ThetransitionfromtheEocenetotheOligoceneepochsfromapproximately47to27millionyears ago was one of the most dramaticepisodes of climaticand biotic changesince the demise ofthedinosaurs.ThemildtropicalclimatesofthePaleoceneandearlyEocenewerereplacedbymodernclimaticconditionsandextremes, includingglacialice in Antarctica.The bestterrestrialrecordoftheEocene-OligocenetransitionisfoundinNorthAmerica,includingthespectacularcliffsand spires of Big Badlands National Park in South Dakota.ThefirstpartofthebooksummarizesthelatestinformationindatingandcorrelationofthestrataoflatemiddleEocenethroughearlyOligoceneageinNorthAmerica,includingthelatestinsightsfromargon/argondatingandmagneticstratigraphy.Thesecondpartreviewsalmostalltheimportantterrestrialreptilesandmammalsfoundnearthe Eocene-OligoceneboundaryintheWhiteRiverChronofauna,fromtheturtles,snakes,andlizards,tothecommonrodents,carnivores, artiodactyls, and perissodactyls.Thisisthefirstcomprehensivetreatmentoftheserocksandfossilsinoversixtyyears.TheTerrestrialEocene-OligoceneTransitioninNorthAmericawillbeaninvaluableresourcetovertebratepaleontologists,geologists, mammologists,and evolutionarybiologists.MorrisF. Skinner in the Big BadlandsofSouthDakota duringthe1950s.(Photo courtesyMarieSkinner).Morris F. Skinner1906-1989Our present understandingoftheWhiteRiverGroupanditsfossilswouldneverhavebeenpossiblewithouttheenormouscontributionsofMorrisSkinner.AlthoughhewasoriginallyhiredbyChildsFrickin1927tocollectlateCenozoicmammalsofwesternNorthAmerica,hespentmuchtimein the WhiteRiverGroupaswell.Beginningin1938and continuingthroughthe1940sand1950s,Skinnermadelarge,stratigraphicallyzonedcollectionsfromtheBigBadlandsofSouthDakota.In the1950sand1960s, hemadesomeofthemostimportantcollectionsfromWhiteRiveroutcropsin Wyoming,Nebraska,and NorthDakotaaswell.Unlikemanycollectors,however,Morriswasadedicatedgeologistandstratigrapher.Hemeasuredhundredsofstratigraphicsections,andmadesurethateveryspecimenheandhisfieldpartiescollectedhadthebestpossiblestratigraphicinformation.Thus,theFrickWhiteRivercollectionsmade bySkinnerandpartieshavethebestbiostratigraphicdataavailable(frequentlyzonedtothenearestfootfrommarker ashes), allowingthe firstdetailed range-zonebiostratigraphyafter150yearsofstudyintheWhiteRiverGroup.MostofthesystematicpaleontologicalstudiesinthisvolumearebasedlargelyontheFrickCollections,andtheir insightswouldnot bepossiblewithoutthe excellentstratigraphicdata providedbySkinnerandcrew.Skinnerwasmorethanoneofthebestfossilcollectorsofthiscentury,however.Hewasalsoanexcellentfieldgeologist,andhismanyinsightsintoWhiteRiverstratigraphywerelargelyunappreciatedbecausetheyremainedinhisfieldnotebooks,unpublished.OnlyhisbriefsummaryoftheNorthDakotasequence(Skinner,1951)waspublishedinhislifetime,buthiscontributionstothestratigraphyofWhiteRiverdepositsatFlagstaffRim(Emry,1992)and the LuskandDouglasareasofeasternWyoming(seeEvanoffetal.,1992;partiallysummarizedinthisvolume,Chapter13,andProtheroandWhittlesey,inpress),havebeenthebasisofmanylaterpublicationsbyothers.Forexample,SkinnerrecognizedthatthedivisionsoftheChadronFormationusedbyhiscontemporarieswereinadequate,anddescribedalatestChadronianunithecalledthe"TrunkButteMember."Thisconceptwasrevived30 yearslaterastheBigCottonwoodCreekMemberoftheChadronFormation(Terryetal.,1995).Asearlyas1953, Skinner collectedbrontotherebonesfromBruleFormationequivalents(seeProtheroandWhittlesey,inpress),andrecognizedthattheclassicdefinitionsoftheChadronianandOrellanneededrevision.This,too,isfinallyoccurring40yearsafterSkinner'sinsight.Basedonhisknowledgeofbiostratigraphy,SkinnerrealizedthattheChadronianandearliestOrellanwerepoorlyrepresentedintheBigBadlands,butmuchthickerandmorecompletelyexposedineasternWyoming.ThishasmajorimplicationsforinterpretationsoftheChadronianorOrellanbasedonthelesscompleteBigBadlandssequence(e.g.,Clarketal.,1967;Retallack,1983).Skinner'sstratigraphicconceptsabout the WhiteRiverGrouponlyreachedprintasanillustrationinMellett(1977,fig.71,pp.128-129).HisprofoundunderstandingofWhiteRiverstratigraphyand paleontologyisfinallybeingappreciated.AttheWhiteRiverGroupsymposiumheldattheNorthCentral-SouthCentralsectionmeetingoftheGeologicalSocietyofAmericain Lincoln, Nebraska,onApril27,1995,theprevailingrefrainfromthespeakersandalltheir"new" researchwas, "MorrisSkinner knewthis yearsago!"Muchofthe bestscienceinthisbookrepresentsMorrisSkinner'scollectionsorideasfinallyseeingpublication.It isappropriatethat it bededicatedto hismemory.TheTerrestrialEocene-OligoceneTransitioninNorthAmericaTheTerrestrialEocene-OligoceneTransitioninNorthAmericaEdited byDONALD R.PROTHEROOccidental CollegeROBERT J. EMRYSmithsonianInstitutionCAMBRIDGEUNIVERSITYPRESSCAMBRIDGE UNIVERSITY PRESSCambridge, New York, Melbourne, Madrid, Cape Town, Singapore, Sao PauloCambridge University PressThe Edinburgh Building, Cambridge CB2 2RU, UKPublishedin the UnitedStates of America by Cambridge University Press, New Yorkwww.cambridge.orgInformationon this title:www.cambridge.org/9780521433877 Cambridge University Press1996This publicationis in copyright.Subject to statutoryexceptionand to the provisionsof relevant collective licensingagreements,no reproductionof any part may take placewithoutthe written permissionof Cambridge University Press.First published1996This digitally printedfirst paperback version2005A cataloguerecord forthis publicationis availablefromthe BritishLibraryLibraryofCongressCataloguingin PublicationdataThe terrestrial Eocene-Oligocenetransitionin North America / editedby Donald R. Prothero, Robert J. Emry.p.cm.Includes bibliographical referencesand index.ISBN 0-521-43387-8(he)1. Eocene-Oligoceneboundary North America.2. Geology,Stratigraphic.3. Geology North America.4. Paleontology,Stratigraphic.5. Paleontology -North America.I. Prothero,Donald R.II. Emry, Robert J.QE692.8.T471996551.7' 84-dc2095-40903CIPISBN-13978-0-521-43387-7hardbackISBN-100-521-43387-8hardbackISBN-13978-0-521-02109-8paperbackISBN-100-521-02109-XpaperbackThe original hardback volume was prepared by Donald Protheroas camera-readycopy on an AppleMacintoshQuadra 630 using MicrosoftWord 6.0, and printed on a 800 dpi laserprinter.All layoutsand paste-ups were done by Prothero.Front cover caption: The strata of the Big Badlands of South Dakota preserve one of the best terrestrialrecordsofterrestrialEocene-OligocenetransitioninNorthAmerica.ThisrenditionisfromHenryFairfieldOsborn's1929titanotheremonograph,showingtheupperEoceneChadronFormationoverlain by the lower Oligocene Brule Formation.Superimposed on this figureare side views oftheskulls of three of the most common oreodonts fromthe Eocene-Oligocene transition (from bottom totop):themiddleChadronianMerycoidodonpresidioensis,thelateChadronianearlyOrellanMerycoidodonculbertsoni,and the late Orellan Merycoidodonbullatus (fromStevens and Stevens, thisvolume, Chapter 25).CONTENTSContributorsixPrefacexiPARTI:TheChronostratigraphyoftheUintanthroughArikareean1.D.R.Prothero:Magnetic stratigraphyand biostratigraphyofthe middle Eocene Uinta Formation, UintaBasin,Utah32.S. M. McCarroll,J. J. Flynn, andW. D. Turnbull:Biostratigraphyand magnetostratigraphyoftheBridgerian-Uintan Washakie Formation, Washakie Basin, Wyoming253.R. K. Stucky, D.R. Prothero,W. G. Lohr, andJ.R. Snyder:Magneticstratigraphy, sedimentology, andmammalian faunasof the early Uintan Washakie Formation, Sand Wash Basin, northwestern Colorado404. S. L.Walsh:Theoreticalbiochronology, the Bridgerian-Uintanboundaryand the "ShoshonianSubage" oftheUintan525.S. L.Walsh: MiddleEocene mammalianfaunasofSan Diego County, California756.S. L.Walsh, D. R. Prothero, and D. J.Lundquist.Stratigraphyand paleomagnetismofthe middle EoceneFriarsFormationand Poway Group, southwesternSan Diego County, California1207.D.R.Prothero and E. H.Vance, Jr.: Magnetostratigraphyof the upper middle Eocene ColdwaterSandstone,centralVentura County, California1558.D.R.Prothero, J. L. Howard, and T. H. H. Dozier:Stratigraphyand paleomagnetismofthe upper middleEocene to lower Miocene (Uintan to Arikareean)Sespe Formation, Ventura County, California1719.D.R.Prothero:Magnetostratigraphyof the Eocene-Oligocenetransition in Trans-Pecos Texas18910.D. R. Prothero and S. G. Lucas:Magneticstratigraphyofthe Duchesneanpart ofthe Galisteo Formation, NewMexico19911.C.B.Hanson:Stratigraphy and vertebrate faunas of the Bridgerian-DuchesneanClarno Formation, north-centralOregon20612.J.E.Storer.Eocene-Oligocenefaunasof the Cypress Hills Formation, Saskatchewan24013.D.R.Prothero:Magneticstratigraphyofthe White RiverGroup in the HighPlains26214.A. R. Tabrum, D. R. Prothero, and D. Garcia: Magnetostratigraphyand biostratigraphyof the Eocene-Oligocenetransition, southwesternMontana27815.R. H. Tedford,J. B. Swinehart, C. C. Swisher HI,D.R. Prothero,S. A.King, andT. E. Tierney:TheWhitneyan-Arikareeantransition in the High Plains312vnPARTII;CommonVertebratesoftheWhiteRiverChronofauna16.J.H.Hutchison:Testudines33717.R. M.Sullivan and J. A.Holman:Squamata35418.T.H.Heaton:Ischyromyidae37319.R. J.Entry andW. W. Korth:Cylindrodontidae39920.X.-F.Xu:Castoridae41721.X.-M.Wangand R.H.Tedford: Canidae43322.H.N.Bryant.Nimravidae45323.R.M.Hunt,Jr.:Amphicyonidae47624.J. A.Baskinand R. H. Tedford: Small Arctoid and FeliformCamivorans48625.M. S. Stevensand J. B. Stevens:Merycoidodontinaeand Miniochoerinae49826.E. A.CoBabe:Leptaucheniinae57427.T.H.Heatonand R.J.Entry:Leptomerycidae58128.D.R.Prothero:Camelidae60929.D.R.Prothero:Hyracodontidae652D. R. Prothero and R. J. Entry:Summary664Index684Vl l lCONTRIBUTORSJon A.BaskinDepartment of GeologicalSciencesTexas A & I UniversityKingsville, TX78363Harold N.BryantMammalogyProgramProvincialMuseum of Alberta12845102nd AvenueEdmonton, Alberta T6G 2E9 CanadaEmilyA.CoBabeDepartment of GeologicalSciencesUniversityofMassachusettsAmherst,MA01003T.H.HuxleyDozierDepartment of GeologyOccidentalCollegeLos Angeles, CA90041-3392RobertJ.EmryDepartment ofPaleobiologyNHB-E207MRC121SmithsonianInstitutionWashington, DC20560JohnJ.FlynnDepartment of GeologyField Museum of NaturalHistoryRoosevelt Road at Lakeshore DriveChicago, IL60605-2496Daniel Garcia8252126th Avenue NE, D301Kirkland,WA98033C. Bruce Hanson5505 Sierra AvenueRichmond, CA94805TimothyH. HeatonDepartment of EarthSciencesUniversityofSouthDakotaVermilion,SD57069J. AlanHolmanThe MuseumMichiganStateUniversityEastLansing, MI48823JeffreyL. HowardDepartment of GeologyWayne State UniversityDetroit, MI48202RobertM.Hunt, Jr.VertebratePaleontologyW436 Nebraska HallUniversity of NebraskaLincoln, NE68588-0541J. HowardHutchisonMuseumofPaleontologyUniversity ofCaliforniaBerkeley, CA94720Steven A.KingDepartment ofGeologyOccidentalCollegeLos Angeles, CA90041-3392WilliamW. Korth928 WhalenPenfield,NY14526Walter G.LohrllDepartment ofGeologyOccidentalCollegeLos Angeles, CA90041-3392Spencer G.LucasNew Mexico Museum ofNaturalHistory1801 Mountain Road NWAlbuquerque, NM87104David J. LundquistDepartment ofGeologyOccidentalCollegeLos Angeles, CA90041-3392StevenM. McCarrollDepartment ofGeologyField Museum of NaturalHistoryRoosevelt Road at Lakeshore DriveChicago, IL60605-2496Donald R. ProtheroDepartment of GeologyOccidentalCollegeLos Angeles, CA90041-3392Jennifer SnyderDepartment of Earth SciencesDenver Museum of Natural History2001 Colorado BoulevardDenver, CO80205James B. StevensDepartment of GeologyLamar UniversityBox10031, LUStationBeaumont, TX77710Margaret S. StevensDepartment of GeologyLamar UniversityBox10031, LUStationBeaumont, TX77710John E. StorerRoyalSaskatchewan Museum2340 Albert StreetRegina, Saskatchewan S4P 3V7 CanadaRichard K. StuckyDepartment of Earth SciencesDenver Museum of Natural History2001 Colorado BoulevardDenver, CO80205RobertM.SullivanState Museum ofPennsylvaniaThird and North StreetsP.O. Box1026Harrisburg, PA17108-1026James B. SwinehartNebraska Conservation and Survey Division113 Nebraska HallUniversity of NebraskaLincoln, NE68588-0541Carl C. Swisher IIIBerkeley Geochronology Center2455 Ridge Rd.Berkeley, CA94709Alan R. TabrumSection of Vertebrate FossilsCarnegie Museum of Natural History4400 Forbes AvenuePittsburgh, PA15213-4080Richard H.TedfordDepartment of Vertebrate PaleontologyAmerican Museum of Natural HistoryCentralPark West at 79th St.New York, NY10024Timothy E. TierneyDepartment of GeologyOccidental CollegeLos Angeles, CA90041-3392WilliamD. TurnbullDepartment of GeologyField Museum of Natural HistoryRoosevelt Road at Lakeshore DriveChicago, IL60605-2496Edward H.Vance, Jr.Department of GeologyOccidental CollegeLos Angeles, CA90041-3392Steve WalshDepartment ofPaleontologyNatural History MuseumP.O. Box1390San Diego, CA92112Wang XiaomingDepartment of Vertebrate PaleontologyAmerican Museum of Natural HistoryCentral Park West at 79th StreetNew York, NY10024Xu XiaofengDepartment of GeologySouthern Methodist UniversityDallas, TX75275PREFACEThe transition from the Eocene to the Oligocene epochs(fromabout47to27millionyears ago)wasoneofthemost dramatic episodes of climatic and biotic change sincethedemiseofthedinosaurs.ThemildtropicalclimatesthatcharacterizedthePaleoceneandearlyEocenewerereplacedbythebeginningofmodernclimaticextremes,including glacial ice in Antarctica and modern deep-water oceanic circulation (summarized in Prothero,1994).Thesechanges were seen in plants and animals worldwide, both in the oceans and on land.Land floraschanged fromdenseforests(foundevenatpolar latitudes)toamixtureofwoodlandandscrubland.Thelandfaunasrespondedwithextinctionofmanyforest-dwellingandleaf-eatinganimals,andreplacementbysnails,reptiles,andmammalstolerant of drier conditions and the more open vegetation.The best terrestrial record of the Eocene-Oligocene transition is found in North America, indepositswhichincludethespectacular cliffsand spiresofBigBadlands NationalParkinSouthDakota,world-famousforitssceneryandabundant fossils. Although the fossils and deposits have been studied since1846, muchcriticalnewinformationhasaccumulated in the last twenty years.Enormouscollectionsoffossilmammalsfromthesebedswere made bytheFrick Laboratory ofthe American Museum of Natural History in New York, but only a smallfractionofthestudiesonthesefossilshasbeenpublished.Onthe150thanniversaryofthediscoveryand descriptionofthefirstfossilmammal from the Badlands, we hopetobringthesubjectuptodate.ThelastcomprehensivemonographsontheWhite River mammals were published in1936-1941by William Berryman Scott,GlennLowellJepsen, and AlbertE. Wood, and many of these mammals have not been reviewed sincethen.Thisvolumeis,inpart, along-overdueupdate of the classic White River monographs.There has also been a vast improvement in our chronologicalunderstanding of thesebeds.Withthenewtoolsofmagneticstratigraphyand ^Ar/ ^Ardating, weare gainingour firsthigh-resolutioncorrelationoftheterrestrialNorthAmericansectionwiththeglobalclimaticrecord.Newcorrelationshavealreadyradicallychangedourunderstanding ofthetimescale,and even changed thepositionoftheNorth AmericanEocene-Oligoceneboundaryitself. Uintan and Duchesnean fossils, long thought to be late Eocene, are now considered middle Eocene; Chadronianfossils,longthoughttobeearlyOligocene,arenowconsideredlateEocene;theOrellanandWhitneyanlandmammal"ages," once thought to be middle and late Oligocene, are now considered early Oligocene.As importantasthese new data are, very little was published in sufficientdetail.In addition to correlations of the classic White Riverand Uinta Basin deposits, this volume also summarizes the geology of relevantdepositsinSaskatchewan, Montana,Oregon, Texas, New Mexico, and California, with detailed faunallists, magnetics, and geochronology not previouslypublished.Contrary to widespread misconceptions, there was no singular, catastrophic "Terminal Eocene Event."Instead, thetransitionwasmarkedbyaseriesofextinctions,beginningattheendofthemiddleEocene(about37Ma).Consequently, our strati graphic coverage spans about20millionyears(47-27Ma), beginningwiththelatemiddleEocene (Uintan and Duchesnean, from 47-37Ma)throughthelateEocene(Chadronian, 37-33.5Ma), and theearlyOligocene(Orellan-Whitneyan-earliestArikareean, from33.5-27Ma).Thechaptersinthefirstpartofthebookreviewthechronostratigraphyofnearlyalltheimportantareas where terrestrialmammalfossilsoftheseagesarefound.The second part of the book summarizes the systematic paleontology of nearly all thecommonland vertebrates ofthe WhiteRiverChronofauna.Theseincludethemostcommonmammaliantaxa,aswellasthereptiles(turtles,lizards, snakes, and amphisbaenians).Unfortunately,itwasnotpossibletoincludeeverytaxon.Somehavebeenrecently revised elsewhere(hyaenodontsbyMellett,1977;horsesbyProtheroand Shubin,1989;rabbitsbyKorthand Hageman, 1988).The taxonomy of other groups (e.g., brontotheres, entelodonts)was notready forpublication.Nevertheless, theupdated systematicsofthemammalsinthisvolumecoversallthetaxawhichare criticaltothebiostratigraphy of the Chadronian through Whitneyan interval.In the final chapter, we summarize the chronostratigraphic and biostratigraphic information presented in thisbook,and suggest outlines of a biostrati graphic zonation for the entire interval.Much work remains to be done, ofcourse,butthissummarypresentsaframeworkforfurtherrefinementofthechronostratigraphy,biostratigraphy,andsystematicpaleontologyof this important intervalin Earth history.ACKNOWLEDGMENTSThis book would never have been possible without the cooperationand supportofmanypeople.First,wethankthe many authors, who workedsohardtoproducepolishedmanuscriptsondiskand finishedart,andthereviewersacknowledged in eachchapter,whogavefreelyoftheirtimetoensurethescientificaccuracyofeachcontribution.WethankCliffordR.Protheroforallhishelpwiththeproductionofthisvolume.WethanktheeditoralstaffatCambridge UniversityPress fortheirsupportofthisproject.TheyincludeCatherineFlack,developmentaleditor;and ElizabethA very, copy editor. Much of the support for Prothero's research over the last 20 yearspublishedhereinwasprovidedbyNSFgrantsEAR87-08221,91-17819,94-05942,grantsfromtheDonorsofthePetroleumResearchFundoftheAmericanChemicalSociety,aGuggenheimFellowship,andaColumbiaUniversityDepartment ofGeologicalSciences research fellowship.Entry's research was supportedbygrantsfromtheCharlesWalcottFund,SmithsonianResearchFoundation,theResearchOpportunitiesFund,andothersourceswithintheSmithsonianInstitution.LITERATURECITEDClark,J.,J.R.Beerbower,andK.K.Kietzke.1967.Oligocenesedimentation,stratigraphy,paleoecologyandpaleoclimatologyof the Big Badlands of South Dakota. Fieldiana: Geology Memoir5:1-158.Emry, R. J.1992. Mammalianrangezones in the ChadronianWhiteRiverFormationatFlagstaffRim,Wyoming;pp.106-115inD.R.ProtheroandW.A.Berggren(eds.),Eocene-OligoceneClimaticandBioticEvolution,PrincetonUniversityPress, Princeton, N. J.Evanoff,E.,D.R.Prothero,andR.H.Lander.1992.Eocene-OligoceneclimaticchangeinNorthAmerica:theWhite River Formationnear Douglas, east-central Wyoming;pp.116-130in D. R. ProtheroandW.A.Berggren(eds.), Eocene-OligoceneClimaticand Biotic Evolution, PrincetonUniversityPress, Princeton, N. J.Korth, W. W., and J. Hageman.1988.Lagomorphs(Mammalia)fromthe Oligocene(OrellanandWhitney an)BruleFormation, Nebraska.Transactions of the Nebraska Academyof Sciences16:141-152.Mellett,J.S.1977.PaleobiologyofNorthAmericanHyaenodon(Mammalia,Creodonta).ContributionstoVertebrate Evolution1:1-134.Prothero, D. R.1994.The Eocene-OligoceneTransition:Paradise Lost.ColumbiaUniversityPress, NewYork.Prothero, D. R.,andN. Shubin.1989.The evolutionofOligocenehorses;pp.142-175inD.R.ProtheroandR.M. Schoch (eds.), The Evolution of Perissodactyls. OxfordUniversityPress, NewYork.Prothero,D.R.,andK.E.Whittlesey.Inpress.MagnetostratigraphyandbiostratigraphyoftheOrellanandWhitney anlandmammal"ages" intheWhiteRiverGroup.GeologicalSocietyofAmericaSpecialPaper(inpress).Retallack,G.1983.LateEoceneandOligocenefossilpaleosolsfromBadlandsNationalPark,SouthDakota.GeologicalSociety of America Special Paper 193.Scott,W.B.,G.L.Jepsen,andA.E.Wood.1936-1941.ThemammalianfaunaoftheWhiteRiverOligocene,Parts I-V.Transactionsof the American PhilosophicalSociety28:1-980.Skinner, M. F.1951. The Oligoceneofwestern NorthDakota; pp. 51-58in J. D. Bump(ed.),SocietyofVertebratePaleontologyGuidebook, 5th Annual Field Conference, WesternSouth Dakota, August-September1951.Terry,D.O.,H.LaGarry,andW.B.Wells.1995.TheWhiteRiverGrouprevisited:vertebratetrackways,ecosystems,andstratigraphicrevision,reinterpretation,andredescription.NebraskaConservationandSurveyDivisionGuidebook10:43-57.xniPART I:THECHRONOSTRATIGRAPHYOFTHEULNTANTHROUGHARIKAREEAN1.MagneticStratigraphyand Biostratigraphyof theMiddleEoceneUintaFormation,UintaBasin,UtahDONALD R.PROTHEROABSTRACTTheUintaFormationin northeasternUtahwas the origi-nalbasis of theUintanland mammal"age."Magnetostrati-graphicstudieswereconductedinfoursectionsinthenortheastern,north-central,and northwesternUintaBasin.TheuppermostEvacuationCreekMemberoftheGreenRiverShale,and all of unfossiliferousUintaFormationunit"A," was ofnormalpolarity. ThisnormalintervalprobablycorrelateswithChronC21n (46.3-47.8Ma), as originallysuggestedbyProtheroandSwisher(1992).MostofUinta"B" wasreversed(= ChronC20r,43.8-46.3Ma). Ashortnormalzonespanningupper Uinta"B" and lowerUinta "C"probablycorrelateswithChronC20n(42.5-43.8Ma).Theupperpartof theUinta"C"and the lowermostportionofthe DuchesneRiverFormationwere alsoreversed(= C19r,41.4-42.5Ma),withnormal(= C19n,41.1-41.4Ma)andreversed(=C18r,40.0-41.1Ma)magnetozonesinthehigherpart of theBrennanBasinMember.AlthoughtheoriginalbiostratigraphicdataformostUintaBasincollectionsareverypoor,distinctionsbetweenthe faunas of Uinta "Bl," "B2,"and"C" arepossi-ble.Uinta"Bl"(the "Metarhinus zone" of Osbora, 1929)spansthe interval45-46Ma,and ischaracterizedbyover-lappingrangesofthebrontotheresSthenodectesandMetarhinus,therhinocerotoidsHyrachyuseximius,For-stercooperiagrandisandTriplopusobliquidens,and theagriochoeridoreodontProtoreodonparvus.Uinta "B2"(the"Eobasileus-Dolichorhinuszone"ofOsbora,1929),includingWhiteRiverPocket,spanstheinterval43-45Ma,and ischaracterizedby the overlappingrangesof thebrontotheresSphenocoelus,Metarhinus,Eotitanotherium,thechalicothereEomoropus,the horseEpihippusgracilis,thecreodontOxyaenodon,andtheartiodactylsDiplo-bunops,Oromeryx,andLeptotragulus.Thetaeniodonts(Stylinodon),uintatheres(UintatheriumandEobasileus),achaenodontartiodactyls,and protoptychidand sciuravidrodentslastappear in UintaB2.Uinta"C" (the "Diplacodon-Protitanotheriumzone"ofOsbora,1929),includingMy tonPocket,KennedyHole,and Leota Quarry, spans theintervalfrom42.5-43Ma,andis characterizedby the firstoccurrences of thebrontotheresProtitanotherium,Metatelmatherium,thelagomorphMytonolagus,the primateMytoniusytherodentJfanimus,andthelastappearanceofnumeroustaxa,includingtherodentsThisbemys,Ischyrotomus,andReithroparamys,thecreodontOxyaenodon,thecarnivoransProcynodictisandUintacyon,theartiodactylsPoebrodon,Oromeryx,Auxontodon,Bunomeryx,and Mytonomeryx,and therhi-nocerotoidsAmynodonand Triplopus.The upperpartofUinta"C"(spanningthe interval42.0-42.5Ma) isunfos-siliferous.Sparsebut distinctivefossilscharacterizethelatestUintanBrennanBasinMemberandtheDuchesneanLapointMember of theDuchesneRiver Formation.INTRODUCTION AND GEOLOGIC SETTINGTheUintaBasininnortheasternUtah(Dane,1954;Untermann and Untermann, 1964; Cashion, 1967)isanasymmetric synclinalstructure about 7000square milesinarea (Fig.1).Itsaxistrendsroughlyeast-west,andthenorthlimbisinclinedmoresteeplythantheshallow-dippingsouthlimb.TheUintaBasinisabout135mileswidealongitseast-westaxisand100milesacross in the north-south direction. It isbounded bytheUintaMountainstothenorth,theDouglasCreek archto the east (which separates it from thesimilarPiceanceBasin of Colorado), the Wasatch Range on the west, andthe Roan Cliffsto the south.Thick sequences ofPaleozoicand Mesozoicrocks arcfound alongtheedgesofthebasinand plungeintothesubsurface. These were deformed during thelatest Creta-ceous-middleEoceneLaramideOrogeny,whichcreatedthe basin initspresent configuration.During Laramideorogenesis, over15,000feetofEocenesediments accu-mulated in this rapidly subsidingstructure. ThebulkofthesedimentarypackageconsistsofthefluviallowerEocene Wasatch Formation(upto4100feetthick) andthe lacustrine lower middleEoceneGreen River Forma-tion(upto7000feetthick).ThelatterispartofanextensivesystemofmiddleEocenelakesthatoncecoveredmuchofnortheasternUtah,southwesternWyoming, and western Colorado. Becauseofitsimpor-tanceassourcerockforoilandoilshale,theGreenRiverFormationhasbeenstudiedingreatdetail(seeBradley,1929,1931,1964;Dane,1954;Cashion,1967;Ryder etal.,1976;SurdamandStanley,1979,1980;Johnson, 1985; and Roehler,1992b,forsomeofthe key features of the Green River lake system).TowardtheendoftheearlymiddleEocenePROTHEROS.N/^t'foOUGLAS/11IARCHvARIZONA|NEWMEXICO02550100MILESFigure1.IndexmapoftheUintaBasin,showingthelocationofthestratigraphicsectionsandkeylocalities.Tdr=DuchesneRiverFormation;Tgr =GreenRiverFormation;Tu =UintaFormation.(TopmapafterCashion,1967;bottommapmodifiedafterDane,1954).UINTA FORMATION, UTAH. . . /.40'.!..I-I^-SJ_JDirke_r ..HPL1 r~ Mahogany --. ^J-l -l -I -._-_-_-_-_r-_-_-_-_-I-^-_-_-_-]01 ]_-jhale^bed--I-~J"'Middlemarkerunit-!:-_+-_-_-_-_-?Wavy- beddedtuffAgrooveMetersFeet150- r 50016Ki l ometersRocks deposited in an open-lacustrine environmentRocks deposited in a marginal-lacustrineenvironmentRocks deposited inan alluvial environmentFormation boundary -- queried where unknown orapproximateSedimentarycontact- - quened where approximateMarker unit -- queried where approximateFigure2. Stratigraphiccross-sectionof theUintaBasin,showingthe interfingeringrelationshipsbetweentheGreenRiver,Uinta,and DuchesneRiver formations(afterFranczyk et al.,1989,fig.14).(Bridgerian,about47-49Ma), the GreenRiverlakesystembegan torecede. Lacustrineshaleswerereplacedbyfluvial-deltaicmudstonesandsandstoneswhichentombed many terrestrial fossilvertebrates. The BridgerBasin (Bridger Formation)and WashakieBasin(KinneyRimMemberoftheWashakieFormation-Roehler,1973,1992a)began to dry up first, withBridgerian-agedfluvialsedimentscappingand interfingeringwith theGreen Rivershales.Much of thisfluvialsediment wassupplied by a largeinfluxof volcaniclasticdebrisfromtheAbsarokavolcanicfieldof northwesternWyomingandtheChallisvolcanicsofIdaho,formingthe"volcaniclithicsandstonepetrofacies"ofSurdam andStanley(1979,1980; see alsoJohnson,1985).ThePiceance Basin began to dry up slightly later as volcanicdebrisspilledsouthfromtheWashakie-SandWashBasins (Surdam and Stanley,1979, 1980; Dickinson etal.,1988; see Stucky et al., thisvolume, Chapter 3).In the UintaBasin,theGreenRiverlakesystem wasgraduallyreplaced by the fluvialUintaFormation pro-gradingwestwardfromthe eastend of the basin (Fig.2).Thus,the lowerfluvialsandstonesof the easternUintaFormationare laterallyequivalenttolacustrineevaporites, and sandstones and limestones in the westernUintaBasin,withcomplexinterfingeringbetween thetwounits(Dane,1954,1955; Ray etal.,1956;Cashion,1967; Ryder et al.,1976).MostlowerUintaFormationsandstoneshavewest-trendingchannels andpaleocurrents(Stagner,1941; Cashion,1967), andapparentlyhad arkosicsourceareas to the southeast inPROTHEROthe Laramide uplifts, especially theUncompahgreupliftin west-centralColorado, and the Park Ranges ofcentralColorado(Stagner,1941; Bruhn etal.,1983;summa-rizedbyDickinsonetal.,1986).BytheDuchesnean,thesesourceswereswampedbyquartzitedebrisandrecycledPaleozoicsedimentaryclastsfromtheUintaMountainstothenorthastheserangesexperiencedrenewed lateLaramideuplift(AndersenandPicard,1972,1974;Picard andAndersen,1975;Dickinsonetal.,1986).Compared totheGreenRiverFormation,theUintaFormationhasbeenmuchlessstudied.Theunitwasfirstnamed byComstock(1875),and fossilsfromtheupper part of the formation were first reportedbyMarsh(1870)andScottandOsborn(1887).ThehistoryofcollectingintheUintaBasinis reviewed byBlack andDawson(1966,pp.326-328).Peterson(inOsborn,1895) first usedtheterms"Uinta A" and "UintaB" forthelower fossiliferoussequence, and "Uinta C" for theupper fossiliferousbeds. Mostoftheearlycollectionsfollowthis terminology.However, Osborn(1929)con-fusedmattersbyreshufflingthenames"UintaA" and"B." Theunfossiliferoussandstonesatthebaseofthesequence(thelowerhalfofPeterson's"UintaA")be-came the totality ofOsborn's"Uinta A,"and the upperhalfofPeterson's"UintaA" was renamed "UintaBl."Peterson's"UintaB"was renamed "UintaB2."Thisunfortunaterecyclingofsimilarterminologyledtomuch confusion, and every museumspecimenlabelhastobereadcarefullytodeterminewhenandwherethestrati graphic data weredetermined. Paleontologistswhounderstood thesechanges(e.g.,Krishtalkaetal.,1987,p. 83) were fooledbyolder museumlabels,and errone-ouslyattributedcollectionsfromUinta"Bl"toOsborn'sUinta"A"(e.g.,Krishtalkaetal.,1987,p.89;seeProthero and Swisher,1992,p.54,for discus-sion).Wood(1934) renamed Uinta"A"and"B" theWagonhound Member and Uinta"C" theMytonMem-ber. Wood et al. (1941) based their Uintan land mammal"age" on the faunas from the Uinta Formation, and con-sidered it late Eocene in age.Osborn(1929)alsointroducedanother changein ter-minologywhichcancauseconfusion.Peterson(inOsborn, 1895) originally drew the boundary between hisUinta"B" and "C" atthecolorchangefromgreenish-gray mudstones intheDevil'sPlaygroundarea ofKen-nedy'sHoleand thereddish beds overlyingthem.ButOsbornand Matthew(1909,fig.8)and Osborn(1929,fig.63and p.92)redefined theUintaB-Cboundary astheAmynodonsandstone, placingtheoverlyinggreen-ish-gray mudstones of Peterson's Uinta B intheir UintaC.Thisconfusionmeansthatsomespecimenswhichare called "Uinta B,Kennedy'sHole" (suchasthetypeofProtoptychushatched) are actuallyfromUintaCascurrently understood. For this reason, itisimportanttogo back to the original locality data oneveryspecimen,and not trust assignmentssuch as Uinta A, B, or C.Overlyingand interfingeringwiththeUintaForma-tion is the Duchesne River Formation. It wasoriginallynamed DuchesneFormationbyScott(1932),andthenrenamedDuchesneRiverFormationbyKay(1934)whentheoriginalnamewasfoundtobepreoccupied.CroppingoutalongthenorthernflankoftheUintaBasin,itlocallyconsistsofmorethan3,000feetoffluvialsandstonesand conglomerateswithlesser flood-plainmudstones(AndersenandPicard,1972,1974).Althoughthedistinctionissubtle,thereddish color ofthe Duchesne River Formationistypicallyused to dis-tinguish it from the greenish-gray-tanUintaFormation.The WoodCommittee(1941)used theDuchesneRiverFormationasthebasisfortheirDuchesneanlandmammal "age," and considered it late Eocene.The age of the Duchesne River Formation, and oftheDuchesnean land mammal "age," has been the subject ofconsiderabledisputeeversincetheWoodCommitteereport. The fossilsof the lower twomembers, Andersenand Picard's (1972) Brennan Basin and DryGulch CreekMembers (source of the Randlettand HalfwayfaunasofPeterson, 1934) are now consideredlatestUintaninage(Clark et al.,1967, p.59;Tedford,1970,pp.690-692;Emry,1981; Krishtalkaetal.,1987,p.84).Onlythefaunaofthethirdmember,orLapointMemberofAndersenandPicard(1972),ispresentlyusedasthebasisfortheDuchesnean.Thefourth,oruppermostmember, the Starr FlatMember ofAndersen and Picard(1972)isunfossiliferous(Krishtalkaetal.,1987).BecauseofthelimitednatureoftheLapointfauna,some authors havesuggestedmakingtheDuchesnean asubageoftheChadronian (Wilson,1978,1984;Emry,1981),butmorerecentlythevalueofretainingtheDuchesneanasa distinctland mammal"age" hasbeenreaffirmed(Krishtalka etal.,1987;Kelly,1990; Lucas,1992).In addition tothisconfusionbetweenrocks,faunas,and timeterms,theLyellianepochassignmentoftheDuchesneanhasalsobeencontroversial.Scott(1945)and Clarketal.(1967) regarded itasearlyOligocene,whereasSimpson(1946),BlackandDawson(1966),and Krishtalkaetal.(1987)considereditlateEocene.Clearly,a better chronostratigraphicframeworkfortheUintaandDuchesneRiverformationsiscriticaltounderstanding the middle-late Eocene transition.MAGNETIC ANALYSISIn the summers of1986,1987, and 1988, we sampledthe Uinta Formation, parts of the underlying EvacuationCreekMember oftheGreen RiverFormation,andtheoverlyingBrennanBasinMemberoftheDuchesneRiverFormation.Thefinallaboratoryworkonthesesamples was completed and presented in 1990 (Prothero,1990; Prothero and Swisher,1990). Asummaryofthisresearch was published(Prothero and Swisher, 1992).UINTA FORMATION, UTAHN , U pS. , Dow nS. , DownFigure3.Vectordemagnetization(**Zijderveld")plotsofAFdemagnetizationofrepresentativesamplesfromtheUintaFormation.AFintensityinGaussshownateachstep.Horizontalcomponentindicatedbycircles,verticalcomponentbyasterisks.I =NRMdirectionofverticalcomponent.Notethatbothsamplesdeclinedrapidlyinintensity,indicatingthatalow-coercivitymineralsuchasmagnetiteisasignificantcomponentoftheremanence.INC INT TRTDEC INC INTNRM13291 .88TD1S84838.16TD25a164 -438.46TD353 169 -36 8.4dTD453 183 -32 8.36aiDFigure4.VectordemagnetizationplotsofselectedthermaldemagnetizationresultsfromtheUintaFormation.Circlesindicatehorizontalcomponent,+symbolistheverticalcomponent.Sampleonlefthadanormaloverprintthatwasremovedby 400C.Sampleon right had a normaloverprintremovedby 250C.PROTHERO2 :DC(Hoccuuc_cuD_100go80706050403020100UINTA FM\--_-.WAGONHOUNDCANYON,GRAYSI LTST.V/\ \/\ \/\ \/\ \ /\V\A\A\T\A V/\ \r NX351030 501003001000MagneticField (mT)UINTAFM.,GRAY SILTSTONE,WAGONHOUNDCANYON5103050100MagneticFi el d(mT)REDSS. ,UINTAC51030 50100300MagneticField (mT)5103050100300MagneticFi el d(mT)Figure5.IRM acquisitionand Lowrie-Fuller testsofselectedsamplesfromtheUintaFormation(seetextandPluharetal.,1991,forfurtherdetails).SolidboxesareARMintensitiesateachAFdemagnetizationstep,openboxesare IRMintensities.NotethatduringIRMacquisition(ascendingcurveon right), mostsamplesreachedsaturationatabout300mT,indicatingthepresenceof magnetite;onlythe red sandstonefromUintaC (lowerright)failedtosaturate,showingthathematiteisa primary componentoftheremanencein thatsample.In themodifiedLowrie-Fullertests(descendingcurves onleft),theARMismoreresistantto AF demagnetizationthantheIRM,showingthattheremanenceis carriedbysingle-domainorpseudo-singledomaingrains.Over350sites(eachcontaininga minimumof threesamples)werecollectedusingsimplehandtools,result-inginover1200individualsamples.Foursections,representingthenortheastern,north-central,andnorth-westernparts ofthebasin, weretaken tosee if themag-netic pattern could be correlated acrossthebasin,and totieinasmanyfossillocalitiesaspossible(Fig.1).Theroutesofeachsectionaredescribedin theAppendix.Giventhetime-transgressivenatureoftheformationalboundaries,andthelateralfacieschanges,suchparallelsamplingwascritical(Fig.2).Aftermeasurementof NRM(naturalremanentmag-netization), a suiteof pilotsampleswasdemagnetizedusingalternatingfield(AF)andthermaldemagnetiza-tion.UnderAF demagnetization(Fig.3), nearly allsamplesdecreasedrapidlyinintensitywithincreasingappliedfields,suggestingthatthecarrieroftherema-nenceisalow-coercivitymineralsuchasmagnetite.Thermaldemagnetization(Fig.4)typicallyshowedanormaloverprintwhichwasremovedby250-350C;thisoverprintwasprobablydueto an ironhydroxidesuchasgoethite. A stablereversed componentwastypi-callyobtainedbetween35O-5OOC,andthatcomponentwasused for furtheranalysisin all samples.AbovetheCuriepointofmagnetite(580C),lessthan10% of themagnetizationremained,suggestingthatverylittle ofthe remanenceis carried byhematite.Thisinterpretationwascorroboratedby IRM(isothermalremanentmagnetization)acquisitionstudies(Fig.5). Mostsamples(Fig.5A-C)fromtheUintaFormationreachedsaturationIRMvaluesat100-300mT(millitesla);theremanencein theserocksis carriedmostlyby magnetite.However,someredsandstonesfromUinta"C"andthe DuchesneRiverFormationUINTA FORMATION, UTAH(Fig. 5D)showednoevidenceofIRMsaturation, evenat fieldsof1300mT;thesesamplesclearlycontainedhematite. AmodifiedLowrie-FullerARM(anhystereticremanentmagnetization)test(e.g.,Johnsonetal.,1975) was alsoconducted alongwiththeIRManalysis(see Pluhar et al., 1991, for details). ThistestcomparestheresistanceofAFdemagnetizationofbothanIRMacquired in a 100 mT peak field, and an ARMgained ina100mToscillatingfield.Inalmostallsamples,theARM (black squares) demagnetizes at higherpeakfieldsthandoestheIRM(opensquares),indicatingthattheremanenceiscarried bysingle-domainorpseudo-singledomain grains.Thestablesampledirectionswerethenclusteredbysite, and statistically analyzed bythemethodsofFisher(1953; see Butler,1992). ClassIsitesofOpdyke etal.(1977)showedaclusteringthatdifferedsignificantlyfromrandom atthe95%confidencelevel.InClassIIsites, one sample was lost or crumbled, butthe remain-ing samples gave a clear polarity indication. In Class HIsitesofOpdykeetal.(1977),twosamplesshowedaclear polarity preference, but the third samplewas diver-gent because ofinsufficientremovalofoverprinting.Afew samples were considered indeterminateiftheir mag-neticsignaturewasunstable,or theirdirection uninter-pretable.The beds of the Uinta Basin ranged in dip from45tohorizontal, so it was possible to conduct a modifiedfoldtestforstability.Beforethedip correction, thecleanedmean inclination(I)fornormalsiteswas340.7,anddeclination(D)was56.3;theprecisionparameter(k)was 2.4and theellipseofconfidence(095)was 40.8.After dip correction, the directionswere muchlessscat-tered [D = 2.9,1= 51.7, k =14.6,0:95 = 5.6] and muchcloser to the Eocene pole position for theregion, show-ing thattheremanencewasacquired beforetilting.Thecleanedbutuncorrectedmeanforreversedsites[D=155.2,I =-35.6,k=1.5,095=44.1]ismuchmorescattered thanthecorrected mean ofreversed sites[D =176.9,1 = -57.8, k =8.9, 095=13.1],alsosuggestingthat the magnetization was acquired prior to tilting.These statistics also provide a reversal test. The meandirection of all cleaned and corrected normalsitesshownabove was antipodal to the mean directionofallcleanedand corrected reversed samples,indicatingthatthe mag-netizationwasprobablyacquiredduringdepositionofthe beds.MAGNETIC CORRELATIONSThe magnetic pattern foralltheUintaBasinsectionsisshowninFig.6.InthenortheasternUintaBasin(WagonhoundCanyon,Bonanzaarea,CoyoteBasin,plusKennedyWash ofthetopographicmaps,orKen-nedy Hole of Peterson and Kay), theuppermost Evacua-tion Creek Member of the Green River Shale, and allofUinta "A" were ofnormalpolarity.MostofUinta "B"was reversed, except for thetop100feet,whichwasofnormalpolarity;thisnormalpolaritypersistedthroughthe lower half of Uinta "C." Therest ofUinta"C" wasof reversed polarity, aswasnearlyallofthelower partoftheDuchesneRiverFormationinKennedyHole(except for thelasttwositesatthetop,whichwere ofnormal polarity).In thecentralUintaBasin,theWillowCreek-Ouray-BrennanBasinsectionshowedasimilarpattern.TheGreen River section below the base of the Uinta Forma-tionwasofnormalpolarity,butmostofwhatwascalled "Uinta A" and "Uinta B" in Willow Creek by Kay(1934;Petersonand Kay,1931)wasreversed.Thisisnot really surprising, since there are rapid facieschangesacrossthebasin,andthemigratingfluvialUinta"A"channelcomplexwouldbeexpectedtobetime-trans-gressive. This reversed magnetozone ended lowinUinta"C," justaboveWhiteRiverPocket,andmostoftherest of Uinta "C" intheLeotaBottomarea wasofnor-malpolarity.AfterareversedmagnetozoneinupperUinta "C," the base ofthetypeBrennan BasinMemberof the Duchesne RiverFormationwasofnormalpolar-ity, and the top three sites in thatsectionwere reversed.As discussed in theAppendix,therestoftheDuchesneRiverFormationtypesectionofAndersenandPicard(1972) wasnotsampleddue todifficultieswithchemi-cal overprinting by iron oxides and hydroxides.TheothersectioninthecentralUintaBasin,My tonPocket,wasentirelyofnormalpolarity.Thisisnotsurprising, sincethefaunaofMy tonPocketisusuallycorrelated with Uinta "C" faunas, such as those ofLeotaand Skull Pass quarries (Hamblin, 1987).In the western UintaBasinsectionatIndian Canyon,comparableresultswereobtained.IftheHorseBenchSandstonecorrelateswiththerocksjustbelowUinta"A"oftheeasternpartofthebasin(Dane,1954;Franczyk et al.,1989), then the normalmagnetozoneinthe upper Evacuation Creek Member probablycorrelateswiththeUinta"A" normalzoneinWagonhoundCan-yon.Assumingnodiscontinuities,thesecondnormalmagnetozone in the middle of thesalinefaciesprobablycorrelateswiththelowerUinta"C"magnetozone.Finally,thezoneofnormalpolarityinthesandstoneand limestone facies at thetopprobablycorrelateswiththe normal magnetozonenear thebaseoftheDuchesneRiver Formation to the east.Geochronologicalcalibration ofthismagneticpatternhas been problematic. Mauger (1977) reporteda numberof K-Ar dates from the Indian Canyon section, includinga date of 43.11.3 Ma from anashabout70mabovethe Horse Bench Sandstone (in themiddle ofthelowestnormal magnetozone), and 42.81. 0Ma foratuff19mbelowthecontactbetweenthesalinefaciesandthelimestoneandsandstonefacies(inthemiddleofthehigher reversed magnetozone).Onthecurrent magneticpolarity time scale(Cande and Kent,1993;Berggren et10 PROTHEROINDIANCANYON MYTON POCKETWILLOW CREEK-OURAYWAGONHOUND CANYONoPFigure6.MagneticstratigraphyoffoursectionsintheUintaBasin,Utah(seeFig.1).Positivevirtualgeomagneticpole(VGP)latitudesindicatenormalpolarity;negativeVGPlatitudesindicatereversedpolarity.Solidcirclesare ClassI sitesofOpdykeetal.(1977);opensquares,ClassII sites;opencircles,ClassIIIsites;X =indeterminatesites.StratigraphyofWagonhoundCanyonafter Osbom(1929); WillowCreek-Ourayarea afterKay (1934); Indian CanyonafterDane(1954)andDyniandCashion(unpublished).SeeAppendixforlocationofsections.UINTA FORMATION,UTAH 11al.,1995), thelowerdatewouldplacethelowestUintanormalmagnetozoneinChronC20n(42.5-43.7Ma),but the upper date is also withintheagespanofChronC20nyet it occurs in reversed rocksthatshouldcorre-late with ChronC18r if the lowest normalmagnetozoneistrulyC20n.Eitheronedateortheother(orboth)mustbewrong.Becauseanumberofauthors(e.g.,Krishtalkaetal.,1987;ProtheroandSwisher,1992)have questionedthequalityofMauger's(1977)dates, Iwill not relyon themtoo heavilyhere.Ideally, 40Ar/39Ardatingwouldprovidemuchbetterchronostratigraphictiepointsforthemagnetostratigra-phy,butthedateof47.40.24MainupperUinta"B2" in Coyote Basin reported byProtheroandSwisher(1990)appearstobeinerror,sincethedateprobablycamefromdetritalcontaminants.Swisher(personalcommunication)hastrieddatingothervolcanicmaterialsfromthesameIndianCanyonashesdatedbyMauger (1977), but so farwithout success. Hence, othercorrelationtie pointsmustbesought.Prothero and Swisher(1992,pp.54-55)attemptedtocalibratetheUintaBasinsectionbasedonsimiliaritiesof the faunasin other magneticallycalibrated areas(Fig.7). Two correlations were possible, and discussed in thatpaper. In one interpretation,the Uinta "A"normalmag-netozonewascorrelatedwithChronC21n,andtheUintaBasinsequencecontinuesthroughC20n(lowerUinta"C")andC19n(lowerDuchesneRiverForma-tion). Wethoughtthisinterpretationwasthemostrea-sonable, because early Uintanfaunasdo notoccuruntilUinta "Bl "in the Uinta Basin(whichwasreversed, andthought to be C20r), and early Uintanfaunasare associ-atedwithupperChronC20rintheWashakieBasin(Flynn,1986), andalsoinTrans-PecosTexas(Walton,1992).TheotheralternativewasthattheUinta"A"normalmagnetozonecorrespondstoChronC20n,thelowerUinta"C"normalmagnetozonecorrelateswithC19n,and the lower Duchesne RiverFormationrecordsC18n.ProtheroandSwisher(1992,p.55)rejectedthatinter-pretation because it conflictswith the K-Ar dateof42.71 . 6MajustabovethelateUintanSerendipityl.f.(Walton,1992).Italsoconflictswiththe40Ar/39Ardateof39.740.07MaontheLapointtuff,whichmarksthecontactbetweentheDryGulchCreekandLapointmembers(ProtheroandSwisher,1992,p.49,tables2.1-2.2). ThisdatewouldfallinChronC18noftheBerggrenetal.(1995)timescale.IftheupperDryGulchCreekandlowerLapointmembersoftheDuchesneRiverFormationarecorrelativewithChronC18n,thenourreversed-normal-reversedmagnetozonesin the BrennanBasinMember cannot also beC18n,butmust correlatewithC19r-C18r.ProtheroandSwisher(1992,p.55)alsosuggestedthatthealternativecorrelationwouldconflictwiththesupposedoccurrenceoflateUintanfaunasintheupperMaCHRONNALMA38"900.80Q700500"300.200-WASHAKIEBASINoFigure 7.MagnetostratigraphiccorrelationofUintaBasinsectionswiththoseoftheWashakieBasin(afterFlynn,1986,and McCarrolletal.,thisvolume,Chapter2)andthemagneticpolaritytimescale(afterBerggrenetal.,1995).Abbreviations:Tgr=GreenRiverFormation;Twkk=KinneyRimMember;Twkal-3=AdobeTownMember,levels1-3.partoftheWashakieBasinsection.Flynn(1986,p.347 and fig. 9) brieflymentionsupperWashakiefaunallevel"D,"whichhecorrelated(Flynn,1986,fig.9)with late Chrons C20nand earlyC19r.AlthoughFlynndoes notspecificallydescribethisfaunaaslateUintan,wefollowedearlierworkers(Roehler,1973;Turnbull,1978),whospeculatedthattheupperlevelsoftheWashakieFormationmightbelateUintanbasedonlithologicchanges. As McCarrollet al. (1993;thisvol-ume,Chapter2)pointout,however,recentdetailedstudyshowsthattherearenolateUintan(Uinta"C")12 PROTHEROfossilsintheWashakieBasin;thesequencespansonlythelateBridgerian,earliestUintan(Shoshonian),andearlyUintan(= Uinta"B").However, thisisaminorpoint. The preponderance of the evidence stillfavorstheoriginalinterpretationofProtheroandSwisherthattheUintaBasinsequencespansChronsC21n-C18r(seeWalsh, this volume, Chapter 4, andthesummarychap-ter to thisvolume).BIOSTRATIGRAPHYJudging fromthese calibrations, theUintanisoneofthe longest of the North American land mammal "ages."It spans late ChronC21n(46.5Ma)toearlyC18n(40Ma), with a duration ofabout 6.5millionyears.Unfor-tunately, ithasneverbeenfinelydividedintobiostrati-graphiczones,butinsteadthelithostratigraphicallybased"zones" ofUinta"Bl,""B2," and"C"havebeenused.Osborn(1929,pp.92-95)gavebiostratigraphicnames to these lithostratigraphicunits."Bl"wascalledtheMetarhinuszone,"B2"theEobasileus-Dolicho-rhinuszone, and "C"theDiplacodonzone.Exceptforthedetailedpositionofafewbrontotherefossils(Osborn,1929, figs. 65,66)and some otherspecimens,however, no detailedrangeinformationwasprovidedtofacilitatebiostratigraphicsubdivision of these units.Osborn'sbiostratigraphiczonalterminologywasnotadopted by later workers, including KayandPetersonoftheCarnegieMuseum,whousedlithostrati graphicterms,orWood,whonamedtheWagonhoundandMy tonmembers.InspiteofthefactthatOsborn'szonalnameswereestablishedlongbefore,Gunnell(1989)namedtwo"zones"(Uil,theEpihippusassem-blage"zone,"andUi2,thecamelid-canidappearance"zone") for the early and late Uintan. However, thesearenotbasedonrecentbiostratigraphicwork,butsimplyrename the distinctionbetweenthefaunasofUinta "B"and "C." In addition, both names arenowinappropriate,as discussed below.It would be expected that the 6.5millionyearsoftheUintan should be divisible by biostratigraphyintomorethanthreezones.However,inmostcasestheoriginalcollections do not have adequate stratigraphicdata,sincethe collectors(mostlyPeterson, Kay, Clark,Riggs,andother earlytwentieth-centuryparties)rarelyrecordedthepositionoftheirfossilsbeyondUinta"B" or"C."Ihavemadeanextensivesurveyofthecollectionsandfieldnotes(primarilyintheCarnegieMuseumandAmericanMuseum)anditisclearthatmoredetailedinformationcannotbeobtainedfrommostoftheseoldcollections.Unfortunately,thebestspecimensthathadweathered out over the centuriesfromtheUintaForma-tion were removed by these earlycollectors, andnumer-ous parties since then have not obtainedsignificantnewcollectionsthatwouldhelprefinethebiostratigraphy.OnlyMytonPocket(Hamblin,1987),andoccasionallysome ofthe other classiclocalities, such as WhiteRiverPocket(e.g.,Dawson,1966),arestillproducing.TabRasmussen(personalcommunication)hasrecentlycol-lected in the Coyote Basin/Bonanza area.Giventheselimitations,Ire-examinedthemuseumcollections and their originallabels to tie down asmanyspecimensaspossibletothenewmagneticsections.Fortunately,manyofthespecimenscomefromnamedquarriesand localitieswhosepositioninthesectionisknown.Ikeptthebiostratigraphyoftheeastern(WagonhoundCanyon-Bonanza-CoyoteBasin-KennedyHole)and central(WillowCreek-Ouray-LeotaBottom-Brennan Basin, plus Myton Pocket) areas separate, sincethe"UintaA"rocksofWillowCreekaretemporallyequivalenttoUinta"B"intheWagonhound-Bonanzaarea (Fig. 6).The results are shown in Table1. As is clear fromthetable, most specimenscome froma single local levelinonly one area,sotherangesare notverylongorover-lapping. In addition,theseare onlypartialrangezones,orteilzones, forasinglebasin.Manyoftheserangeswouldsurelybeextendedifotherregionsweretakenintoaccount(e.g.,BlackandDawson,1966;Stucky,1992). Thisisparticularlytrueofthesmallmammals.Most oftheinsectivores,primates,rabbits,androdentsareknownfromonlytwolocalities:WhiteRiverPocketandMytonPocket.Verylittlecollectingforsmall mammals has occurred in higherorlowerbedsintheUintaBasin,somanyofthesesmallermammalswouldhavelongerrangesiftherewerenotsuchasizebias inthe collections.Nevertheless,someoverlappingrangesofbiostrati-graphic utility canbedetected fromtheexistingcollec-tions.Theserangescanalsobecombinedwithstrati-graphicdatafromtheadjacentWashakie-SandWashBasinsofColoradoandWyoming(McCarrolletal.,thisvolume,Chapter2;Stuckyetal.,thisvolume,Chapter3),toproduceacompositebiostratigraphyforthe Uintan in the greater Green River Basin (Fig.8). Ofcourse, the teilzones forthis basinwouldbeextended ifthebiostratigraphicdata fromotherregions(especiallyTexas,SanDiego,theSespeFormation,theBadwaterarea, andothers)wereadded tothem(seeKrishtalkaetal.,1987).UintaAAs discussed above, approximately500 feetoffluvialsandstonesatthebaseofWagonhoundCanyonwerepartofPeterson'sUintaA(inOsborn,1895),butOsborn(1929)splitofftheupperfossiliferouspartofPeterson'sUintaAandrenameditUintaBl .Hence,most ofthe pre-1929 museum labels that say "UintaA"should be read "UintaB1," andveryfewspecimenscanbe traced positivelytoUintaAsensuOsborn(1929). Ihavedouble-checkedthespecimenlabelsandthemuseumrecords,andthespecimensofAmynodon,Triplopus,Metarhinus,Dolichorhinus,andUINTA FORMATION, UTAH13Table1.StratigraphicdistributionofmammalsfromtheUintaBasin.MostrangesafterOsborn(1929),Peterson(1931,1934)Peterson and Kay (1931), Kay(1934),Blackand Dawson(1966),Hamblin(1987),Emry(1981), andStucky (1992). Abbreviations: WRP, White River Pocket, R/H/L, Randlett, Halfway, Lapoint faunas.TAXON WAGONHOUNDMBR. MYTONMBR. DUCHESNE R.lEasteraMaICentra!areaarea46.0Willow CreekWRP"C"(KennedyMule)44.043.0MytonPocketLeota40.0R/H/L11INSECIWORESTalpavus duplusNyctitheriumsp.Micropternodussp.SimidectesmagnusSimidectesmediusApatemysuintensisProtictopsalticuspidensPRIMATESOurayiauintensisMytoniushopsoniMacrotarsiusjepseniRODENTS"Paramvids"ThisbemysuintensisThisbemysmediusLeptotomusmytonensisLeptotomusleptodusLeptotomussciuroidesLeptotomuskayiJanimusrhinophilusMicroparamysdubiusIschyrotomuspetersoniIschyrotomuscompressidensIschyrotomuseugeneiReithroparamysgidleyiProsci urinesMytonomysrobustusSciuravidsSciuravusaltidensSciuravuspopiProtoptvchidsProtoptychushatchedCvlindrodontsPareumystroxelliPareumys grangeriPareumysmilleriPareumysguensbergiEomyidsProtadjidaumotypusLAGOMORPHSMytonolaguspetersoniMytonolagusrobustusCREODONTSOxyaenodondysclerusOxyaenodonwortmaniLimnocyondouglassiApataeluruskayiHyaenodonvetusWRPB2B2,WRPWRPB2WRPB2WRPWRPWRPWRPWRPWRPWRPWRPB2B2B2MPMPMPMPKH,MPMPMP,KHMPKHKHMPKHMPMPKH (base)MPKHMPKHMPR,L14TAXONWAGONHOUNDMBR.[Easternarea*.--,''-7*; A fBI?,Ma46.0[Centralmm'"..A'""' "WillowCARNIVORESMiacisgracilisMiacisuintensisUintacyonrobustusProcynodictisvulpicepsMimocyonlongipesMiocyonscottiEosictisavinoffiARTIODACTYLS(Gazin, 1955)"Dichobunids"AuxontodonpattersoniBunomeryxmontanusBunomeryxelegansHylomeryxannectensHylomeryxquadricuspisMesomeryxgrangeriPentacemylusleotensisPentacemylusprogressusMytonomeryxscottiSimimeryxminutusAchaenodontsAchaenodonuintensisWCEntelodontsBrachyhyopswyomingensisAgriochoeresProtoreodonpetersoniProtoreodonpumilusProtoreodonparvusB1ProtoreodonparadoxicusProtoreodonmediusProtoreodonprimusProtoreodonminorDiplobunopsmatthewiDiplobunopsvanhouteniDiplobunopscrassusAgriochoerusmaximusOromervcidsOromeryxplicatusB1 ?ProtylopuspetersoniProtylopusannectensCamel idsPoebrodonkayiProtoceratidsLeptotragulusproavusLeptotragulusclarkiLeptotragulusmediusLeptoreodonmarshiPoabromyluskayiMESONYCHIDSHarpagolestesuintensisBlHarpagolestesleotensisMesonyxobtusidensBlHessolestesultimusCreekWRPB2B2B2WRPB2B2B2WRPB2,WRPWRPB2B2B2B2B2MYTONMBR.*C*(KennedyHole)44.043.0MytonPocketLeotaMPMPMP, KH (base)MPMPMPKHMP,KHMP,KHMPMPLMP,KHMP,KHKHMPLQMPKHMPMPMP,KHMPMPMP,KHMPL>PROTHERODUCHESNER.40.0HRLRRRLLLUINTA FORMATION, UTAH15TAXONlEasternMaICentralmem* **ma*-WAGONHOUNDMBR.46.0WillowC?efcWRFMYTONMBR.*&WC (KennedyH44.043.0MvtonPocketDUCHESNE40.0LeotaQj'WWhR.*|IPERISSODACTYLSEquidsEpihippusgracilisEpihippusparvusEpihippus(Duchesnehippus)"Tapiroids"IsectolophusannectensDilophodonleotanusChalicotheresEomoropus amarorumRhinocerotoidsHyrachyuseximiusAmynodonreediAmynodonadvenusMegalamynodonregalisTriplopusimplicatusTriplopusobliquidensTriplopusrhinocerinusForstercooperiagrandisEpitriplopusuintensisEpitriplopusmediusHyracodonprimusBrontotheresSthenodectespriscusSthenodectesincisivumDolichorhinusEotitanotheriumosborniDiplacodonMetatelmatheriumultimumRhadinorhinusMetarhinusProtitanotheriumDuchesneodusuintensisUINTATHERESEobasileuscornutusUintatheriumancepsTAENIODOISTTSStylinodonmirusintermediusBlBlB1,WCBlBlWC (just aboveBlB1,WCB1,WCBlB1,WCBlB2,WRPB2, WRPB2B2B2, WRPB2B2,WRPB2Green River Fm.)B2MP,KHMPMP,KHKH (base)MP,KH?MPMPWC (just belowWRP)KHB2B2B2B2MP,KHKHR,LLRLForstercooperia reported by Krishtalka et al. (1987, p.89)fromUinta"A"are actuallyfromUinta"Bl"inOsborn's(1929)terminology(seeProtheroandSwisher,1992, p. 54).Peterson(inOsborn,1895),Riggs(1912),andOsborn (1929) all foundthe lower 500 feetof theUintaFormation(all ofUinta"A" inmodernparlance)inWagonhound Canyon to beunfossiliferous.Kay(1934,plateXLVI)indicatesthatSthenodectespriscuscomesfromahorizonabout30 feetabovethebaseof theGreenRiverFormationinWillowCreek,whichhecorrelatedwithUintaA.However,thissequenceisreversed in polarity and apparentlycorrelateswithUintaBlinthe Bonanzaarea,not withthe UintaAsand-stones.Hence, thereareno welldocumentedmammalfossilsfromUinta A as it is nowunderstood.UintaBlThe lower part of UintaB is not particularlyfossilif-erous, either, somostof thestrati graphicdatamust beinferredfromRiggs(1912,fig. 1) andOsborn(1929,fig.65)in theWagonhoundCanyon-Bonanzaarea, andfromKay(1934,plateXLVI)for the WillowCreek-Ourayarea.Inaddition,thereare importantlocalitieslike"Wellno.2" (PetersonandKay,1931,plateDQjustnorthof Bonanzathatcanbeplacedhighin UintaB1,allowingthedeterminationof theexactlevelof anumber ofspecimens.Most of thespecimenspositivelyknownfromUintaBlarebrontotheres,butamongthemMetarhinus flu-viatalis last appears in Uinta Bl , and Sthenodectes (bothpriscusand incisivum, if theyare bothvalid)appears toberestricted to thislevel.Mader(1989)indicatesthat16 PROTHERO"Sthenodectes" australis fromthePruettFormationofTexas (Wilson,1978)isnotreferabletothatgenus.Afewtaxa{Protoreodonparvus,Triplopus obliquidens)first appearattheBllevel,and afewmore {Pareumysgrangeri, Harpagolestesuintensis,Hyrachyuseximius,Forstercooperia grandis) last occuratthislevel.Osborn(1929)calledthisintervalthe"Metarhinuszone,"andthatnamecouldstillbeused,sinceMetarhinusisoneofthecommonestmammalsintheinterval.However,Metarhinusis no longer restricted to UintaB1, butfirstoccursinthemiddleAdobeTownMemberintheWashakieBasin(McCarrollet al., this volume,Chapter2),whichcorrelateswithChronC21n.Mader(1989)hasalsosynonymizedRhadinorhinuswith Metarhinus,extendingtherangeofMetarhinusintoUintaB2.Hence, theUintaBlintervalcouldberedefinedbytheoverlapping ranges of Protoreodon parvus and Triplopusobliquidens (firstoccurrence),andHyrachyuseximius,Forstercooperiagrandis,Pareumysgrangeri,andHar-pagolestesuintensis(lastoccurrence).Sthenodectesisthe only taxon restrictedto this interval.UintaB2BycontrastwithUintaBl ,theupperpartoftheWagonhoundMemberisveryfossiliferousduetotheextensivecollectionsofsmallmammalsfromWhiteRiverPocket.Osborn(1929)calledthisthe"Eobasileus-Dolichorhinuszone,"andbothofthosetaxa are still characteristic, and last occurintheinterval(although both haveearlieroccurrences). Alonglistoftaxa(mostlysmallmammals fromWhite RiverPocket)is restricted to the upper Wagonhound Member (Fig.8),includingSimidectesmedius,Apatemysuintensis,Ourayia uintensis, Thisbemysuintensis,Microparamysdubius, Pareumys troxelli,Pareumys milleri, Oxyaeno-donwortmani,Apataeluruskayi,"Miacis"uintensis,Hylomeryxannectens, Mesomeryxgrangeri,Protoreo-donparadoxicus,Protoreodonmedius,Diplobunopsvanhouteni, and Amynodonreedi. Numerousother taxa{Ischyrotomuspetersoni,Oxyaenodondysclerus,Limnocyondouglassi,Miocyonscotti,Or orneryxplicatus,Leptotragulusproavus,Leptoreodon marshi,Isectolophusannectens)firstoccurinUintaB2andcontinueintoUintaC.ThereisamajorfaunalbreakbetweentheWagonhoundandMy tonmembers,withtaxawhichpersistedfromtheBridgerianandearliestUintan{Sciuravus, Eobasileus,Uintatherium,Stylino-don,Eomoropus,Protoptychushatched, Achaenodon,Sphenocoelus,Epihippusgracilis,Pareumys grangeri,and Metarhinus) disappearing at the top of Uinta B.UintaCAgain,thereisalonglistofsmallmammalsfromthelowerpartoftheMytonMemberbecauseoftheextraordinarilydiversecollectionsfromMytonPocket.However,mostoftheotherquarriesandlevelsintheMyton Member aremuchlessrich,sothelocalrangesofUintaCmammalsare oftenrestrictedtothissinglelocality.Nearlyallthefossillocalitiesappeartobelocatedinthelowerpartofthemember(exceptforLeota Quarry), and the upper part of the MytonMemberabove Leota Quarry is virtuallyunfossiliferous.TaxarestrictedtothelowerMytonMember(mostlysmallmammalsfromMytonPocket)includeTalpavusduplus, Simidectesmagnus,Mytoniushopsoni,This-bemysmedius,Leptotomusmytonensis,Leptotomussciuroides, Janimus rhinophilus,Ischyrotomus eugenei,Reithroparamysgidleyi,Uintacyon robustus, Procyno-dictisvulpiceps,Mimocyonlongipes,Auxontodonpat-tersoni,Bunomeryxmontanus,Bunomeryxelegans,Hylomeryxquadricuspis,Pentacemylusprogressus,Mytonomeryxscotti,Protoreodonpetersoni,Pro-toreodon pumilis,Protoreodonminor,Leptotragulusclarki,Leptotragulusmedius,Epihippusparvus,andMetatelmatheriumultimum.Inaddition,Diplacodon,Protitanotherium, Harpagolestes leotensis,andDiplo-bunops matthewiarerestrictedtotheintervalspanningMyton Pocket to Leota Quarry. Pentacemylusleotensis,Protoreodon primus, Dilophodon leotanus, andPentace-mylus progressusfirstoccurattheLeotaQuarrylevel;the firsttwo taxa are also restrictedto thatlocality.In addition to thisuniquelyUintaCfauna,anumberoftaxafromtheearlyUintan{Amynodonadvenus,Poebrodon, Leptotomus leptodus, Protylopuspetersoni,Triplopusimplicatus,Triplopusobliquidens, Ischyro-tomuspetersoni,Ischyrotomuscompressidens,Pro-toreodonparvus,Oxyaenodondysclerus,Limnocyondouglassi, Miocyonscotti,Oromeryx plicatus,Lepto-tragulusproavus,Leptoreodonmarshi,Isectolophusannectens) lastoccurattheMytonPocketlevel.Onlyonetaxon{Mytonolagus)thatfirstappearsinUintaCcontinuesintotheDuchesnean.Thus,thereisabigdrop indiversityand changeinthefaunainthemiddleofthelateUintan(betweenLeotaQuarryand theRan-dletthorizon,around42Ma),asnumerousauthors(BlackandDawson,1966;Krishtalkaetal.,1987;Stucky,1990,1992)havenoted.Osborn (1929)calledUintaCthe"Diplacodon-Proti-tanotheriumzone," andthatnameisstillappropriate,sincebothofthesebrontotheresarerestrictedtoUintaC.However,thenamescoinedbyGunnell(1989)areno longer usefulforthe Uintan.His"Epihippusassem-blage zone" (Uil) for Uinta A-B isnotverydescriptive,since Epihippus parvusoccursinUintaC,andEpihip-pus (Duchesnehippus) intermedius isfoundintheHalf-way fauna. With the discovery of the camelid Poebrodonin the early Uintan middleAdobe TownMemberoftheWashakie Basin (McCarrollet al., this volume,Chapter2),the"camelid-canidappearancezone"(Ui2)isnolongerappropriateforUintaC.NordoesWang(1994)regard any Uintan"miacids" ascanids. Theearliesttruecanid is fromthe Duchesnean.UINTA FORMATION, UTAH17484746454443424140C21nBRIDGSHOSHON11C20rEARLY UINTANa2Twka3U B 1 UB2MC20nC19rC19nLATEUINTANWRPMPLQC18rR: ==================:: : : : : : :: : : ? :LeptotomusbridgerensisSinopa*******Hyrachyusmodestus*=:*:*:=:=*= HomacodonvagansP h iMesatirhinus==== Notharctusrobustior======================================================== Hyrachyuseximius.=:=:=:=:=::=:=:=:=:=:j:i:=:i:=:j:=:5 :i:i:i:i:i:=:=:=:=:-:i:i:i:i:=:=:=:=:5 :-:5 :=:5 :=:5 :i:i:M e t a r h i n u s:=:=======:=:====:Harpagolestesuintensis================ Forstercooperiagrandis:::=::=:=:=:=:=:=:=:=:=:=:=:=:::=:::=:=:=:=:=:=:=:=:=:::::=:ProtoptychushatCheriAchaenodotiEobasileuscornutusSphenocoelus=:=:=:=:=:===:===:=:=:================: ========^^====:===:=:===:=:=:=:====:=:===:===:;==:==;:=Ischyrotomuscompressidferis= =u=^== = = == = = = =.SthenodectespriscusP r o t o r e o d o np a r v u s=:i:========i=i=========i=======================i===i=========i=====i===i=i=i=======i=======i=======iT r i p l o p u so b l i q u i d e n si=i=i=i=^=i===i===;=i===i=================================================i=i=i=i==================: ===: =====SthenodectesincisivumEotitanotheriumosborni:=*Figure8.Lx)calstratigraphicranges(teilzones)ofUintanmammalsintheWashakie,SandWash,andUintaBasins,basedon data from Table1 and McCarrolletal.(thisvolume,Chapter2)andStuckyetal.(thisvolume,Chapter3).TimescaleafterBerggrenetal.(1995);otherabbreviationsasinFig.7.18PROTHERO4847jC21nBRroGSHOSHONTwkal^kaZ46i145C20rEARLYUINTANTwka3UB144UB243C20n4241C19rC19nLATE UINTANWRPMP LQ41C18rRSimidectesmedius***Apatemysuintensis*******Ourayia uintensis*******Thisbemysuintensis******Microparamysdubius********Pareumystroxelli*********Pareumys milleri*******Oxyaenodonwortmani*******Apataeluruskayi******** : : * : : * . : : :Hylomeryxannectens *********Mesomeryxgranger]**********Protoreodon paradoxicus********Protoreodonmedius********Diplobunopsvanhouteni*******AddiIschyrotomus petersoni***********Oxyaenodondysclerus***************MiocyonscottiLeptotragulus proavus I*:*:***********Leptoreodonmarshi*********:*:Isectolophus annectensM:-:*******:*:-:Talpavus duplus* *:*Simidectesmagnus****Mytoniushopsoni*:;::;:;Thisbemys medius*****Leptotomus mytonensis*****Leptotomus sciuroides**Janimusrhinophilus*:= *:=Ischyrotomuseugenei::::::S:Reithroparamysgidleyi: : : : : ;********UINTA FORMATION, UTAH 1948 47 46 45 44 43 42 41 40C21nBRIDCSHOSHON1 Vk a ls wJl i r kiiC20rEARLY UINTANa2Twka3U B 1iUB2MC20nC19rC19nLATEUINTANWRPMP LQC18rRUintacyonrobustusProcynodictisvulpiceps* * * *Mimocyonlongipes::i:: :iAuxontodonpattersoni****Bunomeryxmontanus****Bunomeryxelegans**=*=Hylomeryxq uadricuspis****Pentacemylusprogressus****Mytonomeryx scottixm&iProtoreodonpetersoni:*:**Protoreodonpumilis***Protoreodonminor****Leptotragulusclarki* * * *Leptotragulusmedius-***Epihippus pan/us*?*?*Metatelmatheriumultimum:::::-Diplacodon*****Protitanotherium****Harpagolestesleotensis****Diplobunopsmatthewi***:PentacemylusleotensisProtoreodonprimusDilophodonleotanusPentacemylus progressusi*:*:*:***:*****LeptotomuskayiProtadjidaumotypusDiplobunopscrassusMegalamynodonregalisEpitriplopusmedius20 PROTHERODuchesneRiverFormationandDuchesneanAs discussed above (and is apparentfromTable1 andFig. 8), the faunasof the Duchesne River Formationareso scarce, and their biostratigraphiclevelsaresopoorlyconstrained, that itispointlesstosuggestarange-zonebiostratigraphyin the UintaBasin. ThisismuchbetterdoneintheSespeFormationofCalifornia(seeKelly,1990,andProtheroetal.,thisvolume,Chapter8)andthe Trans-Pecos Texas region (see Wilson,1986; Lucas,1992; and the summarychapter to this volume).CONCLUSIONSAlthoughconfusingstrati graphicproblems,andthelackofprecisebiostrati graphicdataassociatedwithmany specimens, have long hampered ourunderstandingoftheUintan,magneticstratigraphyand detailedstrati-graphicre-examinationofthecollectionsmakesrefine-mentspossible.ItseemsthattheUintancanbesubdi-vided into at least five discrete intervals:EarliestUintan("Shoshonian")spanslateChronC21n-earlyChron C20r(about 46.5-46 Ma), and isbestrepresentedbyfaunasintheTepeeTrailFormationofnorthwestWyoming,themiddleAdobeTownMemberoftheWashakieFormationintheWashakieandSandWashbasins,theFriarsFormationintheSanDiegoarea(Walshetal.,thisvolume,Chapter6;Flynn,1986,pp.379-380),andtheWhistler'sSquatIf.inTrans-Pecos Texas.Uinta Bl^Metarhinuszone" ofOsborn,1929)spansearlyChronC20r(45-46Ma).Itissparselyfossilifer-ous,buthassomedistinctivetaxa.Thefossilsoftheupper Adobe Town Member of the WashakieFormationmay also correlate with this interval.UintaB2("Eobasileus-Dolichorhinuszone"ofOsborn,1929)spanslateChronC20rand earlyChronC20n(43.5-45.0Ma),andincludesmanydistinctivetaxa(especiallythecollectionsofsmallermammalsfromWhiteRiver Pocket).Most"UintaB" correlatives(BlackandDawson,1966;Krishtalkaetal.,1987)appearto fallin this timeinterval.UintaC("Diplacodon zone" ofOsborn,1929)spansmostofChronC20n(42.5-43.5Ma),includingtheextensivefaunasofMytonPocket,KennedyHole,andSkullPass, Leota, and Thorne quarries. Most "UintaC"faunasofotherauthors(BlackandDawson,1966;Krishtalkaetal.,1987)probablycorrelatewiththisinterval,orwiththeunfossiliferousupperMytonMember(whichspansearlyChronC19r,42.0-42.5Ma).Randletthorizon(intheBrennanBasinMemberofthe DuchesneRiverFormationofAndersenandPicard,1972) includes latestUintanfaunas,andcorrelateswithearlyChronC19n-C18r(40.0-41.0Ma).CorrelativefaunasmightincludetheCandelarial.f.ofTrans-PecosTexas.ACKNOWLEDGMENTSIthanktheDonorsofthePetroleumResearchFundoftheAmericanChemicalSociety,andtheNationalScienceFoundation(grantEAR87-08221)forsupport-ing this research. Joe Kirschvinkgraciouslyallowedmeto use the Caltech paleomagneticslaboratorytorunthesamples.PreliminarysampleswererunbyAnnieWalton in the paleomagneticslaboratoryoftheUniver-sityofTexasatAustin.Fieldsamplingwouldneverhave been possiblewithoutthehardwork,enthusiasm,andgoodspiritsofseveralfieldcrews.In1986,theyincludedDanaGilchrist,KeciaHarris,andAnnieWalton. In1987, theyincluded JillBush, Susan Briggs,JohnFoster,andSteveKing.In1988,theyincludedJeffAmato,JenniferChean,and JimFinegan.IthankAldenHamblinand J.R.DyniforalltheirhelpwithUinta Basin stratigraphy, and CarlSwisherforvaliantlytrying to get a decent date out oftheUintaBasinrocks.IthankCraigBlack, AldenHamblin,TomKelly,JayLillegraven,BrynMader,SteveMcCarroll,MalcolmMcKenna, John Storer, Steve Walsh, and AnnieWaltonfor reviewing themanuscript.LITERATURECITEDAndersen,D.W.,andM.D.Picard.1972.StratigraphyoftheDuchesneRiverFormation(Eocene-Oligocene?),northernUintaBasin,northeasternUtah.UtahGeologi-calandMineralogicalSurveyBulletin97:1-23.Andersen,D.W.,andM.D.Picard.1974.EvolutionofsynorogenicclasticdepositsintheintermontaneUintaBasinofUtah.SEPMSpecialPublication22:167-189.Berggren,W.A.,D.V.Kent,M.-P.Aubry,C.C.SwisherIII,andK.G.Miller.1995.ArevisedPaleogenegeo-chronologyandchronostratigraphy.SEPMSpecialPub-lication54:129-212.Black,C. C,andM. R.Dawson.1966. 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Beck.1983.MesozoicandearlyTertiarystructureandsedimentologyofthecentralWasatchMountains,UintaMountains,andUintaBasin.UtahGeologicalandMineralogicalSurveySpecialStudies59:63-105.Butler,R.F.1992.Paleomagnetism.Blackwell,Boston.Cande,S.C,andD.V.Kent.1993.AnewgeomagneticpolaritytimescaleforthelateCretaceousandCenozoic.JournalofGeophysicalResearch97(B10): 13917-13951.Cashion,W.B.1967.GeologyandfuelresourcesoftheGreenRiverFormation,southeasternUintaBasin,UtahandColorado.U.S.GeologicalSurveyProfessionalUINTA FORMATION, UTAH 21Paper548:1-48.Clark, J., J. R.Beerbower,andK.K.Kietzke.1967.Oligo-cenesedimentation,stratigraphy,paleoecology,andpaleoclimatologyintheBigBadlandsofSouthDakota.FieldianaGeologyMemoirs5.Comstock,T.B.1875.ReportuponthereconnaissanceofnorthwesternWyomingincludingYellowstoneNationalPark, for1873, byWm. A.Jones, HouseRep. Exec.Doc.285,43dCongress,1stsession,Jan.1875.Dane,C.H.1954.StratigraphicandfaciesrelationshipsoftheupperpartoftheGreenRiverFormationandlowerpartoftheUintaFormationinDuchesne,Uintah,andWasatchcounties.BulletinoftheAmericanAssociationofPetroleumGeologists38:405-425.Dane,C.H.1955.StratigraphicandfaciesrelationshipsofupperpartofGreenRiverFormationandlowerpartofUintaFormationinDuchesne,Uintah,andWasatchCounties,Utah.U.S.GeologicalSurveyOilandGasChartOC-52.Dawson,M.R.1966.AdditionallateEocenerodents(Mammalia)fromtheUintaBasin,Utah.AnnalsoftheCarnegieMuseum38(4):97-114.Dickinson,W.R.,M. A.Klute,M. J. Hayes, S.U.Janecke,E.R.Lundin,M.A.McKittrick,andM.D.Olivares.1988.PaleogeographicandplatetectonicsettingoftheLaramidesedimentarybasinsin thecentralRockyMoun-tainregion.GeologicalSocietyofAmericaBulletin100:1023-1039.Dickinson,W.R.,T.F.Lawton,andK.F.Inman.1986.Sandstonedetritalmodes,centralUtahforelandregion:stratigraphicrecordofCretaceous-Paleogenetectonicevolution.JournalofSedimentaryPetrology56:276-293.Emry,R. J.1981. 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G.,B. H. Kent, and C. H. Dane.1956.StratigraphyandphotogeologyofthesouthwesternpartoftheUintaBasin,DuchesneandUintahCounties,Utah.U.S.Geo-logicalSurveyOilandGasInvestigationsMap OM-171.Riggs,E.S.1912.Neworlittle-knowntitanotheresfromthelowerUintahformations.FieldMuseumofNaturalHistory,GeologySeries4(2): 17-41.Roehler,H.W.1973.StratigraphyoftheWashakieForma-tionintheWashakieBasin,Wyoming.U.S.GeologicalSurveyBulletin1369:1-40.Roehler,H.W.1992a.DescriptionandcorrelationofEocenerocksinstratigraphicreferencesectionsfortheGreen River and WashakieBasins,southwestWyoming.U.S.GeologicalSurveyProfessionalPaper1506-D.Roehler,H.W.1992b.Correlation,composition,arealdistribution,andthicknessofEocenestratigraphicunits,greaterGreenRiverBasin,Wyoming,Utah,andColo-rado.U.S.GeologicalSurveyProfessionalPaper1506-E.Rowley,P. D., W.R.Hansen,O.Tweto,andP.E. Carrara.1985.GeologicmapoftheVernal1x2quadrangle,Colorado,Utah,andWyoming.U.S.GeologicalSurveyMap1-1526.Ryder,R.T.,T.D.Fouch,andJ.H.Elison.1976.EarlyTertiarysedimentationinthewesternUintaBasin,Utah.GeologicalSocietyofAmericaBulletin87:496-512.Scott,W.B.1932.Anintroductiontogeology,3rded.Macmillan,NewYork,441pp.Scott,W.B.1945.TheMammaliaoftheDuchesneRiverOligocene.TransactionsoftheAmericanPhilosophicalSociety34:209-253.Scott,W.B.,andH.F.Osborn.1887.PreliminaryreportonthevertebratefossilsoftheUintaformation,col-lectedbythePrincetonexpeditionof1886.ProceedingsoftheAmericanPhilosophicalSociety,24:255-264.Scott,W.B., andH.F. Osborn.1895. TheMammaliaoftheUintaFormation.TransactionsoftheAmericanPhilo-sophicalSociety15:461-572.Simpson,G.G.1946.TheDuchesneanfaunaandtheEocene-Oligoceneboundary.AmericanJournalofScience244:52-57.Stagner,W.L.1941.ThepaleogeographyoftheeasternpartoftheUintaBasinduringUintaB(Eocene)time.AnnalsoftheCarnegieMuseum28:273-308.Stucky,R.K.1990.EvolutionoflandmammaldiversityinNorthAmericaduringtheCenozoic.CurrentMam-malogy,2:375-432.Stucky,R.K.1992. MammalianfaunasinNorth AmericaofBridgerianto earlyArikareean"ages" (EoceneandOligo-cene);pp. 463-493in D.R.ProtheroandW.A.Berggren(eds.),Eocene-OligoceneClimaticandBioticEvolution.PrincetonUniversityPress,Princeton,N.J.Surdam, R.C,andK.O.Stanley.1979.Lacustrinesedi-mentationduringtheculminatingphaseofEoceneLakeGoshiute,Wyoming(GreenRiverFormation).Geologi-calSocietyofAmericaBulletin90:93-110.Surdam, R. C,and K. 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TexasMemorialMuseumBulle-tin25:1-42.Wilson,J.A.1984.Vertebratefossilfaunas49to36mil-lionyearsagoandadditionstothespeciesofLeptoreodonfoundinTexas.JournalofVertebratePale-ontology4:199-207.Wilson,J.A.,1986.Stratigraphicoccurrenceandcorrela-tionofearlyTertiaryvertebratefaunas,Trans-PecosTexas:AguaFria-GreenValleyareas.JournalofVerte-bratePaleontology6:350-373.Wood, H. E. II.1934.RevisionoftheHyrachyidae.Bulle-tin oftheAmericanMuseumofNaturalHistory67:182-295.Wood, H. E., R. W.Chaney,J.Clark,E.H.Colbert,G.L.Jepsen,J.B.Reeside,Jr.,andC.Stock.1941.Nomen-clatureandcorrelationoftheNorthAmericancontinentalTertiary.BulletinoftheGeologicalSocietyofAmerica52:1-48.UINTA FORMATION, UTAH 23APPENDIXTheroutes ofthevariousstratigraphicsectionstakenintheUintaBasinaredescribedbelow.ThegeneralgeologyoftheseareashasbeenmappedbyCashion(1967)andRowleyetal.(1985).FurtherdetailswillbedepositedintheArchivesoftheDepartmentofVertebratePaleontologyofthe AmericanMuseum ofNaturalHistory.Northeasternbasin.ThefirstsectionwastakenintheeasternUintaBasin,andranthroughRiggs's(1912,fig.1),Peterson's(1924,fig.1), andOsborn's(1929,fig.63)sectionsat WagonhoundCanyon,nearBonanza,Utah,andthenup throughCoyoteBasintoKennedyHole.Atfirstglancethesesectionsappeartobeclearlydiagrammed,butinactualitythethicknessesandtherouteofthesectiongivenbytheseauthorsareonlyapproximate.In thefielditwasdifficulttotracetherouteoftheoriginalsections,ordeterminetheexactpositionofthekeybedsthatseparateUinta"A" from"Bl,"or"Bl"from"B2."However,aftermuchdouble-checkingandbacktrackingfromknownland-marks, a sectionwasobtainedwhichcloselyapproximatedtheoriginalsectionsinthicknessesandlithologicdetails.TheWagonhoundCanyonsectionbeganattheleveloftheWhiteRiveratthemouthofthecanyon,takingthebottomthreesitesintheuppermostpartoftheEvacuationCreekMemberoftheGreenRiverFormation.Thesectionthenproceededup the dirt road throughtheUinta"A" sand-stonesin WagonhoundCanyon ( NE and SEofNE NW Sec.2,T10SR24E,SouthamCanyon7.5'quadrangle,UintahCounty,Utah). Atthetop oftheroadcuts,therouteofsec-tionthen proceededwestwardup theridges(SE SE SWSec.35,T9SR24E)tothehighestpointinthearea(NE SW SESec.34).Over 900feetofsection,includingallofUinta"A" and "Bl" wasmeasured. Projectingthehighestbedsofthissectiondownthedipslopetothenorth,thenextpartofthesectionwastakenina northeasterlydirectionintheflatsaroundBonanzaand CoyoteBasin.Theupperpartof"Bl" was measured in SW SW SW NWSec.23,T9S,R24E,Bonanza7.5'quadrangle, and thencontinuedthrough"B2"inridgeslocatedinSWSW NW Sec.13,SW SWSWSWSec.12, SENWNESec.11,culminatingintheprominentledgeknownasthe"AmynodonSandstone"(seeRiggs,1912,fig.2; Osborn,1929, fig.64)inNE SWSWSec.34,T8SR24E and Center NW SW Sec. 24, just east ofroad frombenchmark5350.Movingdownthedipslopeofthe"AmynodonSandstone,"thesectionwasresumedinUinta"C" mudstonebadlands(the"Devil'sPlayground")justtothenorth(NE SWSW toSESWNESec.21,T8SR24E,Bonanza7.5'quadrangle).Thissectionculminatedjustbelowthecolorchange(atthe5388benchmark)fromgraybentonitic"popcorn"claystonesofUinta"C" totheredandyellowclaysoftheDuchesneRiverFormation.Over400feetoftheBrennanBasinMemberoftheDuchesneRiverFormationwas takeninseveralsectionsintheKennedyHolearea(SWNWSESec.17,T8SR24EBonanza7.5'quadrangleand finishinginSW SWNE Sec.17,T8SR24E,DinosaurNW7.5'quadrangle),thencontinuing from NW SE SE Sec. 6, T8SR24E, Dinosaur NW7.5'quadrangle, to NE SE SE of thesamesection.ThiswasthehighestcontinuousexposureofDuchesneRiverForma-tionin the area, andtherestoftheformationcouldnotbesampledbecausetheexposuresdisappearcompletelyunderthesod-coveredbenchformilestothenorth.North-centralbasin.ManyimportantCarnegieMuseumlocalities,includingWhiteRiverPocket,andLeota, Thome, andSkullPassquarries,arelocatedalonganorth-southtransectthroughthecentralUintaBasin.Kay(inPetersonandKay,1931,PlateIX,andKayandGar-wood,1953, p.19)gavethelocationofthesequarriesand aroute ofsectionon a verycrudelydrawn, large-scalemapofthearea.Whenthatroutewastraced,however,muchofitprovedtohavenoexposureswhatsoever,andotherpartswerecompletelyinaccessible.Likethecartoonishstrati-graphicsectionsofRiggsandOsbornintheeasternbasin,thegeneralizedstratigraphicsectionsofKay(inKay,1934,PlateXLVI, andPetersonandKay,1931,PlateX)wereveryinaccurateandallthedetailshad tobecarefullyremeasuredandredocumentedinthefield.Consequently,Ipickeda route thatgavebetter exposuresandcloselyparal-leledthe routeindicatedbyKay(1953).Ratherthanfollowthe roadnorthtoOuray,whichhadnocontinuousoutcropalongthetopofthesoil-coveredbench,IfollowedtheWillowCreekdrainage,starting150 feetbelowthecontactwiththeGreenRiverFormation.AseriesofsectionswaspatchedtogetheralongtheeastbankofWillowCreek,startingwithSENESWSec.12,T11SR20E,BigPackMountain7.5'quadrangle. ThesecondlegwastakeninSESESWSec.10 alongtheroadup 'TurkeyTrailHill,"thentraced west along the bedwhichcapsthebenchintheareatoanother outcropalongWillowCreekwherethenext100feetofUintaFormationwereexposed(NE SWSE Sec.30,T9SR20E,Ouray 7.5'quadrangle).TheWillowCreeksec-tionconcludedinSW NE NE Sec.19inthesamequadran-gle. ThehighestlevelwasthenprojectednortheasttotheareaofWhiteRiverPocket(SESWSE Sec.5,T9SR20E,Ouray7.5'quadrangle, justwestofroad),wherethemainWhiteRiverPocketsectionwastaken.ThesandstonecappingtheUinta"B"rocksatWhiteRiver Pocket wasthenprojectedtothenorth,andthesec-tionwasresumedinSE SE Sec.19,T4SR3E,Ouray7.5'quadrangle,wherethelowerpartofUinta"C"couldbemeasured. The nextsegmentwastakeninSWSWNW NWSec.8, T4SR3E, PelicanLake7.5'quadrangle.Aseriesofsectionswasthentakenalongtheeast-facingbluffswestofLeotaBottom(siteofLeota Quarry), insegmentslocatedinSW SE SE Sec. 2, T8S R20E,PelicanLake7.5'quadrangle,then in NW SW NW Sec.1,T8SR20E,BrennanBasin7.5'quadrangle, followedbyNE NW SWSec.36,T7SR20Einthesamequadrangle,endinginthebaseoftheBrennanBasinMemberoftheDuchesneRiverFormation("unit1"ofthetypesectionoftheBrennanBasinMemberofAnder-senandPicard,1972, p. 26). Anadditional300feetofthatmember(spanningAndersenandPicard'sunits2-5)weremeasured and sampled in NW NE NE Sec.18 andNW SW SESec. 7,T7SR21E,BrennanBasin7.5'quadrangle.Atthispoint,thesectionwasdiscontinued,becausethesand-stonesweretoohard forhandsampling,theshalesweretoopoorlyexposed,andeveryunithadadeepredhematiticstain.In our1986reconnaissancesampling,almostallofourdeepredDuchesneRiversamplesprovedtohaveanintractablechemicaloverprintingdue tohematite.Hence,furthersamplingintheDuchesneRiverFormationwasabandoned.Athirdsectionin thecentralUintaBasinran throughtheMytonPocketarea,15mileseastofOuray,and7mileswestofthetownofMyton.Fortunately,thislocalityhasbeencarefullymeasuredandstudiedinrecenttimesbyHamblin(1987).Approximately360feetofsectionofUinta "C" ("MytonMember") were taken in SWSE NE Sec.12 (lowerhalf)andconcludedinNW SW SW Sec.6(upperhalf),T4SR1EoftheUintahSpecialMeridian,WindyRidge7.5'quadrangle,UintahCounty,Utah.Westernbasin.InthewesternportionoftheUinta24 PROTHEROBasin, thefluvialsandstonesand mudstonesarereplacedbytherelictlacustrinefaciesofEoceneLakeUinta.InsteadofUinta"A" sandstones, theEvacuationCreekMemberoftheGreenRiverFormationisoverlainbythe"salinefacies"and"sandstoneandlimestonefacies"oftheUintaForma-tion(Dane,1954,1955;Rayetal.,1956).Themostcom-pletesectionthroughtheregionisinIndianCanyon,southwestofDuchesne, inDuchesneCounty,Utah.AbriefsketchofthesectionwaspublishedbyDane(1954,fig.2,column5),andthestratigraphicrelationshipsweresumma-rized in Franczyketal.(1989,fig.14).A detailed,unpub-lishedstratigraphicsectionthroughIndianCanyonmadeby J. R.DyniandW.B.Cashionwasgraciouslyprovidedfor our researchbyDr.Dyni,and ourstratigraphicsectionfollowedtheirsclosely.ThissectionanditsnomenclaturearealsocitedbyMauger(1977),whoattemptedtodateseveralashlayersintheIndianCanyon.Thesectionbeganonthedistinctive"HorseBenchSand-stoneBed" (bed 221ofDyniandCashion)ofDane(1954,1955),whichcanbe tracedeastwardthroughtheEvacuationCreekMember acrossmostofthebasin,andisapparentlyequivalentto the baseofUinta "A" intheeast(Francyzketal.,1989,fig.14).Thefirstsegment(section6ofDyniandCashion)waslocatedinwestsideoftheleftforkofIndianCanyon,easthalfoftheNWSec.22,T6SR7W,JonesHollow7.5'quadrangle,DuchesneCounty,Utah.Thissegmentran fromtheHorseBenchSandstonetothebase ofthesalinefaciesoftheUintaFormation(unit297ofDyniand Cashion),coveringtheupper 460feetoftheEvacuation CreekMember.Thesecondsegment(DyniandCashion,section7,units298-350)alongthebluffsonthewestsideofIndian Canyon, waslocatedinNW SW Sec.12inthesamemap;itcovered360feetofthelowersalinefacies.Thethirdsegment(section8ofDyniandCashion),also onthe westsideoftheleftforkofIndian CanyoninSESESec.1,T6SR7W,LanceCanyon7.5'quadrangle,cov-eredunits351-390ofDyniandCashion.Thefourthseg-ment(DyniandCashionsection9,units390-428)waslocated in the NW SW Sec.22,T5SR6W,BuckKnoll7. 5'quadrangle; units 429-456were collectedin SW NE Sec. 22.Thefifthsegment(DyniandCashion,section10,units457-484)coverstheuppermost330feetofthesalinefacies, and was locatedinNW NW NW Sec.28,T4SR5W,DuchesneSW 7.5'quadrangle.Thesixthsegmentcoveredthebasal200 feetofthelimestoneandsandstonefaciesoftheUintaFormation(units485-503ofDyniandCashion),and was locatedina west-trendingdrywash1 mileeastofIndian Canyon in NE SWSec.14,T4SR5W, Duchesne7. 5'quadrangle.Theremainingportionofthesandstoneandlimestonefacieswasnotsampledbecauseofdifficultyofaccessandpoorcontinuityofexposures.2.BiostratigraphyandMagnetostratigraphyoftheBridger ian-UintanWashakieFormation,WashakieBasin,WyomingSTEVEN M.MCCARROLL,JOHN J.FLYNN,AND WILLIAM D.TURNBULLABSTRACTWesummarizeandaddtothebiostratigraphyandmagneticpolaritystratigraphyoftheWashakieFormation,WashakieBasin,Wyoming.PreviouslytheWashakieFormation(dividedinto thelowerKinneyRimMemberandtheupperAdobeTownMember)wasthoughttocontainrocksofearlyBridgerianthroughlateUintanage.ContinuingcollectioneffortsintheWashakieBasinbytheField Museum of NaturalHistory (FMNH) allowustorevisethebiochronologicallydeterminedageoftheWashakieFormationtolateBridgerianthroughearlyUintanage.AlateBridgerianagefor the poorlyfossiliferousKinneyRimMember oftheWashakieFormationisindicatedby thepresenceofHyrachyuseximius(ataxonwithalateBridgerianfirstoccurrenceelsewhere).Inaddition,thefollowingtaxaarealsoknownfromtheKinneyRimMember:Peratherium cf.P.knighti,cf.Apatemysbellus,Hyopsodussp., Orohippussp., Mesatirhinussp.,Helaletesnanus,andHyrachyusmodestus(allknownfromtheBridgerianelsewhere,butnonerestrictedtothelateBridgerian,exceptpossiblyMesatirhinus).Inaddition,taxarestrictedtotheearlyBridgerianoftheBridgerBasin(e.g.,Smilodectes)havenotbeenrecoveredfromtheWashakieFormation,exceptfora possiblenewspeciesoftillodontfromtheKinneyRimMember.AnearlyUintan age for the upper unit of the AdobeTownMember,theuppermostunitintheWashakieFormation,isindicatedby the occurrenceofPareumys grangeri(restrictedtotheearlyUintanelsewhere).Inaddition,ParamyscompressidensandEpihippusgracilis(bothknownfromtheUintanelsewhere,butneitherrestrictedtotheearlyUintan)are alsoknown fromtheupperunit.TaxawithlateUintan first occurrencesor lateUintanindextaxahavenotbeenrecoveredfromtheWashakieFormation.ThepresenceofearliestUintan(Shoshonian"Subage")faunasintheWashakieFormation,indicatedbytheco-occurrence ofsmaller-bodiedtaxacharacteristicofthelateBridgerian(e.g.,Notharctusrobustior,Hyopsodus,andDilophodonminusculus) andlarger-bodiedtaxacharacteris-ticoftheearlyUintan(e.g.,Dolichorhinus,Eobasileuscornutus,Amynodonadvenus,andAchaenodon),isdocumentedforthefirsttimeinthemiddleunitoftheAdobe TownMember.INTRODUCTIONThispapercontainsanoverviewofthebiostrati-graphicandmagnetostratigraphicinformationcurrentlyavailable fromthe Washakie Formation in the WashakieBasin, southwestWyoming(seeFig.1). Weprovideaspecies list forthe fourstratigraphicunitsthatmakeuptheformation(Table1),discusscurrentconclusionsregarding the biostratigraphyand magnetostratigraphy oftheformation,anddiscussitscorrelationwithotherformationsthattemporallyoverlaptheWashakieFormation,particularlytheUintaFormation.Thispaperisanexpansionofanearlierabstract(McCarrolletal.,1993).To avoid confusionover terminologywe willstartbygivingafewdefiniti