Subsurface Stratigraphy of Cuba

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212SUBSURFACE STRATIGRAPHY OF CUB BASED ON DEEP WELLS

Jorge R. Sanchez Raphael Segura Rolando Garcia Gustavo EschevarrlaErnesto MIlian JoseFernandez and Carlos PereraCentro de Investigaciones y Desarrollo del PetroleoOtic os 154 ox 167LaHabana 10100Cuba.

INTRODUCTIONThissubsurface geologyof CubaIs based ondeepwellsdrilled duringthe last thirty years FIg. 1 2 . It Isby nomeansanexhaustivelookatthe stratigraphyofthe Island.All the stratIgraphic columns were made based on thestudyof manycores,cuttingsandwelllogs Figs. 3 to 7 .Outcropswerealsoconsidered, mainlyInthevlnclnltyofthewells. Correlationsamongwellsarenot shownInthefigures due to the fact that In many cases they werelocatedIndifferenttectonostratigraphicunits. Mostof thewells were drilled In areas associated with oil and gasreservoirs, mainlywithin two major structural elementsshownInthe recentlypublished TectonicMapofCuba :TheNorthernCubanBasin, scale1:500 000andalsooverdepostlonaJ basinsInthe centre-south of the Island. Theformer Includes different zones that were tectonicallydisplaced by overthrusting, so that severaltectonostratigraphic unitscan be recognised.The Northern Cuban Basin can be subdivided Into thewestern, central and eastern basins. Considerabledifferences Inthe Innerstructureof thethrust sheets, therange of the stratigraphic Interval Involved, the faciesfeatures andtheirteetonlc relationships. canbe observedInthesethreeareas. ThedeposltionaJbasinsare composedbasicallyof Tertiary and Upper Cretaceous sediments.Underneath thesesediments, the sametype of volcanicrockswhich cropout over the restof Cuba, southof theNorthernOverthrust, arefound.

NORTHERN CUBAN BASINln r del Rio regionThe Guanlguanlco, La Esperanza and Bahia Hondatectonostratigraphicunitswereestablished Inthewesternpart of Cuba. At Guanlguanico Sierra de los Organossubunit), well Plnar 1 (Fig. 3) was drilled Into severalallochthonouscarbonatesequences composedofpelagicsediments, rangingfromTithoniantoAlbianage,overlyinga polymict ic clay ollsto-strome of Campanian toMaastrichtian ( or younger) age. These overlyaJlochthonouscarbonaterocks, ofKlmrnarldglantoAlblanage,whicharepossiblyfault Implaced. At thebottomofthe well, stringers of anhydrite and gypsumaccummuJations weredescribed.

Atthe Sierra felRosario subunit, wellPlnar2 Fig. 3)hassofar penetrated 3500metresandIsstilidrilling. Fromthesurfaceto 3450metres, thewell encountered lithologicalsequence consisting of different kinds of limestone.sandstones, sandyshales. argillitesandcherts, ranging Inage from Neocomlan to Maastrichtian. Underneath,calcareous argillites were found, mixed with differenttypesof rocks: serpentlnltes, effusive rocksandcherts,givingriseto a chaotic sequence.Inthe Esperanza unit,well Dimas1 Fig. 3) encounteredathicksequenceofallochthonous,terrigenous- carbonate,flysch-type sediments, frornUpperJurasslctoNeocomlanage, overlying an olistostrome of probable Paleoceneage,whichwasIncompletelypenetrated. Thiswell alsodrilled some non-metamorphosed rocks of the SanCayetano formation (lower-middle Jurassic). TheEsperanz.aGroupIsessentiallycomposedofterrlgenouscarbonatesediments. basedon the results ofthe Dimas,SanRamon, Riodel Medlo and LosArroyoswells. Thelithofacies changes systematically towards the LaEsperanza wells Fig. 3 wherecarbonate sediments aredominant.Recent studies In the Martin Mesa area, near Havana,where several well have been drilled, show lithologicsimilaritieswiththe Pinar2 section. In bothareas, lowerand upperCretaceous sediments are penetrated.Mariel 1 was drilled on the Bahia Hondatectonostratigraphic unit and Is characterised by theexistenceofanophioliticsequence,asamelange togetherwith rocks of the Cretaceous IsJand-arc. Togethertheseform nappesover the carbonate-terrigenous sedimentsof upperCretaceous age of the continentlal margin.

LA HABANA MATANZAANDVARADERQ.CORRAULLOREGIONSTowardstheeastofthe Island, thenorthernbasin Includesthe La Habana-Matanza and the Varadero-Corralillo oiland gas bearing regions. NumerousWells have beendrilled Inthe fieldsofboth areas Via Blanca-Boca deJaruco, Yumurl, Camarloca, Cantel, Varadero sur,Varadero, Guasimas, L1toral, Marbella and Marti . The

1 rtmfQc1iMs Ofthe2ndGeoIogicQ/ Conferenct the CSTI Ed. JG CiIIneau Published byCSTI 1991

2nd Geological Conference of the Geological Society of Trinidad and Tobago - 1991


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UBIC CION DE LOS POZOS MAS REPRESENTATIVOS DE CUBA.REPRESENTATIVE OIL WELLS IN CUBA AND THEIR LOC TION

FIG

N-o)SIMBOLOS CONVENCIONAL ES PAR A L IIS C OL UMNIIS D E POZ OLEGEND

e:23 C.lIZA W Y($O1 I1oI[ TOJI PSUMe: 3 ~ - L I Z A DOLOMITIC , _ 'UDRITADOLOMITIUO L I H ( s T O ~ . tTunlTt;.B 3 tALIlA SlLlCI'ICADA M IH5I\.1el'I(D UNtSlOHE S4lT CAL t IITUMntOSA ( 1 0 1 10InUWltfOUS \.IM(STO ( ,CIIIST CALItA AnCILl.OSA W r[OlRHAL nCILL a CtOUS LIMtSTOtl em.ItEfili CALIZ A OnCANOG['U , TO'A :rosslunnous UNUTOH( TU HtHE CALlI cnAVEI,.JTICA_ W noel . (rUSIVA M(DIACO ICLOM(RATICA DUlltCOIlGLDMUl.AlIC UNUTDJI(ES:9 DOLOJolIU, W IIOCA ltU$IYA DASICADOLOMIT( IAULTEd MARG B ROCA IfITKUS1Vl. IASIC.MARL GAgDnO cnAVtLl1AS nocA V\.TnAN4r1TICA.. COHI:.l.o..tnATE Slnp(tfTltt,UD Ul TIIA urnt AREtuSC' O. .. T l( ... OlISTOS1AO....1 , .. OUMICTIC 1 ,IOSTO ( OLISTOSTROMEffiB l MOllTA a UltrA,S DE SOlnrCORnlMIEHTO SIL1STO ( ,AULTS OY(RTIIftUST0 ARcn.L.I.- Anell B DISCOftDAHC- - CLAY. CJ..AYSTON( DISCOftaAllCE

2 . 0,1;-224 . G odol. t25 : Corrolillo 126 . BlonqvilO t27 . froqOJo 128 . Coyo Coco 229 . P unl O A I. qr . 230 . COllOlO _ I31 . Tina t32 . Ace i o n .l33 . GIorio f34 . C om oq u cy 335 , Giboro 136 . l ipe 237 . Soulh Guonlonomo I38 . Gronmo 39 . L ond.rol 110. Son francisco 1 2II . JOlibonico 78 . JOlibonico Sur I12. COrnUo- Cololino -3-15/ Anqelino _ I.

FIG I

.0 ,: Guonohocobiba -12.0imos-13 . S on R omo n 104.Plo. Esperonzo-25. Plnor-I6. Plnor 27. Condelolio 18.l-Io,lin l Iuo 29. G onobo. -1 9

1 0. V ;o B lo n eo -1 011. Bo co d e Jo,,,eo 312. Ooco de Joruco 50 013. Veqol 414. e rud .. 215. Cochinos -I16. Yum ,, 9 -1 8 -2 011. Comorioco If8. ConI. : I19. Vo,odcro 23 3120. Vorodero Su r 52f . G o l i r n o ~ -7; Lilorol- 122 . Colorodol I



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stratigraphic sequences in these areas belong to thePlacetas andcamajuanltectonostratigraphlcunits.whichare characterised by greatcomplexity and are stronglydeformed. with dips rangingfrom horizontal to vertical.and high angle faults occurring, together with tectonisbecclasandchaoticblocks.Thisprovidessomeevidencefor the existence of the large-scale, low-anglethrustingwhich Iscalled TheNorthernCubanOver-thrust Belt-.Theparautochthonous structuralstage is evidenced bycarbonate-terrigenous sediments, of Oxfordianto earlylowerEoceneage. Thelast phaseincludesa polymicticolistostromewhichunderliestheallochthonousstructuralstage, andconsistsof carbonate-clay rocks,of AptiantoTuronianageat thebase. ThisIsoverlain bytheophioliticmelange which is Itself overlain by over-thrustedterrigenous-carbonate sediments, of Campanian toMaastrichtian age.Theexistence of several of thesethrust sheets from thecontinental margin, associated with those mixed unitsfrom theCretaceous island-arc, can be observed inwellGuanabo19 (Fig.3). Theoldest rocksdrilled inthe areaareof UpperJurassicageandconsistof two sequences.Thebasecanbe seenInwellBocadeJaruco500andwellsVaradero 23 and 31 Figs. 4 5). The sequence iscomposed of quartzi ferous, polymictic and micasandstones and limestones, calcareous shales withcarbonaceousmatter, schlsticrocksandsomeIntercalatedlimestones. The sequence has not been completelypenetrated, and the known thickness to date is 600metres. basedon the drilling of well Varadero 201. Thefauna recovered from this well Is very poor so a preTithonian age is Indicated. ThissequenceIs regarded asthe first observed influxof material derivedfrom anacidsource.The upper part of the Jurassic is overlain by blacklimestones. secondarydolomitesandbituminous argillites.A thickness of 500 metres was measured at Boca deJaruco; the equivalent sectionat Varadero is about 300metres thick.Thefauna includescalpionellids,withspeciesofthegeneraCh/t/no/della andCrass/collar/a Fragmentsof Favreina sp. and Saccocoma sp.and the ammonitesHap/oceras gallardo/ and Paradontoceras sp.werealsodiscovered.ThelowerCretaceousNeocomianage is represented by600metresof brownpelagiclimestones, InterbeddedwithsmaJllenses ofchert.argilliteandclay.Thelimestonesarevery rich In Radiolaria and Nannoplankton, especiallyspecies of Nannoconus Some dense, argillaceouslimestonesandsecondarychertsarealsopresent. Inthemiddlepart ofthe section.fine-grainedquartzsandstonesweredescribed. On the basis of species of the generaCa/p/onella Ca/p/onellops/s and Ca/p/onellltes theNeocomian issubdivided into the Berresian-YalanginianandtheHauterivian-Barremian stages. Thebiostratigraphyof thesedepositsiswellestablishedat biozonelevelintheMarti. Guadal and Varadero23wells Fig. 3) and Inthe

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litoral 4, Yumuri and Varadero 31 wells Fig. 4). Thelimestonesarerichlyorganicandoftengivea bituminousodourwhenbroken. Theserocks areusuallyoverlain byfragmental limestonesofMaastrichtianageIntheBocadeJarucaandYumuriwells.andbyterrigenoussedimentsofupper Paleocene age in theVaradero wells.Theallochthonousnatureof the sediments of AptiantoTuronian age Is well illustrated In Fig. 4 Camarioca.Cantel, Varaderosurand Guaslmas wells . Thesequenceconsistsofthrustsheets composedofdifferentlithologies:gray,dense-to-fine, fragmental, argillaceous limestones;massive-bedded. intenselyfractured limestones. cherts,non-calcareous shales, poly-mlctlc sandstones andIimolites; clays; calcarenites and calcareous breccias.Thelimestonesare usuallyblack in color.Thethicknessis estimated to be800-1,000 metres. Arichfauna of planktonic forams and radiolarians provide agood basisfor subdivision of the differentstages: upperAptian, Albian, Cenomanian andTuronian. TheAlbian Cenomanian at Coloradosand Hicacos Is composed ofinterbedded fragmental limestones, calcirudites,calcareousbreccias,oolitic limestonesandblackprimarychert beds. An interesting aspect of these fragmentallimestones is their content of shallowwater organisms,suchas Nummolocultn he/mi Orblto/ina Dicycllna andChoffatella These sedimentsareinterbeddedwithpelagiclimestoneswith abundantplanktonic forams. Weagreewithwhat hasbeen suggested by Pardo 1975 . that theabruptandrepeated changesfromcoarse. shallow-water,fragmental limestonetodense, pela-giclimestone, cannotbe evidenceof rapidly changing sea level and instead itpoints toward an origin by submarine slidesor turbiditycurrents, ina relatively deepsea. WellColoradospenetratedabout 1.000 metresin this sequence.ConiacianandSantoniansedimentsappearto bemissingInthe Placetas and Camajuani Units.Asa result of a very complicated sedimentary process,contemporaneous with the beginningof overthrusting intheupperCretaceous, andtheemplacementofhorizontallydisplacedsheets ofvolcanicandultramaficrocksovertheNorthAmerican continental margin, faunisticallydistlnctivetypes of Campanian and Maastrichtian sediments weredeposited. Thesesedimentshavebeenestablished basedonpaleontological dataandit isverydifficultto recognizethemotherwisein order to correlatethe sections.Three types of terrigenous-carbonate sediments weredescribed:1.Sedimentsnotcomplicatedbythepresenceofvolcanicand ultramafic sheets. such as in the Boca de Jaruco,Camarioca and Guasimas areas. 2. Sedimentscomplicated by the presence of volcanic and ophioliticsheets, asintheYia BlancaandCantelwells. Transttlonaltype Inwhich the ophiolitic rocks are Nlnterlayered- withthe sediments, as oIistolites slid out into the flyschbasinduring Maastrichtian time (Yumurlwells).



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B. J.ARUCO-3IA BI.ANCA.IO

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GLORIA.I ACeION. TllfA. I CANDELARIA. CDCIlINOS.1COilETA. CATALINA.

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Subsurface Stratigraphy of Cuba

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