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CONTROLID:1807868
TITLE:Improvementsinthechronology,geochemistryandcorrelationtechniquesof
tephrainAntarcticice
AUTHORS(FIRSTNAME,LASTNAME):NelsAntonIverson1,NeliaWDunbar2,
WilliamC.McIntosh1,2,NicholasJPearce3,PhilipRKyle1
INSTITUTIONS(ALL):1.EarthandEnvironmentalSciences,NewMexicoTech,
Socorro,NM,UnitedStates.
2.NewMexicoBureauofGeologyandMineralResources,NewMexicoTech,Socorro,
NM,UnitedStates.
3.InstituteofGeographyandEarthScience,AberystwythUniversity,Aberystwyth,
Wales,UnitedKingdom.
ABSTRACTBODY:VisibleandcryptotephralayersfoundinWestAntarcticice
provideanexcellentrecordofAntarcticvolcanismoverthepast100ka.Tephralayers
aredepositedalmostinstantaneouslyacrosswideareascreatinghorizonsthat,if
foundinseverallocations,provide“pinningpoints”toadjusticetimescalesthatmay
otherwisebelackingdetailedchronology.Individualtephralayerscanhavedistinct
chemical ingerprintsallowingthemtocorrelateovergreatdistances.Advancesin
samplepreparation,geochemicalanalyses(majorandtraceelements)of inegrained
tephraandhigherprecision40Ar/39Ardatingofyoung(<100ka)proximalvolcanic
depositsareimprovinganalreadyestablishedtephrarecordinWestAntarctica.
Fortythreeofthepotentialhundredsofsilicatelayersfoundinarecentlydrilleddeep
WestAntarcticIceSheetDividecore(WDC06A)havebeenanalyzedformajor
elementsandasubsetfortraceelements.Oftheselayers,atleast16arehomogenous
tephrathatcouldbecorrelatedtoothericecores(e.g.SipleDome,SDMA)and/orto
sourcevolcanoesfoundthroughoutAntarcticaandevenextra‐continentaleruptions
(e.g.Sub‐AntarcticislandsandSouthAmerica).Combiningicecoretephrawiththose
exposedinblueiceareasprovidemorelocationstocorrelatewidespreaderuptions.
Forexample,aperiodofheightenederuptiveactivityatMt.Berlin,WestAntarctica
between24and28kaproducedasetoftephralayersthatarefoundinWDC06Aand
SDMAicecores,aswellasatanearbyblueiceareaatMt.Moulton(BIT‐151and
BIT‐152).Possiblecorrelativetephralayersarefoundaticeagesof26.4,26.9and
28.8kainWDC06Aand26.5,27.0,and28.7kainSDMAcores.Thegeochemical
similaritiesofmajorelementsintheselayersmeanthatongoingtraceelement
analyseswillbevitaltodecipherthesequenceofeventsduringthisphaseofactivity
atMt.Berlin.SampleWDC06A‐2767.117(iceageof28.6±1.0ka)appearstocorrelate
toblueicetephraBIT‐152andtotephralayerSDMA‐5683(iceageof28.5ka).This
tephralayeralsoappearstobepresentinblueiceatMt.TerraNovaonRossIsland,
1400kmaway,suggestingthatitmaybeapossibletolinkicecoresinEastAntarctica
(e.g.TalosDomeandLawDome).
Theamountoffeldsparinicecoretephraistypicallytoosmalltobedirectlydatedby
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40Ar/39Armethod,makingitveryimportanttogeochemicallycorrelatetheselayers
toproximaldepositswheremoreandlargerfeldsparcanbesampled.Thecorrelation
ofWDC06A‐2767.117tothecoarse,proximalBIT‐152providesonesuchlink.The
NewMexicoGeochronologyResearchLab(NMGRL)hastwonewmulti‐collector
ARGUSVImassspectrometersthatcanprovidesinglecrystallaserfusionagesthat
areapproximatelyanorderofmagnitudemoreprecisethantheprevious
determinations.Withtheseadvancementsinanalyticaltechnology,wehopeto
improveprecisionon“pinningpoints”inthedeepicecoreswhereannuallayer
countingbecomeslessprecise.
KEYWORDS:8455VOLCANOLOGYTephrochronology,1145GEOCHRONOLOGY
Tephrochronology.
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AdditionalDetails
PreviouslyPresentedMaterial:30%‐GSABulletin(Dunbaretal.2008)and
QuaternaryScienceReviews(Dunbaretal.2011)
ContactDetails
CONTACT(NAMEONLY):NelsIverson
CONTACT(E‐MAILONLY):niverson@nmt.edu
TITLEOFTEAM:
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