademyofSciences,Sofia,BulgariaPierreAntoine,LaboratoiredeGéographiePhysique,UMRCNRS8591,Meudon,FranceJohannaLomax,DepartmentofGeography,Justus-LiebigUniversityGiessen,Giessen,GermanyDenis-DidierRousseau,ENS,UMRCNRS8539,LMD&CERES-ERTI,Paris,FranceNeliJordanova,NIGGG,BulgarianAcademyofSciences,Sofia,BulgariaLouiseMelot,InstitutdePhysiqueduGlobedeParis,SorbonneParisCité,UMRCNRS7154,Paris,FranceTaniaHabel,InstitutdePhysiqueduGlobedeParis,SorbonneParisCité,UMRCNRS7154,Paris,FrancePetarPetrov,NIGGG,BulgarianAcademyofSciences,Sofia,BulgariaMarkusFuchs,DepartmentofGeography,Justus-LiebigUniversityGiessen,Giessen,GermanyOlivierMoine,LaboratoiredeGéographiePhysique,UMRCNRS8591,Meudon,FranceChristineHatté,LSCE,UMRCEA-CNRS-UVSQ8212,Gif-sur-Yvette,FranceMaximeDebret,UFRSciencesetTechniques,UniversitédeRouen,Mont-Saint-Aignan,FranceSamN.Taylor,InstitutdePhysiqueduGlobedeParis,SorbonneParisCité,UMRCNRS7154,Paris,FranceJessicaL.Till,InstitutdePhysiqueduGlobedeParis,SorbonneParisCité,UMRCNRS7154,Paris,France;nowatInstituteofEarthSciences,UniversityofIceland,Reykjavik,Iceland

TheHarletzloesssequenceislocatedinNWBulgariaonthewesternbankoftheOgostaRiver,atributaryoftheDanube.Thesequenceisexposedonaclifffacecarvedbythemeanderingpaleo-OgostaRiver.A20msection,sittingontopoftheriver'salluvialplainwascleanedandsampledforamulti-disciplinarystudy.OSL age determinations and field observations suggest that the section spans the last two glacial-interglacialcyclesequivalenttomarineoxygenisotopestage(MIS)7tothepresent.High-resolutioncontinuousbulksamplingwascarriedouttocharacterisethecomposition,grain-sizeandconcentrationofthemagneticmineralassemblage.Orientedsampleswerealsocollectedforanisotropyofmagnetic susceptibility (AMS) analyses. In addition to features observed in the field, environmentalmagnetismdatarevealunobservedpedogenicalterationrelatedtoMIS3aswellasonebutpossiblytwotephra deposits. Analyses of IRM coercivity distributions, low temperature magnetic data and otherhysteresisparameterscharacterisethepedogeniccomponent,distinguishingitfromtheparentmaterial.OSLagedeterminationsandinferencesbasedonthetephraoccurrencesindicatethattheHarletzsequencearchivesoveradepthof10mafairlyhigh-resolutionanduniqueclimateandenvironmentalchangeduringthepenultimateglaciation(MIS6).Finally,magnetism-basedobservationsseemtobeabletodifferentiateaccretionarypedogenesisversusdown-buildingpedogenesis.

48



Magnetotacticbacteriainaquaticenvironments:implicationsfor

sedimentarymagnetismandglobalironcyclingPresenter:

WeiLin/YongxinPan([email protected])

Authors: WeiLin,InstituteofGeologyandGeophysics,ChineseAcademyofSciences,Beijing100029,ChinaYongxinPan,InstituteofGeologyandGeophysics,ChineseAcademyofSciences,Beijing100029,China

Anumberofmicroorganismsbiomineralizeintracellularorextracellularironminerals,whichnotonlyplayessential roles inbiogeochemical cyclingof ironbutalso representa significantcontribution tonaturalremanentmagnetismofsediments.Oneofthemostinterestingexamplesofthesetypesoforganismsarethemagnetotacticbacteria(MTB),apolyphyleticgroupofprokaryotesthatuptakeironfromenvironmentsandformintracellularnano-sizedironmineralsofmagnetiteand/orgreigite,knownasmagnetosomes.Our recent phylogenetic analysis has revealed an unexpected diversity of MTB in various aquaticenvironments.ItshowsthatthecompositionofMTBcommunitiesrepresentsabiogeographicdistributionacross globally heterogeneous environments, and both environmental heterogeneity and geographicdistanceplaysignificantrolesinshapingtheircommunitycomposition.Atthespatialscaleinthisstudy,thebiogeographyofMTBisrelativelymoreinfluencedbyenvironmentalfactorsthangeographicdistance,suggestingthatlocalenvironmentalconditionsoverridestheeffectsofdispersalhistoryonstructuringMTBcommunity. We also found that the strength of the Earth's magnetic field appears to influence thebiogeographyofMTB,implyinganimpactofgeophysicaleffectsonthesemicroorganisms.BuildingontheknowledgeonMTBdiversityandbiogeography,weestimatethepotentialcontributionsofMTBtotheglobalironcycling,e.g.,theannualyieldofFe3O4byMTBis~10^8kg.Theseresultssuggestthat MTB communities play important roles in the present-day global iron cycling and perhaps thedeposition of iron formation through geological history. Moreover, since the species-specificmagnetosomescouldbepreservedinsediments,magnetofossilswillopenanewavenuetorockmagnetic,paleomagneticandpaleoenvironmentalstudies.References:Lin,W.,Bazylinski,D.A.,Xiao,T.,Wu,L.-F.,andPan,Y.(2014)Lifewithcompass:diversityandbiogeographyofmagnetotacticbacteria.EnvironMicrobiol16:2646-2658.Lin,W.,Pan,Y.,andBazylinski,D.A.(2017)Diversityandecologyofandbiomineralizationbymagnetotacticbacteria.EnvironMicrobiolRep10.1111/1758-2229.12550.

49



IronintheFire:UsingControlledHeatingExperiments,High-ResolutionFORCs,andLow-TemperatureRemanenceExperimentstoRevealFire's

MagneticFingerprintPresenter:

PeterCLippert([email protected])

Authors: PeterW.Reiners,DepartmentofGeosciences,UniversityofArizonaEvidence for recent climate-wildfire linkages underscores the need for better understanding ofrelationshipsbetweenwildfireandmajorclimateshiftsinEarthhistory,whichinturnoffersthepotentialforprognosesforwildfireandhumanadaptationstoit.Inparticular,whatarethelinksbetweenseasonalityandwildfirefrequencyandseverity,andwhatarethefeedbacksbetweenwildfire,landscapeevolution,andbiogeochemicalcycles,particularly thecarbonand ironcycles?Akey firststep inaddressingthesequestionsisrecoveringwell-describedwildfirerecordsfromavarietyofpaleolandscapesandpaleoclimateregimes. Although charcoal and organic biomarkers are commonly used indicators of fire, taphonomicprocesses and time-consuming analytical preparations often preclude their routine use in someenvironments and in high-stratigraphic resolution paleowildfire surveying. The phenomenologicalrelationshipbetweenfireandmagneticsusceptibilitycanmakeitausefulsurveyingtool,but increasedmagneticsusceptibility insediments isnotuniquetofire,andthus limits itsdiagnosticpower.Hereweutilize component-specific rock magnetic methods and analytical techniques to identify the mineralmagnetic fingerprintofwildfire.Weuseacustom-designedair furnace,aseriesof iron-free laboratorysoils,naturalsaprolitesandsoils,andfuelsfromArizonaPonderosapineforestsandgrasslandstosimulatewildfireinacontrolledandmonitoredenvironment.Soil-ashresiduesandsoilandfuelcontrolswerethencharacterizedusingFirstOrderReversalCurve(FORC)patterns,DCbackfieldIRMcoercivityspectra,low-temperature SIRM demagnetization behavior, low-temperature cycling of room-temperature SIRMbehaviorandanalytical S/TEM.Herewesummarize the systematic changes to sedimentmagnetismaspyrolitized organic matter is incorporated into artificial and natural soils. These observations help uselucidatetheprocessesandsourcesresponsibleforincreasesinmagneticsusceptibilityobservedinnaturalburnedsoils,aswellasidentifymineralmagneticpropertiescharacteristictonaturalwildfirethathavethepotentialtobepreservedinsedimentarysequencesinthegeologicalrecord.

50



EnvironmentalinterpretationofgreigitelayersintheCentralParatethys:

evidenceforprimarypaleomagneticsignalsPresenter:

SuzhenLiu([email protected])

Authors: SuzhenLiu,PaleomagneticLaboratory'FortHoofddijk,'UtrechtUniversity;InstituteofGeologyandGeophysics,ChineseAcademyofSciencesWoutKrijksman,PaleomagneticLaboratory'FortHoofddijk,'UtrechtUniversityDanPalcu,PaleomagneticLaboratory'FortHoofddijk,'UtrechtUniversityMarkDekkers,PaleomagneticLaboratory'FortHoofddijk,'UtrechtUniversityChenglongDeng,InstituteofGeologyandGeophysics,ChineseAcademyofSciences

AnaccurateageframworkoftheParatethysiscrucialtounderstandtheevolutionofthisepicontinentalsea. Magnetostratigraphy based on greigite, which was anticipated an ideal dating tool, was oftenhamperedbyremagnetizationduetoa latediageneticgreigite formation. Inthisstudy,wereportrockmagneticresultsofTisasectioncoveringtheBadenian-Sarmatianboundary(~12.8-12.2Ma),fromwhichmagnetostratigraphyhaspreviouslybeenestablished.Four greigite layers are identified, which document primary paleomagnetic signals in Tisa section inSarmatian.DetailedrockmagneticandXRFstudiessuggestthatthegreigitelayerscorrelateneitherwithterrigenous input nor with in-basin biogenic carbonate production. We tentatively link the periodicalgreigiteoccurrencetoeccentricitymaxima,andattributeanearlysyn-depositionalformationofgreigitetoinsufficient sulfate in thewater column.During the Badenian undermarine settings, abundant sulfatesupplyenablesasurplusofH2SoverFe2+andthusproductionofpyriteratherthangreigite.DuringtheSarmatian,periodicplumesthoughtheBaraldGatewaybrings freshwater fromtheEasternParatethysduringeccentricitymaxima,whichreducesthesulfateavailability.AdepressedsulfatereductionlimitstheH2S production and leads to formation of greigite in the sediments. These early diagenetic greigitedocumentsaprimarypaleomagneticsignalwhichturnsoutreliablemagnetostratigraphicdating.OurresultssuggestsapossibledrivingforceofMilancovitchcyclesonthehydrologicalvariationsthroughthe Barlad Gateway, which enables an early formation of greigite and a primary record of thepaleomagnetic field. These findings confirm the early diagenetic greigite as a loyal candidate forpaleomagneticdatingintheParatethysregion.

51



Spatialisationofurbanairborneparticulatematterpollutionusingmagneticproperties:casestudyofParis(France)

Presenter: MelinaMacouin([email protected])Authors: MélinaMacouin,GéosciencesEnvironnementToulouse,UMR5563CNRSUR234IRD,

UniversitéPaulSabatier,Toulouse,FranceSoniaRousse,GéosciencesEnvironnementToulouse,UMR5563CNRSUR234IRD,UniversitéPaulSabatier,Toulouse,FranceAudeIsambert,InstitutdePhysiqueduGlobedeParis,UniversitéParisDiderot,SorbonneParisCité,UMR7154CNRS,Paris,FranceChristineFranke,MINESParisTech,PSLResearchUniversity,CentredesGéosciences,Fontainebleau,FranceHasminaHamid,GéosciencesEnvironnementToulouse,UMR5563CNRSUR234IRD,UniversitéPaulSabatier,Toulouse,FranceAurélioPhilip,InstitutdePhysiqueduGlobedeParis/MINESParisTech,PSLResearchUniversity,CentredesGéosciences,Fontainebleau,France

Themain sources for urban air pollution are anthropogenic processes, notably particularmatter (PM)emissionsbyheavy traffic and industry. Traditional air pollution/qualitymonitoring techniques includeautomaticsamplingstationsandbiomonitoring,followedbychemicalanalyses.However,astheneedforspatially detailed data on air pollution dispersion, particle composition, and grain size increases, thenumber of monitoring stations often becomes a limiting factor as well as the costs for the analyses.Magneticmethodshaveproventheirefficiencyintrackingairandsoilcontaminationbothinurbanandindustrialized zones. The technique presents the advantage of being quick, easy to operate and cost-effective.RecentstudiesdemonstratedthatthemagneticpropertiesoftreeleavesreliablydelineatethedistributionanddispersalpatternsofanthropogenicairbornePMinurbanenvironments.Inthisstudy,wecollected plane tree bark along the Seine River, both in Paris intra-muros and in the upstream anddownstream suburbs.Magnetic property analyseswere performed on ~200 bark samples. The resultssuggestthatthemagneticPMcollectedontreebarksconsistofamixtureofparticlepopulationsderivingmost likely from fuel combustion residuals and the abrasion of disk brakes. High resolution maps ofsusceptibilityandfrequency-dependentsusceptibilitieswerecompiled.Parameters,suchasspeedlimits,traffic lights,crossings,distancebetweenthetreeandthetraffic laneareinfluencingtheconcentrationandgrainsizedistributionofthemagneticparticlesthatweredetected.Themostobviousobservationisthecontributionoffinemagneticparticlestotheoverallmagneticassemblagethatdirectlycorrelatestothe traffic density on the adjacent road. Our study also points out that the concentration ofsuperparamagneticparticlesishigherinplanetreebarksituatedjustbehindtrafficlights.

52



Magnetiteiseverywhere.

Presenter:

BarbaraMaher([email protected])

Authors: BarbaraMaher,LancasterEnvironmentCentre,LancasterUniversity,LA14YQ,U.K.ImadAhmed,DepartmentofEarthSciences,OxfordUniversity.

Distinctivelynanoscaleparticlesofmagnetiteoccuralmostubiquitouslyintheenvironment(includinginsoils,sediments,theatmosphere,organisms).Thesenanoscalemagnetitesplayakeybiogeochemicalrole;as electron donors/sinks; sorption surfaces; and sinks of nutrients, contaminants, and radionuclides.Further, preserved in geological sequences, they encode in their magnetic properties a wealth ofpalaeoclimatic,environmentalandchronologicalinformation.Environmentalmagnetism,theanalysisofthesemagneticrecords,contributesanincreasinglypivotalrolenotonlytoourunderstandingofpastchangesinclimatesandenvironments,butofpossibleenvironmentalriskfactorsinvolvedindamagetohumanhealth.Forinstance,intheworld-famoussedimentsoftheChineseLoessPlateau,theformationandpersistenceofnanoscalemagnetitehasbeenlinkedtoclimaticchangesviaredoxchangesinsoilmicro-sitesfollowingrainfallevents.Anoppositehypothesislinkspedogenicferriteformationwiththeformationofanoxidised,maghemite-likephase('hydromaghemite'),whichitselftransformstohaematiteuponageing.Thislatterpathway would thus be temperature- rather than moisture-dependent. Here, we use high-resolutiontransmissionelectronmicroscopy (HRTEM)to identifymagnetiteasthedominantsoil-formedferrite inthesesediments.We also combine HRTEM with SQUID magnetometry to identify for the first time the presence ofexternally-sourced magnetite nanoparticles in the human brain. This discovery is important becausenanoscalemagnetite is toxic to thebrain, being implicated inproductionof damaging reactiveoxygenspecies(ROS).BecauseenhancedROSproductioniscausallylinkedtoneurodegenerativediseasessuchasAlzheimer'sdisease,exposure to suchairbornePM-derivedmagnetitenanoparticlesmightconstituteapossiblehazardtohumanhealth.

53



MagneticsignaturesrelatedtoNorthBrazilianCurrentinthemarginoffNE

Brazil:Insightsaboutcross-shelftransportPresenter:

GrasianeLuzMathias([email protected])

Authors: GrasianeL.Mathias,LancasterEnvironmentalCentre,UniversityofLancaster,UK.JannaJust,InstitutofGeologyandMineralogy,UniversityofCologne,Germany.ThomasFrederichs,DepartmentofGeosciences,UniversityofBremen,Germany.TilovonDobeneck,DepartmentofGeosciences,UniversityofBremen,Germany.

Wemagneticallycharacterizedfoursedimentcores(GeoB3913-3,3912-1,3911-3and3910-2)fromtheNEBrazilmarginthatrecordedNorthBrazilCurrent(NBC)intensityandcontinentalariditychangesofthepast90ka.Ourstudyaimsforabetterunderstanding,howmeridionalITCZshiftsoriginatingfromfreshwaterpulsesintotheNorthAtlanticOceaninfluencethelocaloceanography,inparticularlongitudinalsedimenttransportandterrestrialenvironmentalchangeinthesemi-aridNEBrazilianregion.Weperformedend-member(EM)unmixingof449isothermalremanentmagnetization(IRM)acquisitioncurvestoseparatethedifferentmagneticcontributionsaccordingtodistinctcoercivities.Theend-membersareinterpretedaccordingtosedimentprovenanceswhichprovideinformationonchangingenvironmentalconditionsonland.TherelativecontributionofmagneticmineralsourceschangesfromwesttoeastacrosstheNEBrazilmargin.Duringstadials,high-coercivephases(hematiteandgoethite)aredominantinthewesternpartofthestudyarea,whilelow-coercivephasesaredominantattheeasternmostcore.Thisdifferenceismainlyduetodifferentialweatheringconditionsonland.However,aweakeningoftheNBCeastofParnaibaRivermouthduringstadials,predictedbypaleoclimatemodels,mayhavemodifiedthedistributionofmagneticmineralsalongthecontinentalmargin.WesuggestthattemporarycoastalflowinversionduringperiodsofweakNBCenabledaneastwardadvectionofhigh-coercivematerial,bringingmaterialfromParna’barivertoourstudyarea.Biogenicmagnetiterepresentingmarineinfluenceispresentinallfourcoresovertheentirestudiedtimeinterval,butplaysaminorroleduringstadialphasesofenhanceddetritalmagneticmineralaccumulation.

54



ClimatevariabilityintheSWIberianMargin:newinsightsfromFORC-PCA.

Presenter:

JoyR.Muraszko([email protected])

Authors: JoyR.Muraszko,UniversityofCambridgeRichardJ.Harrison,UniversityofCambridgeIoanLascu,UniversityofCambridgeSeanCollins,UniversityofCambridge

Arguablyoneof the largest challenges in the fieldof rockmagnetism is thedeconvolutionof thebulkmagneticsignal.InthisstudyweaddresstheissuebyapplyingPrincipleComponentAnalysisonFirstOrderReversalCurvediagrams(FORC-PCA).Themethodallowsfordiscriminationbetweendiagnosticmagneticsignaturesandunmixingofindividualcomponentsinaquantitativeunambiguousway.Theapplicabilityofthemethodforenvironmentalmagnetismisdemonstrated inacasestudyofthesouthwestern IberianMargin,whichisknowntoprovidehighfidelityrecordsofclimatechangeandhasbeenafocalpointofpaleomagneticandpaleoceanographicstudies.AhighresolutionrecordofFORCdiagramswasobtainedfrompistoncoreMD01-2444,spanning194kyrand extending intoMIS 6. The variabilitywithin the dataset can be explained by threemagnetic end-members identified through FORC-PCA, corresponding to non-interacting high coercivity single-domainmagnetite,alowcoercivitysuperparamagnetictosingle-domaincomponentandapseudosingle-domaintomultidomaindetritalend-member.Variationsoftheend-membersweretracedtemporally,yieldingaphysicallyandenvironmentallymeaningfulrecordoftherockmagneticresponsetoclimatechange.Thelargestvariationsinthedatasetareobservedinfine-grainedmagnetite,whichisgenerallyanti-correlatedwith themagnetosomesignalandcontrols thebulkmagneticproperties.Thenatureof theSP-SDend-member is explored, supported by transmission electronmicroscopy studies. The study highlights therelevanceofironreductionprocessestotherockmagneticrecord,providingnewinsightintothemagneticresponsetoclimatechangeandtheinterpretationofconventionalpaleomagneticproxies.

55



EnvironmentalMagneticRecordofHoloceneClimateVariabilityfromLake

Malawi,EastAfricaPresenter:

EllenPlatzman([email protected])

Authors: E.Platzman,UniversitySouthernCaliforniaS.P.Lund,UniversitySouthernCalifornia

MagneticstudiesofHolocenelakesedimentsrecoveredfromlakeMalawihaveyieldeda25,000-yearhigh-resolutionrecordofenvironmentalvariabilityandpaleolimnology.LakeMalawi isthesouthern-mostofthelargeriftvalleylakesofeastAfrica.LikemanyoftheriftvalleylakesLakeMalawiismeromicticwithannualwind-inducedmixingoccurringprimarily in theupper250m.Below thisdepth the lake remainscompletelyanoxicthroughouttheentireyear.Samplesformagneticanalysiswereobtainedfrom9mofcorerecoveredfromthenorthernendofthelakeat~390mwaterdepth.Agesconstrainedusingradiocarbonchronostratigraphy,yieldsedimentationrates of .07- .14cm/yr over an ~25,000 yr interval. Parameters reflecting variability in magneticconcentration (susceptibility, ARM, SIRM) and grainsize (ARM/Chi) were measured on u-channels.Additional rockmagneticparameters, includinghysteresisandS-parameterweremeasuredat selectedintervalstoconstrainthemagneticmineralogy.Thesedatawerecombinedwithmeasurementsofbiogenicsilica (Bsi) and terrestrial mass accumulation (MAR) are used to create a multiproxy record ofenvironmentalvariability.Results from this analysis indicate that the longer-term Holocene variability of Lake Malawi can bedescribedbyasee-sawpatternofalternatingdominanceofsummerorwinterconditionsonmulti-decadal,centennial,andmillennialscales.Australsummer,characterizedbyalow-wind,wetseason,isassociatedwith increased lake stratificationand significant terrestrial flux into theprofundal zonesof the lake. Incontrast, winter conditions are characterized by dry, windy weather pattern where verticalmixing/upwellingproduceshighbiologicalproductivityanddominanceofdiatomaceoussedimentshighinBSi.Theseresultshelpustoconstrainlong-termrecordofeffectivemoistureandpaleo-climateintropicaleastAfrica.

56



DeconvolvingglaciomarinesedimentaryprocessinPetermannFjord,

NorthwestGreenland,usingparticlesizespecificmagneticmeasurementsPresenter:

BrendanT.Reilly([email protected])

Authors: BrendanReilly,OregonStateUniversityJosephStoner,OregonStateUniversityAlanMix,OregonStateUniversityMartinJakobsson,StockholmUniversityAnneJennings,UniversityofColorado,BoulderMaureenWalczak,OregonStateUniversityLaurenceDyke,TheGeologicalSurveyofDenmarkandGreenlandRobertHatfield,OregonStateUniversity

Large calving events of the Petermann Ice Tongue, Northwest Greenland, in 2010 and 2012 seemunprecedentedinthecontextofthelimitedhistoricalrecordofPetermannicetongueextents,datingbacktothe1875-1876BritishArcticExpedition ledbySirNares.Onceconsideredarelativelystablemarine-basedsectoroftheGreenlandIceSheet,studiesinthelastdecadehavedemonstratedthatPetermannGlacierisespeciallysensitivetoice-oceaninteractions,leadingmanytospeculateonitsfuturestability.Toplacetheseobservationsinamoreholisticcontext,a2015internationalandinterdisciplinaryexpeditionoftheSwedishIceBreakerOdencollectedasuiteofsedimentcoresspanningthemid-tolateHolocenefromPetermannFjord.ThesecoresrevealamoredynamichistoryforPetermannGlacierthanwouldbeexpectedbasedonthehistoricalrecordalone,includingthebreak-upofapaleo-icetongueandeventualregrowthofthepresentice-tongueobservedinthehistoricalrecord.In addition to PetermannGlacier, several small glaciers that drain local ice caps, located on the KanePlateautothenortheastandPetermannHalvütothesouthwest,terminateinthefjordandareasignificantsourceofsediment.TheselocalicecapserodePaleozoiccarbonaterocks(lowmagneticsusceptibility,lowTi/Ca)thatcompriseboththelocalsurficialgeologyandtheupto~900mhighwallsofthefjord.Erraticgranites and other crystalline rocks (highmagnetic susceptibility, high Ti/Ca) are visibly identifiable interrestrial Petermann glacial deposits, reflecting deeper excavation into basement rocks by the inlandGreenlandIceSheet.Thesetwosources,withcontrastsinmagneticmineralconcentration,magneticgrainsize,andgeochemicalproperties,provideauniqueopportunitytoquantitativelyassessthecontributionofPetermannGlaciertoavarietyofglaciomarinesedimentaryprocesses.HerewereportparticlesizespecificmagneticmeasurementsacrossninesizefractionsinbothterrestrialandmarinesedimentstoinvestigatetheinfluenceonbulksignalsofPetermannGlaciersourcedsedimentsandtheglacialprocessestheyreflect.WefocusontwocorelocationswithinPetermannFjordfromslightbathymetric highs, where the recovered sediments were primarily transported by turbid meltwaterprocessesorasice-rafteddebris(IRD).Wefocusourmoredetailedanalysesonthegreaterthan63µmcoarse fractions,which largely reflect IRD, and the 10-32 µmnon-cohesive silt fractions,which reflectmeltwater, sediment transport energy, and IRD. Thesedata contributenew insight to thedynamicsofPetermann Glacier over the Holocene, most notably a huge increase in the relative contribution ofPetermannGlaciersourcedIRDfollowingthepaleo-icetonguecollapseandeventualdecreasetonegligiblePetermannGlacierIRDcontributionswiththeestablishmentofthehistoricalice-tongue.

57



Newmeasurementprotocolsforhysteresisreversalcurvesandidentification

ofmagneticmineralcomponentsinenvironmentalmagnetismPresenter:

AndrewP.Roberts([email protected])

Authors: XiangZhaoAndrewP.RobertsDavidHeslop

High-resolution first-order reversal curve (FORC) diagrams are being used increasingly in rock andenvironmentalmagnetism,includingfordetectionofbiomagneticsignalsinsediments.Resolutioncanbeamajorbarriertoobtaininghigh-qualityFORCdiagramsandtime-consumingmeasurementsthatemploysmallfieldstepsarenecessarytoresolvethefinestfeaturesofaFORCdistribution.WehavedevelopedanewexperimentalprotocolwithirregularlyspacedfieldstepsthatallowsdifferentpartsofaFORCdiagramtobemeasuredatdifferentresolutions.Largernumbersofmeasurementscan,therefore,bemadeinkeyregionsofaFORCdistributiontoresolvediagnosticfeaturesathigherresolution.Specificationofthefieldsteps in the irregular grid is basedonmeasurementof amajorhysteresis loop;noapriori knowledgeconcerning the underlying FORC distribution is required. FORC diagrams obtained with conventionalmeasurementsandwithournewmeasurementprotocolgiveconsistentresults.WehavealsoextendedtheapplicabilityofFORC-typediagramsthroughuseofaseriesofhysteresismeasurementsthatprovideinformation about remanent, induced, transient-free, and transientmagnetization components. Thesemeasurements,anddifferencesbetweenmeasurementtypes,enableproductionof6FORC-likediagramswith only double thenumberofmeasurements needed for a conventional FORCmeasurement. Thesediagramsenablediscriminationbetweenmagneticsignaturesassociatedwitheachdomainstate.Whenanalyzingsampleswithcomplexmagneticmineralmixtures,contrastingdomainstatesignaturesaremixedin a traditional FORC diagram, but these signatures can be identified individuallywith the 6 diagramsdiscussedhere.TheabilitytomakedifferentFORCmeasurementsandtoidentifyseparatelyeachmagneticcomponent inaconventionalFORCdiagramby investigatingdifferentmagnetization typescanprovidemuch-improvedunderstandingoftheinformationprovidedbyFORCdiagrams.Thediagnosticinformationprovided by these additional FORC-type diagrams should assist substantially in magnetic unmixing ofcomplexsamplesandinquantitativemineralmagneticinterpretation.

58



Biogenicmagnetiteasanindicatorofchemicalstratificationinthesediment

columnofMamanguáRía(Paraty,Brazil)Presenter:

DanielRodelli([email protected])

Authors: RodelliDanielLuigiJovaneGiorgioniMartinoSicilianoEric,R.CorgnaggiaFlaminiaBenitesMarianaCedrazPatricia,P.Roberts,Andrew,P.

Magnetotacticbacteria(MTB)areagroupofprokaryotesthathavetheabilitytobiosynthesizemembrane-boundmagneticmineralcrystals.Theyarefoundinmanyenvironments,fromfreshtomarshtomarinewaters,commonlyinwatercolumnsandsedimentswithverticalchemicalstratification,attheoxic-anoxicinterface and in anoxic regions. For this reason, they are considered (facultatively anaerobic)microaerophiles. Inmany casesMTB distribution and abundance indicate that they are the dominantspecies,whichsuggeststhattheyareecologicallyimportant.Therefore,studyingthedistributionofMTBin an environment can be a useful tool to understand environmental characteristics of the water orsedimentcolumn.Magnetite produced byMTB has specific characteristics in terms of crystal structure, dimensions, andorganization within chains. Magnetic properties related to biogenic magnetite have been thoroughlystudiedinrecentandpastenvironments.Environmentalmagneticstudiescan,therefore,providearapidandreliablewaytotrackthepresenceanddistributionofMTB,possiblyenablingreconstructionofoxygengradients.Herewepresentanintegratedstudyofmagneticproperties,porewaterchemistry,andmineralogyfromrecent sediment from the Saco doMamanguá (Rio de Janeiro, Brazil).Our objective is to characterizechemicalstratificationinthesedimentcolumninasmall,enclosedbasin,withlimitedinfluxofmaterialfromtheocean,whichcanbeusedasamodernanalogforsimilarpastcontexts.Magnetiteproducedinsitubymagnetotacticbacteriadominatesthemagneticfractioninthetopmost10-35cmofthesediment,wheretheoxygenconcentrationandredoxpotential(RP)aresuitableforthebacteria.ThepresenceofbiogenicmagnetiteislinkeddirectlytotheoxygencontentandRP;whenthesevaluesdecrease,biogenicmagnetitedisappears,possiblyduetodissolutionduetothereducingconditions.Thesedimentationrateinferred from the agemodel (based on 14C dating) and the concentrations of detritalmagnetite andhematiteareconstantalongthecore,whichimpliesthatFeionconcentrationwasconstant,anddidnotlimitgrowthandpreservationofbiogenicmagnetite,which,inturn,iscontrolledbyoxygencontentandRP.SynchrotronlighthasbeenusedtomeasureXANESspectraof4selectedsamplesinthetoppartofthecore(first80cm).ComparisonwithstandardsofdifferentoxidationstatesofironindicatethattheFeinmagnetitebecomesmoreoxidizedatadepthof30 cm, confirmingprevious findings thatmagnetite ispartiallyoxidized intohematitewhenmagnetotacticbacteriadieandbiogenicmagnetite isexposed tooxidizingenvironments.

59



Spatialisationofmetalliccontaminationusingmagneticpropertiesina

carbonatedcontext(JebelRessas,Tunisia)Presenter:

SoniaROUSSE([email protected])

Authors: SoniaRousse,GéosciencesEnvironnementToulouse(CNRSUMR5563,IRDUR234,UniversitéP.Sabatier)14avenueEdouardBelin31400Toulouse,FranceMurielLlubes,GéosciencesEnvironnementToulouse(CNRSUMR5563,IRDUR234,UniversitéP.Sabatier)14avenueEdouardBelin31400Toulouse,FranceMargueriteMunoz,GéosciencesEnvironnementToulouse(CNRSUMR5563,IRDUR234,UniversitéP.Sabatier)14avenueEdouardBelin31400Toulouse,FranceMarilyneSoubrand,UniversitédeLimoges,GRESE,EA4330,IFR145GEIST,123AvenueAlbertThomas,87060LimogesCedex,FranceEmmanuelJoussein,UniversitédeLimoges,GRESE,EA4330,IFR145GEIST,123AvenueAlbertThomas,87060LimogesCedex,France

Among themodernsocietal concerns, theenvironmentalqualityand its impactonhumanhealthhavebecome major challenges. It has been demonstrated that metallic contamination had non-negligibleimpactsonecosystems,andhenceonlivingandhealthconditions.Amongthevarioussourcesofmetalsinnature, abandoned mining sites have to be considered. Countries from the Mediterranean southernriversideownlargeminetailingsquantitiesrichinheavymetalslikePb,Cd,Zn,Sb,As,andHg,comingfromminingsitesabandonedorstillinactivity.Forthemajorityofthesesites,villagesandfarmlandsdevelopedadjacent to the treatment plant. Magnetic methods like magnetic susceptibility and mineralogy haveproventheirefficiencyintrackingheavymetalcontaminationbothinurbanandindustrializedzones.Thesetechniquespresenttheadvantageofbeingquick,easytooperateandcost-effective.However,foreachgivencontext,therelationshipbetweenthemetalliccontaminationandthemagneticmineralogyneedtobe determined. In this study, we acquired different datasets of magnetic susceptibility with threesusceptibilimeters (BartingtonMS2D sensor; ABEM EM38, Terraplus KT10) in an olive grove close theformer Pb-Zn mining site of Jebel Ressas (North-Eastern Tunisia). We completed our in-situ dataacquisitionswithlaboratorymagneticmineralogyanalysesofsoilssampledinthefieldandalongonedepthprofile (up to 50 cm depth). Magnetic susceptibility maps a non-uniform dispersion of the metalliccontamination,whichmainly localize instreamsandtopographicdepressionsfavoringahydrictransferdispersionhypothesisforthecontaminationinthiscarbonatedcontext.Magneticmineralogyoftheminetailing, contaminants impregnation in soils and inter-comparison of the three susceptibilimetersmonitoringresultswillalsobediscussed.

60



ProbingSequentialChemicalExtractionsforIronMineralogyusingMagnetic

MethodsPresenter:

SarahP.Slotznick([email protected])

Authors: SarahP.Slotznick,UniversityofCalifornia,BerkeleyNicholasL.Swanson-Hysell,UniversityofCalifornia,BerkeleyAustinJ.Miller,StanfordUniversityErikA.Sperling,StanfordUniversity

Ironspeciation,apopulargeochemicalenvironmentalproxy,estimatesproportionsofdifferentreactiveironspeciesinfine-grainedsedimentaryrockswhicharemappedtoredoxconditionsbasedonempiricalcalibrationsfrommodernsedimentsamples.Themethodhasbeenwidelyappliedtothesedimentaryrockrecord and has fundamentally revised views of Precambrian and Paleozoic ocean environments. Ironspeciation isbasedonanextraction techniqueof sequentiallyapplyingacetate,dithionite,andoxalatesolutionstoapowderedsampleinordertodissolveironphasesandquantifytheamountofironcarriedby carbonates, ferric iron (oxyhyr)oxides, andmagnetite respectively.Our studyapplied rockmagneticexperimentaltechniquestoshalesamplesdatingfrom50Mato1.5Gawithdiversetotalironcontents,different proportions of iron pools from each extraction, and distinct paleoredox interpretations. Ourapproach was to characterize bulk powders from these samples as well as residues taken after eachsequentialextractionstepinordertoidentifyandquantifytheferromagneticmineralsthatweredissolvedat each step. Coercivity spectra obtained through IRM demagnetization, hysteresis loops, and low-temperature transitions revealed distinct changes through the sequential extraction process thatdocumenttheleachingofdifferentmagneticminerals.Testingtheacetateextractionisdifficultbecausesiderite and rhodochrosite become antiferromagnetic at low-temperatures, but ankerite, ferroandolomite,or ferroancalcitedonotshowsimilar low-temperature transitions in remanence. Insampleswithsiderite,thesharplow-temperaturetransitiondisappearedorwasdampenedaftertheacetatestepsuggesting at least partial extraction of this phase. Inmost samples, the (zero) field-cooled remanentmagnetization at low temperatures decreased after the acetate extractionwithout a change in shapesuggestinglossinparamagneticphaseslikeiron-bearingcarbonates.Thedithioniteextractionsuccessfullyremovedalargeproportionofthegoethitepresentinmostofthesamples.Extractionduringtheoxalatestepistypicallysolelyattributedtomagnetite;however,itwasobservedinsomesamplesthattheoxalateextractiondecreasedtheamountofparamagneticmaterialinthesample,suggestingitalsodissolvediron-bearing clays/silicates or remaining iron-bearing carbonates. Although the oxalate extraction usuallyreduced the amount ofmagnetite in a sample, inmany cases small amounts ofmagnetite remained.Notably, quantification of magnetite weight percent using saturation magnetization suggested anabundancethatwasordersofmagnitudelessthantheironextractedintheoxalatestep.Understandingthisdistinctionisvitaltoaidincommunicationbetweenfieldsandencourageinterdisciplinarytechniqueapplication. Ourwork can aid geochemists andmagnetists alike by refining understanding of the ironspeciationextractionsandhighlightingchemicaltechniqueswhichcanpeelawaysecondaryoverprintsforrockmagneticanalysesofnaturalsamples.

61



ROCKMAGNETICINVESTIGATIONOFTHEMICHIGANBASINSOILSANDSEDIMENTSOVERLYINGTHEOIL-BEARINGSILURIANPINNACLEREEFS

Presenter:

AlekseyV.Smirnov([email protected])

Authors: AlekseyV.Smirnov,MichiganTechnologicalUniversity,Houghton,USAJacobP.Tresnak,MichiganTechnologicalUniversity,Houghton,USAKariL.Anderson,MichiganTechnologicalUniversity,Houghton,USA

Oilandgasreservoirsmaybeassociatedwithsignificantmagneticanomaliesarguablycausedbydiageneticalteration of iron-bearing minerals in hydrocarbon seepage environments. However, completeunderstanding of the physicalmechanisms and pathways of hydrocarbon-inducedmagnetic alterationrequires a robust and representative observational database. In order to facilitate the fundamentalunderstandingofthemagneticsignatureofhydrocarbons,weconductedarigorousinvestigationoftherelationshipbetweenthehydrocarbonmigrationandmagneticpropertiesofsedimentsoverlayingtheoil-bearingformationsoftheSiluriannorthernpinnaclereefbeltoftheMichiganBasin.Severalhundredsofnear-surfacesoilandsedimentsampleswerecollectedacrossseverallongtransectsacrossthetrendoftheNiagaranReefSystemandrepresentedareasbothoverandawayfromknownhydrocarbonsources.Thesampleswereinvestigatedbyavarietyofmicroscopyandrockmagneticmethods.Ourdataindicatethattherelationshipbetweenthehydrocarbonreservoirsandlow-fieldmagneticsusceptibilityovertheNiagaran pinnacle reef belt in theMichigan Basin is not straightforward. Both very high and very lowsusceptibility values have been observed within the extent of the reef belt in the studied area. Theobserved magnetic susceptibility anomalies may reflect the hydrological gradients in the uppermostglaciofluvialaquifer.However,agoodcorrelationwiththeDevonianhydrocarbonreservoirsoutsideofthereefbeltindicatesapotentialofthesurfacemagneticsusceptibilitymethodforhydrocarbondetectionatasmaller-scale.

62



RockmagneticcharacteristicsofDeccanboles:Implicationsfor

paleoenvironmentPresenter:

PriyeshuSrivastava([email protected])

Authors: PriyeshuSrivastava,SchoolofEnvironmentalSciences,JawaharlalNehruUniversity,NewDelhi-110067,IndiaN.SivaSiddaiah,SchoolofEnvironmentalSciences,JawaharlalNehruUniversity,NewDelhi-110067,IndiaS.J.Sangode,DepartmentofGeology,SavitribaiPhulePuneUniversity,Pune-411007,India

Thebolesare significantmarkersofhiatus in theDeccan floodvolcanism.Boles trappedbetween twosuccessiveflowsshowcolorastheirdistinctivepropertywithredbeingthemostabundantandgreenrare.The iron oxides are anticipated to play an important role in such characterization. We studied rockmagneticcharacteristicsof fourdifferentcolorboles i.e.dark red (10R-3/6), light red (10R-4/8),brown(5YR-4/4),andgreen(5G-6/2)tounderstandthepaleoweatheringandpaleoenvironment.Themagneticparameters(ìàlf,SIRMandSoft-IRM)showhigherferrimagneticconcentrationsinbrownandlightredbolecomparedtodarkredandgreenboles.TheS-ratio(-0.97)andcoercivityofremanence(BCR)(~19to29mT)forbrownandgreenboleindicateferrimagneticmineralogy.TheS-ratio(0.26)andBCR(~433mT)fordark red bole indicate dominant antiferromagnetic mineralogy. The antiferromagnetic mineralsconcentrationestimatedbyHIRM,showsmaximumconcentrationindarkredbolefollowedbylightredbole. Brown bole shows minimum concentration of antiferromagnetic minerals whereas negligibleconcentrationisnotedingreenbole.ThegrainsizeparameterìàARMindicatedhighersingledomain(SD)ferrimagneticparticleconcentrationinbrownbole.Theìàfddepictshighersuperparamagnetic(SP)particleconcentration in light red bole. The Deccan parent basalts are rich in pseudo single domain (PSD)ferrimagneticminerals.TheSDferrimagneticrichbrownboleindicatedminimumalterationsowingtoalimitedexposuretimeofsub-aerialweathering.TheSPferrimagneticandantiferromagneticmineralrichlightredboleindicatesrelativelyhigheralterationscomparedtobrownboleandheatingfromupperlavaflow may have led to the genesis of SP particles and antiferromagnetic mineral. The dark red boledemonstratesnearlycompleteoxidationofferrimagneticintoantiferromagneticmineralsduetoheatingfromtheupperlavaflow.Thegreenboleshowsanoveralldepletedmagneticconcentrationpossiblydueto dissolution under acidic environment. The various color boles therefore indicates differentpaleoenvironmentalconditionsduringDeccanfloodvolcanism.

63



CharacterizingMagneticPropertiesinBelizeCorals

Presenter:

AlexisUrbalejo([email protected])

Authors: AlexisAnnUrbalejo,UniversityofColoradoatBoulder,Boulder,CO,UnitedStatesAtreyeeBhattacharya,UniversityofColoradoatBoulder,Boulder,CO,UnitedStatesJeffreySGee,UniversityofCaliforniaSanDiego,LaJolla,CA,UnitedStatesRitayanMitra,UniversityofColoradoatBoulder,Boulder,CO,UnitedStatesJessicaCarilli,UniversityofMassachusettsBoston,Boston,MA,UnitedStatesAlexandraHangsterfer,ScrippsInstitutionofOceanography,LaJolla,CA,UnitedStatesJoshuaMFeinberg,UniversityofMinnesota,Minneapolis,UnitedStates

Measurements ofmagnetic remanence and characterization ofmagnetic phases arewidely applied toenvironmentalandclimatestudies;however,magnetictoolshavenotbeenwidelyappliedtocoralstudies.Assuch,thereisadeficitinourunderstandingofmagneticmaterialsandbehaviorincoralskeletonsandconsequently,ofprocessesbywhichmagneticmaterialsmaygetincorporatedintocoralskeletons.Inthisstudy,wepresentmagneticmeasurementsconductedonfreshlybrokenchipsfromcoralcores;thecoreswerecollectedfromMesoamericansitesinBelize.Trace,minor,andmajorelementconcentrationhavebeenwellstudiedinthesetwocoralcores,usinginductivelycoupledmassspectrometrictechniques(ICP-MS).Thegoalofourcurrentresearchistodetermineareasfollows:(a)Isthereisaviablemagneticsignalthat can be obtained frommeasuring chips broken off of coral skeletons? (b)What are some of thedominantmagneticbehaviors?(c)Whatarethecarrierphasesofmagneticmaterial?(c)canwedeterminepossible variations in the type and quantity of magnetic materials over time and ultimately, (e) canmagneticfingerprintingofcoralscanbeusedastracersofenvironmental,climateorbiologicalprocesses?Here,wepresentpreliminarymagneticremanencemeasurements (IRManddouble IRM)fromthetwocoralcorescollectedfromBelizeanddatingbacktothemid1800s.Earlyresultsusingfreshlybrokenchipsfrombothcoralcoresindicateamagnetite-likesoftmagneticcomponentduringIRMexperiments.Double-IRMexperimentsonthesamesamplesindicateuniaxialsingledomainbehavior.Furthermore,SEMimagessuggestthatthemagneticcarrierphasecouldlikelybemagnetite.WewillalsopresentcomparisonsofourmagneticdatawithnewlycollectedX-RayFluorescence(XRF)dataonthesamecoralcores.Thegoalistoproperlycharacterizethetypeofmagneticsignalsanddeterminepossibleenvironmentaland/orbiologicalimpactsonmagneticcarrierphasesandproperties.

64



Magneticpropertiesofmunicipalsolidwasteincinerationashes

Presenter:

LuigiVigliotti([email protected])

Authors: ValerioFunari,DipartimentodiScienzeBiologiche,GeologicheeAmbientali(BiGeA),UniversitàdiBologna,ItalyLucianaMantovani,DipartimentodiFisicaeScienzedellaTerra,UniversitàdegliStudidiParma,ItalyLuigiVigliotti,IstitutodiScienzeMarine,ConsiglioNazionaledelleRicerche,Bologna,ItalyMarioTribaudino,DipartimentodiFisicaeScienzedellaTerra,UniversitÌdegliStudidiParma,ItalyRobertoBraga,DipartimentodiScienzeBiGeA,UniversitàdiBologna,ItalyEnricoDinelli,DipartimentodiScienzeBiGeA,UniversitàdiBologna,Italy

Coalcombustionrepresentsanimportantworldsourceofenergysupplyandtheironmineralsoccurringinrawmaterials,fuels,oradditivesareacknowledgedtoformhighlymagneticparticleswithtendencytobindsomeelementsduringsuchatechnologicalprocess.Anextensiveliteratureonflyashesandpollutedsoils fromcoal-combustionpowerplants isavailable,but theassessmentof themagneticbehaviourofmunicipal solid waste incineration (MSWI) ashes remains largely overlooked despite their recognisedhazardousnature.Acollectionof31bottomash(BA)and16flyash(FA)samplestakenfromfourMSWIsystemsofnorthernItalywasinvestigatedbyarangeofmagneticmeasurementsincluding:massspecificmagnetic susceptibility (χ), frequency dependence of susceptibility (κfd%), anhysteretic remanentmagnetization(ARM),isothermalremanentmagnetization(IRM),coercivityofremanence(B0cr),S-ratio(S-0.3T),andhysteresis loops,which, inturn,allowedtheparsingoffirst-orderreversalcurves(FORCs).The results are integrated by detailed temperature- and frequency-dependent experiments (i.e.,thermomagnetic analysis,MPMS-Magnetic PropertiesMeasurement System) as well as byMössbaueranalysis,X-raydiffractionanalysisandmorphologicalobservations.Theobjectivesofthisworkare(1)toconduct a systematic investigationofmagneticpropertiesofMSWIashes; (2) to identify themagneticcomponents liable of the strong magnetic signals observed in prior start-point measurements; (3) toevaluatewhetheranewpollutionriskrelatedtoSPgrainsisnotfartobereal.The analysis of the thermomagnetic curves indicates that magnetite with its characteristic Curietemperature(TC)of~580°Cisthemainferrimagneticphaseoccurringinthesamples.ThisisconfirmedbynarrowhysteresiscurvesandMPMSmeasurements.MagnetichysteresisdataofbothBAandFAsamplesapparently detect pure SP magnetite, but likely reflect mixed mineral assemblages of hard and softmagnetic phases with MD- and SP-sized grains. According to many magnetic ratios and MPMSmeasurements,alargercontributionofMDmagnetiteispresentintheBAsampleswithrespecttotheFAsamples that are also characterizedby a finer grain-size. The FORCdiagrams indicate amore complexdistribution of the magnetic minerals that are the result of homogeneous mixtures of differentmineralogical phases. The nonmagnetic techniques corroborate this hypothesis. According to theMössbauer analysis, the calculatedmagnetite to hematite ratio is 2.13 in BA and 0.08 in FA samples.However, the interpretation of Mossbauer spectra is not straightforward due to a pervasivenonstoichiometry and a potential intermediate relaxation effect due to SP grains. A varying degree ofoxidation and cations substitution are highly probable during the production of MSWI ashes and arecontrolledbythefeedwastechemicalcomposition,theresidencetimeinthecombustionchamberofthewastematerial,andtemperatureprofilesalongtheMSWIintegratedsystem.AdistinctmagneticsignaturecharacterisesBAandFAderivingfromMSWIplantsandtheydifferfromthoseofloess,sediments,orsoilsresultingfromnaturalprocesses,aswellasfromotheranthropogenicsourcesofpollutionsuchascoalflyashes,dustfrompowerstationsorFe-smelters,landfillleachates.

65



CyclicmagnetitedissolutioninabyssalNorthwestPacificsediments-

evidenceformassiveglacialcarbontrappingPresenter:

TilovonDobeneck([email protected])

Authors: TilovonDobeneck,MARUMandFacultyofGeosciences,UniversityofBremen,GermanyLuciaKorff,MARUMandFacultyofGeosciences,UniversityofBremen,GermanyThomasFrederichs,MARUMandFacultyofGeosciences,UniversityofBremen,GermanySabineKasten,AlfredWegenerInstitute,HelmholtzCentreforPolarandMarineResearch,Bremerhaven,GermanyGerhardKuhn,AlfredWegenerInstitute,HelmholtzCentreforPolarandMarineResearch,Bremerhaven,GermanyRainerGersonde,AlfredWegenerInstitute,HelmholtzCentreforPolarandMarineResearch,Bremerhaven,GermanyBernhardDiekmann,AlfredWegenerInstitute,HelmholtzCentreforPolarandMarineResearch,Potsdam,Germany

TheabyssalNorthPacificOcean'slargevolume,depth,andterminalpositiononthedeepoceanicconveyormakeitacandidatesitefordeepcarbontrappingaspostulatedbyclimatetheorytoexplainthemassiveglacialdrawdownofatmosphericCO2.AsthemajorbasinsoftheNorthPacifichavedepthsof5500-6500m, far below themodern and glacial Calcite CompensationDepths (CCD), these abyssal sediments arecarbonate-freeandthereforenotsuitableforcarbonate-basedpaleoceanographicproxyreconstructions.Instead, paleo-, rock and environmentalmagneticmethods turned out to be well applicable to thesehololyticabyssalmudsandclays.In2009,theinternationalINOPEX('InnovativeNorthPacificExperiment')researchcruiseoftheGermanRVSONNEcollectedtwoocean-spanningEWsedimentcoretransectsoftheNorthPacificandBeringSearecovering a total of 50 piston and gravity cores from 45 sites. Out of seven here considered abyssalNorthwestPacificpistoncorescollectedatwaterdepthsof5100to5700mwithmostlycoherentshipboardsusceptibility logs, the20.23m longSO202-39-3, retrievedfrom5102mwaterdeptheastofnorthernShatskyRise(38°00.70'N,164°26.78'E),wasratedasstratigraphicallymostpromisingrecordoftheentirecore transect and selected for detailed paleo- and environmental magnetic, geochemical andsedimentologicalinvestigations.ThiscorewasdatedbycorrelatingitsRPIandBa/Tirecordstowell-datedreferencerecordsandprovidesacontinuoussequenceofthepast940kyrs.Themoststrikingrockmagneticfeaturesarecoherentmagnetite-depletedzonescorrespondingtoglacialperiods.Intheinterglacialsections,detrital,volcanicandevensubmicronbacterialmagnetitefractionsareexcellently preserved. These alternating magnetite preservation states seem to reflect dramaticoxygenationchangesinthedeepNorthPacificOceanandhintatlarge-scalebenthicglacialcarbontrappingfollowed by subsequent interglacial carbon burn-down and CO2 release. Abyssal Northwest Pacificsedimentsmayhaveservedasamajorglacialcarbonreservoirinparticularsincetheonsetofsystematic100kyriceagecyclesattheendoftheMid-Pleistocenetransition(MPT).StagnantglacialAntarcticBottomWater, which expanded primarily into abyssal South Atlantic basins during the MPT interim phase,thereafterseemedtoflowpreferentiallyintothedeeperandlargerabyssalIndo-Pacificbasins,whereitappears to have enabled efficient sedimentary and bottom-water carbon-trapping. More intensivescavenging of theNorthwest Pacific surface oceanby enhanced glacial Asian dust flux is suggestedbyparallelTOCandquartzcontents,enhancingglacialcarbonaccumulationdespitepotentiallylowerexportproduction.Themagnetic recordsalso identifynumerouspartlyconsistent tephra layers,whichcanbematchedbetweenmostrecordsofthecoretransect.

66



FirstglimpseontheenvironmentalmagneticrecordoflateEocenetolate

OligoceneagedUlantatalSequence,Nei-Mongol,ChinaPresenter:

JoonasWasiljeff([email protected])

Authors: JoonasWasiljeff,DepartmentofGeosciencesandGeography,P.O.Box64,FI-00014UniversityofHelsinki,FinlandAnuKaakinen,DepartmentofGeosciencesandGeography,UniversityofHelsinki,FinlandJohannaSalminen,DepartmentofPhysics,UniversityofHelsinki,FinlandZhaoqunZhang,KeylaboratoryofVertebratePaleontologyandHumanOriginsofChineseAcademyofSciences,InstituteofVertebratePaleontologyandPaleoanthropology,ChineseAcademyofSciences,Beijing,China

Ulantatal isarenownedfossil locality inAlxaLeftBanner, Inner-Mongolia(Nei-Mongol),China,andhaswitnessednumerouspaleontologicalexcavationssince1970s.Althoughtheareahasproducedasignificantcollectionofvertebratefaunas,knowledgeofthestratigraphy,agesanddepositionalenvironmentshasremainedpoorornearlynon-existent.ThisstudycorrelatesthesedimentsoftheUlantatalareawiththeGeologic Time Scale (GTS), thus providing age estimations for the fossil-bearing horizons. In addition,preliminaryresultsofthefirstmulti-parametermagneticmeasurementsfromtheareaarepresented.Landscape of the Ulantatal formation, named after the Ulantatal gulley, is predominated by gentletopographywithlowuplandsandsmallgullies.Outcropsoftheareamostlyshowaratheruniformpatterncharacterizedbyfine-grainedmassivesedimentsoccasionallyinterbeddedwithcoarsergrainedhorizons.Our field investigations in Ulantatal have yielded over 10 000 specimens, including insectivores,lagomorphs, rodents, artiodactyles,perissodactyls and carnivores. The sequenceproduces fossils alongmostofthesection,withtherichestfossiloccurrencesinthelowerhalfofthesequence.Rockmagneticmethodswereutilizedtogainbetterunderstandingofthemagneticmineralcomposition,concentrationandgrainsizeintheUlantatalsequence,andtoplaceitinatemporalframework.Orientedpalaeomagneticsampleswerecollectedevery20-50cmthroughseveral20-25-m-thicklocalsections.OurmagneticsectionbasedontentativebiostratigraphysuggestsacorrelationinmagnetozonesC15ntoC9n,withanagerangeofabout35-27Ma,andplacesthelowermostfossilsiteinUlantatalinthelatestEocene.Sedimentation rates derived from thesemagnetostratigraphic results are in order of 1-6 cm/kyr. Ouranalysesshowthereisvariationinmagneticgrainsizeandconcentrationthroughoutthesection.However,characteristic remanentmagnetization ismainlycarriedbymagnetiteassuggestedby thermomagneticandhysteresismeasurements.Diagnosticratios indicatingthegrainsizeofferrimagneticmaterials,andrelative abundance of ferri- to antiferromagnets were calculated, of which the latter also attest toferrimagnetpredominance.Amountofsingledomain(SD)grainsalternatealongthesequenceaccordingto ìàARM/SIRMand ìàARM/ìàlf,whereas variance in superparamagnetic (SP) sized grain distribution issubtle as indicated by frequency dependency of susceptibility. Preliminary hysteresis parametermeasurementsalsoimplyvaluessimilartopseudo-singledomain(PSD)loessandpaleosols.ThiscorrelationplacesforthefirsttimeaprecisetemporalcontrolontheOligocenestratigraphyoftheUlantatalareaandprovidesauniqueareato investigate indetail thephysicalandbioticchangesduringaperiodofmajorglobalpalaeoenvironmentalchangesacrosstheEocene-OligoceneTransition(EOT).

67



FifteenyearsofmagneticmonitoringofPMatINGV(Rome,Italy):keyresults,perspectivesandoutreachactivities

Presenter: AldoWinkler([email protected])Authors: AldoWinkler,INGV,Italy

LeonardoSagnotti,INGV,Italy

FollowingtheoriginalimpulsefromtheMAG-NETEuropeanproject(1999-2002),theINGVpaleomagneticlaboratory has been involved inmany research activities about themagnetic properties of particulatematter (PM), ranging from biomonitoring studies on leaves and lichens to analyses on filters from airmonitoring stationsanddustsemittedby cars. The first surveywasaddressed to thebiomonitoringoftrafficrelatedPMinasouthernsectorofRome,samplingPlatanussp.andQ.ilexleaves.Theconcentration-dependentmagneticparametersprovidedexcellentevaluationsofthelong-termpollutionloadings,withthe production of susceptibility maps of the investigated area.Further biomagnetic studies in Romedemonstrated that airbornemagnetic PM substantially reduces at a distance of 10m tomajor roads;subsequentcleaningexperimentsindicatedthatthemagneticPMismostlycaughtindepthintotheleafstructureofQ.ilexleaves.AboutPM10airfilters,anexperimentalapproachwassuggestedforestimatingthepercentageofPM10transportedfromnaturalexogenoussources;moreover,itwaspointedoutthatthemostofanthropogenicPM10inRomeoriginatedfrommotorvehicles.Afterwards,coupledmagneticand electron microscopy analyses were effective to discriminate the source of various magnetic PMpopulations;Fe-richparticlesfromdiskbrakespowdersandfromdieselandgasolineexhaustpipeswerecomparedtothosefromleaves,whichshowedmixedcontributionfromallthesources.Pilotstudieshavebeen conducted on the magnetic properties of dusts from cabin air filters. Further analyses werespecifically addressed to the evaluation of the contribution of superparamagnetic (SP) particles to theoverall magnetic assemblage of traffic-related PM, showing that the SP fraction mainly occurs inassociationtocoarsermultidomainmagnetite-likegrains.Thenextresearchdirectionwasaddressedtotransplantedlichens,whichwereexposedfor180daysaroundacementplantinSlovakia,comparingthemtonativelichensandneighboringbark,soilandrocks.Theresultspointedoutthesuitabilityoflichensasair pollutionmagnetic biomonitors, after taking into account that the geological characteristics of thesubstratemayaffecttheirmagneticproperties.Transplantedlichenswerealsoexposedfor2monthsinagridcoveringagricultural, forested, industrialandurbanareas innortheastern Italy.Thepost-exposureelementcontentandthemagneticdataagreed,revealingamodestanthropogenicimpactontheterritory,mostly limited to an industrial park. Lichens were effective accumulators for biomagnetic monitoringstudies,theirmagneticpropertiesbeingexcellentproxiesforheavymetalpollution.Withagridoflichentransplants, it is possible to investigate the variations of their magnetic properties according to theexposureperiodandtheirinitialunpollutedconditions,withthepossibilityofcoveringunvegetatedareas,thusbypassing the intrinsic limitsofmagneticmeasurementson leaves.Theseresultshaveoftenbeenpresentedduringpublicoutreachevents;moreover,teamsofsecondaryschoolstudentshaveconductedsurveysofthemagneticpropertiesofleavesinRome,thusintroducingrock-magnetismbasicswhileraisingawareness of urban environmental pollution. This review aims to stimulate the integration of rockmagneticmethodswithtechnical,biologicalandmedicalaspects,toensurenewperspectivesandwideapplicationstothisfieldofresearch.

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Determininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterials

Orals:ThursdayJuly13–08:30-12:00


Posters:FridayJuly14–13:00-15:30deVagant

Convenors:LisaTauxe&NickSwanson-Hysell

start end talk+Q&A presenter abstracttitle

08:30 08:35 5 Introduction 08:35 09:10 25+10 ClaireNicols FromMetaltoDust:InterrogatingPaleomagnetic

SignalsinMeteoriticMetalandOlivineInclusions09:10 09:25 15 Lightningtalks GreigPaterson,MichaelVolk,MichaelWack,

LouiseHawkins,AndyBiggin09:25 10:00 25+10 DennisKent LateJurassic-EarlyCretaceousApparent(orTrue)

PolarShifts10:00 10:30 30 coffeebreak 10:30 10:40 10 Lightningtalks AnnikaGreve,SaioaCampuzano,JoséCarlos

PérezFuentes,ShelbyJones-Cervantes,WilborPoletti

10:40 11:15 25+10 JoshuaFeinberg Obtaininghigh-resolutionrecordsofshort-termgeomagneticbehaviorusingspeleothems.

11:15 11:25 10 Lightningtalks HannaAsefaw,StanislavaAkimova,PierreCamps,MiriamGómezPaccard,MercedesRivero-Montero,AnnemariekeBéguin

11:25 12:00 25+10 RonShaar Short-termsecularvariationsfromLevantarchaeomagnetism:methods,applications,andchallenges


Posters


abstracttitle

StanislavaAkimova NewArcheointensityDatafromLate(Pottery)NeolithicPre-HalafandHalafSettlementsYarimTepe1And2(NorthernIraq)

HannaAsefaw PaleointensityEstimatesfromtheGolanHeightsAnnemariekeBéguin TheevolutionoftheLevantgeomagnetichighcapturedinMediterranean

sedimentsAndyBiggin Thegeomagneticreversalfrequencyrecordanditspotentiallinksto

mantledynamicsPierreCAMPS InsearchofthepastinclinationandintensityoftheEarth'smagneticfield

recordedinbuildingmaterialsofbakedclay.SaioaA.Campuzano PalaeosecularvariationsofthegeomagneticfullvectorinIberiaforthelast

3000years.UpdatingtheIberianarchaeomagneticcatalogue.JoséCarlosPérezFuentes

AnupdatedregionalgeomagneticfieldmodelforEuropeinthelast3kabasedontheRSCHA-2Dtechnique

MiriamGómez-Paccard TRManisotropycorrection:anessentialrequirementtoassesspastgeomagneticfieldstrengthfromancientpotteries.EvidencefromnewarcheointensitydatafromNWArgentina.

AnnikaGreve PalaeointensityandrockmagneticinvestigationsonHolocenelavasfromNewZealand

LouiseHawkins TowardsabetterunderstandingofPhanerozoicgeomagneticfieldvariation:PalaeointensitydatafortheLateSilurian-EarlyCarboniferousfromthenorthernUK

ShelbyA.Jones-Cervantes

DatarecoveryofNorthAmericandirectionalarchaeomagneticrecordsforthedevelopmentofarobustreferencecurveforthe'FourCorners'regionoftheAmericanSouthwest

GreigA.Paterson RockmagneticcontrolsonpaleointensitydataWilborPoletti ArcheomagneticfieldstrengthintheSouthAmerica:Areviewforthelast

twomillenniaandpreliminaryresultsfromAmazonregionMercedesRivero-Montero

REVISITINGTHEAGEOFTHEFIRSTIRONAGEINTHEEASTERNIBERIANPENINSULAFROMARCHEOMAGNETICDATINGRESULTS

MichaelVolk Theuseofpressuredemagnetizationasmeanstoimproveabsolutepaleointensitymeasurements

MichaelWack MagneticPropertiesofIron-NickelParticlesPreparedbyMechanicalAlloying


DetermininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterialsPoster - Friday July 14 - 13:00-15:30 & 2 min. lightning talk - Thursday July 13 - 11:05-11:20

NewArcheointensityDatafromLate(Pottery)NeolithicPre-HalafandHalafSettlementsYarimTepe1And2(NorthernIraq)

Presenter: StanislavaAkimova([email protected])Authors: StanislavaAkimova,InstitutdePhysiqueduGlobedeParis(France)/InstituteofPhysicsofthe

EarthRAS(Moscow,Russia)YvesGallet,InstitutdePhysiqueduGlobedeParis(France)ShahmardanAmirov,ArcheologicalInstituteRAS(Moscow,Russia)NataliaPetrova,ArcheologicalInstituteRAS(Moscow,Russia)

Mainobjectiveof this study is to recover thegeomagnetic field intensity variations in theMiddleEastduringthe7thand6thmillenniaBC,withaparticularinterestonrapidvariations.Wewillreportonnewarcheointensity data obtained from two ancient settlements, discovered by Soviet archeologists inNorthernIraqbetween1969-1976YarimTepe1andYarimTepe2.YarimTepe2isdatedfromtheLateNeolithicHalafperiod(~5950-5300BC)andisrepresentedasa7-mthicksequenceofculturaldeposits,dividedinto9archeologicallevels(buildinghorizons).YarimTepe1isdatedfromtheLateNeolithicPre-Halafperiod(~6300-5950BC,includingthreeregionalculturalphases:HassunaI,IIandIII)andrepresentsa6,5-msequenceofculturaldeposits,dividedinto12archeologicallevels.AveryimportantcollectionofartifactsfromYarimTepe1and2,inparticularseveralthousandsofpotsherds,isstoredattherepositoryofArcheologicalInstituteinMoscow,whereoursamplingwasundertaken.

We collected 30 groups of fragments from Yarim Tepe 2 and 14 groups from Yarim Tepe 1 fromsuperimposedstratigraphiclayersofabout20cmthicknessinaverage.Eachgroupconsistsofatleast3(upto10)fragments.Alldatawerecarriedoutusingthethree-axisvibratingsamplemagnetometerTriaxe,whichallowsmagnetizationmeasurementsofasmall samples (~1cm3)directlyathigh temperatures.Archeointensity results were obtained using the experimental protocol developed for the Triaxemagnetometer. This protocol takes into account both the anisotropy and cooling rate effects onthermoremanentmagnetizationacquisition.TogetherwithotherdatapreviouslyobtainedfromSyriaandBulgaria the new archeointensity results show the occurrence of rapid geomagnetic field fluctuationsduringthe7thand6thmillenniumBC.DatafromYarimtepe2alsoconfirmstheoccurrenceofashort-lastinggeomagneticfieldintensitypeakaround~5500BC,withintensityvariationratesashighas~0.35-0.15µT/yearoverafewdecades.

71



PaleointensityEstimatesfromtheGolanHeights

Presenter: HannaAsefaw([email protected])Authors: HannaAsefaw,ScrippsInstitutionofOceanography

LisaTauxe,ScrippsInstitutionofOceanographyRonShaar,HebrewUniversityofJerusalemNicoleBehar,HebrewUniversityofJerusalem

ZheHaratashShaamvolcanicfieldintheGolanHeightsformedoverthelast0-5Mabasedonrecent40Ar-39Ardating.Wesampled10cinderconesand4lavaflowsspanningfrom0.11to4.71Ma.WethenappliedtheIZZIpaleointensityprotocol(Yuetal.,2004)toestimateancientfieldstrength.Afterapplyingstrictcriteria(Cromwelletal.,2015),wefoundthatonly66ofour302specimenspassed.Ofthesuccessfulsamples,63werecindercones,whileonly2were lavaflows.Ouraverageestimateofpaleointensity is33.02µT±15.1µT.Theagesofthesuccessfulsamplesfallinthreegroups:~0.01,~0.7and4.8Ma.Iwillpresentourpreliminaryrockmagneticandpaleointensitymeasurements.

References:Yongjae, Y., Tauxe, L., andGenevey, A. "Toward an optimal geomagnetic field intensity determinationtechnique."Geochemistry,Geophysics,Geosystems5.2(2004).Cromwell,G.,etal."PaleointensityestimatesfromhistoricandmodernHawaiianlavaflowsusingglassybasaltasaprimarysourcematerial."PhysicsoftheEarthandPlanetaryInteriors241(2015):44-56.

72



TheevolutionoftheLevantgeomagnetichighcapturedinMediterraneansediments

Presenter: AnnemariekeBéguin([email protected])Authors: AnnemariekeBéguin,UtrechtUniversity

LennartdeGroot,UtrechtUniversityAmaliaFilippidi,UtrechtUniversityGertdeLange,UtrechtUniversity

Thegeomagneticfieldcanvarydramaticallyoveronlydecadesandthousandsofkilometers;the'Levantgeomagnetichigh'isprobablythebest-knownexampleofsuchshort-livedfeatureoftheEarth'smagneticfield. Yet, the size, shapeand temporal variationsof thisphenomenonare currently still enigmatic. Tobetter constrain the Levant geomagnetic high in time and space, we obtained continuous full-vectorrecordsfromthreemarinesedimentcoresformtheMediterraneanSea.Thecoresarelocated(1)betweenSpainandMorocco(Alboran),(2)EastofCalabria,Italy(Adria),and(3)NorthoftheNileDelta(Levant).Thesedimentation rate in all three cores is high, typically 20 to 65 cm/kyr, resulting in 15-50 years perpaleomagnetic sample of 1 cm3; age-depth models are available for all cores. The geomagnetic fieldvariationsbetween8and1kaarecaptured,intotal681sampleswereanalyzed.

We first analyzed the rock magnetic properties of the sediment cores to assess the reliability of thesedimentsasrecordersofgeomagneticfieldvariations.Themagneticcarryinggrainswithinthesedimentsaremainlypseudo-singledomainmagnetitegrains,withsmoothandlittlevariationintheconcentrationofmagneticmaterialthroughoutthecores.Thesamplesunderwentalternatingfielddemagnetizationtoobtainthepaleodirections(e.g.declinationandinclination),followedbyapseudo-Thellierexperimenttoobtain the relativepaleointensity.Periodsofhigh intensityarepresent inall threecores;although thetimingdiffersslightlyfromthe'Levantgeomagnetichigh'.Highpaleointensitiesarefirstlyobservedinthewesternpart(Alboran)at2.6kyrBP,theninthecentralpart(Adria)at2.4kyrBPandlastlyintheeasternpart(Levant)at2.2kyrBP,implyinganeastwardmovementoftheintensityhigh.Thehighpaleointensitieswe find are all younger than the short-lived, high-fidelity peaks present in the LevantArcheomagneticCompilation (3.0-2.8 kyr BP), and the high paleointensities seem to coincide with periods of shallowinclination, a counterintuitive observation if the high paleointensities are to be explained by a dipolarphenomenon.WethereforearguethatthehighpaleointensitiesintheMediterraneaninthefirstcenturyBCmustarisefromahighordergeomagneticphenomenon.

73



Thegeomagneticreversalfrequencyrecordanditspotentiallinkstomantledynamics

Presenter: AndyBiggin([email protected])Authors: AndrewBiggin,UniversityofLiverpool

MarkHounslow,LancasterUniversityMatDomeier,UniversityofOslo

Thelong-termvariabilityinaveragegeomagneticreversalfrequencyoverthePhanerozoic,consistingofsuperchronsinterspersedwithperiodsofhyper-reversalactivity,remainsoneofthemostprominentandenigmatic featuresevidentwithinpalaeomagnetic records.This variability iswidelyexpected to reflectmantle convection modifying the pattern and/or magnitude of core-mantle boundary heat flow, andthereby affecting the geodynamo's operation, but actual causal links to surface geological processesremain tenuous. Previous studies have argued thatmantle plumes, superplume oscillation, true polarwander,andavalanchingofcoldslabsintothelowermantlecouldallbeatleastpartlyresponsible.Herewewillpresenta re-evaluated reversal frequency record for thePhanerozoicanduse it, togetherwithpublished findings from numerical geodynamo simulations, to push further towards an integratedexplanationofhowthegeomagneticfieldhasrespondedtomantleprocessesoverthelastfewhundredsofmillionyears.

RecentworkonabsoluteplatemotionsbackthroughthePhanerozoichaveallowedestimationstobemadeastotheglobalsubductionfluxthroughtime.Astheprimarydriverofmantleconvection,variationsintherateofcoldslabsfluxeddowntowardsthebaseofthemantlemightbeexpectedtoshowsomecorrelationwiththereversalfrequency,albeitwithanassociatedtimedelaytoallowthecoldmaterialtodescendfarenoughtoinfluencecore-mantleheatflow.Herewewillreporttheresultsofastatisticalanalysisaimingto determine if significant correlations exist and what the associated time delay is. The results arepreliminarybutsuggestaconsiderablylongertransittimethanisimpliedbynumericalmodelsofmantlecirculation.Muchfutureworkneedstobefocusedonimprovingpalaeomagneticrecordsandintegratingtheirfindingswithgeodynamicalmodelling.Ifsuccessful,theywouldpotentiallyopenupanewfrontinapplyingpalaeomagnetismtotacklelong-standinggeodynamicalproblems.

74



InsearchofthepastinclinationandintensityoftheEarth'smagneticfieldrecordedinbuildingmaterialsofbakedclay.

Presenter: PierreCAMPS([email protected])Authors: PierreCAMPS,GéosciencesMontpellier,CNRSandUniversityofMontpellier,Montpellier,

France.PatrickNICOL,GéosciencesMontpellier,UniversityofMontpellier,Montpellier,France.ThierryPOIDRAS,GéosciencesMontpellier,CNRSandUniversityofMontpellier,Montpellier,France.

TakingadvantageofarenovationprojectontheBrevenneaqueductinLyon(France),wecarriedoutanarcheomagneticstudyonseverallevelingcourseoffiredbricks.Thereconstructionsiteislocatedontheupperpartoftherampofasiphonclosetothereceivingtankgivingtothesiteaspecialandverytouristiccharacter.BuiltearlyinthefirstcenturyADbytheromans,theaqueductmusthavedelivereditswatertotheancientcityofLugdunum.

First,weappliedthemethoddevelopedforarchaeomagneticdatingofdisplacedbricks(Thellier,1938;Goulpeau&Langouet,1980;Lanos,1987).Thismethod,althoughwelldescribedintheliterature,seemstobeverylittleusedinpractice.TheprincipleistofindtheinclinationoftheTRMofbrickspresumedtohavebeenfiredinahorizontal,upright,oron-edgepositiononthestatisticallyhorizontalfloorsofkiln.Themean inclinationfound(62.5°+/-2.3°) is inperfectagreement,whencomparedtoaregionalmodelofsecularvariation,withthearcheologicalageoftheconstructionofthewaterinfrastructure.

Second,wedeterminedthepalaeointensitywithmultispecimenprotocol(MSP-DSC,FabianandLeonhardt,2010).Theexperimentswereperformedwithaprototypeofaveryfast-heatinginfraredfurnacedevelopedinMontpellier(FURéMAG,patent#1256194).Twokeypointsdetermineitscharacteristics.Thefirstistoheatuniformlyasinglerocksampleofa10-cm3standardvolumeveryfast.Thesecondistoapplytothesampleduringtheheating(andthecooling)aprecisemagneticinductionfield,perfectlycontrolledin3Dwith a measured precision better than 1°. The study is also a nice opportunity to present a Shiny-Rinteractivewebapplicationdevelopedtoprocess,analyze,andreportontheMSP-DSCdata.

75



PalaeosecularvariationsofthegeomagneticfullvectorinIberiaforthelast3000years.UpdatingtheIberianarchaeomagneticcatalogue.

Presenter: SaioaA.Campuzano([email protected])Authors: AlbertoMolina-Cardin,UniversidadComplutensedeMadridandInstitutodeGeociencias

(IGEO-CSIC)SaioaA.Campuzano,UniversidadComplutensedeMadridandInstitutodeGeociencias(IGEO-CSIC)M. LuisaOsete,UniversidadComplutensedeMadridandInstitutodeGeociencias(IGEO-CSIC)MercedesRivero-Montero,UniversidadComplutensedeMadridandInstitutodeGeociencias(IGEO-CSIC)FátimaMartin-Hernández,UniversidadComplutensedeMadrid,InstitutodeGeociencias(IGEO-CSIC)andInstitutoMagnetismoAplicado(IMA)SaraGuerrero-Suárez,UniversidadComplutensedeMadridandInstitutodeGeociencias(IGEO-CSIC)AliciaPalencia-Ortas,UniversidadComplutensedeMadridandInstitutodeGeociencias(IGEO-CSIC)JoséCarlosPérez-Fuentes,UniversidadComplutensedeMadridandInstitutodeGeociencias(IGEO-CSIC)F. JavierPavón-Carrasco,UniversidadComplutensedeMadridandInstitutodeGeociencias(IGEO-CSIC)MiriamGómez-Paccard,InstitutodeGeociencias(IGEO-CSIC)AnnickChauvin,GéosciencesRennesUMR-CNRS6118,UniversitédeRennes1

WepresentthefirstupdateofthearchaeomagneticdatacataloguefortheIberianPeninsulacoveringthelast3000years.ThefirstarchaeomagneticdatacompilationforIberiawaspublishedin2006,including63archaeomagnetic directions and making possible the generation of the first directional PalaeosecularVariationCurve(PSVC)inIberia.Sincethen,thenumberofdirectionaldatahasincreasedbymorethan80%,ofwhicharound20%havebeenstudiedinthiswork.Regardingarchaeointensitydata,wepresent20newhighqualityarchaeointensities,inadditiontopreviouslypublishedones(about100data),bycreatingthefirstarchaeointensitycatalogueforIberiaspanningthelast3000years.ThedifferentqualitiesofthedataincludedinthisIberiandatasethavebeenevaluatedfollowingdifferentpalaeomagneticcriteria,suchasthenumberofspecimensanalysed,thelaboratoryprotocolappliedandthekindofmaterialstudied.TheimprovementofthedatabaseisespeciallynotableforthefirstmillenniumBC(about50%ofthenewincludeddata),aperiodforwhichtherewasnotpossibletodevelopanintensitypalaeosecularvariationcurveduetothelackofhighqualityarchaeointensitydata.ThisnewcompilationofarchaeomagneticdatahasprovidedenoughnewinformationtogeneratethefirstPSVCofthegeomagneticfullvectorforIberiafor the last three millennia, which have been obtained by hierarchical bootstrap method using onlyselectedhighqualitydatafromthecatalogueinordertoobtainthemostreliablesecularvariationcurve.No important differences between these curves and those calculated from regional and globalgeomagneticfieldmodelsareregistered,withthemostnotablediscrepanciesobservedinthe intensitycurveandduringthefirstmillenniumBC.ThesenewPSVCsofferacomprehensiveviewofthevariationsof thegeomagnetic field in IberianPeninsulaand issuitableasaMasterCurve inthearchaeomagneticdatingtechniqueforarchaeologicalcombustionstructureslocatedinthisregion.

76


DetermininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterialsOral (invited) - Thursday July 13 - 10:40-10:55

Obtaininghigh-resolutionrecordsofshort-termgeomagneticbehaviorusingspeleothems.

Presenter: JoshuaM.Feinberg([email protected])Authors: JoshuaM.Feinberg,InstituteforRockMagnetism,UniversityofMinnesota

Precise determination of the timing and duration of short-lived geomagnetic behavior, includingexcursions,jerks,andspikes,willhelpelucidatemajorscientificquestionssituatedattheintersectionofgeology, geophysics, paleoclimatology, and even anthropology. Speleothems (chemical sedimentarydepositsformedincaves)havecertainkeyadvantagesfordocumentingshorttermgeomagneticbehaviorover traditional paleomagnetic archives. They are crystalline, and therefore the issues associatedwithremanenceacquisition insoftsedimentsareavoided.Thetimelagbetweenthedepositionofmagneticparticles on speleothem surfaces and their encapsulation in the crystalline structure is short, asdemonstratedbyactivelygrowingstalagmitesthatrecordthemagneticdirectionoftheambientmagneticfield.Speleothemsmaygrowcontinuouslyforthousandsofyears,andcanbedatedwithveryhighaccuracyandprecisionusing230Thdating,atechniquethatcanbereliablyusedonspecimensyoungerthan600ka(wherefiner-scaleageconstraintscanbederivedbycountingannualgrowthlaminae).Recentspeleothemmagnetism studies have shown that magnetic minerals encapsulated in stalagmites can be usedsuccessfullyindatinggeomagneticexcursionssuchastheBlake(Oseteetal.,2012)andLaschamp(Lascuetal.,2016).Althoughthereistremendouspotentialforpaleomagneticstudiesusingspeleothems,therearestillnumerouschallengesthatmustbeovercome,suchas (1) low intensitymagnetizations thatarefrequentlybelowthesensitivityofmostSQUIDmagnetometers,(2)differencesintherecordingpotentialbetween stalagmites, flowstone, and stalactites, and (3) looking beyond the 600 ka limit of the 230Thtechnique.Thispresentationwilladdresssomeofthesechallenges,anddiscussapproachesthatmayallowresearcherstomovebeyondthem,sothatourcommunitymayexaminethebehaviorofthegeomagneticfieldwithgreaterresolutionandindeeptime.

77



AnupdatedregionalgeomagneticfieldmodelforEuropeinthelast3kabasedontheRSCHA-2Dtechnique

Presenter: JoséCarlosPérezFuentes([email protected])Authors: IssacharR.,DepartmentofGeosciences,Tel-AvivUniversity,Tel-Aviv,IsraelandGeological

SurveyofIsrael,Jerusalem,Israel.LeviT.,GeologicalSurveyofIsrael,Jerusalem,Israel.MarcoS.,DepartmentofGeosciences,Tel-AvivUniversity,Tel-Aviv,

Recentyearshaveseenasignificantimprovementinthearchaeomagneticandvolcaniccatalogues,withdirectional data growing as much as 40%, and intensity data growing by 25%. The higher density ofpalaeomagneticdatainEuropecomparedtotherestoftheglobeallowsforthedevelopmentofregionalmodelscoveringonlythisarea,withthebenefitsofhigherspatialresolutionandtheremovalofinfluenceofoutlierdatameasuredelsewhere.In2009,Pavón-Carrascoetal.publishedthefirstregionalmodelforEuropebasedontheSCHAtechnique(Haines,1985),whichallowsforthemodellingofgradientfields(suchasthegeomagneticfield)overthesurfaceoftheEarth,gatheringbotharchaeomagneticandinstrumentaldataspanningroughly3000years.Inthiswork,anupdatedregionalgeomagneticfieldmodel,coveringthelastthreemillenniainEurope,ispresented.ThisstudyhasbeencarriedoutusinganoveltecnhiquecalledR-SCHA-2D,developedbyThebault(2008)asanimprovementoverSCHAespeciallysuitedtothemodellingofdataatequalorsimilaraltitude,pairedwithphysicallymeaningfulregularization,andresultsinamodeloflowmathematicalcomplexityandwellsuitedforarchaeomagneticdating.

78


Determininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterials Poster - Friday July 14 - 13:00-15:30 & 2 min. lightning talk - Thursday July 13 - 11:05-11:20

TRManisotropycorrection:anessentialrequirementtoassesspastgeomagneticfieldstrengthfromancientpotteries.Evidencefromnew

archeointensitydatafromNWArgentina.

Presenter: MiriamGómezPaccard([email protected])Authors: MiriamGómez-Paccard,InstitutodeGeociencias(CSIC-UCM),CiudadUniversitaria,28040

Madrid,Spain.AnnickChauvin,Géosciences-Rennes,CNRS,UMR6118,UniversitédeRennes1,35042,Rennes,France.MariaEsterAlbeck,CONICET,FacultaddeHumanidadesyCienciasSociales,UniversidadNacionaldeJujuy,Otero262,4600,SanSalvadordeJujuy,Jujuy,Argentina.MariaAmaliaZaburl’n,FacultaddeHumanidadesyCienciasSociales,UniversidadNacionaldeJujuy,Otero262,4600,SanSalvadordeJujuy,Jujuy,Argentina.DiegoMartinBasso,UNIHR-ISHIR,CONICET,UniversidadNacionaldeJujuy,ArgentinaFacultaddeHumanidadesyCienciasSociales,UniversidadNacionaldeJujuy,Otero262,4600,SanSalvadordeJujuy,Jujuy,Argentina.

Improvinggeomagneticfieldreconstructionsclearlyposesahigh-prioritychallengeinEarthSciencestoday.Abettercharacterizationofthevariationofthegeomagneticfieldstrengthatcentennialtomillennialtimescales in the southern hemisphere is particularly crucial to disentangle the long-term evolution of theEarth's dipole moment, a global characteristic of our planet. Here we present new high-qualityarcheointensitiesobtainedfromthestudyoffourcollectionsofwell-datedpotteryfragmentsfromLaPuna(Northwest Argentina). The classical Thellier method including regular partial thermoremanentmagnetization (pTRM) checks and TRM anisotropy and cooling rate corrections has been used forarcheointensity determination. The new data obtained shed new light on the past fluctuation ofgeomagneticfieldstrengthinSouthAmerica,aratherpoorlyknownregionintermsofgeomagneticfieldintensity fluctuations. Inaddition, the results confirm thatTRManisotropycorrectionsareanessentialrequirementwhenstudyingpastgeomagnetic fieldstrength fromthearcheomagnetic studyofpotteryfragments.FuturegeomagneticfieldreconstructionsdowelltohavetheTRManisotropyrequirementinmindwhentryingtounravelgeomagneticfieldvariationsfrompottery-basedarcheointensitydata,bothatregionalorglobalscales.

79



PalaeointensityandrockmagneticinvestigationsonHolocenelavasfromNewZealand

Presenter: AnnikaGreve([email protected])Authors: AnnikaGreve,SchoolofChemicalandPhysicalSciences,VictoriaUniversityofWellington,NZ

GillianTurner,SchoolofChemicalandPhysicalSciences,VictoriaUniversityofWellington,NZMimiHill,GeomagnetismLaboratory,SchoolofEnvironmentalSciences,UniversityofLiverpool,UKAndreasNilsson,DepartmentofGeology,LundUniversity,Sweden

We report the results of rock magnetic studies and palaeointensity experiments on andesitic and/orrhyoliticlavasfrom28sitesrepresentingtendistincteruptiveunitsoftheTongariroandOkatainaVolcanicCentres, Taupo Volcanic Zone, New Zealand. Palaeointensity experiments were conducted using bothtraditionaldouble-heatingandmicrowavemethods.Rockmagneticinvestigationsincludedacombinationofmineral-opticalinvestigations,backscatteredelectronimaginganddetailedrockmagneticexperiments.Success rates varied somewhat with the location within the lava flows sampled and correspondingdifferences intherockmagneticproperties.Highqualitypalaeointensityresultswereobtainedfrom10unitswithvaluesrangingfrom37.0±5.7µTto70.6±4.1µT.TheyfallwellintotherangeofPSVexpectedforthetime-frameinNewZealandandreproducefeaturesofcontinuoussedimentrecords.

80



TowardsabetterunderstandingofPhanerozoicgeomagneticfieldvariation:PalaeointensitydatafortheLateSilurian-EarlyCarboniferousfromthe

northernUK

Presenter: LouiseHawkins([email protected])Authors: LouiseHawkins,UniversityofLiverpool

AndyBiggin,UniversityofLiverpoolSheikerraThomas-Cunningham,UniversityofLiverpoolPatipanSaengduean,UniversityofLiverpoolEdSage,UniversityofLiverpoolElliotHurst,UniversityofLiverpool

Based on palaeomagnetic records for the past ~600Ma, it has been suggested that variations ingeomagnetic field behaviour occur on timescales of 10-100Ma and are related tomantle convectioninfluencingthegeodynamo.Thisincludesatransitioninthetime-averagedgeomagneticfieldbehaviourobservedintheMesozoicEra;fromapeakinreversalrateintheJurassic(~170Ma),associatedwithaweakgeomagnetic field, going into an apparently stronger than average field during theCretaceousNormalSuperchron (CNS; 121-84Ma). Recent palaeointensitywork has been aimed at determining if a similartransition in field behaviour occurredpreceding the Permo-Carboniferous Reversed Superchron (PCRS;310-265Ma).NewpaleointensityresultsfromtheMinusaBasinandKolaPeninsulasuggestthatbetween408-375Ma,thefieldwasweakcomparedtothemoderndaywithallbutonesitegivingVDMvalues~40ZAm2and,inconjunctionwiththestrangepalaeodirectionsassociatedwiththesesites,maysuggestthattherewasagreatermulti-polarcomponenttothefieldatthistime.Further,asyetunpublished,workonsamplesfromtheViluyTrapsandtheZharovskcomplexofthePatomMargininSiberiafor377-362Magiveevenlowersitemeanvalues,withVDMvaluesintherangeof7-25ZAm2.ThisworksuggeststhattheremayhavebeenasustainedlowfieldleadinguptothePCRS,althoughfurthermeasurementsareneedtoconfirmthisandtoconstrainhowlonglowfieldstrengthspersisted.Totestthis,samplesrangingfromtheLateSiluriantotheEarlyCarboniferous(~425-325Ma)havebeencollectedfromScotlandandnorthernEngland.Allofthesiteshavepreviouslybeenusedfordeterminingthepolepositionfor'Stable'EuropeanPlatee.g.Baltica,withQfactorsof5-7.Someofthesampledsiteshavebeendeterminedtobesuitableforpalaeointensityexperimentswithdirections consistentwith thepreviouslypublisheddataand suitablemagneto-mineralogy.TheinitialpalaeointensityresultsfromThermalThellierandMicrowaveThellier-typeexperiment using IZZI protocol with pTRM checks are between 3.2-28.1µT (6-65 ZAm2). These valuessuggestthatthestrengthofthefieldremainedrelativelylowforalongtimeprecedingthePCRS.

81



DatarecoveryofNorthAmericandirectionalarchaeomagneticrecordsforthedevelopmentofarobustreferencecurveforthe'FourCorners'regionof

theAmericanSouthwest

Presenter: ShelbyA.Jones-Cervantes([email protected])Authors: ShelbyA.Jones-Cervantes,ScrippsInstitutionofOceanography,LaJolla,CA,USA

LisaTauxe,ScrippsInstitutionofOceanography,LaJolla,CA,USAEricBlinman,NewMexicoDepartmentofCulturalAffairs,OfficeofArchaeologicalStudies,SantaFe,NM,USA

Since1964,anacademiclineageofarchaeologists,includingRobertL.Duboisandhisstudents,hasbeencollectingdirectionalarchaeomagneticsamplesfromsitesallovertheworldbutprimarilyfromwithinthe'FourCorners'regionoftheAmericanSouthwest(NewMexico,Arizona,Colorado,Utah).Fewofthedatahavebeenpublished, and if published, typically theywereat the sampleaverage levelwithinhard-to-accessarchaeologicalreports.Moreover,mostthedirectionswerebasedonan'optimumstep'approach,whichmaybelessaccuratethanthemorecommonlyusedprincipalcomponentanalysis(PCA)approach.Thegoalofthisdatarecoveryprojectistodigitize,reanalyzeusingPCA(wherepossible),andpublishthemeasurementlevelresultsforabout6000samples,housedinfourcollections-Dubois,Wolfman-OfficeofArchaeologicalStudies(OAS),Eighmy-Lengyel,andSternberg.

During his lifetime Dubois, the patriarch of the academic lineage, collected and analyzed nearly 2000archaeomagnetic samples. Nearly all the measurement-level data and many of the original orientedspecimensexistwithinhisscientificestate.Thesedataarerecordedinoriginalprintoutsandhandwrittenlogs.EffortsareongoingtoscananddigitizetherecordsintoausefulconsistentformatforreanalysisusingPCA.Currently,almostallmeasurementdatahavebeenscannedandabouthalfofthemeasurement-leveldatahavebeendigitized.Locationandgeochronologicaldataexistseparatefromthemeasurement-levelmagnetic data and have not yet been digitized. The transformation of these data into a useful andconsistentformatisproceedingapace.

PreliminarymagneticdatafromtheDuboisestatehavebeenanalyzedandsubjectedtoqualitythresholdsusingPmagGUI(Tauxeetal.2016,doi:10.1002/2016GC006307).Theresultinginterpretationshavebeensortedintothreebins.1) Samplesthatmeetallthequalitythresholdsandyieldastatisticallysignificantcharacteristicremanentmagnetization(ChRM)2) SamplesthatdonotmeetthequalitythresholdsanddonotprovideastatisticallysignificantChRM3) Qualitysamplesthatwouldbenefitfromfurtheralternatingfielddemagnetization

Similaranalyseswillbeconductedontheestimated4000sampleswithintheremainingthreecollections.TheWolfman-OAScollectioncontainsover1400 samplesand is activelygrowing.Thedataset containsmeasurement data for all specimens preserved in a currently unusable digital form andmost originalorientedspecimens.Over2000samplesexistwithintheEighmy-Lengyelcollection.Thedatafrom1978-2004havealreadybeencontributedtothisprojectbutarecurrentlyinanchallengingtousedigitalform.Thedatafrom2004-presentareforthcoming.DiscussionsareongoingwithSternberg,butitseemslikelythat hewill bewilling to contribute his time, samples, and/or data to the recovery project. Followinganalysisofalldatafromthesefourcollections,thedatawillbeincorporatedintoglobalfieldmodels,whichcanbeusedtodefineareferencecurveforthe 'FourCorners'regionoftheAmericanSouthwest(NewMexico,Arizona,Colorado,Utah).Onlythehighestqualitydatawithindependentgeochronologywillbeincluded.

82


DetermininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterialsOralpreferred

LateJurassic-EarlyCretaceousApparent(orTrue)PolarShifts

Presenter:

DennisKent([email protected])

Authors: DennisKent,Earth&PlanetarySciences,RutgersUniversity,Piscataway,NJ08854,&Lamont-DohertyEarthObservatoryofColumbiaUniversity,Palisades,NY10964,USA.

InapaperpublishedwithTed Irving,oneofhis last (1),weconstructedacompositeAPWpathfortheindependentlyreconstructedcontinentalrealmfromtheTriassicthroughPaleogenebasedon70individualpaleopolesfromallEarth'smajorcratonsandranging inagefrom243to43Ma;thesepoleshadbeenderivedfromigneousrocksandfromonlycertainsedimentaryformationstowhichcorrectionsforI-errorhavebeenmade.Ahithertounappreciatedcuspwasfound,alarge/fastpolarswingacrossadatagapfrom160and145Maandasomewhatsmaller/slowerbackswingbetween145and120Ma,formingacusp.Several kimberlites associatedwithhighprecisionU-Pbperovskite ageswere subsequently sampled inOntario,Canada, inanefforttofill theolderdatagap(2).The154.9±2.4MaPeddiekimberliteyieldsastablenormalpolaritymagnetizationthatiscoaxialwithinlessthan5°ofthereversepolaritymagnetizationofthe157.5±1.2MaTripleBkimberlite.Thecombined~156MaTripleBandPeddiepoleliesaboutmidwaybetween igneouspolesfromNorthAmericanearest inage,consistentwithpolarmotionatarelativelysteadyyetrapid(~1.5°/Myr)pace.AsimilarlargerapidpolarswinghasbeenrecognizedintheMiddletoLateJurassicAPWpathforAdria-Africa(3),suggestingamajormassredistribution.OnepossibilityisthatslabbreakoffandsubductionreversalalongthewesternmarginoftheAmericas(4)triggeredanepisodeoftruepolarwander(5).TheEulerpivotforthepolarshiftfrom160to145MaisinthevicinityofwhatisnowtheBightofBeninofwesternAfrica,aboutthesameplacewherethepivotseemstobelocatedfortherotationintheoppositesensebetween145and120Ma.Whetherreflectingtrue(global)orapparent(continental realmonly)polarwander, thepolar shift(s) imply rapid latitudinal changes that in specificcircumstancesmayhaveinfluencedthedevelopmentofclimate-sensitivefacies(6).1. D.V.Kent,E.Irving,JGR115,B10103,doi:10110.11029/12009JB007205(2010).2. D.V.Kent,B.A.Kjarsgaard,J.S.Gee,G.Muttoni,L.M.Heaman,G-cubed16,983-994(2015).3. G.Muttoni,E.Dallanave,J.E.T.Channell,Paleo3386,415-435(2013).4. K.Sigloch,M.Mihalynuk,Nature496,50-57(2013).5. M.Greff-Lefftz,J.Besse,G-cubed15,4599-4616(2014).6. G.Muttoni,D.V.Kent,GSAToday26,4-10(2016).

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DetermininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterialsOral- Thursday July 13 - 08:35-09:00

FromMetaltoDust:InterrogatingPaleomagneticSignalsinMeteoriticMetalandOlivineInclusions

Presenter: ClaireNichols([email protected])Authors: ClaireNichols,UniversityofCambridge

JamesBryson,UniversityofCambridgeBenjaminWeiss,MITJohnTarduno,UniversityofRochesterRoryCottrell,UniversityofRochesterJuliaHerrero-Albillos,CentroUniversitariodelaDefensa,UniversidaddeZaragozaFlorianKronast,HelmholtzZentrumBerlinRichardHarrison,UniversityofCambridge

Meteoritesprovideawealthofinformationabouttheearlyhistoryofoursolarsystem,theformationandevolution of planets, and their internal dynamics. Here we focus on the paleomagnetic informationrecordedbystony-ironmeteorites,providinguswithauniqueview-pointforplanetesimaldifferentiation,andthegenerationandvariabilityofcoredynamoactivity.

Thepallasitesareadistinctgroupofmeteorites,composedofolivinecrystalssurroundedbyametallicFeNimatrix.Whenetched,themetalrevealstheWidmanstÌlttenpattern;anintergrowthoftaeniteandkamacite lamellae. Between these lamellae, a range of microstructures develop, dictated by the 'M-shaped' Ni diffusion profile. Among thesemicrostructures is the cloudy zone, a region of tetrataeniteislandsinaFe-richmatrix,formedbyspinodaldecomposition.Thetetrataeniteislandsareoftheorderof100 nm in diameter, and their size, structure and composition make them extremely reliablepaleomagneticrecorders.ThedirectionoftheirmagnetisationcanbeimagedusingX-rayPhotoemissionElectronMicroscopy(X-PEEM),andthedistributionoftheirmagnetisationdirectionsprovidesinformationaboutthestrengthofthemagneticfieldthecloudyzoneexperiencedduring itsformation.Wepresentresults fromfivepallasites: Imilac,Esquel,Brenham,MarjalahtiandSpringwater.AllX-PEEMdatawerecollectedattheBESSYIIsynchrotronfacility,Berlin.

WecomplementpaleomagneticstudiesofmeteoriticmetalwithmeasurementsofmagneticinclusionsinolivinecrystalsfromtheSpringwaterpallasite.Alternating-fieldandthermaldemagnetisationexperimentswere carried out at theMIT andUniversity of Rochester Paleomagnetism Laboratories, using both 2GEnterprisesSQUIDmagnetometers,andaWSGIsmall-boreSQUIDmagnetometer.Heatingwascarriedoutusingbothathermaldemagnetizingoven,inacontrolledH2-CO2atmosphere,andusingaCO2laserinair.Resultssuggestthecoredynamoonthepallasiteparentbodywasperiodicallyactive;itwasdrivenbyboththermalandcompositionalconvection,separatedbyaperiodofquiescence.Paleomagneticstudiesonthecloudy zone suggest this is an very promising paleomagnetic recorder, however quantifying accuratepaleointensities remains a challenge. Paleomagnetic studies on thepallasite olivines suggest these areextremelychallengingmaterialstomeasure,andeasilyalterduringheatingevenatlowtemperatures.Thenatureofthemagneticcarrierswithintheolivinesalsoneedsfurtherclarification.

84


Determininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterials Poster - Friday July 14 - 13:00-15:30 & 2 min. lightning talk - Thursday July 13 - 09:10-09:20

Rockmagneticcontrolsonpaleointensitydata

Presenter: GreigA.Paterson([email protected])Authors: GreigA.Paterson,InstituteofGeology&Geophysics,ChineseAcademyofSciences,China

YuhjiYamamoto,CenterforAdvancedMarineCoreResearch,KochiUniversity,,JapanYongxinPan,InstituteofGeology&Geophysics,ChineseAcademyofSciences,China

Linkingrockmagneticpropertiestotheresultsofpaleointensityexperimentshasbeenalongtermgoalinefforts to improve paleointensity reliability, but no clear relationship has yet been identified. Usinghysteresisdata frommagnetitespecimensofknowngrainsize,weusePCAtoquantifyadomainstatetrend(PC1)thatisconsistentwithgrainsizevariations,grainsizedistributionmixing,andtheeffectsofmagnetostaticinteractions.PC1thereforerepresentsaneffectivebulkdomainstatetrendthatcannotbeeasily attributed to a single underlying factor. This trend is consistentwith data frommore that 2000natural volcanic specimens typically used for paleointensity experiments, which suggests that it is aunderlying trend inmostgeological samples.We 'unmix' this referencePC1trend fromhysteresisdatafromspecimensusedforcontrolpaleointensityexperiments(knownNRMinducingfield)andcomparetheobtainedPC1valuesthepaleointensityresults.WefindastrongcorrelationbetweenthereferencePC1andtheaccuracyoftheCoe-typepaleointensityresults,indicatingthatlessstablemagneticcarriersyieldlessaccurateresults.ThereferencePC1isalsostronglycorrelatedwithAraiplotcurvature,indicatingthatbulkdomainstatedominatesthelinearityoftheAraidataand,consequently,theaccuracyoftheresults.Asimilaranalysisusinghistoricalpaleointensitydata,whichcanbecomparedtodirectobservationsofthefield strength, reveals similar, but weaker correlations between rock magnetism and paleointensityaccuracy and Arai plot curvature. This is despite the presence of laboratory alteration, a diversity ofexperiments(varioustemperaturesteps,labfieldstrengths,andfieldangles),andspecimenheterogeneity(rockmagnetic properties weremeasured on sister specimens), all of which will hinder our ability toidentify rockmagnetic controls on paleointensity data. These analyses indicate that the effective bulkdomainstateofaspecimencontrolsthefidelityofitspaleointensitydataandisafactorinmostnaturalmaterials.Therelationshipsthatwehaveidentifiedcanbeusedasameanstopre-selectspecimensthataremostlylikelytoyieldaccurateresults,toimprovedataselectioncriteria,andtoretrospectivelyanalyzethereliabilityofpreviouspublishedresults.Workiscurrentlyunderwaytodetermineifthesetrendscanbeidentifiedinoldermaterials.

85



ArcheomagneticfieldstrengthintheSouthAmerica:AreviewforthelasttwomillenniaandpreliminaryresultsfromAmazonregion

Presenter: WilborPoletti([email protected])Authors: WilborPoletti,DepartamentodeGeofisica,InstitutodeAstronomia,GeofisicaeCiencias

Atmosfericas,UniversidadedeSaoPaulo,RuadoMatao,1226,05508-090,SaoPaulo,Brazil;GeomagnetismLaboratory,DepartmentofEarth,OceanandEcologicalSciences,UniversityofLiverpool,Liverpool,UK.RicardoI.F.Trindade,DepartamentodeGeofisica,InstitutodeAstronomia,GeofisicaeCienciasAtmosfericas,UniversidadedeSaoPaulo,RuadoMatao,1226,05508-090,SaoPaulo,Brazil.AndrewJ.Biggin,GeomagnetismLaboratory,DepartmentofEarth,OceanandEcologicalSciences,UniversityofLiverpool,Liverpool,UK.GelvamA.Hartmann,InstitutodeGeociencias,UniversidadeEstadualdeCampinas,RuaJo‹oPandiaCalogeras,51,13083-870,Campinas,Brazil.HelenaP.Lima,CoordenacaodeCienciasHumanas,MuseuParaenseEmilioGoeldi,Av.Perimetral1901,66.070-530,TerraFirme,Belem,Para,Brazil.MarcosP.Magalhaes,AreadeArqueologia/MuseuParaenseEmilioGoeldi,Av.Perimetral1901,66.070-530,TerraFirme,Belem,Para,Brazil.HannahF.Nascimento,AreadeArqueologia/MuseuParaenseEmilioGoeldi,Av.Perimetral1901,66.070-530,TerraFirme,Belem,Para,Brazil.

Recordsof theEarth'smagnetic field strength inarchaeologicalandvolcanicmaterialsprovide insightsaboutprocessesthathaveoccurredintheEarth'scoreduringthelastfewmillennia.Severaltechniqueshave been developed to recover the archeointensity recorded by these materials resulting in a largedatasetwhose geographic location is strongly concentrated in thenorthernhemisphere (~ 96%of thedata).ForSouthAmericathediscrepancyrelativetothenumberofintensitydatabecomeslargerwhentheyarefilteredbythecurrentselectioncriteria.Inordertocontributewithnewarcheointensitydataforthesouthernhemisphere,samplesfromAmazonregion(NorthBrazil)coveringthelasttwomillenniaarebeinginvestigated.DuetothevastethnologicaldiversitythatinhabitedtheAmazonregion,longbeforeEuropeancolonization,thisregionbecameacradleofmaterials,madeandabandoned,throughoutseveralgenerationsofnativepeoples.Themostcommonlyfoundandstudiedmaterialsareceramicsfordomesticuseandfunerals.Consideringtheuniquenessofthismaterial,weareperformingthemeasurementswiththemicrowavemethod(exclusivetotheUniversityofLiverpool),whichneedslessmaterial,andalsotendstominimizesamplealterationbiasrelativetoclassicaldouble-heatingtechniques.

ThisworkpresentsareviewofthearcheomagneticdataforSouthAmerica,elucidatingthecurrentstatusofarcheomagnetismforthisregion,andpreliminarydatafortheAmazonregion.Thedirectimplicationfromtheseresultsisadescriptionofthemagneticfieldintensityevolutioninaregionthatisstilldevoidofrecords(NorthBrazil).ThenewdatahasthepotentialtoprovideabetterunderstandingofthegenerationmechanismsoftheEarth'smagneticfield.

86



REVISITINGTHEAGEOFTHEFIRSTIRONAGEINTHEEASTERN IBERIANPENINSULAFROMARCHEOMAGNETICDATINGRESULTS

Presenter: MercedesRivero-Montero([email protected])Authors: MercedesRivero-Montero,InstitutodeGeociencias(IGEO),CSIC.Spain

MiriamGómez-Paccard,InstitutodeGeociencias(IGEO),CSIC.SpainDavidGarcia-Rubert,UniversitatdeBarcelona.Spain

Oneofthemostimportantapplicationsofthestudyofgeomagneticfieldvariationsintherecentpastisarcheomagnetic dating. This method is based on the comparison between well-established regionalgeomagnetic field secular variation curves or models and the archeomagnetic signal acquired andpreservedbywell-heatedarcheologicalstructures.Inthisworkweillustratehowthismethodcanprovideapowerfultooltodatearcheologicalremainsthatcannotbeproperlydatedbyotherarcheologicalandgeochronologicalmethods. Inparticular,wepresent thearcheomagnetic studyof severalarcheologicalkilnssampledintwoarcheologicalsitesfromtheEasternpartoftheIberianPeninsula.Thestudiedkilnsclearlycorrespond to theFirst IronAge,period thathasbeenclassicallydated in the IberianPeninsulabetween 675 and 575 BC based on ceramic typology studies. However, new archeological evidenceschallengethisclassicalviewsincetheimpressivenumberofculturalandtechnologicaladvancesrecentlydiscoveredindifferentarcheologicalexcavationscanbehardlyascribedtothisveryshortintervaloftime,suggestingthattheFirstIronAgeinthisregioncorrespondsprobablytoalongerperiodoftime.Inordertotestthishypothesisweapplyherethearcheomagneticdatingmethodandpresentthedatingresultsobtainedfrombothregionalsecularvariationcurvesandgeomagneticfieldmodels.

87


DetermininggeomagneticfieldbehaviorfromterrestrialandextraterrestrialmaterialsOral - Thursday July 13 - 11:20-11:45

Short-termsecularvariationsfromLevantarchaeomagnetism:methods,applications,andchallenges

Presenter: RonShaar([email protected])Authors: RonShaar,TheInstituteofEarthSciences,TheHebrewUniversityofJerusalem,Jerusalem,

IsraelLisaTauxe,ScrippsInstitutionofOceanography,UniversityofCaliforniaSanDiego,LaJolla,California,USA

Archaeologicalmaterialsareextremelyusefulpaleomagneticrecorderswiththepotentialadvantageofproviding chronometrically dated information about the geomagnetic field with decadal to centennialresolution. The ability to exploit the full potential of archaeomagnetism relies on an approach thatmaximizes the accuracy, precision, and robustness of archaeomagnetic data. The key challenge in thisregardistoreduceasmanysourcesofuncertaintyaspossibleinboththeageconstraintsandthemagneticvectorsthemselves.Seeminglythemoststraight-forwardisreducingthearchaeologicalageuncertainty,but there is also a long list of paleomagnetic experimental uncertainties starting from field sampling,continuingwith laboratoryprocedures, andendingwithdataanalysis.Allof theabovebecomecriticallimitingfactorswhenassemblingaregionalcompilationandsecularvariationcurve.

Herewereviewoureffortstoaddresstheabovechallengesintheon-goingarchaeomagneticprojectinthe Levant.Over the lastdecadewehaveanalyzedover650 samples forpaleointensity and30 in situstructures for directional analysis from the vast archaeological resourcesof ancient Israel, Jordan, andCyprus.Thesamplecollectionincludespottery,slag,ovens,andburntstructures.Eachmaterialhasitsownadvantages anddisadvantages. In an attempt to address plaeointensitymethodological difficulties,wehavedevelopedaMagIC-basedtoolforautomaticinterpretationoflargeandcomplicateddatasets.Tothisarchaomagneticcompilation,wealsodevelopacontinuoustimeseriesfromlakesedimentdata,whoseagesarebasedonarchaeomagnetictiepoints.

ThecurrentLevantinecompilation,stillunderdevelopment,revealsofalocalgeomagneticanomalycalledthe'LevantineIronAgegeomagneticanomaly,whichspannedthefirst350yearsofthefirstmillenniumBCE. The anomaly was characterized by a high averaged geomagnetic field, short decadal-scalegeomagnetic spikes, fast field variations, and substantial deviation from dipole field direction. TheLevantineanomalywassimilarinscaleandmagnitudetothecurrentlyactivesouthAtlanticanomaly,butwithaoppositeinsign.

88



Theuseofpressuredemagnetizationasmeanstoimprove absolutepaleointensitymeasurements

Presenter: MichaelVolk([email protected])Authors: MichaelVolk

StuartGilderJoshuaFeinberg

Theabilitytorecoverarobust,high-fidelityrecordofthepastmagneticfieldstrengthisimportanttopaleo-andgeomagnetism.Thisisoftendifficultbecausenaturalrockscanconsistofnon-idealmagneticrecorders(e.g. pseudo-singledomain (PSD) andmultidomain (MD) grains).Adominance innon-ideal remanencecarriers can contribute to concave up Arai diagrams. This sagging, in turn, leads to ambiguity in theinterpretationandtheeventualrejectionofthedata.Ithasbeenshown,thatpressuredemagnetizationcanpartially remove thesenon-ideal remanencesduringThellier-typepaleointensityexperiments [VolkandGilder,2016id].

Herewepresenttheuseofpressuredemagnetizationasawaytoimprovethequality(i.e.qualityfactor)ofpaleointensitydeterminationsusingtheCoe-modifiedThelliermethod.Experimentswereconductedondifferentmaterials(obsidian,basalt)withPSDandMDcharacteristicswithdifferentmineralogies(varyingTi titanomagnetite). The 'natural remanent magnetization' in these experiments was mimicked by athermalremanenceimpartedinthelab.Theabsolutepaleointensityexperimentswerecarriedoutbeforeand after pressure cycling to 1.2 GPa. We further model the results of the experiments with aphenomenologicalmodelforPSDandMDremanences[Fabian,2001;Leonhardtetal.,2004].

Pressurecyclingresulted inthe loweringoftheNRMmomentfrom10%(PSD)-80%MD.MultidomainsamplesaremorestronglyaffectedbypressuredemagnetizationthanPSD.Theexperimentssuggest,thatlowerunblockingtemperaturesarepreferentiallydemagnetized,whichisalsoreflectedinthemodelingresults. Experiments on unpressurized specimens produced concave Arai diagrams and yieldedunderestimatedpaleointensities.NormalizingthedatawiththeratioR=TRM(Pn)/TRM(P0)resultedincorrectpaleointensityvaluesandgreatlyincreasedthequalityoftheexperiments.

89



MagneticPropertiesofIron-NickelParticlesPreparedbyMechanicalAlloying

Presenter: MichaelWack([email protected])Authors: MichaelWack,LMUMünchen

MichaelVolk,InstituteforRockMagnetism,UniversityofMinnesota

Meteoritesprovidenatural sampleswhich can carry information aboutour early solar systemand themagneticfieldspresentatthattime.Grainsize,andthereforedomainstate,ofmagneticparticlesisthekey to understanding their ability to record magnetic information on geological timescales. Materialspecific properties can be easier studied and optimized for technological applications from syntheticsamples.WesynthesizedFeNinanoparticleswithdifferentcompositionsbymechnicalalloying.Wepresentdatacompiledfromtheliteraturetogetherwithourownresults.Inparticular,wedemonstratecontinuouschangesinhysteresisandbackfieldparametersduringthemilingprocessaswellasCurietemperaturesofthefinalalloys.Thesingledomain(SD)thresholdinFeNialloysremainsunknownduetomethodicallimitsingrainsizeandstrongmagneticinteractionsbetweenindividualparticles.

90


SedimentMagnetization–AcquisitionandPreservation

Orals:ThursdayJuly13–13:00-16:30


Posters:FridayJuly14–13:00-15:30deVagant

Convenors:AndrewRoberts&MarkDekkers


13:00 13:30 20+10 RamonEgli Huntingreliablesedimentarymagnetizationacquisitionmechanismsafter70years:insightsfromanewmodel

13:30 14:00 20+10 DavidHeslop Howdosedimentsacquirearemanence:insightsfromdataandsimplemodels

14:00 14:30 20+10 JosephStoner Observationsonpost-DepositionalRemanentMagnetization(pDRM)fromHolocenePaleomagneticRecords:ProvidingConstraintsonProcessandImpacts

14:30 15:00 30 coffeebreak 15:00 15:30 20+10 ToshiYamazaki DRMlock-indepthandmagnetofossils15:30 16:00 20+10 JannaJust Thepreservationofmagneticpolarityina1.2Ma

greigitebearingsedimentcorefromLakeOhrid16:00 16:15 10+5 StuartGilder Canmagneticanisotropyimproverelative

paleointensityestimatesfromsediments?16:15 16:30 10+5 RobvanderVoo Datingillitewithargon-argonmethodsand

determiningtheageofsyn-tiltingremagnetizations

91


Posters


abstracttitle

Anne-ChristineDaSilva RemarkableLowerDevonianrecordofMilankovitchcyclicitiesfromNewYorkState-Approachandpreliminarydata

MarkDekkers Thermalalterationofpyritetopyrrhotiteduringearthquakes:Newevidenceofseismicslipintherockrecord

YaelEbert MagneticForceMicroscopyofmicrobialsulfatereductionmagnetizationfromtheDeadSea

DariaElkina PaleomagneticStudiesofSedimentCoresfromtheMendeleevRise,ArcticOcean:EvidenceofCatastrophicPleistoceneVolcanicEvent

RobertJ.Musgrave ProgressiveandpunctuateddeepmagneticdiagenesisHéctorPIZARRO Linkbetweensedimentationrates,climaticchangeandmagnetic

propertiesofcoarse-grainedsedimentsdepositedinhyper-aridcontext(AtacamaDesert,Chile).

KarinSant Resolvingmulti-polaritypaleomagneticdirectionsingreigite-dominatedsediments:acasestudyinLakePannoninHungary

StephanieScheidt AdetailedstudyofPlio-PleistocenefluvialsedimentsfromtheHeidelbergBasin(Germany):magnetostratigraphy,magnetomineralogy,andenvironmentalmagnetism

SteffenWiers DiageneticmagneticoverprintofsedimentsontheArlisPlateau,ArcticOcean

92


Sedimentmagnetization-acquisitionandpreservationPoster-FridayJuly14-13:00-15:30

RemarkableLowerDevonianrecordofMilankovitchcyclicitiesfromNew

YorkState-ApproachandpreliminarydataPresenter:

Anne-ChristineDaSilva([email protected])

Authors: DaSilva,A.C.,UtrechtUniversity(TheNetherlands)Bartholomew,A.,UniversityofNewPaltz(NewYork,USA)Brett,C.,UniversityofCincinnati(Ohio,USA)Gabeler,G.,UniversityofNewPaltz(NewYork,USA)Hilgen,F.J.,UtrechtUniversity(TheNetherlands)Juarez,C.S.,UniversityofNewPaltz(NewYork,USA)Maracek,C.,UniversityofNewPaltz(NewYork,USA)VerStraeten,C.,NewYorkStateMuseumAlbany(NewYork,USA)Dekkers,M.J.,UtrechtUniversity(TheNetherlands)

TheuncertaintiesontheDevonianstageboundariesarecurrentlyintheorderofseveralmillionsofyears.Cyclostratigraphy is a foremost tool to improve the Devonian time scale. Therefore, we need goodcontinuousstratigraphicrecordsontheonehandandreliablepaleoclimaticproxiesontheotherhand.TheRoad199section,nearKingston(NewYork,USA)isaroadcut,whichencompassesmostoftheSchoharieFormation,EarlyDevonianinage.ThesectioncorrespondstotheupperhalfoftheEmsian(~393to~400Myr),spanningadurationofabout7Myrwithrelativelycontinuousdeposition.Thelithologycorrespondstoshalycarbonates,withvariousdegreesofbioturbation(zoophycos,planolitesandchondritesmostly),andwithcolorsrangingfrombeigeorwhitetobrownordark.Thequalityofmostoftheoutcrop issoremarkable that the color variations allow to clearly distinguish Milankovitch cycles, with prominentbundlesoflightanddarkbeds.Onetypeofcycleexpressioncorrespondstosuccessionsof6darkerbedsstraddled between distinctly lighter beds which is interpreted as 6 precession cycles in one shorteccentricitycycle(thedurationofprecessionintheEarlyDevonianisabout18kyr).Apilotsampling(first5mof theoutcropsampledevery2.5cm;about20samplesdistributedmoreor lessevenlyalong theremainder of the section) shows that the averagemagnetic susceptibility is ~6.10-8m3/kg. Hysteresismeasurementsprovideahighfieldsusceptibilityof~5.10-8m3/kgandmostofthehysteresis loopsarestraightlines,withonlyasmallinfluenceofferromagneticgrains.Thecorrelationbetweenthehighfieldsusceptibility and the magnetic susceptibility is high (r = 0.91), while the correlation between theferromagnetic susceptibility and the magnetic susceptibility is much lower (r = 0.17). Thus, theferromagneticmineralshavealowimpactonthetotalmagneticsusceptibility;itsvariabilityisdrivenbyparamagneticclayminerals.Importantly,despitebeingremagnetized(throughouttheAppalachians,thesePaleozoic rock sequences are all remagnetized during the Variscan-Alleghanian orogeny) themagneticsusceptibilityreflectsdepositional information.Thissectionisthenanidealtargetforcyclostratigraphicstudy, through direct cycle identification on the outcrop itself and further cycle identification throughspectralanalysisonthemagneticsusceptibilityrecord.

93



Thermalalterationofpyritetopyrrhotiteduringearthquakes:Newevidence

ofseismicslipintherockrecordPresenter:

MarkDekkers([email protected])

Authors: TaoYang,HubeiSubsurfaceMulti-ScaleImagingKeyLaboratory,InstituteofGeophysicsandGeomatics,ChinaUniversityofGeosciences,Wuhan,ChinaMarkJ.Dekkers,PaleomagneticLaboratoryFortHoofddijk,DepartmentofEarthSciences,UtrechtUniversity,Utrecht,NetherlandsJianyeChen,HPTLaboratory,DepartmentofEarthSciences,UtrechtUniversity,Utrecht,Netherlands

Geological records of earthquakes along exhumed faults remain scarce. During earthquakes energy isdissipatedalongfaultslipzones;co-seismicpeaktemperaturesconveyinformationonitsamount,seismicslipbeingassociatedwithfrictionalheating.Peaktemperaturesareassessedwithavarietyofmethods,eachwith certain assets and disadvantages. Herewe describe amineralmagneticmethod to identifyseismicslipalongwithitspeaktemperaturethroughexaminationofmagneticmineralassemblageswithinafaultzoneindeep-seasedimentscoredfromtheJapanTrench-oneoftheseismicallymostactiveregionsaroundJapan-duringtheIntegratedOceanDrillingProgram(IODP)Expedition343,theJapanTrenchFastDrillingProject(JFAST).Fortysamples, includingfaultzoneandadjacenthostsediments,wereanalyzedmineralmagnetically,supplementedbyscanningelectronmicroscopeobservationswithassociatedX-rayenergydispersivespectrometermeasurements.Thepresenceofthemonoclinicpyrrhotiteappearstoberestrictedtothreefaultzonesoccurringat~697,~720and~801meterbelowseafloorinthefrontalprismsediments.Importantly,itdoesnotoccurintheadjacenthostsediments.Elevatedtemperaturesandco-seismichotfluidsasaconsequenceoffrictionalheatingduringearthquakeslipinducedpartialreactionofpre-existingpyritetopyrrhotite.Thepresenceofpyrrhotiteincombinationwithpyrite-pyrrhotitereactionkinetics constrain the temperature rise to a range of 560-780 °C. The integrated mineral-magnetic,microscopic,andkineticapproachadoptedhere,isausefultooltoidentifyseismicslipalongfaultswithoutfrictionalmeltandestimatetheassociatedmaximumtemperature.

94



MagneticForceMicroscopyofmicrobialsulfatereductionmagnetization

fromtheDeadSeaPresenter:

YaelEbert([email protected])

Authors: EbertYael,TheInstituteofEarthSciences,TheHebrewUniversityofJerusalemShaarRon,TheInstituteofEarthSciences,TheHebrewUniversityofJerusalemEmmanuelSimon,TheInstituteofEarthSciences,TheHebrewUniversityofJerusalemNowaczykNorbert,GFZGermanResearchCentreforGeosciencesSteinMordechai,GeologicalSurveyofIsrael

Lacustrine and marine sediments are primary sources for paleomagnetic information. The naturalremanentmagnetizationofsuchsedimentsisoftencomplex,particularlyunderredoxconditionswheregreigiteisprecipitatedandmagnetiteisdissolved.HerewepresentMagneticForceMicroscopy(MFM)ofmagneticmineralsaffectedbymicrobialsulfatereducing(MSR)activityintheancientDeadSea,aterminalhypersaline lake. Given a large sulfate inventory, the limiting factor forMSR activity is organicmattersupplied by fresh water. We analyze ancient Dead Sea sediments pertaining to two contrastingenvironments, namely, sediments characterized by greigite precipitation from the dry Holocene, andsedimentscharacterizedbypyriteprecipitationfromthewetterLastGlacial.MFMofmagneticextractionsreveal variousmagnetic species: single-domain greigites, interacting framboids, and partially dissolvedmultidomaintitanomagnetite.Eachoftheaboveleavesadifferentmagneticfootprintonthesedimentarymagnetism.

95


Sedimentmagnetization-acquisitionandpreservationOral(invited)-ThursdayJuly13-13:00:13:30

Huntingreliablesedimentarymagnetizationacquisitionmechanismsafter70years:insightsfromanewmodel

Presenter: RamonEgli([email protected])Authors: RamonEgli

Since the first experimentsondepositional remanentmagnetization (DRM)acquisitionexperimentsbyJohnson et al. almost 70 years ago, the mechanics of magnetic grain alignment during the complexsequenceofsyn-andpost-depositionalprocessesisnotfullyunderstood-sothatimportantlimitationspersistinthecapabilityofdisentanglingpaleomagneticandenvironmentalsignals.DRMacquisitionmodelscanbedividedintotwomaincategories:thosebasedonadynamicequilibriumwiththemagneticfieldinpresence of decaying randomization processes (e.g. bioturbation-driven [1]), and thosewhere particlerotationishaltedbeforefullalignmentisreached(e.g.particlessettlinginarestingenvironment[2]).Theformerbearsthesamewell-behavedpaleomagneticcharacteristicsofthermoremanentmagnetizations,whilethelatteryieldsmagnetizationswhoseintensityissensitivetothetimingoftheprocess,whichinturndependson the thicknessof thewater columnand the (environmentally-driven) concentrationofsuspended particles [2]. A severe limitation of current syn-depositionalmodels is the assumption thatsettling occurs in a resting fluid, where hydrodynamic torques depend only on the characteristics ofsuspendedflocsandtheir reciprocal interactions.Naturalbasins,ontheotherhand,provideastronglyanisotropichydrodynamicenvironment-theturbulentboundarylayer-whichhasthelargestinfluenceonflocorientation.Numericalmodelsofso-calledwallflowsshowthattheresultingDRMisaffectedbystronginclination shallowing, while the magnetization intensity is modulated by the mean flow speed. Sucheffectsareparticularlypronouncedinthelimitcaseofturbidites,explainingnaturalobservations[3],andremainsignificanteveninthequietestdeep-seasettlingenvironments.Thisimpliesthatsyn-depositionalDRMalwaysprovidebiasedandenvironmentallymodulatedrecordsoftheEarthmagneticfield.Reliablesedimentarypaleomagneticsignals thereforeappear torelyon furtherparticle reorientation insidetheuppermostfewcmofsediment.

[1] Zhaoetal.,Nat.Comm.7(2016).[2] MitraandTauxe,EarthPlanet.Sci.Lett.286(2009).[1] ShcherbakovandSycheva,Geochem.Geophys.Geosys.11(2010).[2] Tantyetal.,Geochem.Geophys.Geosys.17(2016).

96



PaleomagneticStudiesofSedimentCoresfromtheMendeleevRise,Arctic

Ocean:EvidenceofCatastrophicPleistoceneVolcanicEventPresenter:

DariaElkina([email protected])

Authors: DariaElkina,1GrambergAll-RussianResearchInstituteforGeologyandMineralResourcesoftheWorldOcean(VNIIOkeangeologia)2St.PetersburgStateUniversityAlexeyPiskarev,1GrambergAll-RussianResearchInstituteforGeologyandMineralResourcesoftheWorldOcean(VNIIOkeangeologia)2St.PetersburgStateUniversity

Nowadays, the Arctic Ocean, considered to be an essential key for understanding of the Earth'spaleoclimate,isanareaofhigherscientificandgeopoliticalinterest.DespiteanumberofstudiesoftheArcticBasinisincreasingannually,theageofmarinesediments,retrievedfromthedeepoceanfloor,hasbeen the subject ofmuch controversy. Due to the lack of adequatematerials for isotopic dating andbiostratigraphic correlations, and restrictionsofa radiocarbonmethod,magnetostratigraphyofmarinesedimentsfromtheArcticOceanissubsequentlyinterpretedindifferentways.Thepaleomagneticstudyhasbeenperformedoneightsedimentcores,carriedoutfromtheMendeleevRiseareain2000and2012.Accordingtotheresults,agesuptotheearlyPliocenecanbeidentifiedinthecoresstudied.Thus,themeansedimentationratesdonnotexceed1.58mminka.Thatmeansthatagainstcommonassessmentsofmeansedimentationrates,extendedforthewholeArcticOcean,theMendeleevRise tends to have the low sedimentation rates during theQuaternary and themost of the Pliocene.Moreover,thinsections,carryinghighvaluesofmagnetizationintensityandmagneticsusceptibilityincoreof 2012, have revealed the presence of tuffites. This pronounced volcanogenic component could bereferredtopossiblevolcanicactivity,leadingtotheformationofacalderaontheGakkelRidge.ThegiantcalderalocatedintheeasternsegmentoftheGakkelRidgewascrossedbytwoseismicreflectionlinesin2014,accompaniedwiththemultibeamechosounding.Thecalderais80kmlong,40kmwideand1.2kmdeep.IntroductionofahugeamountofvolcanicmaterialinthewatersoftheArcticOceanshouldhaveleftanoticeableimpactoncompositionandpropertiesofsedimentsformedduringandaftertheeruption.Thathasbeenconfirmedwiththemineralogicaland lithologicalanalyses implementedonmarinesedimentsfromtheMendeleevRisementionedabove.Timeoftheeruptionhasbeenestimatedas~1.1Maafterthepaleomagneticdata.

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Sedimentmagnetization-acquisitionandpreservationOral-ThursdayJuly13-16:00-16:15

Canmagneticanisotropyimproverelativepaleointensityestimatesfrom

sediments?Presenter:

StuartGilder([email protected])

Authors: StuartGilder,Ludwig-MaximiliansUniversity,DepartmentofEarthandEnvironmentalSciences,Munich,GermanyMichaelWack,Ludwig-MaximiliansUniversity,DepartmentofEarthandEnvironmentalSciences,Munich,GermanyKuangHe,Ludwig-MaximiliansUniversity,DepartmentofEarthandEnvironmentalSciences,Munich,GermanyJosefJezek,DepartmentofAppliedMathematicsandComputerScience,CharlesUniversity,Prague,CzechRepublicSophieRoud,Ludwig-MaximiliansUniversity,DepartmentofEarthandEnvironmentalSciences,Munich,Germany

Redepositionexperimentswereperformedoverarangeofmagneticfieldintensitiesandinclinationsusingmagnetite-bearing, natural sediments. Paleointensity values defined by NRM over SIRM, ARM orsusceptibility systematically increasewith appliedmagnetic field, yet relative paleointensities from 25repeat redeposition experiments performed at identical field conditions vary by a factor of two. Thequestion arises as to what accounts for the variability and what can we do to diminish/remove thevariabilitytoimprovetheprecisionofrelativepaleointensityestimates?RecallingthatMsliesinthelongaxisdirectionofamagnetitegrain, thenthemaximumaxisof themagneticanisotropyellipsoidshouldparallelthepaleomagneticdirectionifthemagnetizationreflectsatruedepositionalremanenceacquiredvia torque.Ashigherexternal fields increaseNRMby tightening thealignmentof the grains,magneticanisotropy should become increasingly prolate proportional to field strength. This effect is indeeddemonstratedinournewexperimentsusinganisotropyofanhystereticremanentmagnetization(AARM):nearlyallAARMindicesvaryinproportionwithmagneticfieldstrength.Conversely,anisotropyofmagneticsusceptibility does not show a relationship withmagnetic field strength, as it is overwhelmed by theparamagneticfractionthatdisplaysasedimentaryfabric.AARMthusholdspromiseto improverelativepaleointensityestimatesfromsediments.

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Sedimentmagnetization-acquisitionandpreservationOral(invited)-ThursdayJuly13-13:30-14:00

Howdosedimentsacquirearemanence:insightsfromdataandsimple

modelsPresenter:

DavidHeslop([email protected])

Authors: DavidHeslop,AustralianNationalUniversityAndrewP.Roberts,AustralianNationalUniversityLiaoChang,PekingUniversity

Major questions remain concerning the mechanisms by which sediments acquire a remanentmagnetization.Thedetrital remanentmagnetizationconcept isbasedonthepremisethatsedimentarypaleomagneticsignalsareacquiredwhentinynanomagnets,derivedfromtheerosionofigneousrocks,alignwiththeambientmagneticfieldandrecordthefielddirectionatthetimeofdeposition.Theenduringtextbook treatment of isolatedmagnetic particles aligningwith the ambient geomagnetic field duringdeposition remains questionable at many levels. In recent years, we have learned that the inorganicremainsofmagnetotacticbacteriaarewidelypreservedinthegeologicalrecord.Whenthesebacteriadie,theirstablesingledomainnanomagneticremainsactasidealpaleomagneticrecorders.Recognitionofthewidespread presence of magnetofossils in the geological record is providing new insights into themechanismsbywhichsedimentsacquirepaleomagneticsignals.However,eventhoughwehaveamuch-improvedunderstandingofthecontributionofmagnetofossilstosedimentarymagnetizationacquisition,muchremainsunknown.Wecombineempiricalevidenceandsimplemodelstodemonstratethatthelowmagnetizationefficienciesobservedinsedimentsareconsistentwithbothdetritalandbiogenicparticleorientationsthatarenearlyrandomwithaslightbiastowardtheambientgeomagneticfielddirection.Thispictureofparticleorientationinsedimentsprovidesanalternativepathwaytobothourunderstandingofsedimentaryremanencesandtheframeworkinwhichweinterpretthem.

99



Thepreservationofmagneticpolarityina1.2Magreigitebearingsediment

corefromLakeOhridPresenter:

JannaJust([email protected])

Authors: JannaJust,InstituteofGeologyandMineralogy,UniversityofCologneandFacultyofGeosciences,UniversityofBremen,GermanyLeonardoSagnotti,IstitutoNazionalediGeofisicaeVulcanologia,Rome,ItalyNiklasLeicher,InstituteofGeologyandMineralogy,UniversityofCologne,GermanyAlexanderFrancke,InstituteofGeologyandMineralogy,UniversityofCologne,GermanyNorbertR.Nowaczyk,HelmholtzGFZGermanResearchCentreforGeosciences,Potsdam,GermanyPaulTauber,InstituteofGeologyandMineralogy,UniversityofCologne,GermanyBerndWagner,InstituteofGeologyandMineralogy,UniversityofCologne,Germany

SedimentcoreICDP-5045-1(DEEP)fromLakeOhrid,theoldestexistinglakeofEurope,wassubjectedtopaleo- and rock-magnetic measurements. The age-model of the core was developed on the basis oftephrostratigraphicworkandorbitaltuning,andrevealsedimentationratesof~30cm/kyr.TogetherwithFourier Transform Infrared Spectroscopy data, the magnetic data reveal a change on diagenetic Fe-mineralsthroughoutthepast640ka,withadominanceofiron-sulfidespriorandsideriteafter~320ka,likelyreflectingachangeinpore/lakewaterchemistry(Justetal.,2016).Thischangemayreflectadecreaseinsulfate/sulfidefluxtothelakeortoadilutionofsulfatebythebiggerwatervolumeofthesubsidinglakebasin.Currently sulfur isotopemeasurementsareunderway todeterminewhethersulfate/sulfidewasderivedfromtheterrestrialecosystem,thekarstsystemoftheGalicicaMountainrange,eastofLakeOhrid,orisofthermogenicorigin.Moreover,sideritesandFe-sulfidesmineralsonlyoccuringlacialsediments,associatedwithhighFe-concentrations.Newdata from the lowerpartof the core sequence imply that theglacial-interglacial variabilityof Fe-sulfidespersistsdowntothebaseofthecore,correspondingtoabout1.2Ma.Inconsequence,polaritytransitions are clearwhen they are locatedwithin interglacial sediments, i.e., the Brunhes/MatuyamaboundaryandthebaseoftheJaramilloareverysharp.IncontrastthetopoftheJaramilloisuncertain,andpossiblyduplicatedbyalatergrowthofgreigitebelowthesedimentsurface.Ongoinganalyticalworkonhigh-resolutionsamples(4cm)aimsontheinvestigationofthetimingofchangesintheEarth«sMagneticFieldduringpolaritytransitions.InthisregardaspecialemphasiswillbeputontheBrunhes/Matuyamaboundary.Incore5045-1,varioustephralayerspotentiallytobecorrelatedto40Ar/39ArdatedtephraintheSulmonarecord,Italy(Sagnottietal.,2016;Sagnottietal.,2014),arefoundclosetothereversal.Just,J.,Nowaczyk,N.R.,Sagnotti,L.,Francke,A.,Vogel,H.,Lacey,J.H.,Wagner,B.,2016.Environmentalcontrolontheoccurrenceofhigh-coercivitymagneticmineralsandformationofironsulfidesina640ÛøkasedimentsequencefromLakeOhrid(Balkans).Biogeosciences13,2093-2109.Sagnotti,L.,Giaccio,B.,Liddicoat,J.C.,Nomade,S.,Renne,P.R.,Scardia,G.,Sprain,C.J.,2016.Howfastwasthe Matuyama-Brunhes geomagnetic reversal? A new subcentennial record from the Sulmona Basin,centralItaly.Geophys.J.Int.204,798-812.Sagnotti,L.,Scardia,G.,Giaccio,B.,Liddicoat,J.C.,Nomade,S.,Renne,P.R.,Sprain,C.J.,2014.ExtremelyrapiddirectionalchangeduringMatuyama-Brunhesgeomagneticpolarityreversal.Geophys. J. Int.199,1110-1124.

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Progressiveandpunctuateddeepmagneticdiagenesis

Presenter:

RobertJ.Musgrave([email protected])

Authors: RobertJ.Musgrave,GeologicalSurveyofNewSouthWales,NSWDepartmentofPlanningandEnvironment,Maitland,NSW,AUSTRALIAMyriamKars,CenterforAdvancedMarineCoreResearch,KochiUniversity,B200Monobe,Nankoku,783-0004,JAPAN.MartaE.Vega,GeologicalSurveyofNewSouthWales,NSWDepartmentofPlanningandEnvironment,Maitland,NSW,AUSTRALIA

Magneticdiagenesisinthetuffaceousmuds,mudstonesandvolcaniclasticrocksofthevolcano-boundedsedimentarybasincoredatInternationalOceanDiscoveryProgramSiteU1437isaproductofprogressiveprocesses that continue throughout the1800-m-thick sequence,punctuatedby superimposed featurescorrespondingtoaseriesoffluid'events'markinginfluxoffluidsandconcentrationsofhydrocarbons.X-raydiffraction,visualexaminationandscanning-electronmicroscopyofcoresamplesindicatethepresenceofbothmagnetiteandthemagneticsulfidegreigite.Inferencesfromhighvaluesofsaturationisothermalremanence(SIRM)normalisedbymagneticsusceptibilityl(SIRM/chi),distributionofhysteresisdatanearadiageneticgreigite curveonaDayplot, and 'humping'of low-temperaturecyclesofSIRMsuggest thatdetritalmagnetiteanddiageneticgreigitearebothsignificantcontributorstothemagneticassemblage,withgreigiteconstitutingahigherproportioninsamplesfromtheshallowesthole,U1437B.Progressivemagneticdiagenesis isexpressedasabackground log-lineardecrease inSIRM/chi.Hysteresisand first-orderreversalcurvesindicateaninitialdiageneticgrowthofoneormorehigher-coercivityphasesinHoleU1437B,followeddownholethroughHolesU1437DandU1437Ebyincreasinglossofallbutlow-coercivitymaterial. The downhole pattern is consistent with progressive loss of fine-grained magnetite, initialauthigenesisofgreigite,andprogressivepyritisationof thegreigite.Shipboard fluidanalysis revealedacomplex profile of interstitial-water geochemistry,markedby several fluid influxes, including inputs ofsulfate-richwateratabout275and460metersbelowseafloor(mbsf).Methaneconcentrations,mostlylow,markedlyincreaseintheintervalbetween750and1460mbsf,andethaneappearsbelowaninferredfault at 1104mbsf. Each of these fluid events is marked by offsets in the rock magnetic parametersSIRM/chi,S-0.3T,andDJH,representingrepeatedphasesoflatediageneticgrowthofgreigiteinresponsetosuppliesofsulfate,intervalsofenhancedpyritisationofgreigitewhereconcentrationsofdeeplysourcedmethanemaybeaccompaniedbyH2S,andamoreenigmaticresponsetothethermogenicethaneintervalwhichseemstobothdissolveanyremainingfine-grainedmagnetiteandgrowanewgenerationofgreigite.

101



Linkbetweensedimentationrates,climaticchangeandmagneticproperties

ofcoarse-grainedsedimentsdepositedinhyper-aridcontext(AtacamaDesert,Chile).

Presenter:

HéctorPIZARRO([email protected])

Authors: HéctorPIZARROSoniaROUSSEEduardoCAMPOSRodrigoRIQUELME

TheAtacamaDesert innorthernmostChile,correspondstothedriestplaceontheplanet,withameanannualprecipitation(MAP)~10mm/y.Itcomprisesalargenumberofhydrographicbasinsfilledbycoarse-grainedsedimentarydeposits,widelyexposedalongtheprecordilleraandwesternforearc(e.g.LoaGroup,Atacama Gravels; Blanco, 2008). These sedimentary products mainly come from precordillera erosioninitiatedduringtheEocene-OligoceneIncaictectonicphase.TheprevailingclimaticconditionssincetheLate Eocene correspond to an arid-hyperarid context (Dunai et al., 2005). The Centinela Basin(22°55'S/69°05'W),inwhichthisstudywascarried,isfilledbyfivecoarse-grainedunits(i.e.fromoldesttoyoungest: Esperanza Gravels, Atravesados Gravels, El Tesoro Gravels, Arrieros Gravels and Ratonessediments),reflectingthedifferentclimaticand/ortectonicconditionsprevailingatthetimeofdeposition.These units contain interbedded paleosoils (calsisols and gypsisols) and exotic-Cu mineralization. TheArrierosGravelsandTesoroGravelshaveasedimentary thicknessof300and370mrespectively,withintercalatedcalcisols(MAP:~40mm/y;Rechetal.,2006),buttheypresentdifferencesinthedepositionalenvironment.ThetransitionfromTesorogravelstoArrierosgravelsismarkedbyadecreaseinsedimentarythicknessfrom370mto80m,thereplacementofinterbeddedcalcisolbygypsisol(MAP~10mm/y:Rechet al., 2006), and variations in depositional environment, which depict an arid to hyperarid climaticconditionsevolution.TheendofTesorodepositioncoincideswiththeendoftheIncaictectonicphase.Bycontrast,thetransitionfromArrierosGravelstoRatonesSediments(ca~10Ma)mainlyrelatestochangesindepositionalenvironment,linkedtochangeinprecipitationrate.Magneticpropertiesanalysesofthesesediments, combinedwithmicroscopy indicate that ferromagneticminerals tend to concentrate in thefinerfractionofthematrix(~0.5mm).Detritalmagnetiteandtithanomagnetitedominateinthegravelsandpaleosoils,whereasauthigenicmaghemiteandhematiteonlydominateinmudlevelsoftheRatonesSediments.Magneticsusceptibility(X)decreasefromAtravesadosGravelstoArrierosGravelsandRatonesSediments following the hyper-aridification climatic trend. A more marked susceptibility drop alsocoincideswith the endof the Incaic tectonic phase.High frequency-dependentmagnetic susceptibility(Xfd%)andAnhystereticRemanentMagnetization (ARM)/Xparametersvalues indicate thepresenceofsuperparamagnetic/single domain size particles in themud level of Ratones Sediments interpreted astracingtheauthigenicFe-mineralslinkedtoless-aridlocalclimaticconditions.Theresultsdemonstratetherelevanceofthemagneticpropertiesanalysesincoarse-grainedsedimentsdepositedunderarid-hyperaridconditions, the latter being favorable to the preservation of the primary magnetic mineralogy in thesedimentsafterdeposition.

102



Resolvingmulti-polaritypaleomagneticdirectionsingreigite-dominated

sediments:acasestudyinLakePannoninHungaryPresenter:

KarinSant([email protected])

Authors: NickKelder,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,Utrecht,NLKarinSant,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,Utrecht,NLWoutKrijgsman,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,Utrecht,NLMarkDekkers,PaleomagneticlaboratoryFortHoofddijk,UtrechtUniversity,Utrecht,NLImreMagyar,ResearchGroupforPaleontology,HungarianAcademyofSciences-HungarianNationalHistoryMuseum-EötvösUniversity,Budapest,Hungary

Magnetostratigraphic dating in marginal and lacustrine sediments is often difficult because of theomnipresenceofgreigite,whichcanoccur inearly to latediagenetic forms thatmaymask theoriginalmagneticsignalpartlyorcompletely.Forthisreason,sedimentswiththeironsulphidegreigiteareoftenconsidered unsuitable for magnetostratigraphy. In the last decade, greigite formation and itsdemagnetization behavior has received more attention, and several studies presented successfulstratigraphiccorrelations (e.g.,VanBaaketal.,2016;Abenetal.,2014;Vasilievetal.,2007).Here,weinvestigatetheviabilityofmagnetostratigraphicdatinginthreerecent~400-500mthickcorescoveringtheLate Miocene ‘Pannonian Stage’(~11.5 to 6 Ma) of ancient Lake Pannon in SW Hungary. Thechronostratigraphy of the Pannonian is generally poorly constrained due to the presence of endemicfossils, scarcity of independent age constraints and lack of surface outcrops. In addition, availablemagnetostratigraphic records are often very inconsistent; a behavior that is typically attributed todiageneticgreigite(Babinzkietal.,2007;Magyaretal.,1999;2007).Wefoundthatthemajorityofthethermallydemagnetizedsamplescontainseveralmagneticcomponents.Thesesamplesconsistofamediumtemperature(MT;210-290°C)andhightemperature(HT;300-max.400°C)vector,inmanycaseswithanti-paralleldirections.Thisbehaviorisnotvisibleafteralternatingfield(AF)demagnetization;thesedirectionsreflectonlythecomponentwiththehighestintensity,whichmaybeeithertheMTorHT.Rockmagneticresults,includingthermomagneticplots,IRMcomponentanalysisandFORCdiagrams,suggestthatonecomponentisdiageneticgreigite,whereastheother,oftenweakercomponentmaybeeithergreigiteor(slightlyoxidized)magnetite.Byusingacarefullabmethodincludingsmall(10-20°C)stepsandsubsequentthermalandAFdemagnetization,wewereabletoseparateandplotboth components even for relatively weak multi-polarity samples. This method revealed a delayedacquisition of the MT inclinations, suggesting that the HT is of primary/early diagenetic origin. ThemagnetostratigraphybasedontheHTcomponentcorrelatesbesttoChronsC4n.2ntoC3Bnwithanagebetween8.2and7.3Ma.Theaveragesedimentationrateinthedeeplaketoshelfdepositsincreasesfrom29to~35cm/kyr.Ourstudyshowsclearlythatgreigite-bearingsedimentsshouldalwaysbedemagnetizedthermally, as AF demagnetization cannot distinguish between primary and secondary magneticcomponents. The chaoticand/orbiasedpolaritypatterns inoldermagnetostratigraphic studies in LakePannonaremostlikelycausedbytheuseofAFdemagnetization.ReferencesAben,F.M.,Dekkers,M.J.,Bakker,R.R.,vanHinsbergen,D.J.J.,Zachariasse,W.J.,Tate,G.W.,McQuarrie,N., Harris, R. and Duffy, B., 2014. Geochem. Geophys. Geosyst., 15, p. 2531–2554, doi:10.1002/2014GC005294.vanBaak,C.G.C.,Vasiliev,I.,Palcu,D.V.,Dekkers,M.J.andKrijgsman,W.,2016.FrontiersinEarthScience,4,p.1–18,doi:10.3389/feart.2016.00060.

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Babinzki, E., Márton, E., Márton, P., Ferenc Kiss, L., 2007. Palaeogeography, Palaeoclimatology,Palaeoecology252,p.626-636.Magyar,I.,Geary,D.H.,Sütő-Szentai,M.,Lantos,M.andMüller,P.,1999.ActaGeologicaHungarica,42,p.5–31.Magyar,I.,Lantos,M.,Ujszászi,K.andKordos,L.,2007.GeologicaCarpathica,58,p.277–290.Vasiliev, I., Dekkers, M.J., Krijgsman, W., Franke, C., Langereis, C.G. and Mullender, T.A.T., 2007.GeophysicalJournalInternational,171,p.613–629.

104



AdetailedstudyofPlio-PleistocenefluvialsedimentsfromtheHeidelberg

Basin(Germany):magnetostratigraphy,magnetomineralogy,andenvironmentalmagnetism

Presenter:

StephanieScheidt([email protected])

Authors: StephanieScheidt,LeibnizInstituteforAppliedGeophysics,Hannover,Germany/UniversityofBayreuth,ChairofGeomorphology,Bayreuth,GermanyUlrichHambach,UniversityofBayreuth,ChairofGeomorphology,Bayreuth,Germany/BayCEER,UniversityofBayreuth,Bayreuth,Germany/LaboratoryforPalaeoenvironmentalReconstruction,FacultyofSciences,UniversityofNoviSad,SerbiaChristianRolf,LeibnizInstituteforAppliedGeophysics,Hannover,Germany

DeepdrillingsintheHeidelbergBasinprovideaccesstooneofthethickestandmostcompletesuccessionsof Quaternary and Upper Pliocene continental sediments in Central-Europe. Although unconsolidatedfluvialsedimentsareafundamentalchallengeforpalaeo-androckmagneticapproaches,longsequencesfrom three sites (Heidelberg, Ludwigshafen P36, and Viernheim)were successfully analysed. Here,wepresent the final results: a consistent and independent chronology, a completemagneto-mineralogicaldescriptionandaninterpretationofthecontainedenvironmentalandclimaticinformation.Theapplicationofmagneticpolaritystratigraphyprovidesaconsistentagedetermination.IdentificationoftheBrunhes-MatuyamaboundaryandtheJaramillosubchronsucceededonlyforcoreHeidelberg,butallowforinferenceofitspositionswithintheothertwocoresbylithostratigraphiccorrelations.TheOlduvaisubchron and the Matuyama-Gauss boundary are defined by clear polarity changes in each core.ContinuationofthestratigraphicframeworkintotheGilbertchronallowsalternativecorrelationschemes.Byapplyingage-depthplotsandassumingsteadysubsidencewetentativelyidentifiedthemostplausiblescenariosthatyieldagesof~5Maand~4MaforthedeepestsectionofthecoresViernheim(350m)andHeidelberg(500m),respectively.AstrongdrillinginducedoverprintpreventspalaeomagneticanalysisofTertiarysedimentsofcoreLudwigshafenP36.Detailed information about the magnetic components is obtained by combination of EDX /SEM,thermomagneticcurves,FORCmeasurements,andcoercivityanalysisofIRMacquisitioncurves.Onlytheseinformationallowforunravellingofthemulticomponentsystemsandidentificationofinvolvedmagneticminerals.Classicalmono-proxyrockmagneticapproaches,bycontrast,comehardlytoresults.TheTertiarysedimentsareessentiallycomposedofferrianilmenites,ferrianchromites,haematite,andgoethiteaswellasminorquantitiesofmagnetiteandmaghemite.TheQuaternarysequencesaredominatedbygreigite;detritalmagnetitesarepresentinporousremainders.CoreHeidelbergisstronglyinfluencedbytheNeckaralluvial fan,varying itsmagneto-mineralogydependingonsedimentyield,composition,anddiagenesis.Here,greigiteispresentintheTertiarypartandhaematiteoccursintheQuaternarysuccession.All information considered,we suggest sub-tropical toMediterranean climatic conditions to prevail inPliocenetimes.Theice-freeAlpscausedseasonalandlong-termrecurrentriseandfallofthegroundwatertablecausingchangesintheoxygenlevelofsoilsandporewatersandrepetitivedesiccationoftop-layers.Hereby,sulphideformationoccurredonexpenseofmagnetitedissolution;re-oxidisingofdissolvedFe2+anddecompositionof ironsulphideminerals ledsubsequentlytoFe3+(oxy)hydroxidesandferrihydriteaccumulation.Haematitewasformedduringaridanddryperiods,eitherbytransformationofmagnetite/maghemiteorfromconversionof(oxy)hydroxides/ferrihydrite.Arapidchangeoftheclimaticconditionsis indicatedclosetotheTertiary-Quaternary-boundary.Thedisappearanceofauthigenichaematiteand

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theperseveringpresenceofgreigiteintheQuaternarysuccessionindicateconstantlycoolerandwetterenvironmentsandthecontinuityofreductiveconditions.OurchronostratigraphicandenvironmentalmagneticresultsderivedfromsedimentcoreslocatedintheUpperRhineGraben(Germany)supportascenarioofanatleastnorthern-hemisphere-widerapidclimaticchange close to the Tertiary-Quaternary-boundary going along with an intensification of NorthernHemisphereglaciations.

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Observationsonpost-DepositionalRemanentMagnetization(pDRM)fromHolocenePaleomagneticRecords:ProvidingConstraintsonProcessand

ImpactsPresenter:

JosephStoner([email protected])

Authors: JosephS.Stoner,CollegeofEarth,Ocean,andAtmosphericSciences,OregonStateUniversitySarahStrano,CollegeofEarth,Ocean,andAtmosphericSciences,OregonStateUniversityBrendanReilly,CollegeofEarth,Ocean,andAtmosphericSciences,OregonStateUniversityChuangXuan,SchoolofOceanandEarthScience,NationalOceanographyCentreSouthampton,UniversityofSouthampton

Theageandfidelityofsedimentarymagnetizationhaslongbeenasubjectofdebate.Toprovidebetterconstraintsforthisproblem,wearemakingroutineobservationscomparingradiocarbonorotherwisewelldatedpaleomagneticsecularvariation(PSV)recordswith'known'regionalpaleo-geomagnetictemplates.HerewepresentacasestudyusingthissimpleapproachforthenorthernNorthAtlanticandiftimepermitswewillhighlightsomeadditionalexamplesfromwesternUSLakes.PaleomagneticrecordsfromsevenwelldatedHoloceneageddeep-seasedimentcoreswithmeansedimentationratesrangingfrom15-65cm/kyr,collectedfromacrossthenorthernNorthAtlantic,arecomparedwithregionalPSVrecordsderivedfromultrahighresolution(~200cm/kyr)sedimentscollectedfromtheGreenlandandIcelandmarginsandlakes(wecallthePSVcompositederivedfromtheseultrahighresolutionrecordsGreenIce).Assumingtheage,baseduponmorethan40radiocarbondatesfurtherconstrainedby8terrestriallydatedtephra,andfidelityofthenorthernNorthAtlantic'spaleo-geomagneticrecordaremostaccuratelydefinedbytheultrahighresolution and reproduced PSV records, we tune deep sea sediment PSV records using a variety ofapproachestotheGreenIcePSVcompositetoderivean'agefortheirmagnetization',independentoftheradiocarbonderived 'age for their sediment.' Thedeep sea sedimentPSV records showclear temporaloffsetsrangingfrom~350to900yrsforrecordswithsedimentationrate~30cm/kyrand~700to2000yrsfor records with sedimentation rates ~ 20 cm/kyr. These offsets are in most cases greater than theradiocarbonagemodeluncertaintiesandlargerandmorevariablethancouldreasonablybeexplainedbyunaccountedformarinereservoirages.Alldeep-seaPSVrecordsappeartobesubstantiallysmoothedandwithcalculateddepthoffsetsfrom18-26cmforthehighersedimentationratecoresand12-27cmforlowersedimentationratecores.Usinganassumptionthat themagnetization is locked-inwithinazonebelowthemixed layerwedevelopaconvolutionmodelingapproach toconstrain theseprocesses.Theresultsandimplicationswillbepresented.

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Sedimentmagnetization-acquisitionandpreservationOral-ThursdayJuly13-16:15-16:30

Datingillitewithargon-argonmethodsanddeterminingtheageofsyn-tilting

remagnetizationsPresenter:

RobVanderVoo([email protected])

Authors: BenA.vanderPluijjmRobVanderVoo

Thelasttwodecadeshaveseenconsiderablescientificprogressinourunderstandingofclaydiagenesisandradiogenicisotopedatingofpotassicphases,notablyillite.Enhancementofthelow-gradesmectite-illitereactionappearstooccurindeforming(faulting,folding)materials,andallowsthedeterminationoftheage(s)oforogenesis.Apparentlysimultaneouswiththisillitization(and,hence,itsagedates)isalargecontingentofchemicalremagnetizations, observed in shale/carbonate sequences that are globally distributed. SuchremagnetizationsarethesubjectofthepresentstudyandhavebeeninvestigatedintheMontanaRockyMountainsandtheMexicanFoldandTrustBelt.TheArdennes,Cantabria,andthePaleozoiccarbonatesintheAppalachianBasin andValley&Ridgebelt have also contributed evidence. In all these rocks, syn-deformational remanence is carried by stable single-domain and occasional pseudo-single-domainmagnetite.Magnetiteisalsomanifestedassuperparamagneticnano-grains.As a working hypothesis, the deformation of shale/carbonate sequences containing new illite, andubiquitoussyn-tiltingremanence,arecoupledinspaceandtime.Ifdemonstratedasviable,ourmodelmayallowthedatingwithargon-argonmethodsofthetimingofillizationaswellassyn-tiltingremagnetization.Thiswillallow,inturn,tohaveatooltodatescoresofpaleopolesofcarbonateremagnetizations,insteadofimpreciseattemptstodatebycomparisonwithAPWPsegments.

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DiageneticmagneticoverprintofsedimentsontheArlisPlateau,Arctic

OceanPresenter:

SteffenWiers([email protected])

Authors: SteffenWiers,DepartmentofEarthSciences,UppsalaUniversity,SwedenIanSnowball,DepartmentofEarthSciences,UppsalaUniversity,SwedenMattO'Regan,DepartmentofGeologicalSciences,StockholmUniversity,SwedenBjarneAlmqvist,,DepartmentofEarthSciences,UppsalaUniversity,Sweden

TheArcticOceanbasinyieldscontroversialpaleomagneticresultswhere,despitelowsedimentationrates,excursionalandfully-reversedpaleomagneticdirectionshavebeenreconstructedfrommanycores.InthecentralArcticOceantheratiobetweennormalandreversedpolarityisalmost1:1belowasedimentdepthofusually3-4m.Atthesamedepthaprominentchangeindensityandbulkgrain-sizetoless-denseandfiner material occurs. Fitting such inclination records from the central Arctic Ocean to establishedmagnetostratigraphy would require unreasonable changes in sedimentation rates that coincide withchanges in the paleomagnetic directions. An environmental control on the paleomagnetic record,connected to self-reversal during maghemitization of titanomagnetite has been proposed as oneexplanationforthewideoccurrenceofanomalouspaleomagneticdataintheArcticOcean,butitremainsunclearpreciselywhatmechanism(s)is(are)responsible.Withoutindependentstratigraphiccontrolandindependentlydatedlevelsitisdifficulttodistinguishbetweentrueandfalserecordsofthepaleomagneticfield.Herewepresentapaleo-androckmagneticrecordfroma7.6mlonggiant-pistoncore(SWERUS-L2-13-PC1)collectedat1119mwaterdepthontheArlisPlateau(76.18°N179.29°W),situatedofftheSiberiancoast,betweentheChukchiPlateauandtheMendeleevRidge.Thecorerecoveredasequenceofglacial(greylayers)andinterglacial(brownlayers)cycles.Interglacialsarecharacterizedbybioturbationandtheoccurrenceofforaminifera;botharelackinginglacialsediments.StepwiseAFdemagnetizationandsubsequentPCArevealsacomplicatedpicturewithmultipleinclinationchangesandaratioofnegativetopositiveinclinationsofabout1:3.NRMintensityisgenerallylow(~10mA/m),exceptfortwoshortintervals.Rockmagneticparametersthataresensitivetofine-grained(titano-)magnetite (e.g. frequency dependent susceptibility, ARM) show a narrow zone of enriched, very finemagnetiteatapproximately250cm,whichcoincideswithalowinorganiccarbonandapeakininorganiccarbon.Thiszoneislimitedtoabrown,interglaciallayer(B2).Ontheotherhand,mineralogicalsensitiveparameters (e.g. Bcr) show a drastic change at approximately 400 cm, accompanied by an upwardsdecrease inthedegreeofanisotropyofmagneticsusceptibility(Pj).Thechangeinsedimentcolorfromgreytobrownat400cmisinterpretedasachangefromglacialtointerglacialconditions,coincidingwithchangesinallrockmagneticparameters.WeinterprettheinterglaciallayerB2asazoneinwhich(titano-)magnetitehasbeenpartiallydissolved,with the Fe-Redox boundary at approximately 250 cm, which leads to finer magnetic grain size andpotentialpartialremagnetizationofthesediments.Thus,thereconstructedinclinationshavetobetreatedwithgreatcautionandweregardthenaturalremanentmagnetizationinandbelowthiszoneaseitherlost,orasasecondarychemicalremanence,notaprimarydepositionalremanence.SedimentsbelowthiszoneshowslightlyelevatedNRMandARMvalues,possiblyreflectingauthigenicgrowthofmagneticminerals.However,NRMintensityisgenerallyloweringrey,glacialsedimentsandelevatedinthebrown,interglacialsedimentssuggestingsomesortofdepositionalcontrolonthepaleomagneticrecord.

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DRMlock-indepthandmagnetofossils

Presenter:

ToshiYamazaki([email protected])

Authors: ToshitsuguYamazaki,AtmosphereandOceanResearchInstitute,TheUniversityofTokyoRemanentmagnetizationacquisitionprocessesofsedimentsarenotfullyunderstoodyetdespitealonghistoryofresearch.TheflocculationmodelofTauxeetal.(2006)succeededtoexplainthelowefficiencyoftheremanenceacquisitionofsediments.Themodelpredictsa~0cmDRMlock-indepth.However,thelock-indepthisstillcontroversial;nearzerotodecimeter-scalelock-indepthswerereportedsofarusingthe samemethod, that is, the comparison of the variations of relative paleointensity and cosmogenicnuclide10Be flux in a single core.Our recent studies also showed that sediment cores in thewesternequatorialPacific,whichareadjacentwitheachotherandundersimilaroceanographicconditions,havevariouslock-indepthsfrom~0to15cm(Suganumaetal.,2010;Horiuchietal.,2016;Sakuramotoetal.,submitted).Recently ithasbecome recognized thatbiogenicmagnetite isamajor constituentofmagneticmineralassemblagesinglobaldeep-seasediments(e.g.,Robertsetal.,2011;2012,YamazakiandIkehara,2012).Biogeochemical remanent magnetization carried by magnetofossils may contribute to remanenceacquisition processes of sediments, but details are not understood yet. The abundant occurrence ofmagnetofossils with equant octahedral morphology in oxic red clay indicates that some species ofmagnetotacticbacteria(MTB)thatproduceequantoctahedralmagnetosomesdonotavoidoxicconditionsandmaybeaerotorelant(YamazakiandShimono,2013).ThepopulationofsuchMTBmaybelargestnearthesediment-waterinterfacebecauseofthehighestavailabilityofnutrientsthere.Ontheotherhand,itisrevealedthatMTBthatyieldbullet-shapedmagnetosomespreferchemicalconditionsneartheoxic-anoxictransitionzone(Yamazakietal.,2016,AGUFallMeeting).Remanentmagnetizationofsedimentsisconsideredtobeamixtureofdetritalremanentmagnetizationandbiogeochemicalremanentmagnetization(BRM).Iftheflocmodelistrue,theremanencecarriedbythedetritalcomponentdoesnotshowdelay.TheBRMcarriedbymagnetofossilswithequantmorphologymayalsohavenodelay,whereas theBRMofbullet-shapedmagnetofossilsmay contribute todelayedremanence acquisition. Lock-in depth of sediments may be determined by balance of these threecomponents.Thedelayedcomponentmayhavehighercoercivityduetolargershapeanisotropyofbullet-shapedmagnetofossils.

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AdvancedapproachestoRockMagneticCharacterizationandDataAnalysis

Orals:FridayJuly14–08:30-12:00KoningsbergergebouwPangea

Posters:FridayJuly14–13:00-15:30

deVagant

Convenors:FranceLagroix&MikeJackson


08:30 09:15 30+15 DavidHeslop Harnessingthedatasciencerevolution09:15 09:38 15+8 NathanChurch Characterisingstrongremanencecarriersusing

non-linearPreisachmaps09:38 10:00 15+7 IoanLascu FORCmodeling10:00 10:30 30 coffeebreak 10:30 11:15 30+15 AnnHirt Magneticfabricanalysis:currentstatusand

futureprospects11:15 12:00 30+15 RichardHarrison Nanopaleomagnetismfiveyearson:a(domain)

state-of-the-unionaddress.

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Posters


abstracttitle

LuisManuelAlva-Valdivia

MineralogicalandmagneticcharacterizationofOlmecilmenitemulti-perforatedartifactsandinferencesonsourceprovenance

AndreaReginaBiedermann

Influenceofalternatingfielddemagnetizationonsusceptibilityandanisotropyofsusceptibility

MiguelGarcés AMS-basedpaleocurrentanalysisfromfluvialsedimentsoftheEscanillaFm(SouthernPyrenees)

MichaelGrappone Prototypingahigh-temperature,SQUIDmagnetometersystemMagdalenaGwizdala ThermaltransformationsofmixtureofironoxidesandironsulphidesRanIssachar SeparationofmagneticfabricsincarbonaterocksFranceLagroix Anewtoolforseparatingthemineralmagneticbehavioratlow

temperaturesJiaboLiu Isothermalremanentmagnetizationdecompositionusing1-Dgaussian

mixturemodel

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AdvancedapproachestorockmagneticcharacterizationanddataanalysisPoster-FridayJuly14-13:00-15:30

MineralogicalandmagneticcharacterizationofOlmecilmenitemulti-

perforatedartifactsandinferencesonsourceprovenancePresenter:

Alva-ValdiviaLuisManuel([email protected])

Authors: LuisM.Alva-Valdivia,InstitutodeGeof’sica-UNAM,MexicoAnnCyphers,InstitutodeInvestigacionesAntropológicas-UNAM,MexicoMariadelaLuzRivas-Sánchez,InstitutodeGeofísica-UNAM,MexicoAmarAgarwal,InstitutodeGeof’sica-UNAM,MexicoJudithZurita-Noguera,InstitutodeInvestigacionesAntropológicas-UNAM,MexicoJaimeUrrutia-Fucugauchi,InstitutodeGeof’sica-UNAM,Mexico

TheOlmecculturearoseandflourishedonMexico'ssouthernGulfCoastbetween1800and400BC,anddevelopedextensivetraderelationshipsforprocurementofexoticmaterialsfromdistantregions.TheearlycapitalofMesoamerica'sfirstcivilization,thearchaeologicalsiteofSanLorenzo,flourishedbetween1400and1000BC,inthehumidtropicalcoastalplainsofsouthernVeracruz.Previousstudieshaverevealedtheregional importation of iron-ore, minerals and stone, such as obsidian, greenstone, and mica, forsculptures,grindingtoolsandartifactsusedindomestic,ceremonialandproductiveactivities.Thisstudyfocusesonthesourcingofnon-localartifacts,madefromiron-titanium(ilmenite)oxidemineralandiron-ores,foundinlargequantitiesinthearcheologicalexcavations,inordertoshedlightonEarlyPreclassictrade.Westudymulti-perforatedilmeniteartifactsandiron-titaniumoxideoresfrompotentialprovenanceareasusingrockmagneticanalyses,macroscopicobservations,petrography,scanningelectronmicroscopyand micro-geochemistry. Magnetic analyses include magnetic susceptibility as a function of hightemperature,magnetic hysteresis, isothermal remanentmagnetization (IRM) acquisition and backfielddemagnetizationofsaturationIRM,andfirst-orderreversecurves(FORC).BasedontheCuriepointsandcoercivity ranges, we suggest that the geographically unidentified source III-a, proposed earlier,corresponds to theHuitzo anorthosites. Themineralogical associations and textural relations betweenilmeniteandgranulitehost-rocksalsosuggestfortheilmeniteinOlmecsamplesanoriginthatissimilartotheHuitzoanorthosites.ThecompositionalsimilaritybetweenlargeapatitegrainsintheHuitzoandOlmecsamples,andthehighMgOcontentofOlmecilmeniteareadditionalevidencethattheprovenanceoftheOlmec ilmenite artifacts is in the Huitzo area, within the northern part of the Oaxaquia Precambriancomplex.

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Influenceofalternatingfielddemagnetizationonsusceptibilityand

anisotropyofsusceptibilityPresenter:

AndreaReginaBiedermann([email protected])

Authors: AndreaR.Biedermann,InstituteforRockMagnetism,UniversityofMinnesota,Minneapolis,USAMikeJackson,InstituteforRockMagnetism,UniversityofMinnesota,Minneapolis,USADarioBilardello,InstituteforRockMagnetism,UniversityofMinnesota,Minneapolis,USAJoshuaM.Feinberg,InstituteforRockMagnetism,UniversityofMinnesota,Minneapolis,USA

Anisotropyofmagneticsusceptibility(AMS)isoftenusedasaproxyformineralfabric,becauseitdependsmainly on the crystallographic (CPO) and shape preferred orientation (SPO) of a rock's constituentminerals. However, AMS can additionally be affected by domain alignment, stress or pressure. Twocontradictingrecommendationshavebeenputforwardregardingwhetherornottodemagnetizesamplesusingalternatingfields(AF)priortomeasuringAMS:somestudiesrecommendmeasuringAMSpriortoAFtreatment, in order to avoid effects of artificial, field-impressed anisotropy,whereas others claim thatsamplesshouldbedemagnetizedpriortomeasuringAMStoremovetheeffectsofstress-induceddomainwallpinningaswellasstrongnaturalremanentmagnetizations(NRM).Inthisstudy,thechangeofmeansusceptibilityandAMSareinvestigatedduringprogressiveAFdemagnetizationupto200mT,inaseriesofigneous, sedimentary andmetamorphic rocks. Samples are demagnetized along their x, y, and z axes,inverting the order of the axes during each demagnetization step in order to investigate a possibledirectional dependence of the AMS on the last AF direction. Mean susceptibility, principal-axis axesdirections, and degree and shape of the AMS ellipsoid in the NRM state, and after each AF step aredescribed,aswellasthedifferencetensorsbetweentheNRMstateandeachAFstep.Initialresultsshowchangesinmeansusceptibilityupto5%.ThemaximumincreaseinsusceptibilityisgenerallyclosetothelastAF direction, but is also affectedby theAMS in theNRM state. The shapeparameterU generallychangesbyupto0.3(upto1.6inbasaltsamples),andsmallchangesinanisotropydegreeP(upto4%)areobserved.Theeffectonprincipal-axisdirections isnegligible inallsamplesexceptforbasalt,wherethemaximumsusceptibilitybecomessub-paralleltothelastappliedfielddirection.TheseresultscanlikelybeexplainedbyacompetitionbetweengrainSPO,whichinfluenceswhichdomainconfigurationsrequireleastenergy,andtheeffectoftheAFfield,inducingdomainswithwallsparalleltothelastappliedfielddirection.Dependingonthesamples,andaspectofanisotropyinvestigated,high-fieldmethodssuchashysteresisortorquemagnetometry,whicharenotaffectedbydomainanisotropy,maybepreferable.Alternatively,low-temperaturedemagnetizationisnotexpectedtointroduceanypreferredorientationontheAMS,andwillbe investigated. AF-induced changes in principal axes directions will affect AMS-based predictions ofmineralfabricsorflowdirections.TheseresultshighlighttheimportanceofunderstandingthesourcesandcarriersofAMSpriortointerpretation.

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AdvancedapproachestorockmagneticcharacterizationanddataanalysisOral(invited)-FridayJuly14-09:15-09:38

Characterisingstrongremanencecarriersusingnon-linearPreisachmaps

Presenter:

NathanChurch([email protected])

Authors: NathanChurch,NTNU,Trondheim,NorwayKarlFabian,GeologicalSurveyofNorway,TrondheimSuzanneA.McEnroe,NTNU,Trondheim,Norway

Naturalmagneticmixturescontainingabundantmultidomainmaterialmayexhibitcoercivitydistributionsspanningseveralordersofmagnitude,andin-fieldmeasurementscanbedominatedbythissoft,stronglymagneticphase.RemanentPreisachdiagrams-animplementationofsecond-orderreversecurves-offerenhancedsensitivityforlow-fieldmeasurementsofsuchmixtures.Wepresentaprotocolfornon-linearsampling of the Preisach space that captures the large dynamic range of magnetic moments andcoercivitiesinatime-efficientmanner,andenhancestheresolutionoftheremanentsignal.Thetechniqueuseslogarithmicmeasurementstepsthatmorecloselymimicsthenear-log-normalcoercivitydistributionofnaturalsamplesthanlinearfieldsteps.ThePreisachmapcancalculatedasabsolutemagnetisationforease of comprehension, or can be scaled to permit comparison between measurement schemesindependentoffieldstepspacing.Inbothcases,improvedsensitivityduetotheabsenceofstronginducedmagneticsignalsreducesoreliminatestheneedtosmoothofthedata.Toillustratethecapabilitiesanddistinctivefeaturesofnon-linearPreisachmaps,examplesfromsyntheticandnaturalsamplesarediscussed,withemphasisonspecimenswithbothstrongremanencecarriersandabundantcoarse-grainedmagnetite.Domainstatesthatarecontrolledbythedemagnetisingfield(vortexand multidomain) show a wide distribution of coercivities and interaction fields that can be clearlydistinguished from particles with symmetric switching fields, such as non-interacting single-domainmagnetite, even when the coercivity distributions overlap. Samples containing hematite orhematite/ilmenite exsolution show a characteristic peak offset downwards by 17 ± 2%of the intrinsiccoercivity,whichisfoundtobestableoveralargerangeofintrinsiccoercivities.SuchpatternsinremanentPreisachmapsserveasfingerprintsformineralphasesandmicrostructuresincomplexmixturesandthesensitivity to high-coercivity signals offers a new tool to study the physical basis and provide data formodelsofthesecomplexmagnetisationbehaviours.

115



AMS-basedpaleocurrentanalysisfromfluvialsedimentsoftheEscanillaFm

(SouthernPyrenees)Presenter:

MiguelGarcés([email protected])

Authors: MiguelGarcés,UniversitatdeBarcelonaDavidGarciaMartinez,UniversitatdeBarcelonaAndreuVinyoles,UniversitatdeBarcelonaLuisValero,UniversitatdeBarcelona

The Anistropy ofMagnetic Susceptibility (AMS) tensor in sedimentary rocks is known to respond to acombinationofabedding-parallel,oblatedepositionalfabric,andasecondaryfabricrelatedtovarietyofpost-depositional processes such as mechanical bioturbation, compaction, chemical precipitation ortransformation of Fe-bearing minerals, and tectonic deformation. In non-deformed siliciclasticsedimentaryrocks,themagnetic lineation isreadily interpretedasparallel tothecurrentdirection,thesedimentary slope, or a combination of both. FromAMS data alone, the sense of flow remains oftenunconstrained, and itmustbederived fromcoherencywithother sedimentary structures suchas toolmarks,flutecastsandcross-lamination.Exceptionsoccurwhenthemagneticfoliationimbricatesagainstbeddingsurface,inwhichcasethesenseofflowisinferredoppositetothedipoffoliation.InthisstudyweinvestigatetherelationshipbetweentheAMSfabricandtheerosionalanddepositionalgeometries of fluvial sandstone beds of the Eocene Ainsa Basin (Southern Spain). A broad range ofsedimentaryfacies,fromcoarsesandstonechannelfills,cross-beddedsandstonebars,tooverbanktabularsandstonebedsandsiltstonesareinvestigated.ByunderstandingtheroleofsedimentaryslopesandwatercurrentintheorientationoftheAMSfabricatsinglebedformscaleweaimatconstraining,notonlythedirection,butalsothesenseofflow.Toachievethiswefocusonsandbodieswhichdevelopsedimentaryslopesobliquetothemaincurrentdirection.Ourworkinghypothesisisthatwatercurrentmaycombinewithgravitationalforcesalongsedimentaryslopestoyieldauniquesolutiontothesenseofflow.Conclusions of this studywill be relevant to better understand the evolution of the sediment transfersystems in theAinsabasinduring its transition from theorogen-parallel axial fluvial systemduring theEocene (paleocurrent directions towardsNNW), to the orogen-transverse southwards directed alluvialsystemsoftheOligocene.

116



Prototypingahigh-temperature,SQUIDmagnetometersystem

Presenter:

MichaelGrappone([email protected])

Authors: J.MichaelGrappone,UniversityofLiverpoolGeomagneticsLaboratoryJohnShaw,MagneticMeasurementsAndrewJ.Biggin,UniversityofLiverpoolGeomagneticsLaboratory

High-sensitivitySuperconductingQuantumInferenceDevices(SQUIDs)andµ-metalshieldinghavelargelysolvedpaleomagneticnoiseproblems.Combiningthetwoallowssuccessfulmeasurementsofpreviouslyunusablesamples,generallysedimentswithveryweak(~10pAm^2)magneticmoments.Advancesinhightemperature superconductors allow SQUIDs to operate at liquid nitrogen temperatures (-196 °C),drastically reducing their costs.While the improved sensitivity increases the fidelity of magnetic fieldvariationexperiments,theyremaintime-consuming.Step-wisethermalpaleomagneticsstudieshavelargelag times from the numerous heating and cooling cycles required. Removing the cooling step reducessurveytimebyatleasthalf.AvailablemagnetometersgenerallyprovideeitherSQUID-level(0.1-1pAm^2)sensitivityorcontinuousheating.Thefewthatofferhightemperaturecapabilitieswithlownoiselevelsrequire either spinning or vibrating the sample, increasing complexity and potentially causing sampledamage.Combiningasolid-statemagnetometerwithahightemperatureovenisthelogicalnextsteptodecodethepaleofield'smysteries.Twoprimary factorshaveplaguedpreviousdevelopments:oven-inducednoise levelsandtemperaturegradients.Ourentire system is shielded fromtheenvironmentusing4 layerseachofµ-metaland thinaluminium shielding. Our oven (designed for 7 mm diameter samples) sits inside 4 mm thick coppershieldinganduseshigh-frequency(40kHz)ACcurrentstoreduceradiofrequencyelectromagneticnoiseby99%.AttheSQUID'slocation(16mmfromtheoven),aresidualfieldofapproximately0.5nTremains.AEurotherm3216thermalcontrollerregulatesthetemperaturewithin±0.5°Cofthesetpoint,andtheSQUIDdataarerecordedusingLabVIEW.Reaching700°C,abovehematite'sCurietemperature,requiresatemperaturedifferenceofnearly900°CbetweenthesampleandSQUID.Sincedipolefieldsdecayrapidlywith distance (r^-3), the equipment handles temperature gradients above 500 °C cm^-1 formaximumsensitivityusingapassivevacuumseparationsystem.Allpartsusedarecommerciallyavailable,reducingoperating costs and increasing versatility. Initial results from artificially, uni-axially-magnetized basaltsshowhighsensitivity(2pAm^2),aswellassuccessfuldemagnetizationandremagnetizationcurves.

117



Thermaltransformationsofmixtureofironoxidesandironsulphides

Presenter:

MagdalenaGwizdala([email protected])

Authors: MagdalenaGwizdala,InstituteofGeophysics,PolishAcademyofSciences,Warsaw,PolandMariaJelelska,InstituteofGeophysics,PolishAcademyofSciences,Warsaw,PolandLeszekllczylski,InstituteofOceanography,UniversityofGdansk,Gdynia,Poland

Theaimofthisstudyisunderstandingofthethermomagneticbehaviourofpyrrhotite-magnetitemixture.Thestudywasperformedonglacial-marinesedimentsoftheNottinghamBayinSWSpitsbergen,Svalbard.Surfacesedimentswerecollectedfromaninnerpartofthebay,closetotheestuaryofglacierriver.Thefirst experiment was the low-field volume magnetic susceptibility dependence on temperature κ(T),conductedintheairduringheatingfromroomtemperature(RT)to700˚CandcoolingtoRT.Theresultofthisanalysisistwopeaksontheheatingcurveattemperaturesjustbelow320°Cand590°C,theCurietemperatures forpyrrhotite andmagnetite, respectively. Therefore, the followingmeasurementswerecarriedout:partialanalysesofκ(T)(RT–350°C,RT–500°C,RT–550°C,RT–600°C,RT–650°C,RT–700°C),magnetisationdependenceontemperatureMag(T)(RT–350°C,RT–500°C,RT–550°C,RT–600°C,RT–700°C),andhysteresisparametersperformedaftereachthermomagneticexperiment.Theκ(T)analysisrecordsphasetransitionsandstructuralchanges,whiletheMag(T)analysisreflectsonlyphasetransitions. Another difference between both measurements is oxygen access to sample, what has asignificant impact on the progress of the oxidation process. Oxygen access is limited during the κ(T)experiment,whileitisfreeduringtheexperimentofMag(T).TheHopkinsonpeakofpyrrhotiteisindicatedonpartialκ(T)heatedupto350°C.Inthenextstep(RT–500°C),oxidationofpyrrhotitetomagnetitewasobserved.Thisprocesswasfinishedinthestageof550°C,wheretheHopkinsoneffectofmagnetitewasnoticed. Partial Mag(T) analyses indicate a presence of pyrrhotite and oxidation of this mineral tomagnetite.Themaximumofoxidationisobservedinthestageof500°Cwhenpyrrhotitetransformintomagnetite.TheDay-Dunlopdiagramwasusedtodeterminethechangesofthedomainstateduringtheheatinginbothexperiments.Freshsampleisplacedintheareacharacteristicofpyrrhotiteandmagnetitewith predominance of single-domain (SD) grains. Heating to 350 °C in limited access of oxygen (κ(T)experiment)didnotchangethemagneticdomainstructure.Afterheatingto500°Candabove,thesamplehasthesamemixtureofSDgrainswiththeincreasedamountofmulti-domain(MD)magnetite.Whereasintheconditionswithfreeoxygenaccess,theSDmixtureofpyrrhotiteandmagnetitetransformintoSDandMDmixtureofmagnetiteafterheatingto500°C.TofurthertransformintoSDandsuperparamagnetic(SP)grainsfromthetemperatureof550°C.Summarize,bothexperiments,conductedindependently intwodifferentdevicesindicatethatwearedealingwiththeHopkinsoneffectattemperaturesjustbelow320and590°C,anddocumentedthetransformationofpyrrhotiteandmagnetitemixture,fromSDgrainsthroughtoSDwithMDandSDwithSP.

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Nanopaleomagnetismfiveyearson:a(domain)state-of-the-unionaddress.

Presenter:

RichardHarrison([email protected])

Authors: RichardHarrison,UniversityofCambridgeNonoLascu,UniversityofCambridgeJoshEinsle,UniversityofCambridgeJamesBryson,UniversityofCambridgeClaireNichols,UniversityofCambridgeJoyMuraszko,UniversityofCambridgeRobertsBlukis,UniversityofCambridgePaulMidgley,UniversityofCambridge

Atthe2012SantaFemeetingIpresentedtheoutlineofthenanopaleomagnetismconcept:amulti-scaleapproachtopaleomagneticanalysisofgeologicalmaterials.Fiveyearson,thistalkwillprovideasummaryoftheprogressthatbothweandothershavemade,andsharesomethoughtsonaroadmapforfutureprogress.Thetalkwillfocusonfivekeyareas:TomographyRecent developments in X-ray absorption tomography, X-ray ptychotomography, Focussed Ion BeamNanotomography,ElectronSTEM/EDStomographyandAtomProbeTomography,areprovidingaccessto3Dinformationaboutmagneticcarriersacrossarangeoffields-of-viewandspatialresolutionsthatareofcentralimportancetorockmagnetism.Itisnowpossibletocharacterisesamplesthatareoftheorder~100microns in size (i.e. the entirety of a crystal that might be used for single-crystal paleomagneticmeasurements)withaspatialresolutionof~50nm(i.e.reachingthecruciallengthscaleofsingle-domainmagnetite).Thisopensupthetantalisingpossibilityoflocatingeachandeveryremanencecarrierwithinyourpaleomagneticsample.MicromagneticmodellingAmajoradvanceinfinite-elementmicromagneticmodellingarrivedwiththereleaseofMERRILLbytheEdinburghgroupandothers.MERRILLputsadvancedmicromagneticswithineasyreachoftheentirerockmagnetismcommunity,andhascomealongjustastomographicmethodsareabletoprovidethenecessary3Dinputintothesimulations.Herewedemonstratehowthepowerfulcombinationoftomographyandmicromagnetics is providing unprecedented new insights into surprising nature of real remanencecarriers.MagneticimagingRecentdevelopmentsinmagneticimagingusingsynchrotronX-raysprovidedramaticnewopportunitiesforrockmagnetism,fromhigh-resolutionimagingofnaturalremanencestatesinmetallicmeteoritestoin-situimagingofindividualnanoparticleswitchinginfieldsupto1T.Aswellasimaging,thehighintensityofsynchrotron X-rays allows other characterisation methods, such as Mössbauer spectroscopy, to beperformedwithunprecedentedspeed(30minsperspectrum)andspatialresolution(~10microns).FORCunmixingOneofthecentraltasksofanyrockmagneticstudyischaracterisesamplesintermsofthepopulationsofSP,SD,PSDandMDparticlestheycontain.FORC-PCAisanewmethodthatallowsmultipleFORCdiagramstobequicklyandeasilyunmixedtoprovideafullquantitativebreakdownoftheunderlyingensembleofdomainstates.AlthoughoriginallydesignedwithaviewtoextractingthereliableSDcomponentfraction

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ofarockforthepurposeofpaleomagneticmodelling,themethodisalsoprovidingexcitingnewinsightsintoenvironmentalmagneticsignalswithinsedimentcores.EnsemblemodellingTheultimategoalofnanopaleomagnetismistodevelopphysicalmodelscapableofpredictingthemagneticresponseofthesystemtochangesinfield,temperatureandtime.Firststepstowardsthisgoalhavebeenmade with the release of FORCulator, which enables FORC diagrams to be predicted for arbitraryensemblesofinteractingsingledomainparticles.Extendingthisapproachtoaccountfornonsingledomainbehaviourwillbethenextmajorchallenge

120



Harnessingthedatasciencerevolution

Presenter:

DavidHeslop([email protected])

Authors: DavidHeslop,AustralianNationalUniversityAndrewP.Roberts,AustralianNationalUniversityXiangZhao,AustralianNationalUniversity

It isessential inpalaeomagnetismandenvironmentalmagnetismthattheinformationcarriedbymixedmagneticmineralassemblagescanbequantifiedintermsofmeaningfulcomponents.Theprimaryrouteto 'unmixing' magnetic assemblages is via a sequence of well-designed experiments, with each steptargetingadifferentmineralcomponent.However,inmixedmagneticparticleassemblagestheresultsofsuchexperimentscanbeambiguousanddetailedanalysisframeworksandvisualizationtoolsarerequiredtofacilitateinterpretation.Overthepast40yearsabroadfamilyofempirical,theoretical,andnumerical'unmixing'techniqueshavebeendevelopedbytherockmagneticcommunitytocharacterizeandquantifymagnetic mineral assemblages. Many of these techniques now provide cornerstones for interpretingcomplexmagneticdata.However,allofthesetechniqueshaveinherentlimitationsandcriticalissues,suchasmodelnon-uniqueness,whichareoftennotaddressedquantitatively.Thedatasciencerevolutionhasgivenrisetoamultitudeofnewnumericalanalysistechniqueswiththepotentialtoprovideourcommunitywith tools to extract more andmore quantitative information from experimental data. However, theincreasingcomplexityofmoderndataanalysistechniquesmakesitchallengingforend-userstoappreciatethefullpotentialandpitfallsofthisrapidlydevelopingfield.Inthiscontribution,wereviewsomeofthelimitationsofcurrentunmixingmodelsandconsiderwherethefutureofmagneticunmixingmayliewithafocusonthespecificneedsofthemagneticcommunity.

121



Magneticfabricanalysis:currentstatusandfutureprospects

Presenter:

AnnM.Hirt([email protected])

Authors: AnnM.HirtMagneticfabricshavebeenusedforover60yearsasindicatorsforstructuraldeformation,flowdirectionsinsedimentsandigneousrocks,ormineralalignmentingeneral.Wehavegainedagoodunderstandingofhowmagneticfabricsarise,wherebythetwomainfactorsthatcontrolthemagneticanisotropyofarockorsedimentaretheintrinsicanisotropyofmagneticsusceptibility(AMS)ofconstituentmineralsandtheirpreferentialorientation.Inrocksinwhichferrimagneticmineralsdonotcontributetoarock'smagneticfabric,twoapproacheshavebeentakentounderstandhowmagneticfabricreflectsmineralalignment.Theseincludeempiricalstudiesonnaturalrocksanddeformationstudiesonrock-analogues.Numerousstudieshaveexaminedmineralandmagneticfabricsinnaturalrocks,andhavedemonstratedthepotentialtodefineamineralfabricfromtheAMS,orpredictthemeasuredAMS,usingthecarrier'sintrinsicmagneticanisotropy. These studiesaremost successful if a singlemineralphase is responsible for themagneticfabric.Whenseveralmineralscontributetotheobservedmagneticfabric,modelingfabricbecomeslesstractable. This is particularly the case in igneous rocks, in which intrinsic anisotropies of constituentminerals may not be additive, but annihilative. The use of analogue rocks allows for control overconstituent minerals in the material and the style of deformation. Examples range from sandboxexperiments for sandsandclays to theuseofdeformation rigs toexamineaggregatesofoneofmorephases.Whenferrimagneticmineralscarrythemagneticfabric,theeffectoftheiralignmentonremanentmagnetizationisoftenofinterest.Althoughtheferromagneticfabricofrockswillbedependentontheirpreferredalignment,theirintrinsicanisotropyisdependentuponanadditionalfactor,thegrainshapeinthe case of minerals with a high spontaneous magnetization. Similar approaches have been made ininvestigating ferrimagnetic fabrics through empirical and experimental studies. A novel approach toexamineferrimagneticanisotropyinvolvestheuseofnewmaterials.Anumberofadvancementshavebeenmadeinproducingdeformablematerialsthatcarryaremanentmagnetization.Findingagoodanalogueforarockisnottrivial,butinitialresultsusing3Dprintingdemonstratethepromiseofthisapproach.Futuredevelopments in understanding the origin of magnetic fabrics will follow several paths. Firstly, it isimportanttocontinueexploringtheintrinsicanisotropyofrock-formingmineralstounderstandhowtheseare affected by variations in composition. Secondly, we need to broaden our understanding of howmineralsandtheirfabriccontributetothetotalanisotropyofarock,togetherwiththeroleofdifferentdeformationmechanisms.Thirdly,weshouldexploretheprocessesthatleadtoferromagneticfabricsingreaterdetail,andassess the influenceof fabricon theabilityofa rock to faithfully record theEarth'smagneticfield.

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Separationofmagneticfabricsincarbonaterocks

Presenter:

RanIssachar([email protected])

Authors: IssacharR.,DepartmentofGeosciences,Tel-AvivUniversity,Tel-Aviv,IsraelandGeologicalSurveyofIsrael,Jerusalem,Israel.LeviT.,GeologicalSurveyofIsrael,Jerusalem,Israel.MarcoS.,DepartmentofGeosciences,Tel-AvivUniversity,Tel-Aviv,Israel.Harlavan,Y.,GeologicalSurveyofIsrael,Jerusalem,Israel.WeinbergerR.,GeologicalSurveyofIsrael,Jerusalem,IsraelandDepartmentofGeologicalandEnvironmentalSciences,Ben-GurionUniversityoftheNegev,Beer-Sheva,Israel.

Separationofmagneticfabricsisessentialinstudyingthedeformationhistoryofmulti-mineralrocks.Wemanage to separate the magnetic fabrics in chalk samples into diamagnetic, paramagnetic andferromagnetic fabrics.Weshowcasestudiesoftwosites locatedwithintheDeadSeaFault (DSF)plateboundary in southern Golan Heights and Arava areas. The separation is achieved by combining roomtemperature and low temperature anisotropy of magnetic susceptibility (RT-AMS and LT-AMS) andanisotropyofanhystereticremanencemagnetization(AARM)measurements.TheLT-AMS,measuredat~77K,representthefabricofparamagneticclayminerals.TheAARMrepresentthefabricofferromagneticFe-oxides.BysubtractingtheparamagneticandferromagneticfabricsfromtheRT-AMS,thediamagneticfabricisseparated.Inthestudiedsamples,theferromagneticcontributiontothebulkmagneticfabricisnegligible.Ouranalysis indicates that in chalkswithnegligible ferromagnetic contribution,diamagneticmineralsdominanttherockbulkmagneticfabricifthemeansusceptibilityis11x10E-6SI.Intherangeofmean susceptibilities between -6 to 11x10E-6 SI competing effect of diamagnetic and paramagneticmineralsproducesacompositeAMS.Inaddition,wesuggestamechanismofcoccolithsrotationthatmaycontributetothedevelopmentofthediamagneticfabricparalleltotectonicshorteningdirection.Weinferthatthediamagneticfabricsofthestudiedrocksindicatestrainregimeof~N-ShorizontalshorteningclosetostrandsoftheDSFandsuggestthedeflectionoftheregionalstrainfieldthatisassociatedwiththeleft-lateralmotionalongtheDSFsystem.Ontheotherhand,theparamagneticfabricofclaymineralspreservesthedepositionalorigin.Thus,weinferthatdiamagneticfabricinchalksismoresensitivetotectonicstrainthanparamagneticfabricandprovideavaluablestrainindicator.

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Anewtoolforseparatingthemineralmagneticbehavioratlow

temperaturesPresenter:

FranceLagroix([email protected])

Authors: FranceLagroix,1InstitutdePhysiqueduGlobedeParis,SorbonneParisCité,UnivParisDiderot,UMR7154CNRS,1rueJussieu,75005,Paris,FranceYohanGuyodo,InstitutdeMinéralogie,dePhysiquedesMatériaux,etdeCosmochimie(IMPMC),SorbonneUniversités-UMPC,UMR7590CNRS,MuséumNationald'HistoireNaturelle,UMR206IRD,4placeJussieu,75005Paris,France

One timeless challenge in rock magnetic studies, inclusive of paleomagnetism and environmentalmagnetism, is decomposing a sample's bulk magnetic behavior into its individual magnetic mineralcomponents.Wepresent amethodpermitting to decompose themagnetic behavior of a bulk sampleexperimentallyandat lowtemperatureavoidinganyambiguities indata interpretationduetoheating-induced alteration. A single instrument is used tomeasure the temperature dependence of remanentmagnetizationsandtoapplyanisothermaldemagnetizationstepatanytemperaturebetween2and400K.Theexperimentalmethodisvalidatedonsyntheticmixturesofmagnetite,hematite,goethiteaswellasonnatural loesssampleswherethecontributionsofmagnetite,goethite,hematiteandmaghemitearesuccessfully isolated. The experimental protocol can be adapted to target other iron bearingmineralsrelevanttotherockorsedimentunderstudy.Onelimitationrestsonthefactthatthemethodisbasedonremanent magnetizations. Consequently, a quantitative decomposition of absolute concentration ofindividual components remains unachievable without assumptions. Nonetheless, semi-quantitativemagneticmineral concentrationswere determined on synthetic and natural loess/paleosol samples inordertovalidateandtestthemethodasasemi-quantitativetoolinenvironmentalmagnetismstudies.

124



FORCmodeling

Presenter:

IoanLascu([email protected])

Authors: IoanLascu,UniversityofCambridgeDepartmentofEarthSciencesRichardHarrison,UniversityofCambridgeDepartmentofEarthSciencesJoyMuraszko,UniversityofCambridgeDepartmentofEarthSciences

FORCdiagramsallowresearchers to fingerprintdomainstates,extractcoercivitydistributions for thesedomainstates,anddetectgeometry-specificmagnetostaticinteractionfieldsratherunambiguously.FORCdiagramsalsolendthemselvestoquantitativeanalysisandmodeling.HerewepresentthelatestresearchundertakenwithintheNanopaleomagnetismLabattheUniversityofCambridge.Onemajordirectionisgearedtowardprovidingamodelofmagneticcomponentmixing innaturalsamplesbasedonprincipalcomponent analysis (PCA). PCA provides an objective and robust statistical framework for unmixing,becauseitrepresentsdatavariabilityasalinearcombinationofalimitednumberofprincipalcomponentsthatarederivedpurelyonthebasisofnaturalvariationscontainedwithinthedataset. IndividualFORCdiagramsarerecastaslinearcombinationsofend-member(EM)FORCdiagrams,locatedatuser-definedpositionsinPCAspace.TheEMselectionisguidedbyconstraintsderivedfromphysicalmodeling,andisimposedbydatascatter.ThesubjectivityofEMselectioncanbeminimizedbyincludingconstraintsfromgranulometricfiltering,physicalmodeling,additionaldatasets,orstandardreferenceFORCs.Themethodworksbestwhenthesamplesuitecoversalargeregionofmixingspace.However,evenwhenthevariabilityislimited,PCAstilldoesareasonablejobofrevealingthenatureoftheEMs.TheseconddirectioninvolvesmodelingFORCdiagramsbasedonindividualparticlesintheSDandPSDgrainsizeranges,aswellasonentireSDensembles.SingleparticleFORCmodelingreliesonfiniteelementmicromagneticmodeling.Theparticlesusedforthistypeofmodelingarerecreatedas3DvolumesgeneratedfromstackedSEMimagesobtainedfromfocusedionbeam(FIB)nanotomographyofnaturalsamples.Suchmicromagneticmodelsare the state of the art for computing themagnetic response of a system, however, calculations arerelativelyslowandresource intensive.Ensemblesof interactingSDparticlesaremodeledusingaFORCsimulatorthatcalculateseitherthedirectsolutionoftheStoner-Wohlfarthmodel,assumingaquasi-staticdistribution of interaction fields, or an approximate iterated solution to the Landau-Lifshitz-Gilbertequation. Ensembles of SD grainswith uniaxial or cubic anisotropy can be generated automatically invariousconfigurations(randomlyinteracting,chains,tightlypacked).Aswell,realistic3DvolumesofSDparticlescanbeimportedfromFIBnanotomographicreconstructions,fittedwithellipsoids,andusedinFORCsimulations.AllthesefeatureshavebeenrecentlyintegratedinFORCinel3.0.

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Isothermalremanentmagnetizationdecompositionusing1-Dgaussian

mixturemodelPresenter:

JiaboLiu([email protected])

Authors: JiaboLiu,HelmholtzCentrePotsdam,GFZGermanResearchCentreforGeosciences,14473Potsdam,GermanyNorbertNowaczyk,HelmholtzCentrePotsdam,GFZGermanResearchCentreforGeosciences,14473Potsdam,Germany

Theacquisitioncurvesofan Isothermal remanentmagnetizations (IRM)ofnatural samples, ingeneral,reflectvariousmagneticmineralassemblages.To identifythedifferentassemblagesand interprettheirenvironmental informations, magnetic unmixing techniques are adopted in order to perform thequantificationoftheinvolvedcomponents.Inpreviousstudies,thenumberofcomponentsandtheinitialparametersforfittingcurves,likegaussiandistribution,aregenerallyrequiredtobesettledtoachievethemathematicallybestfit.Toavoidthosepre-assumptions,adimensionalityreductionmethodisintroducedhere.WhenthenormalizedgradientIRMacquisitioncurveisregardedasafrequencydistributioncurveofmeasured field, then a pseudo-random sequence can be generated, depending on the frequencydistribution curve. As a result, the fitting of gradient IRM curves are turned to be the clustering of asequenceofrandomnumbers.Withoutanypre-assumptions,the1-Dgaussianmixturemodel(GMM)doclustering of the random sequence in a range of component numbers and iterating using expectationmaximization (E-M)algorithm.Bysetting theaimtoachievetheminimumAkaike informationcriterion(AIC)initerations,thebestfitmodelandnumbersofcomponentswillbegiven.Intermsofasetofsamples,eachsamplegenerateapseudo-randomsequenceandassemblethemintoonesequence,thenusing1-DGMMandthecomponentsareregardedasend-members.Inaddition,whenusingtheend-membersof1-DGMMtoinitializethematrixfornon-negativematrixfactorization(NMF),theresultsaregettingmorestableandunique.SamplesofcorePS97-804-1fromtheDrakePassage,Antarcticocean,aresubjectedtothecasestudy.ThemagneticmineralsaredominantlyPSDtoMDmagnetiteinmostofthesamples.Using1-DgaussianmixturemodelandNMF iterations, the studied samplesaredecomposed into threeend-members. Due to the homogeneous mineralogy of the studied samples, the end-members representdifferencesamongdifferentmagneticgrainsizegroups.

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10 14 july 2017 utrecht, the netherlands abstracts...welcome and key-note: oliver plümper...

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