pleistocene geomorphology and geochronology of eastern ... et al. 2005 qsr.pdf · standing of...

ARTICLE IN PRESS

0277-3791/$ - se

doi:10.1016/j.qu

�Correspondfax: +1435 797

E-mail addr1Present add

Logan, UT 843

Quaternary Science Reviews 24 (2005) 2428–2448

Pleistocene geomorphology and geochronology of eastern GrandCanyon: linkages of landscape components during climate changes

Matt D. Andersa, Joel L. Pedersona,�, Tammy M. Rittenourb,1, Warren D. Sharpc,John C. Gossed, Karl E. Karlstrome, Laura J. Crosseye, Ronald J. Gobleb,

Lisa Stocklif, Guang Yangd

aDepartment of Geology, Utah State University, Logan, UT 84322, USAbDepartment of Geosciences, University of Nebraska-Lincoln, Lincoln, NE 68588, USA

cBerkeley Geochronology Center, Berkeley, CA 94709, USAdDepartment of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5

eDepartment of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USAfDepartment of Geology, University of Kansas, Lawrence KS 66045, USA

Received 15 October 2004; accepted 22 March 2005

Abstract

We report new mapping, soils, survey, and geochronologic (luminescence, U-series, and cosmogenic-nuclide) data from

Pleistocene deposits in the arid setting of eastern Grand Canyon. The result is a stratigraphic framework of inset fill gravels and

associated terraces that provide a record of the responses of hillslopes, tributary streams, and the Colorado River to the last

�400 kyr of glacial–interglacial climate change. The best-preserved last 80 kyr of this record indicates a stratigraphic–chronologic

disconnect between both deposition and incision along the Colorado River versus along the trunks of local tributaries. For example,

the Colorado River finished aggrading and had already begun incising before the main pulse of aggradation in the trunks of local

catchments during Marine Isotope Stage 3, and then tributary incision followed during the millennial-scale fluctuations of the last

glacial epoch, potentially concurrent with mainstem aggradation. The mainstem record appears to broadly correlate with regional

paleoclimate and upstream geomorphic records and thus may be responding to climatic–hydrologic changes in its mountain

headwaters, with aggradation beginning during full-glacial times and continuing into subsequent interglacials. The contrasting lag

time in responses of the dryland catchments within Grand Canyon may be largely a function of the weathering-limited nature of

hillslope sediment supply.

r 2005 Elsevier Ltd. All rights reserved.

1. Introduction

Climate controls on the incision of elevated terrainand the response of landscapes to climate change are thetopics of some of the most vigorous recent research inthe Earth Sciences (e.g. Molnar and England, 1990;

e front matter r 2005 Elsevier Ltd. All rights reserved.

ascirev.2005.03.015

ing author. Tel.: +1435 797 7097;

1588.

ess: [email protected] (J.L. Pederson).

ress: Department of Geology, Utah State University,

22, USA.

Small and Anderson, 1995; Brozovic et al., 1997; Tuckerand Slingerland, 1997; Whipple et al., 1999; Hancockand Anderson, 2002; Wegmann and Pazzaglia, 2002,and many more). This large body of research has beenfocused mostly on relatively wet areas undergoingorogenesis. As a result, our understanding of the roleof climate in such environments is arguably moreadvanced than for the rest of the world’s landscapes,particularly in terms of well-dated records that lead toan understanding of processes. Our understanding ofdrylands, for example, is relatively poorly developed interms of longer timescale geomorphic responses to

ARTICLE IN PRESSM.D. Anders et al. / Quaternary Science Reviews 24 (2005) 2428–2448 2429

climate, yet these extensive but marginal landscapes andthe people that inhabit them are particularly vulnerableto climate changes (Intergovernmental Panel on ClimateChange (IPCC), 2001). Regardless of setting, the processlinkages, or coupling, between hillslopes and streams aswell as along the length of drainage systems affect thetiming and nature of responses to climate change (e.g.Harvey, 2002). But the rates at which depositional orerosional signals propagate through drainages and thecoupling of hillslope sediment sources to streams ispoorly understood.

As a starting point to meet these challenges, a generalconceptual model does exist for the relation betweenglacial–interglacial-scale climate cycles and geomorphicprocesses in drylands, particularly the southwestern US.This holds that increases in bedrock weathering andvegetation cover cause colluvium to accumulate onhillslopes during cooler and wetter periods (globalglaciation), and that stored sediment is stripped fromhillslopes and transported to fluvial systems by vegetationdisturbance and high precipitation intensity duringglacial–interglacial transitions (e.g. Bull and Schick,1979; Gerson, 1982; Bull, 1991; Harvey and Wells,1994; McDonald, et al., 2003). This model, though, isbased on records extending only to the last glacialmaximum with relatively limited age control, and there issignificant variability in responses evident just within thesouthwestern US region (Harvey, et al., 1999; Nichols,et al., 2002; McDonald, et al., 2003). A richer under-standing of dryland responses to climate change isneeded, and this starts with well-constrained field records.

Eastern Grand Canyon is an excellent area to studygeomorphic responses to climate change and thelinkages between landscape components in these re-sponses. Foremost, active tectonics does not obscureany potential climate signal. Also, the colluvial andalluvial deposits found here are well enough preservedand exposed that stratigraphic relations can be resolved,and numerical ages can be obtained using one or moretechniques. Lastly, there are local and regional paleo-climate studies available that can be correlated with thisgeomorphic record to decipher the influence of climatechange on the landscape.

In this paper, we describe the stratigraphic record ofhillslope, tributary drainage, and mainstem ColoradoRiver landscape components in eastern Grand Canyonand then report results from three independent butcomplimentary geochronometers, defining a geomorphicrecord spanning �400 kyr. This dated stratigraphy canbe used to calculate the long-term bedrock incision rate,which we do elsewhere. Here we focus on discerning theresponses to climate change that are superimposed uponthat incision. Results thus far indicate that the timing ofresponses and the linkages between landscape compo-nents of this famous dryland are more complicated thanmight be expected.

2. Background

This research focuses on the suite of impressive fillterraces and hillslope deposits best preserved in therelatively broad canyons west of the inactive Butte faultin eastern Grand Canyon (Fig. 1). The study areaincludes 34 km of the Colorado River corridor betweenComanche and Unkar Creeks and the Nankoweap,Kwagunt, and Lava Chuar drainages. It ranges inelevation from 790m along the Colorado River to2560m at the north rim of the canyon and has a meanslope of 311 below the canyon rims. Climate andvegetation vary strongly with elevation in GrandCanyon. Mean annual precipitation (MAP) is higherand mean annual temperature (MAT) is lower on thecanyon rim than the bottom, resulting in a downslopetransition from upland vegetation to desert scrubcommunities (Cole, 1990; Weng and Jackson, 1999).

Field observations indicate hillslopes in eastern GrandCanyon are mostly weathering-limited and dominated byphysical weathering. Bedrock is exposed at or near thesurface almost everywhere and comprises alternating cliffand slope-forming Paleozoic sedimentary rocks and lateProterozoic sedimentary and volcanic rocks, creating theclassic compound escarpments of Grand Canyon. Relictcolluvium mantles parts of the hillslopes, and presently itis being eroded by mass movements and overland flow(e.g. Griffiths et al., 1996).

Tributary catchments in eastern Grand Canyon havedrainage areas of 5–85km2 and have ephemeral andperennial, mixed bedrock-alluvial streams. Debris flowsand flashfloods are presently the primary modes ofsediment transport in tributary catchments and are aconsequence of intense summer monsoonal precipitationor long-duration, low intensity late fall or winter storms(Webb et al., 1989; Melis et al., 1994; Griffiths et al., 1996).

The greater Colorado River receives negligible dis-charge but significant amounts of coarse sediment fromthe immediate Grand Canyon area. The drainage areaof the Colorado River above the study area isapproximately 292,000 km2. Prior to construction ofGlen Canyon Dam above Grand Canyon, the ColoradoRiver had a median discharge of 230m3/s, a meanannual maximum discharge of 2440m3/s, and floodsexceeding 14,160m3/s (Howard and Dolan, 1981).Inputs of coarse sediment form debris fans at themouths of tributary drainages, causing the HoloceneColorado River to have a rapid-pool channel hydraulicgeometry (Leopold, 1969; Howard and Dolan, 1981;Kieffer, 1990; Schmidt and Rubin, 1995).

2.1. Previous geomorphic and paleoclimate research in

eastern Grand Canyon

Previous mapping and stratigraphic studies focusedon deposits found along the Colorado River corridor.

ARTICLE IN PRESS

Fig. 1. Study area in eastern Grand Canyon. Mapped Quaternary deposits are represented as dark gray polygons, major drainage basins are

delineated with dashed black lines, the Colorado and Little Colorado Rivers are solid black lines, and the Butte Fault is a thin dashed line.

M.D. Anders et al. / Quaternary Science Reviews 24 (2005) 2428–24482430

Machette and Rosholt (1991) identified seven ColoradoRiver deposits in eastern Grand Canyon and determinedthat they ranged in age from 4700 to 5 ka, based onuranium-trend dating. Lucchitta et al. (1995) identifiedseven mainstem and eight tributary stream terraces inthe Lava Chuar-Comanche reach. They determinedterrace ages of 101–1 ka based on radiocarbon andterrestrial cosmogenic nuclide (TCN) dating. A series ofmiddle-to-late Holocene Colorado River deposits thatwe group in our M1 unit has been the focus of extensiveprevious research (Lucchitta et al., 1995; Hereford,1996; Hereford et al., 1996). These deposits arefundamentally different in texture, sedimentology, andscale from older fill-terrace deposits along the ColoradoRiver corridor, and are not a focus of this research.

Comparison of our stratigraphy with those developedby previous workers is discussed in the results below.

Previous workers attributed these deposits in easternGrand Canyon to glacial–interglacial-scale climatefluctuations. Machette and Rosholt (1991) suggestedthat mainstem terrace formation in eastern GrandCanyon was caused by changes in sediment yield andvegetation cover in the Colorado River catchment.Lucchitta et al. (1995) likewise proposed that glacialadvances in headwater areas of the Colorado Rivercatchment during the Pinedale (Marine Isotope Stage[MIS] 2) and Bull Lake (MIS 6) glaciations increasedsediment load and caused two of the aggradationepisodes they identified in eastern Grand Canyon. Theyalso suggested that a mainstem Holocene aggradation


episode was the result of local reworking of olderalluvial and colluvial deposits due to reduced vegetationcover and intense monsoonal precipitation. Otherorigins proposed for the eastern Grand Canyon depositsinclude regional Miocene–Pliocene aggradation due todryer climate (Elston, 1989), and deposition in lakesbehind lava-dams in western Grand Canyon (Hamblin,1994).

Several paleoclimate reconstructions have been devel-oped in and near Grand Canyon based on pollen andfloral macrofossils. Collectively, these reconstructionsestimate that, from 45 to 20 ka, MAT was 2.9–4.3 1Clower and MAP was greater relative to today. Theranges of some plants were up to 900m lower (e.g.Anderson, 1993; Coats, 1997). At the peak of globalglacial conditions �20 ka, MAT is estimated to havebeen �7 1C lower, MAP was �90mm higher, and theranges of some plants were up to 1000m lower (e.g.Phillips, 1984; Cole 1990; Coats, 1997). The glacial–in-terglacial transition from 15 to 9 ka was marked by asignificant migration of plant species to higher eleva-tions with the onset of more arid conditions (Cole 1990;Weng and Jackson, 1999).

3. Methods

3.1. Field techniques

Our focus here is on surficial deposits and thesedimentologic and hydrologic linkages between land-scape components that they record. Colluvial andalluvial deposits were mapped at 1:12,000-scale inseveral tributary drainages and along the ColoradoRiver corridor in eastern Grand Canyon, an areaencompassing �300 km2 (Anders, 2003). Deposits werecorrelated based on stratigraphic position, soil-profiledevelopment, surface characteristics, and absolute age.Key outcrops were described in detail with particularattention given to stratigraphic and sedimentologicrelations between hillslope, tributary stream, and Color-ado River deposits. Heights of terrace treads and strathswere measured relative to the present active streamchannels in tributary drainages and measured relative toa reference stage at 283m3/s (10,000 cfs) along theColorado River. Height measurements were taken at�150 locations, including 21 high resolution crosssections measured with a total station (Anders, 2003).A total of twelve soil pedons were described on the fullsuite of tributary terraces, including laboratory analysesfor texture and carbonate percentage (Anders, 2003).

3.2. Geochronological techniques and approaches

We utilized optically stimulated luminescence (OSL),U-series, and TCN methods to date surficial deposits

and landforms. OSL was primarily used to date youngerdeposits due to the saturation of the luminescence signalin older sediments. However, in a couple of instances wedated the same deposit with more than one technique todetermine if there were discrepancies between geochron-ometers. The OSL and U-series ages represent the timeof deposition, whereas TCN ages represent minimumestimates for terrace surface formation after sedimentdeposition. Although we bracket the timing of deposi-tion for individual deposits using the ages we obtained,in almost all cases the actual time of deposition startedprior to and ended after the constraining OSL and U-series ages. Detailed information regarding the methodsemployed and analytical errors for each technique canbe found in the accompanying data repository.

OSL samples were collected in light-safe sample tubesfrom sand lenses within the predominantly coarse-grained tributary and mainstem deposits. The OSLtechnique determines the time elapsed since sedimentwas last exposed to sunlight during transport. Allsamples analyzed contained some evidence for partialbleaching, or incomplete solar re-setting of the lumines-cence signal, which may produce age overestimates. Inorder to minimize this affect, a relatively small numberof sand grains were measured in each aliquot, allowingoutliers containing partially bleached grains to be easilydetected and removed. Our sampling strategy was toanalyze sand samples from different depths within thickalluvial deposits to determine the timing and duration ofits deposition/aggradation. Samples were analyzed usingthe quartz single-aliquot regenerative-dose method(Murray and Wintle, 2000) at the LuminescenceGeochronology Laboratory at the University of Ne-braska-Lincoln.

Samples of dense, sparry travertine that drape andinterfinger with Colorado River alluvium were dated byuranium-series at the Berkeley Geochronology Center.In some areas of eastern Grand Canyon, travertine wasdeposited contemporaneously with the river gravelbased on intercalated stratigraphy and presence offlowstone. By determining the age of this primarytravertine, we were able to determine the age of therelated Colorado River alluvium. Our sampling strategyfor this technique was to analyze samples from differentdepths within a deposit to determine the timing andduration of its emplacement. Travertine was slabbedand polished to reveal delicate internal textures, and100–200mg samples were removed by drilling. U and Thwere separated using ion exchange techniques and thenanalyzed by thermal ionization mass spectrometry(TIMS). Ages for two sub-samples were determinedfor travertine from several localities. In each case, sub-sample ages were in good agreement, consistent withclosed evolution of the U-series system.

Surface and subsurface samples were dated fromtributary and mainstem deposits for measurement of

ARTICLE IN PRESSM.D. Anders et al. / Quaternary Science Reviews 24 (2005) 2428–24482432

terrestrial cosmogenic nuclide (TCN) 10Be exposureages. Desert pavements composed of clasts suitable forTCN dating have formed to varying degrees on depositsin tributary drainages and along the Colorado River. Incontrast to OSL and U-series, our TCN analysesprovide minimum estimates for the timing of terracesurface abandonment and the initiation of stream/riverincision. AMS measurements of 10Be/9Be were com-pleted at Lawrence Livermore National Laboratory,and sample collection, preparation, and data interpreta-tion methods are summarized in Gosse and Phillips(2001). All samples were composed of pebble amalga-mates (e.g. Anderson et al., 1996). Samples providingchronology were collected from flat stable terracesurfaces away from slopes or gullies with good-to-excellent pavements of tightly interconnected and highlyvarnished pebbles underlain by Av horizons. Goodnatural exposures afforded collection of deep (essen-tially 100% shielded) samples to adjust the measuredconcentrations for inheritance in each fill unit. The ageshave also been adjusted for partial shielding of incidentsecondary cosmic rays by the canyon walls. Despite this,we feel our TCN ages are the least accurate and precisein comparison with our other two chronometers,especially due to potentially variable amounts ofinheritance within the strata of individual deposits.

4. Results

We present our results here according to landscapeposition from hillslopes to tributaries to the mainstemriver, describing the deposits first from younger to older,then relying upon photographs and illustrations toclarify key stratigraphic relations. Deposit ages aresupplied for those deposits that we have successfullydated (Table 1, Fig. 2). For the surficial mapping andmore detailed data regarding sedimentology, stratigra-phy, and soil development see Anders (2003).

4.1. Hillslope deposits

Though recent or active colluvium such as landslidedeposits, talus, and slopewash can be found in easternGrand Canyon, hillslopes are dominated by a combina-tion of bare bedrock and distinct remnant deposits thatare dissected and beheaded from modern escarpments(Fig. 3, for example). The texture and composition ofthis remnant colluvium is highly variable, but itgenerally is poorly to moderately sorted with pebble toboulder-sized clasts, and has medium-to-massive, lenti-cular bedding roughly parallel to the underlying bedrockslope. In upper hillslope areas, deposits are clast-supported with a partly to completely filled frameworkand are similar to modern rock fall and avalanchedeposits in the area. Medial hillslope deposits are

predominantly matrix-supported pebble to bouldergravel, but a minor amount of locally imbricated,clast-supported, pebble-to-cobble gravel is present.Lower hillslope deposits are a mixture of matrix-supported and clast-supported, roughly imbricated,pebble-to-boulder gravel. The matrix-supported faciesin medial and distal hillslope areas is interpreted to bedebris flow deposits, and likewise they match thecharacteristics of nearby recent deposits resulting fromthese processes. The clast-supported facies in medial anddistal hillslope areas is interpreted to be the result ofoverland flow reworking the matrix-supported deposits.This progression of remnant colluvial deposits locallycontinues to grade down-catchment to tributary streamdeposits.

4.2. Tributary stream deposits

Four well preserved fill-terrace deposits and an older,grouped set of poorly preserved gravels have beenrecognized and studied in cross-sectional exposuresalong the tributary drainages of eastern Grand Canyon(Fig. 4). Deposits are up to 40m thick and have basalunconformities that can be irregular or planar (Fig. 5).Each deposit represents an episode of stream aggrada-tion that buried canyon-bottom topography, followedby incision that can be associated with one or more fill-cut degradational terraces. Deposits are composed oftwo distinct, interbedded facies: sandy matrix-supportedgravel, and clast-supported, locally imbricated gravel.Both facies consist of unconsolidated to carbonate-cemented, poorly to moderately sorted, sub-angular tosub-rounded gravel containing pebble to boulder-sizedclasts. Beds are medium to thick and broadly lenticular.We interpret the matrix-supported facies to be debrisflows that moved sediment from headwater hillslopes tovalley bottoms. The interbedded clast-supported faciesbecomes more prevalent down-catchment and is inter-preted to be streamflow deposits, which commonlyappear reworked from debris flow deposits. Bar-and-swale topography is present on S1 and weakly formeddesert pavements are present on S2, S3, and S4, butgeomorphic surfaces are rarely preserved on S5.

S1 is composed of a series of inset deposits. Up to 5mof S1 gravel is exposed, and its base is near or belowpresent tributary streambeds. There is little or no soildevelopment on this deposit (Anders, 2003). Chronolo-gic data indicate that the main body of this deposit wasemplaced during an aggradation episode that began priorto 572 ka and continued until after 471 ka (Table 1,Figs. 2 and 4). However, notable inset deposits havebeen emplaced as recently as 100 years ago based onradiocarbon ages (Pederson, unpublished data), or inhistoric time by debris flows (e.g. Griffiths et al., 1996).

S2 occupies a larger area than the S1 deposit. It isinset into the S3 deposit, but locally overlies erosional

ARTICLE IN PRESS

Table 1

Age control for eastern Grand Canyon Quaternary stratigraphya

Age (ka)b Depositc Locationd Method Description

3.971.0 S1 Unkar OSL 1m below top of deposit locally

4.971.6 S1 Tanner OSL 2m below top of deposit locally

3.670.5 S1 Lava Chuar OSL 4m below top of deposit locally

7.071.5 S2 Lava Chuar OSL 4m below top of deposit locally, see Fig. 5

9.573.1 S2 Nankoweap OSL 4.5m below top of deposit locally

1273 S2 Lava Chuar OSL 9m below top of deposit locally, see Fig. 5

3076 S3 Nankoweap TCNe Prominent fill-cut terrace near top of deposit

3475 S3 Lava Chuar OSL 7m below top of deposit locally, see Fig. 5

3679 S3 Unkar OSL 7m below top of deposit locally

48710 S3 Lava Chuar TCNe Desert pavement, disregard age or instead may be abutting S4

fill-cut terrace

5078 S3 Nankoweap OSL Just above bedrock strath

54712 S3 Lava Chuar TCNe 0.7m depth, disregard age or instead may be abutting S4 fill-cut

terrace

55712 M3 RM 69.5L TCNe Inset fill-cut terrace, see Fig. 7

64710 M3 RM 67L OSL 3m below top of mainstem deposit overlain by tributary deposit,

see Fig. 10

67711 M3 RM 72L OSL 2m below top of deposit locally

68712 M3 RM 67L OSL 5m below top of mainstem deposit overlain by tributary deposit,

see Fig. 10

6979 M3 RM 69.5L OSL 19m below top of deposit locally, see Fig. 7

71711 M3 RM 69.5L OSL 27.5m below top of deposit locally, see Fig. 7

92719 S4 Lava Chuar TCNe Lower fill-cut terrace in S4

109723 S4 Lava Chuar TCNe Highest S4 tread

11972f M4 RM 56L U-series Travertine within upper M4 deposit, see Fig. 8

12572 M4 RM 57L U-series Within M4, above local bedrock step in strath

15372f M4 RM 56L U-series Travertine on bedrock underlying colluvium that is overlain by

M4, pre-M4 erosion, see Fig. 8

157733 M5/M4g RM 73R TCNe 0.8m depth, mapped as M4 fill-cut terrace

161734 M5/M4g RM 73R TCNe Desert pavement, mapped as M4 fill-cut terrace

283714 M5/M4g RM 57L U-series Travertine in gravel just above bedrock surface intermediate

between M5 and M4

14071 M5 RM 57L U-series Secondary void infill, post-M5

326713 M5 RM 61L U-series Travertine within deposit, �30m above strath

385714f M5 RM 57L U-series Travertine in gravel just above bedrock strath

aComplete chronologic data from eastern Grand Canyon and discussion of errors are available in data repository, see the online version of this

article.b2s errors given, which include: (a) for OSL, combined random errors (e.g. in dose-rate measurement and calculation and equivalent dose standard

deviation) and systematic errors (including calibration of the OSL reader and Sr90 irradiation source); (b) for U-series, analytical uncertainties (95%

confidence level) and uncertainties related to minor corrections for detrital U and Th; and (c) for TCN, AMS measurement precisions and other

random errors added in quadrature according to Gosse and Phillips (2001), including an estimated 20% 2s systematic error primarily due to

uncertainties in production rate scaling and bulk density. The TCN uncertainty does not include geological error due to erosion, burial, mixing, or

inheritance.c‘‘S’’ is for side or tributary deposits, ‘‘M’’ is for mainstem Colorado River deposits.dTributary drainages identified by name (Fig. 1). Mainstem given as river miles (RM) downstream from Lees Ferry. L and R are left and right

riverbank, respectively, when facing downstream.eTerrestrial cosmogenic-nuclide date of surface sample corrected for inheritance with shielded sample, interpreted as minimum age for terrace

abandonment.fAge different than reported in Pederson et al. (2002) due to subsequent analysis of duplicates or superior samples.gSample may be from obscured deposit stratigraphically between M5 and M4.

M.D. Anders et al. / Quaternary Science Reviews 24 (2005) 2428–2448 2433

remnants of the cemented base of S3. Roughly 15m ofthe S2 deposit is exposed on average, and its base is nearor below tributary streambeds. A calcic horizon withstage I+/II� carbonate morphology and a weak argillichorizon are characteristic of soil development on thisdeposit. S2 was deposited during an aggradation episodethat began prior to 1273 ka and continued until after772 ka according to OSL dates.

S3 is the most conspicuous surficial deposit intributary drainages and it generally occupies the largestportion of valley bottoms. It can be �40m thick and itsbase ranges from the level of streambeds to 30m abovethem. This variability in the height of the basalunconformity represents buried valley topography andlocal differences in preservation. A calcic horizon withstage II/III� carbonate morphology, an argillic horizon,

ARTICLE IN PRESS

400350300250200150100500

Age (ka)

GC-09-11-10

GC-09-13-11GC-09-04-20

GC-09-11-6

GC-09-09-2GC-09-11-7

NAN-103

GC-09-03-16GC-09-05-24

LC-111

GC-09-09-1

GC-2000-011

BAS-119GC-09-04-19GC-09-04-23GC-09-04-18GC-09-04-21GC-09-04-22

GC-2000-013GC-2000-015

GC-5/01-56.3L-A2GC-5/01-56.3L-B1

GC-S'01-56L-A-2

UNK-124UNK-123

GC-5/01-57LBGC-9/00-61LK02-57-2

Sam

ple

Num

ber

TributaryDrainages

Colorado River

OSL AgeU-series AgeTCN AgeDepositional

Episode

S1

S2

S3

M3

S4

M4

M5

Fig. 2. Age control summary. Ages reported with 2s errors (see Table 1) and questionable TCN ages are gray. Samples in each deposit are arranged

according to depth, and inferred timing of deposition is represented by gray boxes, though their height only reflects the number of samples analyzed.


and polygentic development are characteristic of soils onthis deposit. S3 was deposited during an aggradationepisode that began just prior to 5078 ka and endedsometime after 3475 ka according to OSL dating. ATCN age of 3076 ka from a S3 terrace tread in theNankoweap catchment lies above the outcrop thatprovided the 50 ka basal date. However, TCN ages of48710 and 54712 ka from the S3 terrace in the LavaChuar catchment are in disagreement with an OSLdepositional age of 3475 ka in that underlying deposit.The OSL age is unlikely to be too young, considering itsconsistence with other OSL data and the lack ofevidence for partial bleaching of this sample. Despitecorrecting all TCN ages with local shielded samples, it islikely that we do not adequately understand TCNinheritance in this particular deposit.

S4 averages �25m in thickness and the base is30–70m above streambeds. A calcic horizon with stageIII/IV carbonate morphology and an argillic horizon arecharacteristic of soil development on this deposit. S4was deposited during an aggradation episode thatoccurred prior to �109723 ka, based on a tentativeTCN age from its highest (oldest) tread and supportedby a tentative TCN age of 92719 from a fill-cut terraceon this deposit.

S5 is composed of poorly preserved or obscuredgravel deposits that are stratigraphically older than S4

and up to 200m above streambeds. Age control is notavailable for the S5 deposit.

4.3. Colorado River deposits

At least six mainstem deposits have been identifiedalong the Colorado River corridor (Fig. 6). DepositsM7–M3 are composed primarily of clast-supported,poorly to moderately sorted, subangular to wellrounded, imbricated, pebble-to-cobble gravel. Depositsare characterized by thin to medium scale, planar-tabular and trough cross-bedding and tabular tolenticular bedding geometries. Cross-bedded or ripplecross-stratified silt and sand are a subordinate facies inthese deposits. The basal sections of deposits M5, M4,and M3 are cemented in some areas by non-pedogeniccalcium carbonate. Most clasts are derived from rockunits exposed in Grand Canyon, but a few percent arecomposed of far-travelled lithologies such as volcanicporphyry and quartzite from upstream in the ColoradoRiver catchment (Anders, 2003). The predominance ofcoarse bedload sediment relative to fine-grained faciespreserved in these deposits suggests that the channelform of the Colorado River during the M7–M3aggradation episodes may have been different than thepresent-day pools and sandbars between rapids.

ARTICLE IN PRESS

M3

S3

S2

Colluvium

RemnantColluvialMantle

TributaryStream

25 m

Fig. 3. An example of a colluvial mantle blanketing a hillslope, extending into a drainage, and grading laterally into a S3 tributary stream deposit.

Stratigraphic evidence indicates these colluvial mantles are generally continuous with stream deposits rather than forming later due to locally raised

baselevel. Long-profile schematic depicts spatial relation of photograph to stratigraphy of overall catchments.


M3 is the most conspicuous mainstem deposit ineastern Grand Canyon. It is at least 38m thick and thebase is below river level. Emplacement of this depositbegan prior 71711 ka, based on an OSL age for asample collected near its base, and ended prior to55712 ka, based on a TCN age for the tread of a fill-cutterrace (Fig. 7).

The M4 deposit is relatively poorly preserved orobscured by colluvium, but it is up to 52m thick and thebase is near river level. It was deposited during anaggradation episode that began after 15372 ka based ona U-series date from travertine stratigraphically belowthe deposit and continued until after 11972 ka accord-ing to a U-series age from the upper deposit (Fig. 8). We

also obtained TCN ages of 161734 and 157733 kafrom the surface of a deposit presently mapped as M4.This discrepancy between the TCN and deposit agesmay be, again, related to variability in TCN inheritance.However, there is some ambiguous stratigraphic evi-dence for an intermediate deposit between what wecurrently have mapped as M4 and M5, raising thepossibility that what we dated with TCN may actuallybe a terrace of this intermediate deposit.

The M5 deposit is also poorly preserved or obscuredby colluvium. The base of the deposit is presently found28m above river level and the top is estimated to be 66mabove river level. The onset of this aggradation episodebegan after 385714 ka based on a U-series date from

ARTICLE IN PRESS

Fig. 4. Generalized stratigraphy of tributary drainages. Colluvium is solid gray; ‘‘S’’ ¼ side/tributary stream deposit. A stratigraphic connection

exists between colluvial mantles and S3 and S4 deposits, but not between colluvial mantles and S2 or S1 deposits. The range of ages with 2s errors is

given for each dated deposit and surface.


immediately above the basal unconformity. The conclu-sion of aggradation is constrained by U-series ages of326713 ka for the upper portion of the deposit and283714 ka from travertine that post-dates M5 (Peder-son et al., 2002).

Two undated deposits older than M5 are only partlypreserved in the study area. The present base of M6 is�117m above river level and approximately 18m of thedeposit is preserved. The M7 remnant is 8m thick andits base is presently �175m above river level.

There is no mappable Colorado River deposit in thestudy area stratigraphically between M3 (71–55 ka) andM1 (middle to late-Holocene). However, the ubiquity ofterraces associated with the most recent glacial max-imum (15–25 ka) elsewhere in the interior-western USsuggests that a deposit of this age should exist in easternGrand Canyon (e.g. Ritter et al., 1993; Phillips et al.,1996, 1997; Repka et al., 1997; Chadwick et al., 1997).We hypothesize that such a deposit may be preservedunder the present-day channel of the Colorado River(Fig. 6). Though the Colorado is a mixed bedrock-alluvial river, an underwater filming project indicatedthat the bed of the river is mostly alluvium rather thanbedrock (R. Anima, pers. comm., 2001) and dam-siteexploration drilling records indicate 15–30m of sedi-ment below the channel in a few locations (US Bureauof Reclamation, unpublished data).

4.4. Correlations with previous work in eastern Grand

Canyon

The stratigraphy presented here for tributary catch-ments differs somewhat from that produced by Luc-chitta and others (1995). This may be related to the factthat these previous workers mapped only the compli-cated transition zone at the mouth of tributaries alongthe mainstem corridor, whereas we studied and mapped

entire tributary drainages. Our S4 deposit is their ld7,and our S3 deposit, which has multiple terracesdeveloped on it, probably correlates to Lucchitta andothers (1995) ld6, lpc, ld5, and ld4 terraces (Table 2).There is an age discrepancy between our S3 unit andtheir ld6/lpc/ld5/ld4 surface ages, but the Lucchitta et al.(1995) study was conducted before TCN dates werecommonly corrected for inheritance.

Concerning just the mainstem Colorado River strati-graphy, our results are similar to those reported byMachette and Rosholt (1991) and Lucchitta and others(1995). Our contribution to the mainstem stratigraphy isimproved age control and investigating the stratigraphicrelations between mainstem and tributary deposits(Table 3). Measured heights of mainstem deposits arequite comparable, and we also concur with Machetteand Rosholt’s suggestion that an obscured depositbetween M5 and M4 might exist. Although uranium-trend dating is not widely applied, the ages reported byMachette and Rosholt (1991) are consistent with theages we obtained using TCN and U-series. Ourdepositional age for M4 is expectedly older than theuncorrected TCN surface age of 101 ka reported for unitmp4 by Lucchitta et al. (1995). They reported the sameage for ld7 and mp4, and it therefore may be the age of atributary S4 surface.

4.5. Relations among deposits

We focus here on well-preserved relations among theyounger (o80 ka) hillslope, tributary drainage, andmainstem deposits and terraces in eastern GrandCanyon. Starting with the upper reaches of tributarycatchments, there are two distinct relations betweenhillslope and adjacent tributary stream deposits. In thecase of the S3 terraces, relict colluvial mantles thatblanket hillslopes extend continuously down slope and

ARTICLE IN PRESS

M3

S3

S2

Colluvium

strath

S3

S210 m

S3fill-cut terrace

S2terrace

OSL = 12±3 kaOSL = 7±2 ka

OSL = 34±5 ka

Fig. 5. Example of fill deposits in Lava Chuar tributary drainage. Note the inset relation between S2 and S3. OSL samples were collected at depth in

each deposit and constrain the time of deposition.


grade into thick, poorly sorted alluvium of the S3deposit (Fig. 3). In contrast, S2 and S1 deposits, whentraced to the toes of hillslopes, lie at the base oferosional scarps cut into the S3 deposit rather then beingrelated to their own hillslope-sedimentation event(Fig. 9). Several OSL samples from S2 and S1 depositsin eastern Grand Canyon are partially bleached,indicating they underwent relatively short, abrupttransport (e.g. Godfrey-Smith et al., 1988), consistentwith a sediment source from older, nearby deposits.

Stratigraphic evidence indicates that the bulk of theS3 deposits are younger than the Colorado River M3.An example of the S3–M3 relation is exposed at the

mouth of Comanche Creek (Fig. 10). Sediment from thetributary drainage is interbedded at the meter scale withM3 at the very base of the outcrop, but mostly itprogrades over M3 in the upper section. We have notidentified a sharp unconformity or a paleosol along thiscontact, but it is abrupt and mainstem and tributarycomponents are distinct compositionally and texturally.We interpret the tributary sediment in the lower sectionof this outcrop to represent deposition in just the lowestreach of this steep drainage as the Colorado Riveraggraded (Fig. 10). This is consistent with researchrecognizing the limited upstream affects of a rise inbaselevel (e.g. Leopold and Bull, 1979; Merritts et al.,

ARTICLE IN PRESS

Fig. 6. Generalized stratigraphy of the Colorado River corridor in eastern Grand Canyon. Tributary colluvium and alluvium is solid gray;

‘‘M’’ ¼ mainstem Colorado River deposit. Reference stage of Colorado River is a discharge of 283m3/s (10,000 cfs). The range of ages with 2s errors

is given for each dated deposit and surface.

M3

S3

S2

Colluvium

PCG

CBS

OSL = 71±11 ka OSL = 69±9 ka

15 m

M3(fill-cut terrace)TCN = 55±12 ka

Fig. 7. The M3 Colorado River deposit near Basalt Creek. CBS ¼ cross-bedded silty sand, PCG ¼ pebble to cobble gravel. OSL samples collected at

depth in this deposit constrain the timing of its deposition, whereas the inheritance-corrected TCN date from a fill-cut terrace relates to the timing of

subsequent incision by the river.


1994). Alternatively, a similar stratigraphic effect couldbe produced by the tributary maintaining its transportgrade as the mainstem channel shifted laterally away

from it, and there is local evidence for this preservedelsewhere in the eastern Grand Canyon stratigraphy.However, this mechanism is inconsistent with the

ARTICLE IN PRESS

Fig. 8. Travertine-cemented M4 gravel near mouth of Kwagunt Creek. The age of this deposit was constrained through U-series dating of travertine,

with the 153 ka sample collected from travertine formed on the hillslope prior to emplacement of the M4 deposit and the 119 ka sample from

travertine 25m from the base of the deposit.

Table 2

Comparison of eastern Grand Canyon tributary data with previous workersa

Lucchitta et al. (1995) This research

Terrace Max. htb (m) Surface agec (ka) Deposit Max. htb (m) Deposit aged (ka) Surface aged (ka)

ld8 56 — S5 70–242 — —

ld7 44 101732 S4 40–111 — 109 & 92

ld6 28 8278 S3 24–62 50–34 30

Lpc 17726 82717

ld5 17 —

ld4 10 89

ld3 5 — S2 9–27 12–7 —

ld2 2 — S1 6–10 5–4 —

aSee Anders (2003) for a more detailed comparison.bMaximum height above the present tributary streambed, probably minimum heights for the deposit due to exhumation. Range in heights

represents variability between drainages and along the profile of each drainage.cAges obtained through cosmogenic-nuclide dating (26Al and 10Be), apparently not corrected for inheritance.dSee Table 1 for errors.


continuous thickness of S3 up catchments and OSL agesfrom the S3 that are significantly younger than OSLages from M3, even when 2s errors are taken intoaccount (Fig. 2).

Distinct absolute ages confirm the somewhat discon-nected S3-M3 stratigraphy, but indicate they are bothbroadly timed within the middle Wisconsin glaciation(MIS 4-3). OSL analyses from M3 outcrops indicatedeposition was occurring 71711–64710 ka, and thatincision of the M3 deposit had begun by 55712 ka,based on a TCN age obtained from a fill-cut terracetread (Fig. 7). This mainstem incision apparently hadalready started before the bulk of deposition along thetrunks of tributary drainages began by 5078. One OSLsample and one TCN sample from a fill-cut terrace on

the S3 deposit suggest incision in tributary drainageswas not underway until between 3475 and 3076 ka.

Fig. 11 is a summary of key stratigraphic relationsamong deposits formed in the last �80 kyr. S3 depositsare continuous with thick colluvial mantles on hill-slopes, and both of these deposits primarily overlie andpostdate the Colorado River M3 deposit. At thislocation, the M3 deposit does not contain any of thedistinctive basalt clasts that comprise the overlyingcolluvial–alluvial mantle. Younger S2 deposits are insetinto and emerge from S3 and are composed of sedimentthat was derived from dissection of S3 deposits andcolluvial mantles, rather than being graded to sedimentsources on hillslopes. S2 has no apparent mainstemequivalent, at least that is exposed.

ARTICLE IN PRESS

Table 3

Comparison of mainstem Colorado River data with previous workersa

Machette and Rosholt (1991) Lucchitta et al. (1995) This research

Terrace Max. htb (m) Surface agec

(ka)

Terrace Max. htb (m) Surface age

(ka)

Deposit Max ht.b (m) Deposit aged

(ka)

Surface aged

(ka)

— — — — — — M7 183 — —

7 135 4700 — — — M6 133 — —

6 90 — mp5 466 — M5 94 385–326 —

?6 — — — — — ?e — — 161–157?

5 50 150730 mp4 448 101732f M4 52 153–119 161–157?

4 36 75715 mp3 36 — M3 38 71–64 —

3 25 40724 mp2 29 — M3 (fill-cut

terrace)

24 — 55

60760

2 7 ma 9 3.670.06 M1 8 — —

1 3 mo 2.5 late Holo. — — — —

aSee Anders (2003) for a more detailed comparison.bMaximum height above the present tributary streambed, probably minimum heights for the deposit due to exhumation. Range in heights

represents variability between drainages and along the profile of each drainage.cAges obtained through uranium-trend dating, as distinct from U-series dating.dSee Table 1 for errors.eThere is uncertain evidence (mentioned by Machette and Rosholt (1991) as well) for one or more deposits stratigraphically between M4 and M5,

probably dating from 280 to 160ka.fMp4 age obtained through cosmogenic-nuclide dating (26Al and 10Be), apparently not corrected for inheritance. Holocene ages from 14C dating.

Fig. 9. Example stratigraphic relations at the head of the Comanche

tributary drainage. The S2 deposit can be traced to the toe of the

hillslope and originates from the eroded remnants of the S3 colluvial

mantle.


5. Discussion

We are confident that climate changes are the maincontrol on the formation of surficial deposits in easternGrand Canyon rather than tectonic or baselevelchanges. Evidence for this includes: (1) cyclic aggrada-tion and incision as well as contemporaneous responsesin different catchments, the common signatures ofclimate controls; (2) a setting where the nearest activefaulting is 130 km to the west; (3) thick colluvial andalluvial packages that can be readily explained by

changes in hillslope sediment production and hydro-logy but, at this scale, not by baselevel changes; and(4) a chronology of aggradation/incision cycles atMilankovich timescales that have consistent relationsto documented global and regional changes in climate.With respect to another proposed origin, these depositsare certainly not coarse-grained deltas progradinginto lakes created by the lava-dams Hamblin (1994)proposed in western Grand Canyon. They are signifi-cantly younger and do not match the timing of mostof the lava flows of western Grand Canyon (Pedersonet al., 2002; McIntosh et al., 2002), and they do nothave the distinct sedimentology of Gilbert-style fandeltas.

5.1. Responses of the Colorado River to climate change

Comparison with global and regional records such asSPECMAP and Devil’s Hole indicates deposition of theM5, M4, and M3 gravels in eastern Grand Canyonapparently began during glacial episodes and continuedwell into subsequent interglacials before the onset ofincision (Fig. 12). Considering the stratigraphic–chro-nologic disconnection between M3 and the local changesrecorded by S3, one might anticipate that late Pleisto-cene aggradation and incision of the Colorado River ineastern Grand Canyon are linked to changing condi-tions in upstream regions of the greater drainage basin.Fluvial-glacial records from these upstream areasprovide a means to investigate potential forcing fromthe upper drainage basin.

ARTICLE IN PRESS

M3

S3

S2

Colluvium

OSL = 64±10 ka

4 m

M3

S3

OSL = 68±12 ka

Colorado River~ 200 m

Comanche CreekTributary Catchment

covered

Fig. 10. Outcrop at the mouth of Comanche Creek, with wash running at the base of the outcrop from right to left. Mainstem sediment of the upper

M3 deposit interfingers with tributary sediment in the lower 5.5m of this outcrop as the tributary locally maintained grade during Colorado River

aggradation. The overlying bulk of the tributary deposit (�13.5m preserved here, note foreshortening in photograph) physically correlates with

catchment-filling S3 deposits preserved further up the Comanche Creek drainage.


Repka et al. (1997) used TCN to date the treads of fillterraces in southern Utah along the Fremont River, atributary of the Colorado River. They determined thatgravels were deposited prior to 6079 (FR2), 102716(FR3), and 151724 (FR4) ka. Ages from a poorlypreserved younger terrace (FR1) were not reported dueto inconsistencies in the results. Though just over theContinental Divide from being in the Colorado Riverdrainage, the Wind River record from Wyoming isrelatively well constrained and thus important to reviewhere. U-series and TCN dating of strath terracesproduced minimum ages for terrace formation of16–23 ka (WR 1), 5578.6 ka (WR 2), 125737–118 13 ka(TCN ages from WR 3) or 15078.3 ka (interpolated

age for WR 3 from U-series on pedogenic carbonate),and 16776.4 ka (WR 4) (Gosse, 1994; Chadwick et al.,1997; Phillips et al., 1997; Hancock et al., 1999; Sharpet al., 2003).

These results from the Fremont River and WindRiver indicate their respective deposits are broadlycorrelative with those of the Colorado River in easternGrand Canyon. M3 (71–55 ka) in eastern GrandCanyon appears to be contemporaneous with WR 2along the Wind River and FR 2 along the FremontRiver. M4 in our study is approximately contempora-neous with WR 3. An eastern Grand Canyon equivalentto the WR 4 and FR 4 (minimum ages of 151–167 ka)has not been clearly identified, but may be the potential

ARTICLE IN PRESS

50 ka34 ka

30 ka12 ka

7 ka

71 ka

69 ka

55 ka 68 ka

64 ka

M3

S3

S2

Colluvium

ColluvialRemnants

& S3

25 mM3

Fig. 11. Summary of key stratigraphic relations over the last �80 kyr. Top is a photo along Colorado River corridor west of Tanner Creek and

bottom is a schematic summary of key stratigraphic relations among deposits and dates from multiple catchments. S3 deposits are linked to thick

colluvial mantles on hillslopes, and these overly and postdate the Colorado River M3 deposit. Younger S2 deposits are inset into and composed of

sediment from dissected S3 deposits, but have no mainstem equivalent.


intermediate deposit between M5 and M4 with TCNages of �160 ka. Conversely, M5 (385–326 ka) in easternGrand Canyon has no dated equivalent in the region,but older, undated deposits exist elsewhere, for exampleWR 5 and WR 6 along the Wind River.

Hancock and Anderson’s (2002) modeling associatedwith the Wind River record suggests deposits in thelower reaches of a large river system should not becoeval with deposits in the headwater areas, insteadreflecting transient deposition as the bedload sedimen-tary signal moves downstream from glaciated areas.Further investigation is required, particularly withrespect to age control, but thus far there is no evidencefor such a delay at the scale of the Colorado River

drainage. Instead, it appears that aggradation is con-temporaneous at the few places in the basin where dataexist. This leads to the possibility that, like the moderncondition, the Colorado River’s hydrology has beenstrongly linked to its upper drainage basin over theQuaternary, but not its sediment load.

5.2. Responses of local catchments to climate change

Both incision and aggradation appear nearly anti-phased between the Colorado River and local catch-ments in the late Pleistocene (Fig. 12). Focusing on thebest-dated tributary gravel, S3 was deposited from 50 to34 ka after the peak of the middle Wisconsin glaciation

ARTICLE IN PRESS

Marine Isotope Stage1 2 3 4 5 6 7 8 9 10 11

(A) EGC - Hillslopes/Colluvium

(B) EGC - Tributary Streams

(C) EGC - Colorado River

S3

S2S1

M4M3M2M1

M5

S4

Z

Z

Z

(E) Owens Lake

δ18Ο

%C

aCo

3

20

0

δ18Ο

Incr

eas.

Pre

cip.

(D) Devils Hole20

-2 Dec

reas

.Lo

cal

Tem

p.

(F) SPECMAP1

0

-1

Incr

eas.

Glo

bal I

ceV

olum

e

100 200 3000

Years (ka)

400

Fig. 12. Schematic of hillslope and stream sedimentary activity in eastern Grand Canyon (EGC). (A) Colluvium on local hillslopes; (B) tributary

streams; (C) Colorado River; (D) Devil’s Hole record (modified from Winograd et al., 1992); (E) Owens Lake record (modified from Smith et al.,

1997); (F) SPECMAP record (modified from Martinson et al., 1987 and Imbrie et al., 1984). The shaded bars represent glacial periods. ‘‘Z’’ on the

right axis represents relative elevation.


(Fig. 12). Paleoclimate reconstructions suggest that theGrand Canyon area was becoming cooler and wetter atthis time, vegetation density was increasing, and thesummer monsoonal thunderstorms important in theHolocene were less intense (Thompson et al., 1993;Coats, 1997). Unlike in landscapes with soil-mantledhillslopes, this massive infilling of valley bottoms andlower hillslopes evident in eastern Grand Canyon isdifficult to explain through only changes in hydrology(e.g. Reneau et al., 1990; Ritter and Gardner, 1993), thatis, without increased hillslope sediment production. Ifhillslope sediment production did, somehow, stayconstant throughout glacial–interglacial changes in thissetting, the decrease in Hortonian overland flow during

glacial maxima due to increased infiltration capacity andlower precipitation intensity could potentially induce thestorage of colluvium on hillslopes. However, it seemsunlikely that these catchments would both store sedi-ment at toeslopes and simultaneously transport enoughdownstream to cause the tributary aggradation weobserve, unless there was, in fact, an increase in hillslopesediment production. In any case, strong climate-induced changes in hillslope weathering and sedimentproduction have been documented at this timescaleelsewhere in the southwestern US (e.g. Whitney andHarrington, 1993; Pederson et al., 2000, 2001), and thesame should be expected in the Grand Canyon area withthe changes evidenced by paleoclimate reconstructions.


We hypothesize that the apparent lag time between M3and S3 could be associated with these changes in rates ofhillslope sediment production. Increased weatheringmay initially serve mostly to mantle the bare slopes,with sediment transport and storage then transferringdown the catchment. This may explain the delaybetween the onset of the MIS 4 glacial–pluvial climateand stream aggradation along the trunks of tributaries.Alternatively, local climate changes that do not matchthe timing of global records may have influencedsedimentation in Grand Canyon catchments. Forexample, the Owen’s Lake record appears to record astrong shift from dryer to wetter climate west of GrandCanyon at 60–50 ka (Smith et al., 1997; Fig. 12). Moreage control for the tributary record is needed to test forsuch time-transgressive sedimentation and confirm theextent of the time lag.

In terms of the timing of incision of local drainages, aTCN date for the S3 tread and an OSL age near thebottom of the S2 fill indicates incision occurred between�30 and 12 ka. This is surprising because this last glacialepoch is when aggradation is typically documentedelsewhere. The post-M3 incision of the mainstemColorado River apparently started well before this timeaccording to our 55 ka TCN age on a fill-cut terrace.This earlier mainstem incision would have loweredbaselevel for tributary streams, yet tributary aggrada-tion subsequently began and continued in the middlereaches of drainages, and so this baselevel fall appar-ently took several thousand years to effectively transferupslope. We hypothesize that this buffering of thebaselevel signal may have been related to continuedsediment loading of local drainages by hillslopes andpotentially low peak discharges prior to �30 ka. It isintriguing that the tributary incision between �30–12 kacorresponds to a time of intense millennial-scale climateoscillations, both globally and in the American South-west as recorded at Searles Lake and Mono Lake(Phillips et al., 1994; Benson et al., 1998; Lin et al., 1998;Tchakerian and Lancaster, 2002). An hypothesis forfurther investigation is that the high amplitude andfrequency of these millennial-scale climate changescould have caused enough hydrologic disturbance tofinally take advantage of lowered baselevel and driveincision in local catchments.

Turning to the latest-Pleistocene and Holocenerecord, the S2 of tributary catchments has no exposedmainstem Colorado River equivalent. It was beingdeposited 12–7 ka when local paleoclimate proxiesindicate conditions were becoming warmer and drier,vegetation density was declining as some plant speciesmigrated to higher elevations, and the summer monsoonwas becoming more intense (Cole, 1990; Weng andJackson, 1999). Field evidence indicates that during thistime, channel heads dissected upslope through oldercolluvial mantles (Fig. 9), thus mobilizing and redepo-

siting stored sediment in upper catchments. This isconsistent with the results of previous workers in theAmerican Southwest (Bull, 1991; Harvey and Wells,1994, 2003; McDonald et al., 2003), but this event ineastern Grand Canyon was notably subordinate inmagnitude to the sedimentation occurring during S3time, which does not match the results of Bull (1991) orHarvey and Wells (1994), but was noted in northernNevada by Harvey et al. (1999). The incision of S3 anddownstream deposition of S2 may be an example ofcomplex response in the traditional sense of Schumm(1973), wherein a single impetus of incision results in asequence of upstream-migrating, depositional–incisionalevents passing through the system. In this context, therecent S1 deposits represent the continued remobiliza-tion of stored sediment and the complex response ofcatchments during overall incision, perhaps influencedby changes associated with smaller-scale climate fluctua-tions, as interpreted elsewhere on the Colorado Plateau(e.g. Patton and Boison, 1986; Graf, 1987; Ely et al.,1993; Hereford, 2002). Finally, if there is a latest-Pleistocene-to-Holocene deposit beneath the mainstemColorado River’s channel, it would be consistent withcorrelative and ongoing incision and high sediment yieldfrom local catchments.

5.3. Conceptual model for eastern Grand Canyon

There is more to learn about dryland responses toclimate change from the Grand Canyon record withfuture research. But we feel it is worth reviewing ourcurrent results and working hypotheses for the easternGrand Canyon record in light of previous knowledge,including the conceptual model from some of theprevious research in drylands (e.g. Bull and Schick,1979; Gerson, 1982; Bull, 1991; Harvey and Wells, 1994;McDonald et al., 2003), as well as research in wetter,soil-mantled landscapes that provides general insightinto geomorphic responses to climate change (e.g.Montgomery and Dietrich, 1989; Ritter and Gardner,1993; Tucker and Slingerland, 1997; Harvey, 2002). Thetwo key interpretations to address are related to processlinkages at two different scales (Harvey, 2002). Theseare: (1) that the response of the mainstem ColoradoRiver to glacial–interglacial climate change has beensomewhat decoupled from that of local drainages,perhaps responding primarily to hydrologic changes inits headwaters; and (2) that local dryland catchmentshave distinct and delayed deposition-incision responsesto climate change related to sediment supply beingweathering-limited (Fig. 13).

The increased effective moisture and increased vege-tation cover that others have reconstructed in easternGrand Canyon during global glacial conditions wouldenhance chemical and physical weathering of bedrock.This sediment may have been stored on hillslopes

ARTICLE IN PRESS

global glacial conditions (MIS 4-3) high sediment production, lower peak discharges

response = aggradation proceeding downslope after lag time?

channel head

S3earlier

mainstemaggradation,then incision

mainstemaggradation?

MIS 2 to presenthydrologic-biotic disturbance?, high peak discharges?

response = incision and redeposition

channel head

S3

S2

M3

(A)

(B)

Fig. 13. Hypothetical model based on last �80 kyr of the record of landscape responses to climate change in eastern Grand Canyon tributary

catchments. (A) Enhanced bedrock weathering and decreased precipitation causes colluviation at hillslope toes, contraction of drainage networks,

and eventually delayed tributary stream aggradation. (B) Tributary incision appears delayed relative to baselevel fall along the mainstem river,

perhaps by continued sediment loading from hillslopes. Possible increased precipitation intensity and vegetation disturbance may eventually start

upslope extension of drainage networks and dissection and temporary redeposition along channels.


because of some combination of increased soil cohesionassociated with increased vegetation cover and areduction in overland flow and sediment transportcapacity accompanying increased infiltration and de-creased precipitation intensity (Fig. 13A). These changesin hydrology would be expected to cause channel headsto migrate downslope (e.g. Montgomery and Dietrich,1989; Ritter and Gardner, 1993; Tucker and Slinger-land, 1997), and aggradation would likely be associatedwith decreased long-profile concavity (e.g. Dade andFriend, 1998; Sklar and Dietrich, 1998; Knighton,1999). Hypothetically, the delay in timing of streamaggradation in this desert setting may be due to theextended time needed for increased weathering to firstmantle slopes, and then to translate down to highsediment loads in streams.

Incision of tributary drainages should have beeninfluenced by lowered baselevel along the ColoradoRiver starting at �60 ka. But this signal may have beeneffectively delayed in Grand Canyon drainages becauseof continued sediment loading from hillslopes, withincision happening unexpectedly during the millennial-scale climate fluctuations of MIS 2. During thesubsequent glacial–interglacial transition, increased pre-cipitation intensity with the development of summer

monsoons may have further helped in the reworking ofolder deposits (Fig. 13B). As channel heads migratedupslope and colluvium was stripped from hillsides, theresulting increase in stream sediment load may accountfor the temporary sediment storage along the axis ofdrainages represented by S2 and ongoing with smallerS1 deposits.

6. Summary

�
The preserved stratigraphy of tributary catchments ineastern Grand Canyon includes remnant colluvialmantles on hillslopes that are presently being erodedand four major inset tributary stream deposits. Ourdates for these deposits range from 4109723 ka(S4), 5078 to 3076 ka (S3), 1273 to 772 ka (S2),and o572 ka (S1). � The mainstem Colorado River record consists of at
least seven inset Colorado River deposits and our agecontrol for the deposition of these ranges from385714 to 326713 ka (M5), 15372 and 11972 ka(M4), and 71711 to 55712 ka (M3). We suggest thatone or more obscured deposits may exist between M5and M4, and that a younger Pleistocene deposit (M2)


may lie below the modern channel based on evidenceof thick alluvium under the Colorado River locally.
� Stratigraphic relations for the last 80 kyr of the
record are relatively well preserved and dated. S3deposits are stratigraphically continuous with hill-slope deposits and sediment sources, whereas insetlatest Pleistocene and Holocene (S2 and S1) depositsare composed of sediment that was remobilized fromdissected S3 deposits. The bulk of the S3 depositstratigraphically overlies and postdates ColoradoRiver M3 deposits. Unexpectedly, the last majoraggradation in tributary drainages was occurringmainly during MIS 3 when the Colorado River wasapparently incising. Subsequent tributary incisionstarted during MIS 2, and this ongoing high localsediment yield may correlate to Colorado Riveraggradation.
� Results thus far indicate the mainstem Colorado
River and the local tributary catchments of GrandCanyon seem to have independent, or at leastdifferently timed, responses to climate change. Incontrast, local tributary drainages are themselves welllinked to hillslope sediment sources, though char-acterized by significant lag times in responses toclimate change. The key to the responses of thesedesert catchments may be the weathering-limitednature of the hillslope sediment supply, which resultsin relatively extreme cycles of sediment storage andthen remobilization.

Acknowledgments

Funding for this research was provided by NSF EAR-0107065 to Pederson and Karlstrom, NSF EAR-9903126 to Gosse, a Geological Society of AmericaGladys Cole Memorial Award to Pederson, andGeological Society of America student research awardsto Anders. We would like to thank Grand CanyonNational Park for permission to access eastern GrandCanyon for this research. We sincerely thank AdrianHarvey, R. Craig Kochel, Richard Hereford, and ananonymous reviewer for suggested improvements.

Appendixes A. B. and C. Electronic Supplementary

Material

The online version of this article contains additionalsupplementary data. Please visit doi:10.1016/j.quascirev.2005.03.015.

References

Anders, M.D., 2003. Quaternary geology and landscape evolution of

eastern Grand Canyon, Arizona. MS Thesis, Logan, Utah State

University, p. 153.

Anderson, R.S., 1993. A 35,000-year vegetation and climate history

from Potato Lake, Mogollon Rim, Arizona. Quaternary Research

40, 351–359.

Anderson, R.S., Repka, J.L., Dick, G.S., 1996. Explicit treatment of

inheritance in dating depositional surfaces using in situ 10Be and26Al. Geology 24 (1), 47–51.

Benson, L.V., Lund, S.P., Burdett, J.W., Kashgarian, M., Rose, T.P.,

Smoot, J.P., Schwartz, M., 1998. Correlation of late-Pleistocene

lake-level oscillations in Mono Lake, California, with North

Atlantic climate events. Quaternary Research 49, 1–10.

Brozovic, N., Burbank, D., Meigs, A., 1997. Climate limits on

landscape development in the northwestern Himalaya. Science 276,

571–574.

Bull, W.B., 1991. Geomorphic Responses to Climate Change. New

York, Oxford University Press 326pp.

Bull, W.B., Schick, A.P., 1979. Impact of climatic change on an arid

watershed: Nahal Yeal, southern Israel. Quaternary Research 11,

153–171.

Chadwick, O.A., Hall, R.D., Phillips, F.M., 1997. Chronology of

Pleistocene glacial advances in the central Rocky Mountains.

Geological Society of America Bulletin 109, 1443–1452.

Coats, L.L., 1997. Middle to late Wisconsin vegetation change at Little

Nankoweap, Grand Canyon National Park, Arizona. MS Thesis,

Flagstaff, Northern Arizona University, p. 139.

Cole, K.L., 1990. Late Quaternary vegetation gradients through

the Grand Canyon. In: Betancourt, J.L., Van Devender, T.R.,

Martin, P.S. (Eds.), Packrat Middens: The Last 40,000

Years of Biotic Change. University of Arizona Press, Tucson,

pp. 240–258.

Dade, W.B., Friend, P.F., 1998. Grain-size, sediment-transport regime,

and channel slope in alluvial rivers. Journal of Geology 106,

661–675.

Elston, D.P., 1989. Pre-Pleistocene Deposits of aggradation, Lees

Ferry to western Grand Canyon, Arizona. In: Elston, D.P.,

Billingsley, G.H., Young, R.A. (Eds.), Geology of Grand Canyon,

Northern Arizona (with Colorado River Guides), Lees Ferry to

Pierce Ferry Arizona. Washington, DC, American Geophysical

Union, pp. 174–185.

Ely, L.L., Yehouda, E., Baker, V.R., Cayan, D.R., 1993. A 5000-year

record of extreme floods and climate change in the southwestern

United States. Science 262, 410–412.

Gerson, R., 1982. Talus relicts in deserts: a key to major climate

fluctuations. Israel Journal of Earth-Sciences 31, 123–132.

Godfrey-Smith, D.I., Huntley, D.J., Chen, W.H., 1988. Optical dating

studies of quartz and feldspar sediment extracts. Quaternary

Science Reviews 3–4 (7), 373–380.

Gosse, J.C., 1994. Alpine glacial history reconstruction: 1. Application

of the cosmogenic 10Be exposure method to determine the glacial

chronology of the Wind River Mountains, Wyoming, USA; 2.

Relative dating of Quaternary deposits in the Rio Atuel Valley,

Mendoza, Argentina [Ph.D. Dissertation]. Bethlehem, Lehigh

University, p. 175.

Graf, W.L., 1987. Late Holocene sediment storage in canyons of the

Colorado Plateau. Geological Society of America Bulletin 99,

261–271.

Griffiths, P.G., Webb, R.H., Melis, T.S., 1996. Initiation and

frequency of debris flows in Grand Canyon, vol. 35. US Geological

Survey Open-File Report 96-491, Arizona.

Hamblin, W.K., 1994. Late Cenozoic lava dams in the western Grand

Canyon. Geological Society of America Memoir 183, 139.

Hancock, G.S., Anderson, R.S., 2002. Numerical modeling of fluvial

strath-terrace formation in response to oscillating climate. Geolo-

gical Society of America Bulletin 114 (9), 1131–1142.

Hancock, G.S., Anderson, R.S., Chadwick, O.A., Finkel, R.C., 1999.

Dating fluvial terraces with 10Be and 26Al profiles: application to

the Wind River, Wyoming. Geomorphology 27, 41–60.

dx.doi.org/10.1016/j.quascirev.2005.03.015

dx.doi.org/10.1016/j.quascirev.2005.03.015


Harvey, A.M., 2002. Effective timescales of coupling within fluvial

systems. Geomorphology 44, 175–201.

Harvey, A.M., Wells, S.G., 1994. Late Pleistocene and Holocene

changes in hillslope sediment supply to alluvial fan systems: Zzyzx,

California. In: Millington, A.C., Pye, K. (Eds.), Environmental

Change in Drylands: Biogeographical and Geomorphological

Perspectives. New York, Wiley, pp. 67–84.

Harvey, A.M, Wells, S.G., 2003. Late Quaternaryvariation in alluvial

fan sedimentologic and geomorphic processes, Soda Lake Basin,

Eastern Mojave Desert, California. In: Enzel, Y., Wells, S.G.,

Lancaster, N. (Eds.), Paleoenvironments and Paleohydrology of

the Mojave and Southern Great Basin Deserts. Boulder, Colorado,

Geological Society of America Special Paper 368, pp. 207–230.

Harvey, A.M., Wigand, P.E., Wells, S.G., 1999. Response of alluvial

fan systems to the late Pleistocene to Holocene climatic transition:

contrasts between the margins of pluvial Lakes Lahontan and

Mojave, Nevada and California, USA; Catena, vol. 36,

pp. 255–281.

Hereford, R., 1996. Map showing surficial geology and geomorphol-

ogy of the Palisades Creek area, Grand Canyon National Park,

Arizona. US Geological Survey Miscellaneous Investigations

Series, Map I-2449, Scale 1:2000.

Hereford, R., 2002. Valley-fill alleviation during the Little Ice Age (ca.

A.D. 1400–1880), Paria River basin and southern Colorado

Plateau, United States. Geological Society of America Bulletin

114 (12), 1550–1563.

Hereford, R., Thompson, K.S., Burke, K.J., Fairley, H.C., 1996.

Tributary debris fans and late Holocene alluvial chronology of the

Colorado River, eastern Grand Canyon, Arizona. Geological

Society of America Bulletin 108, 3–19.

Howard, A.D., Dolan, R., 1981. Geomorphology of the Colorado

River in Grand Canyon. Journal of Geology 89, 269–298.

Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C.,

Morley, J.J., Pisas, N.G., Prell, W.L., Shackleton, N.J., 1984. The

orbital theory of Pleistocene climate: support from a revised

chronology of the marine d18O record. In: Berger, A.L., et al.

(Eds.), Milankovitch and Climate, Part 1. The Netherlands, Reidel,

pp. 269–305.

Intergovernmental Panel on Climate Change (IPCC), 2001. Contribu-

tion of working group 1 to the third assessment report of the ICPP.

In: Houghton, J.T., et al. (Eds.), Climate Change 2001: The

Scientific Bias. Cambridge University Press, Cambridge, p. 892.

Kieffer, S.W., 1990. Hydraulics and geomorphology of the Colorado

River in Grand Canyon. In: Beus, S.S., Morales, M. (Eds.), Grand

Canyon Geology. New York, Oxford University Press,

pp. 333–383.

Knighton, A.D., 1999. Downstream variation in stream power.

Geomorphology 29, 293–306.

Leopold, L.B., 1969. The rapids and the pools—Grand Canyon. In:

The Colorado River Region and John Wesley Powell. US

Geological Survey Professional Paper 669-D, pp. 131–145.

Leopold, L.B., Bull, W.B., 1979. Base level, aggradation, and grade.

Proceedings of the American Philosophical Society 123 (3),

168–202.

Lin, J.C., Broecker, W.S., Hemming, S.R., Hajdas, I., Anderson, R.F.,

Smith, G.I., Kelley, M., Bonani, G., 1998. A reassessment of U–Th

and 14C ages for late-glacial high-frequency hydrological events at

Searles Lake, California. Quaternary Research 49, 11–23.

Lucchitta, I., Dehler, C.M., Davis, M.E., Basdekas, P.G., Burke, K.J.,

1995. Quaternary geologic map of the Palisades Creek-Comanche

Creek area, eastern Grand Canyon, Arizona. US Geological

Survey Open-File Report 95-832, p. 39.

Machette, M.N., Rosholt, J.N., 1991. Quaternary geology of the

Grand Canyon. In: Morrison, R.B. (Ed.), The Geology of North

America Volume K-2, Quaternary Nonglacial Geology: Contermi-

nous US Geological Society of America, Denver, pp. 397–401.

McDonald, E.V., McFadden, L.D., Wells, S.G., 2003. Regional

response of alluvial fans to the Peistocene–Holocene climate

transition, Mojave Desert, California. In: Enzel, Y., Wells, S.G.,

Lancaster, N. (Eds.), Paleoenvironments and Paleohydrology of

the Mojave and Southern Great Basin Deserts. Geological Society

of America Special Paper 368, Boulder, CO, pp. 189–205.

McIntosh, W.C., Peters, L., Karlstrom, K.E., Pederson, J.L., 2002.

New 40Ar–39Ar dates on basalts in Grand Canyon: constraints on

rates of Quaternary river incision and slip on the Toroweap fault,

and implications for lava dams. Geological Society of America

Abstracts with Programs 33 (4), 61.

Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore Jr., T.C.,

Shackleton, N.J., 1987. Age dating and the orbital theory of the Ice

Ages: development of a high-resolution 0 to 300,000-year

chronostratigraphy. Quaternary Research 27, 1–29.

Melis, T.S., Webb, R.H., Griffiths, P.G., Wise, T.J., 1994. Magnitude

and frequency data for historic debris flows in Grand Canyon

National Park and vicinity, Arizona. US Geological Survey Water-

Resources Investigations Report 94-4214, p. 285.

Merritts, D.J., Vincent, K.R., Wohl, E.E., 1994. Long river profiles,

tectonism, and eustasy: a guide to interpreting fluvial terraces.

Journal of Geophysical Research 99 (B7), 14,031–14,050.

Molnar, P., England, P., 1990. Late Cenozoic uplift of mountain

ranges and global climate change: chicken or egg? Nature 346,

29–34.

Montgomery, D.R., Dietrich, W.E., 1989. Source areas, drainage

density, and channel initiation. Water Resources Research 25,

1907–1918.

Nichols, K.K., Bierman, P.R., Hooke, R.L., Clapp, E.M., Caffee, M.,

2002. Quantifying sediment transport on desert piedmonts using10Be and 26Al. Geomorphology 45, 105–125.

Patton, P.C., Boison, P.J., 1986. Processes and rates of formation of

Holocene alluvial terraces in Harris Wash, Escalante River basin,

south-central Utah. Geological Society of America Bulletin 97,

369–378.

Pederson, J.L., Pazzaglia, F., Smith, G., 2000. Ancient hillslope

deposits: missing links in the study of climate controls on

sedimentation. Geology 28 (1), 27–30.

Pederson, J.L., Smith, G., Pazzaglia, F., 2001. Comparing the Modern,

Quaternary, and Neogene records of climate-controlled hillslope

sedimentation in southwest Nevada. Geological Society of America

Bulletin 113, 305–319.

Pederson, J., Karlstrom, K., Sharp, W., McIntosh, W., 2002.

Differential incision of the Grand Canyon related to Quaternary

faulting—constraints from u-series and Ar/Ar dating. Geology 30

(8), 739–742.

Phillips, A.M., 1984. Shasta ground sloth extinction: fossil packrat

midden evidence from the western Grand Canyon. In: Martin, P.S.,

Klein, R.G. (Eds.), Quaternary Extinctions. Tucson, University of

Arizona Press, pp. 148–158.

Phillips, F.M., Cambell, A.R., Smith, G.I., Bischoff, J.L., 1994.

Interstadial climatic cycles: a link between western North America

and Greenland? Geology 22, 1115–1118.

Phillips, F.M., Zreda, M.G., Benson, L.V., Plummer, M.A., Elmore,

D., Sharma, P., 1996. Chronology for fluctuations in late

Pleistocene Sierra Nevada glaciers and lakes. Science 274,

748–751.

Phillips, F.M., Zreda, M.G., Gosse, J.C., Klein, J., Evenson, E.B.,

Hall, R.D., Chadwick, O.A., Sharma, P., 1997. Cosmogenic 36Cl

and 10Be ages of Quaternary glacial and fluvial deposits of the

Wind River Range, Wyoming. Geological Society of America

Bulletin 128, 1453–1463.

Reneau, S.L., Dietrich, W.E., Donahue, D.J., Jull, A.J.T., Rubin, M.,

1990. Late Quaternary history of colluvial deposition and erosion

in hollows, central California Coast Ranges. Geological Society of

America Bulletin 102, 969–982.


Repka, J.L., Anderson, R.S., Dick, G.S., Finkel, R.C., 1997.

Quaternary geology and geomorphology, northern Henry Moun-

tains region: dating the Fremont River terraces: Part 7. In: Link,

P.K., Kowallis, B.J. (Eds.), Mesozoic to Recent Geology of Utah,

vol. 42. Geology Studies, pp. 398–404.

Ritter, J.B., Gardner, T.W., 1993. Hydrologic evolution of drainage

basins disturbed by surface mining, central Pennsylvania. Geolo-

gical Society of America Bulletin 105, 101–115.

Ritter, J.B., Miller, J.R., Enzel, Y., Howes, S.D., Nadon, G., Grubb,

M.D., Hoover, K.A., Olsen, T., Reneau, S.L., Sack, D., Summa,

C.L., Taylor, I., Touysinhthiphonexay, K.C.N., Yodis, E.G.,

Schneider, N.P., Ritter, D.F., Wells, S.G., 1993. Quaternary

evolution of Cedar Creek Alluvial Fan, Montana. Geomorphology

8 (4), 287–304.

Schmidt, J.C., Rubin, D.M., 1995. Regulated streamflow, fine-grained

deposits, and effective discharge in canyons with abundant debris

fans. In: Costa, J.E., Miller, A.J., Potter, K.W., Wilcock, P.R.

(Eds.), Natural and Anthropogenic Influences in Fluvial Geomor-

phology, vol. 89. American Geophysical Union Geophysical

Monograph, pp. 177–195.

Schumm, S.A., 1973. Geomorphic thresholds and the complex

response of drainage systems. In: Morisawa, M. (Ed.), Fluvial

Geomorphology, Publications in Geomorphology. State University

of New York, Binghamton, pp. 299–310.

Sharp, W.D., Ludwig, K.R., Chadwick, O.A., Amundson, R., Glaser,

L.L., 2003. Dating fluvial terraces by 230Th/U on pedogenic

carbonate, Wind River Basin, Wyoming. Quaternary Research 59,

139–150.

Sklar, L., Dietrich, W.E., 1998. River longitudinal profiles and

bedrock incision models: stream power and the influence of

sediment supply. In: Tinkler, K.J., Wohl, E.E. (Eds.), Rivers Over

Rock: Fluvial Processes in Bedrock Channels, vol. 107. American

Geophysical Union Geophysical Monograph, pp. 237–260.

Small, E.E., Anderson, R.S., 1995. Geomorphically driven late

Cenozoic rock uplift in the Sierra Nevada, California. Science

270, 277–280.

Smith, G.I., Bischoff, J.L., Bradbury, J.P., 1997. Synthesis of the

paleoclimate record from Owens Lake core OL-92. In: Smith, G.I.,

Bischoff, J.L. (Eds.), An 800,000-year Paleoclimatic Record from

Core OL-92, Owens Lake, Southeast California, vol. 317,

Geological Society of America Special Paper, pp. 143–160.

Tchakerian, V.P., Lancaster, N., 2002. Late Quaternary arid/humid

cycles in the Mojave Desert and western Great Basin of North

America. Quaternary Science Reviews 21, 799–810.

Thompson, R.S., Whitlock, C., Bartlein, P.J., Harrison, S.P.,

Spaulding, W.G., 1993. Climate changes in the western United

States since 18,000 yr B.P. In: Wright, Jr., H.E., Kutzback, J.E.,

Webb, T., Ruddiman, W.F., Street-Perrott, F.A., Bartlein, P.J.

(Eds.), Global Climates Since the Last Glacial Maximum.

University of Minnesota Press, Minneapolis, pp. 468–513.

Tucker, G.E., Slingerland, R., 1997. Drainage basin responses to

climate change. Water Resources Research 33 (8), 2031–2047.

Webb, R.H., Pringle, R.T., Rink, G.R., 1989. Debris flows in

tributaries of the Colorado River in Grand Canyon National

Park, Arizona. US Geological Survey Professional Paper 1492, 39.

Wegmann, K.W., Pazzaglia, F.J., 2002. Holocene strath terraces,

climate change, and active tectonics: the Clearwater River basin,

Olympic Peninsula, Washington State. Geological Society of

America Bulletin 114, 731–744.

Weng, C., Jackson, S.T., 1999. Late glacial and Holocene vegetation

history and paleoclimate of the Kaibab Plateau, Arizona.

Paleogeography, Paleoclimatology, Paleoecology 153, 179–201.

Whipple, K.X., Kirby, E., Brocklehurst, S.H., 1999. Geomorphic

limits to climate-induced increases in topographic relief. Nature

401, 39–43.

Whitney, J.W., Harrington, C.D., 1993. Relict colluvial boulder

deposits as paleoclimatic indicators in the Yucca Mountain region,

southern Nevada. Geological Society of America Bulletin 105,

1008–1018.

Winograd, I.J., Coplen, T.B., Landwehr, J.M., Riggs, A.C., Ludwig,

K.R., Szabo, B.J., Kolesar, P.T., Revesz, K.M., 1992. Continuous

500,000-year climate records from vein calcite in Devils Hole,

Nevada. Science 258, 255–260.

pleistocene geomorphology and geochronology of eastern ... et al. 2005 qsr.pdf · standing of...

Documents