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Trilobite Extinctions, Facies Changes and the ROECE Carbon Trilobite Extinctions, Facies Changes and the ROECE Carbon

Isotope Excursion at the Cambrian Series 2–3 Boundary, Great Isotope Excursion at the Cambrian Series 2–3 Boundary, Great

Basin, Western USA Basin, Western USA

Luke E. Faggetter University of Leeds

Paul B. Wignall University of Leeds

Sara B. Pruss Smith College, spruss@smith.edu

Robert J. Newton University of Leeds

Yadong Sun Friedrich-Alexander-Universität Erlangen-Nürnberg

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Recommended Citation Recommended Citation Faggetter, Luke E.; Wignall, Paul B.; Pruss, Sara B.; Newton, Robert J.; Sun, Yadong; and Crowley, Stephen F., "Trilobite Extinctions, Facies Changes and the ROECE Carbon Isotope Excursion at the Cambrian Series 2–3 Boundary, Great Basin, Western USA" (2017). Geosciences: Faculty Publications, Smith College, Northampton, MA. https://scholarworks.smith.edu/geo_facpubs/121

This Article has been accepted for inclusion in Geosciences: Faculty Publications by an authorized administrator of Smith ScholarWorks. For more information, please contact scholarworks@smith.edu

Authors Authors Luke E. Faggetter, Paul B. Wignall, Sara B. Pruss, Robert J. Newton, Yadong Sun, and Stephen F. Crowley

This article is available at Smith ScholarWorks: https://scholarworks.smith.edu/geo_facpubs/121

1

Trilobiteextinctions,facieschangesandtheROECEcarbonisotopeexcursionatthe1

CambrianSeries2-3boundary,GreatBasin,westernUSA.2

Faggetter,LukeE.a;Wignall,PaulB.

a;Pruss,SaraB.

b;Newton,RobertJ.

a;Sun,Yadong

c;Crowley,3

Stephend;4

aTheSchoolofEarthandEnvironment,theUniversityofLeeds,Leeds,WestYorkshire,LS29JT,5

UnitedKingdom.ee08lef@leeds.ac.uk;P.B.Wignall@leeds.ac.uk;r.j.newton@leeds.ac.uk;b6

DepartmentofGeosciences,SmithCollege,Northampton,MA01063,UnitedStates.7

spruss@smith.edu;cSchoolofGeographyandEarthSciences,Friedrich-AlexanderUniversity8

Erlangen-Nürnberg,Schloßgarten5,91054Erlangen,Germany.yadong.sun@cug.edu.cn;dSchoolof9

EnvironmentalSciences,UniversityofLiverpool,JaneHerdmanBuilding,LiverpoolL693GP,United10

Kingdom.sfcrow@liverpool.ac.uk.11

Correspondingauthor:LukeFaggetter,ee08lef@leeds.ac.uk.12

13

Abstract14

ThemassextinctionoftheolenellidtrilobitesoccurredaroundtheCambrianSeries2-Series315

boundary.Likemanyothercrises,itcoincidedwithanegativecarbonisotopeexcursionbutthe16

associatedpalaeoenvironmentalchangesremainunclear.Toinvestigatethecausalmechanismfor17

thisevent,wereportfacieschanges,pyriteframboidpetrographyandcarbonisotopevaluesfrom18

CambrianSeries2-Series3(traditionallyEarly-MiddleCambrian)boundarystrataoftheCarrara19

Formation(DeathValleyregion,California)andPiocheFormation(Nevada).Thesedatareveal20

regionallychangingwaterdepthsfromhigh-energy,nearshorefacies(ooliticgrainstone)tomore21

offshoresiltymarlandfiner-grainedcarbonatemudstone.IntheCarraraFormation,theseries22

boundaryoccurswithinadeepeningsuccession,transitioningfromhigh-energy,nearshorefacies23

(ooliticgrainstoneandoncoliticpackstone)tooffshoremarl,thelatterofwhichcontainspyrite24

2

framboidpopulationsindicativeoflow-oxygen(dysoxic)depositionalconditions.Intermittent25

dysoxiapersistedbelowsub-wavebasesettingsthroughouttheearlyandmiddleCambrian,butdid26

notintensifyatthetimeofextinction,arguingagainstanoxiaasaprimarycauseintheolenellid27

trilobiteextinction.Withinbothfieldareas,theextinctionintervalcoincidedwithaminimumin28

d13Ccarbvalues,whichweinterpretastheregionalmanifestationoftheRedlichiid-OlenellidExtinction29

CarbonisotopeExcursion(ROECE).TheSeries2-Series3boundaryisreportedtocloselycoincide30

withalarge-amplitudesea-levelfallthatproducedtheSaukI/IIsequenceboundary,butthe31

placementoftheSeries2-Series3boundarywithinatransgressiveintervaloftheCarrara32

Formationshowsthatthisisnotthecase.Themainsequenceboundaryinthesuccessionoccurs33

muchlowerinthesuccession(atthetopoftheZabriskieQuartzite)andthereforeprecedesthe34

extinctionoftheolenellidsandROECE.35

Keywords:Olenellidextinction,CarraraFormation,PyramidShaleMember,PiocheFormation,C-36

ShaleMember37

38

1.! Introduction39

ThefirstmajorbioticcrisisofthePhanerozoicoccurredduringtheCambrianSeries2,an40

intervalthatsawthecollapseofarchaeocyathanreefs(Newell,1972;Boucot,1990;Debrenne,1991;41

ZhuravlevandWood,1996).Thiswasfollowed,attheSeries2-Series3boundary,bysevere42

generic-levellossesofolenellidandredlichiidtrilobites(Palmer,1998;Zhuetal.,2004;Zhuetal.,43

2006;Fanetal.,2011;Wangetal.,2011;Zhangetal.,2013).Thistrilobiteextinctionhasbeenused44

todelineatetheSeries2-Series3boundary;however,theboundaryremainsunratifiedas45

internationalcorrelationisconfoundedbyalackofglobally-distributedtaxaatthistime(Sundberg46

etal.,2016).Thetrilobiteextinctioncoincideswithamajornegativeδ13Cexcursionthathasbeen47

termedtheRedlichiid-OlenellidExtinctionCarbonIsotopeExcursionorROECE(Zhuetal.2004,48

2006).49

3

InthewesternGreatBasinoftheUnitedStates,aCambriansedimentarysuccession50

developedonarapidlysubsidingpassivemargin(Prave,1999;Stewart,1972;FedoandCooper,51

2001;Hoganetal.,2011;Kelleretal.,2012;Morgan,2012).SectionsinthesouthernNopahRanges52

(Kelleretal.,2012)exposestratafromCambrianSaukIandSaukIIsupersequencesthatareof53

importancetothisstudy(Prave,1991).Thesearewidespread,large-scaleLaurentiansequencesthat54

providearegionalstratigraphicframework.ThetransitionfromSaukItoSaukIIrecordsamajor55

lithologicalchangethatsawthesiliciclasticdepositionoftheZabriskieQuartzitereplacedby56

carbonatedepositionoftheCarraraFormation(Kelleretal.,2012;Morgan,2012).Thecontact57

betweenthesetwounitsisconsideredtobetheSaukI/IIsequenceboundary(Kelleretal.,2012;58

Morgan,2012).59

ThroughoutthePhanerozoictherelationshipbetweenenvironmentalperturbationand60

extinctionisacommonfocusofstudies,includingthoseintheCambrian(HallamandWignall,1997;61

Wignall,2015).Inparticular,sea-levelchange,marineanoxia,carbonisotopeexcursionsand62

eruptionsofLIPs(largeigneousprovinces)oftencoincidewithmassextinctions(Zhuravlevand63

Wood,1996;Wignall,2001;GlassandPhillips,2006;Jourdanetal.,2014).Thus,Zhuravlevand64

Wood(1996)notedthetemporallinkbetweenwidespreaddepositionofblackshalesandthe65

disappearanceofthearchaeocyathansintheCambrianofSiberia,andtrilobiteextinctionsat66

“biomere”boundariesarealsoascribedtodysoxia(Palmer,1984).However,theroleofanoxiain67

Cambrianextinctionshastobeviewedinthecontextofpersistentlyoxygen-restrictedoceansatthis68

time(e.g.Montañezetal.,2000;Hurtgenetal.,2009;Prussetal.,2010;Gilletal.,2011;Saltzmanet69

al.,2015;Tarhanetal.,2015).70

VolcanismmayalsohaveplayedaroleinROECE(GlassandPhillips,2006).TheKalkarindji71

LIPisaCambrianfloodbasaltprovinceofnorthernandcentralAustraliawithanestimatedoriginal72

surfaceareaof~2.1x106km

2(GlassandPhillips,2006;Jourdanetal.,2014;Marshalletal.,2016).73

4

Latestdatingeffortsyieldazirconageof510.7±0.6Ma,whichisclosetothatoftheCambrian74

Series2-Series3boundary(Jourdanetal.,2014).75

InordertoimproveourunderstandingoftheeventsassociatedwithROECE,thisstudy76

examinessectionsspanningtheCambrianSeries2-Series3boundaryintervalinthewesternGreat77

Basin.TheolenellidextinctionhorizonhasbeenlocatedwithinthePiocheFormationinNevada78

(Palmer,1998).WehaveexaminedthislevelandthecorrelativelevelsintheCarraraFormationin79

Californiainordertheexaminechangesoflithofacies,carbonisotopevariabilityandpyrite80

petrography.81

82

2.! Geologicalbackgroundandbiostratigraphy83

FollowingbreakupoftheRodiniasupercontinentinthelateNeoproterozoic,the84

northwesternmarginofLaurentiasubsidedrapidly(BondandKominz,1984;LevyandChristie-Blick,85

1991;Prave,1999;Howleyetal.,2006).BytheearlyCambrian,thewesternGreatBasin(USA)was86

positionedalongthewesternmarginofLaurentiawhereawide,clastic-dominatedshelfdeveloped87

inanequatorialsetting(PalmerandHalley,1979;MacNiocaillandSmethurst,1994;Fig.1).Clastic88

inputdecreasedinlateSeries2andwasreplacedbycarbonatedeposition(ErdtmannandMiller,89

1981;Howleyetal.,2006;Landing,2012).90

WehaveassessedenvironmentalconditionsacrosstheSeries2-Series3boundaryfrom91

sectionsintheGreatBasinincludingEmigrantPass(NopahRange,DeathValley,easternCalifornia),92

andOakSpringsSummit(BurntSpringsRange,easternNevada;Fig.1).Theregionallithostratigraphy93

ofthePiocheFormation(atOakSpringsSummit)wasdescribedindetailbyMerriamandPalmer94

(1964),andtheCarraraFormation(atEmigrantPass)byPalmerandHalley(1979).Inaddition,we95

examinedasectionofthePiocheFormationatRuinWashineasternNevada.96

97

5

2.1.EmigrantPass98

AtEmigrantPasstheZabriskieQuartziteandCarraraFormationareeasilyaccessibleand99

wellexposed.ThestrataareseenonthenorthsideofOldSpanishTrailHighwayasacontinuous100

sectionofquartzareniteandshaleformingslopesandmoderatelysteephillsideswithlimestone101

formingprominentledges(Figs.1and2).TheZabriskieQuartziteisdominatedbyburrowedand102

hummockycross-beddedquartzarenitebeds(Prave,1991;Kelleretal.,2012).Itlacksage-diagnostic103

fossils,butrocksimmediatelyaboveandbelowhaveyieldedfaunafromtheBonnia-Olenellus104

trilobitezoneofSeries2(Diehl,1974;PalmerandHalley,1979;Prave,1991;Pengetal.,2012).105

TheCarraraFormationcomprisescyclesofsiltymarlandlimestonewithatrilobitefauna106

spanningtheBonnia-OlenellustotheGlossopleurazones,andthustheSeries2-Series3boundary107

(Adams,1995;PalmerandHalley,1979;SundbergandMcCollum,2000;Babcocketal.,2012;Keller108

etal.,2012;Fig.3).TheunithasbeendividedintoninemembersinthewesternGreatBasin:Eagle109

MountainShale,ThimbleLimestone,EchoShale,GoldAceLimestone,PyramidShale,RedPass110

Limestone,PahrumpHillsShale,JangleLimestoneandtheDesertRangeLimestone(Palmerand111

Halley,1979).However,thereissignificantlateralvariationwithintheCarraraFormationandat112

EmigrantPass,theThimbleLimestoneisnotpresent(PalmerandHalley,1979;Adamsand113

Grotzinger,1996).OverallthecarbonatecontentoftheCarraraFormationdecreasesinmore114

basinwardsettingstothewest(Hoganetal.,2011;Kelleretal.,2012;Foster,2014).Withinthe115

CarraraFormationatEmigrantPass,fivemembersareimportanttothisstudy.116

TheEagleMountainShaleMemberconsistsofgreentogrey-brownsiltyshalewith117

interbeddedlensesandbedsofbioclasticlimestonedevelopedtowardsthetop(PalmerandHalley,118

1979).ThisisoverlainbytheEchoShaleMemberwhichconsistsofgreen,platyshaleandbrown-119

orangelimestone.TheEchoShaleiscorrelatedwiththebasalCombinedMetalsMemberofthe120

PiocheFormationineasternNevada(PalmerandHalley,1979).ThesucceedingGoldAceLimestone121

isaprominent,cliff-forminglimestone(CornwallandKleinhampl,1961).Thestrataincludethinto122

6

medium-beddedlimemudstone,withdolomiticbedsandoncoliticlimestone(PalmerandHalley,123

1979).Basedonsharedtrilobitezones,theGoldAceLimestonecorrelateswiththeCombined124

MetalsMemberofthePiocheFormationatOakSpringsSummit(MerriamandPalmer,1964).125

TheoverlyingPyramidShaleMemberisagreenshalewithinterbedsofbrownandmaroon126

siltymarlandlensesofoncoliticandbioclasticlimestone.Trilobitebiostratigraphyindicatesthe127

PyramidShaleisequivalenttotwomembersofthePiocheFormationineasternNevada:theC-Shale128

MemberandtheSusanDusterLimestoneMember(PalmerandHalley,1979;Palmer,1998).TheRed129

PassLimestoneMemberistheyoungestunitexaminedinDeathValley.Itformsprominentcliffsof130

oncoliticandbioclasticlimestone,laminatedlimemudstoneandfenestrallimemudstone(Palmer131

andHalley,1979).ThereisnoequivalentlimestoneunitinthePiocheFormationofNevada(Palmer132

andHalley,1979).133

134

2.2.OakSpringsSummit135

AtOakSpringsSummit,thePiocheFormationcropsouttothewestofaparkingareainadry136

riverbed.Limestoneformsmoreprominentledgesandplatformswhilstshaleformsrecessively137

weatheredoutcrop(Figs.1and2).TheCombinedMetalsMemberiscomposedofsilty,oncolite-138

bearingdarklimestonewithOlenellus(Palmer,1998;SundbergandMcCollum,2000;Hollingsworth139

etal.,2011).ItisoverlainbytheC-ShaleMember(formerlytheCometShale),aseriesofshaleand140

thin-beddedlimestonebedswithpinch-and-swellbedboundaries(Palmer,1998;Sundbergand141

McCollum,2000).TheSeries2-Series3boundaryisplacedatthebaseoftheC-Shaleduetothe142

suddendisappearanceoftheOlenellidae,andtheirreplacementbyafaunadominatedby143

Eoptychopariapiochensisatthislevel(Palmer,1998;SundbergandMcCollum,2000).The144

succeedingSusanDusterLimestoneMemberisawell-bedded,greymarlwithoccasionalargillaceous145

andbioclasticlimestonebedscomposedoftrilobitefragments(MerriamandPalmer,1964).146

147

7

2.3.Biostratigraphy148

TrilobiteassemblagesfromtheCarraraandPiocheformationsbelongtotheOlenellus,149

Eokochaspisnodosa,AmecephalusarrojosensisandthePlagiura-Poliellazonesthatprovidea150

frameworkforregionalcorrelation(MerriamandPalmer,1964;PalmerandHalley,1979;Fig.3).The151

OlenellusZonerangesfromtheZabriskieQuartzitetothebasalportionofthePyramidShale152

MemberwithinDeathValley(PalmerandHalley,1979;Fig.2).InNevada,thiszonespansthe153

DelamarMembertothebaseoftheC-Shale(MerriamandPalmer,1964;SundbergandMcCollum,154

2000).Allolenellidtrilobitesdisappearovera~2cmintervalatthetopofthezone,forminga155

distinctextinctionhorizon(Palmer,1998;Fig.2).Thisisimmediatelyfollowedbyfirstappearanceof156

theptychopariidtrilobiteEokochaspisnodosa,whichdefinesboththebaseoftheE.nodosaZone,157

andtheSeries2-Series3boundary(SundbergandMcCollum,2000;Fig.2).E.nodosaZonefaunas158

alsooccurinthePyramidShaleMemberinDeathValley(SundbergandMcCollum,2000).159

ThesucceedingAmocephalusarrojosensisZonecontainsA.arrojosensis,Mexicellarobusta160

andKochina?walcotti.ThezoneisbestdefinedatHiddenValley,Nevada,whereitsbaseis30m161

abovethebaseoftheC-ShaleMember(MerriamandPalmer,1964),butithasnotbeenrecordedin162

theCarraraFormationduetoapaucityoffossilsabovetheE.nodosoaZoneinthePyramidShale163

(PalmerandHalley,1979).However,trilobites,fromthePlagiura-PoliellaZone,reappearinthe164

uppermostPyramidShaleandlowerRedPassLimestone(PalmerandHalley,1979).165

166

3.Methods167

SedimentaryloggingoftheCarraraandPiocheformationswasundertaken.AtEmigrant168

Pass,170moftheCarraraFormationwasloggedfromthebaseoftheformation(atthecontactwith169

theZabriskieQuartzite)uptotheRedPassLimestoneMember.AtOakSpringsSummita53m-thick170

sectionofthePiocheFormationwaslogged,rangingfromthebasalCombinedMetalsMemberto171

SusanDusterLimestoneMember,anintervalcorrelativewiththeEmigrantPasssectionbasedon172

8

trilobitebiostratigraphy(MerriamandPalmer,1964;PalmerandHalley,1979;Fig.2).Fromthese173

logs,fourfaciesweredefined(discussedbelow,Table1).Atthetwostudysections,30samplesfrom174

thePiocheFormationand57samplesfromtheCarraraFormationwereanalysedforδ13Ccarb(Table175

2).InLincolnCounty,Nevada,wealsosampledtheRuinWashlocation(Palmer,1998;Lieberman,176

2003)foradditionalfaciesandframboidanalysis.RuinWashprovidedasecondsection(afterOak177

SpringsSummit)wheretheextinctionhorizonoftheolenellidsisclearlyseen(seeSupplementary178

Material,Fig.S1).Faciesanalysiswasundertakeninthefieldandcomplementedbypetrographic179

examinationof49thinsections.Inordertoevaluateredoxconditions,pyriteframboidsize180

distributionwasalsoassessedon21samplesusingascanningelectronmicroscope(FEIQuanta650181

FEG-ESEM)inbackscattermode(seeBondandWignall(2010)forprocedure).182

Thecalcitecarbon(13C/

12C)andoxygen(

18O/

16O)isotopevaluesofpowderedbulk183

sedimentsamplesweremeasuredonatotalof98samplesattheGeoZentrumNordbayern,FAU184

Erlangen-Nurnberg,Germany(27samples)andtheSchoolofEnvironmentalSciences,Universityof185

Liverpool,UK(71samples).Carbondioxidewaspreparedbyreactionwithphosphoricacideitherat186

70oCusingaGasbenchIIpreparationsystem(FAU)orat25

oCusingtheclassical,‘sealedvessel’187

method(UoL).MassratiosoftheresultantpurifiedgasesweremeasuredwithaThermoFisherDelta188

Vplusmassspectrometeroperatingincontinuousflowmode(FAU)oraVGSIRA10dual-inletmass189

spectrometer(UoL).Rawgasdatawerecorrectedfor17OeffectsandcalibratedtotheVPDBscale190

usingacombinationofinternationalreferencematerials(δ13Cvaluesareassignedas+1.95‰to191

NBS19and–46.6‰toLSVECandδ18Ovaluesof–2.20‰toNBS19and–23.2‰toNBS18)and192

laboratoryqualitycontrolmaterialsandreportedasconventionaldelta(d)values.Analytical193

precision(1σ)isestimatedtobebetterthan0.1‰forbothisotoperatiosbasedonreplicate194

analysisofstandards.Somenotabledifferencesinoxygenisotopevalueswerereportedwhere195

specificsampleswereduplicatedbybothlaboratories.Thereasonforthesedifferencesisuncertain.196

Althoughsomediscrepancieswerefoundtobesignificant,theydonotimpactoneitherthe197

palaeoenvironmentalorchemostratigraphicinterpretationofthecarbonisotopedata.198

9

Thetopmost8samplesoftheCarraraFormationwereanalysedattheUniversityof199

Massachusetts,Amherst.Powdered,homogenizedsampleswereanalysedforδ13Ccarbandδ

18Ocarb200

valuesusingaFinniganDeltaXL+isotoperatiomassspectrometerwithanautomatedcarbonate201

prepsystem(KielIII).WereportresultsasthepermilledifferencebetweensampleandtheVPDB202

standardindeltanotationwhereδ18Oorδ

13C=(Rsample/Rstandard−1)!1000,andRistheratioofthe203

minortothemajorisotope.Resultswerecalibratedusingahousestandard(crushed,washedand204

sievedmarble)withVPDBvaluesof+1.28forδ13C‰and–8.48‰forδ

18O.Reproducibilityof205

standardmaterialsis0.1‰forδ18Oand0.05‰forδ

13C.206

Totalcarbon(TC)andtotalorganiccarbon(TOC),followingremovalofcalcitebyacid207

decompositionofbulksedimentsamples,wasmeasuredusingaLECOSC-144DRDualRangecarbon208

andsulphuranalyserattheUniversityofLeeds.Totalinorganiccarbon(TIC)wassubsequently209

calculatedbydifference(TIC=TC-TOC).Anestimateofthecalcitecontentforeachsamplewas210

madebyassumingthatallTICishostedbycalcite(wt%calcite=TICx8.333).211

212

4.Results213

4.1.FaciesAnalysis214

Fourfaciesandninesub-facieswereidentified(Table1):grainstone,packstone,siltymarl215

andmarlandtheyhavebeengroupedintoanonshore-offshoretrendspanningshallowsubtidalto216

outershelfenvironments(Table1).Theshalloweststrataconsistofgrainstonefacieswithcommon217

shellhashthatisoftenabraded.Bedsaretypicallydecimetresthickandcanshowahummockytop218

surfaceandsharp,erosivebases.Inclinedstacksofflat-pebbleintraclastswithherringbone-likecross219

stratificationarepresent,suggestingstormwaveprocesses(Fig.4D).Bioturbatedpackstone,with220

sub-faciesofoncolitic,bioclasticandsiltypackstonevarieties(Fig.5B),areinterpretedtobea221

deeperfaciesbasedonthepresenceofamicriticmudmatrix.Deeperwatersiltymarlincludefissile,222

homogenousandthoroughlybioturbatedvariants.Deepest-water,mostoffshoresuccessionsare223

10

dominatedbyfinegrainedmarl,includingsub-faciesoflaminated,pyriticdolomicriteand224

bioturbatedmarlwithichnofabricindex(II)valuesof2-3(II2andII3)intheschemeofDroserand225

Bottjer(1986).!226

Thefaciesdistributionrevealsconsistenttrendsinthetwoprincipalstudysections.Thebaseof227

theCarraraFormation,seenatEmigrantPass,isdominatedbydeeperwaterfacies(Facies4)ofthe228

EagleMountainShale.Commonly,themarlhasagrey-greencolourproducedbytheabundanceof229

chloriteandclinochloreinthematrix(Figs.4F,5Aand6E).Laminatedintervalsarecommon,230

althoughtheseoccurinterbeddedwithburrowedstratasuggestingtherewerefrequentfluctuations231

ofredoxconditions.232

Theexceptiontothegenerallyquiet,low-energydepositionoftheEagleMountainShaleis233

recordedbyasharp,erosive-basedbedofFacies1developedjustover30mabovethebaseofthe234

section.Thisshelly,oncoliticpackstonecontainsrip-upclastsoftheunderlyingmarlandsolemarks235

onitsbase(Fig.7A).Internally,thinintraclastsandshellsdisplayachevron-stackingpattern(Fig.236

4D).Amajorstormeventseemslikelytohaveproducedthishorizonwiththeshell-stacking237

producedbypowerfulbi-directionalcurrents.ThesucceedingEchoShaleandGoldAcemembers238

recordshallowing.Grainstoneandpackstonedominatethis20-m-thickintervalwhichincludes239

erosive-basedoncoliticpackstonebeds(Fig.7B).AbovethisinthePyramidShaleMembermarl240

faciesdominate,takentobeindicativeofasustaineddeepening.Grainstoneandpackstonefacies241

developedinthelower~15mofthememberareinterpretedtohavebeentransportedduring242

stormevents.ItiswithinthistransgressivephasethattheSeries2-Series3boundaryisrecorded,243

alongwiththeolenellidextinction(Foster,2014).Deep-watersedimentationisabruptlyterminated244

bythedevelopmentofshallow-watergrainstoneatthebaseoftheRedPassLimestoneMember245

(Fig.7).Ooidsandabradedfossilmaterial(Table1,Sub-Facies1.1)suggestanearshoresetting.246

ThePiocheFormationatOakSpringsSummitrecordsamoredistalversionofthesuccession247

seenwithintheCarraraFormationwithrelativelydeep-waterFacies3and4dominating(Fig.2),248

11

thoughthesameoveralldeepening-upwardstrendisseen.Thus,thelowerhalfoftheCombined249

MetalsMemberconsistsofalternatingsiltymarlandpackstone.Abovethis,theremainderofthe250

sectionisdominatedbydeeper-waterfacies(Fig.2).TheuppermostCombinedMetalsMemberand251

themajorityoftheC-ShaleMemberrecordasimilartransgressivedeepeningseenwithinthe252

PyramidShaleMemberoftheCarraraFormation.Theolenellidextinctionleveloccurswithinthis253

transgressivesuccessionbetweenamarlandasiltymarlinthebaseoftheC-ShaleMember(Fig.4E).254

Thisminorfaciesshiftdoesnotrepresentasignificantlydifferentenvironmentandassuch255

extinctionisnotthoughttobeafunctionoffacieschange.Immediatelyabovetheextinction256

horizon,chloriteintheformofbothroundedgrainsandcementbecomescommon(Fig.5A).The257

remainderoftheC-ShaleMemberisathickpackageofmarlthattransitionstosiltymarlatthebase258

oftheSusanDusterLimestone.259

260

4.2.PyriteFramboidAnalysis261

FramboidsizeanalysiswasperformedontheSeries2-Series3boundarystrata(andthus262

theextinctionhorizon)fromthePiocheFormationatOakSpringsSummit,where11sampleswere263

collectedina7mintervalspanning3.5meithersideoftheextinctionhorizon.Allsamplescontained264

abundantscatteredcrystalsofpyriteranginginsizefrom1-10µm,oftenfoundagglomeratedin265

clusteredpatches.Fivesamplesyieldedframboidspreservedasironoxyhydroxidesdueto266

weathering,withonlyminoramountsoforiginalpyritepreservedintheircore.Theframboids267

showedasizedistributionspanningananoxic-dysoxicrange(Fig.8).Themostdysoxicsample268

(smallestmeanframboiddiametersizeandsizerange,loweststandarddeviation)occurredinamarl269

approximately1mbelowtheextinctionhorizon.Dysoxicframboidpopulationsalsooccurredinthe270

1mofstrataoverlyingtheextinctionlevel.However,asamplefrom20cmbelowtheextinction271

leveldidnotyieldanypyriteframboidssuggestingfullyoxygenatedconditions.Thisvariabledegree272

12

ofoxygen-restrictionsuggestedbytheframboidanalysisisalsoseeninthevariabilityofthe273

associatedsedimentaryfabrics,whichvariesfromlaminatedtoslightlyburrowed(II2).!274

SevensampleswerealsoanalysedfromthePiocheFormationatRuinWashwherethe275

olenellidextinctionhorizonhasbeenlocatedwithinasuccessionofmarls(Palmer,1998;Lieberman,276

2003;Fig.S1).Generally,framboidalpyritewasabsentatthislocationwiththeexceptionoftwo277

samplesfrom10and15cmbelowtheextinctionhorizonwheretheyhadsizerangesthatplotinthe278

anoxicfield(Fig.8).AnadditionalfoursamplesfromaroundtheextinctionhorizonatEmigrantPass279

werealsoanalysed.Inthiscase,allsamplesonlyyieldedscatteredpyritecrystalsbutnotframboids,280

suggestingbetteroxygenatedconditionsinthisshallower-watersection.281

!282

4.3.Chemostratigraphy283

Inthebasal20moftheCarraraFormationδ13Cvaluesarehighlyvariableanddonotshowa284

cleartrend(Fig.7),buttheythenbegintostabilisearound–2‰beforeaconsistentpositivetrend285

develops.InthePyramidShaleMemberthebaseofthenegativeexcursionbeginswithat–0.1‰,286

abovethisδ13Ccarbvaluesbeginadeclinetoalowpointat105mof–3.5‰(anegativeshiftof3.4287

‰).Intheoverlying25m,nodatawasobtainedbecausecarbonatevaluesweretoolowfor288

analysis.Abovethisgap,δ13Ccarbvaluesshowapositivetrend,returningtovaluesaround–0.1‰,289

similartothosefromthebaseofthesection.290

Barringoneoutlieratthebaseofthesection,δ13Ccarbvaluesfromthefirst13mofthe291

PiocheFormationremainaround–2.5‰beforethereisasharp,positiveshiftto–1.0‰overthe292

next15m(Fig.7).Fromthisvalueof–1.0‰anegativeshiftoccurs,resultinginpeaknegative293

valuesof–4.8‰.ThenadiratthebaseoftheC-ShaleMembermarksanoverallshiftof–3.8‰,a294

similarsizetothatfoundatEmigrantPass.Atthetopofthesectionvaluesreturntoaround0‰.295

296

13

5.Discussion297

5.1.Carbonisotopesanddiagenesis298

Inordertoevaluatethereliabilityofourisotopedataweassessthepreservationofa299

primarycarbonisotopesignalinoursamples.InboththeCarraraandPiocheformationstheisotope300

analysesarederivedfromsampleswithawiderangeofcarbonatevalues(Table2).ThehighTIC301

samplesarelikelytorecordprimarycarbonisotopesignaturessincetheyarebufferedfromexternal302

changebyalargecarbonate-carbonreservoir(SaltzmanandThomas,2012).LowerTICsamplesare303

moresusceptibletopostdepositionalisotopicalterationoradditionofcarbonatewithanon-304

primarycarbonisotopecomposition(BrandandVeizer,1981;BannerandHanson,1990;Marshall,305

1992).Inbothsections,theexcursiontothelowestδ13Ccarbvaluesoccursatthelevelofthetrilobite306

extinction(mid-PyramidShale,CarraraFormationandbasalC-Shale,PiocheFormation)whereTICis307

<2wt.%.Hereweassessthepreservationofaprimarycarbonisotopecomposition,particularlyin308

sampleswithlowTIC.309

Twodiageneticprocessescanaltertheprimaryisotopiccomposition:recrystallizationof310

carbonateorprecipitationofadditionalauthigeniccarbonatewithadistinctisotopecomposition311

(Marshall,1992).Bothmarineporefluidsandmeteoricwaterscanhavedissolvedinorganiccarbon312

(DIC)enrichedin12Cfromtheoxidationoforganicmatterandthesemechanismshavediffering313

predictionsoftheδ13Ccarbandδ

18Ocarbvaluespreserved(Marshall,1992).BoththeCarraraand314

Piocheformationsdisplaycommonalitiesintheirrelationshipsbetweentheirδ13Ccarbandδ

18Ocarb315

ratiosandtheirTICandTOCconcentrations.Firstly(point1),neitherformationshowsaclear316

relationshipbetweenδ13Ccarbandδ

18Ocarb(Figs.S2andS3).Secondly(point2),sampleswiththemost317

negativeδ13Ccarbandthemostpositiveδ

18OcarbaremostlycharacterisedbylowTIC(definedas<2318

wt.%).BoththeCarraraandPiocheformationsexhibitgenerallylowTOC(point3).IntheCarrara319

FormationTOCconcentrationsrangefrom5.17to0.0wt.%TOCwithameanconcentrationof0.14320

wt.%TOC.InthePiocheFormationconcentrationsrangefrom2.69to0.0wt.%TOC,withameanof321

14

0.12wt.%TOC.Finally(point4),highTOCsamplesarecharacterisedbymorepositiveδ13Ccarb.The322

majordifferencebetweenthesectionsfortheseparametersisamuchclearerpositiverelationship323

betweenTICandδ13CcarbwithinthePiocheFormation.324

Theseobservationsruleoutwholesalerecrystallizationinameteoricfluidsinceneither325

sectiondisplaysapositivecorrelationbetweenδ18Ocarbandδ

13Ccarb(point1,Figs.S2andS3).The326

generallylowTOCconcentrationsandtherelationshipbetweenTOCandδ13Ccarb(point3and4)also327

makeslocalisedprecipitationoforganic-carbonderivedDICdoubtful.Fromtherelationships328

betweenδ18OcarbandTIC(point2)itislikelythataproportionofthelowTICsamples(<2wt.%)329

haveundergonevariableresettingoftheirδ18Ocarbtowardsmorepositivevalues.Thisobservationis330

notconsistentwithprecipitationofadditionalcarbonatefromunmodifiedmeteoricormarineearly331

diageneticporefluids,wheretheexpectationwouldbeachangetowardsmorenegativeδ18Ocarb332

values(Marshall,1992;KnauthandKennedy,2009;Cochranetal.,2010;SaltzmanandThomas,333

2012).Theremainingpossibilitytoexplaintheoxygenisotoperelationshipsisvariableexchange334

with,orprecipitationofcarbonatefrom,ahypotheticalhighδ18Ofluid(GlumacandWalker,1998).335

Sincetheclimateatbothsitesiscurrentlyarid,onepossibilityisthatthefluidinquestionisderived336

fromevaporatedmodernmeteoricwater,butotherpossibilitiesexist(SaltzmanandThomas,2012).337

Therelationshipsbetweenδ13CcarbandTICdiffersomewhatfromthosebetweenδ

18Ocarband338

TIC:fromtheCarraraFormation,therangeofδ13Ccarbinthe<2wt.%TICsamplesoverlapsstrongly339

withtherangefoundinnearpurelimestonesamplessuggestingthattheinfluenceofdiagenetic340

processonδ13Ccarbatthissiteislikelytobeminimal(Fig.S4).Incontrast,samplesfromthePioche341

Formationdisplayamuchclearerdivisionbetweenthesetwogroups(TICgroupsannotatedinFig.342

S5).Thissuggeststhattheinfluenceofpost-depositionalprocessonδ13Ccarbmayhavebeenmore343

pronouncedatthissite.However,theδ18OcarbrangesofbothhighandlowTICsamplesofthePioche344

Formationoverlap(Fig.S6),indicatingthatatleastsomeofthecarbonisotopevalueshave345

undergoneminimalresetting.346

15

Insummary,thereisclearevidenceforavariabledegreeofoxygenisotoperesetting347

towardsmorepositivevalues,whichisparticularlypronouncedinsampleswithlowTIC(<2wt.%).348

Thereisalsosomeevidenceofconcurrentvariableresettingofcarbonisotopestomorenegative349

valuesinlowTICsamples,withthisbeingsomewhatmorepronouncedinthePiocheFormation.350

Nonetheless,thepresenceofthenegativeδ13Ccarbvaluesandtheconsistencyofthemagnitudeof351

theexcursionatleveloftheSeries2-Series3boundary(e.g.,Zhuetal.,2006;Faggetteretal.,352

2016),correlatedindependentlybybiostratigraphybetweenthetwosectionssuggestthatthese353

samplesrecordapredominantlyprimarysignal.Assuch,weconcludethatthenegativeδ13Ccarb354

excursionwithintheCarraraandPiocheformationspreservesaprimaryrecord,givenitsco-355

occurrencewiththeolenellidextinctionhorizon,weinterpretittobeROECE.356

357

5.2.Extinctionandpalaeoenvironmentalchange358

IdentificationoftheROECEinthePiocheandCarraraformations(Fig.7)confirmstheclose359

temporalrelationshipbetweentrilobiteextinctionsandcarbonisotopeexcursions(Zhuetal.,2006;360

Faggetteretal.,2016).Italsoallowsexaminationoftheassociatedfaciesandrelativesea-level361

changesatthistime.InitiallytheSaukI/IIsupersequenceboundarywasplacedaroundtheSeries2-362

Series3boundary(Sloss1963).However,morerecentlythishasbeenplacedlowerinthesuccession363

atthetopoftheZabriskieQuartzite,underlyingtheCarraraFormation(Prave,1991).Thusthe364

CarraraFormationfallsentirelywithinSaukII(Kelleretal.,2003,2012;Morgan,2012).Nonetheless,365

therearealternativeregressionsurfacesintheCarraraFormation.Acandidateforasequence366

boundaryoccursatthebaseoftheRedPassLimestonewherethereisasharptransitionfromdeep-367

watertoshallow-water.Thislevelliesaround45maboveROECEintheCarraraFormation.368

Ratherthanregression,theolenellidextinctionoccurswithinadeepeningsuccession.369

Transgressionandshelfanoxiaoftengohand-in-hand,andoxygenstresshasbeenimplicatedin370

ROECEextinction(Montañezetal.,2000).However,atOakSpringsSummit,pyriteframboidanalysis371

16

suggestsdysoxicbutnoteuxinicconditionsintheextinctioninterval,andtheshallowerstudy372

locationsshownoevidenceforoxygenrestriction.Theevidenceforintensifiedoxygen-restricted373

depositionatthetrilobiteextinctionlevelisthereforeweak.Italsonoteworthythatlow-oxygen374

conditionswerecommoninCambrianoceans(Hurtgenetal.,2009;Prussetal.,2010;Gilletal.,375

2011),andthereisnosuggestionthatanoxiawasintensifiedatthelevelofROECE.376

TheSeries2-Series3boundaryintervalsawtheeruptionoftheKalkarindjifloodbasalt377

province(GlassandPhillips,2006;Jourdanetal.,2014;Marshalletal.,2016).Inyoungerintervalsof378

thePhanerozoic,theformationoflargeigneousprovincesfrequentlycoincideswithmass379

extinctions(Wignall,2015;BondandGrasby,2016)andtheeruptionoflargevolumesofvolcanic380

volatilesprovidesacausalmechanismfordrivingbiologiccrises.Thecontemporaneousnegative381

δ13CsignalofROECEisoftenseenattimesofLIPeruptionsandmayrecordtheinfluxofisotopically-382

lightvolcanicCO2(e.g.,Payneetal.2004).Thus,inmanyregardstheROECEhasthehallmarksof383

laterPhanerozoicLIP-relatedmassextinctionsalthoughevidenceforthecommonlyassociated384

environmentalchangessuchasthespreadofanoxia(Wignall,2015),isnotclearlyestablishedfor385

thisCambrianexample.386

387

6.Conclusions388

InthewesternGreatBasin,USA,theextinctionofthedominantolenellidtrilobitesoccurs389

withinadeepening-upwardshelfsuccession.Amajor–3.5‰negativecarbonisotopeexcursion390

(ROECE)occursatthesamelevel.Thisextinction/isotopeeventoccursaroundtheCambrianSeries2391

-Series3boundaryinterval.Pyriteframboidsizedistributiondataandlaminatedfaciessuggest392

periodicdysoxiaoccurredinthefaciesimmediatelysurroundingtheextinctionhorizon.However,393

theseconditionswereneitherwidespread(shallower-waterboundarysectionsinDeathValleydo394

notrecordoxygenstarvation)norespeciallyunusual(laminatedstrataaresporadicallydeveloped395

throughouttheoffshoreunitsoftheCarraraFormation)suggestingdysoxiadidnotplayamajorrole396

17

intheextinction.TheenvironmentaleffectsofthecontemporaneousKalkarindjifloodbasalt397

provinceofAustraliaprovideabetterpotentialcausalfortheextinctionattheSeries2-Series3398

boundary,althoughdetailedcorrelationwiththesectionsinNorthAmericaisrequired.399

400

Acknowledgments401

WethankEmilySmith,KristinBergmann,andJessicaCrevelingforvaluablediscussionsinthefield.402

WealsothankTessaBrowne,alongwithHelenaTatgenhorstforallowingtheuseoftheirCisotope403

datainthetop25mofEmigrantPass,andStephenBurnsinthestableisotopelaboratoryatthe404

UniversityofMassachusettsatAmherstforprovidingthesecarbonisotopeanalyses.Wethankan405

anonymousreviewerfortheirconstructivefeedback,andJessicaCrevelingforherextensiveand406

thoroughreview.ThisresearchwasfundedbyaNERCpostgraduatestudentshiptoLEF.407

408

Figurecaptions409

Figure1.LocationmapshowingstudysectionsatEmigrantPass,DeathValleyregion,California(35°410

53’29.24”N,116°04’39.08”W)andOakSpringsSummit,BurntSpringRange,LincolnCounty,411

Nevada(37°37’04.32”N114°43’17.20”W).Starindicatesapproximatelocationoffieldareaduring412

theCambrianSeries2(afterMcKerrowetal.,1992).413

Figure2.BiostratigraphiccorrelationofthetrilobitezonesoftheCarraraandPiocheformations414

(PalmerandHalley,1979;SundbergandMcCollum,2000).Faciescolumnisbasedonfieldand415

petrographicobservations,andnumbersrelatetofaciesdetailedinTable1.Ageneralised416

stratigraphiccolumnofPrecambrianandCambrianformationsinDeathValleyisgiven(fromCorsetti417

andHagadorn,2000).418

Figure3.CorrelationoftrilobitebiozoneswithintheCarraraandPiocheformations(Merriamand419

Palmer,1965;PalmerandHalley,1979;SundbergandMcCollum,2000).O.isOlenellus,P.isPoliella.420

18

Figure4.Fieldphotographs.421

A.Trilobitedebris(spinesandcarapacesandhyoliths)inabioclastichashonbeddingplanesof422

ooliticgrainstone,CarraraFormation.B.OncoliticpackstonefaciesatEmigrantPass.C.Bifurcating423

burrowsinwellbioturbatedsiltymarlatEmigrantPass,notebookforscale.D.Ooliticgrainstone424

faciesshowinginclinedchevron-stylepackingofthinintraclastandbioclasts(hyolith,ooidandother425

detritalfragments).E.OlenellidextinctionlevelatthebaseoftheC-ShaleMemberatOakSprings426

Summit.RedlineindicatesextinctionhorizonfromPalmer(1998).F.Fissile,laminatedmarlandsilty427

marlinthelowerEagleMountainShaleatEmigrantPass.G.Thalassinoidesinfine-grained,siltymarl428

oftheCarraraFormation.H.Verticalburrows(atthehammertip)insiltymarlbedsoftheCarrara429

Formation.430

Figure5.Scansofthinsectionsandphotomicrographs.431

A.Photomicrographofarangeofchloriteinthesiltymarlfaciesimmediatelyabovetheextinction432

horizonatOakSpringsSummit.Chloriteoccursaselongategrainsandalsoascement.B:433

PhotomicrographofasiltybioclasticpackstoneintheupperEagleMountainShale.C:Scanofslideof434

oncoliticpackstone(EagleMountainShale)showingoncoidswithbioclasticnucleusofechinoderm435

platesamongstamatrixofshelldetritusandmicrite.D:Scanofslideofbioclasticgrainstone.436

Elongate,trilobitefragmentsdominatethisfaciesalongsidehyolithremainsandechinodermplates.437

Darkbrownmineralgrowthshowsironoxidepreferentiallyreplacingshellmaterial.438

Figure6.Scansofthinsectionsandphotomicrographs.439

A:Scanofsiltymarlshowingquartzgrainsanddetritalchloritegrains(green).B:Photomicrographof440

marlfaciesintheCombinedMetalsMember,PiocheFormation.Trilobitecarapaceexhibitsbrown441

needlelikeironoxidereplacementofthecalciteshell.C:Photomicrographofpeloidalgrainstone442

faciesintheCombinedMetalsMember,PiocheFormation.Wellroundedmicritepelletsalongside443

roundedquartzgrainsamongstafinemicritematrix.D:Photomicrographofoolitic,bioclastic444

grainstonewithironoxidespartiallyreplacingooids.E:Photomicrographofsiltychloriticlimestone445

19

showingroundedchloritegrains(whitedashedlines).F:Photomicrographofchloriticsiltymarl446

faciesshowingsub-angulartoangularquartzsandgrainsalongsidehyolithandtrilobitedebris.447

Figure7.CarbonisotopechemostratigraphyoftheCarraraFormationatEmigrantPassandPioche448

FormationatOakSpringsSummit.A.Insetlogshowscontactbetweensiltymicriteandanerosive-449

basedoncoliticpackstonewithripupclastsoftheunderlyingsiltymicrite.Thishorizongrades450

laterallyintoanooliticgrainstone.B.Insetlogofcontactbetweensiltybioclasticpackstoneandan451

erosive-basedoncoliticpackstone.Botherosionalsurfacesmarkthetransportofshallowwater452

bioclasticmaterialduringstormevents.453

Figure8.SizeversusstandarddeviationforframboidsfromSeries2-Series3boundarystrataof454

CaliforniaandNevadashowingthepresenceofoxygen-restrictedfacies.Thethresholdseparating455

euxinic/anoxicanddysoxic/oxicsizerangesinmodernenvironmentsisfromWilkinetal.(1996).456

Table1:FaciesoftheCarraraandPiocheformations.457

Table2.GeochemicalandframboidmeasurementsfortheCarraraandPiocheformationsat458

EmigrantPass(EP)andOakSpringsSummit(OSS)andframboiddatafromthePiocheFormationat459

RuinWash(RW).460

461

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