The late Pleistocene environment of the Eastern West Beringia based on the principal section at ...

16 Pages·2011·3.38 MB·English

by  Svetlana A. Kuzmina

QuaternaryScienceReviews30(2011)2091e2106
ContentslistsavailableatScienceDirect
Quaternary Science Reviews
journal homepage: www.elsevier.com/locate/quascirev
The late Pleistocene environment of the Eastern West Beringia based
on the principal section at the Main River, Chukotka
Svetlana A. Kuzminaa,b,*, Andrei V. Sherc,1, Mary E. Edwardsd,e, James Hailef, Evgeny V. Yanb,
Anatoly V. Kotovg,1, Eske Willerslevf
aDepartmentofEarth&AtmosphericSciences,1-26EarthSciencesBuilding,UniversityofAlberta,Edmonton,AB,CanadaT6G2E3
bPaleontologicalInstitute,RussianAcademyofSciences,Profsoyuznaya123,117868Moscow,Russia
cSevertsovInstituteofEcologyandEvolution,RussianAcademyofSciences,33LeninskyProspect,119071Moscow,Russia
dSchoolofGeography,UniversityofSouthampton,Highfield,SouthamptonSO171BJ,UnitedKingdom
eAlaskaQuaternaryCenter,UniversityofAlaska-Fairbanks,Fairbanks,AK99775,USA
fCentreforAncientGeneticsandEnvironments,NaturalHistoryMuseumandInstituteofBiology,UniversityofCopenhagen,JulianeMariesVej302100Copenhagen,Denmark
gChukotskyBranchoftheNorth-EastComplexScienceandResearchInstitute,EnergtikovStreet,15,686710,Anadyr,ChukotkaRegion,Russia
a r t i c l e i n f o a b s t r a c t
Articlehistory: ChukotkaisakeyregionforunderstandingbothQuaternaryenvironmentalhistoryandtranscontinental
Received31October2009 migrationsoffloraandfaunaduringthePleistoceneasitliesatthefareasternedgeofAsiaborderingthe
Receivedinrevisedform Bering Sea. The now submerged land bridge is the least understood region of Beringia yet the most
30March2010
criticaltounderstanding migrations betweenthe Old and NewWorlds.The insect fauna of the Main
Accepted30March2010
RiverLedovyObryv(IceBluff)section,whichislatePleistoceneinage(MIS3-2),ismarkedlydifferent
Availableonline8May2010
fromcoevalfaunasofareasfurthertothewest,asitischaracterizedbyveryfewthermophiloussteppe
elements.Fromthefaunawereconstructasteppe-tundraenvironmentandrelativelycoldconditions;
thereconstructedenvironmentwasmoisterthanthatoftypicalsteppe-tundradescribedfromfurther
west. The data from this locality, if typical of the Chukotka Peninsula as a whole, may indicate that
a barrier associated with the environments of the land bridge restricted trans-Beringian migrations,
particularlythemorethermophilousandxeric-adaptedelementsoftheBeringianbiota,supportingthe
hypothesisofacoolbutmoistland-bridgefilterinferredfromevidencefromseveralotherstudies.
(cid:1)2010ElsevierLtd.Allrightsreserved.
1. Introduction ofAsia(Fig.1),andassuchitshistoryisimportanttoourunder-
standingofthelandbridge.
For decades, ever since the Quaternary geological history of The dominance of cold- and dry-adapted vegetation and
Beringia became broadly understood, there has been strong a diverse mammalian fauna in Beringia in glacial stages is well
interestintheinterconnectedtopicsofspeciesmigrationbetween documented(seereferencesabove;Colinvaux,1964;Guthrie,1968,
the Old and New Worlds and the Pleistocene climate and envi- 1982;Sheretal.,2005).IthasbeendescribedbybothRussianand
ronmentofthislargelyunglaciatedhigh-latituderegion(seepapers American authors as a steppe-tundra ecosystem capable of sup-
in Hopkins (1967); Hopkins et al., 1982, and Quaternary Science porting a high faunal biomass and it was compositionally and
ReviewsVolume20(2001),forexample).Theregioniswellstudied, structurallyquiteunlikecontemporarybiomes,althougharangeof
givenitsremoteness,asitcontainsarichbiologicalarchiveinthe modernlocalBeringiancommunitieshavebeeninvokedaspossible
formoffossilflorasandfaunas,preservedinarangeofdepositional small-scale analogues (Giterman et al., 1982; Yurtsev, 1982;
environments that were, in many cases, uninterrupted byglacia- Edwards and Armbruster, 1989; Zazula et al., 2006a,b). Closer
tion.However,thelandbridgeitselfremainspoorlystudiedasmost inspection,however,revealsdifferencesinbothfossilandmodern
ispresentlysubmarine.Chukotkaisthenorth-easternmostregion speciesacrossBeringia,particularlyacrossthelandbridgeregion.
For example, the modern Chukotka biota most closely resembles
thatofneighbouringSiberia,butitalsoincludesendemicspecies
and species originating in North America, such as the common
* Correspondingauthor.DepartmentofEarth&AtmosphericSciences,1-26Earth
AmericanweevilLepidophoruslineaticollis,whichhasitsonlyAsian
SciencesBuilding,UniversityofAlberta,Edmonton,AB,CanadaT6G2E3.
footholdinChukotka(Bermanetal.,2002).Borealplanttaxaalso
E-mailaddress:[email protected](S.A.Kuzmina).
1 Deceased. differbetweenthetwoportionsofBeringia(Swanson,2003).Such
0277-3791/$eseefrontmatter(cid:1)2010ElsevierLtd.Allrightsreserved.
doi:10.1016/j.quascirev.2010.03.019
2092 S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106
Fig.1. Mapofthestudiedarea.Redcirclesediscussedfossilinsectlocalities,redshadingeareasoffossilinsectresearchinWesternBeringia,trianglesepollenrecord:1e“E”Lake
(El’gygytgyn),2eAmguemaexposure,3ePatriciaandGytgykailakes.
patterns suggest that filters to species interchange were in place provide the opportunity for multi-proxy reconstructions of past
during the late Quaternary (Murray et al.,1983; Swanson, 2003; environments. In this paper we present the results of a palae-
EliasandCrocker,2008).Inparticular,severalauthorshaveargued oentomologicalstudyoftheMainRiverdeposits.Afurtherpaper
thattheland-bridgeclimateand/orlandsurfacewascoolerand/or willdetailreconstructionsbasedonancientDNAretrievedfromthe
moister thanthatofmostof the region (Elias,2007a; Eliaset al., frozensediments.
1996,1997;Guthrie,2001;EliasandCrocker,2008). Fossil insects are an important tool for palaeoenvironmental
Chukotka is thus a key area for Beringian Quaternary studies, reconstructions. The method itself, its advantages and disadvan-
but it remains an under-studied part of Siberia. This is partly tages,andapplicationsfordifferentregionsaredescribedinarange
because if its remoteness, as it is situated far from Russia’s main ofbooksandarticles,forexample,Elias(1994),Encyclopediaarti-
scientificcentres.Thegeographicfocusofpreviousstudieshasalso cles(Elias,2007b),specialissuesofjournals:QuaternaryProceed-
beenstronglydeterminedbythepresenceoftheskeletalremains ings(Volume51997)andQuaternaryScienceReviews(Volume25,
of large mammals, which are more abundant in regions where 2006).
ancient terrestrial deposits are widely distributed, such as the Themainadvantagesoffossilbeetlestudiesarehighsensitivity
coastal lowlands of Yakutia. Furthermore, only the western Chu- toenvironmentalchanges,thepresenceofmostlylocalfaunainthe
kotkanareasoftheChaunlowlandsandAionIslandandtheMain fossil records, and a low possibilityof reworking. However, fossil
RiverIceBluffinsouth-centralChukotka(Fig.1)havewidespread beetleanalysisisnotaroutinemethodinQuaternarystudies;the
and significant Quaternary outcrops of loess-like sediment that approach presents challenges from adequate field sampling to
S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106 2093
identification of the fossil remains (beetles are the largest taxo- meanannualtemperatureinthisareaisclosetoaverageforChu-
nomic group); thus it is demanding of both time and expertise. kotka, mean July temperature is the warmest of all Chukotka
Andrei Sher understood the importance of insects as palae- weatherstations.
oenvironmentalindicators,andheprovidedconsiderablesupport ThefirstmentionofalluvialQuaternarysedimentsandthefirst
to two Russian Quaternary entomologists: S. Kiselev and S. geologicalmapoftheMainRivervalleydatestothebeginningof
Kuzmina. 20thcentury(Polevoy,1915).Thesection’sageandformationhave
ThisChukotkanstudyformspartofalargerresearchquestion beenmuchdisputed.Vtyurin(1964)andTomirdiaro(1972)focused
being addressed by Andrei Sher’s group: understanding the on lithology and on the permafrost features of the exposure.
palaeoenvironments ofdifferentpartsofBeringiaduringtheLast Tomirdiaro’s interpretation of mid- and late-Pleistocene ice-rich
Glacial Maximum(LGM)withafocusonfossilinsects. Thiswork sediments of aeolian originwas opposed by Svitoch (1980), who
wasbegunin1998followingthefirstexpeditiontotheLenaDelta foundresemblanceswiththeTurkutskySuiteoftheMiddlePleis-
region under a GermaneRussian project “The Laptev Sea System tocene (Svitoch, 1975; Kaplin, 1980). However, studies of rodent
2000”. A multidisciplinary investigation at Mamontovy Khayata, remains indicate that the age is Middle Pleistocene or younger
Bykovsky peninsula, east Lena Delta, showed that sedimentation (Kaplin, 1980). Kiselev (1980b, 1981) initially adopted the older
wasmostlycontinuousfrom48to12(cid:1)ka.Thefossilinsectassem- chronology,butlateracknowledgedayoungerageforthedeposits
blagesappearedtoclearlydifferentiateenvironmentsthroughtime (Kiselev,1995).Thelate-Pleistoceneageofmuchofthedepositsat
(Schirrmeisteretal.,2002).Thesectionwasstudiedinmoredetail the three key exposures on the Main River (Ust’-Aldan (Aldan
from1999to2001(Hubbertenetal.,2004;Sheretal.,2005)and Mouth), Mamontovy Obryv (Mammoth Bluff) and Ledovy Obryv
taxawereassignedtobioclimaticgroups;thismethodunderscored (IceBluff))isnowsecure(Dort-Gol’ts,1982;KotovandRyabchun,
thedominanceofcold-resistantinsectsduringtheLGMandiden- 1986; Kotov, 1988; Kotov et al., 1989; Lozhkin et al., 2000;
tified a short but well developed phase dominated by steppe AndersonandLozhkin,2002).AttheIceBluffexposureaseriesof
insects at the end of the Weichselian. The site was unique in radiocarbondates(conventionalages)rangesfrom42,000(cid:4)1300
Beringiainhavingsuchacontinuousanddetailedinsectrecord.In nearthesectionbase to19,500 (cid:4)500nearthe top; thetopmost
otherareastherewereonlyfragmentaryfossilinsectrecords,none material was dated to late-Holocene age (Anderson and
ofwhichcoveredthecompleteLGM.Thustherewasanincentiveto Lozhkin,2002).
find other localities that could yield comparable results. In the Kiselev (1980a,b,1981) reports insect faunas from Chaun Bay,
summerof2003AndreiSherledfieldworktotheSewardPeninsula, AionIsland,andtheMainRiverIceBluff.Whileinsectsfromwest
Alaska, where Kuzmina et al. (2008) studied LGM insects from Chukotkahavebeenwell-studied(Kiselev,1980a,1981;Sheretal.
a buried paleosol (Höfle et al., 2000); and in 2004 he led the Database,2006;KiselevandNazarov,inpress),onlyninesamples
Chukotkaexpedition.Theparticipantsof thesummer2004field- with fossil insects have been reported from south-central Chu-
workincludedbothAndreiSherandAnatolyKotov,ageologistwith kotka:onespecies-poorsamplefromtheMammothBluffsiteand
awideknowledgeofChukotkaingeneralandtheMainRiversitein eightfromtheIceBluff,ofwhichonlyfourassemblagesarespecies-
particular.Sherdevelopedtheideaforthispresentarticle,which rich(Kiselev,1980b,1981;Sheretal.Database,2006).
wastobethenextonehesubmitted.Sadly,Kotovdiedduringthe
winterof2004,andthusthispaperlackstheinputofthetwomost 3. Materialsandmethods
experiencedinGeologyteammembers.
3.1. Themodernexposure:stratigraphyanddating
2. Regionalsetting
TheMainRiverIceBluffexposureextendsforabout1kmatan
The Quaternary deposits of the Chukotka Peninsula have elevationof30montheleftbankoftheMainRiver(Fig.2).Inthe
multiple origins: marine and glacial-marine deposits in eastern 1970sand 1980s the sectionwas betterexposed, particularly the
coastal regions, glacial deposits in mountain and foothill regions, southern part, which is currently covered by vegetation, as is
andinotherareas,lacustrine,alluvial,oreoliandeposits.Theloess- thelowerpartoftheentirebluff.Kotovetal.(1989)differentiated
likesedimentoftheYedomaSuiteisthoughttohavepolygenetic the exposure into northern and southernparts. The lowest three
origin (Svitoch,1980; Kotov, 2002). The Main Riverarea contains units(alluvialandflood-plain;thermokarstlakedeposit;andpeat
the best exposed and continuous Quaternary section among all that developed after lake drainage and dated to 42 ka) are now
interiorChukotkasites. covered (Fig. 2). These are common to the whole section. The
TheIceBluff(LedovyObryv)siteissituatedontheMainRiver2, northernexposureisdominatedupwardbyice-richdepositsthat
notfarupstreamfromVaiegivillage,alefttributaryofAnadyrRiver aresimilartowidespreadyedomasedimentsonthecoastalYakutia
inthecentral-southernpartofChukotka(64060N,171110E;Fig.1). lowlands. The southern portion of the exposure is dominated
Themodernvegetationislarchforest;stonepine,birchandaspen upward byafurther sequenceofsuperimposedthermokarstlake
alsooccur.Modernbeetles(collectedbyS.KuzminaandE.Yan)are deposits.TheoverallsettingoftheexposureisshowninFigs.2and
riparianandforestspecies,andnotundraorsteppespecieswere 3.Theslumpedlowermaterialisevident,andthelocationsofthe
observed.Thisareaiswarmenoughpermitrestrictedagriculture; trenchesintheupperpartoftheexposureareindicated.
local people from the closest villages plant vegetables in open Inthesummerof2004onlythenorthernpartoftheexposure
ground,whichisunusualforChukotka.Theclimatedatafromthe was accessible. It consists of an ice-rich silty and sandy outcrop
nearestweatherstationatMarkovoindicateameanJulytemper- withinterbeddedpeatlayers(Figs.2and3).Grassrootsandshrub
atureof13.6(cid:1)C,meanJanuarytemperature(cid:3)25.2(cid:1)C,meanannual remains are visible in the silty sediment, while plant and insect
temperature(cid:3)8.9(cid:1)C,andannualprecipitation432mm(Melnikova, remains,althoughpresentinthesandysediment,areonlyrevealed
1965).Becausethesiteissituatedfarfromthesea,theclimateis afterscreening. Six trenches werecleaned at the exposure. Large
morecontinentalthanthatof coastalregionsofChukotka. While bulk sediment samples were taken for insect analysis (for
screening) and frozen samples were collected for DNA analysis
(Figs.2and4).DNAsamplesweretakenintriplicate(Fig.4),and
2 Thename“Main”hasnoEnglishmeaning;itisadirecttransliterationofthe they were kept frozen in a field freezer with power supplied by
localname;pronunciationisclosetoEnglishword“mine”. a portable generator. The duplicates were back-up samples as
2094 S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106
Fig.2. IceBluffexposure.SeedetailsinFigs.3and4.
returningsamplestothelabsuccessfullycanbedifficultduetothe someHeteroptera(truebugs),andoccasionallyspecimensofother
longdistancethatmustbetravelled.Fortunately,allfrozensamples insect orders. Most fossils retrieved here belong to terrestrial
were returned in good condition; the extra volume allows other habitats;aquaticinsectsareuncommon.Weusebeetles,antsand
analyses, for example, radiocarbon dating and pollen studies. true bugs for environmental reconstructions; other fossils are
Radiocarbon dating was carried out at the radiocarbon facility in representedbysinglechitinscleritesbutthesearehardtoidentify.
Oxford,UK(Fig.4,Table1). Theinterpretationofthefossilinsectassemblagesusestraditional
The geological description, including permafrost features and approachesbasedonecological/bioclimaticgroups(seeSheretal.,
sectionstratigraphy,wasmadebyAndreiSherandAnatolyKotov; 2005; Kuzmina and Sher, 2006; Sher and Kuzmina, 2007). By
unfortunately,theirdetailedfieldnotesareunavailable.Shermade screening a large sediment volume, we are able to retrieve
thesectionschemebasedonhisfieldobservationsandthisforms numerousinsectfossils,andthisenablesustoworknotonlywith
the basis of Figs. 2 and 4. Further geological and stratigraphic a list of species but with estimates of the relative abundances of
observationsweremadebySK.Wehaveusedthesedataanddata differentecologicalgroupsofinsects.
reported earlier (see Anderson and Lozhkin, 2002) to provide Inthisresearchweusethefollowingecologicalgroupsfoundin
abasicdescriptionofthelocality. PleistocenefaunasfromSiberia(SherandKuzmina,2007;seeFig.4):
St e thermophilous steppe insects that are never associated
3.2. Insectsamplingandanalyticalmethods withmoderntundra.Thisgroupisusuallyaquitediverseassem-
blage of exotic southern steppe species, although some of them
During the summer of 2004 insect sampling was one of the surviveinthesteppecommunitiesofYakutiatoday.
main tasks of the fieldwork. The lowest sample B9, comes from Msemeadow-steppespeciesthataremoretoleranttoacold
asandyunitwithsmallice-wedgecasts3maboveriverlevel.Based environmentthanStspecies;thesemayliveonsteppe-likepatches
onitsheightaboveriverlevel,thisbedistentativelyassignedtothe insidethetundrazone.
first,alluvial-flood-plainunit(KotovandRyabchun,1986),butfossil Ssesedgesteppeorcryoxeropliloussteppeinsects.Thisgroup
insects from here are not in concordance with an aquatic envi- includes only one, but a very important species e the pill beetle
ronment,andfurthermore,nooverlyingpeatlayerwasobserved; Morychus viridis, which is extremelyabundant in the most Pleis-
thestratigraphicrelationofthisunittootherdescribedunitsisthus toceneinsectassemblagesofWestBeringia.
unclear.Allotherinsectsamplesfrom2004fieldseasonweretaken Weattributeinsectsinthesethreegroupstoasteppeassocia-
fromtheice-richupperpartofthesection. tion,andtheirpresenceamongcommontundraspeciesindicates
Intotal,48bulksedimentsamplesweretakenandscreenedfor asteppe-tundraenvironment;thiscanberepresentedbyarangeof
insectremainsusingasievewitha0.4mmmesh.Allsedimenttypes assemblagesandisconsideredaspecificecosystemthatisdifferent
werescreened,notonlyorganic-richones.Theweightofscreened frommoderntundra.
sedimentwasabout50kg,butinorganic-poorbedswescreened Ksexerophilousinsectswithwideecologicalpreferences.
additionalmaterial.Thedrieddetrituswasprocessedinalaboratory, Dt e xerophilous tundra insects; the group includes various
andfossilinsectswerepickedupunderalow-powerstereobinoc- insects such as Curtonotus alpinus, which is common in modern
ular microscope. Kerosene flotation (Elias,1994) was not used to tundra(inEastBeringiarepresentedbyAmara(Curtonotus)alpina)
extracttheinsectremainsasourexperienceshowsthatfossilinsects ontheonehand,tothePleistocenerelictspeciesPoecilusnearcticus,
frompermafrosthavesuchextremelygoodpreservationthatuseof whichisraretodaydthespecieswasdescribedonlyin1966.
kerosenecanactuallycausemissingofsomeheavyremains. Ttecold-resistantinsectstypicalofarctictundra.
Mteinsectsofmoistorwettundrahabitats.
3.3. Interpretationoffossilinsectassemblages Thesethreegroupsbelongtothetundraassociation.
OthergroupsusuallydonotplayanimportantroleinthePleis-
Terrestrial permafrost sediment is usually rich in subfossil tocenefossilinsectassemblagesofWestBeringia(althoughtheymay
insectswithrelativehardchitinexoskeletons:Coleoptera(beetles), dominateintheHolocene).Theseareasfollows:sheshrub,mee
some Hymenoptera e mostly ants and parasitic Hymenoptera, meadow,foeforest,rieriparian,aqeaquatic,andotheotherinsects.
S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106 2095
Fig.3. DetailsoftheIceBluffexposure.AetrenchIB-2,alt.21m,sandwithsparseplantremains;BetrenchIB-2,alt.15mfinesandwithplantremains;CetrenchIB-4besandthe
icewedgecastmarkedbyironishlayers;Detopofthesection,icewedgeandgreyfinesand;E(cid:3)icewedgeandtrenchIB-2.
Each species is assigned a group, even when there may be Thedatesarenotreversedwithintrenches,butbetweentrenches
ambiguity. For example, the tundra ground beetle Pterostichus therearesomediscrepancies(Fig.4).Accordingtotheradiocarbon
brevicornis canbe found in foresthabitats orin dry placesin the chronology, if we assume that the rather even overall rate of
tundra.Weplacedthisspeciestothemtgroup,however,because depositionshownbythedatesinthemaintrench,IB-2(z1mper
the main habitat of this species is wet tundra. This formalized 800yr),alsoappliestothesidetrenchesnearthetopofthesection,
systemobviouslyhassomelimitations,butithasprovedeffective thesedimentoflefttrenchIB-3awouldbeolder,butthesediment
in clarifying the structure of ancient insect communities and ofrighttrenchIB-6isyoungerthansedimentsinIB-2atthesame
allowingustotrackenvironmentalchangesintimeandspace. level. The bedding in the upper partof the sectionappears tobe
oblique (Fig. 3 a,b,e, Fig. 4). We observed in trench IB-2 that the
4. Results bedsrisetowardthefaceoftheoutcrop,andwecanspeculatethat
the reasons of such tilted bedding are related tothe influence of
4.1. Chronology a complicated system of large ice wedges (one of which can be
tracedalmostacrosswholesectionfrom1.5mbelowthesurfaceto
The radiocarbon data show that the studied deposits were 11 m above river level and probably continues deeper; Fig. 4,
formedapproximatelybetween33kaand16ka(seeTable1,Fig.4). Fig. 3e) or possibly from neotectonic warping of the area, in
2096 S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106
Fig.4. SchemeoftheIceBluffshowingsamplingpoints,radiocarbonagesandfossilinsectassemblages.1-3samplingpoints:1insect,2bulk,3DNA;4eicewedge;5eicewedge
cast;6epeat;7esiltandsandwithpeatlenses;8esand;9,10esiltysandwithdifferentbedding:9oblique,10horizontal;11efinesandwithgrassroots;12esilt.Ecological
groupoffossilinsects:stesteppe,msemeadow-steppe,ssecryophytesteppe,ksexerophilousinsects;dtetundraxerophilous;tteinsectsoftypicalandarctictundra;mte
tundrameso-hygrophilous;sheshrub;meemeadow;foeforest;rieriparian;aqeaquatic;otheothers.
which case small unobserved faults may explain the dating 4.3. 1e4m
differences.
ThelowestvisiblematerialwasincutIB-4b(Fig.4).Theunitis
sandy; it has a small ice-wedge cast and is overlain by a peat
4.2. Stratigraphy (probablyreworked)layer(Fig.3-c).Itliesbelowthesampledated
at 29,780 (cid:4) 21014C yr B.P. Above this unit the sectionwas inac-
Wedevelopedaseriesoftrenchesintotheexposureatdifferent cessibleforseveralmeters.
but overlapping elevations and at different lateral locations that
enabled an almost continuous upward examination of the sedi- 4.4. w8.5e28.5m
ments. Lateral shifts were determined by the presence of ice
wedgesandtheaccessibilityofthecliff(seeFigs.2and4).Inthe ThemajorityofthesectionheightisexposedincutIB-1andcut
followingdescriptiontheriverlevelisthe0-mdatum. IB-2 (see Fig. 4). The radiocarbon dates indicate it covers the
Table1
RadiocarbonfromtheIceBluffsections.
Laboratoryno SampleID Trench Heightaboveriver(m) Corresponding DeltaC13 Uncalibratedage Materialdated
faunalsample
OxA-15347 29C IB-2 12.6 n/a d13C¼(cid:3)26.1 33190(cid:4)240 Plantremains,rootlets
OxA-14928 28C IB-2 13.1 n/a d13C¼(cid:3)25.9 29780(cid:4)210 Plantremains
OxA-15349 33C IB-2 16.4 ChM-B14a d13C¼(cid:3)26.6 28190(cid:4)160 Plantremains,rootlets
OxA-14957 36C IB-2 18.6 ChM-B16a d13C¼(cid:3)26.2 25440(cid:4)130 Plantremains
OxA-15348 39C IB-2 21.0 ChM-B19a d13C¼(cid:3)26.9 22960(cid:4)120 Plantremains,rootlets
OxA-14929 44C IB-2 23.3 ChM-B21b d13C¼(cid:3)25.9 21050(cid:4)100 Plantremains
OxA-15667 47C IB-2 24.4 ChM-B25 d13C¼(cid:3)26.7 20830(cid:4)90 Plantremains,rootlets
OxA-14958 56 1B-3A 26.0 ChM-B26 d13C¼(cid:3)25.1 20900(cid:4)110 Plantremains
OxA-15668 51 IB-2 26.3 ChM-B23a d13C¼(cid:3)27.1 19850(cid:4)80 Plantremains,rootlets
OxA-14930 58 IB-6 27.4 ChM-B31b d13C¼(cid:3)26.1 15810(cid:4)75 Plantremains
S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106 2097
interval from>30to<20ka.Based ontheobservedstratigraphy insects that are typical of a Pleistocene steppe-tundra fauna, as
(Fig. 4) and the previous descriptions of Kotov et al. (1989) and describedpreviouslybyKiselev(1981)andKuzmina(1989,2003);
Anderson and Lozhkin (2002) we have not divided the major thecryophyte-steppepillbeetleM.viridis,dominatestheremains
portionoftheexposureintosmallerunits.Thematerialisice-rich (more than one third of all insects), the ground beetle Harpalus
grey silt grading upwards to sandy silt with numerous plant vittatus alaskensis is common and there are xerophilous species
remains:shrubroots,grasses,andleaves(Fig.3-b).Itbecomesless suchasthegroundbeetlesNotiophilusaquaticus,C.alpinus,Amara
organicnearthetopofthesection.TheupperpartoftrenchIB-2 glacialis, and weevils Mesotrichapion wrangelianum and Sitona
consistsoffinesandwithnumerousgrassroots.Closetotop,coarse borealis.Mesictundraspeciesarepresentbutlessabundant.They
yellow-greysandbecomesprevalentandplantremainsaresparse arerepresentedbythegroundbeetlesPterostichussubgenusCry-
(Fig.3c). obiusandtherovebeetleTachinusbrevipennis.Oneinterestingfind
TheuppermostpartoftheexposurewasstudiedinthecutsIB-3, istheleafbeetleChrysomelablaisdelli,whichfeedsonwillowandis
IB-3a, and IB-6 (Fig. 4). These sediments are grey fine sand and rarelyfoundtonorthofthesouthernshrubtundrazone.
silty-sand;incutIB-6theyareobliquelybeddedwithgrassroots The following five samples were taken from trench IB-1. The
whileincutsIB-3andIB-3atheyarehorizontalandcontainfewer lowestsample(B-2)fromthistrenchwastakenat10maboveriver
plant remains. Datesof 15,810 (cid:4)75 and 20,900 (cid:4)11014C yr B.P. level and the upper one (B-8) from 12.5 m above river level. All
withintheseshortsectionsindicatethatsedimentsinIB-6andIB- samples are fairly rich in insect remains. The steppe association
3/3a are not coeval (Table 1; Fig. 4), and this is supported by increases in dominance upwards. The two lowermost samples,
differencesobservedintherespectiveinsectfaunas(seebelow). while containing a relatively low percentage of steppe insects,
TheHoloceneislikelyrepresentedbyanabruptshifttopeator containasingleindividualofthetruesteppegroundbeetleCym-
silt and sand with peaty layers in the uppermost 1e2 m of the indis arctica and a few remains of the meadow-steppe weevil
sectionincutsIB-6andIB-3a,butwedidnotobtaindatesfromthis Coniocleonussp.,butbothbeetlesareotherwiserareattheIceBluff
level. Anderson and Lozhkin (2002) list a date of 2300 (cid:4)100 on site. Relative proportions of the pill beetle M. viridis increase
woodyfragmentsandpeatfrom1.0to0.5mbelowthetopofthe upwards. There are also single occurrences of the arctic weevil
exposure. IsochnusarcticusandthearcticleafbeetleChrysolinatolli.Thereare
noradiocarbondatesassociatedwiththissequenceofsamples.
4.5. Fossilinsectresults Themajorityofsamples(29inall)weretakeninthemaincut,
IB-2b, between w11 and 26 m above the river (see Table 2 and
Thefirstfossilinsectsamplesfromthislocalitycomefromthe Fig.4).Itshouldbenotedthatthelowersamples(B-11a,bandB-39)
Svitoch expedition of 1975. Noentomologists participated in this overlapwiththeuppersamplesofcutIB-1inelevation,buttheyare
expedition,andonlyorganic-richplanthorizons,wheregeologists represented by different fossil insect assemblages e the assem-
expectedtoseeinsectremainswithoutscreening,weresampled. blages B-11a,b and B-39 have a less pronounced steppe element.
By using the description of the sequence by Kiselev (1980b), we The sediments also differ, suggesting that either one or other
have correlated our new samples to those taken previously. The section contains displaced material, or that the sections are not
richest previouslycollected insect samples (Kiselev’s LO.2 and 3) coeval.IntrenchIB-2b,wefocusonsamplesabovetheradiocarbon
werecollectedfromthelower,nowinaccessiblepartoftheexpo- dateof29,780(cid:4)210.
surerepresentedbyshallow-waterlakesediment,andthesecon- TheassemblagesinsamplesB-12toB-15,fromw12tow18m
tainedahighnumberofaquaticspecies(Kiselev,1980b,1981).The abovedatum,and,accordingtotheradiocarbondates,representing
nextassemblage,fromsampleLO.4,reflectsadryenvironmentand aperiodfromw30tow2514CyrB.P.,showagradualdecreaseof
islikelytocomefromthebaseofthefourthunit(ice-richdepositor steppe insects and all xerophilous groups, while mesophilous
Yedoma).SampleLO.5comesfromthesouthernpartoftheexpo- tundra insects increase in dominance and shrub insects become
sure and again contains significant numbers of aquatic insects; more significant. One of the assemblages (B-13,14,8 m) contains
here,lakesedimentsarecorrelatedwithsubaerialloess-likesedi- abundantremainsofaquaticinsects(thewaterscavengerbeetles
mentsatthesamelevelinthenorthernpartoftheexposure.The Hydroporus acutangulus, Hydroporus lapponum, Agabus moestus).
lastofKiselev’s (1980b)samples, LO.6andLO.7,weretakenfrom Thesefeaturesofthissequence,thehighcontentoftundrameso-
Yedoma in the upper part of the exposure and correlate with philous and shrub group, the less important role of xerophilous
samples taken in 2004 from an elevation 24e26 m above river species,unstablevariationofsteppegroupinsects,whichispoorin
level. speciesdiversity,andpermanentpresenceofthearcticgroup,are
Insect faunas recovered from old (Kiselev,1981) and our new typicalfortheMIS3intervalandthisfaunalsequenceinagreement
samples are similar, with the exception of aquatic species, which with what was observed in the Bykovsky Peninsula fossil insect
areknownonlyfrompreviousstudies.Otherobservationssuchas fauna(Sheretal.,2005).
anearabsenceofthermophiloussteppeinsectsandabundanceof Inthenextupwardportionofthesection(samplesB-16toB-20,
dung beetles Aphodius sp., were noted both in the previously w18e22 m) radiocarbon dates of 25,440 (cid:4) 130 (w18 m) and
collectedandinthenewsamplesandillustratethepeculiarityof 21,050 (cid:4) 100 (w23 m) bracket the sequence. Xerophilous taxa
thelocalentomofauna.ThespecieslistispresentedinTable2and again dominate, with steppe taxa gradually increasing until the
theimagesoffossilinsectsareshowninFig.5.ThesamplesinTable steppegroupisonceagainassignificantasitwasinsampleB-9.All
2 are placed first by trenches, and second within trenches by samplescontainthearcticweevilI.arcticus.
elevation,fromoldertoyounger.Thesamplenumbersweregiven Thenextthreehighersamples,B-21a,bandB-22,arecloseto
in the field and reflect the order of sampling. Thus, the reader eachotherandcharacterizedbyanincreaseinarcticspecieseupto
should follow the height designations rather than the sample 41%intheassemblageB-21b.Thissetofsamples,whichareclosely
numbersfororientation. spaced, are dated to w21ka. The uppermost insect assemblages
The assemblages are described upward, beginning with the fromtrenchIB-2(samplesB-24eB-23)aresimilartothosebelow
lowermostunit.Theoldestandlowestsamplefrom2004wastaken samplesB-21andB22.
fromtrenchIB-4b(Fig.4).Theinsectsamplesweretakenfromgrey Asdescribedabove,theupperpartofthesectionisrepresented
sand; there was no visual organic matter, but plant and insect by trenches IB-3 and IB-3a, which are situated just to left of the
remainswererecoveredafterscreening.Thesampleisrichinfossil maintrench,andtrenchIB-6,whichliestotheright(Figs.2and4).
2098 S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106
Table2
FossilinsectdatafromtheIceBluffsections,reportedinminimumnumberofindividualspersample.Samplesarereportedinstratigraphicorderratherthansamplingorder,
beginningwiththelowestelevation.
S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106 2099
Table2(continued)
SamplesB-30,31,32(fromrighttrench,IB-6)areallsimilar;they Individuals (see Elias, 1994) using the best preserved parts. The
containlowamountsofsteppetaxa,althoughmostoftheinsects radiocarbondatumofthisunitis15,810(cid:4)75;thisistheyoungest
are xerophilous. All three samples contain abundant ladybird dateobtained.Thelowersample(B-30)oftrenchIB-6overlapsin
beetles of the genus Coccinella, most likely Coccinella trans- heightwiththeuppersampleB-23boftrenchIB-2,butwesuspect
versoguttata.Thefossilladybirdpreservationisnotperfectbecause thattheageoftheinsectassemblageB-30isyoungerthanB-23b;
of their minimal chitin and rounded form; we extracted many asmentionedabove,thelevelsdatedat19,850(cid:4)8014CyrB.P.inIB-
separated pieces and calculated the Minimum Numbers of 2and15810(cid:4)7514CyrB.P.inIB-6areseparatedbylessthan1m,
2100 S.A.Kuzminaetal./QuaternaryScienceReviews30(2011)2091e2106