1

Continental carbonate facies of a Neoproterozoic panglaciation, 1

NE Svalbard 2

IANJ.FAIRCHILD*,EDWARDJ.FLEMING*†‡,HUIMINGBAO§,DOUGLASI.BENN†¶,IAN3

BOOMER*,YURIV.DUBLYANSKY�,GALENP.HALVERSON◊,MICHAELJ.HAMBREY⌂,CHRIS4

HENDY☺,EMILYA.MCMILLAN*,CHRISTOPHSPÖTL�,CARLT.E.STEVENSON*ANDPETERM.5

WYNN●6

7

*SchoolofGeography,EarthandEnvironmentalSciences,UniversityofBirminghamB152TT,8

UK.(E-mail:i.j.fairchild@bham.ac.uk)9

†DepartmentofGeology,TheUniversityCentreinSvalbard(UNIS),N-9171Longyearbyen,10

Norway11

‡Presentaddress:CASP,WestBuilding,181AHuntingdonRoad,Cambridge,CB30DH,UK12

§DepartmentofGeologyandGeophysics,E235Howe-RussellComplex,LouisianaState13

University,BatonRouge,LA70803,USA14

¶SchoolofGeographyandGeosciences,UniversityofStAndrews,StAndrewsKY168YA,15

Scotland,UK16

◊DepartmentofEarth&PlanetarySciences/Geotop,3450UniversitySt.Montreal,QuebecH3A17

0E8,Canada18

⌂DepartmentofGeographyandEarthSciences,AberystwythUniversity,Aberystwyth,19

CeredigionSY233DB,UK20

☺DepartmentofChemistry,UniversityofWaikato,PrivateBag3105,Hamilton3240,New21

Zealand.22

�InstitutfürGeologie,Leopold-Franzens-UniversitätInnsbruck,Innrain52,23

A-6020Innsbruck,Austria24

2

●LancasterEnvironmentCentre,UniversityofLancaster,LancasterLA14YQ,UK25

RevisionsubmittedtoSedimentologyAugust31st2015 26

3

ABSTRACT27

TheMarinoanpanglaciation(?650-635Ma)isrepresentedinNESvalbardbytheWilsonbreen28

Formationwhichcontainssyn-glacialcarbonatesintheupper100mofthe130-175m-thick29

formation.ThesesedimentsarenowknowntohavebeendepositedunderaCO2-rich30

atmosphere,lateintheglaciation,andglobalclimatemodelsfacilitatetestingofproposed31

analogues.Precipitatedcarbonatesoccurinfourofsevenfaciesassociations:FluvialChannel32

(includingstromatoliticandintraclasticlimestonesinephemeralstreamdeposits);Dolomitic33

Floodplain(dolomite-cementedsandandsiltstonesandmicrobialdolomites);CalcareousLake34

Margin(intraclasticdolomiteandwave-rippledoraeoliansiliciclasticfacies)andCalcareousLake35

(slump-foldedandlocallyre-sedimentedrhythmic/stromatoliticlimestonesanddolomites36

associatedwithice-raftedsediment).Thereisnostrongcyclicityandmodernanaloguessuggest37

thatsuddenchangesinlakelevelmaybecharacteristic.38

Bothcalciteanddolomiteinstromatolitesandrhythmitesdisplayeitherprimaryorearly39

diageneticreplacivegrowth.Oxygenisotopevalues(-12to+15‰VPDB)broadlycovarywithδ13C.40

Highδ13Cvaluesof+3.5to+4.5‰correspondtoequilibrationwithanatmospheredominated41

byvolcanicallydegassedCO2withδ13Cof-6to-7‰.Limestoneshaveconsistentlynegative42

δ18Ovalues,whilst,rhythmicandplayadolomitespreserveintermediatecompositions,and43

dolocretespossessslightlynegativetostronglypositiveδ18Osignatures,reflectingsignificant44

evaporationunderhyperaridconditions.Meltwatercompositionsinferredas-8to-15.5‰45

couldreflectsmallerRayleighfractionationrelatedtomorelimitedcoolingthaninmodernpolar46

regions.Acommonpseudomorphmorphologyisinterpretedasareplacementofikaite47

(CaCO3.H2O),whichmayalsohavebeentheprecursorforwidespreadreplacivecalcitemosaics.48

Localdolomitizationoflacustrinefaciesisinterpretedtoreflectmicroenvironmentswith49

fluctuatingredoxconditions.Althoughdifferingin(palaeo)latitude,tectonicsetting,and50

4

carbonateabundance,theWilsonbreencarbonatesprovideauniquepre-Cenozoicanaloguefor51

theMcMurdoDryValleysofAntarctica.52

53

Keywords:Cryogenian,oxygenisotopes,carbonisotopes,lacustrine,ikaitepseudomorphs,54

SnowballEarth 55

5

INTRODUCTION56

57

ThesecondoftwoNeoproterozoicpanglaciations,inwhichicesheetsreachedsealevelinthe58

tropics,terminated635Myagoatthebaseofatransgressivecapcarbonatedefiningthe59

Cryogenian-EdiacaranSystemboundary(Table1).DepositsofCryogenianiceagesarepreserved60

onmostcontinentsandareofteninterpretedasglacimarine(Arnaudetal.,2011).However,in61

NESvalbard,theMarinoan-aged130-175mthickWilsonbreenFormation(Halverson,2011)62

uniquelycontainsnon-marinecarbonatesaswellassubglacialtillites(Fig.1).Theseevince63

hyperaridterrestrialenvironments(Fairchildetal.,1989)andanatmosphererichincarbon64

dioxideduringglaciation(Baoetal.,2009),thelatterconclusionfulfillingapredictionofthe65

SnowballEarthhypothesis(Kirschvink,1992;Hoffmanetal.,1998).BecauseWilsonbreen66

Formationoutcropsarerestrictedtoremoteicefieldnunataks(Fig.2),theyhaverarelybeen67

visited,andhenceourknowledgeofthesedimentaryarchitecturehasbeenincomplete.The68

WilsonbreenFormationcarbonatescontainprobablythehighestcarbonateandsulphateδ18O69

valuesandlowestsulphateΔ17Osignaturessofardiscoveredinthegeologicalrecord,features70

whichevokeoneofthemostextremeclimaticeventsinEarthhistory(Baoetal.,2009,Bennet71

al.,2015).Herewecharacterizearangeofnon-marineenvironmentsinwhichthecarbonates72

wereprecipitatedusingacombinationoffield,petrographicandstableisotopeevidence,and73

scrutinizeaclaim(Fairchildetal.,1989)thatthesedepositsareananalogueoftheextreme74

terrestrialenvironmentsofthemodernMcMurdoDryValleyregionofAntarctica,albeitformed75

atmuchlowerpalaeolatitudes.76

ThestudyareaintheSvalbardmainlandofSpitsbergen(Figs.1,2)andthebasin77

continuationtotheNEhavelongbeenrecognizedasclassicareasforlatePrecambrian78

glaciation(Kulling1934).ThefirstdetaileddescriptionoftheWilsonbreenFormationwasby79

6

Wilson&Harland(1964),althoughcarbonateswerediscussedonlyintermsofitsbounding80

dolomitesasstratigraphicmarkers.Alatersedimentologicalsynthesis(Hambrey,1982;Fairchild81

&Hambrey,1984)showedthatevidenceofglacialactivitywasconfinedtotwoglacialunitsin82

thePolarisbreenGroup:theWilsonbreenFormation,andanewlydiscovered,thin,olderunitin83

theElbobreenFormation(PetrovbreenMemberalsoknownasE2)(Table1).Severaldistinctive84

formsofcarbonateinassociationwiththeglacialdeposits.Thefirstoftheseisdolomiticglacial85

rockflour,demonstratedinultra-thinsections(Fairchild,1983).Subsequently,stableisotope86

studiesdemonstratedthepresenceofglacimarineprecipitatesinthePetrovbreenMemberand87

glacilacustrinedepositsintheWilsonbreenFormation(Fairchild&Hambrey,1984;Fairchild&88

Spiro,1987;Fairchildetal.,1989).Itwasalsoshownthatthesecarbonatescontrastwitha89

distinctivemarinetransgressive‘capcarbonate’(followingWilliams,1979)overthe90

WilsonbreenFormation.Halversonetal.(2004)providedamuchmoredetailed91

chemostratigraphicframeworkforthePolarisbreenGroupandpostulatedthatbothdiamictite92

unitsbelongedtothesame,Marinoanglaciation.However,newchemostratigraphicdataledto93

areversiontotheprevioustwo-foldglaciationinterpretationofolderliterature(Halverson,94

2006;Halversonetal.,2007).NodirectgeochronologicalconstraintsexistonSvalbard,butthe95

low87Sr/86SrvaluesatthebaseofthePolarisbreenGroupcorrelatewellwiththoseassociated96

withthefirstevidenceofNeoproterozoicglaciationelsewhere(Halversonetal.,2010).Also,the97

majormarinetransgressionsuccessionabovetheWilsonbreenFormationcloselyresemblesthe98

basalEdiacaranfacieselsewheredatedat635Ma(Rooneyetal.,2015).Palaeomagnetic99

constraintssuggestthatNESvalbardlayinthesubtropicsthroughouttheCryogenian(Lietal.,100

2013)aspartoftheequatoriallycentred,fragmentingRodiniasupercontinent.101

ThecloselysimilarstratigraphyincentralEGreenland(nowofficiallyredesignatedas102

NortheastGreenland)(Hambrey&Spencer,1987;Moncrieff&Hambrey,1990)indicatesthatit103

7

representsasouthwesternbasincontinuation(Hambrey,1983;Knolletal.,1986;Fairchild&104

Hambrey,1995),subsequentlyoffsettothesouthbyleft-lateralstrike-slipfaulting(Harland,105

1997).TheNeoproterozoicsuccessioninwesternSvalbardisquitedifferentandwasprobably106

notdepositedinthesamebasin(Harlandetal.,1993).107

108

Cryogenianeventsandpanglaciation109

110

TheconceptofNeoproterozoiclow-latitudeglaciationwaschampionedbyHarland(1964)who111

arguedfromthewidespreadoccurrenceoftillitesthattheyweregloballydistributedandhence112

shouldbeusedincorrelation.Subsequentlyittookanenormouseffortfromthegeological113

communitytoestablishthatthediamictiteunitsarepredominantlyglacigenicoratleast114

glaciallyinfluenced,thatconvincingevidenceoflow-latitudeglaciationexists,andthatthe115

correlationsaresupportedbyageochronologicalframework(Fairchild&Kennedy,2007).116

Despitethecomplexityofindividualsuccessions,summarizedinArnaudetal.(2011),itisnow117

widelyrecognizedthattwopanglacialeventsoccurredduringtheCryogenianperiod(c.720–635118

Ma),referredtoastheSturtian(orearlyCryogenian)andMarinoan(orlateCryogenian)119

glaciations(Halversonetal.,2007;Macdonaldetal.,2010;Hoffmanetal.,2012;Calveretal.,120

2013;Rooneyetal.2014,2015;Lanetal.,2014).Thetraditionalgeologicalapproachrecognized121

theroleoflowatmosphericCO2levelsintriggeringglaciation,buttherewasalackof122

understandingofwhole-Earthbehaviouruntilinsightsfromclimatemodellingofapossible123

future“nuclearwinter”(e.g.Budyko,1969)ledtotherealizationthatafrozen,highalbedo124

planetrepresentsastableclimaticstate.Kirschvink(1992),incoiningthetermSnowballEarth,125

suggestedthatlowpalaeolatitudesofcontinentsinNeoproterozoictimescouldhavehadarole126

intriggeringpanglaciation,andthattoescapetheSnowballstateabuild-upofvolcanically127

8

derivedCO2wasneeded(Caldeira&Kasting,1992)toovercomethedominanceofthealbedoof128

Earth’sicysurfaceonitsenergybalanceandtriggerdeglaciation.Hoffmanetal.(1998)and129

Hoffman&Schrag(2002)subsequentlyexpandedupontheSnowballmodel,incorporating130

insightsfromplanetarymodellingtoenlightennewstratigraphic,sedimentologicaland131

geochemicaldata.SnowballEarthisbestregardedasatheory,notmerelyahypothesis,because132

itisbuiltaroundaseriesofpropositionswhichare,toagreaterorlesserextent,interacting133

(Fairchild&Kennedy,2007).Thetheoryhasstimulatedahugeaccelerationindata-gathering134

andmodellingwhichhassignificantlyclarifiedtheextenttowhichagivenphenomenonis135

essentialtoorcharacteristicofaSnowballEarth.Initially(Hoffmanetal.,1998),therewasa136

focusontheassociatednegativecarbonisotopeanomaly,apparentlyencompassingtheglacial137

period,whichwasregardedasacharacteristicofloworganicproductivityinanoceanwhich138

becameisolatedfromtheatmosphereoncetheSnowballstatehadbeenestablished.139

Additionally,thepost-glacialcapcarbonatesandtheassociatedtransientsinthenegative140

carbonisotopeanomalieswereregardedasapositivetestofthehypothesis,reflectingrapid141

meltdownandsea-levelriseunderapost-Snowball,ultra-greenhouseenvironment.However,142

afterfurtherscrutinyallofthesepropositionshaveemergedasflawedorambiguous(Kennedy143

etal.,2001a.b;Hoffman&Schrag,2002;Halversonetal.,2002;Schragetal.,2002;Trindadeet144

al.,2003;Hoffmanetal,2007;LeHiretal.,2008,2009;Kennedy&Christie-Blick,2011;Hoffman145

etal.,2012).146

IntheearlyyearsoftheSnowballhypothesis,missingwasanaccountofhowtheglacial147

formationsthemselvescouldbeusedtoprovidesupportforthetheory.Inthe“hard”Snowball,148

theconceptisofauniversallythickicecoverovertheoceans,composedofanupperzoneof149

glaciericeandlowerzoneoffrozenseawater(Pierrehumbert2005;Pierrehumbertetal.,2011).150

Ifso,sealevelshouldbegreatlyloweredandmarineicemarginsshouldoccuratmuchgreater151

9

depthsthantheshallow-waterpre-glacialsediments.Evidencetosupportthishypothesiswas152

foundinNamibia.Onplatformtops,glacigenicdepositsarerare,whereasonplatformmargins153

tidewater-glaciergrounding-linephenomenacanbedemonstrated,inferredtobesome154

hundredsofmetrestopographicallylower(Hoffman,2011;Domack&Hoffman,2013).Onthe155

otherhand,mostglacialsedimentologistswerehostiletoSnowballtheory,insistingthatthereis156

evidenceofrepeatedadvancesandretreatsoficeinmarineenvironmentsduringglaciation,157

andalsothatlocallywave-andstorm-generatedstructuresarepresent,indicatingopenwater158

(Xiaoetal.,2004;Etienneetal.,2007;Allen&Etienne,2008;LeHeronetal.,2011,2013).159

Apparentsupportfrommodelsshowingequatorialopenwater(e.g.Hydeetal.,2000)facedthe160

problemthatthesimulatedclimatesolutionswerenotstable.Hence,theresponseofHoffman161

(2011)wasthat“counterarguments[totheSnowballmodel]basedontemperate-typeglacial162

sedimentologyfailtograspthatthepreservedglacialsedimentaryrecordreflectstheendofthe163

SnowballEarth,whenmeltingwasboundtoemergetriumphant”.Afurthertwisthoweverwas164

thatasimulationofalong-livedmarineice-freeequatorialfringewasachievedbyAbbotetal165

(2011),inwhattheytermtheJormangundstate.Hoffmanetal.(2012)notedthatwhereasthe166

Jormangundstatepreservedthepatternofmodernlow-latitudeclimatebelts,withamoister167

equatorialregion,theSnowballclimaticpattern(Pierrehumbertetal.,2011)wouldresultin168

higherprecipitationminusevaporationinthesubtropicsandanextremelyaridequatorialzone.169

Thisdrawsattentiontotheneedforstudyofcontinentalglacialdepositssuchasthe170

WilsonbreenFormationwheremoredirectevidenceofclimaticconditionscanbeobtained.171

ThesurvivingessentialpredictionsofSnowballEarththeorycanbesummarizedas172

follows:1)glaciationsmustoccursynchronouslyglobally,2)theymustbelong-lasting(>1Ma)173

toallow3)thebuildupofatmosphericCO2tohighlevelswhen4)sedimentationoccursina174

briefperiodpriortotermination.Althoughearliergeochronologicalcompilationshadlegitimate175

10

doubtsabout1)and2)(AllenandEtienne,2008),theyarenowmorefirmlyestablished(Rooney176

etal.,2015),althoughthedurationoftheMarinoan(?5-15My)isimpreciselyknown.The177

WilsonbreenFormationhasnowpermittedpositivetestsof3)and4).178

ComparedwithCenozoicstrata,thereareveryfewapproachestodeterminationof179

atmosphericCO2concentrationsintheNeoproterozoic.Aboldnewapproachwasappliedby180

Baoetal.(2008)basedonprocessesoccurringduringstratosphericozoneformationwhich181

resultsinanenrichmentintheisotope17Oinozoneandcarbondioxideanddepletioninoxygen182

(O2).Thisisanonmass-dependenteffectwhichdoesnotinfluence18Oabundances.The17O183

signalcanbepreservedintheoxygenatomsofsulphateinrocksifatmosphericoxygenisused184

tooxidizesulphidesonthelandsurface.Sulphatehasthepeculiarpropertyofnotexchanging185

oxygenatomswithotherspeciesover1000Mytimescalesatsurfaceconditions,providedthere186

isnomicrobialredoxcyclingofsulphur-bearingions.Baoetal.(2008)testedtheideathatat187

timeperiodswhenatmosphericPCO2wasenhanced,therewouldbe17O-depletedsulphatein188

thegeologicalrecord,andindeedfoundthemostsignificantanomalythathadatthattimebeen189

discovered,recordedinbaritecrystalfansoccurringinthecarbonatesuccessionoverlying190

MarinoanglacialdiamictitesinSouthChina.191

Baoetal.(2009)thenfocusedonlacustrinecarbonatesofthecentralpart(memberW2)192

oftheWilsonbreenFormationandfoundmoreprofound17O-deficienciesincarbonate-193

associatedsulphate(CAS)inlimestones,consistentwithveryhighatmosphericPCO2during194

glaciation.Morerecentstudiesinothergeographicregions,coupledwithprocessmodelling195

approaches,havesupportedthisapproachinMarinoancapcarbonates(Baoetal.,2012;Cao&196

Bao,2013;Killingsworthetal.,2013;Bao,2014),buttheWilsonbreenFormationremainsthe197

onlyunitwherePCO2canbeestimatedduringglaciation.198

11

Subsequently,Bennetal.(2015)haveusedthesameisotopesystematicsofCASona199

muchlargerdatasetoflimestonesfrommembersW2andW3toarguethatsimilarhighPCO2200

values(estimatedatbetween1and10%atmosphericCO2)occurredthroughoutthedeposition201

oftheWilsonbreenFormation.SinceitwouldhavetakenalongtimetoaccumulateCO2,the202

inferencewasthatthebulkoftheWilsonbreenFormationwasdepositedinarelativelyshort203

periodneartheendoftheglaciation.Inturn,thisimpliesanextendedhiatusearlyinthe204

glaciationwhichwasidentifiedwithapermafrostedhorizonatthebaseoftheWilsonbreen205

Formation.206

CoupledicesheetandatmosphericgeneralcirculationmodelresultsinBennetal.(2015)207

usingSnowballEarthboundaryconditionsdemonstratethatat2%atmosphericPCO2thick208

glaciersexistonthecontinentsalongwithextensiveareasofbaregroundandthathyperaridity209

iswidespread.Precessionalforcinggeneratesmovementsoficemarginsbyatleasthundredsof210

kilometresandwaslinkedtothepresenceofdistincticeadvanceswithintheWilsonbreen211

Formation(Fig.1).AlthoughconclusionsbasedontheMarinoanglaciationshouldnot212

necessarilyapplytothemuchlongerSturtianglaciation,thenewresultsprovideapossible213

routetoreconciletheopposedpositionsstatedinAllen&Etienne(2008),oftemperateglacial214

conditionsduringpanglaciation,andHoffman(2011),ofsedimentdepositionoccurringrapidly215

duringmeltdown.Itisthepurposeofthecurrentpapertoprovideadetailedsedimentological216

analysistounderpinthisnewsynthesisandinparticulartodemonstratetheplausibilitythatthe217

Wilsonbreencarbonatesweredepositedwithinacoherentgeomorphic-climaticsystem.Asa218

firststep,weneedtoexaminethepossiblemodernanalogue.219

220221

TheAntarcticMcMurdoDryValleysasanaloguesfortheWilsonbreenFormationcarbonates222

223

12

Fairchildetal.(1989)previouslyusedtheDryValleysregionasanexemplarforthecarbonates224

inmemberW2oftheWilsonbreenFormation.Conversely,leadingworkersonthemodern225

environment(Lyonsetal.,2001)commentedthatthisfrigid,drymodernenvironmentmightbe226

avaluableanalogueforProterozoicSnowballEarthenvironments.TheDryValleyshavealso227

beenusedasanaloguesfortheMartiansurface(Marchant&Head,2007;Dicksonetal.,2013).228

Thelocal“alpine”glaciersoftheDryValleysarecold-based,butoutletglacierssuchasthe229

TaylorGlacierarewarm-based.Giventhecriteriaforrecognitionofglacialthermalregime230

presentedbyHambrey&Glasser(2012),warm-basedanaloguesareneededtounderstand231

muchoftheglacigenicfaciesoftheWilsonbreenFormation(Flemingetal.,2016).Nevertheless,232

forthecarbonatefacies,thecontextoftheDryValleyregion,uniquelyforpresent-day233

environments,providesparallelsforthefollowingevidenceprovidedbyFairchildetal.(1989):234

(1)arecordofextremeevaporationwithpotentiallyupto20‰differenceinδ18Obetween235

inputwatersandthoseresponsiblefortheprecipitationofthecarbonateswithheaviestδ18O236

signaturesand(b)alternatingdepositionofglacialsedimentandcontinentaldepositsindicating237

iceadvanceandretreat,specificallyincludingrhythmicandmicrobial,presumedlacustrine238

carbonatesandevidenceofformerevaporites.239

Fig.3illustratesthecontextofthemodernsettingwhichhasbeenextensivelystudied240

overseveraldecadesbyAntarcticgroupsledfromNewZealand,JapanandtheUSA,withTaylor241

valleybeingthefocussince1993oftheMcMurdoDryValleysLong-termEcosystemResearch242

(LTER)ProgramoftheNationalScienceFoundation.TheDryValleysisa4800km2region243

occupyingpartoftheTransantarcticMountainsbetweentheEastAntarcticIceSheet(EAIS)and244

theRossSea.TheindividualvalleysthemselvesmostlytrendE-Wandareupto80kmlongand245

upto15kmwideandareinternallydrained,oftenwithseveraldiscretelakebasinsineach246

valley.TwooutletglaciersfromtheEAIS(WrightUpperandTaylorglaciers)onlyjustcrossthe247

13

regionalbedrockaltitudedivideintotheeastward-drainingcatchments,whilsttheFerrarglacier248

flowsallthewaytothecoast(Fig.3).Localvalleyglaciersextendfromthemountainsintodry249

valleys,e.g.CanadaGlacierinTaylorValley(insetinFig.3)andephemeralstreamsdevelopfor250

shortperiodsinsummer.Avarietyoflakesoccur,includingthoseoccupiedbyicefrozentothe251

bedintherelativelyhigh-altitudeVictoriaValley,highlysalinelakeswithnoicecover(e.g.Don252

JuanPond,UpperWrightValley)andfinallylakeswitha3-5micecover(e.g.Lakes253

BrownsworthandVandainWrightValleyandLakesBonney,HoareandFryxellinTaylorValley),254

whichmeltonlyinamarginalmoatinsummer(Green&Lyons,2009;Dicksonetal.,2013).255

Microbe-dominatedbiotasflourishwhereverandwheneverthereisliquidwaterintheregion,256

includingmatsonstreamandlakebeds,andphotosynthesizingalgaeareimportantinlakes257

duringthespringseason(Fountainetal.,1999).Thesematstakeupnutrientsrapidlyfrom258

streamwaterandthebiogeochemicalpatternsarestronglyinfluencedbyexchangeof259

hyporheicwaterswithstreamwater(McKnightetal.,1999).260

Thereisaspatialmicroclimaticzonationcomprisingacoastalzonewithjust-thawedsoils261

insummerandastablecolduplandzonewithparticularlylowrelativehumidity(Marchantand262

Head,2007;Marchantetal.,2013).Theinterveningvalleyshaveameanannualtemperatureof263

-16to-21°Candthemaximumdailytemperatureisbelowzeroonaveragethroughouttheyear264

(Fountainetal.,1999).Thevalleysreceivelessthan10mmwater-equivalentofprecipitation265

peryear,almostalwaysassnow.Becauseoftheprevailinglowrelativehumidities(e.g.between266

50and60%inTaylorValley,Fountainetal.,1999),ablation(mostlyassublimation)greatly267

exceedsprecipitation.Wilson(1981)describedtheconsequencesofthisgeographic268

configurationandclimatologyusingphysicalandchemicalprinciples.Precipitationriseswith269

altitude,butfallsinlandfurtherfromtheRossSea.Thesnowlinemarkstheboundarywhere270

ablationexceedsprecipitationanditrisesinlandasprecipitationdeclines.Wilson(1981)271

14

attemptedtoexplainthedistributionofsaltsbasedonanunderstandingofdownslope-272

increasingaridity,butitseemsthatvariablemeteorologyconfoundsthepredictionsindetail.273

Nevertheless,itisthecasethatdeliquescentsaltsflowdownhillinthesub-soilabovea274

permanentlyfrozenlayer.Lakeswithalidoficedisplayabalancebetweenablationatthe275

surfaceandfreeze-onoflakewaterbeneaththelid,replenishedseasonallybystreaminflow.276

Oncesnowhasbeenremovedbyablation,sunlightcanpenetratethroughverticalicecrystals277

andsignificantsolarheatingoflakescanoccur.Thepresentconfigurationofsaltsallows278

deductionsofbothlong-andshort-termhistory.Specifically,spatialvariabilityinsaltsrequiresa279

long-term(>105-106years)stabilityoftheice-freesubaerialvalleysides.Ontheotherhand,280

somelakeshaveabasalbrinelayerwhichdiffusionmodellingshowsoriginatedfromaperiod281

around1200yearsagowhensomelakeswereice-freeshallowbrines,beforebeingre-filledby282

freshmeltwater.283

OneaspectnottreatedbyWilson(1981)istheeffectofwind.Animportant284

reinforcementmechanismforaridityisprovidedbytheregionaldevelopmentofkatabatic285

windsflowingofftheEastAntarcticIceSheet.Asthisairwarmsadiabatically,humidity286

decreases,particularlyinwinter(Nylenetal.,2004).Itisnowclearthattheepisodicallystrong287

summerwindsareactuallywarmfoehnwinds,whicharisefromstrongpressuregradients288

duringtheoccurrenceofcyclonesovertheRossSea,theincidenceofwhichdependson289

hemisphericclimaticanomalies.Thesetopographicallyenhancedandchannelledwindsflowat290

typically>5ms-1westerlyalongtheDryValleysandcauseverylargeintra-annualandinter-291

annualincreasesinmeltwaterproductionandstreamflow(Doranetal.,2008;Speirsetal.,292

2013).Thehighincidenceofthesewindsinsummer2001/2,whenpositivedegreedays293

increasedbyanorderofmagnitude,ledtorisesinlakelevelof0.5-1m,effectivelywipingout294

theprevious14yearsofloweringoflakelevelinaperiodofthreemonths(Doranetal.,2008).295

15

Thesedetailseffectivelydemonstratethesensitivityoftheenvironmenttoclimaticchangesthat296

willstronglyinfluencethefaciesdeposited.297

Barrett(2013)recentlyreviewedthecontroversiallong-termhistoryoftheMcMurdo298

region.EvidenceforlandscapeevolutionbasedonthepositionofMiocenevolcanicashdeposits299

clearlydemonstratesthataftertheestablishmentofthecurrentlargeEastAntarcticIceSheetin300

theMiocene,onlysurficiallandscapemodificationhasoccurred(Sugdenetal.,1995;Lewiset301

al.,2007).Importantly,thecold,dryclimatesoftheDryValleysremainedstable,evenduring302

significantwarmingeventsrecordedintheRossSeaduringthePliocene.Thislong-termclimatic303

stasiscanbecomparedwiththepredictedlong-termhydrologicalinactivityanticipatedona304

SnowballEarthascarbondioxidelevelsslowlyrose.305

LargelakesformedduringtheLastGlacialMaximuminallthemajorDryValleys.This306

requiredtwoconditions:(1)expansionoftheRossSeaIcesheettoblockthemarinemarginsof307

theDryValleys(Hendy,1980;Halletal.,2013)and(2)increasedmeltwaterproductioninthe308

valley(bywind-inducedmelting,Doranetal.,2008),despitesignificantlycolderconditions.309

Conversely,datingofaragoniticlacustrinedepositsshowsthat,ininterglacialperiods,therewas310

anexpansionofTaylorGlacier,notedforcharacteristicallylightoxygenisotopevalues,in311

additiontoexpansionoflocalvalley-sideglaciers,withheavierisotopevalues(Hendy1979,312

1980).ThesephenomenapresumablyreflecthighersnowaccumulationontheEAIS,enhanced313

meltwaterproduction,andpartialblockageofthevalleybyice.Importantly,theseinferences314

drawattentiontothepotentialanti-phasingofglobaltemperatureandlocalglacieradvanceand315

thegreaterimportanceofregionalhumiditycontrolsonMilankovitchtimescales.316

Inthecurrentpaper,awealthofnewdataontheWilsonbreenFormationcarbonates317

arepresentedwhichallowstheanalogiespreviouslymadetobetestedandevaluatedinmuch318

moredepth.Theinterpretationofthesedataisassistedbymodernanaloguesandnew319

16

computersimulationstudiesofNeoproterozoicclimates(Pierrehumbertetal.,2011,Bennetal.,320

2015).321

322

METHODS323

324

Fieldwork(2010-11)wassupportedbyhelicopterandbyskidoo.Sections,includingsixentirely325

newlocations,weremeasuredby30mtape,orientatedbycompassandAbneylevel,andlinked326

tobeddingdips,withtotalthicknesscheckedbyGPSwithuncertaintyofaround5%.Thebest327

availablesectionsineachregionwerelogged(Figs.1,2),althoughtheyvaryinqualityfrom328

almostperfect,tointermittentgoodoutcropseparatedbyground-levelfrost-shatteredregolith.329

Thecarbonaterocksarechemicallyfresh,butlaboratorystudyofcutorsectionedsampleswas330

necessarytoidentifyfaciesinmanycases.Over350samplesweresawn,210ofwhichwere331

thin-sectionedofwhich60werestainedwithAlizarinRed-Sandpotassiumferricyanideand332

over30polishedsectionsstudiedbycold-cathodecathodoluminescence(CL)at15kV.333

Carbonandoxygenstableisotopedataarepresentedhereasδ13Candδ18Oinpartsper334

thousandwithrespecttotheVPDBstandard.Differencesbetweenlaboratoriesareinsignificant335

inrelationtothewiderangeofisotopevalues(29‰inδ18Oand8‰inδ13C)inthisstudy.336

SupplementarydatainBaoetal.(2009)includedmethodsandalldatacollectedtothatdate.337

NewdatawasobtainedattheUniversityofBirminghamusingacontinuous-flowIsoprimeIRMS,338

withamultiflowpreparationsystem.Samplesofbetween80-250µgpowderedcarbonatewere339

reactedwithphosphoricacidat90°Cfor90minutes.ResultswerecalibratedusingIAEA340

standardsNBS-18andNBS-19.Afluidinclusionstudyisreportedinthesupplementary341

information.SulphateoxygenandsulphurisotopesarepresentedinBennetal.(2015).Wedraw342

onpreviouslypresentedtraceelementdatafromthecarbonatefractionsolubleindilutenitric343

17

acid(Fairchild&Spiro,1987;Fairchildetal.,1989;Baoetal.,2009),whilstnewtraceelement344

andotherisotopeanalyseswillbepresentedelsewhere.345

Infigurecaptions,thelocationandstratigraphicpositionaregiveninastandardformat.346

ForexampleW2,Dracoisen,70m,referstoasamplefrommemberW2fromtheDracoisen347

section,70mabovethebaseoftheformation(orthebaseofthesectionwherethebaseisnot348

seen).Thecontextandoxygenisotopecompositionofthecarbonatefromthathorizoncanbe349

foundinthestratigraphicsectiondiagrams:Fig.4forDracoisenandsupportingFigs.1-6forthe350

othersections.CarbonatesinmembersW1andW3aresummarizedonlyinTable2,butfull351

samplelogsaregiveninBennetal.(2015).352

353

WILSONBREENFORMATIONARCHITECTURE,COMPOSITIONANDPOST-DEPOSITIONAL354

HISTORY355

356

TheWilsonbreenFormation,dominatedlithologicallybysandydiamictites,containsawealthof357

evidenceindicatingthatitislargelyglacigenic,anddepositedinbothaqueousandsubglacial358

settings(Hambrey1982;Fairchild&Hambrey,1984;Dowdeswelletal.,1985;Harlandetal.,359

1993).Newwork(Bennetal.,2015;Flemingetal.,2016),includingfivepreviouslyundescribed360

sections,hasresultedinacoherentstratigraphic-faciesreconstruction(Fig.1).Thispaper361

focusesonbeds(sandstones,rhythmites,mudrocks)containingprecipitatedcarbonate;the362

presenceofsuchstratawasoriginallyusedtodefinememberW2(Hambrey,1982).Inthe363

northernmostsection(Dracoisen),W2isreadilydistinguishedbythreesuchcarbonate-bearing364

bedsseparatedbydiamictites(Fig.2A),andoverallasimilarpatternappliesinothersections365

(Fig.1).HoweverthinrhythmiteunitsalsooccurinmemberW1,onecontainingprecipitated366

carbonate,andmostofthethinnon-diamictite(sandstoneandrhythmites)bedsinmemberW3367

18

containsuchcarbonatefacies(Table2). AlthoughglacigenicrockscontinueNNEtothecoast368

andtoNordaustlandet,thesewerenotincludedinourstudysincediamictitesarethinnerand369

lesswellexposed,andprecipitatedcarbonatesareabsent(Halversonetal.,2004;Hoffmanet370

al.,2012).NeitherdosuchcarbonatesoccurintheequivalentStoreelvFormationofNE371

Greenland,representingtheSWcontinuationofthebasin(Hambrey&Spencer,1987;Moncrieff372

&Hambrey,1990;Hoffmanetal.2012,Fleming,2014).373

374

Terrigenousdetritus375

376

Harlandetal.(1993)summarizedinformationfromfivesites,determiningthatcarbonateclasts377

makeup40-85%,igneousandmetamorphicclasts5-33%andsandstonesandquartzites10-20%378

ofstones(i.e.gravel-sizeddebris);thebasementlithologiesareprimarilygranitoidsand379

gneisses,withsomebasaltinwhichferromagnesianmineralsarecommonlychloritized.Inthe380

widercontextofterranesaffectedbytheCaledonianorogen,detritalzirconstudiesindicate381

provenancefromArchaeanandPalaeoproterozoicrocksofthecratonicinteriorand382

MesoproterozoicdetritusderivedfromtheerodedremnantsoftheGrenville-Sveconorwegian383

orogen(Cawoodetal.,2007).Asystematicstudyofcarbonateclastcompositionswillbe384

presentedelsewhere,butinsummary80%ofpebblesaredolomiterockand20%arelimestone;385

manyofthesecarbonatesresembleunitsfromtheunderlyingsuccession(Table1)inlithology386

andisotopecomposition;nostratigraphictrendsinclasttypeorisotopecompositionwere387

found.Thesandfractionisdominatedbyquartzandfeldsparwithsubordinatedolomiteand388

limestoneandthemudfractionlikewisebyquartzo-feldspathicdebrisanddolomite(Fig.5).The389

dominanceofsiltinthemudfractionisshowningradedrhythmites(Fig.5B,C);notablydetrital390

calciteoccursinthemudfractiononlylocallyandtheproportionofclaymineralsislikewisevery391

19

low.ThedolomitematrixofPolarisbreenGroupdiamictitesispredominantlytheresultofglacial392

transportandcomminutionasshownbythepresenceofsub-micronrelicrockflour(Fairchild,393

1983)inwhichclaymineralsarevirtuallyabsent(Fig.5D).Thisdetritalmatrixcontainsa394

complexmixtureofbothbrightanddullyluminescentreddolomitewhenviewedinCL(Fig.5C).395

Themeancarbonandoxygenisotopecompositionsofdolomiticmatrixindiamictitesand396

wackes(n=43)are+2.4±1.3and-3.5±1.8‰respectively,slightlylowervaluesthanfor397

dolomitepebbles.Thismatrixcompositionformsausefulreferencepointforcomparisonwith398

precipitatedcarbonatesintheWilsonbreenFormation.399

400

Burialdiageneticmodification401

402

TheWilsonbreenFormationisoverlainbyamarinetransgressivesuccession,butmost403

Ediacaranstrata(Table1)arenon-marineplayalakefacies,inturnoverlainby950mofCambro-404

Ordovicianplatformcarbonates(Harland,1997)indicatingaminimumburialof1.5km.Late405

SilurianCaledonianfoldingandlocalthrustingfollowed(Fig.2),butsmall-scalefoldingis406

generallyabsent,asispenetrativedeformation.TheWilsonbreenFormationliesoutsidethe407

thermalaureolesofDevoniangraniteplutonsinthefoldbelt(Harland,1997).Poresinthecap408

carbonatearefilledwithbitumen,indicatingthatthesedimentspassedthroughtheoilwindow,409

butgoodpreservationisindicatedbytheabilitytoremoveindividualstriatedclastsfrom410

diamictitematrix(Hambrey,1982)andsomeunusuallyhighoxygenisotopecompositionsof411

dolomites(Fairchildetal.,1989;Baoetal.,2009).Afluidinclusionstudy(seesupporting412

information)indicatesthatinitialporefluidswereadvectivelyreplacedbyatypicalmeteoric413

fluidwithδ2Hintherange-60to-100‰andthat18Oisslightlyenrichedbyexchangewiththe414

solidphase,butfluidinclusionvolumesareordersofmagnitudetoosmalltohaveaffectedthe415

20

bulksolidcomposition.Physicalcompactioneffectsarenotnoticeablebecauseofthelowclay416

contentofthesedimentsandearlycementationofthecarbonates,butverylocallylamina417

boundariesarestyolitic.Uncementedsandstonesexhibitstraighttoconcavo-convexboundaries418

betweenquartzgrains.419

ManyWilsonbreenFormationoutcropsarereddened,andeveninunreddenedfacies,420

organiccarboncontentsarelow(belowdetectionlevelsof0.2%onthreeW2carbonates).421

Fairchild&Hambrey(1984)regardedthehaematitepigmentaspost-depositionalbasedonthe422

occurrenceofLiesegangbandstructuresandongoingpalaeomagneticstudiesmaythrow423

furtherlightonitstiming.Reddeningislesspervasiveincleansandstones,implyingthatit424

requiresasourceofironinthefinefractionorincarbonates.Thelowpreservationoforganic425

carbonmayreflectlowabundanceofclay(Kennedyetal.,2006)aswellasalow-productivity426

continentalsetting,contrastingwiththedark-colouredglacimarinedepositsoftheearly427

Cryogenianglacialdepositsinthestudyarea(MemberE2,Table1).428

Limitedquartzovergrowthsarecommoninsandstonesandonsandgrainsfloatingin429

dolomites,whilstsomesandstonesdisplaypartialpoikilotopiccalcitecement.Ferroansaddle430

dolomiteandferroancalciteoccludelargerprimarypores,indolomitesandlimestones431

respectively.Thesecarbonatephasesalsooccur,locallytogetherwithquartzandwhitemicain432

crystalpseudomorphs.Saddledolomiteaverages-12.2±1.5‰inδ18Oand-1.8±1.5‰inδ13C433

andcalcitesparlikewise-10.5±1.6‰and+2.0±1.5‰(Baoetal.,2009).434

435

FACIESANALYSIS436

437

FaciesAssociations438

439

21

FollowingBennetal.(2015)sevenfaciesassociations(FAs)arerecognized;Table3presents440

summarydescriptionsandinterpretations,whilstFig.7Aillustratesinferredenvironments441

diagrammatically.Theglacialandperiglacialfaciesassociations(FA1,6,7)arediscussedin442

Hambrey(1982),Fairchild&Hambrey(1984),Bennetal.(2015)andFlemingetal.(2016),and443

onlyafewsalientpointsarementionedhere.Twodistinctglacieradvancesfromthesouthare444

recognized,justbelowandabovememberW2,byoccurrencesofFA1:sheareddiamictite,445

sandstonesandgravels,locallyrestingonhighlydeformedrhythmites(glacitectonites)or446

striatedclastpavements(Fig.1,labelledFA1subglacial).ThebulkoftheWilsonbreenFormation447

ishowevercomposedofweaklystratifieddiamictites(FA6)withdecimetretometre-scale448

lensesofrhythmites,commonlywithprecipitatedcarbonateinmembersW2andW3in449

particular.Localpresenceofdropstonesorisolatedgravelclasts(lonestones),tillpellets,450

stratification,andabsenceofsubglacialshearingphenomena,pointtoasubaqueousice-rafted451

origin.Locallensingconglomeratesareinterpretedassediment-gravityflowswhich,at452

Dracoisen,compriseaconspicuouslow-anglecross-stratifiedunit(Fig.1,labelledFA6,453

proximal),interpretedasagrounding-linefan(Bennetal.,2015;Flemingetal.,2016). 454

GravelwithventifactsoverlyingshattereddolomiterepresentsthePeriglacialFacies455

Association(FA7)atthebaseoftheWilsonbreenFormationandBennetal.(2015)interpretthis456

asamulti-millionyearcontinentalhiatus.FA7alsooccursatthebaseofW2whereaperiglacial457

exposurehorizonwithsandstonewedgespenetratingsubglacialtillisfound(Fig.1)atSouth458

Ormen(ORM),SouthKlofjellet(KLO)andDitlovtoppen(DIT)andalsoattheGolitsynfjellet(GOL)459

section(Fairchildetal.,1989),whichisbetweenMcDonaldryggen(McD)andthe460

Backlundtoppen-KvitfjellaRidge(BAC).Theperiglacialhorizonisoverlainbysandstones461

correlatedwiththoseatthebaseofW2atDracoisen(Dracoisen).462

22

TheotherfourFaciesAssociationscontainprecipitatedcarbonateandaredescribedin463

detailbelow,complementingthetabularanddiagrammaticsummaries(Table3;Fig.6).Eachof464

theFaciesAssociationsoccursasunits0.1to4minthicknessaspresentedinthestratigraphic465

logs(Fig.4,supportinginformationFigs.S1-S6).466

467

FA2(Facies2Sand2T)468

469

Description470

Thisfaciesassociationisrepresentedbyerosionally-based,fining-upwardstabularsandstone471

beds,0.5-4minthickness.Facies2Ttypicallycomprisesmoderatelysortedveryfinetomedium-472

grainedsandstonewithabasalerosionalsurfacecappedbyagravellag.Internalcross-473

stratificationistabular,typicallywithlow-angleaccretionsurfacesandsetthicknessof0.5-1m.474

SuchfaciesareseenatthebaseoftheW2sectionatDitlovtoppen(Supp.Fig.1),SouthOrmen475

(Supp.Fig.2),EastAndromedafjellet(Supp.Fig.3),andReinsryggen(Supp.Fig.4),andarealso476

prominentnearthetopofthememberatDracoisen(Fig.8H)andatDitlovtoppen,wherethin477

siltstonebedsdefinelow-angleaccretionsurfaces(Fig.8G).478

Facies2SisdistinguishedfromFacies2Tbythepresenceoflimestonelaminaeand479

intraclasts,andreducedsiltcontent.Thebest-exposedexampleisa4m-thickunitthatforms480

thebasalpartofmemberW2atDracoisen(Figs.2A,4),restingonmassivediamictitewith481

decimetre-scaleerosionalrelief.Athinbasalpebbleconglomeratepassesupinto0.7mof482

pebblysandstone,whilstthemain,centralpartofthebedisveryfine-tomedium-grained483

sandstonewithlocaltabularcross-stratification,withsetthicknessupto15cmandcurrent484

ripples(Fig.8D).Atbothlevels,thereareabundant(ca.25-50%)layersoflimestone,with485

individuallaminaetypically1-3mmthick(Fig.8A).Universalfeaturesareadomedgrowth486

23

morphology(Fig.8A)anddifferentiatedmicrostructures(Fig.8B)withwelldevelopedslightly487

irregularlaminaeofmicrite,microspar,anddetritus-richcarbonatewithregularmm-scale488

fenestrae(Fairchild,1991;Riding,2000).Verylocallyathrough-goingverticalstructure489

reminiscentofcyanobacterialoralgalfilamentmoulds(Fairchildetal.,1991)isobserved(Fig.490

9B).Alltheselimestonesarelaterallydiscontinuous,breakingdowntotrainsofintraclaststhat491

arelocallystackedathighangles.Inplaces,extensivecrusts,upto0.5-6mmthick,ofradiaxial492

calcitecementdevelop,alsobrokentoformintraclasts(Fig.8C).493

UnderCL,thecalcitefabricsthatarebrokenintointraclastsfluoresceuniformly494

brightly,whereaslaterveincementsshowmorevariableCL(Fig.9A).Chemically,thisis495

reflectedinhighMncontentsofseveralthousandppmandexceptionallyhighMn/Feof1(Bao496

etal.,2009).Strontiumcontentsare150-300ppm,whilstMgis4000-6000ppm(Baoetal.,497

2009),equivalenttoaround2mole%MgCO3.Theradiaxialfabricsappearpristineand498

microdolomiteinclusionsareabsent.Sulphatecontentishigh(2000-5000ppm,Baoetal.,499

2009),whilstthepreservationofanegativeΔ17Oanomalydemonstratesthatthesulphatehas500

notundergonereduction(Baoetal.,2009;Bennetal.,2015).Thestableisotopecompositionof501

stromatoliticlimestonesdefinesacoherentfield(Fig.7A)withδ18Orangingfrom-10.5to-3.4502

‰andδ13Cfrom+0.9to+4.6‰,weightedtowardshighervalues,withoverallisotopic503

covariation(Fig.7B).Amicromilltraversethroughsyndepositionalcalciterevealslaminato504

laminavariationsinδ18Oof2‰andinδ13Cof0.5‰withoutstrongcovariation(Fig.8E,F).The505

clearpetrographicdistinctionbetweensyn-depositionalandlatercalcitesparcementis506

reflectedalsointhelowδ18Osignatureofthesparof-10to-12‰(Fig.8F).507

508

Interpretation509

24

FA2isnotableforadominanceoftractionalsedimenttransport.Theconsistentpresenceof510

laterallyextensivebasalerosionsurfacesimplyachannelcontextforthisfaciesassociation,511

whilstforFacies2Tthelow-angleaccretionsurfaceswiththinsiltbedsisreminiscentofpoint-512

bardepositswhich,althoughnotunexpectedinPrecambriansediments,wouldrequiremore513

extensiveexposurestoconfirm(Davies&Gibling,2010).Thepresenceofhigh-anglecross-514

stratification,goodsorting,anddisruptedintraclastsinFacies2Sarecharacteristicsfoundin515

eithertidalsandflatsorinlowsinuosityfluvialchannels.Thelimestonescontaintwofeatures516

typicalofNeoproterozoicmicrobialdeposits:macroscopicallydomedlaminaeanddifferentiated517

microstructuresformedbyperiodicvariationsinphenomenasuchasedimenttrapping,gas518

generationandcarbonateprecipitation(Fairchild,1991;Riding,2000)andsocanbereferredto519

asstromatolitic.Limestoneswerelithifiedbeforeerosionsincecementcrustsarebrokenand520

derivedintraclastsaredispersedandstacked,forexamplealongforesets,asexpectedfor521

significanttractionalflowsinshallowwater.Thefactthatallofthethinlimestonesdisappear522

laterallytobereplacedbytrainsofintraclasts,orelsearecompletelyerodedindicateshighly523

variableflowconditions.Further,thelocallyhighlyregularmicrobiallamination,includingclastic524

layers,pointstoaperiodiccontrolonflowrates.525

Whentakeninisolation,amarineoriginforfacies2Scouldbepostulatedonageneral526

similaritywithtidalsandflatdepositsandtheoccurrenceofwell-preservedradiaxialcements527

withrelativelyhighδ18Ocompositions(Fairchild&Spiro,1987).However,tidalsandflatdeposits528

inNeoproterozoicsuccessionstypicallyshowwell-developedherringbonecross-stratification529

(Fairchild,1980;FairchildandHerrington,1989).Thereisaclearcontrastwiththemoreregular530

macrostructuresofmarinestromatoliteselsewhereinthebasin(Fairchild&Herrington,1989;531

Knoll&Swett,1990;Halversonetal.,2004)andNeoproterozoicdepositsmoregenerally532

(Grotzinger&Knoll,1999).Thismaybeattributabletoamorehostileenvironment,withhighly533

25

variableratesofsedimentation.ThemostsignificantpointmaybethatNeoproterozoicmarine534

peritidaldepositsareinvariablydolomitized(KnollandSwett,1990),probablyafeatureofhigh535

Mg/Cainseawater(HoodandWallace,2012).536

Thealternativeisafreshwater,fluvialcontext.Wenowknowthatradiaxialfabricsare537

notdiagnosticofmarinewaters,butalsooccurinspeleothems(Neuser&Richter,2007)and538

alsothatsuchfabricsareprimaryandconsistentwiththerelativelowSrcontentofthecalcite539

(Fairchild&Baker,2012).Hence,weinterprettheradiaxialcalciteasthepristineoriginallow-540

Mgcalcitephase.Micriteandmicrosparfabricshavesimilarchemistriesandarealsoconsidered541

toreflectdepositionalconditions.TheimplicationisthattheMncontentofFA2calcitesisalso542

primaryandreflectiveoflowcontemporaryatmosphericPO2(cf.Hood&Wallace,2014),but543

notanoxicconditionselsesulphatereductionwouldhaveoccurredandthedistinctnegative544

Δ17Oanomalywouldhavebeenerased(Baoetal.,2009).Reassuringly,theMgcompositionof545

facies2SlimestoneissimilartomodernspeleothemdepositsinacoolScottishcavedepositing546

fromwaterswithMg/Cacontrolledbydolomitedissolution(Fairchildetal.,2001).Thelamina547

thicknessofthestromatolitesisverysimilartothoseofmodernfluvialmicrobialtufaswhichare548

complexdepositscontainingbothbiologicallymediatedandinorganicprecipitatesjustlike549

Facies2S(AndrewsandBrasier,2005;Andrews,2006).Interestinglythelaminationisannual550

andreflectsastrongannualvariationindischargeandFacies2Spossessesphysical551

sedimentologicalcharacteristicsconsistentwiththoseofephemeralstreams.Inthis552

interpretation,thestableisotopecompositions,whicharesimilarforradiaxialandmicrosparry553

calcites,canalsobeinterpretedasprimary,inwhichcasetheisotopiccovariation(Fig.7B)554

wouldhavetobeinterpretedasanevolutionarytrendtowardsmoreevaporatedequilibrated555

solutions(Talbot,1990),ratherthanthelightervaluesreflectinghigher-temperature556

recrystallization.ModernAntarcticstreamslackthecalcitemineralization,butmicrobialmats557

26

arewell-developedandareadaptedtoephemeralflowconditions,readilyreactivatingeven558

afterbeingdryformanyyears(McKnightetal.,2007).Thefluvialinterpretationwillbe559

developedlaterinthelightoftherelationshipofFA2tootherfaciesassociations.560

561

FaciesAssocation3(Facies3Dand3S)562

563

Description564

Facies3Dismarkedbydiscretezonesofpronounceddolomitecementationwithinasandstone565

orsiltstone;insomecasesthesedimentispervasivelycemented.Wheredolomiteismost566

abundant,detritusfloatsinadisplacivemassofdolomitecrystals(Fig.10B,D,E,F),butother567

dolomite-cementedsiltysandsarestillclast-supported(Fig.10C).Locally,highlydistinct568

dolomite-cementednodulesarevisible(Fig.10A)orastructurelessdolomitebedcanbe569

encounteredwithalowcontentoffloatingsiltandsand.Themostcharacteristicstructuresare570

mm-scalenodulardolomicritestructureswithinmassivedolomite-cementedlayersand571

associatedwithcalcite-filledfractures.Thesephenomenaarefoundatonehorizoninmember572

W3(Fig.10D),aswellasinseverallocationsinW2(e.g.Fig.10F).Ararerphenomenonisthe573

presenceofequantcentimetre-scalecauliflower-likepseudomorphs,filledbyferroansaddle574

dolomitecement(Fig.11A)occurringatthetopofaconglomerate-basedfining-upwardscycle575

(Fig.8G).Sincesaddledolomiteisaburialphase(RadkeandMathis,1980),theimplicationis576

thatthepseudomorphswereoccupiedwithsolublecrystalsthatdissolvedduringburialpriorto577

cementation.578

Facies3Sreferstodolomiticlaminites,withbroadcm-scaledomedmacrostructure,with579

anaspectratiooftypically10:1.Theyarefounduniquelyinacomplexbed,inassociationwith580

Facies3D,andoverlyingfacies2S(at70m,Dracoisen,Fig.4).Ithasbeenstudiedonthe581

27

“Multikolorfjellet”cliffsandthe“Tophatten”nunatak1kmtothenorth.Thebedisarounda582

metreinthickness,butwithvariabilityinitsinternalstructure.Mostcommonlythereisminor583

erosionofunderlyingdiamictiteatthebaseofthebed,overlainbycrudelylaminatedveryfine-584

tomedium-grainedgreensandstone,locallywithmm-scalelimestonelayersthatarepartly585

disruptedintointraclasts(Facies2S).Inplacesthiscanbeseentopassupwardsintointensively586

dolomite-cementedsandinwhichtherockfabricappearstohaveexpanded,associatedwith587

corrosionofquartzdetritusbydolomiteandtheformationofcavities,linedwithdolomicrospar,588

andoccludedbycalcite.Atthe“Tophatten”locality,achaoticbrecciaunitafewdmthickis589

locallyfoundatthebaseofthebedinsteadofsandstone.Everywhere,thetopofthebedis590

markedby10-20cmofdololaminiteswithacomplexmicrostructure,whichalternateonacm-591

scalewithdisplacivelycementedsands(Fig.10E).Thelaminaecanbecomposedofdolomicrite592

ordolomicrosparandcontaincommonfenestrae(Fig.9E,H),whilstsurfaceexposurereveala593

finelytexturedmicrotopography(Fig.10G).Locally,slightlylowerinthebed,limestone594

laminites(FA5)forma10cmhorizonoverlyinga20-30cmchaoticcarbonatebreccia(Fig.10I)595

andgraduallybecomedisrupteddownwards.596

DolomitefromFA3ischaracteristicallybrightunderCL(Fig.11B-D).Infacies3S,597

dolomicriteclotsareuniformlybright,whilstadjacentdolomicrospardisplaysdullergrowth598

fillingsmallfenestraewhilstlargerfenestraearefilledbydolosparwithmorevariableproperties599

(Fig.11B).Manganese(3000-4000ppm),Fe(10000-15000),Na(2000)andSr(250-350)ppm600

valuesareallunusuallyhigh(Baoetal.,1989)andourunpublishedelectronmicrosopeimages601

andmicroanalysesshowenrichmentsalsoinmanytransitionmetalsandrareearthsanda602

consistentchemicalzonationwithincrystalsofdolomicritemosaics.Infacies3D,adifferencein603

meanCLbrightness,andhencetimingofgrowth,cansometimesbeobservedbetweennodules604

andsurroundingmatrix(Fig.11D),whilstlocallyzonationwithinindividualcrystalsgrowing605

28

betweensiliciclasticsandgrainscanbeobserved(Fig.11C).Sulphateconcentrationsarehigh606

(4000ppm);thereisnoΔ17Oanomalybuthighδ18Oinsulphate(Baoetal.,2009;Bennetal.,607

2015).608

Carbonandoxygenisotopevaluesarecorrelated(Fig.7),butFig.12illustratesthatthe609

twoanalysesfrommemberW3lieabout1‰higherinδ13Cthanexpectedfromthistrend.610

Facies3Dhasarangeofδ18Ofrom-1.9to+11.4‰,butthemeanvalueisbiasedupwardsby611

multipleanalysesfromasamplewhichpassesupintofacies3Swhichtendstohavehigher612

values(Fig.12).Thelatterfaciesisnotableforpossessingpossiblytheheaviestoxygenisotope613

valuesofcarbonaterockssofarrecordedinthegeologicalrecord(Baoetal.,2009),withvalues614

upto+14.7‰(VPDB)beingfound(Fig.12).Amicromilltraverse(Fig.10H,J)demonstratesthat615

theseextremehighvaluesaremaintainedonthemm-scale,butthatoverpetrographic616

boundaries,δ18Ovaluescanvarybyasmuchas6‰.617

618

Interpretation619

ForFacies3D,thedolomicritic,syndepositional,passivetodisplacivegrowthwithnodular620

structureandcracksischaracteristicofcalcretesinwhichprecipitationoccursasaresponseto621

evaporativelossesatoraboveawatertable.Althoughrare,thespar-filledpseudomorphs(Fig.622

11A),interpretedasafteranhydrite(Fairchildetal.,1989),providefurtherevidenceof623

evaporativeconditions.Specificallytheevidencefordisplacivegrowth,nodulesandcracks624

servedtoidentifyalphacalcretes(Wright,1990)whichinPhanerozoicexamplestendtooccur625

onnon-carbonatesubstratesandinmorearidconditionsthanthemorecommonbetacalcretes626

containingstructuresresultingfromhigherplants(Wright&Tucker,2009).Thehighδ18Ovalues627

andcovariationwithcarbonisotopesrequireevaporation(Fairchildetal.,1989)whichatthe628

highendofthespectrumreachesextremeproportionsandhencerequiresanextremelyarid629

29

environment.Dolocretesareratherlesscommonthancalcareouscalcretesandtendtobe630

betterdevelopedwhenoriginatingfromgroundwaterthanwhenpedogenic,asinTriassicstrata631

oftheParisBasin(Spötl&Wright,1992).Inthisexample,pedogenicandgroundwater632

dolocreteshadasimilarrangeofstableisotopecompositionstoeachother,buttheir633

covarianceslope(1:1)wassteeperthaninFA3.Overalltheabsenceofanysignaloflightcarbon634

fromoxidationoforganicmatterinFA3isnotable,butconsistentwiththeundetectablylow635

organiccarboncontentsoftherocks.InPhanerozoicrocks,thepresenceofsomebiological636

features(e.g.rootstructures)canservetoidentifypedogeniccalcrete,butthisisnotpossiblein637

theProterozoic.638

TheWilsonbreenFormationdolocretesareinterpretedaspedogenicprimarilybecause639

theextremelyhighδ18Ovalueswouldrequiregroundsurfaceconditionsforsuchextremely640

effectiveevaporationtooccur.Aswillbediscussedlater,thisinterpretationisalsoconsistent641

withtheverticalfaciesrelationships.642

RegardingFacies3S,thedifferentiatedmicrostructuresareagaintypicalofmicrobial643

deposits.Suchlaminitesarefoundinassociationwithsoilsandintermittentlyfloodedsubaerial644

surfaces(Alonso-Zarza,2003),althoughyoungerexamplesincluderootmatsfromhigherplants645

thatareclearlyinapplicablehere.Klappa(1979)ascribedcm-scalelaminateddeposits“hard646

pan”oncalcretizedlimestonesubstratesasoriginatingfromtheactivitiesoflichenwhich647

colonize,boreintoandformaccretionarydepositsonsurfaces.Thelichen-formeddepositsdo648

exhibitfeaturessuchasfenestrae,sedimentincorporationandvariablecrystalsizewhichare649

consistentwiththeWilsonbreenFormationexample.However,noevidenceofalterationof650

underlyingcementedmaterialhasbeenfoundandtheWilsonbreenFormationmicrobial651

laminaearemuchmoredistinctandarenoticeablydomed,contrastingwithlaminarcalcretes.652

Infact,themicrobiallyinfluencedlayeringisindicativeofactiveupwardaccretion,ratherthan653

30

slowpedogeneticalteration.Theaccretiontooktheformbothofgrowthofcarbonate-654

mineralizedmicrobialmats,butalsosandlaminae.Ashallowdepressiononafloodplain/playa655

marginseemsapposite.Acombinationofahighwatertablefromwhichevaporationcould656

occur,orveryshallowwaterinundationfollowedbydryingoutandsedimentaddition,perhaps657

byaeolianactionisindicated.AtDracoisen(Fig.9I),thegradationalrelationshipbetween658

laminatedcarbonateandunderlyingchaoticbrecciaisaclassiccharacteristicofevaporite659

dissolutionbreccias.Thecalcite-cementednatureofthebrecciaisconsistentwithremovalof660

oneormorehorizonsofcalciumsulphateevaporiteseitherduringdepositionofthebed,or661

soonafterwardsfollowingresumptionofglacialconditions.ApossiblysimilarMesoproterozoic662

exampleisprovidedbyBrasier(2011)fromOntarioinwhichstromatolitesareassociatedwith663

collapsebrecciasandcalcretes,andinferredtoformataplayalakemargin.Likewise,the664

modernMcMurdoDryValleyscontainarecordofmanyshallowsalinelakesandsaltpans665

(Wilson,1981).666

Dolomiteisknowntobecapableofprecipitatingasaprimaryphaseorbyreplacement667

ofaCaCO3precursorinarangeofsurfaceenvironments(Warren,2000),althoughtheinitial668

crystals(protodolomite)maylackwell-developedorderingreflectionsandthesecanincrease669

overtime(Greggetal.,1992).ThepetrographiccharacteristicsofFA3dolomicriteareconsistent670

withveryearlydiageneticreplacementofaprecursorcarbonateorofprimarygrowthof671

(proto)dolomiteandthelatterisclearlythecaseforzoneddolomicrosparcavity-linings(cf.672

HoodandWallace,2012).Thepresenceofeuhedralcrystalswithindisplacivefabrics(Fig.11C)is673

distinctive.AlthoughTandon&Friend(1979)interpretedeuhedralgrowthzonesindisplacive674

calciteincalcretesasevidenceofrecrystallizationitismorelogicaltoseeitasaprimarygrowth675

fabric,asarguedfordolocretesbySpötl&Wright(1992).676

31

Theextremelyhighδ18Ovaluesruleoutpost-depositionalmodificationandan677

interpretationofthevaluesasreflectiveofthedepositionalenvironmentisalsoconsistentwith678

thetraceelementchemistryandpreservedcrystalgrowthzones.ThehighMncontentand679

absenceofpyriteimplieslowpO2,butnotanoxia,althoughthesulphateoxygen-isotope680

systematicsareindicativeofmoreredoxvariabilitythaninFacies2S.Specificallybacterially681

mediatedelectronshuttlingbyMn-speciescancatalyzerepeatedtransitionsbetweensulphate682

andsulphitecanpermittheerasureofaΔ17Osignatureandcreationofahighδ18Oinsulphate683

(Baoetal.,2009).Suchprocessescouldcatalyzedolomitenucleationgiventheevidencefrom684

otherfieldandexperimentalstudiesonthecatalyticroleofsulphatereduction(Vasconceloset685

al.,2005;Zhangetal.,2012).Theinferredredoxvariationsmayberelatedtoasupplyofbrine686

primarilyfromwithinthesediment,contrastingwiththesurfacewatersfromwhichFacies2S687

precipitated.Theoccurrenceofthehighestδ18OvaluesinlaminateddolomitesofFacies3Sis688

consistentwiththeirformationbyverynear-surfaceevaporation,whilstabruptvariationsin689

δ18O(Fig.10J)aresuggestiveofoccasionalinundationsbylessevolvedwaters.Insummary,FA3690

providesexamplesoffaciesthatstretchtheboundariesofearthsurfacephenomenaand691

indicatedepositioninunusuallyaridterrestrialenvironments.692

693

FaciesAssociationFA4(Facies4I,4Rand4S)694

695

Description696

Facies4Risthemostcommonfaciesinthisassociationandconsistsofrhythmicalternationsof697

carbonateandsortedterrigenoussediment,whichoccurinassociationwithstructuressuchas698

waveripplelaminationordesiccationstructures.Thefinecarbonatelayersareusually699

dolomitic,ormixeddolomitic-calcitic,butincludesomelimestone(Figs.7A,12).Universally,the700

32

coarsersedimentlayers,composedofsedimentinthesizerangecoarsesilttofinesand,show701

signsoftractionalsorting,whichisakeydiscriminantfromFA5.Whereverlaminaeare702

sufficientlythick,undulatorycross-laminationisdisplayed(Fig.13B)whichcanbeconfidently703

identifiedaswave-generated.Locally,symmetricalripplesarepreservedincross-section(Fig.704

13A)oronbeddingplanes(Fig.13C).Dryingoutiscommonlyindicatedbydesiccationstructures705

withassociatedsmallintraclasts(Fig.13B,H)orsaltpseudomorphs(Fig.13D),althoughsuch706

structuresarenotpresentinthemajorityofsamples.Fourexamplesofapparentlynon-707

evaporiticcrystalpseudomorphshavebeenfound,butthesearemuchbetterdevelopedinFA5708

andaredescribedinthatsection.Carbonatelaminaearemicriticintextureandtypically709

uniform,althoughdifferentiatedclottedmicrostructuresalsooccur,similartothosedescribed710

belowinFA5,consistentwithprecipitationbeneathbenthicmicrobialmats(Riding,2000).This711

facieswaslocallyhighlyaffectedbysubsequentglacitectonicdeformationatthetopofW2at712

Ditlovtoppen,asdescribedbyFlemingetal.(2016).713

TheisotopetraverseofFig.13Jrevealsashiftinisotopesfromthesandylayersinto714

dolomicriteconsistentwithanauthigenicoriginforfinedolomite,whichisconfirmedbyCL715

observations(Fig.14A,B).Thelimestonelaminaeinthisfaciesassociationdisplayarangeof716

δ18Ovaluesfrom-11.9to-3.2withameanof-8.1‰,whereasthedolomiterangesfrom-5.3to717

+1.4withameanof-1.9‰(Fig.7B).Thedifferenceof6‰inmeanvalue,comparedwith718

inferredandobserveddifferencesof2.6-3‰forcalciteand(proto)dolomiteprecipitatingfrom719

equivalentfluids(Land,1980;Vasconcelosetal.,2005)impliesthatthedolomitesprecipitated720

onaveragefromwaterswithhigheroxygenisotopevaluesandthedolomitesdisplayisotope721

covariance(Fig.7B).Traceelementdatawillbepresentedelsewhere,butFA4andFA5722

dolorhythmitesalsoshowacovariationofSr(from100to200ppm)withδ18Oandsomewhat723

33

higherSrvaluesincalcites,andlikeotherWilsonbreenprecipitatedcarbonates,theyareMn-724

rich(>1000ppm).725

Facies4Ioccurstypicallyasdiscretebeds,normally10-20cmthick,ofsharp-to726

erosionallybasedintraclasticsandstonewithwave-generatedlamination.Thesandmatrixis727

moderatelysortedcoarsesilttomedium-grainedsandandintraclastsaresometimesconfined728

tothelowerhalfofthebed.SeveralsuccessivebedsareshowninFig.13Hinasection729

transitionalupwardsfromFaciesAssociation5,andanexampleofthisfaciesinthinsectionis730

illustratedinFig.13G.Twooccurrencesofooids(Fig.13E)havebeenfound.AtNorthKlofjellet,731

highinagenerallypoorlyexposedW2section,isa1mbedofindistinctlycross-laminatedsands732

alternatingwithcm-scaledesiccatedlimestonebedscontainingscatteredsandgrains.Thisisthe733

lateralequivalentoffluvialfacies(FA2)1kmawayatSouthKlofjellet.Ooidsarefoundnearthe734

topoftheunit,butmakeuplessthan5%ofthesandfraction.Arangeofcorticesfrom735

superficialcoatingsthroughtofullydevelopedooidswithnovisiblecorearedeveloped.Fabrics736

aremicriticandmicrospariticwithacrudeconcentricstructure.Themeanoxygenisotopevalue737

ofthelimestone(>90wt.%CaCO3)is-7.6‰.Thesecondexampleistheoccurrenceofasmall738

proportionofooidswithinthin(0.1m)cross-laminatedgreensandstoneunderlyingFA5739

sedimentsinmemberW3atOrmen(Table3).740

Facies4SisrepresentedbydistinctsandstonebedsintheDitlovtoppenandDracoisen741

sections.Thesesandstonesarehighlyuniform,consistingofwell-sortedfine-tomedium-742

grainedsandstone,withverywell-roundedgrains.Beddingstructuresareconfinedtoan743

indistinct,discontinuousparallelstratification.TheDitlovtoppenexamplepresentsasatabular3744

m-thickbedoverthe200mwidthoftheoutcrop.Itslowerfewdecimetresarelocallythinly745

laminatedsandanddolomite,changinglaterallytouniformsandstone.Twothinbedsof746

dolomitewithfloatinggrainsarealsofoundatthetopoftheunit.Grainsareverywell-rounded747

34

andrangefromveryfinetocoarse-grained,butmostoftherockvolumeiscomposedof748

mediumtocoarsesandgrains(Fig.13F).Theonlysedimentarystructuredisplayedisan749

indistinctcm-scalehorizontallaminationwithslightvariationsingrainsize,orlocallywithmm-750

scalelaminaewithsiltydolomiticmatrix.Locallythelaminationdisplayssedimentary751

deformation,suggestiveofupwardfluidescape.Oxygenisotopesinseveralsamplesareslightly752

heavierthanexpectedfordetritalmatrix,consistentwithadditionofprecipitateddolomite.753

Thereisatransitiondownwards(Fig.10H)toFacies4Rinwhichmm-cmscalesandlaminae754

betweenrhythmiccarbonatesdevelopcross-laminationandwave-ripplemorphology,and755

within20-30cmoftheboundaryoccursathinrepresentativeofFacies4I(intraclasticflake756

breccias)anddesiccationstructuresindicativeofemergence.757

758

Interpretation759

Facies4Rand4Idisplayevidenceofsortingandreworkingofthesedimentsbywaveaction.This760

indicatesdepositioninawaterbodythatwasunfrozenatthetimeofdepositionofthecoarser761

layerswhichrepresentdistincttimeperiodswithmorepronouncedwaveaction.Thesharp-762

basedintraclasticbeds(Facies4I)appeartorepresentdistinctstormeventsinwhich763

considerabledisruptionandtransportationofcementedcarbonatelayersoccurred,althoughat764

leastinsomecasestheselayerswerealreadydisruptedbydesiccation.765

Thegrainsandstructuresinfacies4Rand4Iareconsistentwitheitheramarineora766

lacustrineorigin,althoughitisnotedthatthereisanabsenceofdemonstrabletide-related767

phenomenon(cf.Fairchild&Herrington,1989)andalthoughthereisinsufficientinformation768

availabletoprovideaquantitativedescriptionofwaveclimate(Allen,1984),nowave769

phenomenawereseenrequiringoceanicconditions.Althoughooidsarebest-knownfrom770

marineenvironmentsandthickooliticunitswereusedasacriterionforwarmclimatesinthe771

35

NeoproterozoiccontextbyFairchild(1993),ooidshavebeendescribedfromQuaternary772

sedimentsreworkedintoAntarcticmoraines(Raoetal.,1998)andinvariousmodernalkalineor773

hypersalinelakes.Lacustrineooidsforminwaterdepthsof1-5m,withthebestdevelopmentin774

shallowestwater.TheWilsonbreenFormationexamplesdonotresemblehypersalinearagonite775

ooidswithradialstructure(e.g.Halley,1977),consistentwiththeoxygenisotopecomposition776

whichdoesnotindicateanyevidenceforhypersalinity.Ooidsinsmallermodernlakestendto777

besuperficialwithrelativelyirregularoutlines,whereasfullydevelopedooidsarefoundonthe778

largeLakeTanganyikainBurundi(Cohen&Thouin1987)correlatingwithstrongerwaveaction.779

Chemicalargumentsfavouralacustrineoriginforthecarbonates.Theyprobablyarose780

assomecombinationofwatercolumnprecipitatesorwithinthesediment,e.g.asmicrobially781

influencedprecipitates.Dolomitecouldbeprimaryor,giventheCLevidence,beaveryearly782

diageneticreplacementofCaCO3,althoughnotonewithhighSrcontent.Giventheconsistent783

chemicalcharacteristicofMn-enrichment,itseemshighlyimprobablethatburialdiagenetic784

recrystallizationtookplaceandsoitismoststraightforwardtointerpretthestableisotope785

valuesasprimary,inwhichcasethewiderangeofδ18Ocompositionsisnotablebecauseitis786

muchgreaterthanexpectedfrommarinewaters.Inthecaseofthedolomites,thisismuch787

greaterthantherelativesmallchanges(1-2‰)thatmightbeexpectedtoaccompanyincreased788

orderingfromaninitialprotodolomitetoanordereddolomite(Greggetal.,1992;Kaczmarek&789

Sibley,2014).Theformationofdolomitefrommore18O-rich,evaporatedwaters,isconsistent790

withthestandardparageneticmodelinplayalakes(Dutkiewiczetal.,2000),althoughchanges791

insourcewatercompositionaswellasevaporationarelikelytohaveoccurred.792

Thewell-roundedsandgrainsfoundinFacies4Sareconsistentwithaeoliantransportasinthe793

McMurdoDryValleysofAntarctica(Fig.3C;Calkin&Rutford,1974;Hambrey&Fitzsimons,794

2010).Howevergrainswithsuchatransporthistorycanfinallybedepositedinaeolian,fluvialor795

36

lacustrinesettings.Theconsistentgrain-sizecharacteristicsofindividuallaminaeandgood796

sortingofthecoarselaminaeinsteadpointtotractionalflows,butlackofcross-stratification797

rulesoutaeolianorsubaqueousdunes.Hendyetal.(2000)developedtheice-conveyormodel798

toaccountforsandydepositsonthefloorsofcertainice-coveredAntarcticlakeswithfloating799

glacier-icemargins.Wind-blownsandmeltsitswaythroughtheiceincontrasttogravelwhich800

remainsonthesurfacewhereitistransportedbyiceflowtothedistallakemargins.Suchan801

environmentcandeveloptheindistinctparallelstratificationobservedinthisfacies,buttwo802

featuresofthemodernsystemsnotobservedaremoundedbeddingandupwardgradationinto803

coarsegravel(Halletal.,2006).TheDitlovtoppenbedistabular,whereasinthemodernlakes804

sandtransmissiontotheiceisfocused,leadingtomoundsandridgesonthelakefloor.805

AplausiblealternativeforFacies4Iisaninter-duneenvironment,asettingwherewind806

ripplemigrationwouldbeexpected(Lancaster&Teller,1988).Suchphenomenacouldgiverise807

totranslatentsub-horizontallaminae,representingthesetboundaries,withoutinternalripple808

cross-laminationbeingpreserved(Mountney&Thompson,2002).Awatertablethatwasat809

leastseasonallyhighisrequiredtoaccountfordewateringstructuresandtheprecipitationof810

dolomite(incipientdolocrete).Insuchmodernenvironmentsseasonalfloodingbysurfacewater811

oremergentgroundwatermightoccur,accountingforoccasionaldolomicritelaminae.Thestyle812

ofstratificationisinconsistentwithdunedeposition,butisthatexpectedonasandflatorplaya813

withahighwatertableandfitswiththetransitiontoFacies4Rand4IobservedinFig.10H.814

OverallFA4representsshallow-waterandexposedsedimentsassociatedwithawave-815

dominatedshorelineandsusceptibletowindreworking.Althoughdistinctionofmarinefrom816

lacustrinecoastalsettingsisnevereasy,thewiderangeofoxygenisotopecompositionsof817

micriticMn-richcarbonatesfavoursalacustrineorigin.818

819

37

FaciesAssociation5(Facies5Dand5R)820

821

Description822

Thisfaciesassociationisdominatedbyrhythmicalternationsofcarbonatesandpoorlysorted823

clasticsediment(Facies5R).Locally,gradationsareseentobrecciatedrhythmiteswhichare824

distinguishedasFacies5D.FaciesAssociation5isonlyaminorconstituentofmostoftheW2825

sections,beingmoreprominentintheSKlofjelletandBacklundtoppen-KvitfjellaRidge(BAC)826

sections(Figs.S5andS6),butitisthedominantcarbonate-bearingfaciesassociationinmember827

W3whereitalternateswithice-rafteddiamictitesofFA6.828

Fig.11illustratesvariantsofFacies5RfoundinmemberW2.Fig.11Aexhibitshighly829

regularmillimetre-scalealternationsoflimestoneandwacke.Theclasticsedimentincludes830

manymicroscopicdiamictitepellets(arrowed)whichareanormalfeaturefoundinthisfacies,831

whereasthesmallpseudomorphscrossinglaminaboundariesarefoundmorelocally.Pebble-832

sizedfragmentsinclasticlayersareseeninFig.11Cand11D,thelatterdisplayingadropstone833

textureassociatedwithdisruptionoflimestonelaminae.Anindicatorofinstabilityisshownby834

theminorfaultinFig.11Cacrosswhichthenumberoflimestonelaminaechanges,indicating835

erosionontheupthrownsideandhencethatthisisasedimentarygrowthfault.Larger-scale836

disturbanceisshownbythefoldsinFig.11Finwhichcarbonatelaminaedisplaysomeplasticity,837

butarealsofractured,indicatingpartialcementationandasedimentaryoriginforthefolds.838

Abovethis,thesedimentsarevisiblydisruptedandtransitionaltoFacies5D.Thethickest839

exampleofafacies5Dobservedwasa0.4mbedatDitlovtoppen,containingbothintraclastic840

andterrigenoussediment,andwhichdisappearedlaterallywithin100m.Itclearlywasderived841

bylocalizedresedimentationofFacies5R.842

38

InmemberW3,Facies5Rispresentasisolatedbedsupto1mthickexhibitingsimilar843

alternationsofcarbonatelaminaeandwacke/diamictiteasinmemberW2(Fig.16).Fig.16A844

illustratesthebaseofonesuchbedwithclearalternationsofthickdiamictitelaminaeand845

carbonatepassingupwardsintomorecarbonate-dominatedfacieswithonlythinclastic846

laminae.ThedominanceofprecipitatedcarbonateinthisfaciesisshowninFigs.16C,D,E,the847

latterbeingthesoleexampleofprecipitatedcarbonateinmemberW1.Disturbancebysoft-848

sedimentfoldingisnearlyuniversalandthesamecombinationofductileandbrittlebehaviour849

ofcarbonatelayersisshown(Fig.16D,E)asinmemberW2.Fig.16Billustratesthedevelopment850

ofaresedimentedbed(Facies5D)dominatedbyintraclasts,butwithsomepoorlysorted851

sedimentmaterial,overahorizonwithsoft-sedimentfolds.852

ItiscommonforcarbonatelayersinFacies5Rtoshowirregularlaminationordomal853

structures.Therecanbeupwarddomingoflayertops(Figs.15C,16C)uptocentimetre-scale854

(Fig.15F).Topographycanbeinheritedfromunderlyinglayers(Figs.15F,16C),whereas855

sometimesthebaseaswellasthetopofthelayerisdomedupwards(Fig.15C).Fig.15Bdisplays856

boththesefeaturesinlayersunderlainbycomplexcementcrustswithsomeremainingporosity.857

Thecrustsshowneitherabotryoidalnoreuhedralmorphologyandarecomposedof858

polycrystallinecalcitemosaicsinwhicheachcalciteshowsthesamezonationinCL.Thereare859

transitionsthroughbedswithonlyminorclasticdebris(Fig.15F)tomoremassivelimestones860

withcomplexmicrostructures.861

Petrographically,carbonatelaminaecanberegularly(rhythmically)developed,millimetre-scale862

inthickness.Laminaeareoftenheterogeneous,andmaybeeitherdolomitic,calcitic(Fig.17A,B,863

D,F)ormixedmineralogyincomposition(Fig.17C).Whereheterogeneous,laminaemayshow864

anincreaseincrystalsizeupwards(Fig.17A)ordisplaymoreorlessevidentclottedtexturesof865

micritewithinmicrospar.UnderCL,bothcalciteanddolomitepresentcoherentreplacivefabrics866

39

(e.g.Fig.17F),inwhichcrystalswithidenticalzonesgrowthroughoutthefabricandenlargeinto867

fenestrae.Rareexamplesofmicriticrodsaround10-20µmindiameter,withminorassociated868

pyrite,arereminiscentofcalcifiedsheathssuchasfoundinthepre-CryogenianDraken869

Formationinthestudyarea(cf.Knolletal.,1993),butarenotasdistinct.Millimetre-scale870

convexitiesontheupperbedsurfaceappearasthromboliticintexture(Riding,2000)with871

irregularfenestrae(Fig.17B).Clasticlaminaetendtolevelthemicrotopography(Fig.17A),872

whilstindividualsandgrains,dropstonesordiamictitepelletscanoccuranywherewithinthe873

carbonatefabrics(Fig.17D).874

TraceelementcompositionsofcarbonatearesimilartoFA4.Thelimestonelaminaein875

thisfaciesassociationdisplayarangeofδ18Ovaluesfrom-5.6to-12.8‰withameanof-9.2‰876

andtheδ13Cvaluesalsodisplayalargerangefrom-2.1to+3.5‰.Althoughthefullrangein877

δ13CisshownbymemberW2,valuesinmemberW3tendtobelower(Fig.12).FA5dolomite878

rangesfrom-10.3to+3.7‰,withameanof-3.2‰(Fig.7B)andasforFA4,thedolomites879

displayisotopiccovariance.880

CommonexamplesofcrystalpseudomorphsoccurinFA5,usuallyassubhedralto881

euhedralcrystals,variablyjoinedintoconfluentmassesembeddedwithinorapparentlycutting882

acrosslamination(Fig.18E,F,G).Insomecases,trainsofcrystalsarealignedalongor883

concentratedwithinparticularlaminae.Sizeofindividualcrystalsissimilarwithinsamplesand884

rangesfrom0.1-0.2mm(Fig.18F)to1-3mm(Fig.18B,19A),themostcommonsizebeing0.5-1885

mm(Fig.186E,G).Therangeofcross-sectionsisdominatedbyfour-sidedorsix-sidedfiguresof886

crystalswithequanttocolumnarhabit.Pseudomorphsareequallylikelytobedevelopedin887

rhythmiteswithcomplexmicrostructuresasinrhythmiteswithuniformmicrite.Limestone888

hostsforpseudomorphs(n=15)hadameanδ18Ocompositionof-8.8(range-6.2to-12.7)‰889

40

anddolomiteslikewise(n=4)mean=-1.92,(range-6.4to+1.7)‰,thatissimilartoFA5asa890

whole.891

Whilstthewithin-sedimentmodeofoccurrenceisfoundinbothmembersW2andW3,892

themostspectacular,upward-growingcrystalshaveonlybeenseenattwolevelsintheS.893

KlofjelletsectionofW3.Apolishedhandspecimen(Fig.19A)displaysthreedistinctcrystal894

horizonsofwhichtheuppertwoareshowninthephotomicrographofFig.18B.Thecrystals895

evidentlygrewfreelyupwardsandcrystalterminationsarestronglydrapedbyoverlying896

sedimentlayersindicatingthatthecrystalsformedatthesediment-waterinterface.Indifferent897

cases,theyaredrapedeitherbycarbonate(e.g.formingroundedmassesonthelowerhorizon898

ofFig.18B),orpoorlysortedsediment(wackeordiamictite).Inthelattercase,crystalfacesare899

variablycorrodedatthecontact(Fig.18B,D).Measurementoftheinternalcrystalangles(=180°900

minustheapparentinterfacialangle)incutsectionsofthissampleyielded75measurements901

assignedto10°bins.Theresultsdisplaytwomodescentredaround40-50°and90-110°(Fig.902

18C).Inspectionofthecrystalpseudomorphswhichgrewwithinsediment(Fig.18E,G)is903

consistentwiththeseresults.904

Thepreservationofthepseudomorphsistypicallyinthesamemineralasthehost905

carbonate,dolomiteorcalciteasappropriate.Insomecases,theinfillingphaseiswholly906

cementing(Fig.18E),whilstinothersthevariableinternalfabricspointtoadominantly907

replaciveorigin(Fig.18G).Suchanoriginisveryclearfortheupward-growingcrystalswhere908

eachispseudomorphedinamosaicof20-100µmcalcitecrystals,whichinstainedthinsection909

showanon-ferroancoreandaferroanperiphery(Figs.18D,20A).910

911

Interpretation912

41

Thelackofsize-sortinginFA5sedimentsindicatestheywerelaiddowninawaterbody913

lackingsignificantcurrentactivity,butonunstableslopesassuggestedbythesoft-sediment914

folds,interpretedasslumpstructures.Alltransitionsoccurfromdisturbedandslump-folded915

Facies5Rtoresedimenteddiamictites(Facies5D,interpretedasdebrisflows)composedlargely916

ofFacies5Fblockswithsomeexoticclasts,areseen.TheclasticsedimentinFacies5Risclearly917

glaciallyderivedbecauseitisinvariablyverypoorlysorted,containsdiamictitepelletslikelyto918

bederivedbyicerafting(tillpellets)andlocalice-raftedclasts(dropstones),andgravelis919

presentinthickerlaminae.AlsoFA5transitionsupwardsanddownwardsintostratified920

diamictitesinterpretedbyFlemingetal.(2016)asrepresentingmorecontinousdepositionfrom921

floatingice.Incontrast,nodistinctfine-grainedsediment-gravityflowswereobserved,implying922

lackofproximitytofluvialinputtothewaterbody.Thecarbonatelaminaecommonlydisplay923

evidence(thromboliticdomalgrowthmorphologyandcomplexmicrostructures)ofamicrobial924

origin(Fairchild,1991;Riding,2000),includingmuchevidenceforin-situcarbonate925

precipitation,coupledwithsomesiliciclasticsedimentincorporation.Acombinationof926

photosynthesisandfavourablenucleationofcarabonatewithinextracellularpolymeric927

substanceanddeadcellularmaterialpresentinmicrobialmatscanbeenvisagedaspromoting928

carbonateprecipitation(Riding,2000;Bosak&Newman,2003).However,insomecases,there929

isnoclearmicrobialstructurewithincarbonatelayersandwecannotruleoutsettlingofwater-930

columnprecipitatesinthesecases.931

Thehighlyregularnatureofthemm-scalecarbonate-siliciclasticcouplets,particularlyin932

thethicknessofthecarbonatelayers,isstriking(Figs.15,16)andtherearemanymodernand933

lateQuaternarylacustrineanaloguesinwhichsuchcoupletsareannual,i.e.varves.Although934

thereisnobarriertosuchsedimentsformingundermarineconditions,itistruethat935

photosynthesisraisescarbonatesaturationfasterinlowionicstrengthwatersthaninseawater936

42

(Fairchild,1991)andnomodernmarineanalogueshavebeendescribed.Thedominantprocess937

creatingcarbonatesinAlpinelakesiswater-columnphotosynthesisfromalgalblooms(Kelts&938

Hsü,1978),andthishasguidedmanyinterpretationsoflateQuaternaryvarves,allowing939

inferenceofasuccessionofeventsthroughtheyear(e.g.Neugebaueretal.,2012).However940

lakesvarygreatlyintheirhydrology,internalstructure,salinityandstateofcarbonate941

saturationandtherearemanydifferentpatterns,e.g.carbonatemineralproductionmay942

continuethroughtotheautumn(Shanahanetal.,2008)ormaypartlydependonperiodswhen943

thereisinputofionsfromriverineinput(Stockheckeetal.,2012),ormayinpartrelateto944

winterfreezingconditions(Kaluginetal.,2013).Variationsinredoxconditionsovertime945

influencethepreservationofvarvesinmodernlakesandinthecaseoftheGotlanddeepofthe946

brackishBalticSeaepisodicoxygenationepisodesmaytriggerachainofeventsleadingto947

characteristicMn-carbonatelayerssuperimposedontheannualpattern(Virtasoloetal.,2011).948

TheabsenceofburrowingorganismsinCryogeniantimesledtocontinuouspreservationof949

varvestructure,buttheMn-chemistryofthesecarbonatesisquiteconsistent(Fairchildetal.,950

1989;Baoetal.,2009)implyinglessstrongredoxfluctuationsinthewaterbody.951

Thecrystalpseudomorphsalsopresentimportantenvironmentalevidence.Thefacies952

occurrenceofthesepseudomorphsarguesagainstanevaporativeorigin.Althoughdolomite953

sampleswithhighisotopevaluesindicatessomeevaporation,theoxygenisotopecomposition954

ofthedominantlimestoneanddolomiteoccurrencesistypicalforfaciesassociation5andlacks955

evidenceforincreasedsalinity.This,togetherwiththecarbonatecomposition,impliesa956

carbonateprecursor.Theveryregularmodeofreplacementbycalcitewithinternalcrystal-957

growthzonation(Fig.17E)indicatesthattheprecursorwasmoresolublethancalcite,butstill958

capableofformingeuhedra,andhencecrystallineratherthanamorphous.Vateriteand959

monohydrocalcitecanberuledoutbecausetheyinvariablyformspherulitesormicrocrystalline960

43

precipitates(Dahl&Buchardt,2006;Pollocketal.,2006;Rodriguez-Blancoetal.,2014).961

Althougharagonitetypicallyformsmosaicsofmicrocrystallineorthorhombicfibres,itiscapable962

offormingradiatingpseudo-hexagonaltwinned“ray”crystalsofsimilarsizetothoseseeninthe963

presentstudy(Fairchildetal.,1990,Riccionietal.,1996).However,wheresix-sidedcross-964

sectionsareseenintheWilsonbreenFormation(Fig.16E),theyareoftenelongatedratherthan965

equant,andthemostelongatedcrystalsincross-sectionshowapairofterminatingfaces,nota966

basalpinacoidcharacteristicofaragonite.StrontiumcontentofWilsonbreenrhythmitesisalso967

low,whereasitistypicallyhighinformerlyaragoniticlimestones(e.gFairchildetal.,1990).968

Ikaiteisahigh-pressurephase,metastableatEarthsurfaceconditions,butbecomes969

relativelymorestableatcoldtemperatures(Kawanoetal.,2009),andnearlyalwaysforms970

naturallyatcooltemperatures(-1.9to+7°C,Huggettetal.,2005),onthesedimentsurfacein971

spring-fedalkalinelakesandfjordsandwithinmarinesediment(Buchardtetal.,2001).Itreadily972

disintegratestoformcalciteunlessthesolutioncontainsaninhibitorforcalciteprecipitation.973

Bischoffetal.(1993)foundthatphosphatewasmosteffectiveinthisrespectandindeed974

significantphosphatelevelsaretypicalofmodernikaiteoccurrences(Huggettetal.,2005;975

Sellecketal.,2007).Itisacknowledgedthatikaitemayhavebeenmuchmorewidelypresentas976

aprimaryphasethanhadbeenrealized(Shearman&Smith,1985;Bischoffetal.,1993;977

Buchardtetal.,2001).Thisisbeingborneoutbynewdiscoveriessuchasinseaice(Fig.19C,978

Nomuraetal.,2013)andasmillimetre-scalecrystalsincoldlakes(Fig.19D,E;fromthe979

PatagonianArgentinianLagunaPotrokAlke,Oehlerichetal.,2013).980

Inthediscussionabove,ikaiteastheprecursorphaseforthepseudomorphsintheFA5981

wasdeducedbyaprocessofelimination,butitisimportanttodemonstratethattheobserved982

propertiesareconsistentwiththisidentification.Ikaiteisamonoclinicmineralthatvaries983

considerablyinhabit,fromequant(Sekkal&Zaoui,2013)toelongateprismatic(Buchardtetal.984

44

2001;Lastetal.,2013)andthedominantcrystallographicformsvarygreatly,andmaybe985

steppedorcurved(Shearman&Smith,1985),whichmakeitspositiveidentificationdifficult.986

Mostofourknowledgeofitslikelymorphologycomesfrompseudomorphs,includingthe987

“bipyramidal”aggregatesofcrystalsknownasglendonites(Davidetal.,1905;Fig.18A),foundin988

shalesassociatedwithPermianglacialdepositsandothercool-waterenvironmentsandthe989

“thinolites”ofQuaternarylakesofthewesternGreatBasin,USA,figuredbyDana(1884)[Fig.990

19B]andinterpretedasikaitepseudomorphsbyShearman&Smith(1985)andShearmanetal.991

(1989).Swainson&Hammond(2001)reinforcedthisidentificationfollowingdeterminationof992

refinedlatticecellparametersofa=8.8,b=8.3andc=11.0Åwithangleβbetweenaandcof993

110°.994

ThepseudomorphsoftheWilsonbreenFormationareinterpretedtorepresenta995

combinationofforms.Prismandpinacoidformsmeetatinternalanglesof90°and110°when996

cutatahighangletothefaces.Thiswouldaccountforthehighermodeinthecrystalangle997

distribution(Fig.18C)andthecommon“rhomb”shapesinsection,similartothecrystalsinFig.998

19C.Secondlythe30-60°modeisinterpretedasrepresentingthejunctionsbetweenprismatic999

facessuchasthoseseentoterminatecrystalsinFigs.18A,19B,E.Itisnotablethatikaiteisonly1000

one-thirdasdenseascalciteandsopseudomorphsincalcitewouldbeexpectedtobeinitially1001

highlyporouseveniftheCaCO3wasprecipitatedlocally.Thisisconsistentwiththestylesof1002

preservationobserved(Fig.16),theexampleofFigs.17Eand18Dcomparingwellwithexamples1003

inLarsen(1994),Huggettetal.(2005),Sellecketal.(2007)andFranketal.(2008).Animportant1004

corollaryisthatthereplacivecalcitemosaicsobservedinFA5(andFA4)limestonesmore1005

generally(Figs.15B,17F)arelikewisealsolikelytobeafterikaite.1006

Identificationofadiageneticprocess,ikaitereplacement,thatisexpectedtobe1007

syngenetic,andpreservationofthecrystalgrowthzonesinCL,lendsweighttothepreservation1008

45

ofprimaryisotopicchemistryinFA5(andFA4)carbonates.Furthermore,forFA5thealternation1009

withice-raftedsedimenttakentoindicatetemperaturesconsistentlyclosetofreezingand1010

hencegiventhelowδ18Osignatures,thewaterbodymusthavebeenfresh.ApplicationofKim&1011

O’Neil’s(1997)experimentallydeterminedfractionationfactorsextrapolatedto0°C,indicates1012

thatwatercompositionsontheVSMOWscaleareapproximately2.7‰higherthancalcite1013

compositionsontheVPDBscale,i.e.-8.3to-15.5‰,arangewhichislikelytoreflectmixingof1014

differentwatersources.Dolomitefacieshavevaluesonaverage6‰higher,implyingformation1015

fromwatersofonaveragehighersalinityandhighermeanMg/Ca(Mülleretal.,1972).1016

Thereareplentyofmodernanaloguesforcalcareousmicrobiallaminaeincoldlakes,1017

eveninsuchextremeenvironmentstodayastheice-coveredlakesoftheMcMurdoDryValleys1018

ofAntarctica(Parkeretal.,1981),orreducingsolutionhollowsbeneaththeGreatLakes1019

(Voorhuisetal.,2012).OnecuriousphenomenonarethickcementcrustsfoundinbothFA5and1020

FA2.ApossibleoriginfortheseisthephenomenonobservedincertainAntarcticlakesofthe1021

localizedliftingofmatsbygasgeneration(Parkeretal.,1981).Earlycementationofthemat1022

wouldallowamoregradualfilloftheresultingfenestraeasfoundinmodernAntarcticlakes1023

(Whartonetal.,1982).1024

Inrespectofseasonality,manywell-studiedmodernlakesshowaturnoverassociated1025

withcoolinginwinterandmayhaveafrozensurfaceinthatseason.Inthatcase,winter1026

sedimentationistypicallydominatedbyclayandorganicmatter(e.g.Lauterbachetal.,2011,1027

Kaluginetal.,2013),butboththesecomponentsarescarceintheWilsonbreenFormation1028

examples.InAntarctica,carbonateprecipitationislinkedtopeakwatercolumnormicrobialmat1029

photosynthesisinlateSpringtoearlysummer(e.g.Whartonetal.,1982;Lawrence&Hendy,1030

1985),limitedalsobynutrientavailability.Highersedimentinputwouldbeexpectedinthelate1031

summertoautumnwhenicecoverwasataminimum.1032

46

Acluetotheoverallsimilarityofthemicrobialfabricsinthedifferentfaciesassociations1033

maybediscernedintheworkonAntarcticstromatolites.Thefirstmajormat-formertobe1034

identified(PhormidiumfrigidumFritsch)wasknowntobepre-adaptedtocoldenvironments1035

andlowlightconditions(Parkeretal.,1981)andtoleratesconditionsfromfreshtosalineand1036

anoxictooxygen-saturated.Simmonsetal.(1993)amplifiedthatthisspeciesisfoundnotonly1037

inlakes,butalsoinglacialmeltstreams,soilsandcryoconiteholesonablatedglaciersurfaces,1038

thatiseasilyspanningtherangeofenvironmentsencounteredformicrobialdepositsinthe1039

WilsonbreenFormation.Voorhuisetal.(2012)foundthataspeciesofPhormidiumalso1040

dominatedthematcommunityatlowoxygenlevelsina23m-deepGreatLakessinkholeand1041

demonstratedthatthegenushasgeneticpropertiesthatfacilitatetolerationofsulphideor1042

utilizationofitforanoxygenicphotosynthesis.Itthereforeseemsthatitislikelythatthe1043

WilsonbreenFormationmicrobialcommunitieswereoflowdiversity,asexpectedfor1044

extremophiles,withPhormidiumorasimilarancestor,dominatingthebiota.1045

1046

1047

Verticalandlateralfaciesrelationships1048

1049

Verticalfaciestransitionscanbeusedtoestablishwhethersedimentarysuccessions1050

havepredictablycyclic,Markovproperties(Powers&Easterling,1982).Atransitionmatrix1051

derivedfromalltheloggedW2sections(Fig.S7)demonstratesthatthereareverticaltransitions1052

betweenallofthefaciesassociations,exceptFA1/FA7whichareonlyfoundboundingW2,not1053

withinit.Thisindicatesastochasticelementtothefaciesaccumulation,buttherearealso1054

clearlypreferredtransitions.Althoughdataareinsufficientforformalstatisticalanalysis,since1055

totaloccurrencesofeachFaciesAssociationaresimilar,therelativenumberoftransitionsisa1056

usefulguide(Fig.22).Twosetsofthemostcommontransitionsconcurwiththeinterpretations1057

47

madeearlier.Firstly,fluvialchannels(FA2)mostcommonlypassupintofloodplainsediments1058

(FA3)andvice-versa.SuchacloserelationshipcouldnotbeanticipatedifFA2weremarine.1059

Secondly,calcareouslakesediments(FA5)passintoFA6(glacilacustrine)andvice-versa(andthis1060

isalsothedominantpatterninmemberW3).Thisrelationshipemphasizesthetransitional1061

natureofchangebetweenmajoramountsoffloatingiceandreductioninicesufficientto1062

permitcarbonateaccumulationinmicrobialmats.Othertransitions,suchasthosebetweenice-1063

raftedsedimentation(FA6)andfloodplainandlake-marginalsediments(FA3and4),would1064

requiremoresuddenchangesinlakelevel.1065

Overall,theNortheastGreenland-NESvalbardNeoproterozoicsedimentarybasinis1066

envisagedaselongate,withbasementexposedinthefarSWinGreenland(Fairchild&Hambrey,1067

1995)andaxialglacierflowtotheNNEinNESvalbard(Flemingetal.,2016).IntheFormationas1068

awhole(Fig.1)theinferredpalaeogeographyisreflectedinsourcingthesubglacialadvances1069

fromtheSSWcorrelatedwithgrounding-linefaciesinW3onlyinthenorthernsections.Within1070

memberW2however,thefaciesmosaicsdonotillustratethisoverallpatternsoclearly.Fig.221071

illustratesthecumulativethicknessofeachofthefaciesassociationsanddemonstratesthat1072

thereisnosimplespatialtrendinfacieswithinW2,exceptperhapsforthehighincidenceof1073

fluvialfacies(FA2)inthesouthernmostsection.Suchacomplexfaciesmosaicimpliesthatwater1074

andsedimentarederivedfrommultiplesources.1075

1076

1077

Integrationofsedimentological,geochemicalandmodellingevidence1078

1079

InthissectionweextendtheargumentsastowhytheWilsonbreenFormationenvironments1080

canbeconsideredasacoherentwholeandhencebeconsideredbyamodernanalogueina1081

48

singleclimaticsetting.Consideringfirstthesedimentologicalevidence,FA5containsclear1082

evidenceofsyn-glacialdeposition(ice-raftedsedimentandikaiteformation)andFacies4Rand1083

4Ishowsimilartypesofcarbonateaccumulation,andlocalizeddropstonedeposition,butmore1084

evidenceofreworkingbywavesinshallowwater.FA3evincesahyperaridterrestrial1085

environmentthatneverthelessbordersaccumulationofmicrobialtufasinstreamswith1086

regularlyfluctuatingdischarge(Facies2S).Facies4Sevokesalandscapewithsignificantaeolian1087

sedimenttransport.Allofthesefaciesareconsistentwithacold,aridterrestrialenvironment,1088

butfewresemblestandardNeoproterozoicfaciesbetweenglaciations(Fairchild,1993).1089

Secondly,thegeochemicalevidencefromsulphateisotopesystematics(Baoetal.,2009;1090

Bennetal.,2015)demonstratesthatthroughoutthedepositionofallthecarbonatefaciesin1091

W2andW3,atmosphericPCO2wasveryhigh(probablyoftheorderof0.1bar)andyettheseare1092

icehouse,notgreenhousesediments.1093

Thirdly,avarietyofmodellingconstraintsindicatethatglaciationandhighPCO2canonly1094

coincideinthecaseofaSnowballEarth,thatisaplanetthatisundergoingahysteresisofCO21095

andclimateinwhichinitiallowPCO2triggersglaciationwhichatacriticalstageofdevelopment1096

becomesgloballydistributedbecauseofice-albedofeedbacks.Anecessaryconditiontoescape1097

fromsuchanextremeiceageisbuild-upofhighPCO2.Modellingofcontinentalenvironments1098

withtheWilsonbreencaseinminddemonstratesthatatsufficientlyhighPCO2,glacialadvances1099

andretreatscanbetriggeredbyprecessionalforcing(Bennetal.,2015),butthattheclimate1100

remainsuniformlycold,changingprimarilyintermsoftheaccumulationofsnowandablationof1101

snowandice.Continentalicevolumeschangelittleandsosignificantsealevelchangewould1102

notbeexpected.Deglaciationtowarm,ice-freeconditionsisnotreversiblewithouta1103

necessarilyslow(multi-millionyear)fallinPCO2(LeHiretal.,2009).Inthisperspective,onceone1104

hasdemonstratednon-marineconditionsforpartoftheWilsonbreenFormation,thenthe1105

49

expectationwouldbethatitwouldallbecontinentalincharacter.Marinetransgressionwould1106

notbeexpecteduntilglaciationisover,andindeedsuchadistincttransgressionisfound1107

truncatingtheWilsonbreenFormation(Fairchild&Hambrey,1984;Halversonetal.,2004).1108

OverallthisimpliesthatinSvalbard,isostaticdepressionbyneighbouringicesheetswasmuch1109

smallerthaneustaticsealevelfallduetobuild-upofice(Bennetal.,2015).Insummary,the1110

Wilsonbreenfaciesarelikelytoreflectamosaicofaridterrestrialenvironmentssubjectedto1111

glaciation,whichbringsusbacktothemodernanalogue.1112

1113

ComparisonwiththeMcMurdoDryValleysandsynthesis1114

1115

Theaimofthissectionisbothtoassessthedegreeofsimilarityofthemodernand1116

NeoproterozoicsettingsandtogainfurtherinsightsfrommodernandQuaternaryphenomena1117

intothelikelycontrolsonWilsonbreendeposition.Westartbyexaminingthreetopicswhere1118

differencesmightbeexpected:tectonicsetting,(palaeo)latitude,andthecompositionof1119

bedrocksundergoingweatheringwithimplicationsforcarbonatemineralogy,andthenuse1120

insightsfromtheDryValleystoaidsynthesizingtheinterpretationofstableisotopefieldsofthe1121

carbonates.1122

TheWilsonbreenFormationrepresentsasmallpartofalargelymarinedepositional1123

basinthatpersistedformorethan300Myanddepositedapileofsediments(HeclaHoek1124

Supergroup)manykilometresthick.TheoutcropbelthasaNNE-SSWtrend,andtheoriginal1125

basinmayhavebeenanintracratonicriftwithasimilartrend(Cawoodetal.,2007)leadingto1126

thetabularnatureoftheFormationfromnorthtosouth.TheDryValleysregionoccupiesa1127

hingebetweentheupliftingTransantarcticMountainsandthesubsidingMcMurdoSound1128

(Etienneetal.,2007).Whilstuplandareasnotcoveredbyicehaveneithererodednor1129

50

accumulatedsediment,significantQuaternarysedimentaccumulationshavebeendrilledin1130

LowerTaylorValley(McKelvey,1981).Meltwaterissuppliedbothfromoutletglaciersandlocal1131

valleyglaciers,andicesheetadvancefromtheadjacentRossEmbaymenthasoccurred1132

repeatedly.Incontrast,sincetheSvalbardareawasalreadyatsealevelpriortoglaciation,anda1133

panglaciationthenensuedwithnothickicecoverlocally,apronouncedeustaticsealevelfall1134

shouldhaveisolatedthebasinfromthesea.Theproximityofuplandareastosourceglaciersis1135

alsounknown,butthisbasinconfigurationoffersthepossibilityofglacieradvancebothalong1136

andacross-strike,leadingtocreationanddestructionoflakes,ashasbeenthecaseinthelate1137

QuaternaryintheDryValleys.Suchexternallyimposedchangesinlakelevelorglacialadvances1138

andretreatswouldbesuperimposedonanyintrinsictendencyforfaciesmigrationandarethe1139

mostlikelyreasonforthemyriadverticalfaciestransitionsandcomplexlateralgeometriesin1140

theWilsonbreenFormation.1141

ThehighpalaeolatitudesoftheDryValleysensuresahighseasonalityoftemperature1142

suchthatmeltwaterproductionislimitedtoacoupleofmonthsinsummer.TheWilsonbreen1143

Formationisthoughttohavelaininthesub-tropics(Lietal.,2013)whereseasonalitytoday1144

primarilyrelatestomoisturebalance.ThisalsoappliesinthelatestagesofaSnowballEarth,1145

sincegeneralcirculationmodellingindicatesthatalternatingseasonsinwhichprecipitation1146

exceedsablationinthesummerandvice-versainthewinterwouldhavebeenastrongfeature1147

oftheclimateinlatitudes20-30°fromtheequator(Bennetal.,2015).TheSnowballclimatealso1148

hasgreatlyenhanceddiurnalandannualtemperaturevariabilityatagivenlatitudecompared1149

withtoday(Pierrehumbert,2005)sincetemperaturerespondsdirectlytoinsolation,withless1150

effectivesmoothingthantodaybylaterallatentheattransportbymoisture.Theimplications1151

remaintobefullyexplored,butBennetal.(2015)givesanindicativeplot(theirFig.S15)1152

demonstratingthat,inthemonthofApril,althoughmeantemperaturesremainbelowzero,1153

51

lowlandareasinthetropicsandsub-tropicsshouldexperienceasignificantnumberofpositive1154

degreedayswhenmeltingcanoccur.Theoveralleffectisthat,openwaterinWilsonbreenlakes1155

wasclearlyextensive,atleastseasonally,contrastingwiththeperennialicecoverintheDry1156

Valleys,apartfrommarginalmoats.1157

Anotherlatitude-relatedfactoristherelativesensitivitytoclimaticchangerelatedto1158

orbitalforcing.WhilsttheDryValleyregionissusceptibletofacieschangesrelatedtosubtle1159

environmentalchangesoninter-annualtomultimillennialscales,themostsignificant1160

environmentalchangesrelatedtoglacialadvancesandretreatsareonorbitaltimescales(Hendy1161

1980).Fig.1illustratesthatfortheWilsonbreenFormationasawhole,thereareaboutten1162

periodsofcessationofglacialdeposition,withuncertaintiesbecauseofthethinandlensing1163

(possiblyeroded)intervalsinW3inparticular.Accumulationratesofannuallylaminated1164

carbonatefacies,bothfluvially(FA2)andinlakes(FA4/FA5)isoftheorderof1mm/year:hence1165

suchretreatphasesrepresentminimumperiodsof103-104yearssinceperiodsofnon-1166

depositionduetolackoflocalaccommodationspaceorsedimentsupplyarelikely.Such1167

timescalesareapproachingthepresent-dayMilankovitchscaleofclimaticfluctuation,an1168

observationwhichstimulatedthemodellingofprecessionalcyclesinBennetal.(2015).Given1169

thatprecession(ontheca.20kytimescale)isgreatlyenhancedduringhighereccentricity(on1170

the100katimescale),aplausibleinterpretationofmembersW2andW3isthattheyrepresent1171

oneortwoeccentricitycycles,withineachofwhichseveralprecession-relatedfluctuationsare1172

recorded.1173

ModernAntarcticahasverylittlecarbonatebedrock.Nevertheless,alkalinityis1174

generatedbothbycarbonateandsilicateweathering,permittingcarbonateprecipitation,1175

particularlyinlakes,controlledbyseasonalphotosynthesis.Bycontrast,theWilsonbreen1176

Formationreflectstheerosionofcarbonate-richcatchmentsandcalciteprecipitationis1177

52

recognizedalsoinstreams.Althoughlimestonemakesup20%ofthegravelfraction,dolomiteis1178

theonlycarbonateinthefinefractionofdetritusbecauseofpreferentialcalcitedissolution,1179

implyingthatunmodifiedmolarMg/Caratioswillonaveragebe<1,althoughwillincreaseas1180

calciteisreprecipitatedwithinthebasin.DatafromstreamsandmostlakesintheDryValleys1181

alsohaveMg/Ca<1,althoughextensiveCaCO3precipitationinLakeFryxellleadstoenhanced1182

Mg/Ca(Greenetal.,1988)andpresumablysuchwaterswereresponsibleforprecipitationof1183

aragoniteinmanylateQuaternarylakes(Hendy,1979).Ratherthanaragonite,ikaiteis1184

recognizedasaprecursortocalciteintheWilsonbreencase.Modernexamplesofikaite1185

formationareassociatedwithhighaqueousphosphatewhichactsasaninhibitortocalcite1186

precipitation(Bischoffetal.,1993)andyetmodernAntarcticlakesareoligotrophic.However,1187

Burton(1993)stressedthattheroleofinhibitorsiscomplexbecausetherearemanypotential1188

inhibitingspecies(e.g.magnesium,phosphate,sulphate,organicradicalsandmanyother1189

speciesdependingonconcentration)andtheycaninteract.Onepossiblefactoristhatacircum-1190

neutralpHwouldbeexpectedinWilsonbreenwatersbecauseofhighatmosphericPCO2which1191

hastheeffectofincreasingthebalanceofHPO42-toPO4

3-andstrengtheningthephosphate-1192

inhibitioneffectoncalcite;thiseffectisalsoaccentuatedbyhighsulphate(Burton,1993).1193

ModerndolomitehasnotyetbeenrecognizedinAntarctica,yetitiscommoninthe1194

Wilsonbreenfacies,apparentlyaidedbyfactorssuchasevaporationandfluctuatingredox,and1195

possiblyalsothewidespreadoccurrenceofdolomiterockflourasnuclei.1196

Intheprevioustext,extensiveevidencehasbeenpresentedforthedevelopmentof1197

stablemineralogyintheenvironmentbyprimaryprecipitationorearlydiagenesis,astability1198

favouredbylowenvironmentaltemperatures.Inturnthisarguesfortreatingthestableisotope1199

dataasdirectindicatorsofdepositionalconditions.Giventheverywiderangeofδ18Ovalues,1200

theeffectsofvariationindepositionaltemperature,orminorpost-depositionalexchange,are1201

53

minimized.Carbonisotopesareinanycaseresilienttosecondaryalteration(Banner&Hanson,1202

1990).AsynthesisoftheWilsonbreencarbonatesinrelationtothestableisotopefieldsisgiven1203

inFig.23.Theδ13Csignatureislinkedtoacquisitionofcarbonfrombedrockandoxidationof1204

organicsourcesandvariableequilibrationwithatmosphericcarbondioxide,whilstvariabilityin1205

δ18Oisinterpretedasduetomixingofmeltwatersordifferentcompositionsofprimary1206

meltwaterscoupledwithevaporation.WenowdiscusstheseasfactorsintheDryValley1207

context.1208

Regardingcarbonisotopes,intheDryValleystheδ13Ccompositionofacarbonatesource1209

isnotwelldefined,butapotentialorganicsourceisfoundintheformofdark-coloured1210

cryoconiteholes,whichperiodicallyareflushed,providingnutrientsforephemeralstreamsand1211

lakebasins(Bagshawetal.,2013).Additionofrespiredcarbonfromthissourcecanbeseenin1212

thechemistryofsomeAntarcticstreamswithδ13Cvaluesaslightas-9.4‰(Lyonsetal.,2013).1213

Mostvaluesare-3to+2‰,possiblyreflectingcarboncontributionfromacarbonatesource1214

rock(Leng&Marshall,2004)andrangingupto5‰whichLyonsetal.(2013)attribute1215

qualitativelytoprogressiveequilibrationwithatmosphericCO2.Chemicalequilibrationbetween1216

atmosphericCO2andanAlpinemeltstreamwasshowntobeattainedwithinafewhundred1217

metresofflow(Fairchildetal.,1999),althoughthissituationfallsshortofisotopicequilibration,1218

requiringmoreextensiveexchangeuntilthelargegaseoussourceofcarbondominates1219

(Fairchild&Baker,2012,chapter5).Moreefficientprocessesformodifyingδ13Carefoundin1220

DryValleylakes,whereverticaltrendscausedbywater-columnphotosynthesisatshallow1221

depths(leadingtopositivevaluesofδ13C),organicmatteroxidation(causingadecreaseinδ13C1222

withdepth),andlocalmethanogenesis(releasingCO2withcomplementaryhighδ13Cvaluesat1223

depth)havebeendescribed(Lawrence&Hendy,1985;Neumannetal.,2004).Coldlakesin1224

54

othersettingscansometimesdevelopverylowδ13Cvaluesthroughreleaseofmethanefrom1225

solidhydrates(PropenkoandWilliams,2005).1226

1227 Foroxygenisotopesinstreams,Gooseffetal.(2006)gathereddataonδ18Ovariationfor1228

glacierice,snow,streamsandlakes,althoughinterpretationwascomplicatedbyevidentstrong1229

inter-annualvariations.InTaylorValleythemeancompositionofglaciericeineachsub-basin1230

feedingaspecificlakevariedfrom-21to-33‰andsomesampleswereaslightas-45‰.1231

Streamsamplesvariedfrom-42to-22‰andlayclosetothemeteoric-waterlineupto-32‰,1232

butdivergedfromitathighervalues,reflectingtheconsequencesofevaporation.This1233

correspondedalsotostreamlengthsofgreaterthan2km.Inadditiontosimplesurface1234

evaporation,mixingwithisotopicallyheavyshallowsubsurface(hyporheic)waterwasalsoa1235

factor,indicativeoftheeffectivenessofevaporationofsubsurfacewateratashallowwater1236

table.Furtherisotopefractionationoccurswherewaterresideslongerinsalinelakes.1237

Matsubayaetal.(1979)measuredandmodelledthe18O-enrichmentsinthemostsalineponds1238

intheDryValleyareaandfoundupto20‰highervaluesintheunfrozenDonJuanPondand1239

theeastlobeofLakeBonneycomparedwiththesource.Likewise,Nakaietal.(1975)1240

documenteda23‰variationinδ18Ocompositionofcalciteswiththehighestvalues1241

representingevaporativedepositsonlandsurfaces.Suchpronounced18Oenrichmentsalong1242

streamcoursesandtheca.20‰totalvariationareonlypermittedbecauseofthe1243

meteorologicalfactorsleadingtopersistentlylowrelativehumiditiesof50-60%.1244

Fortheancientcarbonates,itisusefultoconsiderthepresenceorabsenceofcovariance1245

ofδ18Oandδ13C(Figs.7,23).Talbot(1990)compileddatafromavarietyofmodernandancient1246

lakesandfoundthatalackofisotopiccovariationistypicalofopenlakesinwhichcontrolling1247

factorsforthevariationinthetwoisotopesaredecoupled.Thiscanbecomparedwiththe1248

limestonesofFA4andFA5(Figs.7b,23).Conversely,covaryingtrendsinlacustrinecarbonates1249

55

(FA4andFA5dolomites)wereidentifiedasacharacteristicfeatureofclosedlakesandreflected1250

acombinationofevaporationtocauseincreaseinδ18O,andresidencetime,permitting1251

equilibrationwithatmosphericCO2asafirst-ordercontrolonultimateδ13Cvalues.Although1252

δ13Candδ18OdataonAntarcticstreams(Gooseffetal.,1006;Lyonsetal.,2013)wasobtained1253

separatelyandsohasnotbeencross-plotted,theseenvironmentstoocanbeanticipatedto1254

displaycovariation.TheslopesofcovariationinTalbot’s(1990)datawerefoundtobequite1255

varied,withlowerslopesinterpretedasreflectingbroad,shallowlakesinwhichevaporation1256

wouldplayamoreprominentrole.Thedatawereprimarilyfromlimestoneandwater-column1257

precipitates,althoughexampleswereshownwherebenthiccarbonateanddolomitesfittedthe1258

trends.Apartfromattaininghighabsolutevaluesforδ18OinFA3,theWilsonbreenFormation1259

carbonatesshowcovaryingslopesandrangeswithinthosepresentedbyTalbot(1990),1260

providingaconfirmationthattheevaporation-equilibrationexplanationfordatatrendsis1261

reasonable.1262

Firstweconsiderδ13Cdata:wherecovariationsareabsentandatthestartingpointsfor1263

covaration.Theinitialcarbonisotopecompositionofaglacialmeltstreammaynotreflectany1264

atmosphericinfluencebecausemanymeltwatersderivefromicewithlowaircontentandhave1265

PCO2valueswellbelowatmospheric(Fairchildetal.,1994).Themeanδ13Cofdetritaldolomitein1266

theWilsonbreenFormationis+2.4‰(Fig.6B),butwithsignificantlocalvariations(±1.3‰)and1267

additionaluncertaintybecauselimestoneappearstohavepreferentiallydissolvedfromthe1268

matrix.Acombinationofmoderatelypositiveδ13Cfromdetritusandorganiccarboncouldhave1269

fixedthestartingδ13Cvalueofaround+1‰fortheFA2covaryingtrend.Thehigherstarting1270

pointforFA3reflectsthemoreevolvednatureofthesefluidswhichareconsistentlyforming1271

dolomite.ThetrendforFA4andFA5dolomitesstartsatlowervaluesof0to+1‰,withinthe1272

rangeofcalcitesintheselacustrinefacies.Carbonisotopesignatures<+1‰,thatislowerthan1273

56

thoseinfluvialfacies,presumablyreflectsadditionofcarbonfromanorganicsource,butoverall1274

variationsarenotlargeenoughtosuggestaroleformethanogenesis.Intheopenlakesimplied1275

bythelackofisotopecovariationinFA4andFA5calcites,thehighδ13Cvaluescouldreflect1276

eithertheeffectsofphotosynthesisorgreaterCO2-equilibrationwithoutevaporation.Themost1277

extremehighδ13C-lowδ18OlimestonesinFA4arefrommemberW3(Fig.12);theseare1278

intraclasticbrecciasimplyingpossibleexposurewhichwouldhaveaidedatmospheric1279

equilibration.Nodifferenceisnotedbetweenobviouslymicrobialandotherlimestones,a1280

commonpatternintheNeoproterozoic(Fairchild,1991).Lowδ13Cvaluesoccurineachsection1281

studiedlocationandarealmostalwaysstratigraphicallyclosetovaluesthataremuchhigher,1282

possiblyindicativeofchanginglakelevels.TheFA5sedimentsfromW3allhaverelativelylow1283

valueswhichmightreflectarelativelydeepwatersetting,consistentwiththedominanceofice-1284

raftedsedimentationinthismemberinthesouthernsectionsandtheuniversaldisruptionof1285

FA5sedimentsbyslumping.1286

Nowweconsiderthetheoreticalδ13Cend-pointresultingfromequilibration.Carbonate1287

precipitatedfromasolutioninisotopicequilibriumwithatmosphericCO2isexpectedtodisplay1288

δ13Cvaluesheavierthantheatmosphereby10.4‰at0°C(fallingto9.1‰at20°C),as1289

calibratedbytheexperimentalworkofMooketal.(1974).Thelong-term(>108year)δ13C1290

compositionoftheatmosphereshouldshowvariationlargelyinparallelwithoceanwaterwith1291

whichittendstoequilibrate,andoceanwaterinturnhasacompositionconstrainedbythe1292

proportionalburialofisotopicallylightorganiccarbon.Asaresult,short-termvariationscanbe1293

expectedbecauseoffluxvariabilities,asdemonstratedbydirectmeasurementofpast(pre-1294

industrialHolocene)atmospheresfromicecoresshowingarangefrom-6.3to-6.6‰(Elsiget1295

al.,2009).Afurthermass-balanceconstraintisthebulkEarthmeancompositionofcarbon1296

(Berner,2004).Thelattercanbeestimatedfrommantleandmeteoritesamplesasaround-7‰,1297

57

butvolcanicgasesaretypicallysomewhatheavier(Javoyetal.,1986).Anatmospherewitha1298

compositionaround-6‰wouldbeinequilibriumatzerodegreeswithcarbonatesaround+4.41299

‰.1300

ThecarbondioxidelevelintheSnowballEarthatmosphereshouldhaveprogressively1301

risenbecauseofsustainedinputfromvolcanicsourcesandlimitedremoval,mainlyby1302

dissolutionintheoceanwherevergapsintheicecoveroccurred(LeHiretal.,2008).Thelimited1303

opportunitiesforback-exchangefromtheoceansimplythattheatmosphereshouldhave1304

providedagoodsampleofthecarbonisotopecompositionofvolcanicemissions.FortheW21305

data,eachofthefaciesassociationfields(Figs.12,23)topsoutataround3.5to4.5‰whichis1306

closetotheexpectedvaluesforequilibrationwiththeatmospheredominatedbyvolcanic1307

emissionsasdiscussedabove.MemberW3dolocreteshaveδ13Cvalues1‰higherthan1308

consideredsofar(Fig.12),butthisdifferenceisdifficulttointerpretwithoutanoveralldata1309

trend.Onepossibilityisthatthereisalocalcontributionbyfreezing,whichLyonsetal.(2013)1310

invoketoexplainδ13Cvaluesintherange+5to+12‰oncarbonate-encrustedrocksontheDry1311

Valleys’landsurface.1312

Wenowfocusattentiononδ18O,startingwiththerangeofvaluesincovaryingtrends.1313

Therangeofδ18OinFA2limestonesisratherlessthanobservedintheDryValleystreams,1314

demonstratingthefeasibilityofevaporationasadriverforvariability,althoughsomevariation1315

insourcewatercompositionisalsopossible.SimilarremarksapplytothedolomitesofFA4and1316

FA5,althoughlargelyopenlacustrineenvironmentssuchasthesearenotfoundintheDry1317

Valleys.TheslopeofcovariationismuchlowerfortheFA3thanfortheotherfaciesassociations,1318

whichisconsistentwithasurficialoriginleadingtomoreefficientevaporation(Talbot,1990).1319

Allowingfora3‰offsetbetweendolomiteandcalcite(Land,1980),theevaporativetrend1320

(Figs.7B,12)extendsbeyondthecompositionoffluviallimestonesbyafurther11‰for1321

58

dolocretes(Facies3D)and15‰forstromatoliticlaminites(Facies3S).Evaporationofcoastal1322

seawater,undertypicalhighhumidityconditionswouldcauseanincreaseinδ18Oofatmost61323

‰,whereas17‰increasefroma-10‰startingpointwasobservedinafreshwaterTexan1324

pondunderconditionsoflessthan50%humidity(Lloyd,1966).TheextremeenrichmentsinFA31325

stromatoliticcrusts,requiresimilarlylowhumiditiestothisexampleandtheDryValleys,and1326

couldonlybepossibleforfaciesdevelopedatthelandsurface.1327

TheFA4andFA5lacustrinecalciteshavelowerδ18OcompositionsthanthoseofFA21328

fluviallimestones.Byanalogywithmodernenvironments,thisislikelytoreflectalocal,low1329

altitudesourceofwaterforFA2,whereasthevariabilityinδ18OwithinFA4andFA5couldreflect1330

varyingmeltwatersources,includinglargeglacierswithlowδ18O.Therangeofδ18Oisactually1331

ratherlessinFA2thanintheDryValleystreamsandgiventhatthevaluesaretypicallyheavier1332

thanthelakes,arelativelylocal,low-altitudesourceformeltwaterisimplied.FortheCarbonate1333

LakeMarginFA4,theδ18OvaluesaresimilartoCarbonateLakeFA5andthereisalackof1334

isotopiccovariationwithbothsetsofdata.Thiswouldimplyanopenlake(Talbot,1990),but1335

careisneededwithsuchaninterpretationbecausethedatarepresentseveraldifferentlakes1336

thatformedsuccessively.Asderivedearlier,therangeofδ18Owatervaluesimpliedfromcalcite1337

precipitationat0°Cisaround-8.5to-15.5‰ontheV-SMOWscale.Thisrangemightbe1338

explainedbyvariablemixingoflocalsnow,localglaciericeandmeltfromlargerorhigher1339

glaciers,byanalogywiththeDryValleyregion.1340

TheultimatedriverforRayleighfractionationintheatmosphere,whichleadsto18O-1341

depletedvaluesinatmosphericprecipitation,ispartialcondensationandremovalofvapourasa1342

resultofafallintemperatureoftheairmass.InferredWilsonbreenmeltwaterδ18Ovalues1343

higherthanthoseinthemodernDryValleysimpliesalesserdegreeoffractionation,as1344

originallynotedbyFairchildetal.(1989).Acomparablemodernglacialareaforthe1345

59

Wilsbonbreenintermsofδ18OistheVatnajökullicecapofIcelandbelowwhichRobinsonetal.1346

(2009)foundarepresentativeice-andsnowmeltcompositionof-12‰.Notethatindirect1347

evidenceformoreisotopicallylightNeoproterozoicmeltwaterhasbeenfoundintworecords1348

fromSouthChina(Zhao&Zheng,2010;Pengetal.,2013),althoughthesedonotnecessarily1349

relatetoapanglacialandintheformercaseisayounger,Ediacaranglaciation.Amorepertinent1350

recordisthatofKennedyetal.(2008)incalcite-cementedMarinoantidalsiltstonesofSouth1351

Australiawherecalciteaslightas-25‰wasanalyzed,andinterpretedtoreflectinputof1352

meltwaterfromhighlyfractionatedlow-latitudeicesheets,althoughtheremaybeother1353

possibleinterpretationsofthesedatabearinginmindtheactivedecompositionofclathratesat1354

thissite.Insummary,thedistinctivelyheavyisotopicsignatureofWilsonbreenmeltwatermay1355

beacharacteristicfeatureoflow-latitudeglaciationandclearlyrequiresstudybyanisotope-1356

enabledgeneralcirculationmodel.1357

13581359

CONCLUSIONS1360

1361

1.CarbonateintheWilsonbreenFormationconfirmsthenon-marineenvironmentof1362

depositioninaglaciatedbasinsuppliedwithdebrisfromerosionofplatformcarbonates.The1363

consistentlydolomiticnatureofthedetritalmatrixofWilsonbreenFormationsediments1364

contrastswiththecommonpresenceoflimestoneincoarserdebrisanddemonstratesthe1365

preferentialdissolutionofcalciteoverdolomite.Carbonate-richmeltwaterswerethusableto1366

precipitateCaCO3oncesupersaturationwasachievedbyprocessessuchasphotosynthesisor1367

evaporation.1368

2.Evidencefromphysicalsedimentarystructuresallowsfourfaciesassociationstobe1369

distinguishedinwhichcarbonatewasprecipitated,distinctfromthreefaciesassociations1370

60

dominatedbyglacialandperiglacialprocesses.TheFluvialChannelFaciesAssociation(FA2)1371

commonlycontainsmicrobiallimestonelaminaewithmm-scalelaminationandnotablesyn-1372

depositionalradiaxialcalcitecements.Thesecomparephysicallywithmodernmicrobialmatsin1373

ephemeralAntarcticstreams.TheDolomiticFloodplainFaciesAssociation(FA3)consistsofsoil1374

zone/playasurficialdolocretesanddolomiticstromatolitesinwhichdolomitewasprobablya1375

primaryprecipitate.TheCarbonateLakeMarginFaciesAssociation(FA4)typicallydisplays1376

micriticandlocallymicrobiallaminaeinterlaminatedwithwave-sortedsiltsandsandswithlocal1377

developmentofintraclasticbreccias.Finally,theCarbonateLakeFaciesAssociation(FA5)1378

displaysmm-scale(varved)alternationsofmicriticcarbonateorlaminatedmicrobialcarbonate1379

(includingmicrospariticandfenestrallaminae)withpoorlysortedsedimentcontaining1380

recognizableice-rafteddebris.LocallyinmemberW2,andpervasivelyinmemberW3,partly1381

lithifiedsedimentsweredisturbedbyslumpfoldingandlocallytransformedtocarbonate-rich1382

debrisflows.1383

3.InbothFA4andFA5,therearetexturalindicatorsofmineralogicalreplacements.1384

DolomitecanbeseentoreplaceaCaCO3precursor.Althoughsomecalciteislikelytobe1385

primary,calcitepseudomorphsafterikaite(CaCO3.6H2O)arecommon.Theikaiteformed1386

individualcrystalswithinthesediment,formedcrustswhichgrewcentripetallyintopores,and1387

locallygrewupwardsatthesediment-waterinterface.Thisparagenesisisnowbecomingbetter1388

knowninmoderncoldlakes.1389

4.Stableisotopedatademonstratethatcarbonatesinthedifferentfaciesassociations1390

formdistinctfieldswhichareallinterpretedasconsistentwithprimarydepositionalconditions.1391

LimestonesinFA4andFA5lackδ13C-δ18Ocovariationandwereprimarilyinfluencedbymixing1392

ofmeltwatersources,thevariableadditionoflightcarbonfromorganicdecomposition,and1393

somere-equilibrationwiththeatmosphere.Othersub-setsdemonstratecovariation,1394

61

interpretedasacombinationofevaporationandequilibrationwiththeatmosphere.Thisallows1395

theδ13CcompositionofCO2releasedfromvolcanismduringtheglaciationtobeconstrainedto-1396

6to-7‰.Directevidenceofprimaryfluidcompositionsisunavailablebecauseofsecondary1397

fluidmigrationintoinclusions,despitethepresenceofprimarytraceelementgrowthzones.1398

Nevertheless,theverywiderangeofδ18Ovaluesmustbeprimarilyrelatedtochangesinwater1399

composition,giventheconsistentlycooldepositionalconditions.Theexceptionallyhighδ18O1400

signaturesofFA3dolomites,upto+14.7‰VPDB,attesttothehyperaridityoftheenvironments.1401

Conversely,theinferredδ18Ocompositionsoftheinputmeltwaters(-8to-15‰VSMOW)aremore1402

comparabletomodernIcelandthantopresent-daypolarregions.Thisislikelytoreflect1403

relativelylimitedRayleighfractionationintheatmospherebecauseofitsrelativewarmthlinked1404

toenhancedabsorptionofinfra-redradiationfromhighCO2levels.1405

5.Althoughpreferredfaciestransitionsoccur,thereisnodevelopmentoverallofmulti-1406

faciescyclicity.Thestrongisotopiccovariationsassociatedwithclosedlakesandstreams,and1407

rhythmiccarbonatelaminaearestrongmotifsofnon-marinefacies.Intheseenvironments,the1408

landscapewasrepeatedlytransformedbydamminganddrainingoflakesastheglaciers1409

advancedandretreated.Inturnthesearelikelytohaverepresentedamplifiedgeomorphic1410

responsestosubtleclimaticshiftsinapersistentlyhyper-aridsettingforwhichtheMcMurdo1411

DryValleysprovidearichmodernanalogue.AlthoughWilsonbreenlakeswerenotperennially1412

ice-coveredasinthemodernenvironment,manypointsofsimilaritybetweenthemodern1413

Antarcticandtheancientenvironmentshavebeendrawninthisstudy,specificallyincludingthe1414

ratesandstylesofsedimentdeposition,biogeochemistry,andextreme18O-enrichmentrelated1415

tothehyperaridclimate.1416

6.ThecarbonatesoftheWilsonbreenFormationaredistinctiveandincludeunique1417

faciesandrecord-breakingisotopecompositions.Theyrepresent,alongwithinterbedded1418

62

diamictites,thecomplexenvironmentalresponsetochangingratesofaccumulationand1419

ablationforcedbyaseriesofprecessionalcycleslateintheevolutionofaSnowballEarth.1420

1421

1422

ACKNOWLEDGEMENTS1423

1424

ThefieldworkandsubsequentanalyseswerefundedbyNaturalEnvironmentResearchCouncil1425

grantGR3/NE/H004963/1withinprojectGAINS(GlacialActivityInNeoproterozoicSvalbard).1426

WearegratefultotheNorwegianauthoritiesinSvalbardandthelogisticaldepartmentofthe1427

UniversityinSvalbardinfacilitatingourfieldwork,andothermembersoftheGAINSteamfor1428

theircollegialityandscientificzest.TheseniorauthorrecordshispersonalappreciationtoPaul1429

Hoffmanforhisinspiration,andsupportforthisprojectatacriticalstage,toMartinKennedyfor1430

hisfriendship,andrigorouslycriticalfeedbackonNeoproterozoicdataandideas,andtoTony1431

Spencerforhisinsight,andcarefuleditorialcommentsonadraft.Journalreferees,including1432

AlexBrasier,gaveinvaluableadvicethatledtoarestructuringofthepaperandsharpeningofits1433

arguments.1434

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73

Table1:NeoproterozoicchronostratigraphyandNESvalbardlithostratigraphy(afterHalversonetal.,2007,Halverson,2011,updatedbyunpublisheddata).Glacialunitshighlightedinred.ThispaperdealswiththeWilsonbreenFormation,representingtheyoungerofthetwoCryogenianglaciations.

GeologicalSystem Group Formation Member

Thick-ness(m)

Lithologies Interpretedenvironment

Ediacaran

Polarisbreen

DracoisenD4toD7 265

Sandstonesandmudstones(D4andD6);dolomiteD5andD7 Playas(D4toD6);Coastal(D7)

D1toD3 200Capcarbonate(D1)transitional(D2)toblack

shaleD3) Transgressivecoastal(D1)tooffshore(D2-D3)

Cryogenian

Wilson

breen

W3(Gropbreen) 65-95

Diamictitesandsandstoneswithminorlimestone Glacilacustrine;subglacialatbase

W2(MiddleCarbonate)

20-30

Threemainintervalsofcarbonate-bearingsandstonesandsiltstoneswithintervening

diamictites

Carbonateintervalsarefluvialandlacustrinewithglacialinfluence;diamictitesare

glacilacustrinerainoutdeposits

W1(Ormen)

55-85

Brecciatedunderlyingdolomitelocallyoverlainbysandstonesandconglomeratespassingupintodiamictitesandsandstones

withlocalrhythmites

Basalperiglaciatedsurface,locallysucceededbyfluvialdeposits,thenglacilacustrinerainout

depositsandsedimentgravityflows

Elbobreen

E4(Slangen) 20-30 Ooliticdolomite Regressiveperitidal

E3(Macdonaldryggen)

200 Finelylaminateddolomiticsiltyshale Offshoremarine

E2(Petrovbreen) 10-20 Dolomiticdiamictites,rhythmitesandconglomerates

Glacimarine

(basetobedefined)

E1(Russøya) 75-170 Dolomitesoverlainbylimestonewithmolartoothstructure,blackshaleanddolomite

Shallowmarine

Tonian

Akadem

iker-

breen

Backlund-toppen

530 Limestoneanddolomite Carbonateplatform

Draken 350 Intraclasticdolomite Peritidal

Svanberg-fjellet

425 Limestoneanddolomite Carbonateplatform

Grusdiev-breen

700 Limestoneanddolomite Carbonateplatform

74

75

Table2.SummaryofcharacteristicsofcarbonatesinmembersW1andW3.Analysesareofcalciteexceptwhereitalicized(dolomite).s=standarddeviation;n=numberofsamples.

Section

Member,mabovememberbase(frommembertop)

Faciesassociation Lithology

δ18O δ13C

mean s mean s n

AND W330(-15)5

Intraclasticstromatoliticrhythmites(carbonatelayers5-10mmthick)withinterveningdiamictite.Somecalcite-filledpseudomorphs -9.22 0.20 0.27 0.33 5

AND W338(-7)5

Stromatoliticlimestone(laminae5-10mmthick)withdiamictitelaminae,variablybrokenupwithindiamictite.Observedover100mlaterally. -8.16 0.55 0.23 0.70 6

AND W340.5(-4.5) 5 Brecciatedlimestone - - - - -REIN W356(-6.5) 5 Limestonewithscatteredsand -8.92 - -0.44 - 1

KLO W325(-18) 5 Carbonatesinterlaminatedwithdiamictiteatbaseofbed.EFK15closelyresemblesthemiddlecarbonatelayeratsectionAND.

-7.97 - 1.83 - 1-5.03 - 1.04 - 1

KLO W328(-15) 5 Laminatedcarbonatesindiamictite.Somecrystalpseudomorphsbothwithinsedimentandgrowingupwards. -8.86 0.4 -0.38 0.1 3

-4.04 - 1.16 - 1

KLO W331(-12)5

Laminatedcarbonatesinice-raftedsedimentswithprominentupwardgrowingcrystalpseudomorphs(indolomite)ofikaite. -9.44 2.38 0.31 1.09 4

KLO W335(-8) 5 Similartohorizon4mlowerinsection. - - - - -

PIN W3n/a(-26)5

Slumpfoldedandbrecciatedthicklylaminatedstromatoliticlimestoneinredsiltysandydiamictites.Traceablelaterallyfor30m

-12.53 0.28 -0.04 0.29 3

ORM W13.5(-20.5)5

Slump-foldedrhythmiteswithdistinctmm-scalestromatoliticlimestonelaminae,somewithbulboustops,separatedbydiamictite. -12.5 - 0.32 - 2

ORM W328(-30)3

Sandstonewithconvolutebeddingwithnodulardolocrete(floatingquartz,micro-nodulesandcracks)alongspecificlaminae. -9.78 - -5.60 - 2

ORM W333(-25) 4Diamictiterestsonmassivestromatoliticlimestonewithpseudomorphsandslumpfolds

orintraclastsovergreenishcross-laminatedsandstonewithooids. -10.76 1.12 2.20 1.56 6

ORM W346.5(-11.5)5

Red,thicklylaminatedandslump-foldedstromatoliticlimestoneindiamictite.Locallymassivewithlotofearlycement. -9.44 2.38 0.31 1.09 4

76

Table3.FaciesandfaciesassociationsoftheWilsonbreenFormation.Thefaciesassociationsare1numberedtorepresentanenvironmentalcontinuumasdepictedinFig.7A.23FaciesAssociation ConstituentFacies EnvironmentalInterpretation1:DeformedDiamictiteDetailedfaciesanalysisinFlemingetal.(2016)

Dominatedbymassivediamictites,locallywithdeformedstratificationwithlenticularsandandgravelbodies(1-5mthick)withdisruptedmargins.Locallyassociatedwithupwards-increasingshearofunderlyingsedimentandstriatedboulderpavements.

Subglacialtillandchannelbodies;glacitectonites.

2:FluvialChannel 2S:Bedsof0.5-4mveryfinetomedium-grained,locallycross-stratifiedsandstonewitherosionalconglomeraticbase.Somevariantshavelow-angleaccretionsurfaceswithsilt-dominatedbeds.Stromatoliticlimestoneiseitherabsentorabundant,formingdmpackageswithmm-cm-scalelaminaeseparatedbysandlaminaeandlaterallyerodedintotrainsofintraclasts.2T:Asabove,butlackingcarbonateprecipitates

Ephemeralstreamchannelsandswithstronglyseasonalflows.Insomecasesthereisawidespreadcarpetofcalcifiedmicrobialmats.

3:DolomiticFloodplain

Allfaciescontaindolomitewithapositiveδ18Ocompositionthatactivelycements,displacesand/orupwardlyaccretesthesediment.3D:Nodules,cm-todm-scaleofdolomite-cementedsiltsandsandstransitionaltostructurelessdm-tom-scalebedswithfloatingsiltandsandindolomite,internalnodulesandcalcite-cementedfractures3S:Stromatoliticdololaminites,dm-scaleandmm-laminated

Dolocretesrepresentingsoilhorizons,typicallyabovefluvialdeposits,withlocallyraisedwatertable3N:Nodulardolocrete3D:Beddeddolocrete3S:Subaerialstromatolites

4:CalcareousLakeMargin

4R:Rhythmiteswithmm-scaledolomite,limestoneormixedmineralogylaminae,commonlydesiccated,alternatingwith1-10mmwavycross-laminatedsiltysandstones.Carbonatelaminaeareoftenstromatolitic.Almostinvariablyreddened.4I:Intraclastic,dm-scale,veryfine-tomedium-grainedsandstones.Verylocallycontainooids.4S:Indistinctlyhorizontallystratifiedwell-sortedfine-tomedium-grainedsandstone,withwell-roundedgrains,locallywithcm-scaledolomitelaminae.

3R:Shallowlaketoplayaenvironmentwithwave-reworkedsedimentalternatingwithmicrobialmataccretion.3I:Discretestormhorizonsinshallowlake/playareworkingsandandstromatoliticcarbonate3S:Aeoliansandflatdeposits

5:CarbonateLake 5R:Rhythmiteswithmm-scalelimestone,dolomiteormixedmineralogylaminae,usuallywithstromatoliticmicrostructureandlocallybuildingdmstromatoliteswithcm-scalerelief.Alternatewith0.1-5mmlaminaeofdiamictite/wacke,commonlywithtillpelletsandoccasionallonestones.Slumpfoldingandbrecciationcommon.5D:Discretegraveltodiamictiteunitswithsignificantintraclasticdebrisinadditiontoterrigenousgravel.

5R:Carbonatemicrobialmatdepositsinlacustrineenvironmentsubjecttoseasonalice-raftingandslopeinstability.5D:Slope-relatedresedimentation.

6:GlacilacustrineDetailedfaciesanalysisinFlemingetal.(2016)

Dominatedbymassiveandstratifieddiamictiteswithcommonlonestonesandtillpellets.Decimetre-tom-scaleintervalsofsiltyrhythmitesoccurlocally,especiallyinmemberW1.Maycontainlensesofconglomerate,sometimeschannelled,andlensesorthinbedsofsandstoneformingpackageswhichcanbeinclinedatupto20°.

Ice-raftedglacilacustrinesedimentlocallyreworkedassediment-gravityflows.Inclinedpackagesformgrounding-linefans(termedproximalglacilacustrineonFig.1)andrhythmiteslikewisereflectice-marginretreat.

7:PeriglacialSeeFairchild&Hambrey(1984)andBennetal.(2015)

Decimetre-widesandstonewedgespenetratingupto2mintounderlyingsedimentfromadiscretesurfacethatmayhaveagravellag.AtbaseofWilsonbreenFormation,gravelwithventifactsoverlyingshattereddolostone.

Exposedperiglaciatedbedrockandsandwedgesfromexposedperiglacialenvironment.

4 5

77

6FigureCaptions7

8

Fig.1.Reconstructionofthesedimentaryarchitectureandpalaeoenvironmentsofthe9

WilsonbreenFormationanditsconstituentmembers(W1toW3).Precipitatedcarbonateis10

presentinthepalaeoenvironmentalgroupcalled“CarbonateLacustrineandFluvial”throughout11

W2(exceptlocallyatthetopandbase),alsoinW3andatoneofthelocationsinW1aslistedin12

Table2.TheSvalbardarchipelagoisshownbottomrightandSpitsbergenisthemainislandofthe13

group,whilstNordaustlandetistheislandtotheNE.TherectangleontheSvalbardmapshowsthe14

studyareaasenlargedupperrightwithWilsonbreenFormationoutcrops(red)withinnunataks15

(grey)risingfromthehighlandsnowfield.Fromnorthtosouth,studylocationsare:DRA16

(Dracoisen);herethemainsectionislocatedonanunatakinformallyknownasMultikolorfjellet17

withsomeadditionalsamplingfromW2atasecondnunatakwetermTophatten1kmtothe18

north;DIT(Ditlovtoppen);AND(EastAndromedafjellet);REIN(aridgeonSouthAndromedafjellet19

informallyknownasReinsryggen);KLO(SouthKlofjellet);withsomeadditionalobservationsfrom20

apartialW2section1kmaway,atNorthKlofjellet;McD(MacDonaldryggen);GOL(Golitsynfjellet,21

intermediatebetweenMcDandBAC)–apartialW2sectionwasillustratedbyFairchildetal.22

(1989);BAC(Backlundtoppen-Kvitfjelletridge);PIN(anunnamednunatakinformallytermed23

Pinnsvinryggen);SLA(SoutheastSlangen)andORM(SouthOrmen).24

25

Fig.2.Examplesofstudiedsectionoutcrops.A.MemberW2atMultikolorfjellet,Dracoisen(DRA)26

illustratingthethreegroupsofglacialretreatfaciesbeds(numbered1to3)separatedby27

diamictiteswhichalsomakeupmembersW1andW3.B.MemberW2atORM(SouthOrmen)with28

palesand-dominatedunitsanddarkredfinerunits.Beddingisinvertedanddipssteeplyaway29

fromthephotographer.C.REIN(Reinsryggen)sectiononthesouthflankofAndromedafjellet30

78

illustratingWilsonbreenFormationmembersoverlainbycapcarbonatememberD1.D.KLO31

(SouthKlofjellet)sectionoftheentireWilsonbreenFormationonsteepslopescutbyminorfaults,32

oneofwhichishighlighted.E.BAC(Backlundtoppen-Kvitfjelletridge)photomontagefrom33

helicopterhoveringabovetheglacierWilsonbreen.Thevisiblesectionisvertical(thrustfault34

shown)andtheaccessiblepartdefinesanarrowridgebetweenthecliffandasnowbankonthe35

ridgecrest.36

37

Fig.3.A.ObliqueaerialviewoftheMcMurdoDryValleys(1/1/1999imageryfromUSGeological38

SurveyviaGoogleEarth)withlocationarrowedininsetofAntarctica(upperright).EAIS=East39

AntarcticIceSheet.LGM=LastGlacialmaximum.Abbreviationsonupperrightinset:EA=East40

Antarctica,WA=WestAntarctica,RIS=RossIceShelf.Thelowerleftinsetshowsanobliqueaerial41

photographlookingwestupTaylorValleywithcold-basedvalleyglaciersonhillsideonleft,ice-42

coveredLakeBonney(valleyfloor,right)withthetipoftheTaylorGlacierbeyond.B.Despitesub-43

zerotemperatures,runoffoccursfromtheLowerWrightGlacier(anoutletglacierofthecoastal44

WilsonPiedmontGlacier)andfeedstheOnyxRiver.Thisstreamflowsinlandtothewest,45

eventuallytoLakeVanda,visibleinA.inthecentralpartofthevalley.Notetheaeoliansands46

bankedagainstheglacier.C.ObliqueaerialviewofVictoriaLowerGlacier(EendofVictoriaValley)47

whichfeedsastreamflowinginland,westwardstoLakeVida,seeninthedistance.Aeoliandunes48

tranversetothestreamarevisibleonright-sideofthethevalley.49

50

Fig.4.ProfileofmemberW2atDracoisen.Thelithologicallogemphasizesphysicalcharacteristics51

(seekey,upperright)whilsttheassignmenttofaciesassociations(centre)alsodrawson52

petrologicalandstableisotopeinformation.FA1toFA6representanenvironmentalcontinuum53

(cf.Fig.6)andFA7isgroupedwithFA1astheterrestrialglacialend-member.Eachdatapoint54

79

representsthestratigraphicpositionofastudiedsampleorobservedlithologicalboundaryinthe55

field.Theoxygenisotopecompositionofprecipitatedcalcitesanddolomites(thelatteradjusted56

by-3‰)areshown.Mixed-mineralogysamples(<90%calciteordolomiteincalcite-dolomite57

mixtures)arenotplotted.Thesameconventionsareusedforprofilesoftheotherstudied58

sections,whicharepresentedassupportingfigures(Figs.S1-S6).59

60

Fig.5.Detritaltexturesandminerals.A.andB.PairedimagesofapolishedthinsectionunderCL61

andintransmittedlightrespectivelyofthematrixofasiltysandstone(W2,81.2m,Dracoisen)62

illustratingtheabundanceoffaintblue-luminescingfeldsparandvariedfragmentsofbothbright63

anddullred-luminescingdolomiteinthemudfraction.C.Thinsection,transmittedlight.Siltstone64

gradedrhythmites(W3,60.4m,EastAndromedafjellet)displayingseveralsand-sizedtillpellets.D.65

Crossedpolars.Matrixatthetopofagradedsiltlayerillustratingquartzo-feldspathicdebrisand66

micron-sizeddolomite,butnoclayminerals(W1,10mSlangen).67

68

Fig.6.Summarycartoonoffaciesassociations.FaciesAssociations2to5arecolour-codedhere69

andinisotopeplots.Themarginofanicesheetisdepicted,terminatingpartlyonlandand,inthe70

foreground,inthelake.FA1isshowninasubglacialenvironment(subglacialsedimentsare71

colouredbrown);periglacialphenomenaarealsogroupedinthisfaciesassociation.FA2andFA372

bothoccurinafluvialsetting(sedimentscolouredyellow),whilstFA5andFA6weredepositedin73

lakes(sedimentscolouredlightbrown).FA4includesbothshallowlacustrineandcoastal74

sediments.75

76

Fig.7.A.Summaryofstableisotopecompositionsofprecipitatedcarbonate,togetherwiththe77

meancompositionofdolomiticdetritus.Dolomiteandcalcitegroupingsareseparatedandonly78

80

sampleswith>90%ofeitherdolomiteorcalciteinthecarbonatefractionareplotted.B.Stable79

isotopefieldsillustratingdegreeofcovarianceofthesamplegroups.80

81

Fig.8.Faciesassociation2(FluvialChannel).A-FareFacies2S(W2,Dracoisen,ataroundthe60m82

level),whereasGandHarefacies2T.A.Sandstonewithmicrobiallaminitesandlow-domed83

stromatolitesvariablybrokenintointraclasts.B.Stainedthinsectionintransmittedlightof84

stromatolitemicrostructurewithmicrite(M),microspar(S),fenestral(F)anddetrital(D)laminae.85

C.Stainedthinsectionintransmittedlightshowingthebrokenedgesofstromatoliticintraclasts86

withradiaxialcalcitecementcrustsinacalcareoussandstonematrix.D.Cross-stratifiedsandstone87

(set30cmhigh)withstromatoliteintraclastsoverlainbycurrentrippleforms.E.Polishedrock88

slicewitharrowdenotingmicromilledtraverseshowninF.F.Micromillisotopetraverseacross89

twomicrite/microsparlaminaandacentralzoneofcalcitesparwhichhasamuchlowerisotope90

signature.G.Sandstonebody(withpebblybase)showingaccretionarysurfaces(e.g.dashedline).91

Palaeohorizontalshownbysolidblackline.(W2,Ditlovtoppen,119m).H.Photomontageof92

tabularsandstoneunitofFA2withapebblehorizonnearitstop(arrowed).Itrestserosivelyon93

floodplain(FA3)siltsandisoverlainbyredlakemargin(FA4)sediments;ruleris25cmlong(W2,94

Dracoisen,83m).95

96

Fig.9.PhotomicrographsofstromatoliticlimestonesfromFA2.A.Pairedtransmittedlight97

(left)andCL(right)micrographs.Stromatoliticlaminaeoforange-luminescingmicrospar(MS)with98

subhedralauthigenicquartzandclasticlayer(M)includingquartzandfeldspargrains(thelatter99

luminescesdarkblue).Largefenestraisfilledbyradiaxialcalcite(R)seeninbothtransverseand100

basalsectionsanddisplayingbrighterearliergrowthanddullerlatergrowth.Thesefabricsarecut101

byavein(V)filledwithbrighttodullluminescingcalcite.W2,Dracoisen,58.5m.B.Stainedthin102

81

section,transmittedlight.Alternatingmicrite,microsparandclasticlaminaewithprominent103

irregularvertical“filamentous”structureofclearcalcite.W2,Dracoisen,58.5m.104

105

Fig.10.FA3(Dolomiticfloodplain).Facies3DisshowninA-D,Facies3Sintheothers,andboth106

faciesinE.AlloftheFacies3SimagescomefromW2,Dracoisen,70m.A.Nodulardolocretewith107

calcite-linedvugsinsiltstonewithscaleinmm(W2,EastAndromedafjellet,35m).B.Stainedthin108

sectioninplanepolarizedlightshowingmatrix-supportedfabricofdolomitecementationofsandy109

siltstone.Dolomicrosparlinesafenestrawhichisoccludedbycalcite.W2,Dracoisen,70m.C.Thin110

sectioninplanepolarizedlight.Grain-supporteddolomicritecementofsiltysandstone.The111

dolomitehasaδ18Ocompositionof+2.7‰andhasauniformtextureincontrasttoclastic112

dolomiteofFig.4D.W2,SouthKlofjellet,57m.D.Displacivedolomitecementsupportingsiltand113

sandgrains.Well-developedstructureofdarknoduleswhichshowdifferentCLcharacteristics114

fromsurroundingdolomitefromwhichtheyareseparatedbycurvedcracks.W3,SouthOrmen,78115

m.E.Stainedthinsectionofinterlaminateddolomite-cementedsandandmicrobiallaminaewith116

fenestrae,someoccludedbyferroandolomite(turquoisearrow)orferroancalcite(purplearrow).117

F.Stainedthinsectionillustratingsimilarfabricto(D.),butwithcalcitecementationofcracksand118

largerpores(W2,Dracoisen,83m)G.Fieldphotographoftexturedbeddingsurfaceof119

dololaminiteidentifiedasmicrobialmattexture(W2,Dracoisen,70m).H.Polishedrockchipof120

microbialdololaminiteswitharrowmarkingpositionof5.2mmmicromilltraverse(showninJ.121

below).I.Microbiallaminitesdrapingdownwardsintounderlyinglaminatewhosebrecciationis122

attributedtoevaporitedissolutioncollapse.Outlinedruleris20cmlong.J.Stableisotopeprofile123

(in‰withrespecttoV-SMOW)ofmicrobialdololaminitesalonglineillustratedinH.Theisotopes124

covaryoveramagnitudeof6‰forδ18Oand1‰forδ13C.125

126

82

Fig.11.FA3(dolomiticfloodplain).A.Transmittedlight,stainedthinsection.Sandydolocrete(FA3)127

containingequantnodulecementedbyferroansaddledolomite(turquoise),withlocallatecalcite128

(red),interpretedasafillofasmallanhydritenodule.W2,Backlundtoppen-Kvitfjelletridge,74.7129

m.B.Facies3Sstromatolitewithfenestrae.Pairedtransmittedlight(left)andCL(right)images.130

Brightlyluminescingdolomitemaybeprimaryoranearlyreplacementofaprecursor.W2,131

Dracoisen69.95m.C.Pairedtransmittedlight(left)andCL(right)images.Dolocreteshowingvery132

fine-grainedquartzsandgrainsfloatingindolo(micro-)sparwithcrystalsdisplayingacommon133

zonationofbrighttodullCL.Displaciveprimarydolomitegrowthisthepreferredinterpretation.134

W2,Ditlovtoppen,118.5m.D.Pairedtransmittedlight(left)andCL(right)images.Dolocrete,135

similartoFig.10D,F,withsparsefloatingquartzandfeldspar(blackandbluerespectivelyinCL)136

andcalcite-filledcracks(centre)andpores(base).Uniformlyluminescingdolomicritecrystals,differ137

inbrightnesswithinnodulespresumablyformingatdifferentstages.Calcite-filledporesshowCL138

zonation(base)ornoCL(cracks,centre).W2,Dracoisen,82.9m.139

140

Fig.12.Stableisotopeplot,differentiatingfacieswithinFA3and(inpurpleandlargersymbols)141

samplesfrommemberW3.142

143

Fig.13.FA4(CalcareousLakeMargin).ImagesA,B,DandH-JareFacies4R;C,EandGareFacies4I144

andFisFacies4S.A.Laminatedrhythmiclimestonesandsiltysandstoneswithconspicuous145

isolatedwaveripplestructureincentreofview.W2,Dracoisen,90m.B.Sand-richexampleof146

facies4Rwithcross-laminatedsiltysandsanddolomiticrhythmites,inpartdesiccatedoreroded147

toformintraclasts.Whiteareasneartoparemineral(probablesalt)pseudomorphs.W2,148

Ditlovtoppen,109m.C.Waverippleswith15cmwavelengthonbedtopW2,Dracoisen149

(Tophatten),approximatelyequivalenttothe87mlevelonFig.4.D.Carbonaterhythmitesurface150

83

cutbydesiccationcracksandbearingsaltpseudomorphs.W2,Reinsryggen,82.5m.E.Stainedthin151

section,planepolarizedlightofooliticintraclasticsandstone.Ooidsarebimineralic(calciteand152

dolomite)withdominantconcentricstructure.W3,SouthOrmen,84m.F.Partofscannedthin153

sectionintransmittedlight.Well-sortedquartzosesandstonewithverywell-roundedgrainsand154

low-anglelaminationmarkedbysubordinateinterstitialdolomite.W2,Ditlovtoppen,114.2m.G.155

Stainedthinsectionintransmittedlight.Sandstonewithconspicuousstromatoliticrhythmite156

limestoneintraclasts.W2,Backlundtoppen-Kvitfjelletridge,76.5m(supportingFig.6).H.Two-157

metrehighsectionatofDitlovtoppen(108.5-110.5onsuppl.Fig.1)showingpoorlystratified158

sandstonebed(Facies4S)overlyingFacies4Rwithseveraldiscretegradedintraclasticsandstone159

beds(Facies4I).I.Polishedslabofdolomiticrhythmiteswithdesiccationcracks(C).The3.2mm-160

longmicromillisotopetraverseofJisindicated.W2,SouthOrmen,31.3m.J.Isotoperesultsfrom161

themicromilltraversewithlighterisotopevaluescorrespondingtodetritaldolomitematrixand162

theheaviestvalues(atright)indicativeofprecipitateddolomitecomposition.163

164

Fig.14.FA4illustratingcontrastbetweendetritalandreplacivedolomite.AandB.Paired165

transmittedlightandCLimagesrespectively.Enlargementoftheboundarybetweenadolomicrite166

lamina(below)andadetritallamina(top)ofthesamesampleasinFig.13I,J.Thedetritallayer167

showsquartz(blackinCL),feldspar(blue),adolomiteclast(brightring)whilstthedolomicrite168

showsaconsistentzonationofcrystalswithabrightcoreaswellassomefinesilt-sizedsiliciclastic169

debris.Thedolomicriteisinterpretedasanearlydiageneticreplacementofanearlycarbonate170

phase.W2,SouthOrmen,31.3m.171

172

Fig.15.FA5(CalcareousLake)inmemberW2.AllillustrateFacies5R,buttransitionstoFacies5D173

areshowninDandE.A.Thinsectionintransmittedlight.Calcareousrhythmiteswithsubordinate174

84

clasticsedimentincludingtillpellets(e.g.yellowarrows).Whiteareas,1-2mmacross,aremineral175

pseudomorphs.Reinsryggen,81m.B.Calcareousrhythmiteswithirregularlaminatopsindicative176

ofmicrobialstructureandgrowthdomesabovevuggyareaswithsyn-depositionalcalcitecements.177

Notescaleinmm.Reinsryggen,80.5m.C.Sawnandpolishedhandspecimenillustratingagrowth178

faultacrosswhichthestratigraphyofstromatoliticrhythmitelayerschanges.Notescaleincm.179

EastAndromedafjellet,30.3m–notethisisathinrhythmiteoccurrencewithindiamictite180

(supportingFig.1).D.Stainedthinsectionintransmittedlight.Dolomitedropstone(d)deforms181

underlyinglimestonerhythmiteandliesatthebaseofacoarserresedimentedlayerincluding182

limestoneintraclasts.Ditlovtoppen,108m.E.Lowerhalfofadiscrete40cmdiamictitedebrisflow183

unitwithrhythmitesdeformedbyslumpingatthebase.Numerals1cmapartontape,lowerright184

corner.Ditlovtoppen,109m(wedgingoutover100mtothesectionshowninsupportingFig.1).F.185

Stromatoliticrhythmites,alternatelypurewhiteandimpuresediment-bearinglimestone.186

Backlundtoppen-Kvitfjelletridge,77m.LocationofmicromilltraverseofGillustrated.G.Micromill187

traverseasinFillustratingasystematicshiftinδ18O,butwithinarelativelynarrowrangeof1‰,188

similartorangeofuncorrelatedvariationinδ13C.189

190

Fig.16.FA5(calcareouslake)inmembersW3andW1.AllshowFacies5Rwithvarioustransitions191

toFacies5D.A.Diamictitesoffacesassociation6becominginterlaminated(yellowarrows)with192

limestonerhythmites.Slumpfoldsinupperleft.Lenscapforscale.W3,SouthKlofjellet,116.5m.193

B.Limestonerhytmitesdevelopingslumpfoldsupwardsandtransitioningtoanintraclastic194

diamictite.W3,SouthKlofjellet,116.5m.C.Polishedhandspecimenillustratingerosional195

truncationofstromatoliticrhythmitelaminaebydiamictitewithprominentcm-scalepebbles.W3,196

SouthKlofjellet,120m.D.Thinsectionintransmittedlightofpartlybrecciatedrhythmitewith197

laminaeuptocmscalewithinterstitialice-raftedsediment.Equantwhiteareasafewmmacross198

85

aremineralpseudomorphs.W3,EastAndromedafjellet,63m.E.Slump-folded1-3mmlimestone199

rhythmitelayerswithinterstitialgreenice-raftedsediment.Scaleisincm.Thisistheonly200

precipitatedcarbonatehorizoninW1(SouthOrmen,3.5m).201

202

Fig.17.StromatoliticfabricsinFA5.A.Transmittedlight.Millimetre-scalecalcitelaminites203

separatedbythinnerice-raftedlaminaeandlocallycontainingtillpellets(P).Calcitelaminites204

displaypeloidalclotsandlocalfenestraeandhavevariablybulboustops.W2,Reinsryggen,79.8m.205

B.Transmittedlight.SimilarhorizontoC.displayingclasticlaminaoverlainbyclottedandfenestral206

microbiallaminawithbulboustop.W2,EastAndromedafjellet,13.5m.C.Stainedthinsection,207

transmittedlight.Dolomiticmicrobiallaminatecontainingdolomicriteanddolomicrosparlaminae208

andfloatingdetritus(white).Conspicuousfenestraearefilledbypink-stainedcalcite.W2,South209

Ormen,31.4m.D.Transmittedlight.W2,Reinsryggen,79.8m.Faintlyclotted(peloidal)micrite210

(examplesarrowed)andmicrosparlaminaewithinterveningcalcite-filledfenestra.Darkpatches211

aremicro-tillpellets(somearelabelledP),nowpartlysilicified.212

213

Fig.18.Crystalpseudomorphs.B-GareallFA5.A.PermianglendonitefromSouthAustralia:ikaite214

pseudmorphsthatoriginalgrewinglacimarinemudrocks.Pencilforscale.Sampleprovideby215

MalcolmWallace.B.Transmittedlightviewofinterlaminateddiamictitesandlaminated216

limestones,microbialinpart,anddisplayingtwodistincthorizonsofupward-growingcrystals.217

Crystalsinfluencesubsequentsedimentationpatternandhencegrewintothewatercolumn.W3,218

SouthKlofjellet,116.5m.C.Histogramofapparentinterfacialanglesfromthinsectionsofsamples219

showninB.Modesaremostconsistentwithanikaiteprecursor(seetext)D.Transmittedlight,220

stainedthinsectionofsamesampleasB.Pseudomorphsarecompositeofmosaicsofzoned,221

mostlyferroan(bluish)calcitecrystals.Outeredgesofcrystalshaveinpartbeendissolvedandin222

86

partsilicified.W3,SouthKlofjellet,116.5m.E.Transmittedlight.Calcite-cementedcrystal223

pseudomorphs,morphologyconsistentwithikaite,instromatoliticlimestone.W3,SouthOrmen,224

85m.F.Transmittedlight.Indistinctcalcite-cementedprobablyikaitepseudomorphs,morphology225

probablyconsistentwithikaite,instromatoliticlimestone.W2,Reinsryggen,81.2m.G.226

Transmittedlight.Dolorhythmiteshostingdolomitepseudomorphs,inferredtobeafterikaite,227

withvaryingmicrite-microspar-sparreplacivetextures.W2,NorthKlofjellet,67m.228

229

Fig.19.Wilsbonbreencrystalpseudomorphs(A)comparedwithikaitecrystals(C)and230

pseudomorphsofdifferentagesandcontexts(B,D,E).A.Polishedhandspecimen(samesample231

asFig.16B.Notesmallpinkpebbletoleftindiamictitelayeroverlyingtopcrystallayer.Crystals232

grewupwardsatthreehorizonsandweredrapedbyoverlyingsedimentsbeforebeingreplacedby233

calciteasillustratedinFigs.18Dand20A.W3,SouthKlofjellet,116.5m.B.Examplesof“thinolite”234

crystalsfromDana(1884),interpretedasikaitepseudomorphsbyShearmanetal.(1989).Scale235

notgivenintheoriginal,butcrystalsaretypicallycm-dm-scale.C.Profilesofikaitecrystals236

recoveredfromArcticseaicebypartialmelting(Nomuraetal.,2013).D.andE.ikaite237

pseudomorphsfromaPatagonianlake(Oeherlichetal.,2013).D,illustratescrystalswithequant238

habitandsteppedfacesasseenbyscanningelectronmicroscopy.E.illustratespseudomorphs239

attachedtomossfilaments.240

241

Fig.20.CalcitefabricsofFA5.A.Transmittedlight,stainedthinsection.Enlargementoftheikaite242

pseudomorphsofFig.15Ashowingreliccrystaloutlinesindarkmicriteandreplacivecalcite243

(micro-)sparmosaicofzonedeuhedralnon-ferroancalciteovergrowthbyferroancalcite.W3,244

SouthKlofjellet,116.5m.B.Pairedtransmittedlight(left)andCL(right)images.Fenestral245

microbialfabricsimilartoFig.17Ddisplayingconsistentcrystalzonation:brightertodullerin246

87

micriticmatrixandsharperzoneswithinfenestralcements.Fabricisconsistenteitherwithprimary247

calcitegrowthwithinextracellularpolymericsubstanceorreplacementofikaite,followedby248

cementationoffenestrae.W2,Reinsryggen,80.6m.249

250

Fig.21.Vertical(upward)faciestransitionsinmemberW2.ForthispurposeFA1andFA7are251

conflated.Thewidthofthearrowsisproportionaltothenumberoftransitionsminusone.The252

transitionmatrixshowninsupportingFig.8indicatesthatatleastoneverticaltransitionoccurs253

betweeneachofthefaciesassociationsexceptFA1.Seetextfordiscussion.254

255

Fig.22.Relativethicknessofstratabelongingtothedifferentfaciesassociationsinthefive256

sectionswithcomparablythickcarbonatefaciespreservedinW2,fromsouthtonorth.Seetextfor257

discussionandabbreviationsinFig.1.258

259

Fig.23.Diagrammaticsummaryoftheprocessesresponsibleforvariationinisotopecomposition260

oftheWilsobreencarbonateand,interpretationsoftheirparageneseswith(atbase)acartoon261

environmentalprofile.LargenumbersrefertoFaciesAssociations2to5.262

263

N.B.SupportingInformationissuppliedasafree-standingpdfandanExceldocument;supporting264

figurecaptionsarenotrepeatedhere.265

266