elizabeth solleiro-rebolledo, hector cabadas, birgit terhorst · genetic horizons of modern soil...

22 E&G / Vol. 62 / No. 1 / 2013 / 22–33 / DOI 10.3285/eg.62.1.03 / © Authors / Creative Commons Attribution License

E&G Quaternary Science Journal Volume 62 / Number 1 / 2013 / 22–33 / DOI 10.3285/eg.62.1.03

www.quaternary-science.net

GEOZON SCIENCE MEDIA

ISSN 0424-7116

Paleopedological record along the loess-paleosol sequence in Oberlaab, Austria

Elizabeth Solleiro-Rebolledo, Hector Cabadas, Birgit Terhorst

How to cite: Solleiro-Rebolledo,E.,Cabadas,H.,Terhorst,B.(2013):Paleopedologicalrecordalongtheloess-paleosolsequenceinOber-laab,AustriaPaleopedologicalrecordalongtheloess-paleosolsequenceinOberlaab,Austria.–E&GQuaternaryScienceJour-nal,62(1):22–33.DOI:10.3285/eg.62.1.03

Abstract: Adetailedstudyofaloess-paleosolsequenceinOberlaab,UpperAustria,ispresentedwithemphasisonmacro-andmicromor-phologicalfeatures,grainsizedistribution,rockmagnetismproperties,andweatheringdegreethatallowscorrelationwithoth-erloess-paleosolsequencesinneighboringareas,andinterpretationofmainpedogenictrends.Thestudiedsequencecomprisesfourpaleosolcomplexes,whichlikelydevelopedduringfourinterglacialstagesMIS11,9,7and5e,andamodernsoil.Theoldestpaleosolcomplex(OL5)representsthreephasesofsoilformation,anddistinctsedimentaryeventsneverreportedinthearea,withstrongreductomorphicproperties.TheOL4profilealsoresultsfromthreephasesofpedogenesiswithincreasedreducto-morphicfeaturesinthedeepestzone(affectedbycryoturbationevents).OL3hasabundantfeaturesrelatedtogleyic/stagnicprocesses,butshowssignsofclayilluviation.OL2(Eemiansoil)correlateswiththeMIS5e.Thispaleosolshowshigherdegreesofclayilluviationandweathering,andfewerfeaturesrelatedtoreductomorphicprocesses.Themodernsoilisalsopolygeneticandconstitutesapedocomplex.ItslowermostpartisformedbyWürmianglacialdeposits,wherenowell-developedsoilsarefound;onlyreworkedmaterialsandpedosediments.Mainpedogenictrendsinthesequenceareclearlydifferentiated.Allofthepaleosolswereformedinhumidenvironments,butdifferingindrainageconditions.Thebase,withOL5andOL4paleosols,wasmoreaffectedbygleyicprocesses,whileintheupperpaleosols,especiallyOL2,clayilluviationisdominant.Weinterpretsuchdifferencestobecausedbythetopographicposition.Thebasalpaleosolsweremoreaffectedbyfluvioglacialprocessesduetotheirpositionontopoftheterrace.Theupperpaleosolsreceivedincreasedamountsofsedimentthroughfluvial,colluvialandaeolian(loess)input.

Das paläopedologische Archiv der Löss-Paläoboden-Sequenz in Oberlaab, Österreich

Kurzfassung: EinedetaillierteUntersuchungeinerLöss-Paläoboden-SequenzinOberlaab,Oberösterreich,wirdvorgestellt,derenSchwer-punktaufmakro-undmikromorphologischenMerkmalen,derKorngrößenverteilung,magnetischenGesteinseigenschaftenunddemVerwitterungsgradliegt.DieuntersuchtenAspekteermöglicheneinerseitseineKorrelationmitanderenLöss-Paläoboden-SequenzeninbenachbartenGebietenundandererseitsdieInterpretationwichtigerpedogenetischerEntwicklungen.Dieunter-suchteSequenzbestehtausvierPaläoboden-Komplexen,derenEntwicklungsehrwahrscheinlichwährenddervierInterglazialeMIS11,9,7und5estattfand,sowieeinemrezentenBoden.DerälterePaläobodenkomplex(OL5)beinhaltetdreiPhasenderBodenbildungmitunterschiedlichenSedimentationsereignissen,dieindiesemGebietbislangnochnichtbeschriebenwurden.DarüberhinausfindensichstarkredoximorpheMerkmale.DasProfilOL4zeigtebenfallsdreiBodenbildungsphasenmitzuneh-mendredoximorpherPrägungimunterenBereich,wobeieineÜberprägungdurchkryoturbateProzessesichtbarist.AuchanOL3konntenMerkmalegrund-bzw.stauwasserbeeinflussterProzessedokumentiertwerden,esfindensichaberauchHinweiseaufTonverlagerung.DerEembodenOL2entsprichtdemMIS5e.HierzeigensichdieintensivsteTonverlagerungundderstärks-teVerwitterungsgrad,sowieeinRückgangderredoximorphenMerkmale.AuchderrezenteBodenistpolygenetischundstelltsichalsPedokomplexdar.DeruntersteBereichbestehtauswürmzeitlichenglazialenAblagerungen.IndiesemProfilteilfindensichkeinegutentwickeltenBöden,sondernausschließlichumgelagertesMaterialundPedosedimente.DievorherrschendenpedogenetischenProzesseinderSequenzkönnenklarabgegrenztwerden.AllePaläobödenentstandenunterhumidenBedingungen,wobeiaberjeweilseineunterschiedlicheDrainagevorhandenwar.DieProfilbasis,diedurchdiePaläobödenOL5undOL4gebildetwird,iststärkervonGrundwasserbeeinflusst,währendindenoberenPaläoböden,v.a.inOL2,dieTonverlagerungdominiert.Esistanzunehmen,dassdieseUnterschiedeindertopographischenPositionbegründetsind.DieunterenPaläbödensindaufgrunddertieferenLagederTerrassestärkervonglazifluvialenProzessenbetroffen,wäh-renddieoberenPaläobödennachderSedimentationvongroßenMaterialmengen(fluvial,kolluvialund/oderLöss)einehöherePositioneinnehmen.

Keywords: Middle Pleistocene, loess, paleosol, Oberlaab, pedogenesis

Addresses of authors:E. Solleiro-Rebolledo,UniversidadNacionalAutónomadeMéxico,InstitutodeGeología.CircuitodelaInvestigaciónCientí-fica,04510,MéxicoDF,Mexico.E-Mail:solleiro@geologia.unam.mx;H. Cabadas,UniversidadAutónomadelEstadodeMéxico,FacultaddeGeografía,CerrodeCoatepecs/n,Cd.Universitaria,Toluca,México.E-Mail:hvcabadasb@uaemex.com;B. Ter-horst, UniversityofWürzburg,InstituteofGeographyandGeology,AmHubland,D-97074Würzburg/Germany.E-Mail:birgit.terhorst@uni-wuerzburg.de

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1 Introduction

Loess/paleosol sequences are a valuable source of infor-mationaboutpastclimaticandenvironmentalconditionsduringtheQuaternary,andareoneofthemostcompleteterrestrialrecordsofglacial-interglacialcycles(Pécsi1990;Pécsi&Schweitzer1993;Muhs&Bettis2003)success-fullycorrelatedtotheglobalclimateproxiesasmarineiso-topecurves(Kukla1978;Brongeretal.1998).Intemper-ate zones they have provided reliable information aboutpaleoenvironmental change, particularly for the last gla-cial/interglacial cycle, as in Eurasia (Liu 1985; Rozycki1991;Sunetal.1997;Muhs&Bettis2003;Fengetal.2007),UnitedStates(Muhs&Bettis2000;Bettisetal.2003),andSouthAmerica(Muhs&Zárate2001;Quattrocchioetal.2008).InAustria,severalworkscontaindetaileddescrip-tions for loess-paleosol sequences (e.g. Fink 1976; Kohl1976;Haesaertsetal.1996;Neugebauer-Maresch1996;Niederhuber1997;Terhorst2007).However,ourunder-standingofthepedostratigraphyandpedogenesisofloes-sic paleosols remains incomplete. In particular, in UpperAustria,whereoveracenturyofresearchonPleistocenelandscape history has been conducted since the classicalworksofPenck&Brückner(1909),loess-paleosolrecordsarestillyieldingnewdataforregionalpaleoenvironmentalreconstructions.

Westudiedaloess-paleosolsequenceinUpperAustria,situatedon the topof aMindelfluvioglacial terrace.TheAustrian stratigraphic table classifies the classical Min-del glacial asbelonging to theMIS 12 (ÖsterreichischeStratigraphische Kommission 2004). Van Husen (2000)andVanHusen&Reitner(2011)correlateMindelglacialsediments in the Eastern Alpine Foreland with the MIS12,whiletheRissiandepositsareassociatedtotheMIS6.On thebasisofpedostratigraphical analyses in theLinz/Wels area, Terhorst (2007; 2013, this volume) and Ter-horst et al. (2011) propose a similar correlation for theloess/paleosol sequenceofOberlaab,which includes fourinterglacialpaleosolslocatedontopoftheMindelterrace.These paleosols are linked to MIS 11, 9, 7 and 5, respec-tively (Terhorstetal. 2011,2013),andspanpartsof theMiddletotheUpperPleistocene.AccordingtoTerhorst(2007)andTerhorstetal.(2011,2013)MiddlePleistocenesequencesinUpperAustriaaretheresultofanalternationofgeomorphogenetic-pedogenicprocesses.DuringMiddlePleistocenetimes,geomorphodynamicsintheregionwerecontrolled by unstable glacial periods (causing phases oferosionandsedimentation),whichalternatedwithstableinterglacialperiodsandsoilformation.Usingtheconceptof “soil memory” (in the sense of Targulian & Gory-achkin2004) theresultingpaleosolscontain informationaboutenvironmentalconditionsoftheinterglacials.

In Oberlaab, we conducted a paleopedological survey,which involved a multidisciplinary approach to identifytypesofpedogenesisanddegreesofpaleosoldevelopment.Previously,Terhorst(2007)studiedasimilarsequenceintheloampitofOberlaab,whichcomprisesthickpedocom-plexes,relatedtofourinterglacialperiods,coveringatimespanof>400ka.Inthispaper,wecontributeadetailedmor-phologicaldescriptionofpedostratigraphicunitsaccompa-nied by a set of quantitative pedogenetic characteristics:

morphometric analysis of diagnostic pedofeatures, grainsize distribution, magnetic parameters (magnetic suscep-tibility and frequency dependence of susceptibility), aswellasgeochemicalindicatorsofweathering.Thesechar-acteristicsprovideabaseforreliablecomparisonbetweenburiedpaleosolsandtheHolocenesurfacesoil,inordertoestablishdifferencesinthetypologyandgradeofdevelop-mentofthemainpedogenicprocesses.Theresultingpale-opedological record contributes to the reconstruction oftheenvironmentalconditionsofthefourlastinterglacialsandprovidescomplementarydatafortheregionalgeomor-phologicalandstratigraphicschemes.

2 Materials and methods

The study site is situated in a quarry exploited for clayforbrickproduction,1.5kmtothenorthofWels,Austria(fordetailsseeTerhorst2013, thisvolume).ThegeneralstratigraphywaspresentedbyTerhorst(2007),whohasrecognized four interglacial paleosols. The loess/paleosolsequenceofOberlaabwasdevelopedonaMindelterrace(YoungerDeckenschotter).Thebasementof the sequenceis formedbygravels, exposedpreviously in a cutopera-tion during 2003. The whole sequence has a thickness of15.80m,whichhasbeensectionedandlabeledastheunitsOL1,OL2,OL3,OL4andOL5.Eachofthesesectionscon-tainsasoil/paleosol/pedocomplexunit(Figure1).

Genetichorizonsofmodernsoilandpaleosolswerede-finedaccordingtotheirmorphologyfollowingtheWorldReference Base (IUSS Working Group WRB 2007). Weobservedpedfeaturesundera10Xlensinthefield.Inallcases,interpretationwasbasedoncomparisonofpaleosolswiththemodernsoil.

2.1 Micromorphology

Formicromorphologicalstudieswetookundisturbedsam-ples fromeverygenetichorizon (Figure 1).Thin sectionswerepreparedanddescribedwith theguideofBullocketal.(1985).

Toquantifytheproportionofpedofeaturesindifferenthorizons, selected thin sections were scanned with highresolution(4800and9600dotsperinch);thedigitalimagewaslateranalyzedwiththeImageProPlusv.6.0software.Acontrastenhancementofeveryimagewasproducedtodistinguishzoneswithdiffusecontactstothegroundmass,usingtheblueRGBchannelacquisition.Thefalsecolorwasusedforthesegmentationofareasoccupiedbyeachped-ofeaturewithapreviousconversiontoshadesofgrey.Themost important features analyzed were: 1) iron nodulesandimpregnations,2)bleachingareasand3)claycoatings.However,inmostofthethinsectionsthecomplexmixtureofironandclaywasverydifficulttoseparatebythesoft-warealgorithms.Thus,wedecidedtostudyclaycoatingssemi-quantitatively using visual schematic petrographicdiagrams(Castro1989).Porositywasnotestimatedinthetotalaverage,becauseinsomethinsectionsvoidshadthesamecolorasfelsicminerals.

Besidesmicromorphometricanalysisofselectedpedofea-turesweestablishedtheassemblageoftheprimaryminerals,theirdistributionindifferentsizefractionsandtheirweath-

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Fig. 1: Oberlaab loess/paleosol sequence on top of a Mindel terrace (Young Deckenschoter), which includes four interglacial paleosols and the modern soil.

Abb. 1: Stratigraphie der Löss-Paläoboden-Sequenz Oberlaab, sowie ein allgemeiner Überblick über alle vier Paläoböden und den rezenten Boden.

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eringstatusbasingonthecrystalloopticalpropertiesundermagnificationwithapetrographicmicroscope.

2.2 Laboratory analyses

SizefractionswereseparatedinOL1,OL2,OL4andOL5.OL3 was not evaluated due to the lack of samples. Thesandfraction(2–0.063mm)wasseparatedbysieving;silt(0.063–0.002mm)andclay(<0.002mm)fractionsbygrav-ity sedimentation with previous destruction of aggregat-ing agents; H2O2 (15%) was used for organic matter, anddithionite-citrate-bicarbonate (DCB) for iron oxides. Asthe deposits had no carbonates, no additional pre-treat-mentswerenecessaryfortheirdestruction.

For magnetic measurements, 200 g samples were col-lectedatroughly20cmintervals,homogenized,andplacedin8cm3acrylicboxes.Magneticsusceptibility (χ),whichis a measure of the concentration of magnetic minerals,was registered in all samples at low (0.47 kHz) and highfrequencies (4.7 kHz) with a Bartington MS2B dual sen-sor. We calculated frequency dependence of susceptibil-ityχfd%as[(χlf–χhf)/χlf]100,toapproximatepossibleul-trafine (< 0.05 μm) superparamagnetic (SP) contribution.Dearing (1994) and Dearing et al. (1997) suggest thatvaluesofcfd%<2%pointtoacontentof<10%ofSP(su-perparamagnetic) grains; values around 8% indicate a SPcontributionof75%,andbetween10–14%, thematerial isdomainbySPparticles.

2.3 Geochemical indices of weathering

BulkchemicalcompositionwasobtainedbyX-rayfluores-cence inaSiemensSRS3000spectrometer,usingpowderpelletsattheInstituteofGeology,UNAM.Allresultswerecalculatedbyweightonovendry(105°C)soil.

Astheparentmaterialofthesectionismainlyloessrichin silica,wedecide toevaluate thedegreeofweatheringusing the chemical index of alteration (CIA). CIA meas-ures changes in major cation content in relation to im-mobile alumina, instead of changes in the silica/aluminacomposition. This proxy was first proposed by Nesbitt&Young(1982)andintroducedinloessstudiesbyLiuetal. (1995). CIA is evaluated following the formula: CIA=(Al2O3/(Na2O+CaO+MgO+K2O))*100.Thereasontousethisweathering index is thehighconcentrationofK-feldsparfoundinthemineralogicalassemblage,accordingtoBug-gleetal.(2011)andthelackofcarbonates(thustheCaOcontent is only associated to silicates). A value near 100representsthehighestdegreeofweathering,whilevalueslowerthan50correspondtofreshsediments.

3 Results3.1 Morphology of the Oberlaab paleosol sequence

The study sequence in Oberlaab includes a modern soil(OL1)and4paleosolunits(OL2toOL5)fromthetoptothebottom(Figure1).

OL1.Modernsoil(depth0–190cm).TheOL1soilshowsa well-developed profile with Ah-AE-E1-E2-EBt-EBtg-Btg1-Btg2-G-Cwhorizons.TheAhhorizon is thin (5cm-thick),darkbrown,veryporous,withaconsistentgranular

structureandahighdensityofroots.ThetransitionalAEhorizonisalsothin(10cmthick)andpalerthanAh.TheunderlyingEhorizon is30cmthick,divided intoE1andE2.This division wasmadebecauseE2 is notablydarkerwithlesssilt. Ingeneral,theEhorizonislightgray,siltyandwithsubangularblockystructure.ThecontactwiththeunderlyingBtg1 isalso transitional, throughtheEBtandEBtghorizons(45–100cm).Lightgraytonguesofcompact-ed, siltymaterial, starting fromtheEhorizon,enter intoBtg(100–150cm).Thesetonguesareseparatedfromeachotherby15cminsomecases,and25cminothers.Rootsdonotpenetratethetongues.TheBtg1horizonisgrayish-yellowishbrown,withyellowishbrownmottles.Claycoat-ingsarethickandfrequent.TheBtg2horizonhasasimi-larcolor,butisdistinguishedbyanetworkofcracks.Thecracksboundariesaregray,contrastingwiththebrownishcolorofthematrix.ThelowermostGhorizon(150–160cm)is gray in color, more dense and has a silty texture. Thesubangularblockypedsexhibitaplatystructure.TheCwhorizon(160–190cm)correspondswiththeuppermostpartofapale-yellow,silty,loess-likedeposit,showinghorizon-talgraybands.

TheunderlyingCwhorizoncorrespondstoaloess-likedeposit (190–390 cm). This material constitutes a pedo-sediment,whichcontainsamixtureofsedimentsandre-workedsoils.

OL2. Eemian soil (depth 390–670 cm). The next strati-graphic level corresponds to the Eemian soil (Figure 1),andcontainsasequenceof(E1)-(E2)-Btg1-Btg2-BCtg-BCg-Chorizons.Verticalcrackscrossthefirst200cm(390–590cm),filledbyagraymaterial, ofwhich the innerpart isblack.Theboundarybetweenthegrayandblackmaterialsisreddish.

Becauseofthepalercolor(brownishyellow)ofthefirst60 cm (390–450 cm), we initially assumed that the mate-rialcorrespondstoanEhorizon,whichisdividedintoE1andE2withasiltyloamtexture.However,amoredetailedmorphological study revealed that the horizon is consti-tutedbytwolayersofreworkedpedosediments.Theloess-likesedimentisaffectedbyweakpedogenesis,withround-edsedimentgrainsandsoilfragments.Thesoilfragmentsoccur as small subangular blocks breaking into granularaggregates,with a tendency to formaweakplaty struc-ture.Moderateamountsof2–3mm-diameterFe/Mn-con-cretionsweredetected, varying fromdarkbrown to red.ThetransitionallimittotheunderlyingBtghorizon(Btg1and Btg2) is wavy. The Btg horizon (450–540 cm) is yel-lowishbrown,darkerthanthereworkedpedosedimentsoftheupperpart,morecompact,andclayey.Btg1hasabet-terdevelopedplatystructure,whichbreakstosubangularblocks. Clay coatings are abundant. In the upper surfaceof the platy aggregates, discontinuous dark brown claycoatingsarepresent.Inthishorizontheverticalcracksarecoveredbyclayandsiltcoatings(thelatterareobservablewith a 10X-hand lens). Fe/Mn-concretions are abundant.Thehorizonshowsstrongmottling,whichconsistofbrightyellowareaswithbrownishandgrayishzones.Thesespotsaremainlyorientedalongtheverticalcracks.InBtg2,claycoatings are fewer and more disperse. The BCtg horizon(540–570cm) ispalerandalsocompact.Here, fewerclaycoatings and Fe-Mn concretions are detectable. Vertical

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orientedchannelsarealsopresent.Theyarefilledbylami-natedclay(darkbrown)andsiltcoatings(yellowandgray).TheBCghorizon(570–635cm)issimilar,butherecoatingsareveryrare.Themostconspicuousfeatureisthechangeof color as well as the intensity of gleyic characteristicsthroughoutthehorizon.Grey,horizontallyorientedlens-esappearinthefirst15cm.Thematrixofthenext30cmis grayish-yellowish brown with some yellow spots. Thelowerpartislightyellowishbrownandhasdiffusemottles.TheChorizon(635–670cm)hasasiltyloamtextureandabrowntoyellowishbrowncolorwithrustymottles.TherearenoFeconcretions.Structureisweakvaryingfromsub-angularblockytomassive.

OL3.Secondpaleosolcomplex(depth670–900cm).Simi-lartotheEemiansoilinOL2(Figure1)thisunithastwolevelsofreworkedpedosediments(E1andE2)onthetop(670-730 cm), which are superimposed on the followingcompact horizons:Btg1-Btg2-BCg. The first pedosedimentlevel(30cmthick) isstronglymottled.Matrixhasalightbrownishyellowcolorwithgraystagnicmottlesandroundrusty patches (1 to 1.4 cm in diameter). Structure showslarge subangular blocks and inside the block aggregates

Fig. 2: Micromorphology of the study section: a. Coalescent excremental infillings in chambers in AE horizon of the modern soil. High resolution image (4600 dpi) of scanned thin section.b. Concentric iron nodule in G horizon of the modern soil, photomicrograph, plane polarized light (PPL). c. Bleached zones in the groundmass of BCg1 horizon in OL4. High resolution image (4600 dpi) of a scanned thin section. d. Same as 2c: Image analysis in false color.e. Bleached zone (center) with sharp contact with the groundmass in OL3-BCg horizon. Fe nodules showing abrupt boundaries with the groundmass, photomicro-graph (PPL).f. Same as 2e, cross polarized light (XPL). g. Clay coatings around a void associated with a bleached zone in OL3-Btg1 horizon. The dark-yellowish color of the clay is related to the presence of iron and coarse silt fraction, photomicrograph (PPL). h. Same as g, XPL. Note the high interference color related to the presence of 2:1 clay structure.

Abb. 2: Mikromorphologie des untersuchten Abschnitts:a. Koagulierte Exkrementfüllungen in Hohlräumen im AE-Horizont des rezenten Bodens. Hochauflösende Darstellung (4600 dpi) von gescanntem Dünnschliff. b. Konzentrische Eisenkonkretion im G-Horizont des rezenten Bodens. Mikroskopaufnahme unter eben polar-isiertem Licht (plane polarized light, PPL).c. Gebleichte Zonierung in der Matrix des BCg1-Hori-zonts von OL4. Hochauflösende Darstellung (4600 dpi) von gescanntem Dünnschliff. d. Wie 2c: Falschfarbenbildanalyse. e. Gebleichter Bereich (Zentrum) in scharfer Abgrenzung zur Matrix im BCg-Horizont von OL3. Mikroskopauf-nahme (PPL). f. Wie 2e., gekreuzte Polarisatoren (cross polarized light, XPL).g. Kugelförmige Struktur (roter Rahmen rechts) in OL4. Hochauflösende Darstellung (4600 dpi) von gescanntem Dünschliff. h. Tonüberzüge in einem Hohlraum in Verbindung mit einer Bleichzone in Btg1 in OL3. Die dunkelgelbe Farbe des Tons ist bedingt durch den Eisengehalt und der Korn-größenfraktion Grobschluff. Mikroskopaufnahme (PPL).

there is a tendency to forma thinplaty structure.Verti-calcracksarefrequentandfilledbyclaypellets.Therearebleached areas with light colors that contrast with withdarkerstagniczones.Thesecondlevelofreworkedpedo-sediments(30cmthick)correspondstoastronglypatchysiltyloam.Inthiscasethecolorispalerbecauseofdomi-nantgrayishmottles.Roundedmottlesarecoveredbydarkbrownclaycoatings.Btg1(730–790cm)ischaracterizedbyadarkbrownmatrixwithevendarkermottlesthatalter-natewithbrownishgrayspots.Structureisverywellde-velopedinstrongangularblocks,whichbreakintosmallerangular aggregates. Dark brown Fe/Mn-concretions withasizefrom1to5mmdiameterarefrequent.Darkbrownclaycoatingsarepresent;however,theyareveryrareandappearinfewpeds.Smallquantitiesofcharcoalarepresentand associated to thin root channels.Due to an increaseofverticallyorientedgleymottles,Btg2(790–860cm)hasaclearchangeincoloraswellasinstructure(subangularblocks).Inthishorizonwedetectadecreaseintheabun-danceofclaycoatings,andinthequantityandsizeoftheFe-concretions. Some rounded rock fragments are found.TheBCghorizon(860–900cm)isstronglypatchy.Matrixis

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cm)andBCtg2(1140–1180cm)arealike,butBCtg1ismoreclayeyandshowsdarkclaycoatings.Roundverticalchan-nelsarecommon.G(1180–1200cm)ismorehomogeneousin color with a grey matrix, showing small brown rustymottles.Structureiswelldevelopedandconsistsofsmallsubangularblocks.Itisclearthatverticalchannelsdonotenterintothishorizon.

OL5. Fourth paleosol sequence (1200–1520). This low-ermoststratigraphiclevelisclearlyapedocomplex,com-posed by Bg-G-2Bg-2BCg-3Ah-3EBg-3Bg-3Cg horizons(Figure 1). The upper Bg (1200–1250 cm) is pale brown-ish yellow with rusty and grey mottles. It is constitutedbyveryfragilesubangularblockswithasiltyclaytexture.ItstransitiontotheGhorizoniswavyandgradual.TheGhorizon(1250–1290cm)isbluishgraywithblackandrustymottles.Duetotheoccurrenceofsmallsubangularblocksthe structure isbetterdeveloped than in theBghorizon.Mnsegregationsarecommon.Theboundarywiththenext2Bg horizon (1290–1370 cm) is clear and wavy. It is palebrownwithbrown,rustyandblackmottles.Ithasasiltyloamtexture.Friablesubangularblockystructureisdomi-nantwithatendencytobreakintocrumby,granules.Mnissegregatedinporesandchannels.Veryfewclaycoatingsarepresent inchannelsandonpedsurfaces.Thebound-arywiththelessstructured2BCg(1370–1415cm)iswavyandgradual.Roundedrock fragmentsarepresent in this

yellowishbrownwithmottlesvaryingfromgraytobrown-ishgrayandred.Thestructure is subangularblockyandplaty. Vertical cracks filled by grayish material cross thehorizon.Fe/Mn-concretionsare frequent (0.1 to0.5 indi-ameter).

OL4.Thirdpaleosolcomplex(depth900–1200cm).ThisunitisconstitutedbyBg1-Bg2-BCg1-BCg2-BCtg1-BCtg2-Ghorizons (Figure1),whichareverycompactandhavesiltyloamtextures.Theunitiscrossedbyverticalfissuresfilled by dark gray, stagnic materials. In the central partof thefissuresweobserveclayandsilt coatings (the lat-estdistinguishbytheircoarsertexture).TheBg1horizonisstronglypatchyandwavy(900–950cm).Darkbrownmate-rialalternateswith lightgreyverticallyorientedmottles.Theexteriorpartofthemottlesissurroundedbyyellow-brownoxidizedzones.Structureisplatyandangularblocky.Abundant Fe/Mn- concretions (0.5–1cm in diameter) arefound.Darkcoatingsarepresent,especiallyonthesurfaceofplatyblocks.Bg2(950–990cm)clearlydiffersfromtheprevioushorizonbytheincreaseofgrayareas(stagnic)onthepedsurfaces.Fe/Mn-concretionsarealsopresentbutinlesseramounts.BCg1(990–1030cm)ispatchy,palerthanthepreviousBtg,butwithasimilarstructure.Inthishori-zontheverticalfissuresarethickerthanintheupperpart.FeandMncoatingsarefrequent.BCg2(1030–1100cm)isvery similar to BCg1 but less patchy. BCtg1 (1100–1140

Fig. 2: Micromorphology of the study section: i. Deformed pedofetures. Deformed clay coat-ings showing a “twisted” morphology and displacing the groundmass (red arrow) around blocky microstructure in Btg2 horizon of OL3, photomicrograph (PPL). j. same as 2j, (XPL). The red discontinuous lines show the “twisted” morphology with the displacing of the groundmass. Note the high interference color inside and outside of the blocky microstructure, related to a primary phase of clay illuviation (2:1 clay structure).k. Orbiculic fabric (blue discontinuous line) in Bg2 horizon in OL4. High resolution image (4600 dpi) of scanned thin section.l. Fragmented clay cutans possibly associated to bioturbation in Bg2 horizon of OB4. High resolution image (4600 dpi) of scanned thin section.

Abb. 2: Mikromorphologie des untersuchten Abschnitts:i. Wie h., gekreuzte Polarisatoren. Man beachte die hohen Interferenzfarben aufgrund der 2:1-Struktur der Tonminerale.j. Fragmente illuvialer Tonüberzüge verdrän-gen die Matrix im Btg2-Horizont von OL3. Mikroskopaufnahme, (PPL). k. Wie 2j., gekreuzte Polarisatoren. Auch hier ist die hohe Interferenzfarbe innerhalb des primär illuvial verlagerten Fragments zu beachten. Der rote Pfeil kennzeichnet teilweise in der Matrix assimilierte Toncutane. l. In der Bildmitte Fragmentierung von Ton-cutanen in Bg2 (OB4), möglicherweise durch Bioturbation. Hochauflösende Darstellung (4600 dpi) von gescanntem Dünnschliff.

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horizonmarkingaclearandstraightlimittothenext3Ahhorizon(1415–1430cm),whichhasaverydarkgraycolorwithrustyandbrownmottles.Itisasiltyclayloamwithaveryfragilesubangularblocky-granularstructure.Char-coal fragmentsand fewclaycoatingsare found inchan-nelsandpores.Thetransitiontothe3EBghorizonisclearandslightlywavy.3EBg(1430–1450cm)ispalegray.Rusty,brown,andblackmottlesarepresent.Itsstructureiscon-stitutedbyfragile,smallsubangularblocksandgravelsarefrequent. 3Bg1 (1450–1490 cm) is yellowish brown withgrayish mottles. It is a silty clay with a fragile structurecomposedofsubangularblocks.Mnsegregationsandfer-ruginous hypocoatings are abundant in pores and chan-nels.Thelowerpartofthishorizonismoregrayish.Itscon-tactwiththeunderlying3Cg(1490–1520cm)isabrupt. ItisbuildupbygravelswithabundantMnsegregationsanddark-brownmottlesaroundthegravels,whichincreaseinsizewithdepth.

3.2 Micromorphology

The main micromorphological features observed in theOberlaabsectioncanbedividedintofourkinds:biogeniccomponentsandfeatures,redoximorphicpedofeatures,claycoatings,anddeformedpedofeatures.Inmostcasesthepro-portionsareobtainedbyusingthescannedthinsectionsandtheImageProsoftware.

Biogeniccomponentsandfeatures.Thesematerials in-cluderoottraces,humus,coprolites,channels,andcharcoal.TheyareclearlyrecognizableinboththemodernsoilandtheOL4profiles.TheAhandAEhorizonsofthemodernsoil(OL1)arecharacterizedbystrongbioturbationincludingthepresenceofchamberswithlooseanddiscontinuouscoales-centexcrementalinfillings(Figure2a)associatedwithroottraces(insomecasesmoreorlessdegraded).Darkhumusimpregnatesthematrix,incaseswhereagranularstructuredominates.BiogenicmaterialsinOL4arelessdiverse.Theyarepresentedonlybycharcoalfragmentswithawellpre-servedcellularstructure,aswellaspassagefeaturesofmeso-fauna.

Redoximorphic pedofeatures. These kinds of pedofea-tures include ferruginous concretions, hypocoatings, andbleachedareas.Paleosolscontainthehighestconcentrationsincomparisontothemodernsoil(Figure3).However,FeconcretionsarefrequentintheGhorizonsofthemodernsoil,wheretheyshowsharpboundariestothematrix(Figure2b).Feconcretionsandhypocoatingsreachthemaximum(19%)intheBCg1horizonofOL4.Thehighestproportionofbleachedareas(65%),whichpermittheestimationofzoneswhereironhasbeenremoved,wasfoundintheBg2horizonofOL4(Figures2cand2d,Figure3).Itisinterestingthatthecontactbetweenbleachedzonesandgroundmassisdiffuseinsurficialhorizons,however,inthelowerpartofthepro-files,boundariesaremoreabrupt.Figures2eand2fclearly

Fig. 3: Proportion of micropedofeatures in the Oberlaab sequence, according to the image analysis using the software Image Pro in high resolution image (4600 dpi) of scanned thin section.

Abb. 3: Quantifizierung von Mikrobodenmerkmalen, basierend auf der Bildanalyse mit der Software Image Pro, in hochauflösender Darstellung (4600 dpi) von gescanntem Dünnschliff.

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showthiskindofcontactintheBCghorizonofOL3.Claycoatings.Claycoatingsarecommoninthemodern

soil;coatingcontentvariesfrom1to3.5%.Surprisingly,theGhorizonreachesa7%themaximuminthewholesequence(Figure3).IntheEemianpaleosol(OL2),particularlyintheBtgandBCtghorizons,theamountsarealsohigh(2.1to4%).ThelowestconcentrationofclaycoatingsispresentintheOL3andOL4profiles(Figure3).The“impurity”oftheclaycoatingsvariesintheprofiles.Inthemodernsoilmostofthecoatingsarepureandlimpid(withyellowishcolors),mean-whileinthepaleosolscoatingsshowFemicrolaminationsandpigmentations(Figure2gand2h).

Deformedpedofeatures.Allstudiedpaleosols,aswellasthemodernsoilshowdeformationofsomepedofeatures.Thisdeformation ismoreevident inBtghorizons,where

theclaycoatingsareassimilatedinsidethebleached,siltygroundmassandexhibita“twisted”morphology(Figure2iand2j).Thepresenceoffragmentedanddisplacedground-massblockswith“cloud”structuresaswellasorbiculicfab-ricsarealsocommon(Figure2k).Additionally,inOL3andOL4 small blocks are fragmented and displaced. In suchblocksweobservetwodifferentgenerationsofclaycoatings:thefirstone(thinanddiscontinuousclaycoatings)isinsidetheblocks;thesecondone(withthickercoatings)coverstheaggregates.Anotherkindof“deformed”coatingsispresentinBCghorizons(particularlyinBCghorizonofOL4).Thesecoatingsarefragmentedandrounded,indicatingreworkingprocesses(Figure2l).

Besides the micromorphological descriptions madefor the thin sections we analyzed thebulkmineral com-

Fig. 4: Selected analytical properties of the study sequence: Magnetic suscepti-bility (χ E-6 m3/g); frequency depend-ence of susceptibility (χfd%): grain size distribution (%).

Abb. 4: Ausgewählte Analyseergebnisse des untersuchten Abschnitts.

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positionofsandandsiltfractions.Themineralcontentismostlyconstitutedbyquartz,potassiumfeldspar,andmica(muscovite),whicharemoderatelytowellsorted.Biotiteispresent in lowquantitiesandmostlyconcentrated in thesandfraction.Heavymineralssuchasamphiboles(insomecaseswith“serrated”morphology),epidote,andgarnetareconcentratedinthesiltfractionanddemonstrateangularshape.Someschistfragmentsarerecognizableinprimarysedimentary layers. This mineralogical assemblage coin-cideswellwiththereportsfromotherloess-paleosolsse-quencesofUpperAustria(Terhorstetal.2011).

3.3 Analytical properties

Thesiltfractioninthemodernsoilrangesfrom33to67%.The surficial Ah horizon shows a high amount of sand(30%),contrastingtothatobtainedintherestoftheprofile(Figure 4). The clay fraction exhibits similar proportionsinallhorizons,however,itincreasesinEBtandBtghori-zons.TheCwhorizoncontains thehighestproportionofsilt(64–66%).Magneticsusceptibility(χ)isgenerallylowinallhorizons,butwithhighvaluesinCw1andAhhorizons.Thelowvaluesofthefrequencydependenceofsusceptibil-ityχfd%indicateanullcontributionofsuperparamagnetic(SP),ultrafinegrains(<0.05µm).Tothecontrary,SPparti-clesdominateinAEhorizon(Figure4).CIAvalues(chemi-calindexofalteration)arehigh,increasingfrom77%inAhto85%inEBt(Figure4).Thelowermostpartoftheprofilesrecordsslightlylowerpercentages.

IntheEemiansoil(OL2)thesiltfractionisdominant(55-70%).Thewholeprofile showsa lowproportionof sand.ClaycontentreachesamaximuminBtg2horizon,although(E1)and(E2)horizonsonthetopshowahighproportionaswell(Figure4).Thevaluesofmagneticsusceptibility(χ) areverylowin(E1)and(E2)butincreaseinBtg.χfd%valuesareverylowinthewholeprofile,revealingthatnoneofthehorizonshasSPcontribution(Figure4).CIApatternshowsamaximumintheBtg2horizon(87%)andreachthelowestvalueinBCg(80.3%).

OL3hasahigherpercentageofsand(7to12%)thantheEemiansoil,however,siltstilldominates(61to70%).Inthisunittheclayamountislower(25–29%)andthereisnosig-nificantdifferenceamongthehorizons,althoughaslightlyhighercontentisobviousinBtg2(Figure4).Incaseofmag-neticparameters,χhas similarvalues,whileχfd%showsstrongdifferencesvaryingfromzerointhe(E1)to14%in(E2),5%inBtg1,14%inBtg2,andzeroinBCg.Thiscontrastevidencesthepresenceofdiscontinuities (Figure4). CIAvaluesarealsoverysimilar(83–85%).Thehighestweather-ingdegreecorrespondstoBtg1(Figure4).

OL4profileshowsverylowandhomogeneousχvalues,buthighpercentagesofχfd%indicateanelevatedcontri-butioninSPparticles.However,thisbehaviorisnotcon-tinuous,becauseinBg2,inthelowermostpartofBCg2(in180–200 cm depth), and in the G horizon, χfd% drops tozero(Figure4).CIAvariesfrom84%inBghorizondecreas-ingto82%inBCtg2.

OL5hashighvariabilityintheproportionsofthediffer-entsizefractions,whichrevealtheinfluenceofalluvialsedi-mentation.Sandvariesfrom8%intheBghorizonto42%inthelowermostpartoftheprofile,wheregravelappears.OL5

hasverylowvaluesinχ,althoughanenhancementwithoutcontributionofSPgrainsisnotedinthe3Ahhorizon,whichisdetectableintheuppermostpartoftheprofileintheBgandGhorizon(Figure4).CIAisequallyvariable.TheupperBgaswellasGhorizonareslightlylessweatheredthan2Bgand2BCgand3Ahand3CgshowthelowestCIApercent-ages.

4 Discussion4.1 Chronostratigraphy and correlation of the Oberlaab profile

Althoughno instrumentalabsolutedatesareavailable inOberlaab it is possible to establish a local chronostrati-graphicschemetakingintoaccountthestratigraphicclas-sificationofScholger&Terhorst(2011)andTerhorstetal.(2011)developedfortheMiddlePleistoceneprofilesintheNorthwestofAustria.

Terhorst(2007)pointsoutthattheOberlaabsequencecontainsfourinterglacialpaleosols(1st,2nd,3rd,4th)thuscoveringatleastthelastfiveglacialperiods(thusthede-velopmentoftheMindelterrace(YoungerDeckenschotter)occursatleastduringMIS12).Accordingtothestratigraph-icschemes,Oberlaabrecordscompletelythemainpaleocli-maticstagesfromMIS12toMIS5e,partsofthelastglacial,aswellastheHolocenesoil.Thisinterpretationisingoodagreement with the pedostratigraphical schemes of thecoverlayersinWels-Aschet,Neuhofen,andOberlaabandourstudiescanclearlybepositionedintheregionalstrati-graphic context of the area. This contradicts to the viewof Preusser & Fiebig (2009), who propose younger agesfor the Wels-Aschet sequence including the Older Deck-enschotteroftheGünzglaciation,basedonluminescencedating.Forinstance,theysuggestanageof252±29kyforthe4thinterglacialpaleosol(MIS7).Paleomagneticstudiesdone in the same sequence also contradict the chronos-tratigraphyofPreusser&Fiebig(2009)documentingthepresenceoftheCalabrianRidgeexcursions:CR1(325–315ka)andCR2(525–515ka)insidethe3rdandinthebaseofthe4th interglacialpedocomplex,respectively(Scholger& Terhorst 2011). Consequently, OL5 can be attributedtoMIS11withthreephasesofsoilformation:Bg-G-2Bg-2BCg-3Ah-3EBg-3Bg-3Cg.TheupperBghorizoncorrelateswiththe4thinterglacialpaleosol,describedbyTerhorst(2007)andTerhorstetal. (2011) inOberlaab,Neuhofen,andWels-Aschet,butinourcaseclaycoatingsarenotob-servedinthisunitasinothersequences.Terhorst(2007)mentionsanunderlyingGhorizoninNeuhofenandWels-Aschet, but without the 2Bg-2BCg horizons, which arepresentinoursection.Furthermore,thelowerpaleosolhasnotbeendescribedbeforeinthearea.Therearecleardif-ferencesinanalyticalproperties,whichreflectsoilforma-tioncycles:CIAvaluesarelowintheBg-G,3Ah,3EBg,andhighin2Bg-2BCg,3Bghorizons(Figure4).

ThesubsidingstratigraphiclevelsofOL4andOL3cor-relatewiththe3thand2thinterglacialpaleosolsdescribedforUpperAustria(Terhorst2007;2013,thisvolume;Ter-horstetal.2011).OL4 isdevelopedonsedimentswhichare classified as MIS 10 deposits and represent an inten-siveglacialphase.Thereforepaleosolformationcouldcor-respondbesttotheMIS9(c.f.Lisiecki&Raymo2005).On

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thebaseof thepedostraphicobservations, thenext sedi-mentation events can be correlated to the MIS 8 period,whichrecordsaweakerglacialphase(c.f.Lisiecki&Ray-mo2005).PedogenesisoftheOL3unitcanberelatedtotheinterglacialperiodofMIS7.

Both profiles OL3 and OL4 are pedocomplexes (Ter-horst2007;Terhorstetal.2012).Accordingtoourfieldobservationssignificantdifferencesanddiscontinuitiesarenotdetectablebetweenbothunits.However,somequan-titativeanalyticalcharacteristicsclearlyindicatethem.InOL4wecanseparatethreephasesofpedogenesis:thefirstphasecorrespondstothedevelopmentofthelowermostGhorizon, reflectedbydifferentproperties:CIAvalues arehigherthanintheoverlyingBCtg2,χfd%iszerowithnocontribution of SP magnetic particles. The second phasecomprises the horizons BCgt1 and BCg2, which tend tohavesimilarcharacteristicsalthoughCIAvaluesarehigherinBCtg1,afactwhichisrelatedtoahigheramountofclay.The third phase corresponds to the formation of the up-perhorizonsBg1-Bg2-BCg1-BCg2.TheseresultsarenotingoodagreementwiththoseobtainedbyTerhorst(2007),who reports the presence of a pedocomplex in Oberlaabwithonly2paleosols,onedescribedasaBwhorizonwithstagnicpropertiessuperimposedbyaBtghorizon.InWels-Aschet,Terhorstetal. (2012)findthe3thpaleosol,con-tainingtwoBthorizonswithmoderateweatheringdegree.Coincidencesareintermsofthegleyingprocess,becauseinOberlaabasinothersectionsinLowerAustria,elevatedamountsofMnhavebeenfoundindifferentforms.

On the other hand, OL3 is another pedocomplex. Re-peatedly, the profile has been characterized as monoge-neticduringfieldsurvey,however,analyticalresultscouldhighlightspecificdifferences,althoughtheclaycontentissimilar(Figure4).CIAindexandχrevealmaximaintheBtg1horizon,whichcanberelatedtothehighamountofclay(around30%).χfd%valuesrecordsignificantdifferenc-esinthecontributionofmagneticparticles,andthuscanbeexplainedbythepresenceofdiscontinuities(Figure4).WehaveevenfoundcharcoalinBtg1–probablybecausethishorizonwasclosetothesurface.OurresultsexhibitadiscrepancytothoseobtainedbyTerhorstetal.(2012)fortheWels-Aschetsequence,becauseonthebasisofminera-logicalanalysestheauthorsconcludethatthe2thpaleosolis lessweathered than the3thone.SimilarmineralogicalresultswereobtainedforearlierstudiedOberlaabprofiles(Terhorstetal.2003).However,thepresentedCIAvalues,claycontents (40–32%),aswellas thickclaycoatingsob-served inour study indicate amore advanceweatheringintheOL3unitincomparisontoOL4,andthatmeans2ndpaleosolismoreweatheredthanthe3rdone).

Themultiphasepedogenesisdetectedinbothunits,OL3andOL4,couldbelinkedtotheclimaticfluctuationswithinMIS7andMIS9.Thesestagesdemonstrateacomplexpat-tern in the δ18O-record with warm intervals alternatingwithcoldepisodes.EarlierBrongeretal.(1998)supposedthat pedocomplexes PKII and PKIII in loess-paleosol se-quencesofTadjikistanreflectclimaticfluctuationswithinMIS7andMIS9,respectively.Moredetailedcorrelationofpedocomplexesandmarineisotopecurveislimitedbythelackofareliableagecontrol.

TheOL2profile,regardedastheEemiansoil(1stinter-

glacial paleosol), occupies the next stratigraphic level.Itsagehasbeenwellestablishedbyseveral instrumentaldates:OSLandpaleomagnetisminothersections,inpartic-ularintheWels-Aschetsequence(Preusser&Fiebig2009;Scholger&Terhorst2011),butinthecaseofOberlaabsuchresultsarenotavailable.InWels-Aschet,theEemiansoilisdevelopedonloessicsedimentsoftheRissglaciation,whichis142±18ky(MIS6)accordingtoPreusser&Fiebig(2009).Ontopof theMIS5e-Eemiansoil theBlakeevent(~117ka)isprovedbyScholger&Terhorst(2011;2013,thisvolume)inWels-Aschet.TheEemiansoilinunitOL2iscorrelatedtoMIS5einthisstudy,basedontheresultsoffurthersequencesinAustria.Ingeneral,thepaleosoldis-plays fewer stagnic properties and less compaction thantheolderpaleosols.Furthermore,itsstratigraphicpositionissituatedbelowtheWürmiansediments.Fromtheana-lyticalpointofviewtheinterglacialpedogenesisisprovedby intensive clay illuviation, coinciding with higher CIAvalues.

OL1,whichcorrespondtotheHolocenesoil,isseparatedfromtheEemianpaleosolbyloess-likedepositscharacter-isticfortheWürmianglaciation.Thereisnoevidenceforwell-developedsoilsinthesedeposits,onlyreworkedlayersarepresent.

According to the proposed pedostratigraphy, Figure 5showsthecorrelationofthestudysectionwiththeMarineIsotopeCurve(acc.toLisiecki&Raymo2005).

4.2 Pedogenic trends in Oberlaab induced by climate change or/and geomorphic processes

The loess-paleosol sequence in Oberlaab contains sever-alunits,whichdevelopeddifferentspecificproperties.Al-thoughsomeofthespecificpatternsarefoundinthewholesection,theirintensityisstronglyrelatedtopedogenicandgeomorphicprocesses.Allunitsarecharacterizedaspedo-

Fig. 5: Correlation of paleosols in Oberlaab with the Marine Isotope Curve.

Abb. 5: Korrelation von Paläoböden in Oberlaab mit der marinen Isoto-penkurve.

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complexes,andcanbewelded,thusdifficultiesintherecog-nizanceofeverysinglesoilcyclecanemerge.

Inthesequencewestudieditisclearthatthelowerunits,especiallyOL4andOL5,developedunderconditionspro-ducedbywatersaturation,whichgaverisetoredoximor-phicprocesses.ThelowestOL5unitshowstheformationofadiagnosticGhorizonwithapalereducedsoilmatrixandrelativelyfewironsegregations.Thesepropertiescorrespondtogleyzationinapermanentlyreducedsoilenvironment,which letsus suppose a shallowgroundwater table.OL4demonstratespatchyBghorizons,Fe-Mnconcretionsandhypocoatingswithbleachedgroundmasses.Infact,thehigh-estconcentrationsof ferruginouspedofeaturesaswellasbleachedzonesarefoundinOL4(Figure3).Thesecharacter-isticscorrespondtostagnicpropertiesrelatedtotemporarysaturationwithsurfacewater.Verylimiteddevelopmentofclayilluviationagreeswiththehypothesisofpedogenesisinapoorlydrainedsoilenvironment.

Thestagnicandgleyicfeaturesbecomelessfrequentintheupperpaleosols.Here,clayilluviationisdominant,withthickanddarkclaycoatings.Frommicromorphologicalre-sultstheEemian(OL2)andHolocenesoilshavethehighestpercentagesofilluvialclay(2.1to4%).Ontheotherhand,coatingsinOL3,OL4,andpartlyinOL2(fordetailsseeSE-DOVetal.2013,thisvolume)aredeformedanddisplaced,thusthematerialhasbeenalsoaffectedbygleyzationandcryogenesis.Infact,onlyintheupperpartofthemodernsoilclaycoatingsarepurewithayellowcolor.Itsinferiorpart(Ghorizon)containsthehighestamountofclaycoat-ings,whichare“dirty”,laminatedorhavingreddishcolors,withpigmentations.Thishorizonhasalsoalowmagneticsusceptibilityvalueandconsiderablylowerweatheringde-gree.Terhorst(2007)suggestsitcorrespondstoaprevi-ousphaseofsoilformationthatprobablyoccurred≠duringMIS2to3.

Insummary,themaintrendofchangeofpedogenicproc-essesintheOberlaabsequenceisthefollowing:gleyzationatthebase(OL5-OL4),stagnicprocessesinthecentralpart(OL4-OL3)andclayilluviationintheupperunits(OL2-OL1).

Which soil forming factors control these pedogenictrends?Itseemsthatclimateisonlyonefactorduetothefactthatallunitsareformedunderhumidclimatesevidencedbytheformationofstagnicandgleyicfeatures,clayneoforma-tionandilluviation,andsiltand/orironilluviation.Differ-encesbetweenthepedocomplexesarewellexpressedintheintensityoftheinvolvedprocesses.Additionally,changesintemperaturemaybesomewhatresponsible.Lowerunitscouldreflecttheinfluenceofcoolerenvironments,whiletheupperonesareaffectedbywarmerclimates.

The geomorphic position of the studied paleosols alsoevidentlyaffectedpedogenesis.Thelowermostpaleosolsaresituatedatalowerlevelinthegeoform,andweremoreaf-fectedbywaterloggedconditions(highgroundwatertableorflooding).ThisisevidentinOL5,wherefluvioglacialproc-essesformedagravellyalluvialdepositwithahighcontentofMnconcretions.

Theupperpaleosolsarelocatedinbetterdrainedposi-tionsawayfromtheinfluenceofgroundwaterandinunda-tions.Thiscanbeexplainedbytheaggradationoftheterraceandbylowerlevelsoftheyoungerterraces.Inparticular,theEemiansoilshowsawell-developedformationstagecharac-

terizedbyahighweatheringstatus.Thewell-drainedgeo-morphologicalpositionfavorsclayilluviation.

Anotherimportantprocessobservedinthelowerpale-osolsisrelatedtodeformationofpedofeatures,whichcanbecausedbybioturbation,aswellasbycryogenesisandgelifluction.Orbiculicfabrics,siltconcentrations,andplatystructures are related to such kind of processes. Accord-ingtoourobservationsthesefeaturesaremorefrequentinOL5andOL4(Figure3)duetoahigherintensityofglacialperiods.However,lowersedimentationand/ormoreinten-siveerosionprocessescannotbeneglected.According toLisiecki&Raymo(2005)duringMIS12and10severegla-cialphasesoccurred,afterwhichOL5andOL4areformed(Figure5).DuringMIS8theglacialphaseismuchweaker,thuscharacteristicsfoundinOL3areclearlylessaffectedbycryogenesis.

5 Conclusion

TheOberlaabsequenceontopofaMindelterrace(Young-erDeckenschotter)isconstitutedbyfourinterglacialpale-osols,whichdevelopedmostprobablyduringtheMarineIsotopeStagesMIS11,MIS9,MIS7,andMIS5,respective-ly.SimilartootherinterglacialpaleosolsofthesameageinUpperAustria,thepaleosolsareformedaspedocomplexesin Oberlaab. Studied properties reveal the dominance ofhumidconditionsinthewholesection,butwithdifferencesintheintensityofpedogenicprocessesinvolvedinthefor-mationofeachpedostratigraphiclevel.WeassumethattheoldestpaleosolOL5canbecorrelatedtothe4thinterglacialpaleosols foundinNeuhofen,Wels-Aschet,andinearlierstudiedprofilesinOberlaab.WecorrelatethissoiltoMIS11.Thepedocomplexisaffectedbystronggleyzation.OL4,whichisthe3rdinterglacialpaleosol,ischaracterizedbythesignsofstrongreductomorphicfeatures,partlydeformedandwithorbiculicfabrics,whichareassociatedwithlatercryogenesis,probablyduringMIS8.OL3alsohasproper-tiesrelatedtostagnicprocesses,butclayilluviationandahigherdegreeofweatheringareevidenceofitsformationunder warmer conditions during MIS 7. The Eemian soil(OL2)isthebestdevelopedandreflectswarminterglacialconditions.

Acknowledgments

Wethanktothefinancialsupportoftheproject“Polygen-eticmodelsforthePleistocenepaleosols:newapproachtodecodingthepaleosol-sedimentaryrecords”(InternationalCouncilScienceUnion).WealsoaknowledgesupportfromConacyt-DLR as well as CONACYT grant for “EstanciasPosdoctoralesalExtranjero”toH.Cabadas.ManythankstoLanceWallaceforcorrectingthemanuscript,andtoEl-igioJiménezandJaimeDíazforthinsectionpreparationandthegrainsizeseparation,aswellasJorgeRivasformagneticmeasurements.RufinoLozanocontributedwiththeX-Rayfluorescenceanalyses.

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