Upper Cretaceous diatom biostratigraphy of the Arctic archipelago and northern continental margin

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Earth and Atmospheric Sciences, Department
Papers in the Earth and Atmospheric Sciences
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2002
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Pedro M. Tapia
University of Nebraska-Lincoln
David M. Harwood
University of Nebraska-Lincoln, [email protected]
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Tapia, Pedro M. and Harwood, David M., "Upper Cretaceous diatom biostratigraphy of the Arctic
archipelago and northern continental margin, Canada" (2002). Papers in the Earth and Atmospheric
Sciences. 184.
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Upper Cretaceous diatom biostratigraphy of the Arctic
archipelago and northern continental margin, Canada
PedroM.TapiaandDavidM.Harwood
DepartmentofGeosciences,UniversityofNebraska-Lincoln,Lincoln,NE68588-0340,USA
email:[email protected]
ABSTRACT:StrataintheCanadianArcticcontaindiverseandmoderatelywell-preservedLateCretaceoussiliceousmicrofossilas-
semblages.One-hundred-twelvesampleswereanalyzedfromacompositestratigraphicsection(1094m-thick)oftheSmokingHills,
MasonRiverandKangukformations.Foursectionswereexamined:(1)SlidreFjordonEllesmereIsland;(2)HoodooDomeonEllef
RingnesIsland;(3)CapeNaresonEglintonIsland;and(4)HortonRiverontheAndersonPlains,NorthwestTerritories.Twohun-
dred-threediatomtaxawereidentifiedinforty-nineproductivesamples.FourUpperCretaceousdiatomzonesareproposedfortheCa-
nadianArcticbasedonthebiostratigraphicdistributionofdiatoms:(i)theUpperCenomaniantoUpperSantonian(?)Gladiusantiquus
ConcurrentRangeZone,(ii)theLowerCampanianCostopyxisantiquaPartialRangeZone,(iii)thelowerUpperCampanianTrinacria
indefinitaIntervalZone,and(iv)theupperUpperCampanianStephanopyxissimonseniPartialRangeZone.
ThediatomassemblagesaresimilartothoseofAlphaRidge(ArcticOcean),UralMountains(Russia),andCampbellPlateau(SW
Pacific Ocean), enabling diatom-based biostratigraphical correlations within the northern high-latitudes and to the southern
high-latitudes.Afifthbiostratigraphiczone,AzpeitiopsismorenoensisConcurrentRangeZone,isalsoproposed,basedoncommonand
widespreaddistributionofthenominativetaxoninlowertoupperMaastrichtiansediments.Sufficientdataisnowavailabletoestablish
theconstructionofadiatom-basedstandardzonalframeworkfortheUpperCretaceous.
Twonewcombinations,Trochosiradenticulatum(Strelnikova)TapiaandTrochosiropsispolychaeta(Strelnikova)Tapiaarehere
proposed.
INTRODUCTION Status of Late Cretaceous diatoms: taxonomic studies vs the
stratigraphicrecord
Diatomsintimeandspace
OurknowledgeofLateCretaceousdiatomsishinderedbythe
Diatoms are known from the Lower Cretaceous (Aptian- temporal instability of opal-Aand detrimental effects of silica
Albian)toRecentandrepresentusefultoolsasbiostratigraphic, diagenesis through time. Most published Late Cretaceous dia-
paleoenvironmental, and paleoclimatic indicators (Stoermer tom studies are descriptive and taxonomic, with little or no
andSmol1999).TheCenozoicdiatombiostratigraphicrecord stratigraphic control (table 1). Nevertheless, general trends in
isrelativelywell-developed(BarronandBaldauf1995),though UpperCretaceousdiatombiostratigraphyandevolutioncanbe
manystratigraphicgapsstillexistinthePaleoceneandEocene foundinStrelnikova(1974)andHarwoodandNikolaev(1995).
diatom record around the world. Upper Cretaceous diatom Current knowlegde of Campanian diatom biostratigraphy was
biostratigraphy, however, requires considerable further devel- developed from high-latitude diatomaceous deposits in Russia
opmentthroughcollectionofstratigraphicdata,taxonomicre- andtheS.W.PacificOcean.Thesedepositscontainsufficiently
organization,morphologicaldescription,andbiostratigraphical well-preserved diatom floras and reliable stratigraphic control
analysis such as that presented here. Acompilation of known thatcanbecomparedtoresultspresentedhere.
Upper Cretaceous diatom-bearing sediments (table 1, text-fig.
1) expresses the limitation of our current knowledge for this Outcrops and industrial wells from the Ural Mountains and
stratigraphicinterval.Diatompreservationisthelimitingfactor WesternSiberianlowlandplains,Russia.Thebestsequencethat
onmanyofthesedeposits. contains Upper Cretaceous opaline diatoms is in north-central
Russia. A299m-thick composite core section along the North
ThispaperisanattempttodevelopanUpperCretaceousdiatom Sosva River (Cores 22, 82, and 19; text-fig. 3-A) and outcrop
biostratigraphy for the Canadian Arctic. Our main goal is to samplesfromtheSyinjaRiver[SectionsXI(14)andIX(13)]re-
identifythemaindiatomassemblagesinordertoapplydiatom cordportionsoftheCampanianandMaastrichtian(Strelnikova
biostratigraphy to the stratigraphic sequences of the Kanguk, 1974,1975).StrelnikovadividedtheCampaniansequenceinto
Smoking Hills, and Mason River formations. The moderately three diatom complexes. The First Complex (aleuritic diatom-
goodpreservationofdiatomsfromthesestrataenablesustoin- aceous clays, Lower Campanian) is characterized by diatoms
vestigate changes in diversity and composition of siliceous Paralia cretacea, P. ornata, Costopyxis antiqua, C. uralensis,
microfossil assemblages from the northern high-latitudes Lepidodiscuselegans,Triceratiumschulzii,Hemiaulusdanicus,
(text-fig. 2). Thick stratigraphic sections, like the 125m-thick H. echinulatus, Pterotheca alata, and P. simplex. The
continuousandmoderatelywell-preserveddiatomaceousshale Prunobrachium crassum radiolarian complex and the foram-
of the Horton River section represent an excellent reference iniferal Spiroplectammina lata Zone provide biostratigraphic
sectionfordevelopmentofabiostratigraphicframeworkforfu- control that indicates an Early Campanian age. The Second
turecorrelation. Complex(whitediatomite,lowerpartoftheUpperCampanian)
micropaleontology,vol.48,no.4,pp.303-342,text-figures1-9,plates1-9,tables1-6,appendix1,2002 303
P.M.TapiaandD.M.Harwood:UpperCretaceousdiatombiostratigraphyoftheArcticarchipelagoandnortherncontinentalmargin,Canada
TABLE1 is distinguished by the presence of Stephanopyxis turris, Tri-
OccurencesofUpperCretaceousbearing-diatomdepositsintheworld. ceratium anissimovae, Paralia sulcata, Pseudopodosira sim-
plex, P. punctata, Skeletonema polychaetum, Costopyxis
broschii, Aulacodiscus archangelskianus, A. bifrons, Hemi-
aulus antiquus, H. kittonii, Gladius speciosus f. speciosus,
Pterothecaaculeifera,andP.evermannii.TheThirdComplex
(lightgraydiatomaceousclays,upperpartoftheUpperCamp-
anian) is characterized by Paralia sulcata, Pseudopodosira
aspera, Stephanopyxis turris, S. lavrenkoi, Costopyxis reticu-
lata,Aulacodiscusjouseae,Triceratiumplanum,T.coronatum,
Gladius speciosus f. aculeatus and f. poratus, and Pseudo-
pyxilla rossica. The Prunobrachium articulatum radiolarian
complex and the foraminiferal Bathysiphon nodosariaformis
Zone provide biostratigraphic control that indicates a Late
Campanian age for the Second and Third diatom complexes
(Strelnikova1975).
DeepSeaDrillingProjectLeg29,Site275,SWPacificOcean.
DSDP Site 275 recovered 17.5m (40.6%) of sediment from a
43m-thick cored section on the Southeast Campbell Plateau
(50°26'S,176°19'E).Twocorescontaining13mofglauconite-
bearing silty, radiolarian-diatomaceous ooze recorded the Late
Cretaceous diatom history in the Southwest Pacific Ocean
(text-fig.3-B).ALateCampanianagewasdeterminedbycorre-
lation with the uppermost Campanian radiolarian Patuli-
bracchiumdickinsoniZoneofCaliforniaandbypalynological
correlation to New Zealand and Campbell Island, which sug-
gestedaLateCampaniantoMaastrichtianage(ShipboardSci-
entific Party 1975). The diatom record indicates a Late
CampaniantoMaastrichtianage,whereassilicoflagellatesindi-
cate a Late Cretaceous (probably Maastrichtian) age (Perch-
Nielsen 1975). Extraordinarily well-preserved diatom and
silicoflagellateassemblageswereencounteredinCores1and2.
Hajós and Stradner (1975) examined twenty samples and pro-
posedninebiostratigraphiczonesforthis13m-thicksection.In
ascending order the zones are the Horodiscus rugosus Zone,
ChaseaornataZone,EpitheliumrossicumZone,Anaulussubant-
arcticus Zone, Biddulphia sparsepunctata Zone, Kentrodiscus
armatus Zone, Cerataulus-Odontotropis Zone, Acanthodiscus
antarcticusZone,andPseudopyxillajouseaeZone.
AlthoughmanydiatomtaxapresentatSite275arealsonotedin
theCanadianArcticsediments,otherkeytaxa,includingthose
usedasstratigraphicmarkers,arenotpresentintheArcticdia-
tom flora. For this reason, the zonation of Hajós and Stradner
(1975)cannotbeappliedinthepresentstudy.
GeologicalsettingoftheUpperCretaceousCanadianArctic
Samples examined in this study came from two different geo-
logicalsettings.SamplesfromtheArcticIslandsbelongtothe
SverdrupBasin,whereasthosefromthecontinentalmarginbe-
long to the Anderson Plain Syncline (Yorath et al. 1975,
Plauchut and Jutard 1976). The Sverdrup Basin developed by
rifting during the mid-Carboniferous and was filled by up to
9000m of Mesozoic sediment. Upper Cretaceous strata of the
Kanguk and Expedition formations rest unconformally upon
Lower Cretaceous rocks. A diachronus unconformity (Late
Albian-Late Cenomanian) is present throughout the basin. A
major Late Cenomanian transgression transformed the Arctic
Islandregioninanoffshoreshelf.BytheendoftheCretaceous,
sediment supply increased and the region was occupied by
pro-deltaandfluvial-deltaicplains(Embry1991).IntheAnder-
son Plain Syncline, Mesozoic strata rest unconformably on a
PaleozoicsequenceandareunconformablyoverlainbytheUp-
304
Micropaleontology,vol.48,no.4,2002
TEXT-FIGURE1
GlobaldistributionofselectedCampanian-Maastrichtiandiatomaceousdeposits(SeeTable1).1=AlphaRidge,ArcticOcean;2=ArcticArchipelago,
Canada(thisstudy);3=NorthernContinentalMargin,Canada(thisstudy);4=UralMountains,Russia;5=Gdansk,Poland;6=CentralNegev,Israel;7=
NinetyeastRidge,IndianOcean;8=TongaTrench,PacificOcean;9=CampbellPlateau,PacificOcean;10=Kerguelen,Plateau,SouthernOcean;11=
SeymourIsland,Antarctica;12=MorenoGulch,California.
per Tertiary Beaufort Formation. The Upper Cretaceous se- theheadofSlidreFjordonFosheimPeninsula(JeletzkyinWall
quence is represented by the Smoking Hills and Mason River 1983).ForaminiferaldataindicateanagerangefromTuronian
formationsoftheAmudsenGulfGroup(Yorathetal.1975). toLateCampanian(Wall1983).Thedepositionalenvironment
oftheKangukFormationatSlidreFjordisinterpretedtobema-
MATERIALSANDMETHODS rineofshallowtomoderatedepthontheshelf(J.H.Wall,pers.
CretaceoussiliceousmicrofossilsintheCanadianArcticArchi- comm.).
pelago (Banks Island) were first identified as reworked ele-
mentsinglacialsediments(Vincentetal.1983)fromtheDuck HoodooDome,EllefRingnesIsland,DistrictofFranklin.Hoo-
HawkBluff,MorganBluff,NelsonRiver,andPrinceofWales dooDomeisadouble-plunginganticline,coredandpiercedlo-
formations.Thatreportstimulatedthepresentstudy. cally by a Carboniferous halite diapir (Stott 1969). The 12
samplesexaminedherecamefromthe390m-thickKangukFor-
Four stratigraphic sections within the Canadian Arctic Archi-
mationatHoodooDome,GSCsection73BAA-10002(text-fig.
pelagoandcontinentalmarginwereexamined(text-fig.4,col-
2,site2b;text-fig.4,columnB).Unfortunately,nosectionde-
umns A-D). Samples were collected by scientists from the
scriptionorstratigraphiccolumnisavailablefromthislocality.
Geological Survey of Canada (GSC) (P. T. Chamney, A. F.
Other studies of the Kanguk Formation at Hoodoo Dome
Embry,J.C.Harrison,andJ.H.Wall)andkindlyprovidedby
(Blakwill1974,BlakwillandHopkins1976)reportathickness
David McNeil of the GSC. From these sections, one hundred
ofabout450m,dividingthislithostratigraphicunitintotwoin-
andtwelvesampleswereanalyzedtodeterminethepresenceof
formal(lowerandupper)membersbasedonthepresenceofan
siliceousmicrofossils.Forty-nineofthesecontainedenoughsi-
escarpment-forming, red-brown siltstone between those units.
liceous microfossils to warrant a detailed diatom survey
Thelowermembercomprisesabout240mofsoft,slightlysilty,
(text-fig.4).
pyritic,blackshalewithabundantthinbedsandlaminationsof
SlidreFjord,EllesmereIsland,DistrictofFranklin.TheSlidre yellow-grayjarositicclay.Nearthebaseofthissection,thebeds
Fjord GSC section 74RV-38 is located at 79°47.4'N, 85°22'W arepinkandbrick-redduetotheoxidationofiron-sulfidemin-
(text-fig.2,site2a;J.H.Wall,pers.comm.).Atotalof29sam- erals. No macrofossils are known from this member, however
pleswereexaminedfromthe260.5m-thickKangukFormation thepresenceofmollusksWatinocerassp.andtherecognitionof
(text-fig. 4, column A). There is no available section descrip- theMytiloideslabiatusZoneatthesamestratigraphiclevelon
tion or stratigraphic column from this locality. At an adjacent theadjacentAmundRingnesIslandindicatesanEarlyTuronian
site(GSClocality79EL-3,RemusCreek,FosheimPeninsula, ageforthelowerunit(JeletzkyinBlakwillandHopkins1976).
EllesmereIsland),theKangukFormationunconformablyover- The upper member comprises circa 210m of dark-brown-gray
lies the Upper Albian to Cenomanian Hassel Formation (Wall shaly siltstone and silty shale, with abundant small red-brown
1983) and consists of approximately 220m of dark-gray shale ironstonenodulesandafewjarositicclaybeds.Acollectionof
withminoramountsofsiltstoneandsandstone.Thinbentonite well-preserved mollusks suggests the base of the upper unit is
seams are characteristic of the lower part of this formation. lateEarlyorearlyLateSantonianinage(Jeletzky inBlakwill
Macrofossilsdonotprovidereliableagecontrolatthissite,but and Hopkins 1976). The depositional environment of the
LowerSantonianammonitesarereportedfromthisformationat KangukFormationatHoodooDomerepresentsamiddleouter
305
P.M.TapiaandD.M.Harwood:UpperCretaceousdiatombiostratigraphyoftheArcticarchipelagoandnortherncontinentalmargin,Canada
TEXT-FIGURE2
DiatomaceousdepositsintheCanadianArctic(areas2and3inFig.1).2a=SlidreFjord,EllesmereIsland;2b=HoodooDome,EllefRingnesIsland;2c=
CapeNares,EglintonIsland;3=HortonRiver,NorthwestTerritories.
shelf setting in the lower unit and an upper shelf to pro-delta andsandstonewithafewbedsofbrownferruginoussandstone.
settingintheupperunit(BlakwillandHopkins1976). The age of the Kanguk Formation at Eglinton Island is San-
tonian to Campanian, based on fossil mollusks (Jeletzky in
Cape Nares, Eglinton Island, District of Franklin. The Cape Plauchut and Jutard 1976) and Senonian based on fossil
Naressection(GSC87EL-16)islocatedat75°38'N,119°22'W radiolaria and foraminifera (Fischer in Plauchut and Jutard
(text-fig. 2, site 2c; J. H. Wall, pers. comm.). The 20 samples 1976).TheLowerShaleandEglintonmembersareconsidered
examined here came from a 156m measured section of the tobeUpperTuroniantoLowerCampanianbasedonthepres-
Kanguk Formation at Cape Nares (text-fig. 4, column C). No ence of the foraminiferal Dorotia smokyensis assemblage and
section description or stratigraphic column is available from Trocammina ribstonensis (J. H. Wall, pers. comm.). The
this locality. The Kanguk Formation at Eglinton Island was depositionalenvironmentisinterpretedtobenearshoretoopen
studied by Plauchut and Jutard (1976), who reported a marine for the lower part of the Lower Shale Member and a
312m-thick unit unconformably overlying the Upper Albian shallowtomoderatedepthmarineshelfenvironmentfortherest
HasselFormation.TheKangukFormationisdividedintothree of the formation (Plauchut and Jutard 1976, J. H. Wall, pers.
members: the Lower Shale, Eglinton Sandstone, and Upper comm.).
Shale members. (1) The Lower Shale Member is 200m-thick
andcontainstwounits;thelowerpart(110m)comprisesgrayto Horton River Section, District of Mackenzie, Northwest Terri-
blackshale,siltandsandstonewiththinbandsofyellowjarosite tories.TheHortonRiversequenceisacompositesectioncon-
andconcretionarymassesofmudstoneanddarkironstone,and structed from three adjacent outcrops on the Anderson Plains
theupperpart(90m)comprisesbrowntoblackshaleandminor (text-fig.2,area3).The51samplesexaminedherecamefrom
silt with thin bands of gray and green sand, which increase in thesethreeoutcropsoftheSmokingHillsandMasonRiverfor-
abundance toward the top of the unit. (2) The Eglinton Sand- mations (text-fig. 4, column D). No section descriptions or
stoneMemberis50m-thickandcomprisesgreen,grayorwhit- stratigraphiccolumnsareavailablefromanyofthese3locali-
ish, indurated, medium to coarse quartz sandstone, gravel and ties. (1) The GSC location CR 16A-N68 (69°27'30"N,
conglomerate. The contact between the Eglington and Lower 126°58'W) represents the Smoking Hills Formation (McIntyre
Shalemembersistransitional.(3)TheUpperShaleMemberis 1974,Yorathetal.1975).Thisformationdisconformablyover-
62m-thickandcomprisesgraytogray-brownshale,siltyshale liesthemidAlbianHortonRiverFormation,andcomprisesap-
306
Micropaleontology,vol.48,no.4,2002
TEXT-FIGURE3
UpperCretaceousdiatombiostratigraphyin(A)UralMts.,Russia(fromStrelnikova1974),and(B)CampbellPlateau,SWPacific(fromHajós&
Stradner1975).Notethedifferentscales.Strelnikova(1974)dividedRussiancoresinto4biostratigraphicaldivisions:1=FirstDiatomComplex,2=
SecondDiatomComplex,3=ThirdDiatomComplex,4=ComplexwithStephanopyxisbiseriataandTriceratiumcellulosum;Hajós&Stradner(1975)
erected9zonesfortwocoresinDSDPSite275:I=PseudopyxillajouseaeZone,II=AcanthodiscusantarcticusZone,III=Cerataulus-Odontotropis
Zone,IV=KentrodiscusarmatusZone,V=BiddulphiasparsepunctataZone,VI=AnaulussubantarcticusZone,VII=EpitheliumrossicumZone,VIII=
ChaseaornataZone,andIX=HorodiscusrugosusZone.Key:I=Diatomiteanddiatomaceousmudstone,II=Radiolariananddiatomaceousooze.
proximately100mofavariablesequenceofblack,bituminous based on vertebrate fauna (Russell 1967) and Santonian to
shale,beddedyellowjarosite,andlocallydarkmaroonbedsof Campanian based on palynomorphs (McIntyre 1974). The
earthy hematite (Yorath et al. 1969, McIntyre 1974). The depositionalenvironmentisinterpretedtobenearshoretoopen
Smoking Hills Formation is considered Lower Campanian marine(PlautchutandJutard1976).(2)TheGSClocationCR
307
P.M.TapiaandD.M.Harwood:UpperCretaceousdiatombiostratigraphyoftheArcticarchipelagoandnortherncontinentalmargin,Canada
TEXT-FIGURE4
Schematicstratigraphiccolumnsofthestudiedsections.Thepositionsofdiatom-bearingsamplesareindicatedbysmallarrowsandGSCsamplecodes
(e.g.C-34348).Barrensamplespostionsaremarkedbysmalldots.A=SlidreFjord,EllesmereIsland;B=HoodooDome,EllefRingesIsland;C=Cape
Nares,EglingtonIsland;D=HortonRiver,NWT.NumberswithinthelithologiccolumnsareGSCcodesforstratigraphicsections.1=Diatom
biostratigraphy(thisstudy);2and4=J.H.Wall(personalcommunication);3=Blakwill&Hopkins(1976);5=McIntyre(1974).
16B-N68 (69°28'N, 126°58'W) represents part of the Mason (McIntyre 1974). The Mason River Formation was dated as
RiverFormation(McIntyre1974),whichatthislocalityisap- Campanian to Maastrichtian based on palynomorph biostrati-
proximately125m-thickandcomprisesalowerunitcomposed graphy (McIntyre 1974) and the depositional environment is
ofpalegray-weatheringshalewithminoramountsofmudstone thought to be marine shelf with minor continental influences
andrusty,darkferruginousdolomiteconcretionarybeds.Thisis (PlautchutandJutard1976).
overlainbyamiddleunitofmediumtolocallydarkgrayshale
with some gypsum; and an upper unit of medium to Samplepreparation.Approximately1ccofunconsolidatedsed-
dark-gray-brown and brown ferruginous shale that grades up- imentwasplacedintoa1000mlbeakeranddriedonahotplate.
wardintograysandyshale(Yorathetal.1969,McIntyre1974). Afterthebeakercooled,10-20mlofconcentratedhydrochloric
The Mason River Formation gradationally and conformably acidand40-50mlof30%hydrogenperoxidewereadded.This
overlies the Smoking Hills Formation and is unconformably solution was heated and left to react until the strong reaction
overlain by a Recent unconsolidated gravel and sand unit ceased.Thebeakerwasthenfilledwithfilteredwaterand10ml
(Plautchut and Jutard 1976). (3) The GSC location CR of5%Calgonsolution,stirred,andlefttosettleovernight.The
17A-N68 (69°58'30"N, 127°4'W) represents the upper part of next day, the supernatant solution (approximately 3/4 parts of
the Mason River Formation, measuring approximately 62m thevolume)wasdecanted.Thebeakerwasrefilledwithfiltered
308
Micropaleontology,vol.48,no.4,2002
TABLE2
Selecteddiatomdata(totalcounts)fromSlidreFjordSectionofbothsize-fractions(greaterandlesserthan25m).Preservation:G=Good,M=Moderate,
P=Poor;RelativeAbundance:A=Abundant,C=Common,F=Few,R=Rare.
water,allowedtosettlefor6hoursandthendecanted.Thispro- fractionwassavedina125mlNalgenebottleafterthefinesedi-
cedure was repeated four times to wash out the hydrochloric mentinthebeakerssettledovernight,andthesupernatantwater
acid,hydrogenperoxideandCalgon,aswellastoremovethe was decanted. The coarse (=heavy) sediment residue that re-
finerclaysize-fraction.Thecleanedsamplewasthenfilledwith mained in the 1000ml beaker after the 5 minute gravitational
filtered water, stirred vigorously, and allowed to settle for 5 settlingperiodwasdriedinanelectricalovenat75°Candthen
minutes.Thistimethesupernatantsolutionwassievedthrough savedinalabeledplasticsamplebag.
a 25µm mesh and the finer fraction was collected in two
2000mlbeakers.Thisstepwasrepeatedfourtimesoruntilthe
Strewnslidesofthe25µmsizefractionweremadefortheentire
supernatantwaterwasclearafterfiveminutesofsettling.The
set of samples in order to identify productive samples for sili-
sampleofsize25µmwassavedina10mlvial.The25µmsize
ceous microfossil analysis, and to determine if more chemical
309
P.M.TapiaandD.M.Harwood:UpperCretaceousdiatombiostratigraphyoftheArcticarchipelagoandnortherncontinentalmargin,Canada
TEXT-FIGURE5
DiatomstratigraphyofselecteddiatomtaxaintheSlidreFjordsection.Relativeabundances(percentage)oftaxawerecalculatedafterthecombineddata
(sumofgreaterandlesserthan25micrometerfractions).Crossesindicaterareoccurrences(usually<1%).
treatment was needed. The samples containing siliceous throughout the diatom valves. Finally, these permanent slides
microfossilswerethenconcentratedbyfloatingwiththeheavy werecuredunderultravioletlightfor15-20minutes.
liquidsodiumpolytungstate(SPT)atadensityof2.2g/cc.
TheslideswereexaminedusinganOlympusBH-2Transmitted
LightMicroscopewithDifferentialInterferenceContrast.Pho-
Thesodiumpolytungstateflotationtechniquerequiresthepre-
tomicrographs were taken using B/W Technical Pan Kodak
vious chemical treatment in order to release the diatoms from
film,ASA25.Datawascollectedatmagnification×500(frac-
thesedimentmatrixandcleanthefrustules.Theacid-resistant
tion>25µm),and750X(fraction<25µm).Finalidentifications
subsamplewasthenresuspendedin10mlofdistilledwater.To
were made at magnification ×1250. Specimens were counted
beginthefloatation,3.5mlofSPT(=2.2g/cc)wasplacedinthe
following the convention stated in Schrader and Gersonde
bottom of a 15ml disposable centrifuge tube. The subsample
(1978).Atotalof500specimenswerecountedpersample,300
wasresuspendedandthe10mlsuspensionwascarefullyadded
inthefraction>25µmand200atthefraction<25µm.Afterthe
tothetopoftheSPTinordertopreventmixingofthesetwoso-
counting process was completed, the rest of the slide was
lutions.Thecentrifugetubewasthenfilledupwithdistilledwa-
scanned for rarer diatoms. Several slides contained a limited
terandcentrifugedatlowspeed(500rpm)for3minutes. The
numberofspecimens,inthiscasethewholeslidewasscanned
SPT/waterinterfacewascarefullypipettedoutandplacedinto
andthetotalnumberoffrustulestakenintoaccount.Slideswith
another centrifuge tube. To remove the SPT from the diatom
less than 100 specimen counts should be regarded as highly
frustules,theworkingaliquotwasresuspendedin15mlofdis-
qualitative.
tilledwaterandcentrifugedat1500rpmfor3minutes. Theres-
iduewaswashedagain,uptofourtimesoruntilalloftheSPT
RESULTS
wasremoved. Thecleanedsubsamplewasstoredintoa10ml
labeledvial. Thefossilmicrofloraatthestudiedsections
TheCanadianArcticsamplesyieldedabundantmarinediatoms,
Permanentslidesweremadeforbothsizefractions(greaterand silicoflagellates, radiolarians, chrysophyte statocysts, and pol-
lesserthan25µm)usingcleaned,22x40mm,coverslides.The lenandspores.Diatomsarethedominantgrouppresentinthese
cover slide was placed on a warm hot plate and six to eight samples and they show compositional changes throughout the
drops of distilled water were added. One or two drops of the sections.Silicoflagellatesandchrysophytestatocystswillbethe
concentratedsubsamplewereplacedintothewateratthemid- subjectofasubsequentpaper.
dleoftheslideandthentwotothreedropsofalcohol(ethanol)
were added. Alcohol helped disperse the sample across the SlidreFjordsection.Only5of29samplesfromthemeasured
slide.TwotothreedropsofmountingmediumNorlandOptical 260.5m-thick Kanguk Formation contained sufficiently well-
Adhesive # 61 (R.I. 1.56), was placed on a clean, labeled, preserved siliceous microfossils for biostratigraphic analysis
25x75mm, microscope slide. The microscope slide was fixed (text-fig. 4, column A, table 2). Six samples from the lowest
over the dried cover slip, and then flipped over to warm the 36mcontainedonlyafewoccurrencesofpollenandspores.Si-
NorlandOpticalAdhesiveforafewminutesonthehotplateto liceous microfossils were encountered in the interval 39m to
reducethemedia’sviscosityandassureeffectiveimpregnation 42.5m(samplesC-34348,andC-34349).Poorpreservationand
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Micropaleontology,vol.48,no.4,2002
TABLE3
Selecteddiatomdata(totalcounts)fromHoodooDomeSectionofbothsize-fractions(greaterandlesserthan25µm).Preservation:G=Good,M=Mod-
erate,P=Poor;RelativeAbundance:A=Abundant,C=Common,F=Few,R=Rare.
paucityofdiatomsinsampleC-34349,however,preventsitsin- The diatoms Gladius antiquus, Bilingua sp. 1, and Trochosira
clusioninthefinalbiostratigraphicaccount.Intheinterval42.5 denticulatum first appear in the sample C-34348 at 39m
to62.5monlyafewsporeswereobserved.Asecondhorizonof (text-fig.5,table2).Basilicostephanussp.1andActinoptychus
siliceousmicrofossilsispresentintheintervalfrom62.5to72m heterostrophuswerenotobservedabove72m.TheFirstOccur-
(samples C-34351 and C-34353). The interval from 82 to rence Datum (FOD) of Costopyxis antiqua is noted in sample
242.5misbarrenofsiliceousmicrofossils,butsomepollenand C-34351at62.5m,whereastheFODofTrinacriaindefinitais
spores were present. A third interval that contains siliceous in C-34369 at 252.5m. Lepidodiscus elegans occurs only in
microfossils occurs near the top of the section between 252.5 sample C-34353 at 72m. Common diatom taxa present in this
and254.5m(samplesC-34369andC-34371). section are Basilicostephanus sp. 1, Costopyxis schulzii f.
311