KECK GEOLOGY CONSORTIUM PROCEEDINGS OF THE TWENTY-THIRD

ANNUAL KECK RESEARCH SYMPOSIUM IN GEOLOGY ISSN# 1528-7491

April 2010

Andrew P. de Wet Keck Geology Consortium Lara Heister Editor & Keck Director Franklin & Marshall College Symposium Convenor Franklin & Marshall College PO Box 3003, Lanc. Pa, 17604 ExxonMobil Corp.

Keck Geology Consortium Member Institutions: Amherst College, Beloit College, Carleton College, Colgate University, The College of Wooster, The Colorado College

Franklin & Marshall College, Macalester College, Mt Holyoke College, Oberlin College, Pomona College, Smith College, Trinity University Union College, Washington & Lee University, Wesleyan University, Whitman College, Williams College

2009-2010 PROJECTS

SE ALASKA - EXHUMATION OF THE COAST MOUNTAINS BATHOLITH DURING THE GREENHOUSE TO ICEHOUSE TRANSITION IN SOUTHEAST ALASKA: A MULTIDISCIPLINARY STUDY OF THE PALEOGENE KOOTZNAHOO FM.

Faculty: Cameron Davidson (Carleton College), Karl Wirth (Macalester College), Tim White (Penn State University) Students: Lenny Ancuta, Jordan Epstein, Nathan Evenson, Samantha Falcon, Alexander Gonzalez, Tiffany Henderson, Conor McNally,

Julia Nave, Maria Princen

COLORADO – INTERDISCIPLINARY STUDIES IN THE CRITICAL ZONE, BOULDER CREEK CATCHMENT, FRONT RANGE, COLORADO.

Faculty: David Dethier (Williams) Students: Elizabeth Dengler, Evan Riddle, James Trotta

WISCONSIN - THE GEOLOGY AND ECOHYDROLOGY OF SPRINGS IN THE DRIFTLESS AREA OF SOUTHWEST WISCONSIN.

Faculty: Sue Swanson (Beloit) and Maureen Muldoon (UW-Oshkosh) Students: Hannah Doherty, Elizabeth Forbes, Ashley Krutko, Mary Liang, Ethan Mamer, Miles Reed

OREGON - SOURCE TO SINK – WEATHERING OF VOLCANIC ROCKS AND THEIR INFLUENCE ON SOIL AND WATER

CHEMISTRY IN CENTRAL OREGON. Faculty: Holli Frey (Union) and Kathryn Szramek (Drake U. )

Students: Livia Capaldi, Matthew Harward, Matthew Kissane, Ashley Melendez, Julia Schwarz, Lauren Werckenthien

MONGOLIA - PALEOZOIC PALEOENVIRONMENTAL RECONSTRUCTION OF THE GOBI-ALTAI TERRANE, MONGOLIA.

Faculty: Connie Soja (Colgate), Paul Myrow (Colorado College), Jeff Over (SUNY-Geneseo), Chuluun Minjin (Mongolian University of Science and Technology)

Students: Uyanga Bold, Bilguun Dalaibaatar, Timothy Gibson, Badral Khurelbaatar, Madelyn Mette, Sara Oser, Adam Pellegrini, Jennifer Peteya, Munkh-Od Purevtseren, Nadine Reitman, Nicholas Sullivan, Zoe Vulgaropulos

KENAI - THE GEOMORPHOLOGY AND DATING OF HOLOCENE HIGH-WATER LEVELS ON THE KENAI PENINSULA,

ALASKA Faculty: Greg Wiles (The College of Wooster), Tom Lowell, (U. Cincinnati), Ed Berg (Kenai National Wildlife Refuge, Soldotna AK)

Students: Alena Giesche, Jessa Moser, Terry Workman

SVALBARD - HOLOCENE AND MODERN CLIMATE CHANGE IN THE HIGH ARCTIC, SVALBARD, NORWAY. Faculty: Al Werner (Mount Holyoke College), Steve Roof (Hampshire College), Mike Retelle (Bates College)

Students: Travis Brown, Chris Coleman, Franklin Dekker, Jacalyn Gorczynski, Alice Nelson, Alexander Nereson, David Vallencourt

UNALASKA - LATE CENOZOIC VOLCANISM IN THE ALEUTIAN ARC: EXAMINING THE PRE-HOLOCENE RECORD ON UNALASKA ISLAND, AK.

Faculty: Kirsten Nicolaysen (Whitman College) and Rick Hazlett (Pomona College) Students: Adam Curry, Allison Goldberg, Lauren Idleman, Allan Lerner, Max Siegrist, Clare Tochilin

Funding Provided by: Keck Geology Consortium Member Institutions and NSF (NSF-REU: 0648782)

and ExxonMobil

Keck Geology Consortium: Projects 2009-2010 Short Contributions – COLORADO

INTERDISCIPLINARY STUDIES IN THE CRITICAL ZONE, BOULDER CREEK CATCHMENT, FRONT RANGE, COLORADO

Project Director: DAVID P. DETHIER: Williams College

Project Faculty: MATTHIAS LEOPOLD: Technical University of Munich

FRACTURE DISTRIBUTION AND CHARACTERIZATION IN BETASSO GULCH, CO

ELIZABETH DENGLER

Bates College Research advisor: Dykstra Eusden

TALUS STRUCTURE AND EVOLUTION: A COMPARISON BETWEEN TALUS

NEAR GREEN LAKE 3 AND AT BUMMER’S ROCK, COLORADO

EVAN RIDDLE North Carolina State University

Research Advisor: Karl Wegmann

THE DISTRIBUTION OF TORS IN GORDON GULCH, FRONT RANGE, COLORADO

JAMES TROTTA Williams College

Research Advisor: David P. Dethier

Funding provided by: Keck Geology Consortium Member Institutions and NSF (NSF-REU: 0648782)

Keck Geology Consortium Franklin & Marshall College

PO Box 3003, Lancaster Pa, 17603 Keckgeology.org

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INTRODUCTIONProcessesinthecriticalzone,thelife-sustainingsur-ficialmantleoftheearth,involveweatheredgeologicmaterials,water,andthebiosphere,mediatedbyat-mosphericprocessesthatarecontrolledbychangingclimate.Fieldstudiesthatinvestigatehydrologicandgeochemicalcomponentsofthecriticalzonepro-videvaluableinformationaboutprocessesandthephysicalbasisforintegratingthosedataintomodelsofshortandlong-termgeomorphic,hydrologicandbiochemicalresponse.TheKeckColoradoProjectisworkingincooperationwithalargeinterdisciplin-arystudy(BoulderCreekCriticalZoneObserva-tory:Weatheredprofiledevelopmentinarockyenvironmentanditsinfluenceonwatershedhydrol-ogyandbiogeochemistry—SuzanneAnderson,PI,InstituteforArcticandAlpineStudies,UniversityofColorado)ofthecriticalzone.The“observatory”(CZO)consistsof3small,instrumentedcatchmentsintheBoulderCreekbasin,ColoradoFrontRange:

(1)GreenLakesValley--asteep,glaciallyscouredal-pineareaintheBoulderCitywatershed;(2)GordonGulch--aforested,mid-elevationcatchmentthatexposesisolatedbedrockremnants(tors)developedonasurfaceoflowrelief;and(3)Betassogulch--asteep,lower-elevationbasinwheresurficialdepositsareofvariablethicknessandnumerousfracturescutexposedbedrock(Fig.1).

TheglaciatedGreenLakesValley,lowreliefsurface,andbedrockcanyonsaredevelopedingraniticorgneissicrocksandinfluencedbythestronggradi-entinelevation,climateandvegetationfromwesttoeast.Variationincritical-zonedevelopmentinthesedifferentenvironmentsallowsustotestmodelsofweatheringandregolithgeneration,slopeevolutionandsedimenttransportinanaccessiblefieldsetting.Land-use,vegetationandperhapshydrologicre-sponseineachCZOcatchmentalsoreflectchangesproducedbyanthropogenicactivitiesoverthepast150years.KeckColoradostudiesfocusonusinga

INTERDISCIPLINARY STUDIES IN THE CRITICAL ZONE, BOULDER CREEK CATCHMENT, FRONT RANGE, COLORADO

DAVID P. DETHIERWilliamsCollege

Figure 1. Shaded relief and slope map of upland Boulder Creek. Steepest slopes shaded red; shallowest slopes are blue. Study catch-ments include: A- Green Lakes Valley; B- Gordon Gulch and C- Betasso gulch. Pleistocene glacial limits (white), and two existing USGS gages are shown. Boulder Falls is a knickpoint on N. Boulder Creek; steep-walled canyons mark similar knickzones.

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varietyoftechniquestomapandcharacterizenear-surfacegeologicmaterialsandtheirpropertiesineachofthestudycatchments.

SETTINGThemiddleBoulderCreekcatchment(Fig.1)extendsfromtheglaciatedalpinezoneoftheCon-tinentalDivideeasttothesemi-aridwesternedgeoftheGreatPlains.Deep,U-shapedvalleysintheglaciatedareasbecomeshallowereastwardthroughazoneoflowreliefandrelativelylowslopes,deepenintosteep,narrowbedrockcanyonsastheypassknickzones,andflattentolowerchannelslopesnearthepiedmontmargin.Smallglaciersandlate-per-sistingsnowfieldsdotthealpinezone,whichexpos-esbedrockandrelativelythindepositsrelatedtothelatestPleistocenePinedaleglaciationandHoloceneerosion.Theforestedzoneoflowreliefexposesareasofthick(characteristically3to8m)regolith,sapro-liteandoxidizedbedrock,buttheweatheredmantleisthininotherareas.InthevicinityofknickzonesandindownstreamareassuchasBetassogulch,slopesnearchannelsaresteepwithshallow,freshbedrockwhereasmoredistantareasretainathickerweatheredmantle.

APPROACHInthissecondprojectyear,weusedfieldmappingandsampling,supplementedbygeophysicalmea-surements,inallthreeCZOcatchments,inordertoprovidebasicdataabouttheshallowgeologyanderosionalhistoryofthecriticalzoneandtohelpguidethelocationoffuturestudies.Keckstudentslearnedgeophysicaltechniquesandinitialdatareduction,processingandvisualizationmethodsinthesesettings.Studentschosefromavarietyofpotentialprojectsinthestudycatchments.In2009projecttopicalareasincluded: 1.Fracturedistributionandbedrockgeol-ogy,Betassocatchment 2.Talusstructureandevolution,GreenLakesandBetassocatchments 3.Thedistributionoftors,GordonGulchcatchment 4.Regolithstirringbybiologicprocesses,

GordonGulch

Weranground-penetratingradarandresistivitylinesinGordonGulchandintheGreenLakesVal-leyandworkedincooperationwithinvestigatorsfromtheUniversityofColorado,whoranseismic-refractionlinesinGordonGulch.

STUDENT PROJECTS

ThreeKeckstudents(LizDenglerfromBates,EvanRiddlefromNorthCarolinaState,andJTTrottafromWilliams)joinedBexGilbert(Williams),whowassupportedbyNSFfunding.DavidDe-thiersupervisedstudentsonadailybasisandfieldteamsfrequentlyjoinedinvestigatorsandgraduatestudentsfromtheUniversityofColorado.MatthiasLeopold(TechnicalUniversityofMunich)workedwithKeckstudentsforaboutaweekinthefield.Keckstudentswereamongtheonlyundergraduatestopresentpreliminaryresultsoftheirfieldresearchatthe2ndannualBoulderCreekCZOmeetingon11August2009.KeckColoradoresearchspreadacrossthethreeBoulderCZOstudycatchmentsandstudentsworkedinpairsonadailybasisandsome-timesasgeophysicalsupportteams(Fig.2).Geo-physicaldataprovidedimportantbackgrounddataforTrotta’sworkandforRiddle’stalusstudies.

Figure 2. Resistivity measurements on stabilized talus, Green Lakes Valley.

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LizDenglermappedthefracturedistributionandbedrockgeologyoftheBetassocatchmentandnearbyBummersRock(Fig.3),whichareunder-lainbyrocksoftheBoulderCreekbatholith(Gable,1980).Fracturesproducedbytectonism(Molnaretal.,2007)andlocalstresses(Selby,1980)playacen-tralroleinweathering,inpreparingrockforerosionandingroundwaterrechargeandflow,butregolithmasksfracturesinmostoftheCZO.

Bymeasuringfractureorientationandmappingbedrockat284sites(Fig.4),Lizwasabletodemon-stratethatBetassogranodioriteandquartzmonzo-nitearecutbytwopredominantfracturesetsthatlikelyrecordLaramidereactivationofPrecambrianstructures.SheshowedthatfractureorientationsdefineaconjugateN-NWset(PairA)paralleltoahematite-richfaultzonemappedinBetassoGulchandanE-NEset(PairB).FieldevidencesuggeststhatfaultsandzonesofhydrothermalalterationparalleltoPairBarealsopresent.Regionalevidence(Kelloggetal.,2008)suggeststhatPairAandPairBareLaramideorlateLaramidestructuresandthatthehydrothermalalterationandmineralizationare

relatedtotheColoradoMineralBelt(LoveringandTweto,1953).LocalfieldrelationsdonotclearlydefinetherelativeagerelationshipbetweenPairAandB.

Mostfracturesdipsteeplytotheeastornortheast.Fracturespacinghasameanvaluebetweenabout0.5and1.0m(n=143)andlocalspacingvariesfromlessthan10cmto~7m.(Fig.5).RocksappeartobemoredenselyfracturednearmajorfaultsandmorewidelyfracturedinlocalareasnearthetopofBummersRock,perhapsaccountingforitspersis-tenceinanerosionallandscape.EvanRiddlestudiedthedepositionandmorphologyoftalusbelowBummersRock(Betassocatchment)andaboveGreenLake3(Fig.6),wheredepositshaveaccumulatedinanareathatwasdeglaciatedatabout12ka.WorkingwithMatthiasLeopold,EvanusedGPR(Fig.7)toestimatethethicknessoftalusalongseveraltransectsnearthelake.Combiningthicknessmeasurementsandestimatesallowedhim

Figure 3. Talus survey below Bummers Rock, Betasso Gulch area.

Figure 4. Liz Dengler measuring fractures in Boulder Creek Granodiorite on Bummers Rock.

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toestimatetalusvolume.Evan’sresearchshowsthattalusblocksatthealpinesiteareunstable,suban-gularandrelativelyunweatheredandthattheirsizedistributionmirrorsfracturespacingintheirsourcearea.Incontrast,talusbelowBummersRock(Fig.3)consistsofmorerounded,partiallyweatheredblocksthatonlypartiallycovertheslopebelowtheirsourcearea.EvanpostulatedthatthereleaseoftalusblocksatBummersRockrequiresweatheringandround-ingofblocksboundedbyjointsurfaces,followedbyeventualslidingortoppling.Tocharacterizeblockrounding,Evanconstructedagauge(Fig.8)

andusedittoestimatetheamountofmateriallostfromfresh,partlyweatheredandweatheredjointintersections.Hispreliminaryresultsarepromising,butwillhavemoremeaningwhensurfaceexposureagesfromBummersRockareavailableandcanbeappliedtolocalratesofcliffretreat.

Figure 5. Fracture-spacing frequency diagram, Betasso Gulch area (E. Dengler data).

Figure 6. Oblique view of south-facing talus slope and talus cone studied by Evan Riddle. Light colored outcrops are Silver Plume granite. Green Lake 3 in foreground.

Figure 7. Evan Riddle using ground-penetrating radar on a talus cone, Green Lakes Valley area.

Figure 8. Evan Riddle demonstrates use of block-rounding gauge to estimate the amount of material removed by weath-ering, Bummers Rock area.

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Evan’spreliminaryworkbyGreenLakes3suggeststhattalusaccumulationratesintegratedoverthepast12,000yrsaverage~2m3yr-1,equivalentto<0.1mmofcliffretreatperyear.Theseratesarerela-tivelylow,butaregenerallyconsistentwithvaluesreportedbyCaine(1986)fromtheupperGreenLakesBasin.

JTTrottamappedthemostlyisolatedbedrockoutcrops(tors;Fig.9)ofGordonGulch,whichisdevelopedonarollingsurfaceoflowrelief,anareapreviouslymappedasthicksaproliteandwell-de-velopedsoils(Birkelandetal.,2003).WorkbyKeckstudentsandinvestigatorsfromtheUniversityofColorado,however,suggeststhattheweatheredzonemaybethininmanyareasandthesoilsyoung.Ifthisviewofthelandscapeiscorrect,tordistributionmayreflectrelativelyrecenterosion.JT’smappingshowsthatbedrockexposuresformthesurfacein~4.5%ofthecatchmentandthattorslocallystandashighas15mabovesurroundingslopes.Talltorsap-peartobelessweatheredatgroundlevelthanat5to10mabovetheground,wheregneissiclayerslocallydisplaydecimetersoflocalrelief.

Torsareunevenlydistributedinthebasinandaremorecommononsteep,south-facingslopesthaninadjacentareaswithnorthernaspects(Fig.10).Bedrock,whichconsistsofsillimaniteandgarnet-bearingProterozoicgneissesand1.4Gagraniticrocks,doesnotappeartocontroldirectlythesize,

shapeorlocationoftors.However,foliation,whichstrikesNWanddipsNE,ismainlyslope-parallelonnorth-facingslopes,wheretherearefewerbedrockexposures(Fig.11).Torsarethoughttoberem-nantfeaturestypicalofdeeplyweatheredlandscapes(Street,1971).TheassociationoftorswithsteepareasinGordonGulchsuggeststhatthesefeaturesmayrecordgeologicallyrecenterosionthatstrippedregolithandsaprolite.

Figure 9. Tor developed in granitic rocks, Gordon Gulch.

Figure 10. Outcrop map layer overlay on a DEM-based slope map of Gordon Gulch. The southeastern part of the catchment has the highest slope and the greatest number of outcrops. Black circle shows the location of Figure 11.

Figure 11. Image looking northwest along a steep part of Gordon Gulch that has almost no outcrops. The slope of the north-facing hill in this picture is approximately 35°. See Figure 10 for the location of this photo.

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Rebecca(Bex)GilbertstudiedsoilstirringbybiologicactivityinGordonGulch,focusingontreethrowandonsedimentmovedbyantsandbyprospectorslookingforgold,silverandtungsten.Tohelpcalibraterootandpitmeasurementsmadeatsome150uprootedtrees,BexandtheKeckstu-dentspulledapart15recentrootballsandweighedtherocksandsoilthathadbeendisruptedbythetreefalls(Fig.12).Gilbert’sresultsshowthatofthebiologicagentsstudiedinGordonGulch,prospec-torsdisruptedthemostareaandvolume(Fig.13),overaperiodofacentury.Treethrowliftsandmixesanaverageof~2m3km-2ofregolithfromdepthsof

20to50cmeachyear.Ants(Formicasp.)maybethemosteffectivemixersofshallowregolithinGordonGulch,butadditionalworkisneededtoquantifyhowfrequentlyanthillsareconstructed.Theup-per50cmofregolithcreepsdownslopeundertheinfluenceofasuiteofprocessesinareaslikeGor-donGulch,butbiologicalactivitymaybethemostimportant.

FutureKeckstudieswillbuildonworkbythe2009KeckgroupandontheNSF-sponsoredhydrol-ogyandtreethrowstudiesofEirikBuraasandBexGilbert,respectively,inGordonGulch.Wehopetoinvolvestudentsinadditionalstudiesofrockfallandtalusformation,indocumentingtheeffectsofanthropogenicinfluencesontheGordonGulchand

Betassocatchmentsandinmoredetailedanalysesoftheeffectsofeoliandepositiononsoildevelop-mentandcatchmentchemistryintheBoulderCreekCZO.ACKNOWLEDGMENTS

FieldstudiesandmeasurementsintheBoulderCreekareawereperformedincooperationwiththeBoulderCreekCZOProject(NationalScienceFoundation),theUSDAForestService,andtheCityofBoulderWatershedandParksandRecreationDe-partments.NelCaine(UniversityofColorado)andCraigSkeie(CityWatershedManager)guidedworkintheGreenLakesbasin,PeteBirkeland(Univer-sityofColorado)taughtusaboutsoilsandSuzanneAndersonandAnneSheehan(bothatUniversityofColorado)sharedtheirknowledgeoftheCriticalZoneandhowtostudyitinmanyfield“teachingmoments”.RoryCowie(UniversityofColorado)introducedustothechannelsandslopesofGor-donGulch.WegratefullyacknowledgetheongoingcooperationandcogentadviceofJoergVoelkelandMatthiasLeopold(TechnicalUniversityofMunich)andthehospitalityoftheMountainResearchSta-tion.

Figure 12. Bex Gilbert (Williams College) and fresh rootball, Gordon Gulch

Figure 13. Surface area and volume of regolith disturbed by prospecting, treethrow and ant activity, Gordon Gulch.

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REFERENCES

Birkeland,P.W.,Shroba,R.R.,Burns,S.F.,Price,A.B.,Tonkin,P.J.,2003,Integratingsoilsandgeomorphologyinmountains—anexamplefromtheFrontRangeofColorado:Geomor-phology,v.55,p.329–344.

Caine,T.N.,1986,SedimentmovementandstorageonalpineslopesintheColoradoRockyMoun-tains,inAbrahams,A.,HillslopeProcesses:Boston:Allen&Unwin,p.115–37.

Gable,DoloresJ.,1980,TheBoulderCreekBatho-lith,FrontRange,Colorado:GeologicalSurveyProfessionalPaper1101,88p.

Kellogg,K.S.,Shroba,R.R.,Bryant,BruceandPremo,W.R.,2008,GeologicmapoftheDen-verWest30’x60’quadrangle,north-centralColorado:U.S.GeologicalSurveyScientificInvestigationsMap3000,scale1:100,000,48-p.pamphlet.

Lovering,T.S.,andTweto,Ogden,1953,GeologyandoredepositsoftheBoulderCountytung-stendistrict,Colorado:U.S.GeologicalSurveyProfessionalPaper245,199p.

Molnar,P.,Anderson,R.S.,andAnderson,S.P.2007,Tectonics,fracturingofrock,andero-sion:JournalofGeophysicalResearch,112,F0312,doi:10.1029/2005JF000433.

Selby,M.J.,1980,Arockmassstrengthclassifica-tionforgeomorphicpurposes:withtestsfromAntarcticaandNewZealand:ZeitschriftfürGeomorphologiev.24,p.31-51.

Street,F.A.,1971,AstudyoftorsintheFrontRangeoftheRockyMountainsinColorado,withspecialreferencetotheirvalueasanindicatorofnon-glaciation:M.S.thesis,UniversityofColorado,Boulder,242p.