Contrasts in Style of American Thrust Belts: Alabama, Arkansas-Oklahoma, Wyoming-Idaho, Montana, July 20-31, 1989 PDF
Preview Contrasts in Style of American Thrust Belts: Alabama, Arkansas-Oklahoma, Wyoming-Idaho, Montana, July 20-31, 1989
Contrasts in Style of American Thrust Belts Alabama, Arkansas-Oklahoma, Wyoming-Idaho, Montana July 20-31, 1989 Field Trip Guidebook T380 Leaders: William A. Thomas George W Viele Lucian B. Platt Christopher}. Schmidt American Geophysical Union, Washington, D.C. Copyright 1989 American Geophysical Union 2000 Florida Ave., N.W., Washington, D.C. 20009 ISBN: 0-87590-646-X Printed in the United States of America SoutheastlimboftheBinninghamanticlinorium,arampanticlineintheAppalachianfold-thrustbeltinAlabama(Stop11-10inthe RedMountainExpresswaycutthroughRedMountaininBinningham,Alabama). Thesoutheast-dippingMississippianFort PayneChert(FP),MauryShale(verythin), andSilurianRedMountainFonnation(RM)aredisplacedbyadown-to-southeast nonnalfault. Soft-sedimentdeformation,slumpfaults,andlocalthickeningonthedownthrownfaultblockintheuppennost sandstoneoftheRedMountainFonnation(U-RM)indicatesynsemmentarjfaultmovementduringtheSilurian. Thefaultisa brittlepost-sedimentaryfaultinthelowerbeds. Additionalpost-SilurianslippassesupwardintoamonoclinaldrapeintheFort PayneChert. Duringsubsequent(latePaleozoic)Appalachianthrusting,thenormalfaultwastranslatedandrotatedalongwith thefaultedbedsintothelimboftherampanticline. \ Leaders: William A. Thomas Department of Geology University of Alabama Tuscaloosa, AL 35487 George W. Viele Department of Geology University of Missouri Columbia, MO 65201 Lucian B. Platt Department of Geology Bryn Mawr College Bryn Mawr, PA 19010 Christopher J. Schmidt Department of Geology Western Michigan University Kalamazoo, MI 49008 Contrasts in Style of American ThlllSt Belts IGC FIELD TRIP T380: CONTRASTS IN STYLE OF AMERICAN THRUST BELTS WilliamA. Thomas DeparnnentofGeology,UniversityofAlabama,Tuscaloosa,Alabama GeorgeW. Viele DepartmentofGeology,UniversityofMissouri, Columbia, Missouri LucianB.Platt DeparnnentofGeology, BrynMawrCollege,BrynMawr,Pennsylvania ChristopherJ. Schmidt DeparnnentofGeology,WesternMichiganUniversity,Kalamazoo, Michigan PART I OVERVIEW OF THE FIELD TRIP INTRODUCTION synorogenicdeltaicto shallow-marineclastic-wedge rocks ofCarboniferous age. Possibleshelf-edgefacies Fold-thrustbeltshavemanyattributesincommon, areincludedinallochthonousmetasedimentaryrocks at butsomeoftheimportantattributes varygreatly. The thetrailingedgeofthefold-thrustbelt. purposeofthisfieldtripis toexaminetherangeof Thestratigraphic successionintheIdaho-Wyoming variationofseveralimportantattributesoffold-thrust partofthe Cordilleranfold-thrustbeltincludes a belts,including (1) thetectonic settingofdepositionof Proterozoicwestward-thickeningclasticprism, theallochthonous sedimentaryrocks, (2) thepresenceor Cambrian-Jurassicpre-orogenic shelffacies, andLate absenceofcrystallinebasementrocks intheallochthon, Jurassic toEocene shallow-marinetodeltaic synorogenic (3) thestratigraphiclevelofthebasaldecollement, (4) deposits. Thefrontal thrustfaults oftheMontana the geometryandinternalstructureofthrustsheets, and Cordilleranfold-thrustbeltcrosstheborderofafault (5) theeffectsofbasementstructuresbeneaththe boundedProterozoicdepositionalbasin. ThePaleozoic allochthononthe geometryandkinematicsofthefold andyoungerstratigraphic successioninMontanais thrustbelt. Fourregions inNorthAmericanfold-thrust similartothatinIdaho-Wyoming. belts (Fig.1-1)arevisitedonthisfieldtrip toexaminethe Incontrasttothefold-thrustbelts thatareformedof rangeofvariationinthelistedattributes. Thefour shallow-marinestrata,theOuachitafold-thrustbeltis regionsare (1) theAlabamaAppalachians (the formedentirelyofdeep-waterdeposits,comprisinga southernmostexposuresoftheAppalachianorogen), pre-orogenicoff-shelfsuccession (mainlymudstoneand (2) theOuachitas (exposuresintheOuachitaMountains chert)ofCambrian-Carboniferousageanda synorogenic inArkansas andOklahoma), (3) theIdaho-Wyoming turbiditeclasticwedgeofCarboniferousage. An Rockies (exposures oftheCordilleranfold-thrustbelt), accretionaryprismofoff-shelfstratahas beenthrustover and(4) theMontanaRockies (exposuresofthefrontal atime-equivalentautochthonous shelfsuccession,the partoftheCordilleranfold-thrust beltandbasement outboardmarginofwhichisindicatedbyseismic and structuresoftheRockyMountainforeland). gravitydatatobebeneaththepresentOuachita Mountains. Thepre-orogenic shelfedgemarks the approximatepositionofthemarginofearlyPaleozoic TECTONIC SETTING OF DEPOSITION OF NorthAmericancontinentalcrust. Pre- andsynorogenic ALLOCHTHONOUS SEDIMENTARY ROCKS rocks intheOuachitaallochthonweredepositedon highlyattenuatedcontinentalcrustoronoceaniccrust, StrataintheAlabamaAppalachianfold-thrustbelt whereas the shelf-faciesrocksintheAlabama includeapre-orogenic shelfsuccession (predominantly Appalachian,Idaho-WyomingCordilleran,andMontana carbonaterocks) ofCambrian-Carboniferousageand Cordilleranfold-thrust beltsweredepositedon T380: 1 " k ~\\' Yor ~ w n , o I:__1"----I------~--J( ~II~I"I.,.L--:1 ,)5~I/"If/<JACI1~%<b~~,/fNe/J...'-p%G\..:/I;:);'~//I~WashingtI!&\.______dO"\I<:)~~Q'~~«".~:v"~~~~,-"~,ttf.~~~,~'!;'-----------/--,,')<o".:f..:_I\__----/\,OKLAHOMA~__~~,"~Lr-'Oklah'"0r:'a,..~~:t&~I\ARKANSAS/:.;A"-'7City.),rp';;0",,__----C".."-..I1\----,-~OUACHITAq'll'~.~CJq,<l..LittleRock......,_.'__'.'",...'ICJO,t:_~lrmingham'-~ttf~,;':,',•Atlanta'I,~,~__)fOLD-THRUSTBELTI---\./'~\9-\(\~ALABAMA,'_'•IJ,..:.._,}'\\,\G9-\9-5.....J-..-./--.....I'_',)GU\\0\'\.--- (}Houston."", //~SCALEo./500KM/Miami-N-IIIII~ tedStatesshowinglocationsoftheAppalachian,Ouachita,andCordilleranfold-thrustbelts.detachmentisoutlinedbyboldlines(barbsonoverthrustside).LightdashedlinesshowtheoftheGulfandAtlanticCoastalPlainsandtheSnakeRiverPlain. -T7~------ MONTANASeattle:(,10\~,-oO;L~'\'f~~~fI~Bozeman~-----~~'j)",>1I~-~:(Y-I,'IDAHO~.".~~"J;ckson,"--o/~,-'I_'~'0'/~'------6~--'~'.'lSI,.--vWYOMIN~~--~I~~nciscoOJ'f v~.Q> "> "-7""-r--'",,---TION PPALACHIAN EXTERNALBASEMENTMASSIF OCKYMOUNTAIN FORELANDBASEMENTUPLIFT nakeRiverPlain FIGURE1-1OutlinemapoftheUniTheapproximatecratonwardlimitofofpost-orogenicrocksoverlaplimits a A A R S • r N F A n L P. Sa P ~ R. X • E / S. t-3W(»..o rv continentalcrust. generallytohigherstratigraphiclevelstowardthe Thesynorogenicdeep-waterclastic-wedgedeposits foreland. Locally,thedecollementisnearthebasement oftheOuachitasfuledaremnantoceanbasin,trench,and covercontactonbasementupliftsinMontana. forearc basin associatedwiththegrowthofan IntheOuachitas,thebasaldecollementis beneath·the accretionaryprism, and,inpart,lappedontothe accretionaryprismofoff-shelfdeep-waterrocks. A continentalmargin. Incontrast, the synorogenic largefrontalrampcutsthroughtheoff-shelfsuccession shallow-marinetodeltaicclastic-wedgedepositsofthe atorneartheearlyPaleozoic shelfedgeandemplacesthe AppalachianandCordilleranbeltsfilledforeland basins accretionaryprismofoff-shelfrocksontopofthe oncontinentalcrust. Clastic-wedgeprogradationand autochthonous shelffacies. Towardtheforeland, the foreland-basin subsidenceprogressedinfrontofan Ouachitabasaldetachmentrampsinto synorogenic advancingthrustload, andyoungerthrustfaults cut clastic-wedgerocks. Alongstrikebetweentheoutcrops throughtheoldercomponents oftheclastic wedges. intheOuachitasandthoseintheAlabamaAppalachians Erosionaldetritusfrom specificthrustsheetsispreserved (inthe subsurfacebeneathpost-orogenicMesowic locallyintheCordilleranfold-thrust belt. Cenozoiccoverofthe GulfCoastalPlain,Fig. 1-1), a lateralrampofregionaldimensionsisrequiredtoconnect thebasaldetachmentfromalevelabovethe ALLOCHTHONOUS BASEMENT ROCKS autochthonouspre-orogenicshelfsuccessioninthe Ouachitastothebaseofsamesuccessionwhichis Thethrustsheetstobevisitedonthis tripconsist allochthonousintheAppalachians. almostentirelyofsedimentaryrocksdetachedinthe lowerpartofthecoversuccessionabovecrystalline basementrocks. Relativelysmall "flakes"ofbasement GEOMETRY AND INTERNAL STRUCTURE rocks brokenfrompre-thrustbasementuplifts are OF THRUST SHEETS incorporatedinthefrontalthrustsheetsinMontana. Althoughtheallochthonintheexternalpartofthe Thrustfaults within shelfstratagenerallyhavea sled AlabamaAppalachianscontainsnobasementrocks, runnerprofile, as typifiedbythoseinAlabamaand thrustsheetsofbasementrocks andattachedcoverstrata Idaho-Wyoming. ThethrustsheetsintheAlabama formtheBlueRidgeandotherexternalbasementmassifs Appalachianshavebroadflats andareinternally intheAppalachiansnortheastalongstrikefromAlabama coherent; athickstifflayerofcarbonaterockscontrolled (Fig. 1-1). Similarly, southwestofWyominginthe the geometryofthefaults andfolds. Zonesof Cordilleranfold-thrustbelt, somethrustsheetscontain disharmonicdeformationareassociatedwith basementrocks, suggestingbasement-rootedthrust decollement-hoststratigraphy. Thethrustsheetsinthe faults. Cordilleranfold-thrustbeltaregenerallysimilartothose intheAlabamaAppalachians; however,thegeometryof thrustsheetsinMontanaiscomplicatedbytheeffectsof STRATIGRAPHIC LEVEL OF THE BASAL pre-thrustbasementstructuresandbyinternal DECOLLEMENT shortening. Incontrasttothrustsheetsofshelfstrata, thethrustsheetsintheOuachitasareinternally IntheAlabamaAppalachians, abasaldecollement disharmonic, andolderthrustsurfacesarefolded. nearthebaseofthepre-orogenic shelfsuccession(near Small-scalestructuresandfabrics intheOuachitasare thebasement-covercontact)extendsthroughoutthefold characteristicofanaccretionaryprism. thrustbelt. Frontalramps generallyrisefromthebasal detachmenthoriwntothepresentsurface,butlocally, thefrontalrampsconnecttoanupper-leveldetachment. BASEMENT STRUCTURES BENEATH THE InsomeplacesintheAppalachiansnortheastof ALLOCHTHON Alabama,the basaldecollementrampsfromthehorizon nearthebaseofthesedimentarysuccessiontohigher Inthreeoftheregions, basementstructurebeneath stratigraphiclevelstowardtheforeland, andthefrontal thefold-thrustbeltisinterpretedfromdrilldataand partofthefold-thrustbeltisformedonextensiveupper geophysicaldata, butbasementstructuresareexposedat leveldetachments. thefrontoftheMontanafold-thrustbelt. InMontana, LikethatintheAlabamaAppalachians,thebasal thrustfaults haveoverriddenpre-thrustbasement-cored decollementintheldaho-WyomingCordilleranfold uplifts,whichinfluencedthe geometryandkinematicsof thrustbeltisnearthebaseofthesedimentarycover thethrusts. Obliquethrustramps arepositionedover succession. Thestratigraphicallylowest(oldest) basementfaults (RockyMountainforelandbasement decollement-hostunitsthinandpinchouteastward uplifts,Fig.1-1)thatareapproximatelycoevalwith towardtheforeland, andthedecollementrisesinto thrusting. Thelargestknowntransverserampinthe progressivelyyoungerrocks inthatdirection. Some Cordilleranfold-thrust beltis associatedwithamuch frontal thrustfaultsrampuptohigherlevelswithinthe older,pre-thrustbasementfaultinMontana. Break-back stratigraphicsuccessiontowardtheforeland. thrustsequencesresultedinsomeplacesbecausepre The stratigraphiclevelofthebasaldetachmentin thrustbasementupliftsimpededtheadvanceofthethrust Montanavarieslocallyinresponsetopre-thrust sheets. basementblockfaults, butthedecollementrises Steepbasementfaults, approximatelyparallelwith T380: 3 the strikeofthefold-thrustbelt,underlietheAlabama butsomethrustfaults areinabreak-backsequence, AppalachianandOuachitabasaldecollement,andinboth probablybecauseoftheobstructiveeffectofpre-thrust regions, frontal thrustrampsrise overthebasement basementfaultblocks. Thethrustsequenceinthe faults. Cross-strikestructuraldiscontinuities (CSDs: Ouachitasiscomplexandpolyphase. rough alignments across strikeofthefold-thrustbeltof pointsofalong-strikechangein structureofthrustfaults and/orthrustsheets)areidentifiedintheAlabama Acknowledgments Appalachians,buttheoriginofthesetransverse structuresis notknown. Possibly, theyarepositioned Wegratefullyacknowledgethoroughreviewsofthe abovebasementfaults inawaycomparabl~tothatofthe entire guidebookbyR. P. NickelsenandJohnRodgers, largetransverserampinMontana. Thefold-thrustbeltin as wellas byD. N. Bearce,oneofthecontributors to Alabamagenerallyrecords abreak-forwardsequence, Part II. T380: 4 PART II THE APPALACHIAN FOLD-THRUST BELT IN ALABAMA WilliamA.Thomas DeparttnentofGeology,UniversityofAlabama,Tuscaloosa,Alabama INTRODUCTION bytheBlackWarriorforelandbasinandonthe southeast bymetamorphic thrustsheetsofthePiedmont(Fig. IT Allochthonous strataintheAppalachianfold-thrust 1). IncentralAlabama, thePaleozoicorogenextends beltinAlabamarangeinagefromEarlyCambrianto southwestwardbeneathpost-orogenicMesozoic MiddlePennsylvanian. Thethrustsheetscontainno CenozoicstrataoftheGulfCoastalPlain. Wellsdrilled basementrocks, butautochthonous basementbeneaththe throughtheCoastalPlainstratadocumentthatthe fold-thrust beltis broken by steep,pre-thrust,normal orogenic beltextends southwestward,curves westward, faults. Thefold-thrustbeltis borderedonthenorthwest andcontinues northwestwardtotheexposedPaleozoic ANTICLINES: BC-BlueCreek BH-Birmingham LV-LookoutValley MC-McLemoreCove MV-MurphreesValley PV-Peavine sa- /1 Sequatchie I I WV-WillsValley ~~1'"' SQ:.. "............. SYNCLINES: J- \ - - ...... ICI) 1 ", i WARRlb~:) BTM-BlountMountain CAH-Cahaba BLACK CLB-Coalburg COO-Coosa I FORELAND BASIN FLD-Floyd I1 t\ LKT-Lookout SDM-SandMountain I THRUSTFAULTS: I I B-BigCanoeValley C-Coosa D-Coosadeformedbelt E-Eden G-Gadsden H-Helena \ I- IndianMountainthrustcomplex \ J-JonesValley \ K-SleepingGiantsthrustcomplexklippe M-ChoccoloccoMountainthrustcomplex o-OpossumValley " \ EXPLANATION \ P-PellCity SCALE R-Rome ~ THRUST FAULT 0I 5I0 KM S-StraightMountain ANTICLINE T-Talladega • SITE OF ABRUPT ALONG-STRIKE CHANGE V-Cartersville CENTRAL DOMAIN Y-Yellowleaf FIGURE11-1 OutlinestructuralgeologymapoftheAppalachianfold-thrust beltinAlabamaandGeorgia Thename ofeachcross-strikestructuraldiscontinuity (CSD)isplacedinlinewiththealignmentofpointsofalong-strike changeinstructurealongtheCSD. Thenorthwesternandsoutheasterndomainsofthefold-thrust beltarelocated withrespecttothecentraldomain; wherethecentraldomainisnotrecognized, theRomefaultistheboundary betweenthenorthwesternandsoutheasterndomains. T380: 5
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