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1、Sedimentology(2012)59,17351768doi:10.1111/j.1365-3091.2012.01324.xEvolutionofanorganic-richlakebasinstratigraphy,climateandtectonics:PiceanceCreekbasin,EoceneGreenRiverFormationKATITA¨NAVSUU-MILKEVICIENEandJ.FREDERICKSARGDepartmentofGeologyandGeologicalEngineering,ColoradoScho
2、olofMines,Golden,CO80401,USA(E-mail:ktanavas@mines.edu)AssociateEditorNickEylesABSTRACTThePiceanceCreekbasinformedasacontinentalforelandbasinca53to48MaintheearlytomiddleEocene.Onaglobalbasis,thebasincontainsoneoftherichestoilshaleresourcesknown,wheretheprofundaloilshaledeposit
3、s,kerogen-richmudstones(clayandcarbonate),existovermostofthebasin.Despiteitseconomicimportance,theevolutionofthePiceanceCreekbasinisstillsomewhatunclear.Basedonfaciesassociationanalysis,depositionaltrends,andgammarayandFischerassaydata,sixevolutionarylakestagesarerecognized:(i
4、)freshlake;(ii)transitionallake;(iii)highlyfluctuatinglake;(iv)risinglake;(v)highlake;and(vi)closinglake.Lakestagesarecomposedofdepositionalunitsandcharacterizelarge-scalechangesinsedimentologicalpatterns,depositionaltrendsandfluctuationsintheoilshalerichnessrelatedtochangesincl
5、imateandtectonics.LakestageevolutionisalsoconsistentwiththeglobalEoceneclimatetrend.Stage1formedpriortotheEoceneclimateoptimum.AtthebeginningoftheEoceneclimateoptimum,asaline-restrictedlakeformed(Stage2)andevolvedintothehighlyfluctuatinglake(Stage3)indicatingrapidclimatechanges
6、duringthepeakoftheEoceneclimateoptimum.Thisstagewasfollowedbytherisingandhighlakes(Stages4and5)aftertheclimateoptimumandduringachangetoamorehumidclimate.Theclosingofthelake(Stage6)wascausedbyincreasedsandinputfromthenorth,indicatingtheinfluenceofbothtectonicsandclimate.Basedond
7、epositionaltrendsandclimateevolution,itissuggestedthat,duringthearidclimate,laterallyheterogeneoushighlycyclicdepositionalunitsdominate,whereas,duringthehumidclimate,depositionalunitsformlaterallycontinuoussedimentsthatcanbetracedoverlongdistances.KeywordsClimate,Eocene,GreenR
8、iverFormation,limnogeology,oilshale.INTRODUCTIONtohighlakelev
