Teacher’s Guide to Geology at Meadowcroft …...Page 4 of 19 First Peoples: Archaeology at...

of19FirstPeoples:ArchaeologyatMeadowcroftRockshelterFirstPeoples:ArchaeologyatMeadowcroftRockshelterTeacher’sGuidetoGeology

Teacher’sGuidetoGeologyatMeadowcroftRockshelterAComponentofFirstPeoples:ArchaeologyatMeadowcroftRockshelter


ContentsWhyGeologyinFirstPeoples?.....................................................................................................................2

TeachingGeologyatMeadowcroftRockshelter..........................................................................................3

IntersectionofGeologyThemewithDisciplines......................................................................................3

GeologyGigaPanInquiry..........................................................................................................................4

MajorTermsandConcepts......................................................................................................................5

GeologyoftheMeadowcroftRockshelterandtheCrossCreekDrainage...................................................6

Geography,GeologicOrigins,andPhysiography.....................................................................................6

FormationofMeadowcroftStratigraphy...............................................................................................10

Tables.........................................................................................................................................................14

AncientGeologicalActivityatMeadowcroftRockshelter......................................................................14

PleistoceneGeologicalActivityintheCrossCreekDrainage:FormationoftheMeadowcroftRockshelter.............................................................................................................................................15

StratigraphicProfileofMeadowcroftRockshelter.................................................................................17

GeologicTimeasRelatedtoMeadowcroft............................................................................................18

Bibliography...............................................................................................................................................19


WhyGeologyinFirstPeoples?

WhenavisitorstandsintheparkinglotfacingMeadowcroftRockshelter,theirfirstobservationsareusuallyoneoftwothings:theloomingsandstonecliffthatcontainstheRockshelterandtowersoverthelandscape,orthesteepinclineoftheslopeleadinguptotheexcavationenclosure(whichtheyknowtheymustascend–nearly70steps–it’salongwayup).Heretheyare,standingatthefeetofoneofthemostsignificantprehistoricarchaeologicalsitesinNorthAmerica,andtheirfirstintakeisoverrocks.Somethingaboutthoserocksjustcallspeopletoinvestigatethespace.

Today’svisitorsneednotbeembarrassedabouttheirreaction;forthousandsofyearspeoplesharedthedesiretoclimbtheslope(orthestepsiftheyarrivedanytimeafter2008).AlbertMiller,thefarmerwhodiscoveredthefirstarchaeologicalevidenceatthesite,andDr.Adovasio,theprincipleinvestigatorofthefamousarchaeologicalexcavation,bothcommentedonthegeologicsettingbeforetheyknewthearchaeologicalsignificance.Infact,whenDr.AdovasiofirstencounteredMeadowcroftRockshelterin1973,thefloorofthesitewaslitteredwithgarbageandcharcoalfromrecentcampfires.Thesitewasclearlyanattractivehangoutforlocalteens.Justafewinchesbelowthe1973campfirewasanotherfirepit,thistimeassociatedwithcolonial-eraglass,andjustbelowthatyetanotherfiresiteassociatedwithflintprojectilepoints.

WhatisthemagneticqualityoftherocksatMeadowcroft?Atthemostbasic,perhapsitisthesuggestionofprotection:theoverhangingrocksandthesurroundingcliffembracethelandscape,whiletheelevationholdstheadvantageoverthesurroundinglandscape.Therockformationalsoofferssouthernexposure(warmth),crosswindsforventilation,andproximitytowaterbuthighoutsideofthefloodzone,featuresthatpromise,ifnotcomfort,conveniences,particularlyforprehistoricvisitors.ThemagneticauraistheRockshelteritself.

Inarchaeology,closed-siteslikerocksheltersorcavesareoftenpredictablesitesforculturalevidence.Oncediscovered,sitessuchasMeadowcroft,becomepartofthemarkedlandscape,drawinghumansrepeatedlyaslongastheRockshelterexists.

Thus,geologyisanaturalthemeforinclusionintheFirstPeoples:ArchaeologyatMeadowcroftRocksheltercurriculum.StudentsarenotimmunetotheattractiontotherocksatMeadowcroft,andtheircasualobservationsgeneratemanyconversations.TheyoftenaskhowoldtheRockshelteris,whytherocksarepockmarked,and,mostfrequentlyisitgoingtofallonus?Thesequestionscanallbeansweredthroughgeology.


TeachingGeologyatMeadowcroftRockshelterTheexcavationatMeadowcroftusedgeoarchaeologicalmethodstoinformtheprocessofarchaeology.UsingtheGeologyGigaPanimageactivityguideandtheresourcesinthiscurriculumguide,studentswillgainanappreciationforthemulti-disciplinaryapproachandwillunderstandhowageologicformationwitnessed16,000yearsofhumanactivity.

IntersectionofGeologyThemewithDisciplinesThetablebelowsummarizeshowtheGeologythemeoftheFirstPeoples:ArchaeologyatMeadowcroftRocksheltercurriculumcanbeusedtoexplorevariousacademicdisciplines.

FirstPeoplesTheme

MajorDisciplinesaddressedinFirstPeoples

Science History EnvironmentandEcology

Geography TechnologyandEngineering

Geology NaturalstratigraphyexplainstheevolutionoftheRockshelterovertime.Physicalfeaturessuggesttheoriginsofthelandscape.

Throughout16,000years,geologyhasservedasthefoundationforallhumanactivityatthesite.Atthemostbasic,therocksaroundMeadowcroftanchorallaspectsofthelandscapefromwhichhumansmeettheirbasicneeds.

ThegeologicprocessesthatcreatedtheCrosscreekdrainageimpactedtheflowofwaterthroughoutthewatershed.Theslopeofthelandandproximitytowaterdictatetheecologyofthewatershed.

Topographyinfluencedhowprehistoricpeoplesmovedthroughthelandscape.Inthe20thand21stcenturies,energyextractionresultedindrastichumanalterationtothelandscape.

Lithic(stone)toolswerethebackboneofthePaleo-toolkit.Coalextractioninthe20thcenturyandnaturalgasextractiontodayaremajorindustries.


GeologyGigaPanInquiryTheFirstPeoplesGeologyGigaPaninquiryaddressesthefollowingpointsofinquirywithstudents.

ObjectivesStudentswill...

GradeBands

IndicatorsofMasteryStudentswillbeableto...

• Define,describe,analyze,andevaluatetheuseofgeomorphologyatMeadowcroftRockshelter

• Identify,describeorevaluatehowstratigraphyandtheLawofSuperpositioncanbeusedtodategeologicfeatures

• ExplainthegeologicalprocessesthatformedMeadowcroftRockshelter;Describethelifecycleofarockshelter

• Identify,define,explainoranalyzethegeologicalprocessesthatformedthestratigraphyinsidetheRockshelter

• DefinegeoarchaeologyandexplainhowthestudyofMeadowcroftRockshelterbenefittedfromthismulti-disciplinaryapproach

11th-12thGrade

• AnalyzetheuseofgeomorphologyintheMeadowcroftProject

• Explaintheroleofstratigraphyinrelativedating• AnalyzethelifecycleofMeadowcroftRockshelter;describethegeologicprocessesinvolved

• Analyzethebenefitsofusingstratigraphicprinciplestoexcavateanarchaeologicalsite

• EvaluatetheuseofageoarchaeologicalapproachatMeadowcroft

8th-10thGrade

• DescribehowgeomorphologycontributestoarchaeologyatMeadowcroft

• DescribehowstratigraphyandtheLawofSuperpositioncanbeusedtodiscusschronology

• ExplainthegeologicprocessesthatcreatedMeadowcroftRockshelter

• ExplainhowMeadowcroft’sstratigraphyformed• Evaluatetheuseofageoarchaeologicalapproach

atMeadowcroft

5th-7thGrade

• Definegeomorphologyandgiveanexampleofhowitinformstheexcavationofsites

• DescribehowgeologistsusetheLawofSuperpositionandstratigraphytodategeologicfeatures

• ExplainhowMeadowcroftRockshelterformed• Explainhowthestratigraphyformed;identify

erosionasasourceforsediment• Explainhowgeoarchaeologyismulti-disciplinary

• K-4thGrade

• Recognizethatarchaeologistsneedtounderstandhowexcavationsitesformed

• Recognizethatstratigraphyexamineslayers;describechronology:deeperisolder

• Recognizethatgeologicalprocessescreatedtherockshelter

• Recognizethatthestratigraphyismadeupofsedimentsdepositedbyerosion

• Recognizethatarchaeologistsusedgeologytounderstandtheexcavationsite


MajorTermsandConceptsScatteredthroughoutthecurriculumguideandGigaPanexplorationaretermshighlightedinbold.Theseincludekeyvocabularyterms,concepts,anditemsofsignificance.Teacherscanincorporatethetermsinvocabularyandspellinglists

Terms Concepts IdentificationSignificanceGeoarchaeologyGeomorphologyGeologyMatrixSedimentaryLithologiesShaleSandstoneLimestoneDepositionTributaryStrata

LandformsintheOhiodrainageAncestralOhioRiverdrainageGeologicTimeChartGeologicMapPhysiographicRegionsLithologiesandGeologicDatingRockshelterFormationandlifecycleStratigraphyandtheLawofSuperposition

AppalachianSeaAlleghenyMountainsAppalachianAlleghenyPlateauAppalachianMountainsAppalachianBasinEasternContinentalDivideOhioRiverCrossCreekAtlanticOceanCasselmanformation(UpperConemaugh)PennsylvanianPeriodMonongahela-BeaverRiverSystemTeays-MahometRiverSystem


GeologyoftheMeadowcroftRockshelterandtheCrossCreekDrainageAdaptedfromD.BenyonandJ.Donahue,“TheGeologyandGeomorphologyofMeadowcroftRockshelterandtheCrossCreekDrainage,”inMeadowcroft:CollectedPapersontheArchaeologyofMeadowcroftRockshelterandtheCrossCreekDrainage,editedbyR.C.CarlisleandJ.M.Adovasio,31-51.47thAnnualMeetingoftheSocietyForAmericanArchaeology,Minneapolis,Minnesota,April1982.

Frompriorexperiencewithclosed-siteexcavations,Dr.AdovasiorecognizedthatMeadowcroftRockshelterwastheidealsiteforapplyinggeoarchaeologicalmethodologies.Geoarchaeologyisamulti-disciplinaryapproachthatusesthetechniquesandsubjectmatterofgeography,geology,andotherearthsciencestoexaminetopicswhichinformarchaeologicalknowledge.Generally,geoarchaeologyinvolvesstudiesofthenaturalprocessesthatimpacttheareainandaroundanarchaeologicalsite.Amajorbranchofgeoarchaeologyisgeomorphology,thestudyofhowsitesformedthroughgeologicalprocessesandthesubsequentimpactofthoseprocessesonculturalmaterialsburiedwithinthesites.

Dr.Adovasio’steamsneededafirmgrasponthesite’sgeomorphologyiftheyweretosuccessfullyinformthearchaeologicalprocess.TheirfirsttaskwastounderstandtheevolutionofthelandscapesotheycoulddeterminehowandwhentheRockshelterformed.ThisinformationwouldindicatewhentheRocksheltermighthavefirstbeenavailableforhumanuse.Secondly,geomorphologywouldexplainhowthestratigraphyofthesiteformed,includingthecompositionofthematrix,depositionalmode,force,andrate.Thisevidencewouldhelparchaeologistsanticipatehowlongpeoplehadusedthesite,butalsoanygeologiceventsthatmayhavetransportedculturalmaterials.

Geography,GeologicOrigins,andPhysiographyTounderstandtheformationofMeadowcroftRockshelter,geomorphologistsfirstlookedtothephysicalgeography(physiography)ofthesite.Geologically,MeadowcroftRockshelterislocatedontheunglaciatedportionoftheAppalachianorAlleghenyPlateau,westofthevalleyand

GeologicTimeScalesandGeologicMaps

Geologistsstudytheearthanditshistorythroughthenaturalfeaturesoftheplanet.Theevidencegeologistsstudyisinrocksandlandforms.Likearchaeologistsstudyingartifacts,geologistslookforpatternsthattellthemaboutthepassageoftime.Generally,geologiststalkaboutverylargeamountsoftimesincetheearthisapproximately4.5billionyearsold.

Geologistsusespecificwordstorefertothepassageoftime.Theyseparatethesehugeamountsoftimeintosmallerdivisionsandrefertothedivisionsbyname,similartothewaythatarchaeologistsuseculturalperiods.Thepassageofgeologictimecanbeexplainedusingageologictimechart.Similarlyageologicmapshowstheageandtypeofbedrockclosesttothesurface.GeologicMapsfortheregionofPennsylvaniawhereMeadowcroftRockshelterislocateddemonstratethatthebedrockdatestothePennsylvanianPeriod(299-318millionyears).GeologicTimecanhelpusunderstandanddescribewhathappenedatMeadowcroftbeforepeoplearrivedatthesite.


ridgeprovinceoftheAppalachianMountains,andnorthwestoftheAppalachianBasin.ThisunglaciatedsouthernportionoftheAppalachianAlleghenyPlateauisdrainedbythewestwardflowing

OhioRiverwatershed,ofwhichCrossCreekisasmalltributary.ThesurfacerocksofthisregionarelayeredsedimentaryrocksofMiddletoUpperPennsylvaniaAge(CasselmanFormation),299to359millionyearsold.Thepredominantlithologiesareshale,quartz,sandstone,limestone,andcoalindecreasingorderofabundance.

MeadowcroftRockshelteritselfisformedbeneathacliffofMorgantown-Connellsvillesandstone,athickfluvialorchannelsandstonewithintheCasselmanformation(UpperConemaugh)(SeeFigure1),datingtothePennsylvanianPeriod.Itisanimmaturesandstonecomposedpredominantlyofquartzgrains

withminoramountsofmica,feldspar,androckfragments.TherockunderlyingtheMorgantown-Connellsvillesandstoneisalessresistantlithology,mostlikelyshale.ThesandstoneandshalethatmakeuptheRockshelterformationbeganasalluvialdepositsontheshiftingplainoftheAppalachianSeasome299to359millionyearsagoduringtheCarboniferousPennsylvanianPeriodofthePaleozoicEra.Thesandstonewasdepositedastwo

superimposedsandbar(orpoint-bar)sequences.Therockwithineachsequencechangesfromcross-bedded,coarse-grainedsandstonetolaminated,fine-grainedsandstone.ThecliffabovetheRockshelteris72.2feethigh,withthesandstonedecreasinginthicknessalongtheCrossCreekvalleybothtotheeastandwest;ithasitsmaximumthicknessattheRockshelter.

EmergenceofWesternPennsylvaniaLandforms

Between251millionand299millionyearsago,thecontinentofAfricaslammedintoNorthAmerica,creatingthesuper-continentPangea.Thecollisionputtheeasternseaboardundertremendousstress,formingtheAlleghenyMountainsinaneventknownastheAlleghenyOrogeny.ThiseventpushedthelandofwesternPennsylvaniatoitshighestelevationandinitiatedalongperiodoferosion(250millionyearsandcounting)thathasproducedthelandscapethatweseetoday.MostofthiserosionhappenedduringtheMesozoicEra(66millionto251millionyearsago).

DuringtheTertiaryPeriod(1.8to66millionyearsago)geologiceventscausedPennsylvania’swatersystemstotaketheirpresentform.ThewatershedseastoftheEasternContinentaldivide(suchastheSusquehanna,PotomacandJamesrivers)flowedtotheAtlanticOcean,whilethosewestofthedivide(includingtheancestralOhio)generallycutacrosstheAppalachianAlleghenyPlateautowardthecenterofthecontinent.

Figure1SketchofMorgantown-ConnellsvillesandstoneatMeadowcroftRocksheltershowingthechangeinsedimentarystructureandgrainsizethroughthetwopoint-barsequences(ImagefromCollectedPapers:1982,5.).


Earlyinthispre-glacialperiod,thePlateaudrainagewassignificantlydifferentthanthatseentoday.TopographicreliefwasloweranddrainageflowednorthandnorthwesttotheareathatwouldlaterbeoccupiedbytheGreatLakes.TwoprimaryriversystemsdrainedtheAppalachianPlateau:theMonongahela-Beaver(Figure2)flowednorthtowardtheLakeErieBasin,whiletheTeays-MahometRiverflowedfromVirginiaintoWestVirginiaandnorthwardintoCentralOhio,Indiana,andIllinois.Atthistime,CrossCreekwasatributaryofthenorth-flowingOhio,which,withtheLowerAllegheny,wasatributaryoftheMonongahela-Beaver(UpperOhio).

StratigraphyandGeologicEvidence

Landscapesarebuiltinlayers;eachlayerisarecordofindividualgeologiceventsthatoccurredatsomepointinthepast.Theselayersarereferredtoasstrataandtheyarestudiedthroughstratigraphy.

Stratigraphyisageologythatdealswiththeorigin,composition,distribution,andsuccessionofstrata.TheLawofSuperpositionillustratesabasicprincipleofstratigraphy:layersthataredepositedfirstareoldest,whilelayersonthesurfacearenewest.

GeologistsusetheLawofSuperpositiontointerpretlandscapes;theystudyoutcroppingsandcoresamplestounderstandthesequenceofgeologicevents.Generally,therocksatthelowestpointofaformationareoldest,whiletheuppermostrocksarenewest.

Theappearanceoftherocksoftenrevealshowtheyformed;inPennsylvania,themostcommonrocksaresedimentary.Sedimentaryrocksareformedfromsmallsediments(sandgravelorclay)thathavebecomenaturallycementedtogether.Sandstoneconsistsofvisiblelayersofhardenedsand.Shaleconsistsoflayersthatspliteasilybecausetheyaresimplyhardenedlayersofclayormud.Limestoneisasedimentaryrockthatformedfromcalciumandmagnesiumcarbonatesthatwereproducedbyancientorganismsinthesea.Thesesedimentaryrockscanalsocontainfossilevidencethatcanbeusedtointerpretlifeataperiodwhenthesedimentsintherockswerenotyetcementedtogether.

Inasense,sedimentaryrocksandrockformationsarelikemini-archaeologicalsites:theyarecomposedoflayersthatcontainevidenceofearlierlifeandevents.Inshort,stratigraphyisatoolforinvestigatingsequences,betheygeologicalorcultural.


FormationofMeadowcroftRockshelter

Geomorphologistsstudychangesintheformationoftheland;oncelandisbuiltup(inthecaseofMeadowcroft,ithappenedwiththeAlleghenyOrogeny),itbeginstoerode.Muchoftheerosionoccursasbodiesofwaterdowncutthroughearlierformations.TounderstandhowandwhentheRockshelterformed,specialistslookedatthesize,shape,age,andcompositionoflandformssuchasterracesandfloodplains,remnantsoflakes,andsedimentinvalleysoftheCross-Creekwatershed.Theyusedthisdatatoreconstructthepaleo-topographyoftheCrossCreekdrainage.BycorrelatingthelandformsoftheCrossCreekvalleywiththoseoftheGreaterOhiowatershed,theycouldcreateaveryprecisesequenceforthedevelopmentoftheCrossCreekandtheMeadowcroftRockshelter.TheydiscoveredthatglacialepisodesduringthePleistocene(1.8millionyearsago,endingwithinthepast12,000years)

triggeredgeologicprocessesthatshapedthemodernOhiowatershedandcarvedMeadowcroftRockshelter.

DuringthePre-IllinoisanPeriod(AandBinFigure3),CrossCreekformedabroadterraceboundedbyasteeperascendingslopeasitflowednorthwesttotheOhioRiver.GlacialadvanceseventuallystoppedthenorthernflowoftheMon-Beaver,whichpondedformingLakeMonongahela.Duringthisperiod,allvalleysinthesystemponded;manyoftheterracesseenintheCrossCreekvalleyareevidenceofthisevent.Thelakegraduallyincreasedinvolume(twice)untiliteventuallybreachedadivideatNewMartinsville,WV,causingtheUpperOhiotojointheLowerOhio(Teays-Mahomet)inflowingtowardtheMississippi.Theoutpouringofwaterfromthelakeresultedinrapiddowncuttingthroughoutthesystem;atMeadowcroft,thiscreatedaconstrictedvalleythroughtheCasselmanformation.

WiththeIllinoisanGlacialAdvance(CinFigure3),theOhioandCrossCreekfilledwithalluvialdepositstoadepthof100feet(approximatelytheroofleveloftheRocksheltertoday).Duringtheinterglacialperiod,

Figure2Pre-glacialMonongahela-BeaverDrainage(ImageFromCollectedPapers:1982,34).

Figure3FormationofMeadowcroftRockshelter(ImageFrom:Meadowcroft:CollectedPapersontheArchaeologyofMeadowcroftRockshelterandtheCrossCreekDrainage

of19FirstPeoples:ArchaeologyatMeadowcroftRockshelterTeacher’sGuidetoGeology

streamactionfromCrossCreekcutthroughthefill.ThescouringactioncutbackintothehillsideundertheMorgantown-Connellsvillesandstoneandformedare-entrant,orrockshelter,overshalebedrock.ThesandstonethenremainedasarooftotheRockshelter,withthecreekflowingthroughit.

DuringtheEarlyMiddleWisconsinanGlacialAdvance(21,000-31,000yearsago),aperiodofquietwaterdepositionresultedinafine,siltyblueclayonthefloorortheRockshelter(DinFigure3).ThisfloorwouldeventuallyserveasStrata1duringthearchaeologicalinvestigationoftheRockshelter.Withthefinalglacialadvance(Wisconsinan,21,300YBP),CrossCreekcutafinalterracethroughthevalley,roughlycorrespondingtothemodernfloodplainofthecreek,10-30feetabovethepresentstreamlevel(EinFigure3).Gradually,thecreekentrenchedfurther.By11,000YBP,theMeadowcroftRockshelterstoodhigh,safe,anddryabovethefloodplainofCrossCreek(FinFigure3),anidealcampsiteforanyhumanswalkingpast.

FormationofMeadowcroftStratigraphy

Fromthestart,Dr.AdovasiorecognizedthattheRockshelteronthecliffsoftheCrossCreekwasanidealsiteforanexcavationbecauseitwasaclosedsite,arockshelter.Rocksheltersareoftenlocatedabovethepathofmovingwaterandtheyareprotectedfromwind.Generally,theroof-likestructureofarockshelterprotectstheunderlyinglandscapefromoutsideforces.Atopen-airarchaeologicalsites,alluvialdepositionfrombodiesofwaterandaeoliandepositionfromthewind,cancauselargeamountsofsedimenttoburyanddrasticallymoveculturalartifacts.Insomecases,alluvialandaeolianforcescancompletelyscramblethestratigraphyofasite.Bycontrast,atarockshelter,thestratigraphyisgenerallyintactbecauseithasnotbeenacteduponbyoutsideforces.Anyculturalmaterialsdepositedinthelayersunderarockshelteraregenerallyundisturbedbyhumanorgeologicalforcesuntiltheyareexcavatedbyanarchaeologicalteam.

Dr.AdovasioalsoacknowledgedthatMeadowcroftRockshelterwouldchallengeeventhemostpracticedclosed-sitegeoarchaeologists.Despitetheprotection,rocksheltersoftenhavecomplicatedgeologicandsedimentologichistoriesbecauseerosionandattritionareconstantlyatworkintheseenvironments.Essentially,theformationofarockshelterisalsothestartofitsdemise:erosionshapestheinitiallandformandattritionanderosionultimatelywearitdown.Thesegeologicprocessesdepositnumerouslayersofmaterialsonthefloorofrockshelters.Greatattentiontodetail,requiringpainstakingexcavationanddocumentationisessentialforsiftingthroughthenumerouslayersinsidethesesites.TocompoundmattersatMeadowcroft,evidenceofroofspallsinthedistantpastindicatedthattheshelterwasoriginallymuchlarger.Alargersheltersuggestedahigherprobabilityoflong-termculturalsiteuse,butthespallsindicatedthattheexcavationcrewwouldconstantlyencounterrocks(somethesizeofvehicles)astheydug.Onceagain,thearchaeologicalteamappliedgeomorphologytothestudyoftherockshelter,thistimefocusingtheireffortonstratigraphy.


Methodology

Geomorphologistsusedfourmethodstostudythestratigraphy.Eachmethodappliedadifferentsamplingtechniquetodeterminethesource,mode,andcompositionofsediments.Thefirstsamplingmethodcollectedstratigraphicsedimentcolumns(orcores)fromallmajorareasofthesitefromeasttowestandnorth(inside)tosouth(outside)ofthedripline.Tocollectthecores,geomorphologistscutverticallyfromthesurfaceofthesitethroughallstratatoculturallysterileStratumI.Thesampleswerethenanalyzedforcompositionandorigin.

GeomorphologistswerealsointerestedinestablishingthemodernratesofsedimentationattheRockshelter.Theyplacedasamplingtrayontheroofoftheexcavationenclosurebutundertherockoverhangbeginningin1974andcontinuinguntil1978.Theroofwassweptdailytocollectthefragmentsdroppingfromtheceiling(colluvium)andwalloftheRockshelter.Thisproceduredemonstratedthesedimentationmechanismsandrateofaccumulationimpactingthesite.

Third,geomorphologistsgaugedtheeffectsofsheetwashfromuplandsourcesofthesitebyplacingalargeholdingtankanddrainagesystemontheeasternmarginoftheRockshelterin1976.Thetanktrappedallsedimentandwatermovingacrosstheroofduringrainstorms.TheproceduredemonstratedthekindandvolumeofuplandmaterialstransportedduringrainstormsandanothermethodforstudyingtheaccumulationoftheMeadowcroftColluvialpile.

Last,thegeomorphologistsextractedacolumnofrocksamplesfromthebasetothetopoftheMorgantown-Connellsvillecliffat20-50cm(ca.8-20inch)intervalstocomparethegrainsizeandcompositionoftheclifffacetosamplesfromroofspallsthecolluvialpile.ThecomparisonspermittedthestudyofthepatternsoferosionoftheRockshelterface.

SourcesandModeofSediments

Duringtheexcavation,archaeologistscoulddifferentiatebetweenthestratigraphiclayersbasedonthecolor,composition,andtexture,amongotherfactors.Theyfoundelevenmajorstratigraphiclayerswithinthesite.

Fieldexaminationbygeomorphologistsandlaboratoryanalysisofsamplesindicatethatthesedimentsthatmakeupthestratigraphyhavefoursources:1)thesiltyclayofStratumIwhichwasdepositedontheshaleflooroftheRockshelterduringaperiodofquietwaterdeposition,2)rockfallfromtheMorgantown-Connellsvillecliffrangingfromgranulestolargeboulders,3)grain-by-grainattritionfromthesandstonecliff,and4)sheetwashfromuplandsourcesduringrainstorms.Thefine,bluesiltyclaylocatedinStratumIistheonlyevidenceofstreamorlakedepositsunderneaththeRockshelter.Allothersedimentderivesfromerosion.Essentially,thestratigraphyisacolluvialpileunderthesandstonecliff.Colluviumresultswhensedimentmovesdownslopeandpilesup.Thesedepositslieflat,formingsmoothinterfacesbetweenstrata.


ThesinglemostimportantfactorcontrollingthemodeandrateofsedimentationthatcomposesthestratigraphyistheevolutionoftheRockshelteritself.ThephysicalchangesintheCrossCreekvalleyandtheconfigurationoftheRockshelterdeterminesedimentationstyle.Climaticvariationimpactstherateofsedimentation,butthegeologicalforcesatplayaroundandintheRockshelterarewhatcreatesthesedimentation.Forinstance,theceilingoftheRockshelterisgraduallymigratingupwardandcliff-wardaserosionoccursbothontheRockshelterceilingandthecliffface.Thefreezing,thawing,andmovementofwaterandthepenetrationofrootsincracksintheMorgantown-Connellsvillesandstoneoverhangtriggerperiodicrooffalls.Therateoffallisincreasedbyhigheramountsofrainfallandlowertemperatures,butthedecayoftherockitselfiswhatcausessedimenttoentertheRockshelter.ThetimingoftheOldRoofFall(ca.14,900YBP)andtheNewRoofFall(betweenca.1290and1665YBP)aretriggeredbygradualenlargementoffracturesinthesandstoneoverhangtoapointwheretheblockswerenolongerstableandfell.Allrocksheltersexperiencethiscyclicalprocess;itisinevitablethatsomeday,thousandsofyearsfromnow,theremainingoverhangoftheMeadowcroftRocksheltertoowillfall.However,thecurrentenclosureandconservationeffortsbyMeadowcroftMuseumhavegreatlyslowedtheprocessandensurethesafetyofthesiteandvisitorsformanyyearstocome.


Tables

AncientGeologicalActivityatMeadowcroftRockshelterYearsAgo

EraorEon

Period Epoch ActivityaffectingPennsylvania

TypesofRockorDeposits

ActivityAffectingtheCrossCreekDrainage

0to1.8million

CenozoicEra

Quaternary Holocene Wearehere!

Pleistocene Glaciation Sand,Silt,Clay,Gravel

OverthousandsofyearsCrossCreekcutsthroughtheMorgantown-ConnellsvillesandstonetoformtheRockshelter.ThefirstPeoplearrive.

1.8millionto66million

Tertiary Weathering&Erosion;creationofpresentlandscape

Sand,silt,gravel

Systemofrivers,creeks,andrivuletsthatdrainwaterfromPennsylvaniatodayareinplace.TheOhio(andCrossCreek)andLowerAlleghenyriversaretributariesoftheMonongahela-BeaverdrainagenetworkwhichflowsnorthtotheLakeErieBasin.

66millionto146million

MesozoicEra

Cretaceous SeparationofNorthAmericafromAfricaastheAtlanticOceanOpens;IntenseErosionandWeathering

Clay,sand


Jurassic Diabase


Triassic Shale,Sandstone,Diabase


PaleozoicEra

Permian AlleghenyOrogenychangesPennsylvaniafromadepositionalbasinreceivingsedimenttoanareaabovesealevelthathas

Sandstone,shale


beenerodingeversince.


PennsylvanianandMississippian(Carboniferous)

AlluvialdepositionasAppalachianbasinretreatseast-ward

Sandstone,siltstone,shale,coal,limestone

AlluvialsedimentsaredepositedastheshorelineoftheAppalachianSeamigrates.ThesesedimentswillformthesandstonerockformationthatbecomesMeadowcroftRockshelter.Formationoftheregion’sgreatcoalseamsasthealluvialplainshifts,buryingcarbon-richpeatthatwillbecomecoal.

PleistoceneGeologicalActivityintheCrossCreekDrainage:FormationoftheMeadowcroftRockshelterPeriod Activityaffectingthe

OhiodrainageImpactonCrossCreekdrainage

ImpactonRockshelter

WisconsinanGlacialPeriod

LateWisconsinan

TheOhioexperiencesafinalglacialoutwash.

CrossCreekformsalowterrace10-30feetabovemodernstreamlevel,10-20feetbelowthetopofStratumI.

Therockshelterisavailableforhumanoccupationandsits“highanddry”abovethehigh-waterlevelofCrossCreek.(21,300YBP)

EarlyMiddleWisconsinan(21,000-31,000yearsago)

StreamsdrainingtheglaciersintroducemeltwaterandsedimentintotheOhio.

CrossCreekfurthererodesthevalleyanddepositsfinesiltyblueclayduringaperiodofquietwaterdeposition,followedbyactivedowncutting.

Thesilty-blueclayisdepositedonthefloorofthere-entrant(thiswillbecomeStrataIoftheRockshelterexcavation).AfterwardstheRockshelterenlargesandisneveragainexposedtofluvialdeposition.

SangamonInterglacialPeriod CrossCreekdowncutstheIllinoisanalluvialfillbelowthepresentchannel,undercuttingtheshalebeneaththe

Downcuttinginitiatesare-entrantbeneaththeMorgantown-Sandstonecliff.


Morgantown-Connellsvillesandstone.

IllinoisanGlacialPeriod ExtensiveGlacialsedimentfillspartsoftheOhiovalleyto100feetindepth.valleyelevationsincrease(aggradation)andnortherndrainingstreamspondwhenglacialdepositsblockstreams.

CrossCreekfillsitsvalleywithalluvialsediment(seenatareasabout100feetabovethecurrentstreamlevelandjustabovethemoderncliffoverhangatMeadowcroftRockshelter).Thestreamgradientincreasesto10.5feetpermile.

TheCrossCreekvalleycontinuestoerodeinadeepVshape.Alluvialsedimentfillsthebottomofthevalleytoadepthof100feet.

Pre-Illinoisan

Theglaciationperiodspromotetheunificationofpre-glaciallydistinctriversystemsdrainingtheAppalachianPlateau,unitingthemintheOhioRiver.Inthesouth,theTeays-Mahomet(LowerandMiddleOhioRivers)systemdivertssouthwesttowardtheMississippi.IceblocksthenorthflowingMonongahela-Beaver(UpperOhio),causingthesystemandalltributariestoponduntilthewatersriseenoughtobreachthedivideatnewMartinsville,WV.Asuccessiveglacialadvancerecreatesthepondingeffect,thistimewhenthewaterbreachestheNewMartinsvilledivide,itcreatesapermanentoutletforthesystem,unifyingtheUpperOhiowiththeMiddleandLowerOhiorivers.DuringtheLatePre-Illinoisanperiod,thenewlyformedOhioRiverentrenches,creatingadeepbedrockvalleysimilartothatseentoday.

DuringtheearlyPre-Illinoisan,CrossCreekcreatesabroadterracewithalowgradientof8.9feetpermile.DuringtheformationofLakeMonongahelaIandII,CrossCreekponds,evidencedinterracesinthedrainagesystem.EventuallyCrossCreekflowsinamoreconstrictedvalleywithanincreasinggradienttowardtheOhio.BythelatePre-Illinoisan,CrossCreekflowsinadeepvalleycausingextensivedowncuttingthroughtheCasselmanFormation.

CrossCreekendsthePre-IllinoisanasadeepV-shapedvalleywiththecreekactivelydowncuttingthroughtheCasselmanFormation.Thisdowncuttingshapesthelandwheretherockshelterwillbe.


Pre-Pleistocene TopographyofwesternPAisloweranddrainageoftheAppalachianPlateauregionflowsnorthandnorthwesttowardbasinsthatwillbecometheGreatLakes.TheOhioRiverdoesnotexist;twootherriversystemsdraintheplateau.TheTeays-MahometRiverflowsfromPiedmontVirginiatoWestVirginiaandnorthwardintoCentralOhio,Indiana,andIllinois.TheMonongahela-Beaverdrainagenetwork(includingtheOhioandlowerAlleghenyastributaries)flowsnorthtowhatisnowtheLakeErieBasin.

CrossCreekisatributaryofthenorthflowingUpperOhioRiver.CrossCreekvalleyexistsatahighelevationandiswideandgentlysloping.

StratigraphicProfileofMeadowcroftRockshelterStrata Tag Varying

ThicknessDepositionMode Deposition

ForcesDepositionRate

XI f3,f8 12-15cm Sheetwash 925yearsX f25 1-5cm Siltyclay SheetwashIX f9 5-15cm Siltyclay SheetwashVIII f12 .5-5cm Largeparticles,

sandSheetwash

VII f13 20-40cm Sandyloam Sheetwash,Spalling

365years

VI f63,f129

60-140cm Siltyclay Spalling,Sheetwash

375years

V f14 20-40cm Sandyloam Sheetwash,Attrition

625years

IV f16 30-70cm Sandyloam Sheetwash,Attrition

760years

III f18 30-110cm Siltyclay Attrition,Sheetwash,Spalls

200years

IIb f46 40-130cm SandandSilt AttritionandHighSpall

4,700years

IIaupper F46 Sandandsilt AttritionandHighSpall

13,000years


IIamiddle f46 Sandandsilt AttritionandHighSpall

IIalower f46 Sandandsilt AttritionandHighSpall

I/II f85 Finebluesilt Quietwater *1 F99 bedrock Birminghamshale

(300MillionYearsOld)

swamp *

GeologicTimeasRelatedtoMeadowcroftEraorEon Period Epoch YearsAgo(Approximate)Cenozoic Quaternary Holocene 11,000yearsagoto

presentPleistocene LateWisconsinanGlacial

Advance25,000to11,000yearsago

EarlyMiddleWisconsinanGlacialAdvance

75,000to25,000yearsago

SangamonInterglacial 125,000-75,000yearsagoIllinoianGlacialAdvance 300,000to125,000years

agoPre-IllinoianPeriods(YarmouthInterglacial,KansanGlacialAdvance,NebraskanGlacialAdvance)

425,000to2.5millionyearsago

Mesozoic

Paleozoic PennsylvanianandMississippian(Carboniferous)

299to359millionyearsago


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