Quaternary

Researchdoi:10.1006/qres.2001.2221,available

onlineathttp://w

ww.idealibrary.com

on

SubdivisionofG

lacialDepositsinSoutheastern

PeruBased

onPedogenic

Developmentand

Radiometric

AgesAdam

Y.Goodm

anDepartm

entofEarthSciences,Syracuse

University,Syracuse,N

ewYork

13244

Donald

T.RodbellDepartm

entofGeology,U

nionCollege,Schenectady,N

ewYork

12308

and

Geoffrey

O.Seltzerand

BryanG.Mark

Departm

entofEarthSciences,Syracuse

University,Syracuse,N

ewYork

13244

ReceivedDecem

ber21,1999

The

Cordillera

Vilcanota

andQuelccaya

IceCap

regionofsouth-

ernPeru

(13!30

"–14!00

"S;70!40

"–71!25

"W)contains

adetailed

rec-ord

oflate

Quaternary

glaciationin

thetropical

Andes.Q

uantifi-cation

ofsoil

development

on19

moraine

crestsand

radiocarbonages

areused

toreconstructthe

glacialhistory.Secondaryiron

andclay

increaselinearly

inQuelccaya

soilsand

clayaccum

ulatesat

alinear

ratein

Vilcanota

soils,which

may

reflectthesem

icontinuousaddition

ofeolian

dustenriched

insecondary

ironto

allsoils.

Incontrast,logarithm

icrates

ofironbuildup

insoils

inthe

Cordillera

Vilcanota

reflectchem

icalweathering;high

concentrationsof

sec-ondary

ironin

Vilcanota

tillsmay

mask

therole

ofeolian

inputto

thesesoils.Soil-age

estimatesfrom

extrapolationoffield

andlabora-

torydata

suggestthatthemostextensive

lateQuaternary

glaciationoccurred

>70,000

yrB.P.T

hisprovides

oneofthe

firstsemiquanti-

tativeage

estimatesform

aximum

iceextentin

southernPeru

andis

supportedby

aminim

um-lim

itingage

of#41,520

14Cyr

B.P.A

lateglacialreadvance

culminated

#16,650

calyrB.P.in

theCordillera

Vilcanota.F

ollowing

rapiddeglaciation

ofunknownextent,an

ad-vance

ofthe

Quelccaya

IceCap

occurredbetw

een#13,090

and12,800

calyrB.P.,w

hichcoincides

approximately

with

theonsetof

theYounger

Dryas

coolingin

theNorth

Atlantic

region.Moraines

deposited<394

calyrB.P.in

theCordillera

Vilcanota

and<300

calyr

B.P.

onthe

west

sideof

theQuelccaya

IceCap

correlatewith

Little

IceAge

moraines

ofotherregions.

C$2001

University

ofWashington.

Key

Words:

glacialhistory;soildevelopment;radiocarbon

dates;South

America,A

ndes.INTRODUCTIO

N

Although

anabundance

ofpaleoclim

aticproxy

datadocu-

ment

climate

changesinthe

middle

tohigh

latitudesofthe

Northern

Hemisphere,there

isuncertainty

surroundingthe

na-tureandchronologyofclim

atefluctuationsinlowlatitudesofthe

SouthernHemisphere

(e.g.,Rindand

Peteet,1985;COHMAP,

1988;Klein

etal.,1999).Paleoclimaticrecordsfrom

theAndes

areneeded

tounderstand

betterthechronology

oflateQuater-

naryclim

atechange

inthe

tropics.Thispaperpresents

quanti-tative

soilweathering

dataand

radiocarbonagesthatsubdivide

moraines

insouthern

Peru,which

serveasaproxy

forclimate

oscillationsthroughthem

assbalancechangeofalpineglaciers.The

objectivesofthisstudyare

to(i)develop

soilchronofunc-tionsforfield

andlaboratory

propertiesand(ii)use

thesefunc-

tionstoestim

ateagesofundated

moraines.

STUDYAREA

TheCordillera

Vilcanota(CV

)andQuelccaya

IceCap

(QIC)

region(13

!30"–14

!00"S;70

!40"–71

!25"W)ofsoutheasternPeru

islocated

inthe

easternAndean

cordilleraapproxim

ately100

kmeastofCusco,adjacentto

thewestern

margin

oftheAmazon

Basin(Fig.1).The

highestpeak,Nevado

Ausangate

(6384m),

andthe

surroudingmountains

oftheCV

arecom

posedmostly

ofvolcanic

andgranitic

rockswith

somesedim

entaryrocks

(Audebaud,1973);theQ

ICisunderlain

byignim

brite.Whereas

glaciersinthe

CVhave

recededinto

alpinecirques(Fig.2),the

QICissurrounded

byshort,steep

outletglaciersupto

#2km

long.TheQICcovers70

km2,reaches5645

minelevation,and

isthelargesttropicalice

capinthe

world

(Mercerand

Palacios,1977)(Fig.3).Throughoutthe

mountainousterrain,puna

(highgrassland)m

akesupmostofthe

naturalvegetation.The

CV–QICregion

experienceslargediurnalbutonly

small

seasonaltem

peraturevariations.

Thompson

andMcKenzie

(1979)reporteddiurnaltem

peraturesatthesum

mitofthe

QIC

from6

!to

%14

!CinJuly

butnotedonly

a3

!Cmean

temper-

aturechange

fromsum

mertowinter.A

lthoughmean

annualprecipitation

forthis

areahas

notbeenmeasured

directly,an

0033-5894/01$35.00

CopyrightC$2001

bythe

University

ofWashington.

Allrightsofreproduction

inany

formreserved.

2GOODMANET

AL.

FIG

.1.Location

ofthestudy

areainsouthern

Peru.

icecore

obtainedfrom

thesum

mitofthe

QICrevealed

ap-proxim

ately1.5

mofwater

equivalentannual

accumulation

(Thompson

etal.,1985).Mostof

theprecipitation

inPeru

isconcentrated

duringtheaustralsum

mer(N

ovemberto

April)as

theIntertropicalConvergence

Zoneshifts

southofthe

equator(Hastenrath,1995;K

aseretal.,1990).Meteorologicaldatafrom

Thompson

andMosley-Thom

pson(1987)indicatepredom

inanteasterly

windsduring

thewetseason

andwesterly

windsduring

thedry

season.

METHODS

FieldMethods

Nineteen

soilpitsinthe

CV–QICregion

were

excavatedby

handand

describedfollow

ingthe

methods

outlinedby

Birkeland(1999)

andthe

SoilSurvey

Division

Staff(1993).

Soilpitsare

namedafter

thedrainages

orlocations

inwhich

theywereexcavated.CordilleraVilcanotasoilpitshavethepre-

fixJfor

theJalacocha

Valley,UforU

pismayo

Valley,andM

forPinchim

uroMayo

Valley(Fig.2).A

llQuelccaya

soilpitshave

theprefix

Q(Fig.3).Soilpitsare

numbered

indescending

orderofthe

ageofthe

moraine

onwhich

thepits

were

exca-vated

relativetootherm

orainesinthatvalley.Thus,U

1and

U8

respectivelyare

theoldestand

youngestsoilsdescribed

inthe

Upism

ayoValley.H

owever,the

moraine

onwhich

soilU1was

describeddoes

notnecessarilycorrelate

withthe

moraine

onwhich

J1wasdescribed.A

llsoilpitswere

excavatedonappar-

entlyundisturbed

morainecrestsin

ordertominim

izetheimpact

ofcolluvialprocesses.Bulkdensity

foreachhorizon

wasdeter-

mined

throughthe

paraffinclod

method

(SingerandJanitzky,

1986).Theslopesofmorainesw

eremeasured

usinga2-m

-longPVCpipe

andaclinom

eter.Fivelakesand

onebog

were

coredusing

amodified

Livingstonesquare-rod

pistoncorerto

obtainorganic

matterforradiocarbon

analysistoconstrain

thetiming

ofdeglaciation(Wright,1991).Peatfound

stratigraphicallybe-

neathmoraines

wassam

pledtodeterm

inemaxim

um-lim

itingagesforglaciation.

LaboratoryAnalyses

Samples

fromeach

soilhorizonconsisted

ofover

100gof

soilsievedtorem

ovematerial

>2mmindiam

eter.Particlesize

analysiswasperform

edusing

aCoulterLS230

laserdiffractionparticle-sizeanalyzer.Sam

plepreparationfollow

ingSingerand

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

3

FIG

.2.

Mapofthe

northwestern

sideofthe

CordilleraVilcanota

basedonaerialphotographs,field

reconnaissance,andthe

19931:100,000

Ocongate

topographicmapfrom

ElInstitutoGeografico

NacionalLim

a,Peru.Allages

<20,000

14CyrB.P.areexpressed

incalibrated

yearsB.P.(calyrB.P.)asdetermined

withthe

CALIB

3.0program

(StuiverandReim

er,1993).Allradiocarbon

datesthatprovideminim

um-lim

itingage

controlformorainesare

plottedasa

trianglewithapex

pointingup;those

thatprovidemaxim

um-lim

itingage

controlformorainesare

plottedasa

trianglewithapex

pointingdow

n(Table

1).

Janitzky(1986)w

asmodified

byadding

atotalof4

mlof30%

H2 O

2 intwostepsto

#0.15

gofsoilto

remove

organicmatter.

Threemilliliters

ofsodiummetaphosphate

dispersingsolution

wasadded

priortoperform

ingtheanalyses.Clay

wascalculated

as&2

µm,siltfrom

2to50

µm,and

sandfrom

50to2000

µm.

Analyticalm

ethodsfollowedstandard

procedures.Totalfreeiron

andalum

inumoxides

were

extractedusing

thecitrate-

bicarbonate-dithionite(CBD

)method

(Singerand

Janitzky,1986).CBD

extracts(Fed

andAld )w

ereanalyzed

onadirect

currentplasma(DCP)

emission

spectrophotometer.The

CBDleachate

wasused

asthe

blanksolution

toaccountfor

back-ground

levelscaused

byextraction

chemicals.O

rganiccarbon

wasmeasured

bycoulom

etry.Inthis

technique,between

20to

40mgofsoilw

ascom

bustedfor

5–10minutes

at950!Cand

theCO

2evolved

wasmeasured

bytitration.A

llofthe

CO2

canbeattributed

toorganic

carbonbecause

ofthe

absenceof

carbonatebedrock

andsecondary

CaCO3 in

CVand

QICsoils.

SoilpHdeterm

inationswerem

odifiedfromrecom

mendationsof

Jackson(1979)and

ConyersandDavey

(1988).Awaterto

soilratio

of1:2.5

(4gsoilto

10mlwater)

wasused

becauseof

thelarge

water

retentioncapacities

ofmany

samples

fromA

horizons.Solutionswere

measured

withapH

meterafterone

minuteofshakingandagainafteronehour.Claym

ineralogywas

determined

byX-ray

diffractionorair-dried

samples

(Moore

andReynolds,1997).M

ostsamples

were

alsoanalyzed

inan

ethyleneglycolsolvated

conditiontodeterm

inethe

presenceof

expandableclays.Finally,low

-field(0.46

kHz)and

high-field(4.6

kHz)magnetic

susceptibilities(Thom

psonand

Oldfield,

1986)werem

easuredusing

aBartingtonMS2Bsensorto

calcu-late

frequency-dependentmagnetic

susceptibility,which

iscal-culated

asthepercentagedifferencebetween

low-field

andhigh-

fieldMSvalues.Frequency-dependentM

Sreflectsthepresence

ofultrafinegrainedmagnetite(<

0.1µm),w

hichhasbeen

notedtoform

insom

esoil

environments

(Thompson

andOldfield,

1986;Maherand

Taylor,1988;Singeretal.,1992).

SoilDevelopm

entIndices

Soildevelopmentindices

were

usedtoreduce

soil-propertydatafrom

asoilprofiletoasinglenum

berthatreflectsthedegreeofpedogenicdevelopm

ent.Thisallowssite-to-sitecom

parisons,making

itpossibletoidentify

temporaland

regionaltrendsin

soildevelopment.Birkeland

(1999)recommended

adjustingin-

dicesforsoilsthataredescribedtodifferentdepthsby

extendingthe

depthofthe

lowesthorizons

sothatallprofiles

consideredhave

thesam

etotaldepth.In

thisstudy,weextended

thedepth

4GOODMANET

AL.

FIG

.3.Mapofthe

western

sideofthe

Quelccaya

IceCap

basedonaerialphotographs,field

reconnaissance,andthe

19931:100,000

CoraniandNunoa

topographicmapfrom

ElInstitutoGeografico

NacionalLim

a,Peru.Allages

<20,000

14CyrB.P.areexpressed

incalibrated

yearsB.P.(calyrB.P.)asdetermined

withthe

CALIB

3.0program

(StuiverandReim

er,1993).Allradiocarbon

datesthatprovideminim

um-lim

itingage

controlformorainesare

plottedasa

trianglewithapex

pointingup;those

thatprovidemaxim

um-lim

itingage

controlformorainesare

plottedasa

trianglewithapex

pointingdow

n(Table

1);10Be

and26A

lexposure

agesareplotted

asC10and

C11.

ofthedeepesthorizon

onlyifthe

Cuhorizon

forthatsoilwas

notencountered.These

horizonswere

extendedsothat

totalsolum

thicknessforthese

soilswould

equalthedeepestexca-

vatedsolum

(130cm

inthe

CVand

100cm

inthe

QIC).This

“extended”depth,which

wasused

forallindexcalculations,as-

sumesthatthe

propertiesofthe

lowesthorizon

continuedow

ntoadepth

equaltothatof

thedeepestexcavated

solum.This

assumption

maynotbe

correct,anditisim

portanttorecognize

apriorihow

theuseofacommondepth

forsoildevelopmentin-

dexcalculationsm

ayinfluence

chronosequencetrends.In

most

cases,suchanassum

ptionwilltend

tosystem

aticallyreducein-

dexvalues

forthin,youngsoils

andincrease

indexvalues

forthick,old

soils(Birkeland,1999).Incontrast,notusing

acom

-mondepth

would

resultininflating

indexvaluesforthose

soilsthathappened

tobedescribed

toashallow

depth,whiledeflating

indexvaluesforthose

soilsdescribedtogreaterdepth.

TheProfile

Developm

entIndex

(PDI)isone

ofthe

most

widely

usedmethods

forconverting

qualitativefield

proper-ties

tosem

iquantitativevalues

representingsoildevelopm

ent.PDIcalculationsfollow

edmethodsdescribed

byHarden

(1982),Harden

andTaylor(1983),and

Birkeland(1999)w

herebypoints

areallocated

forstep-wisedeparturesofnum

eroussoilhorizonproperties

fromsoilparentm

aterialvalues.Thesevalues

arenorm

alizedtothe

currentmaxim

umvalue,averaged,and

mul-

tipliedbyhorizon

thickness,summed,and

dividedbyeitherthe

depthtothe

Cuhorizon

or,ifCuhorizon

wasnotexposed,by

thethicknessofthe

deepestsoluminthe

chronosequence.Par-entm

aterialvalueswere

determined

fromthe

Cuhorizon

oftheyoungestm

oraines(U7,U

8,Q5,and

Q6;Figs.2

and3).Values

rangefrom

0(no

development)to

1(maxim

umdevelopm

ent).Twoindices

were

usedtosum

marize

soillaboratory

data.Weighted

mean

(WM)percentageisdeterm

inedbymultiplying

asoilhorizonpropertybyhorizonthickness,summingthevalues

forallhorizonsinasoilprofile,and

dividingbyeitherthedepth

totheCuhorizonor,ifCuhorizonwasnotexposed,by.Theindex

ofprofileanisotropy(IPA)perm

itsquantitativedescriptionofthedeviation

oflaboratorypropertiesofsoilsfrom

parentmaterial

values.Walkerand

Green

(1976)originallydeveloped

theindextorepresenttheanisotropy

ofasoilprofileassuming

thatattime

zeroallpropertiesare

isotropicthrough

agiven

thickness.TheIPA

asmodified

byBirkeland

(1999)is:IPA=[!((D/PM

)'horizon

thickness)]/totalprofilethickness,w

hereDrepresents

thedifferencebetween

ahorizonproperty

andthatoftheparent

material

(PM).Values

ofDwere

calculatedfor

thedifferent

horizons,multiplied

byhorizon

thickness,summed,and

dividedbyeitherthe

depthtothe

Cuhorizon

or,ifCuhorizon

wasnot

exposed,by.TheIPA

indexshould

increasewithage

formost

properties.Finally,assuggestedbyBirkeland

(1999),WMand

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

5

IPAindicesw

erecalculatedusing

bothpercentageand

soilmass

data.Thelatter,derivedfromtheproductofpercentdataandbulk

densityasdeterm

inedonthe

whole

sizerange,enable

themass

accumulation

oftheproductsofsoilformation

tobedeterm

ined.

RESU

LTS

Stratigraphicand

RadiocarbonAge

ControlforM

oraines

CordilleraVilcanota.

Verysubduedmorainesdem

arcatethemaxim

umlimitof

glaciationinthe

CV.Westof

thetow

nof

Tinqui,near

theconfluence

ofthe

RıoLauram

arcaand

RıoPinchim

uroMayo

(Fig.2),theriver

channelisU-shaped

andmoraines

arepoorly

preserved.Theglaciallandform

lowestin

elevationisthe

terminalm

orainewithsoilJ1,w

hichis100

mabove

thefloodplain

(Fig.2).

Thebroad,

undulatingterrain

southoftheRıo

Pinchimuro

Mayo

isdominated

bylargeglacial

erraticsand

relativelyscarce

moraines.The

flat-toppedlateral

moraine

withsoilJ2,w

estoftheRıoLauram

arca,isthe

most

prominentglaciallandform

inthisarea

(Fig.2).The

dividewithsoilU

1(Fig.2)thatseparatesthe

Upism

ayoand

JalacochaValleys

ismantled

byone

ofthe

oldestglacialdepositsin

theregion.Astratigraphicexposure#

0.75km

north-eastofsoilpitU

1through

theouterm

ostsharp-crestedlateral

moraine

(withsoilU

2)inthe

Upism

ayoValley

revealsabout

10moffolded

peatintercalatedwithgravelalong

agully.Peat

samplesin

themiddle

andatthe

bottomofthisexposure

datedto29,980

±1230

and41,520

±4430

14CyrB.P.,respectively

(Table1).The

youngerofthesetwoagesprovidesa

maxim

um-

limiting

ageforthe

moraine

withsoilU

2,andforallyounger

moraines.

Similarly,

theolder

ofthese

twodates

providesa

minim

um-lim

itingage

forallolder

moraines

(e.g.,moraines

withsoilpitsU

1,J1,andJ2;Fig.2).

LagunaCasercocha

(Fig.2),akettle

lakeonabroad

moraine

crest#3km

eastofTinqui,wascored

toprovide

aminim

um-

limitingagefordeglaciationoftheRioPinchim

uroMayoValley.

Basalorganicmaterialabove

inorganicsiltyielded

anage

of15,640

±100

14CyrB.P.(18,540

calyrB.P.).Thisprovides

aminim

um-lim

itingdurationofpedogenesisforthesoildescribedinpitM

1.Aseries

of#seven

sharp-crested,discontinuous,lateralandend

moraines

arepositioned

upvalleyfrom

theconfluence

ofthe

Upism

ayoand

JalacochaRivers.These

morainesterm

inatebetw

een4000

and4150

minthe

JalacochaValley

andbetw

een4200

and4350

minthe

Upism

ayoValley.In

theJalacocha

Val-ley,soilpitJ3

issituated

onthe

lowestend

moraine

ofthese-

ries.Frompeatstratigraphically

ontop

oftillinastream

-bankexposure,M

ercerandPalacios(1977)determ

inedaminim

um-

limiting

ageof14,010±190

14CyrB.P.(16,800

calyrB.P.)forthis

moraine.SoilpitJ4

issituated

onanotherend

moraine

atthe

upvalleyextentofthism

orainesequence.In

theUpism

ayoValley,a

similarsuite

ofmoraineshasa

maxim

umlimiting

ageforglaciation

of13,880±150

14CyrB.P.(16,650

calyrB.P.)obtained

frompeatfound

stratigraphicallyimmediately

belowtillthatcom

posesthe

moraine

withsoilU

2(Table

1).Soilpit

U3wasexcavated

onalateralm

orainewhose

terminalposition

isatthedow

nvalleylimitofthism

orainesuite,and

pitU4was

excavatedonthe

terminalposition

ofamoraine

ataneleva-

tionsim

ilartoU3(Fig.2).A

minim

um-lim

itingage

forthesemorainescom

esfromthebasalorganicm

aterialfromabog

corejustupvalley

fromsoilpitU

4.Peatdatedat10,362

±70

14Cyr

B.P.(12,250calyr

B.P.)records

thebeginning

ofpeataccu-

mulation

following

deglaciationand

constrainstheage

ofthesemorainesto

between

#13,900

and#10,300

14CyrB.P.(16,650

and12,250

calyrB.P.).There

islittle

agecontrolform

orainesinthe

upperhalfofthe

Upism

ayoValley.The

sharpcrestsofthese

morainescan

betraced

highonthe

valleywalls

andsuggestthatthey

were

de-positedduringayoungerphaseofglaciation.Thew

ell-vegetatedend

moraine

withsoilpitU

8(Fig.2)recordsthe

maxim

umex-

tentofarecentreadvance.Glacialm

eltwaterdissected

thislattermoraine

andexposesa

sectionofarched

peatbedsandanother

sectionoftilted

peatbedsalternatingwithgray

siltandpink

claybelow

thetill-mantled

morainesurface.Theupperm

ostpeatbedhasanageof328

±50

14CyrB.P.(394calyrB.P.)andrepresents

amaxim

um-lim

itingagefortheglacieradvancethatform

edthis

moraine.The

basalpeatbedis2830

±70

14CyrB.P.(2910

calyrB.P.),a

minim

um-lim

itingage

forallmoraines

downvalley.

Becauseoftheweak

degreeofsoildevelopmentand

absenceofaloessm

antleonthe

moraine

withsoilpitU

7,webelieve

thatthism

oraineform

edinthe

lateHolocene,perhapsjustpriorto

2910calyr

BP,ratherthan

duringthe

earlyHolocene

orlate

glacial.

Quelccaya

IceCap.

Twosoilpits(Q

1,Q2)w

ereexcavated

onmoraines

thatformasetof

parallelridgesthatdefine

thesouthw

esternlimitofglaciation(Fig.3).Thesouthw

estern-most

moraine,on

which

soilpitQ2wasexcavated,extends

fartherwestand

terminatesin

adrainagethatoriginatesfromthesouth-

ernsideoftheCV.Thehighestandlongestmoraineinthisgroup,

withsoilpitQ

1,isamedialm

orainethatseparatediceemanating

fromthe

CVand

theQIC.Prelim

inarycosm

ogenicages

( 10Beand

26A1)indicatethatthestabilization

ofthemorainew

ithsoil

pitQ2occurred

17,550±300

calyrB.P.,andstabilization

ofamoraine

between

thoseonwhich

pitsQ1and

Q2were

exca-vated

stabilized25,500

±1100

calyrB.P.(Goodm

an,1999).The

largemoraine

withsoilpitQ

1musthave

formedpriorto

25,500calyrB.P.

Thenextyoungersetofmorainesw

asnamedHuancaneIIIby

Mercerand

Palacios(1977);these

moraines

aremuch

smaller

andmantled

bynum

erousweathered

glacialerratics.SoilpitQ3wasexcavated

onone

ofthemoraines

thatcrossesthe

RıoHuancane

drainage,#7km

westofthe

activeglacier(Fig.3).

Approxim

ately1.5

mofinterbedded

peatandclay

isburiedby

outwash

sandand

gravelinastream

cut#1km

upvalleyfrom

thismoraine.M

ercerand

Palacios(1977)

reportedanage

of12,240±

17014C

yrB.P.(14,290calyrB.P.)forthe

basalpeat,which

providesaminim

um-lim

itingage

forthe

Huancane

IIImoraines.Three

exposuresofpeatincorporatedinto

tillunder-lying

thenextyounger,H

uancaneII,m

oraines#4km

fromthe

6GOODMANET

AL.

TABLE 1Compilation of Radiocarbon Dates for Moraines in the Cordillera Vilcanota–Quelccaya Ice Cap Region

Associated soilLocation pit (if present: Elevation Lab Age Calibrated agea Significance

(Figs. 2 and 3) Figs. 2 and 3) (m) Sample context number (14C yr B.P.) ±(14C yr) (cal yr B.P.) of date Reference

Cordillera Vilcanotastream gully through minimum age for moraineleft lateral moraines, lowest peat underlying till of with soil U1 and all olderUpismayo Valley U1 4450 moraine with soil U2 GX-23726 41,520 4430 moraines this study

peat above GX-23726and beneath till ofmoraine with

same site as above U1 4450 soil U2 DIC-677 31,170 #1465 same as above Mercer and Palacios 1977same site as above U1 4450 same as above GX-23724 29,980 1230 same as above this studysame site as above U1 4450 same as above DIC-681 28,560 #735 same as above Mercer and Palacios 1977same site as above U1 4450 same as above GX-8080 27,540 970 same as above Mercer 1984same site as above U1 4450 same as above Beta-1555 27,090 960 same as above Mercer 1984same site as above U1 4450 same as above GX-4917 25,800 1200 same as above Mercer 1984same site as above U1 4450 same as above Beta-1556 21,785 1400 same as above Mercer 1984same site as above U1 4450 same as above Beta-1554 20,780 250 same as above Mercer 1984

top of deformed peat maximum age for moraineunderlying till of moraine with with soil U2 and all younger

same site as above U2 4450 soil U2 GX-8189 14,825 450 18635 (17730) 16688 moraines Mercer 1984same site as above U2 4450 same as above Beta-1725 14,500 105 17658 (17370) 17078 same as above Mercer 1984same site as above U2 4450 same as above Gx-8081 13,950 400 17663 (16730) 15651 same as above Mercer 1984same site as above U2 4450 same as above GX-23725 13,880 150 17044 (16650) 16225 same as above this study

minimum age for morainebasal organics from lake with soil M1 and all older

Laguna Casercocha M1 4010 core AA-27027 15,640 100 18797 (18540) 18288 moraines this studybasal organics from lake minimum age for all

Laguna Comercocha 4580 core AA-27024 14,500 220 17884 (17370) 16836 downvalley moraines this studyminimum age for underlyingtill and all downvalley

Jalacocha Valley J3 4030 peat on till I-9623 14,010 185 17267 (16800) 16311 moraines Mercer and Palacios 1977Upismayo Valley minimum age for allfloor U1-4 4380 basal organics from bog core AA-27041 10,362 73 12479 (12250) 11894 downvalley moraines this studystream cut through minimum age for morainemoraine, Upismayo lowermost peat beneath with soil U7 and allValley U7 4450 moraine with soil U8 DIC-682 2,830 70 3148 (2910) 2771 downvalley moraines Mercer and Palacios 1977

maximum age for moraineuppermost peat beneath with soil U8 and all upvalley

same site as above U8 4450 moraine with soil U8 DIC-678 630 65 672 (600) 519 moraines Mercer and Palacios 1977same site as above U8 4450 same as above AA-27051 547 55 648 (540) 503 same as above this studysame site as above U8 4450 same as above GX-4925 455 130 662 (510) 0 same as above Mercer 1984same site as above U8 4450 same as above AA-27050 328 46 499 (394) 289 same as above this study

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

7Quelccaya Ice Capstream bankexposure along RıoHuancane #1 kmupvalley from minimum age for HuancaneHuancane I moraine Q3 4745 basal peat I-8443 12,240 170 14855 (14290) 13819 III moraines and soil Q3 Mercer and Palacios 1977same site as above Q3 4750 uppermost peat I-8210 11,460 165 13798 (13370) 13026 same as above Mercer and Palacios 1977

basal organics from lakeL. Accocancha 4780 core AA-27037 11,183 109 13350 (13090) 12860 same as above this study

basal organics from lakeL. Churuyo 4675 core AA-27039 9,174 74 10346 (10060) 9982 same as above this study#4 km north of uppermost peat underlying maximum age for HuancaneHuancane Valley Q4 5100 till of Huancane II moraine DIC-687 12,230 180 14865 (14280) 13787 II moraines and soil Q4 Mercer and Palacios 1977

base of peat underlying tillof

same site as above Q4 5100 Huancane II moraine GX-4325 11,185 185 13510 (13090) 12727 same as above Mercer and Palacios 1977#1.5 km north of uppermost peat underlyingHuancane Valley Q4 4925 till of Huancane II moraine DIC-686 11,070 125 13255 (12980) 12725 same as above Mercer and Palacios 1977

peat incorporatedinto till of Huancane II moraine

Huancane Valley Q4 4820 peat and I-8209 10,910 160 13155 (12830) 12495 same as above Mercer and Palacios 1977rootlets incorporated same as above but probableinto till of Huancane contamination by modern

same site as above Q4 4820 II moraine AA-28269 10,170 85 12276 (11890) 11087 rootlets this studybasal organics from lake minimum age for Huancane II

Laguna Paco Cocha Q4 4940 core AA-27032 10,870 72 12962 (12800) 12616 moraines and soil Q4 Rodbell and Seltzer, 2000minimum age for Huancane II

#500 m from modern intact peat beneath till of moraines: maximum age forice margin 5070 Huancane I moraine GX-4933 9,980 255 12426 (11190) 10470 Huancane I moraines Mercer 1984same site as above 5070 same as above DIC-685 9,565 260 11672 (10750) 9991 same as above Mercer 1984modern ice margin aboveLaguna Paco basal peat beneath modern time when QIC was smallerCocha 5180 glacier DIC-680 2,670 95 2954 (2760) 2489 than present Mercer and Palacios 1977

upper peat beneath modernsame site as above 5180 glacier GX-4932 1,950 135 2303 (1880) 1552 same as above Mercer 1984same site as above 5180 same as above I-9625 1,625 85 1710 (1520) 1325 same as above Mercer and Palacios 1977same site as above 5180 same as above GX-4930 1,395 190 1700 (1290) 932 same as above Mercer 1984Huancane I moraine #1.5 kmnortheast of basal peat incorporated into maximum age for Huancane IHuancane Valley Q5 and Q6 5100 Huancane I moraine I-844I 905 100 981 (790) 658 moraines and soils Q5 andQ6 Mercer and Palacios 1977

uppermost peat incorporatedsame site as above Q5 and Q6 5100 into Huancane I moraine I-9624 270 80 502 (300) 0 same as above Mercer and palacios 1977

aCalender age in parentheses bracketed by one-sigma ranges as determined with the CALIB 3.0 program (Stuiver and Reimer, 1993).

8GOODMANET

AL.

activeicefrontsuggestglacierswerereadvancingafter10,910±

16014C

yrB.P.(12,830calyrB.P.).A

nage

of10,870±70

14CyrB.P.(12,800calyrB.P.)from

basallacustrineorganicmaterial

inLaguna

PacoCocha#

1km

downvalley

fromthe

modern

icelimitprovidesam

inimum-lim

itingageforthisadvance.Soilpit

Q4wasdug

onthe

Huancane

IImoraine

thatimpoundsLaguna

PacoCocha.Finally,the

youngestmoraines,on

which

soilpitsQ5and

Q6weredug,arefound

100–200mfrom

theicemargin.

Thesesmallridges

arecom

posedofmostly

fresh,ignimbrite

cobblesand

reveallittlepedogenic

development.Their

strati-graphicposition

upvalleyfrom

theHuancaneIm

oraines,which

weredated

at<270±

8014C

yrB.P.(300calyrB.P.)by

Mercer

andPalacios

(1977),indicatesthatthese

moraines

alsoform

edwithin

thelastseveralcenturies,coincidentw

iththe

LittleIce

Age(Grove,1988;Thom

psonetal.1986).

SoilFieldProperties

SoilsU7,U

8,Q5,and

Q6(Fig.2),w

hichare

<3000

yrold,lack

aloessm

antleand

haveminim

allydeveloped

A/Cprofiles

(Table2).Incontrast,asoil>41,000

14CyrB.P.(U

1,Fig.2)con-tains#

27cm

ofloessand

exhibitsawell-developed

A/Bw

/Btprofile

(Table2).The

youngsoils

haveweak

structuraldevel-opm

entandlack

stickiness,plasticity,andclay

films.Thedepth

ofoxidationincreases

withmoraine

agesuch

thattheCu

hori-zons

inoldersoils

couldnotbe

exposedwithpick

andshovel.

Soilsonmoraines

withestim

atedages

between

#12,800

and17,500

calyr(soilsJ3,U

2–U4,Q

2–Q4;Table

2)havealoess

mantle

ofvarying

thickness,moderate

sizedpeds,sticky

andplasticconsistence,and

fewtocom

monthin

clayfilm

s.SoilU1

(>41,000

14CyrB.P.)has

stronglyvisible

peds,stickytovery

stickyconsistence,and

continuous,moderately

thickclay

films.

ThePDIcalculated

withtwocolorindices

(rubificationand

melanization)and

fourfieldproperties(totaltexture,structure,

clayfilm

s,andpH)is

bestmodeled

byalogarithm

icfunction

(Fig.4).Weselected

thesesixpropertiesbecausethey

allappeartoincreasesystem

aticallywithtime,andbecausethey

wereused

inPDIcalculations

frommany

othersoilstudies

(e.g.,Berry,1987,1994;Rodbell,1990,1993a;Sw

anson,1985).PDIvalues

forbothstudy

areasincreaseatasimilarrate.PD

IvaluesforCVsoilsrangefrom

0.15to0.41,w

hereasthoseforsoilsintheQ

ICrange

from0.00

to0.35.

LaboratoryProperties

Thereare

significantdifferencesbetw

eenCV

andQICsoils

thatappeartoreflectthe

differentbedrockunderlying

thetwo

studyareas.Forexam

ple,soilprofilesontheyoungestm

orainesinthetw

ostudyareasdifferconsiderablyinpedogeniciron(Fed )and

inclay

(Table3).SoilprofilesQ5and

Q6(<300

calyrB.P.)contain

essentialynopedogenic

iron,whereasU

8(<400

calyrB.P.)has#

1.5%Fed throughoutthe

profile.Inaddition,the

Cuhorizonsoftheseyoung

CVsoilspossess#

7–9%clay,w

hereassim

ilaragedsoilsin

theQIChave#

10–14%clay.Thepresence

ofhydrothermally

alteredbedrock

inthe

CVmayexplain

the

relativelyhighFed valuesmeasuredinCuhorizonsofthosesoils,

whereas

thehighly

erosiveignim

britebedrock

underlyingthe

QICmayexplain

thetexturaldifferencesbetw

eenCuhorizons

ofCVand

QICsoils.

Therelative

differencesnoted

inFed

between

thetwostudy

areasaremaintained

throughoutthechronosequence.Vilcanota

soilsU2–U

4,which

dateto

#16,650

calyrB.P.,have#3.5%

Fed ,whereasQ

ICsoilQ

3,which

is>14,290calyrold,hasonly

#0.5%

Fed .Likewisethe

oldestsoilprofilestudied

inthe

CV(soilU

1,Fig.2)hasupto#

5.5%Fed ,w

hereastheoldestsoilsinthe

QIC(soilsQ

1–Q2;Fig.3)reach

Fed valuesofonly#2.5%

(Table3).

Pedogeniciron

(Fed )isausefullaboratory

propertyforas-

sessingtherelativedegreeofsoildevelopm

ent.VariationsinFed

withtimeare

bestmodeled

byalogarithm

icfunction

ofWM

(weighted

mean)values

fortheCV

andasalinearfunction

ofWMvalues

forthe

QIC(Fig.5,Table

4).IPA(index

ofsoil

anisotropy)forFeddata

depictstrends

similarto

thoseofW

MFed ,butthe

CVand

QICdata

differgreatly.WMFed indicates

thatCVsoilscontain

roughlytwicethepercentageofpedogenic

ironthan

QICsoils,butIPA

Fed valuesaretwoordersofm

agni-tudegreaterforQ

ICsoilsthan

forsimilaraged

CVsoilsbecause

thisindexcalculatesdeparturesfrom

parentmaterialvalues.

Indicesofclaycontentforboth

studyareasshow

anincrease

inclay

withincreasing

soilage.Inthe

CV,thereisan

increaseinclay-sized

particlesfrom#8%

intheyoungestsoilsto#

22%inthe

oldestsoil(U1).Soils

inthe

QICincrease

from#5to

13%inclay

content(Table3).M

ostsoils>10,000

calyrold

frombothareaspossessprevalentclayfilm

s,whichsuggeststhat

pedogenicclay

isbeingtranslocated

throughthe

profileand

notsim

plyform

inginsitu

(Birkeland,1999).Weighted

mean

bulkdensity

(WMBD)clay

dataprovidethebestclay-agemodeland

suggestthatclayisaccum

ulatingatlinearratesin

bothregions

(Fig.6).Magnetic

susceptibility(MS)data

revealsignificantdiffer-encesbetw

eenthetw

ostudy

areas(Fig.7A;Table3).Low

-fieldMSforthe

CVsoilsdecreasesata

logarithmicrate,w

hereasalinearincrease

isapparentinthe

QICsoils.In

contrast,theper-

centfrequency-dependentMSfrom

bothareas

increaseswith

increasingpedogenesis(Fig.7B).

X-ray

analysesfrom

varioushorizons

ofthe

oldestand

youngestsoilsfrom

bothstudy

areasindicate

thatforallsoilsillite

isthe

primary

claymineralpresent,w

ithsmallam

ountsofkaolinite

andchlorite

alsopresent.G

lycol-treatedsam

plesgenerated

noswelling

clays.

DISC

USSIO

N

Controlson

PedogenesisandRatesofSoilD

evelopment

PreviousstudiesofPeruviansoilsfrom

theCordilleraBlancaand

CordilleraOrientalsuggested

thatfieldindices,in

particu-larrubification

andPDI,yielded

thebestsoilchronofunctions

(Rodbell,1993a,b).In

many

areasolder

soilsare

more

oxi-dized

togreaterdepths(Birkeland,1999).A

lthoughthisseem

s

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

9

TABLE2

SoilField

Data

forSoils

onMoraine

Crests

inthe

Cordillera

Vilcanota

andQuelccaya

IceCap

Region

Depth

ofsample

Estimated

forcolorage

ofDepth

>2nm

determination

Pitmoraine a

Horizon

c(cm

)Texture d

Consistence dStructure d

Clayfilm

s dBoundary

d(%)

(cm)

Color(dry)Color(w

et)

J1>18,540

A0–7

ND

ND

ND

ND

ND

43.65

10YR5/4

7.5YR3.5

/3AB

7–27ND

ND

ND

ND

ND

40.820

10YR5.5

/47.5Y

R4/4

Bw1

27–40ND

ND

ND

ND

ND

44.533

10YR6/6

10YR4/4

Bw2

40–50ND

ND

ND

ND

ND

69.645

10YR5/6

10YR3.5

/4Bw3

50–65+ND

ND

ND

ND

28.960

7/5Y

R4.5

/610Y

R3/4

J2>18,540

A0–3

ND

ND

ND

ND

a,sND

ND

ND

ND

AB

3–13L

ss,psg,gr,f

0g,w

45.75

10YR5/4

7.5YR3.5

/3Bw1

13–63SCL

ss,ps1,gr,m

0g,s

53.215

10YR5/4

7.5YR4/3

3010Y

R5.5

/47.5Y

R4/4

5010Y

R5.5

/610Y

R4/4

Bw2

63–130+SL

ss,ps2,abk,m

049.2

8010Y

R6/4

10YR4.5

/4110

10YR5.5

/510Y

R5/4

J3>16800

bA

0–13SiL

so,ps1,gr,f

0c,s

12.85

10YR3/2

10YR1/2

2A13–36

SiLso,ps

1,gr,f0

ND

77.920

10YR3/2

10YR1/2

3310Y

R4/3

10YR2/2

2Bw36–60

ND

ND

ND

v1,n,brND

57.750

10YR5.5

/510Y

R4.5

/52Bt

60–90+ND

ND

2,sbk,m3,m

k,br45.7

8010Y

R6.5

/610Y

R5/6

J4>12

,250b

A0–26

Lss,ps

1,sbk,mnone

c,s9.9

147.5Y

R3/2

10YR1/1

2A26–42

Lss,ps

1,sbk,fnone

c,s51.8

337.5Y

R4/2

10YR1.5

/12Bw

142–55

SLss,ps

1,sbk,fnone

c,w43.7

5010Y

R5.5

/510Y

R4/4

2Bw2

55–93SCL

s,p1,sbk,m

1,n,bra,s

42.375

10YR6/4

10YR5/5

2Cox93–130+

Sso,po

1,sbk,mna

g,w69.3

11310Y

R5/4

10YR3.5

/4U1

>41,520

A0–27

Lss,ps

2,sbk,fnone

c,w0.0

157.5Y

R5/4

7.5YR3/3

2Bw1

27–40L

s,p1,sbk,f

1,n,brc,s

63.932

10YR5.5

/47.5Y

R3/4

2Bw2

40–70L

vs,p2,sbk,m

1,n,brg,w

49.450

10YR6/5

10YR5/5

2Bt170–99

L+s,p

3,abk,vc4,m

k,pf,po,brc,s

41.785

10YR6/4

10YR5.5

/52Bt2

99–103+CL

vs,vp3,abk,vc

4,mk,pf,po,br

31.2100

10YR5/6

10YR4.5

/6U2

<16650

bA

0–10L

ss,ps1,sbk,f

nonea,s

25.16

10YR5/4

10YR3/3

Bw10–35

Lss,ps

2,sbk,fnone

a,s51.6

22e

10YR5/5

10YR3/3.5

Bwg

35–84SCL

s,p2,sbk,m

noneg,s

43.137

e10Y

R5.5

/710Y

R4/5.5

55e

10YR6/4

10YR4.5

/4.575

e10Y

R5.5

/610Y

R4/5

Cg84–103+

SCLs,p

2,abk,mnone

50.795

e10Y

R5.5

/510Y

R4.5

/4U3

<16650

bA

0–23L

ss,pssg,gr,f

noneg,s

66.65

7.5YR4/3

7.5YR2/2

2010Y

R4/3

10YR2.5

/2Bw

123–40

SLss,ps

2,sbk,f2,n,br

g,s55.8

3310Y

R5/4

10YR3.5

/2Bw

240–86

SLss,ps

2,sbk,f2,n,br

g,s51.5

5310Y

R6/5

10YR4.5

/475

10YR5.5

/510Y

R4.5

/5Bw

386–102+

SLss,ps

2,abk,m2,n,br

29.4100

10YR5.5

/510Y

R4.5

/4U4

<16650

bA

0–30SL

ss,pssg,gr,f

noneg,s

60.710

7.5YR2.75

/27.5Y

R1/1

257.5Y

R3/2

7.5YR1/1

2A30–52

SLso,po

sg,gr,fnone

g,s60.6

4010Y

R4/2.5

10YR2/2

2Bw52–70

SLss,ps

2,sbk,fv1,n,br

c,w48.2

6010Y

R5/4

10YR3/3

2Bt70–100+

CLs,ps

2,abk,m2,m

k,br32.6

7010Y

R5.5

/410Y

R4/4

9010Y

R6/5

10YR4/4.5

U5

>2910

A0–13

Lso,ps

1,gr,fnone

c,s10.5

87.5Y

R4/4

7.5YR2.5

/2Bw

13–30SiL

so,ps1,sbk,f

nonec,w

35.028

7.5YR4.5

/47.5Y

R3/3

2Bw1

30–37SiL

ss,ps1,sbk,f

nonec,s

33.835

10YR5/4

7.5YR3/4

2Bw2

37–87+SL

s,ps3,abk,c

1,n,br21.2

5010Y

R6/4

7.5YR4/4

8010Y

R6/4

7.5YR4.5

/4

10GOODMANET

AL.

TABLE2—

Continued

Depth

ofsample

Estimated

forcolorage

ofDepth

>2nm

determination

Pitmoraine a

Horizon

c(cm

)Texture d

Consistence dStructure d

Clayfilm

s dBoundary

d(%)

(cm)

Color(dry)Color(w

et)

U6

>2910

A0–6

SLso,ps

1,gr,fnone

a,s16.8

47.5Y

R3.5

/37.5Y

R1/1

2A6–20

SLss,ps

1,gr,fnone

a,s64.9

147.5Y

R3.5

/37.5Y

R1/1.5

2Bw1

20–32L

ss,ps2,sbk,f

nonec,s

53.226

7.5YR4/3

10YR2/2

2Bw2

32–44LS

ss,ps2,sbk,m

v1,n,brg,w

52.937

10YR5/3

10YR3/3

2Cox44–80+

LSss,ps

3,abk,m1,n,br

48.050

10YR6/3.5

10YR4/3.5

7510Y

R6/3.5

10YR4/4

U7

>2910

bA

0–23LS

so,pssg,gr,vf

nonea,s

51.12

7.5YR3/2.5

7.5YR2/2

147.5Y

R3/2

7.5YR1/1

Cu23–80+

Sso,po

1,gr,fnone

c,w84.4

357.5Y

R2.75

/27.5Y

R1/1

607.5Y

R4/2

7.5YR1/1

U8

<394

bAj

0–17SL

ss,ps1,gr,f

nonec,w

57.610

7.5YR5/3

7.5YR3/2

Cox17–35

LSso,po

2,sbk,mnone

c,w18.2

265YR5/2

7.5YR3/2

Cu35–80

SLso,ps

2,sbk,mnone

c,w53.5

445YR5/2

5YR3.5

/270

5YR5/3

7.5YR3/2

2Cu80–85+

Sss,ps

2,sbk,mnone

0.082

5YR5.5

/25YR3/2

M1

>18540

bA

0–7SL

ss,ps2,sbk,m

nonec,s

22.95

7.5YR4.5

/47.5Y

R3/2.5

2AB

7–22LS

ss,ps2,gr,m

noneg,s

71.010

7.5YR4.5

/37.5Y

R2.75

/22Bw

122–40

SLs,p

2,sbk,m1,n,br

g,s55.0

257.5Y

R4.5

/47.5Y

R3/3

2Bw2

40–58SCL

s,p2,sbk,m

1,n,brg,s

44.345

10YR5.5

/510Y

R4/5

5510Y

R5.5

/410Y

R4/6

2Bt58–82+

SCLvs,vp

3,abk,c2,n,pf/br

51.965

10YR5.5

/410Y

R4.5

/582

10YR5.5

/510Y

R4/4

Q1

#25460

bA

0–12SL

so,ps2,sbk,f

nonea,s

3.67

7.5YR4/3

7.5YR2/2

2Bw1

12–27SL

ss,ps2,abk,m

nonea,s

35.320

7.5YR4.5

/47.5Y

R2.5

/22Bw

227–56

SCLss,ps

3,sbk,mv1,n,br

a,w48.2

4210Y

R5/4

7.5YR3/3

2Bt56–95+

SLso,ps

3,abk,c2,n,br

33.760

10YR5.5

/410Y

R4/3

9010Y

R6.5

/410Y

R4/4

Q2

#17554

bA

0–12SL

so,ps2,sbk,m

nonea,s

38.47

7.5YR4/4

7.5YR3/2.5

2Bw1

12–29LS

so,po2,sbk,m

nonec,s

38.720

10YR5/4

10YR3.5

/32Bw

229–55

SCLss,ps

2,abk,mv1,n,br

c,s27.8

4510Y

R5.5

/510Y

R4/4

2Bt55–80

SCLs,p

3,abk,c2,m

k,po/brg,s

49.768

10YR6/5

10YR4/4

2Cox80–95+

SCs,p

3,abk,c1,n,br

20.785

10YR6/4

10YR4/4.5

Q3

>14290

bA

0–10SL

so,ps2,sbk,f

nonea,s

43.25

7.5YR4/3

7.5YR2/2

Bw1

10–20SL

ss,ps2,sbk,m

nonec,s

35.915

7.5YR4/4

7.5YR2/2

Bw2

20–34S

so,ps2,abk,m

nonea,w

41.328

7.5YR5.5

/3.57.5Y

R3/3

Cox134–49

Sso,po

2,abk,mnone

c,s47.1

437.5Y

R6/3.5

7.5YR3.5

/3Cox2

49–85+S

so,po3,abk,m

none42.3

757.5Y

R5.5

/37.5Y

R4/3

Q4

<12800

bA

0–15SL

so,ps1,gr,f

nonea,s

53.28

7.5YR5/4

7.5YR3.5

/3Bw

115–35

LSss,ps

2,sbk,m1,n,br

a,s54.1

257.5Y

R5.5

/37.5Y

R4/3

Bw2

35–70LS

s,p3,abk,m

2,mk,br/po

c,s61.4

457.5Y

R5/3

7.5YR4/3

627.5Y

R5.5

/37.5Y

R4/3

Cu70–94+

Sss,ps

3,abk,c2,m

k,br/po56.1

905YR5.5

/35YR4/3

Q5

<300

bCu

SLso,po

ND

none18.0

2010Y

R6.5

/2.510Y

R4/2.5

5010Y

R7/2

10YR4/2

9010Y

R7/2

10YR4/2

Q6

<300

bCu

SLso,po

ND

none71.9

2010Y

R7.5

/1.510Y

R5/2

6010Y

R7/1.5

10YR5/2

aAgesare

basedeitheron

limiting

radiocarbondatesw

hichhave

beencalibrated

tothe

calendartimescale

usingCALIB

3.0(Stuiverand

Reimer,1993)orare

basedonmodelsofpedogenic

development,w

hich,inturn,are

basedonthese

calibratedradiocarbon

dates.Oneexception

tothisisthe

ageofthe

moraine

with

soilpitU1,w

hichisin

14CyrB.P.,because

thisageisbeyond

therange

oftheStuiverand

Reimer,(1993)calibration

dataset.

bUsed

tocalibrate

soildevelopment(e.g.,Figs.4–7).

cHorizon

nomenclatureand

abbreviationsforfielddescriptionsfollow

SoilSurveyDivision

Staff(1993)andBirkeland

(1999);ifmorethan

oneparentmaterial

isnoted,theupperone

isloessormixed

loessandtilland

thelow

eroneistill;ifonly

oneparentm

aterialisnoted,itistillormixed

loessandtill.

dNDdenotesproperty

notmeasured

forthatsoilhorizon.eM

ottlingpresent;m

ottlesarem,2,7.5Y

5/8.

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

11

FIG

.4.Variation

inPDIwithsoilage

calculatedfrom

twocolorindices(rubification

andmelanization)and

fourfieldproperties(totaltexture,structure,clay

films,and

pH).Both

Vilcanotaand

Quelccaya

soildata(Table

4)were

usedinthe

regression(y

=0.065

ln(x)%0.328;r 2

=0.87).A

rrowtoright(>

)indicatesthatage

assignmentis

basedonminim

um-lim

iting14C

date(s)andtrue

ageisolderthan

thatplottedbyanundeterm

inedamount.Conversely,arrow

toleft(<

)indicatesthatage

assignmentisbased

onmaxim

um-lim

iting14C

date(s)andtrue

ageisyoungerthan

thatplottedbyanundeterm

inedamount.

tobethe

caseforQ

uelccayasoils,an

inversecolortrend

isev-identin

theVilcanota

soilswhere

redparentm

aterialhuesof

5YRcontrastw

iththe10Y

Rcolorsoftheoldestsoils(Table2).

Thisreversalsuggeststhatredcolorisnotan

accuratemeasure

ofpedogenesisinthe

CordilleraVilcanota,perhapsbecause

theiron

oxideproducedduring

pedogenesisislessredthan

theironoxidespresentin

theparentm

aterial.Thehighcorrelationcoefficientfrom

thePDIregressionusing

boththe

CVand

QICdata

suggeststhatfieldpropertiesofsoils

inboth

areasaredevelopingatsim

ilarrates(Fig.4).Incontrast,

severallaboratoryparam

eterssuggestthatCV

andQICsoils

developatdifferentrates

(Figs.5–7).Inthe

CV,youngsoils

(<400

calyr)containasm

uchas#

1.5%secondary

ironinher-

itedfrom

parentbedrock.After#

16,000calyr,the

quantityof

pedogeniciron

roughlydoubled

(Fig.5,Table4).In

contrast,the

youngestQICsoils

containlittle

ornosecondary

iron,butin

#20,000

calyrasmuch

as2.0%Fed had

accumulated.

Differences

inthe

rateofsecondary

ironaccum

ulationbe-

tween

theCV

andQICmayreflect

thecontrasting

effectof

eolianduston

soildevelopmentin

thetworegions.Secondary

ironinQICsoils

increaseslinearly

withtimewhereas

ironin

CVsoils

increaseslogarithm

ically(Fig.5).Because

thepar-

entmaterialofthe

QICand

CVsoils

differinFed

by2orders

ofmagnitude

(Table3),soils

inthe

QIC,w

hichstartw

ithlit-

tleinitialFed

(#0.00–0.06%

;Table3),w

ouldbeaffected

toa

greaterdegreebythe

semicontinuous

inputofdustcontainingsom

epedogenic

ironthan

would

soilsinthe

CV.Consequently,the

QICsoilsw

ouldtend

toshow

alinearincrease

ofFedwith

time;lineartrendsin

soildevelopmenthave

beennoted

insoils

dominated

byeolian

inputs(e.g.,Reheisetal.,1989).Moreover,

dustisabundantinthe#

1500-year-longicecore

fromthe

QIC,

especiallyinthe

layerswhich

formduring

thedry

seasonwhen

winds

arefrom

thewest(Thom

psonetal.,1985,1986),and

theweighted

mean

percentageclay

appearstoincrease

linearlyinsoilsin

boththe

CVand

inthe

QIC(Fig.6).In

contrast,CVsoilsform

fromaparentm

aterialthatisrelativelyenrichedinFed(#1.7%

),much

ofwhich

islikely

derivedfrom

thehydrother-

mally

oxidizedrocks

thatflankthe

Range.Thusindices

ofFeaccum

ulationinthese

soilswould

notbeasaffected

byeolian

additionsaswould

thosefor

QICsoils.The

dominantsource

12GOODMANET

AL.

TABLE 3Laboratory Data for Soils on Moraine Crests in the Cordillera Vilcanota and Quelccaya Ice Cap Region

Magnetic %, <2 mm fractionSample Bulk susceptibility Frequency

Estimated age Depth depth Sample density (MS; 0.47 kHz) dependent Organic Clay Silt SandPit # of morainea Horizon (cm) (cm) name (g cm%3) pHc ' 10%8 m3 kg%1 MS (%) carbon &2 µm 2–50 µm 0.05–2 mm Fed Ald

J1 >18,540 A 0–7 5 J1.1 ND 6.2 ND ND 2.2 18.7 77.7 3.6 2.84 0.15AB 7–27 20 J1.2 ND 7.7 ND ND 0.5 15.0 60.9 24.1 3.09 0.11Bw1 27–40 33 J1.3 ND 8.3 ND ND 0.3 10.4 54.4 35.2 4.17 0.12Bw2 40–50 45 J1.4 ND 8.4 ND ND 0.2 7.6 40.6 51.8 4.21 0.14Bw3 50–65+ 60 J1.5 ND 8.1 ND ND 0.1 6.7 26.3 67.0 3.23 0.14

J2 >18,540 A 0–3 ND ND ND ND ND ND ND ND ND ND ND NDAB 3–13 5 J2.1 1.8 5.6 ND ND 2.5 15.2 59.7 25.2 3.91 0.23Bw1 13–63 15 J2.2 1.6 5.8 ND ND 2.1 14.5 59.7 25.8 3.90 0.22

30 J2.3 1.9 5.9 ND ND 0.8 13.0 59.7 27.2 3.78 0.1650 J2.4 2.0 6.1 ND ND 0.3 11.6 59.1 29.3 3.85 0.12

Bw2 63–130+ 80 J2.5 2.0 6.8 ND ND 0.1 11.4 59.0 29.5 3.75 0.12110 J2.6 2.1 6.7 ND ND 0.1 11.4 59.5 29.1 4.01 0.12

J3 >16800b A 0–3 5 J3.1 1.0 4.2 126.5 8.1 7.2 17.2 60.8 22.0 3.36 0.932A 13–36 20 J3.2 1.3 4.4 112.6 9.0 6.7 16.2 62.9 20.9 3.40 1.14

33 J3.3 1.7 4.8 52.2 8.2 2.4 12.1 55.5 32.5 3.59 0.712Bw 36–60 50 J3.4 2.0 4.9 16.4 1.2 0.5 14.2 57.8 28.1 3.61 0.282Bt 60–90+ 80 J3.5 1.9 5.1 12.4 6.8 0.2 15.2 58.3 26.6 4.13 0.19

J4 >12,250b A 0–26 14 J4.1 1.3 4.1 116.8 7.3 6.6 17.6 64.9 17.5 3.22 0.812A 26–42 33 J4.2 1.5 4.4 77.8 7.5 4.4 16.0 65.9 18.1 3.22 0.832Bw1 42–55 50 J4.3 1.6 4.9 18.3 1.3 1.1 12.1 63.1 24.8 3.29 0.472Bw2 55–93 75 J4.4 1.9 4.9 23.8 0.7 0.2 16.3 60.0 23.7 3.13 0.222Cox 93–130+ 113 J4.5 2.0 5.3 16.2 %0.4 0.3 9.4 35.0 55.6 3.73 0.28

U1 >41,520 A 0–27 15 U1.1 1.4 4.2 43.6 10.5 4.5 21.0 72.4 6.6 4.29 0.552Bw1 27–40 32 U1.2 1.6 4.4 43.0 8.2 2.2 22.1 68.4 9.5 4.49 0.522Bw2 40–70 50 U1.3 1.9 4.7 17.2 0.5 0.6 14.7 62.3 23.0 4.06 0.332Bt1 70–99 85 U1.4 1.9 4.8 12.9 %0.8 0.2 14.2 59.3 26.5 3.29 0.222Bt2 99–103+ 100 U1.5 1.8 5.2 10.6 %1.7 0.2 13.9 63.4 22.6 5.61 0.27

U2 <16650b A 0–10 6 U2.1 1.3 4.2 26.0 12.1 4.9 18.9 64.0 17.1 2.31 0.51Bw 10–35 22 U2.2 1.4 4.6 25.8 8.7 2.9 17.6 64.9 17.5 2.41 0.46Bwg 35–84 37 U2.3 1.9 4.8 9.2 2.1 0.7 13.0 57.2 29.8 5.06 0.25

55 U2.4 1.8 5.0 6.0 8.5 0.3 10.9 59.2 30.0 2.58 0.1775 U2.5 1.9 5.0 7.0 3.8 0.2 11.6 59.7 28.8 3.94 0.18

Cg 84–103+ 95 U2.6 1.9 5.6 9.1 %1.0 0.3 13.8 60.5 25.7 3.88 0.14U3 <16650b A 0–23 5 U3.1 1.0 4.8 48.1 4.5 5.0 12.7 49.3 38.0 3.19 0.52

20 U3.2 1.2 4.7 42.8 7.2 3.1 12.7 54.5 32.8 3.32 0.52Bw1 23–40 33 U3.3 2.0 5.0 16.1 7.7 1.8 10.3 47.5 42.3 3.68 0.55Bw2 40–86 53 U3.4 2.1 5.0 19.8 2.4 0.4 9.8 48.9 41.3 3.33 0.26

75 U3.5 1.8 5.3 20.9 2.6 0.3 9.9 47.2 42.9 3.56 0.21Bw3 86–102+ 100 U3.6 2.0 5.4 16.0 %1.0 0.2 10.2 49.0 40.8 3.46 0.16

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

13U4 <16650b A 0–30 10 U4.1 1.1 4.2 198.6 7.4 9.4 11.3 46.3 42.4 2.71 0.86

25 U4.2 1.5 4.5 106.0 7.9 5.7 9.8 44.1 46.1 2.74 0.842A 30–52 40 U4.3 1.6 5.0 50.6 5.4 1.8 6.7 33.7 59.6 3.06 0.532Bw 52–70 60 U4.4 2.0 5.2 38.6 2.4 0.4 6.1 36.1 57.8 3.64 0.322Bt 70–100+ 70 U4.5 1.7 5.6 39.5 2.5 0.2 9.7 55.8 34.5 3.28 0.18

90 U4.6 1.8 5.7 32.6 1.4 0.2 11.2 67.5 21.3 3.83 0.15U5 >2910 A 0–13 8 U5.1 1.0 4.1 380.5 8.8 7.9 16.4 61.2 22.4 2.79 0.73

Bw 13–30 28 U5.2 0.9 4.4 332.9 8.6 3.5 17.9 62.5 19.6 2.89 0.582Bw1 30–37 35 U5.3 ND 4.7 169.8 8.2 1.9 16.6 64.0 19.4 2.85 0.432Bw2 37–87+ 50 U5.4 1.7 5.0 57.2 1.9 0.4 15.3 64.5 20.2 3.19 0.24

80 U5.5 1.5 5.2 52.0 1.1 0.2 16.2 62.4 21.4 2.91 0.16U6 >2910 A 0–6 4 U6.1 1.1 4.7 135.5 6.6 7.5 14.8 57.9 27.4 2.46 0.78

2A 6–20 14 U6.2 1.1 4.6 120.0 7.1 5.4 12.9 60.8 26.4 2.73 0.792Bw1 20–32 26 U6.3 1.3 4.9 92.8 3.4 3.2 12.1 59.4 28.5 2.90 0.772Bw2 32–44 37 U6.4 1.6 5.0 52.6 1.0 1.4 10.6 56.8 32.6 2.89 0.562Cox 44–80+ 50 U6.5 1.8 5.1 39.3 %1.0 0.3 8.3 49.2 42.5 2.74 0.36

75 U6.6 1.7 5.3 39.1 %0.2 0.3 8.3 47.6 44.2 3.03 0.29U7 >2910b A 0–23 2 U7.1 0.7 4.6 156.1 3.6 7.6 13.8 48.0 38.1 3.25 0.80

14 U7.2 1.0 4.6 133.1 2.2 6.0 11.9 56.1 32.1 2.89 1.23Cu 23–80+ 35 U7.3 1.3 4.8 129.9 2.6 4.5 8.2 57.9 33.9 1.97 1.09

60 U7.4 1.1 5.1 108.0 2.0 2.5 6.8 50.4 42.8 1.49 0.74U8 <394b Aj 0–17 10 U8.1 1.4 5.1 113.6 0.0 1.6 10.9 44.8 44.3 1.54 0.13

Cox 17–35 26 U8.2 1.6 5.5 127.8 1.3 0.4 8.0 38.8 53.1 1.41 0.06Cu 35–80 44 U8.3 1.8 6.2 103.8 0.2 0.3 12.9 49.7 37.4 1.02 0.02

70 U8.4 1.9 7.2 121.4 1.0 0.2 8.6 32.5 59.0 1.69 0.042Cu 80–85+ 82 U8.5 2.0 6.9 138.9 0.7 0.1 9.3 51.4 39.3 1.71 0.03

M1 >18540b A 0–7 5 M1.1 1.4 4.6 27.7 4.7 2.9 17.6 52.1 30.3 1.47 0.252AB 7–22 10 M1.2 1.2 4.6 31.6 3.4 2.2 17.3 50.8 31.9 1.40 0.232Bw1 22–40 25 M1.3 1.8 4.7 ND ND 1.3 17.9 51.7 30.4 1.39 0.222Bw2 40–58 45 M1.4 1.8 5.3 38.6 0.2 0.2 15.2 53.6 31.3 1.48 0.10

55 M1.5 1.9 5.4 25.8 0.9 0.1 14.9 53.6 31.5 1.49 0.082Bt 58–82+ 65 M1.6 1.9 6.2 47.2 3.2 0.1 15.2 54.8 30.0 1.54 0.08

82 M1.7 1.9 7.3 55.6 %1.9 0.2 15.9 56.5 27.5 1.64 0.07Q1 #25460b A 0–12 7 Q1.1 0.9 4.6 44.5 4.0 5.7 12.2 47.4 40.4 2.14 0.43

2Bw1 12–27 20 Q1.2 1.4 4.8 38.7 3.6 2.5 11.8 46.2 42.0 2.29 0.452Bw2 27–56 42 Q1.3 1.6 4.8 28.8 2.7 1.5 12.6 49.7 37.7 2.24 0.442Bt 56–95+ 60 Q1.4 1.7 5.2 20.9 3.5 0.4 10.1 43.6 46.3 1.96 0.26

90 Q1.5 1.9 5.6 25.8 0.3 0.2 11.4 47.4 41.2 2.09 0.13

14GOODMANET

AL.

TABLE 3—Continued

Magnetic %, <2 mm fractionSample Bulk susceptibility Frequency

Estimated age Depth depth Sample density (MS; 0.47 kHz) dependent Organic Clay Silt SandPit # of morainea Horizon (cm) (cm) name (g cm%3) pHc ' 10%8 m3 kg%1 MS (%) carbon &2 µm 2–50 µm 0.05–2 mm Fed Ald

Q2 #17554b A 0–12 7 Q2.1 1.5 4.8 40.8 3.0 4.4 11.1 47.0 41.9 2.33 0.392Bw1 12–29 20 Q2.2 2.0 5.0 16.5 6.2 1.4 12.1 54.0 33.9 2.54 0.322Bw2 29–55 45 Q2.3 1.6 5.5 14.4 7.9 0.3 11.7 55.7 32.7 2.49 0.182Bt 55–80 68 Q2.4 1.9 6.3 25.3 2.4 0.2 12.1 57.3 30.7 2.65 0.142Cox 80–95+ 85 Q2.5 1.9 5.9 25.8 0.6 0.2 9.2 53.7 37.1 2.53 0.12

Q3 >14290b A 0–10 5 Q3.1 1.5 4.7 18.2 %1.4 2.7 7.1 30.0 62.9 0.61 0.18Bw1 10–20 15 Q3.2 1.6 4.9 3.8 18.2 2.0 8.2 32.4 59.4 0.64 0.30Bw2 20–34 28 Q3.3 1.7 5.1 6.0 5.3 0.6 9.2 35.8 55.0 0.47 0.15Cox1 34–49 43 Q3.4 1.9 5.2 7.2 2.1 0.3 7.7 30.2 62.2 0.44 0.09Cox2 49–85+ 75 Q3.5 1.9 5.5 7.1 6.3 0.2 9.9 32.5 57.6 0.43 0.06

Q4 <12800b A 0–15 8 Q4.1 1.6 5.5 16.3 6.9 1.1 9.2 42.6 48.1 0.68 0.15Bw1 15–35 25 Q4.2 1.5 6.7 13.7 9.3 0.4 8.4 39.9 51.7 0.64 0.06Bw2 35–70 45 Q4.3 1.8 8.1 10.4 8.4 0.3 7.7 39.3 53.0 0.78 0.03

62 Q4.4 1.8 8.2 21.4 5.8 0.4 11.3 48.4 40.3 0.86 0.03Cu 70–94+ 90 Q4.5 2.0 8.4 16.7 1.1 0.4 11.4 46.7 41.8 0.75 0.03

Q5 <300b Cu 0–100+ 20 Q5.1 ND 5.1 6.0 0.0 0.4 10.3 33.4 56.4 0.04 0.0650 Q5.2 ND 5.0 4.8 2.1 0.4 13.7 37.4 48.9 0.06 0.0590 Q5.3 ND 5.2 5.3 0.0 0.4 10.5 39.5 50.1 0.05 0.05

Q6 <300b Cu 0–80+ 20 Q6.1 ND 6.1 13.7 1.6 0.1 7.0 27.5 65.5 0.01 0.0160 Q6.2 ND 6.2 12.4 3.3 0.0 4.8 22.8 72.5 0.00 0.00

a Ages are based either on limiting radiocarbon dates which have been calibrated to the calendar time scale using CALIB 3.0 (Stuiver and Reimer, 1993) or are based on models of pedogenicdevelopment, which, in turn, are based on these calibrated radiocarbon dates. One exception to this is the age of the moraine with soil pit U1, which is in 14C yr B.P., because this age is beyondthe range of the Stuiver and Reimer (1993) calibration data set.

b Used to calibrate soil development (e.g., Figs. 4–7).c ND denotes property not measured for that soil horizon.

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

15

FIG

.5.Weighted

mean

percentagesecondary

iron(Fed )in

Vilcanotasoils(y

=0.514

ln(x)%1.432;r 2=

0.91)andinQuelccaya

soils(y=9E-05x%

0.097;r 2=

0.71).Arrow

toright(>)indicatesthatage

assignmentisbased

onminim

um-lim

iting14C

date(s)andtrue

ageisolderthan

thatplottedbyanundeterm

inedamount.Conversely,arrow

toleft(<)indicates

thatageassignm

entisbased

onmaxim

um-lim

iting14C

date(s)andtrue

ageisyoungerthan

thatplottedbyan

undetermined

amount.

ofpedogeniciron

toCV

soilsmaybethe

weathering

ofiron-bearing

minerals.The

observationofa

logarithmicbuildup

ofFed in

CVsoilsisconsistentw

ithachem

icalweathering

source(e.g.,Colm

an,1981;Birkeland,1999).Trendsin

MSwithtimeforsoilsin

theCVand

QICmayalso

reflectthecombined

effectsofdifferingparentm

aterialsandthe

inputofdusttothe

tworegions.There

isaprogressive

declineinthe

MSofCV

soilsincontrastto

theslightincrease

inthe

MSofQICsoils

withincreasing

pedogenesis(Fig.7A

).Thismaybeexplained

bythe

progressivedestruction

ofmagnetite

fromhigh

initiallevels(#150'

10%8m

3kg%1)in

CVsoils,and

theprogressiveaccumulation

ofmagnetitefrom

verylow

initiallevels

(#5

'10

%8m3kg

%1)in

QICsoils

(Fig.7A).H

owever,

itseemsunlikely

thatthestability

ofmagnetite

would

beso

dramatically

differentinthe

tworegions,w

hichshare

asim

ilarclim

ateand

vegetation.Amore

plausibleexplanation

isthat

thesem

icontinuousinputofdustwithamagnetic

susceptibility#30'

10%8m

3kg%1hasacted

toprogressively

dilutetheMSof

CVsoilsw

hileenriching

theMSofQ

ICsoils.The

progressiveincrease

inthe

frequency-dependentMSinboth

theCV

andQICsoils(Fig.7B)m

ayreflectthepresenceofvery

finegrained

magnetiteinthedustthathasbeenaddedtoallsoils,orthein

situform

ationofsuch

grains,orsomecom

binationofboth.A

more

completeunderstanding

oftheroleofdustinthedevelopm

entofsoilsin

theCV

andQICwillrequire

dataondustaccum

ulationratesand

composition.

AgeEstim

atesfromCalibrated

Weathering

Rates

Toestimatetheageoftheoldestsoil,U

1,intheCordilleraVil-canotaarea,w

eextrapolatedthePDI,IPA

Fed ,andWMextended

depthFed regressionsto

therelevantU1soildata(Table4).The

estimated

ageofsoilU

1forthe

PDI,IPA

,andWMregressions

are#96,000,#

92,000,and#77,000

yrB.P.,respectively.Un-

certaintiesinPDI(±

0.01),IPA(±0.02),and

WMFed (±

0.05%)

were

estimated

basedonthe

rangeofvalues

formoraines

ofsim

ilarages(Table

4).Incorporatingthese

uncertaintiesyields

anestim

atedage

rangeforsoilU

1of80,500–114,500

yrB.P.These

agerangesare

unrealisticallysmallbecause

wehave

notattem

ptedtoaccountfor

theunknow

nuncertainty

inthe

ageestim

ates(i.e.,m

inimum

andmaxim

umages)ofthe

moraines

usedinthe

calibrationdata

set(Table4).

16GOODMANET

AL.

TABLE4

SoilDevelopm

entIndexData

forMoraines

inthe

Cordillera

Vilcanota

andQuelccaya

IceCap

Region

Estimated

IPAd

WMe(%

)WMBD

h(g/cm

2)Soil

ageof

pit#moraine a

PDI c

pHOC

ClayFe

Al

pHOC

ClayFe

Al

MSf

%FD

gOC

ClayFe

Al

J1>18,540

0.110.01

2.120.18

0.982.96

8.00.3

9.03.36

0.13ND

ND

ND

ND

ND

ND

J2>18,540

0.220.09

3.280.34

1.303.18

6.40.4

12.03.90

0.14ND

ND

0.0080.237

0.0780.003

J3>16800

b0.32

0.3016.12

0.691.26

11.574.9

1.815.1

3.840.42

38.17.6

0.0230.259

0.0670.006

J4>12,250

b0.24

0.3218.83

0.570.97

12.664.8

2.114.1

3.350.45

ND

ND

0.0290.239

0.0580.007

U1

>41,520

0.410.33

12.190.84

1.569.70

4.71.4

16.54.35

0.3522.7

5.50.021

0.2820.076

0.006U2

<16650

b0.28

0.2810.00

0.571.00

6.515.1

1.214.1

3.390.25

12.96.0

0.0170.237

0.0600.004

U3

<16650

b0.29

0.2710.24

0.171.03

8.105.1

1.210.5

3.440.30

22.93.2

0.0160.186

0.0620.005

U4

<16650

b0.28

0.2620.41

0.171.00

10.755.2

2.29.9

3.390.39

66.35.4

0.0290.163

0.0570.006

U5

>2910

0.330.30

13.470.82

0.748.12

4.91.5

16.32.95

0.30ND

ND

0.0150.218

0.0400.004

U6

>2910

0.310.28

13.560.13

0.7112.45

5.11.5

9.62.90

0.45ND

ND

0.0190.149

0.0470.007

U7

>2910

b0.22

0.3561.46

0.400.78

31.644.6

6.612.6

3.021.08

141.12.7

0.0590.114

0.0280.010

U8

<394

b0.15

0.258.27

0.100.00

1.705.3

1.09.4

1.480.09

120.90.7

0.0140.137

0.0220.001

M1

>18540

b0.35

0.155.54

0.820.00

2.706.1

0.716.3

1.54i

0.12ND

ND

0.0100.283

0.027i

0.002Q1

#25460

b0.35

0.1835.20

0.98526

86.625.0

1.611.7

2.140.33

29.92.7

0.0210.183

0.0340.005

Q2

#17554

b0.35

0.0919.40

0.92621

53.285.6

0.911.3

2.530.20

22.93.5

0.0150.200

0.0450.004

Q3

>14290

b0.25

0.1514.78

0.53115

29.145.2

0.79.0

0.470.11

7.84.4

0.0120.166

0.0090.002

Q4

<12800

b0.31

0.0210.49

0.54180

15.437.2

0.59.1

0.740.06

15.37.4

0.0090.155

0.0130.001

Q5

<300

b0.00

0.000.00

0.000.00

0.005.1

0.412.3

j0.05

0.055.4

0.70.008

0.246j

0.0010.001

Q6

<300

b0.00

0.000.00

0.000.00

0.006.2

0.15.9

0.000.00

3.02.5

0.0010.118

0.0000.000

aAgesare

basedeitheron

limiting

radiocarbondatesw

hichhave

beencalibrated

tothe

calendartimescale

usingCALIB

3.0(Stuiverand

Reimer,1993)orare

basedonmodelsofpedogenic

development,w

hich,inturn,are

basedonthese

calibratedradiocarbon

dates.Oneexception

tothisisthe

ageofthe

moraine

with

soilpitU1,w

hichisin

14CyrB.P.,because

thisageisbeyond

therange

oftheStuiverand

Reimer(1993)calibration

dataset.

bUsed

tocalibrate

soildevelopment(e.g.,Figs.4–7).

cProfiledevelopm

entindex.dIndex

ofprofileanisotropy.

eWeighted

mean.

fMagnetic

susceptibility(0.47

kHz;'

10 %8m3kg %

1);NDdenotesproperty

notmeasured

forthatsoil.g%

frequencydependentm

agneticsusceptibility.

hWeighted

mean

usingbulk

densitydata

todeterm

inemassaccum

ulationperunitarea

ofsoil;forsoilsQ5and

Q6bulk

densityisestim

atedat2

gcm

%3.

iNotused

inFesoilchronofunctionsdue

tolikely

differentparentmaterialFe

valuethan

thatusedforotherCV

soils.jNotused

insoilchronofunctionsashigh

claycontentm

ayreflectthe

presenceofrew

orkedlacustrine

sedimentsin

till.

GlacialC

hronology

Correlation

tothe

preexistingVilcanota–Q

uelccayachronol-

ogy.Thesoil-ageestim

atesforthemorainecontaining

soilpitU1provide

theonly

semiquantitative

supportfortheassertion

byMercer(1984)thattheouterm

ostmorainesintheCV

arerem-

nantsofaglacialm

aximum

fromearly

inthe

lastglacialcycle.However,asnoted

abovethe

80,500–114,500yrB.P.estim

atedage

rangeforsoilU

1isunrealistically

small,and

amore

realis-ticage

rangewould

likelyinclude

allofmarine

isotopestages

(MIS)4–6.Thereisnodirectevidenceofglacierexpansionduringorprior

toMIS4inthe

QICregion.Prelim

inarycosm

ogenic26A

land10Be

agesfromerraticson

thelateralm

orainesthatcontainsoil

pitsQ1andQ

2,whichm

arkthemaxim

umexpansionoftheQ

IC,are

25,460±1600

and17,554

±300

calyrB.P.,respectively(Goodm

an,1999).Thissuggeststhatincontrastto

theCV,the

MIS2glaciallim

itinthe

QICwasasorm

oreextensive

thanearlierphasesofglaciation.Therearenum

erousmorainesthatw

eredepositedduring

lateglacialtim

e.Aminim

um-lim

itingage

of14,290(+570,%

470)

calyrB.P.fromanexposure

1km

upvalleyfrom

themoraine

inwhich

soilpitQ3wasexcavated

isthe

onlyage

controlforthe

Huancane

IIImoraines

attheQIC.The

actualageofthese

morainesisolderthan

theminim

um-lim

itingageand

thuscouldcorrelate

withthe

#16,650

calyrB.P.lateglacialm

orainesin

theCV.Rapiddeglaciation

ofunknownextentin

bothareasafter

thislate

glacialadvancewaspunctuated

byaseries

ofminor

readvances.Amaxim

umageof13,090

(+420,%

360)calyrB.P.from

aHuancane

IImoraine

andaminim

umage

of12,800

(+160,%

180)calyrB.P.fromLaguna

PacoCocha

inthe

QIC

constrainthe

timing

ofonereadvance.SoilQ

4wasexam

inedonthe

Huancane

IImoraine

thatimpoundsLaguna

PacoCocha

(Fig.3).Bycorrelating

thegeneralcharacteristics

ofthis

soilwiththoseofothersoils,thisreadvancecan

betracedthroughout

theregion.In

theCV,PD

Idata

suggestthatsoilsU5and

U6

sharefield

characteristicswithsoilQ

4and

thusthe

moraines

thatcontainthese

soilswere

probablydeposited

duringthislate

glacialreadvance(Fig.4).

Nomoraines

canunequivocally

beassigned

tothe

earlyHolocene.Forexam

ple,itispossiblethatthe

moraine

thatcon-tains

soilU7wasdeposited

duringthe

earlyHolocene

oreven

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

17

FIG

.6.The

progressiveaccum

ulationofclay

inVilcanota

andQuelccaya

soils.Vilcanotasoilsfollow

alineartrend

(y=3E-06x

+0.1227;r 2=

0.76),andQuelccayasoilsfollow

alineartrend(y=

7E-06x+0.1131;r 2=

0.62).Arrow

toright(>)indicatesthatageassignm

entisbasedonminim

um-lim

iting14C

date(s)and

trueage

isolderthanthatplotted

byanundeterm

inedamount.Conversely,arrow

toleft(<)indicatesthatage

assignmentisbased

onmaxim

um-lim

iting14C

date(s)andtrue

ageisyoungerthan

thatplottedbyanundeterm

inedamount.

duringthe

lateglacial.Peatexposed

inastream

cutupvalleyfrom

thismoraine

providesaminim

um-lim

itingage

of2910

(+240,%

140)calyr

B.P.forthis

moraine

(Fig.2;Table1).

TheA/Cprofile

ofsoilU7(Table

2)suggeststhatthismoraine

wasform

edduring

thelateHolocene,probably

notmuch

before#3,000

yrB.P.However,no

similaraged

moraines

havebeen

documented

inthe

QICregion.

Thefinalglacialreadvance

iswelldocum

entedinboth

theQICand

CVwith

maxim

um-lim

itingradiocarbon

agesfrom

peatunderlyingtillin

bothareas.Close

tothe

activeice

inthe

CV,thesmallm

oraineonwhich

soilU8wasdug

wasdeposited

lessthan394±100calyrB.P.andnot600(+

70,%80)calyrB.P.

asMercer(1984)suggested(Table1).Theform

erdatecorrelateswithasim

ilaradvanceinthe

QICthatoccurred

<300

±80cal

yrB.P.(M

ercerand

Palacios,1977).Between

thesemoraines

andmodern

icefrontsinboth

regionsaresmallm

oraines,which

possesslittle

pedogenicdevelopm

ent(e.g.,soilsQ5and

Q6;

Table2);these

moraines

areprobably

theresultof

step-wise

glacialretreatduringthe

lastcentury.

Relationtoglobalchronology.

Themoraine

sequencefrom

theCV

andQICcorrelates

wellw

ithother

recordsofglacia-

tioninSouth

America

andthe

SouthernHemisphere.A

gesof

theoldestglacialdepositsin

theSouthern

Hemisphere

areesti-

mated

mostly

fromminim

um-lim

itingages

andqualitative

as-sessm

entsofpostdepositionalalteration.PreviousstudiesfromPeru

andChileidentified

morainesthatareolderthan

thepracti-callim

itofradiocarbondating

(Clapperton,1972;Wright,1983;

Mercer,1984;Rodbell,1993a;Low

elletal.,1995).Many

ofthese

depositsare

believedtobefrom

MIS4,butno

evidenceexists

topreclude

thesemoraines

frompredating

MIS5.Soil-

ageestimatesfrom

extrapolatedregression

analysisinthisstudy

suggestthatthemostextensivelateQ

uaternaryglaciation

inthe

CVprobably

occurredduring

MIS4though

westillcannotrule

outthepossibilitythatthesem

orainesdatetoanearlierinterval.

Themostextensive

lateQuaternary

glaciationofthe

Quelccaya

IceCap

occurredduring

MIS2.

Asignificant

advanceinsouthern

Peruoccurred

16,650(+390,%

430)calyr

B.P.;thisage

correlateswellw

iththose

ofothermorainesfrom

Peru,Bolivia,Chile,andNewZealand

(Clapperton,1990;Wright,1983;M

ercer,1984;Seltzer,1992;Low

elletal.,1995).Thisadvanceisalsocontem

poraneouswith

increasedice-rafted

detritusinthe

North

Atlantic

Ocean

dur-ing

Heinrich

EventOne(Bond

etal.,1992).Following

rapid

18GOODMANET

AL.

FIG

.7.Weighted

meanlow

fieldmagneticsusceptibility

(A)fortheCV(y

=%27

.003ln(x)+305

.74;r 2=0.65)and

QIC(y

=0.001x

+2.5473;r 2

=0.83).

Weighted

mean

percentfrequencydependentsubceptibility

(B)forallsoilsreflectsthequantity

ofultrafine,superparamagneticgrainsthatcontributeto

themagnetic

susceptibillysignal(Thom

psonand

Oldfield,1986).A

rrowtoright(>)indicates

thatageassignm

entisbased

onminim

um-lim

iting14C

date(s)andtrue

ageis

olderthanthatplotted

byanundeterm

inedamount.Conversely,arrow

toleft(<)indicatesthatage

assignmentisbased

onmaxim

um-lim

iting14C

date(s)andtrue

ageisyoungerthan

thatplottedbyanundeterm

inedamount.

deglaciationthroughoutSouth

America,a

glacialreadvancein

southernPeru

isconstrainedbetw

een13,090

and12,800

calyrB.P.Thisreadvance

occurredaboutthe

timeofthe

onsetoftheYoungerD

ryascooling;numerousrecordsfrom

Ecuador,Peru,Chile,N

ewZealand,and

theNorthern

Hemisphere

suggestthatthis

climate

eventwasregistered

globally(Alley

etal.,1993;

Wright,1983;D

entonand

Hendy,1994;Low

elletal.,1995;Clapperton

etal.,1997;RodbellandSeltzer,2000).

Theearly

Holocene

wasatimeofwarm

inginboth

hemi-

sphereswithlittle

evidenceforglaciation

(Nesje

andKvam

me,

1991;Thompson

etal.,1995).After#

5000calyrB.P.several

episodesofglaciationarerecorded

bymorainesin

partsofSouth

SUBDIVISIO

NOFGLACIA

LDEPO

SITSINSEPERU

19

America,including

inthe

CVand

QIC,buttheirsynchroneity

ispoorly

understood(Rothlisberger,1987;Clapperton,1983,

1990;Seltzer,1990).Themostextensiveadvanceduring

thelateHolocene

insouthern

Peruoccurred

duringthe

LittleIce

Age

andisdated

to<394

±100

calyrB.P.inthe

CVand

<300

±80calyrB.P.in

theQIC.C

ONCLUSIO

NS

Soilchronofunctionsoffield

andlaboratory

propertiesare

quantitative,reliableindicatorsofsoildevelopmentand

moraine

ages,especiallyduring

thelate

Quaternary.In

theCV,logarith-

micincreases

insecondary

ironwithtimeseem

toreflectthe

roleofchem

icalweathering

onsoildevelopm

ent.Significanteolian

additionsofdustcoatedwithpedogeniciron

mayexplain

thelinearincrease

insecondary

ironand

clayinQICsoils.The

inputofdustto

CVsoils,w

hichmayalso

bereflected

inthe

observedlinearincreasein

claycontentw

ithtimein

thesesoils,maybem

askedbyhighparentmaterialvaluesofsecondaryiron.

Ratesofsoildevelopmentasestablished

withradiocarbon

datessuggestthatthe

maxim

umglaciation

inthe

CV–QICregion

oc-curred

before41,520(+5590,%

3270)14C

yrB.P.andprobably

between#

70,000and#115,000yrB.P.,althoughw

ecannotruleoutthepossibility

ofanolderage.In

theQIC,an

advanceduringMIS2wasatleastasextensiveaspreviousadvancesand

proba-bly

occurredsim

ultaneouslywithaM

IS2advancein

theCV.Alateglacialadvanceculm

inated16,650

(+390,%

430)calyrB.P.inthe

CordilleraVilcanota.Follow

ingaretreatofunknow

nex-

tent,anotheradvanceoccurred

between

13,090(+420,%

360)and

12,800(+160,%

180)calyrB.P.attheQICand

coincidesapproxim

atelywiththe

onsetoftheYoungerD

ryas.Moraines

deposited<394

±100

calyrB.P.intheCV

and<300

±80cal

yrB.P.onthe

westside

oftheQICcorrelate

withLittle

IceAge

morainesofotherregions.

ACKNOW

LEDGMENTS

Wethank

ChrisMoy,PeterCastiglia,and

LeonidasandLuisCrispin

forhelpinthe

field.Thisresearchwasm

adepossible

bygrantsfrom

theU.S.N

ationalScience

FoundationtoG.O.S.(EA

R9422424)andD.T.R.(EA

R9418886)andbygrants

fromthe

Geological

SocietyofAmerica

toB.G

.M.(5884-96

and6084-97).Thism

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