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prebreakup geology of the gulf - Centro de Geociencias ::.. UNAM
TECTONICS, VOL. 12, NO. 2, PAGES 441-459, APRIL 1993 PREBREAKUP GEOLOGY MEXICO-CARIBBEAN: TRIASSIC OF THE AND OF THE GULF ITS RELATION JURASSIC RI•T OF TO SYSTEMS REGION Peter Bartok BritishPetroletunResearch,England Abstract. A reviewof the prebreakupgeologyof west centralPangea,comprisingnorthernSouthAmerica,the Gulf of Mexico, and West Africa, combinedwith a studyof the Mesozoicriff trendsof the regionconfirmsa relationbetween the rift systems and the underlyingoldergrain of deformation.The prebreakupanalysisfocusesattentionon the Precambrian,earlyPaleozoic,andlatePaleozoictectonic eventsaffectingthe regionand asstunes a Pindellfit. Two latePrecambrianorogenicbeltsare observed in westcentral Pangea. Alongthe northernSouthAmericanmarginand Yucatana palconortheasttrendingPan-Africanagedfold belt is documented.A secondsystemis observed alongWest Africaextendingfrom theHigh Atlasto theMauritanidesand Rockelides.Similaragedorogenies in the Appalachians are compared.Duringthe latePaleozoic,renewedorogenic activity,associated with the Gondwana-Laurentia suture, affectedlargesegments of westcentralPanget. The general trendof the systemis northeast-southwest andessentially parallelsthe Guayanacratonand WestAfrican and eastern NorthAmericancratons.Mesozoicrifling closelyfollowed eitherthePrecambrian trendsor thelatePaleozoicorogenic belt. The Triassiccomponentfocusedalongthe western portionsof the Gulf of Mexico continuinginto eastern Mexico and western South America. The Jurassic rift trend followedalongthe separation betweenYucatanandnorthern SouthAmerica. At LakeMaracaibothe Jurassic rift system eventuallyoverlapsthe Triassicriffs. The Jurassic rift resultedin the "HispanicCorridor"thatpermittedTethyan and Pacific marine faunas to mix at a time when the Gulf of Mexico underwent continental sedimentation. INTRODUCTION The latePaleozoicpaleoreconstruction of Pangea,published by Rossand Scotese[1988], Pindell andDewey [1982], and Pindell [1985] and adjustedto accommodate the work of Dunbarand Sawyer[1987], providesa startingpointfor developingthe sequence of Mesozoicrifting in "westcentral" Pangea:Gulf of Mexicoand Caribbeanregion(Figure1). Two problemsare the framefor the discussion in this paper: (1) definitionof the causesfor the rift tracesobserved in the regionand(2) evaluationof thetimingandtrendof the tectonicfeaturesassociated with Mesozoicriftingin thefocus area. It is necessary thereforeto considerboththe late Precambrianandmid-Paleozoicgeologicsettingfor the terranesdiscussed in thepresentstudyaswell asthe region's latePaleozoichistory. Specialemphasis is placedon northernSouthAmerica. Intuitivereasoning suggests thatif an inherentzoneof weakness is presentin an area undergoing thermalexpansion, riftingwill eitherfollowor closelyparallelthe traceof the zoneof weakness.The presentstudywill demonstrate that in westcentralPangea thereis a persistentrelationshipbetweenthe ancestral tectonichistoryof the regionandthe Mesozoicrifling events. For a reviewof thepost-Jurassic tectonicdevelopment of the regionthe readeris directedto the Caribbeanreviewpapers by Burke [1988] andPindell and Barrett [1990]. A recently publishedcorrelationchartfor the Caribbeanprovince [Maurasse,1990] may assistreadersnot familiar with the region'snomenclature. Threemajororogeniceventsare documented in the prebreakupof westcentralPangea:a late Precambrian,an earlyto middlePaleozoic[Scotese,1984; Scoteseand McKerrow,1990](Figure2), anda latePaleozoicorogeny associated with the Pangea suture(Figure3). For descriptive purposes the geologyof thePrecambrian to early Paleozoicof westcentralPangeais subdivided into geographic segments, namely,northernSouthAmerica, Yucatan, West Africa, and Florida. Mesozoicriffing in westcentralPangeais well documented alongtheseaboard portionof theNorthAmericanlate PaleozoicAlleghanian/Ouachita foldbeltslI•tcher et al., 1989]. The westerncoastof Africaandportionsof northwesternSouthAmericahaveundergonecontemporaneous rifting[Anderson andSchmidt,1983](Figure4). Jurassic riftinggenerallyparallelstheonshore Triassictrendandsteps outalongitspresent-day seaward side.Fewdirectcontrol points[Bartoket al., 1985]andseveralindirectinferences supportthesouthern extension of theJurassic grabentrend, lyingbetweenYucatanandSouthAmerica[RossandScotese, 1988](Figure5). RossandScotese [1988]suggested thata continuous rift event prevailedin the Gulf of Mexicoand Caribbean regionfromtheTriassicto theJurassic.However, thepresentstudyproposes a moreepisodicrifting system. The Triassicrift systemextendsfrom the Newfoundland andCanadianAtlanticoffshorethroughtheNewarkgraben system,the Carolinasand Georgia[Sheridan,1989; Manspeizeret al., 1989] (Figure6). In centralGeorgia, thetrendeitherwidensor splayswith the northernbranchtrendingalongthe OuachitaMountainfront [Vernon,1970;Walper, 1980]. The southernbranchextends alongthe Suwannee depression of northernFloridaand northwestern Yucatan[Salvador,1987] (Figure4). The Triassicrift systemcontinues southinto easternMexicoand northwesternSouthAmerica. Althoughthe nomenclature differsin the variousareas,the basiclithologicdescriptions of the sequences are quitesimilar. The Mexicanequivalentto theEagleMills Formationis theLa BocaFormation(lower memberof the HuizachalGroup[LopezRamos,1983]. In southernMexico, Yucatan,and northernSouthAmericathere is someevidencefor Triassicsedimentation,but it is much lessclearlydefined.The Payanderift seriesof bothredbed andmarinestrata[Burgl, 1963] andthe La Ge Group (Tinacoaand Macoita formations[Benedettoand Odreman, 1977], respectively,exemplifythesesystemsin Colombiaand Venezuela. Copyright1993 by the AmericanGeophysical Union. Paper number92TC01002. 0278-7407/93/92TC-01002510.00 Jurassicrifting wasoriginallyinferredfrom the biotic exchangeof TethyanandPacificfaunasobserved in the easternPacificregion,from westernCanadato Peru. Tethyan faunasfirst livedin thePacificduringthePliensbachian, at the earliest[Westermann,1980; Smith, 1983] (Figure 7). This occurredat a time of non marine 442 Bartok: Prebreakup ofGulfofMexico-Caribbean and Rifting INORTH AMERICA[ / AR ",4 / LAURENTI / WES T AFRICA WEST CENTRAL PANGEA MARACAIBO,• I 200 ' ! 400 [ I 600 [ ! 800 KM Fig.1.General location ofthewest central Pangea area ofstudy. ForLauentia, abbreviations areT, Texas; L,Louisiana; AR,Arkansas; M,Mississippi; A,Alabama; G,Georgia; F,Florida; SC,South Carolina; SF,South Florida Block; FSB, Florida Straits Block (Bahamas). ForSouth America, abbreviations areYUC, Maya Block (Yucatan); P1L Pinar delRio(western Cuba); V,Venezuela; G, Guyana; S,Surinam; FG,French Guyana; C,Colombia. ForWest Africa, abbreviations areSM,Southern Morocco; M, Mauritania; S,Senegal; GB,Gabon; G,Ghana; andSL,Sierra Leone. deposition intheGulfofMexico rillsystem. In addition, extensive Jurassic grabensystems aredocumented in northwestern Venezuela [Banok etal.,1981; Maze,1984]. Floralassemblages [Gonzalez deJuana etal.,1981]and marine fauna[Banok etal.,1985]provide thebasis for establishing theirage.Themain trace ofthedominantly section focuses onthePrecambrian toPaleozoic sequences of theregion. ThePrecambrian Shield isfollowed northward by anaccreted latePrecambrian terrane thatwassubsequently affected by Palaeozoic orogenic activity. ThePrecambrian Shieldin Venezuela hasbeensubdivided intothreeprovinces (Figure 8) lMartin,1972;Gonzalez Jurassic riftinghasa paleonortheast-southwest trendandlies between thecentralFlorida-Yucatan BlockandtheSouth American Block(Figure5). deJuana etal., 1981;Caseetal., 1984]. ThePastora province ranges in agefrom3000to2000Ma, timeequivalem totheSuperior province oftheCanadian THE PRECAMBRIANTO EARLY PALEOZOIC Shield.The Cuchivero province of Venezuela andthe Amazonas ofBrazilranges in agefrom 2000to 1400Ma. Northern South America Thepresem-day physiography ofa Coastal Cordillera anda Tertiary foreland basin overprims thecomplex pre-Mesozoic geology of thenorthern marginof SouthAmerica.Thebelt isbound tothesouth bytheGuayana Shield andimerrupted inthewest byseveral spurs oftheAndean range.This TheRotalma province, containing thickredsandstones, overlies theolderunits(Figure8). Itsageisatleast Grenvillian. Locally,radiometric agedates from1600to 1800Mahavebeenreported fromdiabase sillsintruding the redbedslMartin, 1972]. Of interestisthedescription ofthenorthcentralCuban Precambrian complex dated atq-900Ma [Renne etal., 1989; LewisandDraper,1990].Some paleo-reconstructions place Bartok: Prebreakup of GulfofMexico-Caribbean andRifting 443 centralCubato the northeastof Venezuela(Figure8) [Andersonand Schmidt,1983;Rossand Scotese,1988]. Therefore the Cuban Precambrian should be related to the similaragedunitsin the adjacentterranes.Similaraged rocksarepresentin theRoraimaregionandareassociated with the orogenesis knownasthe Orinoquean(1300-850Ma) [Martin, 1972]. The currentlyusedreconstruction suggests a relationship betweencentralCubaandtheRoraimaProvince of Venezuela. EIC/I•ALE OCEAN Externalto the provincesdescribed aboveare a seriesof orogenic beltsthatrangein agefrom680 to 500/via. They arecommonlygroupedastime equivalentto thePanAfrican orogenies observed in WestAfrica andthe Avalonianorogeny of easternUnited States[Hatcher,1989b]. Severalwhole rockand mineralspecificradiometricagesin central Venezuelayield agesthat conformto the latePrecambrian eventdescribed above[Irving, 1975;F• Codecidoet al, 1984](Figure8). Theyrepresent partof a buriedcomplex orogenicsystemtrendingessentially east-west to northeast thatappearsto haveaccretedontothe OuayanaShield. The outcropping Avispamassffwasaffected by thisorogeny (660 Ma, Rb/Sr)aswasthe Santander massif(680Ma [Irving, 1975]). Its centralcoreis readilydetectable asa regional magnetichigh [Cabrera,1985] (Figure9). Martin [1978] referredto this orogeniceventastheMeridianPhase. Fragmentsmay extendnorthof the anomalyandinclude featuressuchastheTinacoComplex(642Ma [Martin, 1978] and Sebastopol Complex(425 Ma, wholerockRb/Sr). The rHY8 v v EARLYPALAEOZOIC DEFORMED BELT8 Fig. 2. Globalreconstruction duringtheearlyPaleozoic indicatingthelocationof theCaledonian foldbelts(adapted from Scotese[1984] and Scotese andMcKerrow[1990]. MISSISSIPPI lUSAI OUACHITA YUCATAN COAHUILA PLATFORM (MAYA BLOCK) SIERRA MADRE CUCHUMATANES [VENEZUELA I EL BAUL 0 20o 400 KM CORDILLERA PERIJA•• L. MARACAIBO Fig. 3. Late Palaeozoicfoldbelt acrosswestcentralPangea.Horizontalshadingshowsthetrendof the well-documented Appalachian/Ouachita CentralCordilleratrend. The verticalshadingrepresents the expectedtraceof the latePalaeozoicorogenies alongthe southernmarginof the Gondwanasuture. 444 Bartok: Prebreakup ofGulfofMexico-Caribbean andRifting / / • +• ./ SUWANNEE •ET•'.CE • .•;•-;n /.'., .,•,.• EAGLE ½• ',LLS• •.-.•+..,• SABIN UPLIFT/' •/DEPRESSION .• • LOS NOel /:: / ".......... ' TI*•O•:•• • I -ANG•NA-•ALD'LL I I o • I I 200 KM Fig.4.Trend oftheTriassic synrift sequences inwest central Pangca. Solid linesouth oftheAngelina CaldwellandWigginshighscorresponds totheGulfCoast fromTexastoFlorida. TRIASSIC RIFT MAY HAVE BEEN REACTIVATED YUCATAN HISPANIC IR LOCATION ESPINO SIQUISIQUE GRABEN GIRON O•ITE / '"'" ANTECAL LA QUINTA •M GRABEN I I 200 I I 400 I o KM Fig.5.Distribution ofthemajor Mid-Jurassic rifttrace inwest central Pangea. Stippled linewithin the darkshaded areacorresponds totheGulfCoastfromTexastoFlorida. former iscomprised ofbasiclavasandamphibolite facies metamorphics. Thelatteris a graniticgneiss.Bothwere incorporated intotheMesozoicCoastalCordilleraof north central Venezuela [Gonzalez deJuana, 1981](Figure 9). Notethatin Cuba there isnoknown evidence forsimilar aged orogenic activityIRenneet al., 1989]. Cambrian riftingfollowed in proximity tothelate Precambrian orogenic events affecting northern South America [Martin,1972].Oneexample ofthiseventistherift andpostriftsequences thatcorrespond totheGuejar Group of theColombian LlanosIForero Suarez, 1990].Another isthe HatoViejoandCarrizal formations ofeastern Venezuela IFeo Bartok:Prebreakupof Gulf of Mexico-Caribbean andRifting 445 spreadingmodelmay accountfor the SouthAmerican .•0ø counterpart. In Venezuela,thereis evidencethat the rift systemlies betweenthe late Precambrianorogenicbelt and the shield (Figure7). Two Cambrianrift segments are documemed, the Espinoandthe Apure-Mantecalgrabens(Figure9). Cross sectionAA' (Figure 10), basedon seismicdata,showsthe M •x CANADA \ j 3• ø • TRIASSIC RIFTS ALONG THE APPALACHIAN CHAIN M A f 30ø character of thedepositsin theEspinograben. The ageof the CarrizalFormation(red shales),the oldest datedsediments, hasbeenestablished by the presence of an association of acrytarchs asLate Cambrian to Ordovician [Feo-Codecido et al., 1984]. The underlying unitshaveyet to be dated. At El Baul (Figure9), the fossiliferous lowerPalaeozoicmetasediments of the Caparo Formationcorrelateto similarunitsoutcropping in the southernMerida Andes[Gonzalezde Juanaet al., 1981]. The lattercontainsOrdovicianmarinesediments[Hughes, 1980]whichare mostlikely associated with theMantecal graben.Ulloa et al. [1982] andHughes[1980]reported similaragedsediments in severalwellsdrilledin the ColombianLlanosand in outcropson the Macarena Mountainsof centralColombia(Figure8). McCollough [1990] provideda schematiccrosssectionof theMantecal Grabensystem,suggesting moreintensepre-Cretaceous deformation in the Mantecal area than that observed in the Fig. 6. Generaldistribution of majorterranesandtectonic featuresalongeasternUnitedStatesreferredto in thetext. BMA is BnmswickMagneticAnomaly;ECMA is EastCoast MagneticAnomaly.MajorTriassicgrabens areindicated [Manspeizer,1981]. Codecidoet al., 1984]. Similar agedrifling is alsoreported alongthe Appalachiansystemof easternUnitedStates. There,the rifting is associated with the openingof the Iapetus Ocean(back-arcspreading) andthe openingof the Theic (Paleotethys) Ocean[Hatcher,1989a](Figure2). A back-arc EspinoGraben. The CoastalCordillerasystemburiesthe northernextensionof the EspinoGraben. A description of the tectonicsystemactivein northernSouthAmericaduring the earlyPaleozoicis analogous to the pre-Acadian development of the Appalachiantrenddescribed by Hatcher [1989a]. It is noteworthy that in the Appalachiantrend, Triassicrifting reactivatedseveralof the Cambrianrifts describedabove[Dewey, 1988]. Early to middlePaleozoic(Caledonianequivalent)orogenic eventsare reportedthroughoutthe northernAndes[Irving, 1975; Gonzalezde Juanaet al., 1981; ForeroSuarez,1990]. Burial and overprintingobscurethe preciselocationof the system.Whethertheyparallelthe Precambrianorogenicbelt is yet unclear. However,theyarepresentat leastfrom the Santanrermassifof Colombia[Irving, 1975] to the Merida Andesof Venezuela(Gonzalezde Juanaet al., 1981] (Figure 8). The eventis not considered majorandis partlyinferred in Venezuela.Prehnite/pumpellyite faciesmetamorphics BOREAL TET HYA N / Fig. 7. EarlyBajocianPacificammoniteassociations [Westermann, 1980]. 446 Bartok: Prebreakup ofGulf ofMexico-Caribbean and Ritting 80 o 60 ø 1250 c.cus•. _..• MERIDA ANDES 1400 ISm-SANTA MARTA MASSIF •']- SANTANDER MASSIF 10 o_ VENEZUELA MTS 1690. 2250 4 PASTORA / 1725t/ 1955 ..• X •• 20e4) X COLOMBIA • 1790 1770 I X2• \ X --X GUAYANA • 205 / GUIAN) MACARENA ' \ • BRAZIL 0o_ ( ..• AREA AFFECTED BYCAMBRIAN RIFTING LATE PRECAMBRIAN FOLDBELT RORAIMA 6OO-1400Ma X o CUCHIVERO 1400-2000Ma /• PASTORA 2000-3000Ma [ ß o 200 I I I FEO CODECIDO AND OTHERS (1984) RENEE AND OTHERS (1989) HUGHES (1980) ß ULLOA,PEREZ,AND BALDIS(1982) 400 I IRVING (1975) I KM Fig.8.Northern South America Precambrian toearly Palaeozoic outcrop andsubcrop distribution. GUAJIRA PARAGUANA 265 EL AMAPARO GUARUMEN GRABEN SEBASTOPOL ! ESPINO •C• 425 // 364 ! / 10• GRABEN ICOTEA FAULT 30,000 MERIDA / ANDES / / 595 SANTANDER I 1133 I•)c / AVISPA '/ •o• •. e/ . ß 270 EL BAUL )MASSIF e660 •. 433 •.-./680 • 347 (+) ß400 ß . ,ooO - MAGNETICBASEMENT BASEDONCABRERA (1985) RA• MANTECAL 73 • i GRABEN 71 ø I AGES FEOCODECIDO ANDOTHERS (1984) APURE %% •. 0 50 100 150 I 69ø---...., I GONZALEZ DEJUANA AND OTHERS (1981) •/ 67ø I 65ø I 63ø I . KM I I 61ø I Fig.9.Structural mapofdepth tobasement onaeromagnetic data[Cabrcra, 1985] andagedates from Gonzalez deJuana ctal. [1981]andFcoCodccido ctal. [1984]. associated withtheearlytomiddle Paleozoic orogenies have been observed inthePerija Range andMerida Andes [Martin, 1978]. BoththeEasternCordilleraof Colombiaandthe Merida Andes yieldseveral radiometric agedates ranging from460to390Ma. Scotese andMcKerrow [1990] suggested thatthisearlyPaleozoic orogeny focused along the westernmostportionof Gondwanaand was relatedto active margin deformation. Thebasicsystem of a Proterozoic eraton,a late Precambrian accretion wedge, Cambrian riffing,and subsequent orogenesis, described above, isnotubiquitous over thenorthern portion ofSouth America.Alongits Bartok:Prebreakup of GulfofMexico-Caribbean andRifting 447 iI A CAMPO RUIZ SEA LEVEL ALTAMIRA .•- .... • .... m HIGH STA. R I TA - 1X m CHAGUARAMAS BASAL SS, m ROBLECITO ß o ß 5000' TIGRE GUAYANA SHIELD CARRIZAL M ETAMORP HIC S ' PANAFRICAN AGE' PHASE 10,000' +++•,. G Fig. 10.EspinoGraben, eastern Venezuela (interpretation ofD. Kiserasshown byFiorillo[1982]). northwestern corner,severalelements complicate thetectonic system outlined above.Ontheonehand,Grenvillian aged unitsare found on the SantaMarta Block [Tschanzet al., 1974],theGuajimPeninsula andin theMeridaAndes (Figure8 [Caseet al., 1990],outboard ofthePrecambrian orogenic system thatrimstheGuayana Shield.Totheeastof SantaMarta,in thePerijaRange,Devonianstrataof theRio CachiriGroup[Bowen,1972]arewelldocumented bytheir macrofaunal assemblages [Benedetto, 1982;Sanchez and Benedetto, 1983]. Devoniandeposits aredescribed in other areasof westernColombia[Burgl,1963;ForeroSuarez, 1990]butarenotknownto existin anyareasof Venezuela eastof thePerijaRange[GonzalezdeJuanaet al., 1981]. Furthermore, the Devonianfaunasof thePerijashavea strong Appalachian affinityandmayrepresent portions oftheNorth AmericaLaurentiaBlock[Benedetto, 1982]. The Grenvillian agesobserved in thecentralMeridaAndes(Avispa massif) arepossibly fragments oftheGuayana Shieldincorporated into the late Precambrian fold belt. Sedimentswith Laurentia affinities juxtaposed against a Gondwana suiteof sediments andmetasediments requirethepresence of a majorsuture locatedsomewhat eastof thePerijaRangeandwestofthe MeridaAndes(Figures8 and9). ThecentralLake Maracaibofault system[Bartoket al., 1981] may represent sucha plateboundary(Figure9). The Maya Block (Yucatan,Guatemala.Belize,Western Cuba,andParaguana) The Maya Block,asdescribed by Andersonand Schmidt [1983],is expandedto include not onlythe Yucatan Peninsula,Belize, andthe bulk of Guatemalabut alsowestern Cuba(PinardelRio Province)andtheParaguana Peninsula of Venezuela. The PrecambrianChiapasmassffregionof southernMexico is considered to be the westernmost portion of the Maya Block. TheMayaBlockis definedby smallcratoniccenters located in northcentralGuatemalaandYucatanand the Chiapas massif.The orogenic beltspresentontheBlockincludethe Mayamountains of Belize,the Cuchumatanes Rangeto the south,andtheChiapasmassif;it mayincludethehighly deformedChuacus Range. The oldestrocksontheMaya Blockarelocatedonthe ChiapasMassfl. There,radiometric agedatesof 1760Ma havebeenreported[LopezRamos, 1983]. Zirconageson severalgranitesof southern Guatemala havereportedagesof 1075and345Ma [Donnelly et al., 1990]. The olderdatesmayrepresent inheritedages with emplacement duringthe middlePaleozoic[Donnellyet al., 1990]. To the north,the limit is the edgeof the Campeche Platform(Figure11). The northeastern offshore portionsof theplatformhavebeendrilledby several DeepSeaDrilling Project(DSDP)holes.The radiometric agesof theirbasement rockmineralassemblages, basedon 40At/39At methods, clearly suggest aPanAfrican aged association, 500 to 547 Ma [Dallmeyer,1984]. Onceagain, in the Chiapasregionseveralagedatesrelatedto the late Precambrian havebeenreported[LopezRamos,1983]. On Yucatanproper,evidence to suggest an earlyPaleozoic orogeniceventis scarce.The Yucatan-1well (Figure11) penetrated a rhyolitewith a wholerockageof 410 Ma [Lopez Ramos,1983]. In southcentralGuatemala,the highly contortedmetamorphicrocksof the ChuacusFormationare 448 Bartok: Prebrealmp ofGulfofMexico-Caribbean andRifting 63Ma.•/ 538_ 540/' 0 ,,.t'•/ 23øN + + iER--536 + cl",• (1 •21øN + + / YUCATAN • WELL -19øN+• [--., .... - 17ON + + LATE PRECAMBRIAN EARLY PALEOZOIC ACTIVE MARGIN OVERPRINTED BY LATE PALEOZOIC FOLDING ,•,•_['".-_• •.' ,,._ , ß '• PUS POLOCHIC MOTAGUA , -_• / F.Z. -15øN CHUACUS k•• ß-'•.. ,-' + LATE PALEOZOIC ' '*- FOLD BELT ..... • / LATE PALEOZOIC PENETRATIONS (BISHOP, 1980) 93øW 91 øW 89øW 87øW 85øW i i I I I Fig. 11.MajortrendsontheYucatanPeninsula. estimated tobeasoldasPrecambrian orasyoung asearly Paleozoic [Anderson andSchmidt, 1983]andrangefrom greenschist toamphibolite gradelKesler,1971]. Overlyingthe ChuacusFormationare a seriesof Permo- Carboniferous low-grade metamorphics oftheless tectonically disturbed TacfitandSanta Rosagroups (Macal Series) andMesozoic toTertiary sediments lKesler etal., 1971;Bishop, 1980].TheMacalSeries contains phyllites, conglomerates, limestones,and marbles. In central Guatemala, theMatanzas stock, dated at275Ma [Weyl, 1980],penetrates theChuacus Formation [Anderson and Schmidt, 1983]andthusprovides anupperagelimittothe unit. Kesleret al. [1971] describe thedirectional tracesof foldaxeswithintheCuchumatanes. Thefirstisessentially eastwest,andthesecond is rotated35øto 55ø,to almost northsouth.Regardless oftheirexact age,bothformed prior tothedeposition ofthelatePaleozoic Santa RosaGroup. Could theyrepresent twophases oftheearlyPaleozoic folding TheParaguana Peninsula ofnorthern Venezuela (Figure9) hasa verysimilarrockassemblage to theonedescribed in the MayaBlock.High-grade metamorphic rocks, amphibolite schists, andgneisses oftheMiralejos Formation [FeoCodecido etal., 1974]areintruded bytheAmparo Granite (265Ma, U/Pb[Feo-Codecido et al., 1974]). Associated with theserocksarelow-grade metamorphic phyllites, red sandstones, andconglomerates. It is suggested herethatboth rocksuitesmaybe closelyrelatedto theirYucatan counterparts (Chuacus Formation andMacalSeries) and therefore posethesamedilemmaregarding thetimeof metamorphism. Othermetamorphic suites in Paraguana, slates andphyllites(Pueblo NuevoFormation), arealso observed andcontain Oxfordian toKimmeridgian ammonites [MacDonald, 1968].Thesimilarities ofthehigher-grade metamorphic unitsfoundonParaguana andtheMayaregion andcomparable agesofintrusives suggest thatif theywere proximal, therewouldbenosignificant conflicting geology. or are any of them relatedto the late Precambrianto Cambrianeventsrecorded bytheDSDPwellsnorthof the West Africa Yucatan Peninsula? LewisandDraper[1990]suggested thatthesialicbasement complex of PinardelRioofwestern Cubawaslikely juxtaposed against thepresent daynortheastern Yucatan Severalrecentpublications [Lecorche et al., 1983; DallmeyerandLecorche,1989;Dallmeyer,1989,Lecorche et Block. Its ageis not well established. WestAfrica. A briefsummaryis providedin orderto al., 1989]havefocused attention onthepreriftgeology of Bartok:Prebreakup of Gulf of Mexico-Caribbean andRifting completethe tectonicframeworkof westcentralPangea.The geologyof this regioncanbe subdividedinto two provinces: a complexorogenicbeltanda zoneunaffected by major orogenies (Figure12). The undeformed region, comprises the Leo andReguibatmassifs. Along the westernportionsof eachof theseeratons, radiometricage determinations yieldvalues> 2000 Ma (Pastoraequivalent).The Bullardfit placesthe thePastora provincein closeproximityto theLeo massif. The remainder of the eratonshaveagesfrom 2000 to 1500Ma (Cuchivero and Amazonasequivalent).The sedimentary portionsof the regionhavebeensubdivided into supergroups [Lecorche et .al., 1983](Figure12). Supergroup 1 seriesarePrecambrian red beds similar to the Roraima Series of Venezuela. Supergroup 2 is composed of redbedsof the Tichilit el Beida andMajera groupsconsistingof sandstones and some limestones, rangingin agefrom Cambrianto Ordovician. The descriptions are compatiblewith the contemporaneous rift deposits in northernVenezuela,anda relationship was first postulated by BenedettoandPuig [1982]. However,the natureof depositionof the Africanunitshasasyet notbeen defined. They extendfrom the Anti-Atlas,southernMorocco, [Destombes etal., 1985] to Senegal.Supergroup 3 consists of theDikel Groupandcorresponds to glacialdepositsoverlain 449 by shallowmarineseries,datedLate Ordovicianto Silurian. Supergroup 4, restrictedto the BoveBasinandMauritania, comprisesEarly Silurian to Devonian sediments. The orogenicbelt hasa definitePan African root [Dallmeyerand Lecorche,1989]. Becausemanycomponents of supergroups 1, 2, 3, and 4 are foundincorporatedin the fold belts, there has been extensiveremobilization in the regionas late asthe late Paleozoic.If earlyPaleozoic orogeniesare presentin the region,their impactappearsto havebeennegligible.Early Paleozoicdeformation is suggested by Lecorcheetal., [1983] and is reputedto extend north-south from the High AtlasMountains(Morocco)to the Mauritanide-Rockelides (Senegal;Figure 12). Dallmeyerand Lecorche[1989] suggested that the Pan African componentof thefold belt is clearlyretainedasthe dominantorogenic phasein theRockelides.This is evidenced by the Coyah granite,datedby Dallmeyer [1987] at 586 Ma (PanAfrican; Figure 12). The Mauritanidefold belt, althoughit hasa Pan Africanroot,is stronglyaffectedby the latePaleozoic orogeny. Florida Floridacanreadilybe dividedinto two distinctgeologic provinces[Mueller andPorch, 1983, p. 172] "The ageof the SHIELD FOLD BELT SUPERGROUP PRECAMBRIAN RED BEDS CAMBRO-ORDOVICIAN REDSANDSTONES/ SHALES LATE ORDOVICIAN SILURIAN SILURIAN/DEVONIAN .j' + + + + + + + + + + + + + + + + + + + ) + + + BOVE BASIN + + ..+ + '3 +\+ * TRI•ELIDES COYAH GRANITE ,,. LEOUPLIFT L. + / : 0i o i 1•00 2•00 300ML •o =oo ,oo ,oo •K,. , 15 ø I 10 ø I 5ø 0o I i Fig. 12. WestAfricaPrecambrian andearlyPalaeozoic outcropandsubcropdistribution [Lecorche et al., 1989]. 450 Bartok: Prebrealmp ofGulfofMexico-Caribbean andRifting northernprovinceis minimallyearlyPalaeozoicwhile the southernprovincedeveloped duringtheearlyMesozoic.The provincesprobablywerethe resultof differenttectonic conditions that involveda convergent oceanplateboundaryin the northand a hot-spotinfluenceepisodeof intra-continental rifting in the south"(Figure 13). The sameauthors bothregions.The agesin thenorthernprovincerangedfrom 530 Ma in St.LucieCountyto asyoungas 348 Ma in Flagler County(Figure13). Theseagesrepresent minimumcooling ages. The two zonesflank the Osceolagranitedatedat 528 Ma [Dallmeyer,1987]. It is noteworthy that detritalsamples, obtained from the basal units of the Sohio GNV 707-1 well carded outradiometric agedeterminations (40Ar/39Ar) in PENSACOLA HIGH [] LATE PRECAMBRIAN "' (Figure4), yieldedan agedateof 576 Ma (BP internalreport, 1985). The composition of the northernrocksuitesis calcalkalineandesitic.The felsicrhyolitesextendwestto the Pensacola High [Arden, 1974]. Its possiblecontinuation alongthe northerncollisionfront (OuachitaTrend)was discussed by Burgess[1976]. Dallmeyeret al. [19871>] have studiedtheOsceolagraniteof Floridaandthe Coyahgranite of theRockelides andconcluded thattheyarecloselyrelated. The southern,St. Lucierocksuites,are amphiboliteschists and gneisses.Wells drilled on the TampaArch penetrated granitesandgranodiorite[Pindell,1985]that appearto be pre-Ordovician in age[D. Martin, BP internalreports,1985]. !x.•xyf,•:.•:.pl•.il :•.GRANITE A third microplate,associated with the Floridaregion,has been described in the literature and named the Florida Straits LURAIO SRI)OVICIAN IAN (OR OLDER)/......x Block[Pindell,1985]. The blockunderliesthepresent-day Bahamas.Its basement structure andgeologicdevelopment are notwell documented but maybe similarto the South I•) •EQUIV. PROVINCE '"•",• I •. •:•)•1•1-•'•=' I PANAFRICAN KM 0 80 1•0 240 i i i i ß ,, Fig. 13. FloridaPrecambrian andcarlyPaleozoicsubcrop distribution.References for agedatesareOpplin[1951]and 88 87• 86 ø PENSACOLA Florida Block. Armedwith the description of theterranesthatmakeup the Floridaregion,andreviewingthe gravityandmgnetic signatures in the northeastGulf of Mexico (Figure14 and 15; compiled frommultiplecontractor surveys) aswell asthe extensiveonshoredrilling, the suggestion is madethatthe prominentnortheast-southwest trendinggrain on the gravity 84 ø 30 ø 29 • AREA OFFIG.17 AND GNV-707-1 WELL 0 ' C.I.- 12mg • MILES 70 ' 850 840 83ø 82ø 81ø Fig. 14. IsostaticallycorrectedBougucrgravityanmnalymap of the northeastGulf of Mexico, highs(H) and lows(L). Bartok: Prebrealmp ofGulfofMexico-Caribbean andRifting 84 ø 83 ø 82' 451 81 ø PENSACOLA 30 ø $.FLORIDA O AREA OFFIG. 17 AND GNV-707-1 * C.1.=120 WELL gamma• 0 t MILES 70 • 85ø 84 ø i 8,3ø Fig.15.Reduced topoletotalfieldmagnetic intensity mapofthenortheast GulfofMexico, highs (H) [Gough,1967;Klitgord,1984;King, 1959]. andmagnetic maps,theTampaArch,istheresultofthepreOrdovician orPanAfricanagedbasement.It is likelythat thestrong magnetic anomalies observed alongthenorthern flankofthearch(Figure15)correspond totheOrdovician felsicunits.Theymayberelated totherhyolites observed in theYucatan-1well. However,the currentstateof knowledge doesnotpermitunequivocal linkageofthetwoblocks by means ofgravityandmagnetic lineaments. Theeffects of Mesozoic riftingonthepotential fieldscouldyieldsimilar results. Brunswick MagneticAnomaly(BMA;Figure15). Of the mainfeaturesobserved southof theBMA andnotpreviously described two arenotedin thisdiscussion: the Wigginsuplift andPensacola ridge(Figure15). Preliminary results of W. ThomasandR. B. Dallmeyersuggested thattheseunitsmay represent PanAfricanorogenic beltsthathadundergone somelatePaleozoic orogenic overprinting (Figure15). The natureof thePensacola rocksappears to be similarto thoseof centralFlorida.Felsiclow-grade metaigneous suitesare observed[Dallmeyer,1989]. The areato the north of the Ordovicianrhyolites, designated zone2 and3 onFigure13,comprises sandstones andshales thatrangein agefromCambrian toDevonian. Theyarecomparable totheWestAfrica's supergroups 2 and 3 andapparently havenotbeenseverely deformed byeither theearlyorlatePaleozoic orogenies. In theoffshore Blake Plateau, theU.S.Geological SurveyCostwellG-1penetrated presumably Devonian metasedimentary sequences datedat 346-374Ma [Dallmeyer, 1989]. Theirrelationship tothe othermetamorphic sequences described aboveisunclear. Thepossibility exists thatsequences observed in northFlorida DISCUSSION OF TIlE PRECAMBRIAN TO EARLY PALEOZOIC IN THE AREA OF STUDY Thepurpose of reviewing thegeologic framework ofthe Precambrian to earlyPaleozoic oftheregionis to evaluate its effectonthe subsequent deformation of whatwould eventually become "westcentral"Pangea.Forthisreason the discussionof the trends is noted on a reconstruction of the latePaleozoic.OnlythelatePrecambrian andearlyPaleozoic systems discussed in thetext areindicated (Figure16). The andWestAfricacorrespond to Cambrian rift andpostrift reconstruction followsthe modelMoptedin Figure1. sequences. Theirpaleotrends donotconfiiet withtherestored position oftheEspino Graben system ofVenezuela. African Pan African fold belt hasa distinctnorth-southstrike Several keyobservations canbemme. First,theWest NorthwestFloridaandAlabamacontainseveralinteresting elements thathavebeenunderstudyby W. ThomasandR. D. extending fromtheearlyMauritanides totheRockelides. In a paleosouth direction totheRockelides liea series ofEarly Dallmeyer (personal communication, 1989).Bothauthors suggested thatthereisanabrupttermination ofthe Appalachian mid-Paleozoic orogenic belt,whichnearly conforms to itspresent terminus.Thesouthern limitofthe Appalachian foldbeltis closely associated withthe Cambrianfoldbelts,theEstrondo Hills [Schobbenhaus et al., 1984],andthenorthern extension ofthelatePrecambrian Paraguai-Araguaia foldbelt. Theyseparate theAmazonas Province of Brazil from the Ceara Platform basement complex thatunderlies theMaranon Basinofnortheastern 452 Bartok:Prebreakup of Gulf of Mexico-Caribbean andRifting ORDOVICIAN RHYOLITE YUCATAN- s 1 ./ / ' ,,, V "-..'" c•' -- ..'-' x I 0 • I 200 ' ! --?,. ,,/ • i I ' 400 t • ' • // I 6OO ' G , ,[ ',• FG/ / t \ •, "ß '/ \ /I -" AMAZONAS PROVINCE MARANON BASIN I 8OO Fig. 16. Distributionof thePanAfricanagedsystems reviewedin thetext. SeeFigure1 for abbreviations. Brazil (Figure16). The coreof thefold belt comprises Protemzoiclow-grademetamorphicrocksuitesoverlainby coarseto fine grainedsediments.Their agehasbeen assignedto the Cambrian[Schobbenhaus et al., 1984]. Thereforeit is suggested that the Pan Africanfold belt of West Africa extendsthroughSenegaland SierraLeoneand continues into northeastern Brazil. A second observation arisesfrom the discussions of l heprevioussections.Where do the Yucatan,Florida, and northernSouthAmerica's Precambriantrendsfit into the mostaccepted modelfor the reconstruction of Gondwana? The northern South America late Precambrian/lowermost Paleozoicfold belt hasa distinctpaleoeast-northeast directionthat doesnot conflictwith that of the TampaArch trendof Florida. The similarityin ageof deformationof the Tampa Arch (late Precambrianand earlyPaleozoic)and of the northernMaya Blocksuggests a relationship.The implicationis that the east-westsystemrepresents a separate Precambrianeventor phaseto that observedin WestAfrica. Onepossibleexplanationis that it represents accretionalong the northwestmarginof Gondwanabecause the Rockelide trendis likely to haveoriginatedfrom continem-continem collision(C. Scotese, personalcommunication, 1990). The Cambro-Ordovician sedimems of West Africa are observed to lie between the Pan African fold belts and the cratons.This conceptalsoappliesto northernSouth America,but in FloridaandYucatanthefragmentation appearsto be complexand notfully resolved.CambmOrdoviciansediments[Dallmeyer,1989] are observed both inboardand outboardof the Florida "PanAfrican"system,i.e. betweenSaintLucieandthe Wiggins/Pensacola highs. In fact,theymaysimplylie on a collapsed portionof thePan African agedfold belt. The modelsappliedto the Cambrian rifts, locatednearthe Brevardzoneof the Appalachians [Hatcher,1989a](Figure6) maybe adaptedto rift systems of Florida, West Africa, and northern SouthAmerica. The dominantgrain of the late Precambrianto earlyPaleozoic tectonismof westcentralPangeais east-northeast. THE LATE PALEOZOIC WEST CENTRAL FOLD BELT: PANGEA Contraryto the segmentation into subregions usedfor the Precambrianto earlyPaleozoic,the discussion of the late Paleozoic is described in the context of the reconstructed Pangea.Thereis strongevidencefor Alleghanianaged Bartok:Prebreakup of Gulfof Mexico-Caribbean andRifting orogenies not only alongthe Appalachians/Ouachita/Marathons [Pindell, 1985] but also alongthe CoahuilaPlatform,SierraMadre Orientalof Mexico [Csema,1960;LopezRamos;1983,Handschyet al., 1988]. They extendsouthto the ChuacusRanges,Maya Mountains, Central Cordillera of Colombia,and western Venezuela. Their relationshipsare the focusof this section. The literatureon the Alleghanian(Hercynianaged)orogeny in boththe Appalachianand Ouachitatrendsis exhaustive anddoesnot requirerepeating[WilliamsandHatcher,1983; Fallin, 1985; Hatcheret al., 1989]. The connectionbetween the Appalachianrangeandthe Ouachitas,acrossthe MississippiEmbayment,hasbeena subjectof somedebate. Severallinesof evidencepointto the conclusionof some continuity:(1) the regionalgravitymap (Plate1 from Hinze andHood [1988]) clearlyshoweda changein directionto westnorthwestof the underlyingbasementcomplexat the southernextremityof the Appalachiansand (2) Thomas ß [1989a] consideredthe transitionbetweenthe two to havea strike-slipcomponent,and hencein the pastthe systems were directlyjoined and morerectilinear. The samecondition appliesto severalothersectorsof the belt. In northern Mexico, the Ouachita/Marathon trend has been extended southintothe CoahuilaBlock [LopezRamos,1983]. The southerncontinuationappearsinterruptedby the Sonora/Monterrey megashears andmaybe displaced significantlyeast[PindellandBarrett, 1990]. PermoCarboniferous disturbed belts have been observed underpinning theLaramideorogenyof thepresemSierra MadreOriental[LopezRamos,1983]. Intrusivesin theMaya Mountainsand the Cuchumatanes/Chuacus Ranges(210-340 Ma [Weyl, 1980]) are consistent with the late Paleozoic deformation(Figure 11). The SouthAmericancomponent of the latePaleozoicfold belt is verywell documented in the ColombianCemral Cordilleraandin thepresentlyexposedSantander massifof theEasternCordillera[Irving, 1975]. It extendssouth throughEcuadorand coastalPeru [Ziell, 1979]. By combiningthe previousdiscussion of the centralColombian Devonian with the information on Colombia's late Paleozoic deformation thereis a strongsuggestion for coincidence with the Alleghanianorogenicsystem.The Chuacus range, Guatemala,may representthe continuityof the systemin Central America. In northernVenezuela,the metamorphism of the Carboniferous systemobservedin the Andes[Gonzalezde Juanaet al., 1981; Caseet al., 1990], the intrusiveson Paraguana(El Amparogranite[FeoCodecidoet al., 1974], and at the El Baul complex[KiserandBass,1985] (Figure9) supportthe presenceof the late Paleozoicorogenicevent affectingVenezuela[Martin Bellizzia, 1961]. The Sabaneta andPalmaritoformations,outcropping alongtheMerida Andesarethe shelfequivalents of the deepwaterpellitic MucuchachiFormation(V. Pumpin,personal communication,1979) [Gonzalezde Juanaet al., 1981]. The MucuchachiFormationwasmetamorphosed duringthe late Paleozoicorogeny.At E1Baul, the.latePaleozoic metasediments of the BarbascoGroupandassociated granitic plutons(270 i 10 Ma, K/At [Gonzalezde Juanaet al., 1981] appearto conformto the metamorphism of the Mucuchachi Formationobservedalongthe easternMaracaiboBasin. Thereis no evidenceto carrythe orogenyfarthereastbeyond the El Baul complex.The combinationof trendsfrom 453 westernVenezuela,Chuacus,and Maya Mountainsrepresents the continuationof the late Paleozoicorogenictrend. In westernAfrica, the latePaleozoicfold beltsareverywell documented in Moroccoand Algeriawherethe Anti-Arias Mountains continue into the Mauritanides. Both belts include deformedDevonian sediments[Destorobes et al., 1985]. DallmeyerandLecorche[1989] analyzedthe latePaleozoic systemalongthe southernMauritanides.They described the fold belt as directednorth-south to the BoveBasin(Figure 12), whereit bendssharplyto the west. In summary,it canbe statedthatthe latePaleozoicorogenic beltsare well documented alongthe westernmarginof the Laurentia/Gondwanasuture.They are the Appalachians, Ouachitas,SerraniaOriental (Mexico), and the Centraland Eastern Cordillera of Colombia. The late Paleozoic deformationalongthe southeastern marginof the sutureis morepoorlyconstrained.In northwestAfrica the late Paleozoicorogenyis documented from the Anti-Atlasto the Mauritanides.Neugebauer[1989] suggested thatthe system extendsalongcentralFloridaand is projectedwestward. There is no evidencein the geologyof centralFloridaor in the Pinar del Rio areaof westernCubato supportthis argument. However,the weakly metamorphosed PermoCarboniferous of the Maya Mountainof Belize maybe the continuationof this system.The Maya QuintanaRooarch discussed by Buffier [1989] is coincidentwith a significant magneticanomalyand mayform part of this deformation. The relationshipbetweenthe archandmagneticanomalyis asyet unclearbut is thoughtto be eitherthe effectof overprintingMesozoicrifting or relatedto the original Paleozoicorogenicactivity. In Venezuela,the latePaleozoic orogenyis documented only in westernVenezuelaand Paraguanaand followsthe presentAndeantrend. It is proposed that the two systems, Appalachian/Ouachita and northernSouthAmerica,complementeachotherandbound the PangeaSuture(Gondwana/Laurentia). THE PANGEA SUTURE: A DISCUSSION Amongthe mostsignificantrecentadvances in the understanding of thistopicarethe seriesof papersby Nelson et al. [1985]andMcBrideandNelson[1988]dealingwiththe Consortium for Continental Reflection Profiling(COCORP) lines shotacrossnorthernFlorida. However,a detailed reviewof therecentliteratureonthe geologyof thesouthern Appalachian provinceprovidesimerestinginsightsonthe tectonicsactiveduringthe latePalaeozoic.The discussion followsthework of WilliamsandHatcher[1983],Tauvers andMuehlberger[1988],Fawet andWilliams[1988],and DallmeyerandLecorche[ 1989]andopenquestions onthe studiesby the groupledbyMcBrideandNelson[1988]. Immediatelypriorto theDevonianAcadianorogeny,the Avaloniametamorphic terranewasin closeproximityto North America[Woodcocket al., 1988]. Avaloniacontains severalAppalachian provinces that showaffinityto Laurentia assemblages [Buffier,1989]. Eastof thistrend,theterrane includesthe CharlestonandBrunswickbelts[Higginsand Zietz, 1983] and an extra-Avalonterrane(Figure6). All threearedominantly of a Gondwana association. Zirconages in the sandstones of theBrunswick beltyieldagesof 1800Ma [Opdykeet al., 1987]andthereforearesignificantly older than the Grenvillian basement associated with the Appalachianforeland[WilliamsandHatcher,1983]. This 454 Bartok:Prebrealmp of GulfofMexico-Caribbean andRifting extra-Avalonterrane(Figure6) consists of Eocambrian unmetamorphosed felsicplutonicandvolcanicrocks. It is overlainby unreformedearlyPaleozoic platformsediments comprisinggreywackes andshalesanddatedas Cambro- conflictswith thetectonicdevelopment described for northern South America. THE MESOZOIC RIFT SYSTEM Ordovician [Tauvers andMuehlberger, 1988;Higginset al., 1989]. Becauseall of thesesuspect terraneshaveAfrican affinities,haveundergone similarorogenic histories, postdate the Avalonia-Piedmont suture[FavretandWilliams,1988; Hatcher,1989b],andhavea similargravityandmagnetic signature [I-IinzeandBraile,1988],theyhavebeengrouped astheextra-Avalon terrane.Estimated ageforjuxtaposition is Alleghanian,Hercynian[FavretandWilliams,1988; DallmeyerandLecorche,1989]. The westernlimitsof this regionaremarkedbya seriesofprovinces definedbytheir magneticsignature[Rankinet al., 1989]. The easternlimit extends at leastto theEastCoastMagneticAnomaly(ECMA; The primaryobjectiveof this studyis to demonstrate the relationship betweentheMesozoicrift systems activein west centralPangeaandthe preexistingtectonictrends.Thusfar thereporthasdealtwith theprebreakup geologyof the region. The presemsectionwill focusattentiononthe Mesozoicrift systems.It is interestingto notetherearetwo fundamentally differentrifting eventswithinthe studyarea. The Triassic event has a trace that follows from the western McBrideandNelson[1988]haveindicatedthatthe onshore BrunswickMagneticAnomaly(BMA) andits offshore equivalent, theEastCoastMagneticAnomaly(ECMA), North Atlantic,extendsalongthe rim of the Gulf of Mexico, andcontinues alongthe northwestern sideof SouthAmerica in Colombia,Ecuador,andPeru [Jaillardet al., 1990]. In WestAfrica, the Triassicgrabensare alsodocumented in MoroccoandWesternSahara[Manspeizer,1981]. The Jurassic trendprincipallyaffectsa segmentof theNorth Atlanticthat in generallies seawardof the Triassicrffi trend representsthe easternand southernlimits of Laurenfla. of the East Coast of the United States and northwest Africa. Figure 6). However, basedontheabovediscussion, thereis a strong As a result, the continuationof the trend into westcentral suggestion thatthe Avalon-extra-Avalon suture,locatednear thefall line of theAppalachian foothills,is more representative of theLaurenfia-Gondwana suture(Figure6). Pangeafollowsa tracethat continuesalongsouthFlorida,the present-dayeasternmarginof Yucatan,and northern Venezuela. There was only minor reactivationof the Gulf of Mexicorift systemduringthe Jurassic.The TriassicEagle Mills is unconformably overlainby Calloviansediments.The earlyPaleozoicgrabensthat developed alongnorthernSouth Americaundenvemreactivation in theJurassic.Sym'iftred beds(Figure9) filled theEspinoandApure/Mantecal grabens.In westernVenezuelathe Jurassic Rift essentially overlapsthe Triassicsystem.Therehasbeensomediscussion in theliteratureasto thepossibility of a continuous rifting evemextendingfrom the Triassicthroughto theLateJurassic [Rossand Scotese,1988].However,thepresentstudy suggests an episodicrift system.This is demonstrated by the unconformable relationshipbetweenthe Triassicand Jurassic sequences of the Gulf of Mexicoaswell asdifferences in the arealdistributionof the two rift systems. Asdiscussed earlier,W. ThomasandR. D. Dallmeyer (personal communication, 1989)suggested thattheWiggins andPensacola highs(Figs.4 and6) corresponded to Gondwana and not Laurentia. Therefore the Gondwana sutureis likelyto belocatednorthof theWigginsand Pensacola archesandin closeproximityto theOuachitatrend (Figure3). Thomas[1989b]hadlabelledtheeastern portion of thesutureasSuwannee-Wiggins. Thestunmary paperby Burgess[1976] suggested that the Ouachitasresultedfrom the possiblecollisionof GondwanaandLaurenfla. The continuation of the Ouachita Marathon chain south imo the SierraMadreOrientalof'MexicoandtheChuacus Range resultsin thenecessity for proposing a Gondwana-Laurentia suturelyingnorthwest of therestored positionof Yucatan. Because the SantaMarta-Perijaregionappears to havea closeraffinityto boththeAppalachians andthe Central Cordillerafoldbeltof Colombia, it is proposed thatthesuture lieseastof thistrend.The descriptions of Yucatanand Floridaareincompatible withthelattertwoprovinces but conformmoreclosely to thegeologic description givenfor the northernmarginof Gondwana.Followingthe earlier discussion of northernSouthAmerica,the sutureis therefore likelyto passthroughLakeMaracaibo, Venezuela (Figure3). The eastern flankof thefaultsystem is dominated by a light to moderately metamorphosed possibly Carboniferous pellitic schistof theMucuchachiFormation[Gonzalezde Juanaet al., 1981]. To the westlie a seriesof horstsandgrabens (relatedto Mesozoicrifting)thatcontainunmetamorphosed sedimentsof the CarboniferousCarlodel Nomeste,Carlo Indio andRio Palmarformations[Gonzalezde Juanaet al., 1981]. The horststendto be granificandagedat circa364 Ma [Feo-Codecido et al., 1984]. Burgl [1973] suggested the closeaffinity betweenthe Florestamassifof the Eastern Cordilleraof ColombiaandthePerijaRange. At thevery leastit canbe saidthat if the southeastern segmentof the Maya Block hadbeenattachedto South Americathatneitherthe agedatesof the Chiapasmassifnor the deformation recorded in the Chuacus Formationseriously THE TRIASSIC RIFT SYSTEM TheliteratureontheTriassicrift system in theMississippi SaltBasinandEast TexasBasinis voluminous[Scottet al., 1961;Vernon, 1970;Walper, 1980]. Within the Suwannee basinof northernFlorida(Figure4), Triassicsequences have beenpenetrated by severalwells. The southwestern extension of the grabentrendhasbeenpostulated by severalauthors [e.g.,Buffier and Sawyer,1985]but not confirmed.Where theU.S. East Coastand Gulf CoastTriassicrift systems are well documented, their relationships to previouszonesof weaknessseemclear. Triassicrifling alongeasternNorth Americafollowsalongor is in closeproximityto theBrevard Zone (Precambriansuture)and alongthe Avalon/extraAvalonlate Paleozoicsuture[Manspeizeret al., 1989]. The SouthGeorgiarift basinliesin closeproximityto the BrunswickMagneticAnomaly(the Suwannee-Wiggins Suture)andextendswestandintotheMississippiSaltbasin. A branchof the SouthGeorgiaGrabenextendssouthalong the Suwanneedepression of centralFlorida. It continuesinto the northeastern sectorof the Gulf of Mexico. In general,the trendconformsto the proposedtraceof the GondwanaLaurenfia suture. Bartok:Prebreakupof Gulf of Mexico-Caribbean andRifting To betterunderstand the distribution of • systems, the studyfocuseson the Suwanneeri•. Of significance is the SohioGainsville707-1 well (GNV-707-1), drilled in 1985 (Figure4). More than 300 m of Triassicredbedswere penetratedin the well and datedby pollenasLadinianto Carnian. Underlyingthe sedimentsare a seriesof volcanics andvolcanoclastics thatgradeupwardto redbedsequences. Their ageis at leastMid-Triassic(224 Ma; BP internal report,1985) and wouldthereforeconformto the agesof the Triassicvolcaniccomplexes alongtheNewarkgrabenof the U.S. East Coast. The gravity(Figure 13) and the magnetic anomalymaps,reducedto pole (Figure14) of theFloridaarea (synthesized by G. Flanagan,BP internalreport,1989), provideinterestinginformationnotonlyon theprerift sequences but alsoon the • systemitself. The northeast-southwest graindescribed previously for the centralFloridabasementcomplexalsoappliesto western Florida both onshore and offshore. A seismic line that was recentlyshot,overthe GNV 707-1 well providesa glimpseof the distribution andseismiccharacter of the Triassicgraben system (Figure17). The extentof thegrabensystem conformsto the pattern definedby Bufflet [1989]. Notethe coincidence betweenthe stronggravitylow andSuwannee graben. Thereis irrefutableevidencefor the presence of massive TriassicEagleMills redbedsalongthe southernmarginof the Ouachitafold belt [Scottet al., 1961;Vernon, 1970; Walper, 1980]. For the mostpart, the unitsare underlainby the Atokan(Late Carboniferous) strataandoverlainby Louannsaltthat is at leastOxfordianbutmorelikely Callovianin age. Pollenagedeterminations supporta late Middle Triassicagefor the EagleMills [May andTraverse, 19861. 455 In a generalsense,boththe EastTexas/Mississippi andthe Suwanneeand northwestMexico ri• trends[Salvador,1987] conformto the modelof rifting in closeproximityto an older orogenicbelt. The two are essentiallyparallelfeaturesand conformto the outlineof the northernGondwanaearly Paleozoic and late Precambrian trends as well as the Ouachita latePaleozoicorogeny.The arealyingbetweenthetwo rift trends(Figure4) may correspond to the earlyPaleozoic orogenicsystemproposed by Burgess[1976]. Southward,the EagleMills is the time equivalentof the La Boca red bedsformation,lower memberof the Huizachal Groupof Mexico, and is well definedin outcropsat Los NovillosCanyonnearCiudadVictoria,Mexico (Figure4). Elsewhere,the unit hasbeenconfusedwith the overlyingLate Jurassic La Joyaredbeds(upperHuizachalGroup). Thereforethe precisedistributionof the Triassicsystemin Mexico is difficult to establish.The generaltrendof the Triassicriftingis suggested by Walper[1980] andconforms to Figure4. The distributionof the La Bocagrabensparallel the Alleghanianagedorogenyof easternMexico. On the Maya Block,Yucatanregion,the red bedsobserved are limitedto the La Joyaequivalent.The unitsareknownas the TodosSantosFormationandmaybe asyoungas Neocomian[Richards,1963;LopezRamos,1983]. Similar unitsare alsoreportedin the ChortisBlock (Honduras).The TodosSantosis overlainby saltand anhydritethat are at least Early Cretaceous [Bishop,1980]. Progressing southward,in a paleogeographic sense(Figure4), the next systemof red beds is observed in Colombia and Venezuela. The dominant red bed sequences in thesecountriesare the Giron and its time equivalent,the La Quintaformations[Schubert,1986] (Figure5). Both rangein agefrom Jurassic to lowermost Cretaceouson the basisof their floral associations [Gonzalez NE SW SOHIO GVE 707-1 .......... Fig. 17. NE-SW seismicline crossingthe well locationfor the SohioGNV 707-1 well. 456 Bartok:Prebreakup of Gulf of Mexico-Caribbean andRifting deJuanaet al., 1981]. The interesting aspectof theLa Quintais thatit unconformably overlies theLa GeGroup. Onceagain,thisrelationship suggests thepossibility of a significanthiatusbetweenthe two. The olderunit also contains significant redbedsandhasa strongassociation withvolcanicsequences. The ageof theTinacoaFormation (La Ge Group)mayrangedownto the Triassic.Nearthe contactwith the overlyingLa Quinta, the Tinacoahasbeen datedonthebasisof itsfloralassemblage of Ptiloph¾11um sp., Otozamites sp.,andCyzicus(Euesteria) sp.[Benedetto and Odreman,1977]aslowermostJurassic.In centralColombia, eastof thelatePaleozoic foldbeltof the CentralCordillera, Burgl[1963]described theTriassicPayantic Formationasa system of redbedswithoccasional marineincursions, upto 600 m thick,overlyingdacitesandrhyolites[Cedielet al., 1981]. The Payanticlimestoneshadbeendatedas Carnian basedoncrinoids(Pentacrinus sp.)andthepelecypod M¾ophoria jaworskii[Burgl,1963]. TheupperPayantic containsammonites,suchasNevaditesandAnolcites,aswell asthe pelecypodPseudomontis ochofica,all of whichare guidefossilsfor theNorian. ThePayantic Formationis overlainby the Rhaeticto LiassicGironFormationin Colombia.The SouthAmericanTriassicrift system is,once again,closelyrelatedto theproposed traceof theLaurentiaGondwana suture. MID-JURaSSIC HISPANIC Unfortunately,the literatureon the Middle Jurassicof Cuba, Venezuela,and Colombiais not extensive. In western Cuba,the SanCayetano Formationis unequivocally Oxfordianin its uppermembers[Wierzbowski,1976],but its lowermembers maybe asold asBajocian[Ryabukhin et al., 1983]. An additionalaspectof the lower clasticmemberis the dominance of south to north directional features suggesting a southernprovenance[MeyerhoffandHatten, 1974;Ryabukhinet al., 1983]that possiblycouldbe the GuayanaShield. Pindell[1985]andLewisandDraper [1990] suggested thattheYucatanBlockmayhavebeenthe provenance for the sediments of the SanCayetanoclastics. The opposingviewsdo notby themselves detera palcoreconstruction placingPinardelRio in closeproximity to northern South America and northern Yucatan. Pelecypods foundin the lowerSanCayetanoappearto confirma Middle Jurassic age [Andersonand Schmidt,1983] andthe presence of marineconditions.Whenthe San Cayetanodataare combined with the Siquisique ammonite assemblage andwith thoselocatedin theMorrocoyaloutcrop at the northernextremityof the CentralCordilleraof Colombia[Geyer,1976],an imagebeginsto unfoldasto the traceof the JurassicseparationbetweenYucatanand South America. The tectonicsettingthat gaveriseto the sedimentation at Pinar del Rio has not been documented. Nor CORRIDOR Thegreatbioticexchange between theTethysandPacific oceansis believedto havetakenplaceduringthe Bajocian/Bathonian [Westermann, 1980;Smith,1983]. Liassicammonites maintained a distinctprovinciality of eastern, western,andborealPacificassemblages (Figure7). Mixing of eastPacificandTethyanassociations hadbeen observedin Peruin both spongesand ammoniteassemblages [Westermann,1980] and in westernCanadain ammonites [Smith,1983]. Of particularsignificance werethe anunonite specimens observed in the allochthonous Siquisique regionof northwestern Venezuela,wheretheyhavebeendatedas Bajocian/Bathonian [Bartoket al., 1985]. The faunal assemblage is foundin closeassociation with pillowbasalts whichrepresentthe earlyphaseof oceaniccrustdevelopment in the region. The agedetermination for Siquisique was basedon the presenceof Emileia multiformisand Stephanoceras quiroceras.However,of greatersignificance is the presenceof Parkinsoniasp. Thoughthe specimenis poorlypreserved andadditionalsamplingis suggested, severalinvestigators concurredwith the classification[Banok et al., 1985]. The assemblage presentat Siquisique indicated mixtureof TethyanandPacificfaunasand thereforetraced hastheunderlyingbasement beendescribed in detail. Given thepreviousdiscussions it is suspected thatthe structural settingfor thePinardelRio sequences will eitherconform to the latePaleozoicorogeniceventor be associated with the latePrecambriansystem. Southof the CoastalRangeof northernVenezuelaliesthe GuammenGraben(Figure9). The ageof the oldest sediments in the grabenhasnotbeenestablished. However, its positionandtrend [KiserandBass,1985] wouldbe coincidentwith that suggested for the Jurassic rift eventof northernSouthAmericaandpreviously labelledasthe HispanicCorridor. The precisepositionof the SouthFloridaBlockand its relationship to the Jurassic rift systemis notclearlydefinedin the literature.However,the magneticmap(Figure15) for the Floridaregionsuggests thatif strike-slip faultsarepresent on theFloridaPlatformtherelationships proposed by Pindell [1985] and summarizedin Figure 1 are not unreasonable. PotentialJurassic rffi sequences areobserved alongthe northernedgeof the CoastalRangeof Venezuelaandthe GuammenGraben(Figure9) IKiserandBass,1985],and mid-Jurassic marine faunas are observed in allochthonous blocksat Siquisique andalongthe northernportionof the CentralCordilleraof Colombia[Geyer,1976]. It is proposed that this rift trace follows the trend of the late Paleozoic the "HispanicCorridor"(Smith,1983)throughtheregion lyingbetweenthe YucatanPeninsulaandthe SouthAmerican orogeny andthelatePrecambrian orogenic beltaffecting continent(Figure5). The K-At radiometricagesandalkaliccomposition analyses of SouthFloridaBlocksamples (at HardeeCounty, 192Ma; HighlandCounty,183 Ma; CollierCounty,189Ma) supporta mid-Jurassic volcaniceventrelatedto a continental rifting [MuellerandPorch,1983]. The northernFloridaearly grabenslocatedsouthof the JurassicGuammenrift Paleozoic volcanics are calc-alkalinic whereas the southern (Jurassic) aretransitional betweenalkalicandtholeiitictypes [MuellerandPorch,1983]. The regionaltrendsin thisarea are compatiblewith the rifting affectingnorthernSouth America. northern South America. Some reactivation of the Cambrian mentioned above is also documented. These include the EspinoGraben(Figure10) andMantecalGraben [McCullough,1990]. In westernVenezuelaandeastern Colombia,theJurassic grabens, containingthe GironandLa QuintaredbedsandLate Jurassic/Early Cretaceous salt deposits nearBogota,closelyfollowtheproposed zoneof the Pangeasutureresultingin a bendfrom an east-west trendto a northeast-southwest trend. Severalnortheast trending grabensarereportedwithintheMaracaiboBasin[Bartoket al., 1981; Maze, 1984]. They includethe Machiques,Central Bartok:Prebreakup of Gulf of Mexico-Caribbean andRifting Lake,Uribante,andSanLazarograbens.In all casesthey comprise continental redbedsthatareat leastLateJurassic to Early Cretaceous in age[GonzalezdeJuanaet al., 1981]. The GuajiraPeninsula, locatednorthof theMaracaiboBasin, posesinteresting problems.On theonehand,MiddleJurassic marineconditionsare well documented [Renz, 1960]; on the otherhand,the lack of knowledgeon its Jurassic location preventsitsfaunalassemblage fromprovidingvaluable information on the Jurassic rift trend. 457 affectingearlyPaleozoic,Triassic,and Jurassicrift systems. Triassicrifting is observed both seawardand parallelingthe trendsof the Alleghanian/Ouachita orogenies of easternand southernNorth Americaand parallelto the earlyPaleozoic trendsof FloridaandnorthernYucatan. The rift system continuessouthalongthe SierraMadre Orientalof Mexico and the area east of the Central Cordillera of Colombia. The tracecorresponds to the proposedGondwana/Laurentia suture. The Triassicrifts rangein agefrom Ladinianto Caman. CONCLUSIONS An extensivesynthesis hasbeenmadeof theprebreakup geology of westcentralPangea.A comparison of thetraceof theMesozoicrift systemandtheprebreakup orogenic belts servesto corroborate the hypothesis for a potentialdirect relationship betweena preexisting foldbelt andsubsequent riring. Althoughthebasictenetsof thisrelationship are established in theliteraturethesignificance to thisstudylies in itsapplication to theareaof "westcentralPangea." Because theprebreakup geology is poorlyunderstood andthe rift systems havenotbeenfullyintegrated, twoobjectives havebeenachieved by thepresentstudy.First,a synthesis of the prebreakupdeformationof "westcentralPangea,"namely, northernSouthAmerica,Yucatan,protoGulf of Mexico, Florida,andWest Africa, hasbeendemonstrated to provide the templatefor theMesozoicrift trends. Second,by reviewingthe geologyof theknownrift systems, additional Jurassicrifting in westcentralPangeatendsto parallelthe latePrecambrianorogenicbelt of northwestern Gondwana, betweenthe Maya Block and northernSouthAmerica. Along its westerncontinuation the rift systemchangesdirectionand parallelsthe late Paleozoicorogenicbelt. Its ageis at least Bajocian/Bathonian.The Jurassicrift provided communication betweenthe TethyanandPacificrealms. 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