Glanam 2015 Field Guide Ymerbukta Final...The Holocene glacial history of Svalbard – short version Deglaciation Isfjorden is the largest fjord‐system on Svalbard, cutting into

Field guide 

GLANAM 3rd workshop and field excursion in Isfjorden, Svalbard 15th June 2015 

byLisAllaart,LenaHåkansson&RikoNoormets

 Excursionroute:Longyearbyen‐Ymerbukta/Esmarkbreen–Barentsburg‐Longyearbyen

Bedrock Geology 

GeologicalmapandlegendofouterIsfjordenarea.AtthemouthofIsfjorden,sectionsthroughvariousstructuralgeologicalelementsaredisplayed:thewesternbasementupliftofPrecambrianrocks,theTertiaryfold‐and‐thrustbeltwithCarboniferousthroughTertiaryrocksandthewesternlimboftheforelandbasinoftheCentralTertiarybasin(Dallmannetal1992).Theseelementsarefoundatbothsidesofthefjordmouth.ThePrecambrianbasementisexposedatthebirdcliff,Alkhornet,atthenorthernsideofIsfjorden,immediatelywestofTrygghamna.

Alkhornet

ItconsistsofmetamorphosedProterozoiccarbonates.ThesurroundingbasementwestandnorthwestofTrygghamnaconstitutesphyllitesinterbeddedwithcarbonatesandremnantsofsills.AlloftheserockshavebeensubjectedtointensefoldingandeastwardthrustingandtheirjuxtapositionisassumedtohavehappenedduringtheCaledonianperiod(400–500m.y.,Dallmannetal1999).TheoldbasementcomplexiscalledHeclaHoek(Nordenskiöld1863).EastofTrygghamnaareexposedLower‐CarboniferoustoTertiaryrocks.EarlyCarboniferoussandstonesandMid‐Carboniferousclasticsweredepositedinrestrictedgrabenenvironments(Dallmannetal1992).LateCarboniferoustoPermiancarbonaterockswithsomeevaporitesandMesozoicshale/sandstonesequencesweremainlydepositedwhileSvalbardwassubmerged(Dallmannetal1992).Almostundeformed,flat‐lyingstrataofCretaceoustoTertiaryageareseenonthestrandflatcalledErdmannflya,representingthenorthernlimitoftheCentralTertiaryBasin.Theupper‐Cretaceousdepositscontainsandstoneswithabundantplantfossils.ThetransitiontoTertiarydepositsismarkedbyanerosionalunconformityandthefirstdepositofTertiaryageisathinconglomerate.TwocoalseamsinthelowerTertiarydepositsarebeingexploitedbytheRussiancoalcompanyTrustArktikugol.StrataofLate‐TriassictoCreatceousageareexposedonalargestrandflat,Bohemanflya,NortheastofErdmanflya.Thewholepackageisdipping10‐15°towardssouth.TheLate‐Triassicdepositsconstitutemainlysandstones,theJurrassicaremainlyshalesandtheCretaceousconstitutethicksandstoneswithcoalseams.

The Holocene glacial history of Svalbard – short version 

Deglaciation Isfjordenisthelargestfjord‐systemonSvalbard,cuttingintothecentralpartofSpitsbergenIslandandopeningtowardstheGreenlandSeainthewest.TheIsfjordenbasinwasdeglaciatedbetween12.3–11.0calkaBP(SvendsenandMangerud1997).TheicefrontwasretreatingfromtheouterpartofIsfjordentoBillefjordenbetween11.3and11.2kaBP.Theannualretreatratewasupto170m/ybasedonthedistributionofrecessionalmorainesonthefjordfloorinBillefjorden(Baetenetal2010).Thelastphaseofthedeglaciationofthefjordaround11.2kaBPwasdominatedbyintenseicebergrafting(ForwickandVorren2009).InearlyHolocene,theglaciermarginsretreatedtotheirmodernlimitsorevenfurtherinland,althoughtheSvalbardarchipelagomostlikelydidnotdeglaciatecompletely(Ingólfsson2011,Hormesetal2013).Extensiveseepageofhydrocarbonsfromtheseafloorthroughfaultsandlithologicalboundariestookplaceduringthistimeresultingintheformationofnumerouspockmarksonthefjordfloor(Royetal2015).A B

Bedockgeologyandbathymetry(A)andpockmarkconcentration(B)inIsfjorden(Royetal2015)

Holocene Thermal maximum TheHoloceneThermalMaximum(HTM)isrepresentedinthegeologicalofrecordSvalbardwithchangefromglacier‐proximaltomarinedeposition,abundanceofthermophilemolluscs,lownumberofIRD,raisedbeachesandabsenceofpermafrost(Salvigsenetal1992;Humlum2005;Jessenetal2010;Ingólfsson2011).AlthoughthetimingoftheHTMvariedthroughoutthearchipelago,coredatasuggestHTMaround10.8kaBPinIsfjordenarea(SvendsenandMangerud1997).

Neoglaciation TheactivityofcalvingglaciersinBillefjordenandTempelfjordenincreasedaround5.5kaBP(Baetenetal2010).Linnébreenglacier,situatednearthemouthofIsfjorden,startedformingaround5.0–4.0kaBP(SvendsenandMangerud1997).Atthesametime,thermophilemolluscsappearedinthewatersaroundSvalbard(Salvigsenetal1992).Permafroststartedformingarguablyat3.0kaBP(Humlum2005).

Little Ice Age InSvalbard,thetermtheLittleIceAge(LIA)usuallyreferstotheperiodof600‐100yearsBP(SalvigsenandHøgvard2005).Areasbetweenthemaximumextentofglaciersduring

Neoglacialandtheirmodernextentaremarkedbyseriesofice‐recessionalmorainesformanySvalbardglaciers(SvendsenandMangerud1997;Slettenetal2001).However,itshouldbenotedthatthechronologicalcontrolonthemajorityofthesemorainesispoor,exceptforafewfjordswheretheyhavebeenstudiedindetail(OttesenandDowdwswell2006;Flinketal2015).ForterrestriallyterminatingglacierstheassumedLIAmorainesarefound1–2kminfrontofthepresentdayglacierfronts(Werner1993;Christoffersenetal2005;Friis2015).Theyareicecoredandstandoutassignificantfeaturesinthelandscape(Slettenetal2001).

Ymerbukta  Ymerbuktaisa9kmlongfjordatthenorthernsideoftheentrancetoIsfjorden.TheheadofthefjordisoccupiedbythecalvingglaciermarginofEsmarkbreen.

YmerbuktaandthefrontofEsmarkbreenTheglacialhistoryofYmerbuktahasnotbeenstudiedindetail.Salvigsenetal(1990)suggestthatafterinitialdeglaciation,Esmarkbreenreadvancedshortlyafter9,500BP,whichwasprobablyalocalandshort‐lastingevent.Themarinelimitintheareaisfoundataround60mabovethepresentsealevel,anddatebacktoabout10,000BP(Salvigsenetal1990).

ExtentofEsmarkbreenglacier

RaisedbeachedatErdmannodden

BeachridgesarefoundallthewayfromthemarinelimittothepresentshoreandradiocarbonagesindicatearapidrelativeupliftduringearlyHolocene(Salvigsenetal1990).HistoricalrecordsshowthatEsmarkbreenwasatitsNeoglacialmaximumin1910(DeGeer,1910),anicemarginalpositionmarkedbyprominentlateralmorainesonbothsidesofthefjord.MultibeambathymetricdatafromtheYmerbuktarevealasetoflandformsconsistingoflargetransversemoraines,locallysuperimposedbyglaciallineationsandaseriesofsmallrecessionalmoraines.TheselandformsareconfinedintheYmerbuktabasinthatisseparatedfromtheIsfjordenbyashallowsillfeaturingprobablyalargeterminalmoraine.Althoughthislandformassemblagehasnotbeenstudiedindetail,strikingsimilaritieswiththesubmarinelandformassemblagedocumentedfromtheadjacentBorebukta(Ottesen&Dowdeswell2006)suggeststhattheglacialevolutionofthesetwofjordshasbeenrelativelyalike.AsrecentlyasinAugust‐September2014,theEsmarkbreenunderwentaminisurge.Thiswascapturedonglaciervelocitymaps.Thissurge,however,seemstohavestoppedbynow.

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