AUTHORS

Wenxiu Yang � International Research Insti-tute of Stavanger, 8046 Stavanger, Norway;wenxiu.yang@uis.no

Wenxiu Yang received her Ph.D. from the Insti-

Tectonostratigraphic evolutionof the Guyana BasinWenxiu Yang and Alejandro Escalona

tute of Geology and Geophysics, ChineseAcademy of Sciences, in 2007. At present, sheworks as a postdoctoral researcher for theInternational Research Institute of Stavangerand the University of Stavanger in Norway. Sheis currently interpreting regional seismic andwell data on the northwestern offshore of Cuba.

Alejandro Escalona � Department of Pe-troleum Engineering, University of Stavanger,4036 Stavanger, Norway;alejandro.escalona@uis.no

Alejandro Escalona received his Ph.D. in geologyfrom the University of Texas at Austin in 2003.At present, he is an associate professor at theUniversity of Stavanger in Norway. His researchis about basin evolution of continental margins,tectonics, regional to reservoir-scale analysisto define petroleum systems, and sequence/seismic stratigraphy, using workstations to inter-pret both two-dimensional and three-dimensionalseismic data integrated with well and coredata, GIS Arc/Info database management, andvisualization techniques.

ACKNOWLEDGEMENTS

We thank the sponsors of the Caribbean Basins,Tectonics and Hydrocarbons consortium forthe main economic support, Christopher Kendallat the University of South Carolina for datadonation that made this project possible, andPaul Mann for constructive discussions. We thankLandmark Graphics Corporation, Schlumberger,Zetaware, and Chesapeake Technology for soft-ware support. We thank the reviewers MouradM. Bedir, Jan Golonka, and Joseph J. Lambiasefor their helpful contributions.The AAPG Editor thanks the following reviewersfor their work on this paper: Mourad M. Bedir,Jan Golonka, and Joseph J. Lambiase.

ABSTRACT

The Guyana Basin is located along the passive margin of north-eastern South America. With no major oil discoveries, the re-gion is considered by the U.S. Geological Survey the secondleast explored basin in theworld.We integrated approximately3000 km (∼1870mi) of industry two-dimensional seismic dataand 16 offshore wells in offshore Guyana to provide a regionalframework and its hydrocarbon potential.

Four main stratigraphic sequences from the Cretaceous tothe Pliocene were recognized.

Sequence 1 of the Cretaceous consists of shelfal sedimen-tation and submarine fan systems. The main Cretaceous depo-center is located in the southeastern part of the area, whichcoincides with a free-air gravity low, suggesting a basementdepression inherited from Jurassic rifting.

Sequence 2 of the Paleogene consists of shelfal clastic andcarbonate deposits. Listric faults affect the shelf edge and slope,resulting in large turbidites down the slope.Thewest-southwest–east-northeast–oriented Waini arch developed along the north-ern shelf, and it may reflect a flexural long-distance effect ofthe Caribbean plate convergence with the northwestern SouthAmerican plate.

Sequence 3 of the early to middle Miocene consists ofisolated carbonate platforms at the shelf edge surrounded bysiliciclastics. On the sequence top, a regional unconformitywas identified by large incised valleys. We suggest that thisunconformity was caused by the peak of the Caribbean orog-eny in the Trinidad area.

Sequence 4 of the late Miocene to Pliocene shows thelargest terrigenous progradational event in the shelf, whichwas built up by clear sigmoidal clinoforms.We suggest that thelarge progradation pattern change is caused by paleodrainagesystem changes in northern South America since the middleMiocene and by glacioeustasy.

Copyright ©2011. The American Association of Petroleum Geologists. All rights reserved.

Manuscript received June 18, 2010; provisional acceptance August 3, 2010; revised manuscript receivedSeptember 7, 2010; final acceptance January 3, 2011.DOI:10.1306/01031110106

EDITOR ’S NOTE

Color versions of Figures 1–16 may be seen inthe online version of this article.

AAPG Bulletin, v. 95, no. 8 (August 2011), pp. 1339– 1368 1339

INTRODUCTION AND GLOBAL SIGNIFICANCE

The Guyana sedimentary basin is located alongthe passive margin of northeastern South America(Figure 1A). It includes the offshore of Guyana andSuriname and faces the Atlantic Ocean Basin to thenortheast. According to Mann et al. (2003), con-tinental passive margins fronting major oceanic ba-sins form the dominant tectonic setting for hydro-carbon accumulations. In 2001, the U.S. GeologicalSurvey estimated that the Guyana Basin, includingthe entire offshore areas of Guyana and Suriname,held recoverable reserve potential of approximately15.2 billion bbl oil equivalent (Ahlbrandt et al.,2000; Campbell, 2005).Although this figure is nowconsidered to be overly optimistic, it still suggeststhat significant potential exists.

The basin is characterized by the presence of aworld-class source rock of the Cenomanian to theTuronian (Campbell, 2005), which was found inwells drilled in deep water offshore close to theGuyana-Suriname border in the Demerara Rise bythe Ocean Drilling Program (ODP) (Meyers et al.,2006). In addition, many oil and gas seeps havebeen found along the present-day coastline, indi-cating a working petroleum system. According toprevious workers (Workman, 2000; A. Belfor,2002, personal communication), hydrocarbons arebelieved to have migrated to the southwest fromthe offshore source rock in an updip direction to-ward onshore,where theTambaredjo andCalcuttafields in Suriname were discovered (Figure 1A).Although a lot of information indicates that theGuyana Basin has hydrocarbon potential, until now,no major hydrocarbon fields have been found off-shore. The extension of the basin is quite large, andonly 22 explorationwells have been drilled offshoresince the 1970s. Some of these wells encounteredoil and gas shows in noncommercial quantities.

PREVIOUS WORK AND OBJECTIVES OFTHIS STUDY

The Guyana Basin, covering an area of approxi-mately 3000 km2 (∼1158 mi2) of the passive mar-gin of northeastern South America, remains mostly

1340 Tectonostratigraphic Evolution of the Guyana Basin

underexplored and has not yet been studied in asmuch detail as the neighboring Trinidad and east-ern Venezuela hydrocarbon provinces. Little hasbeen published on the geology of the basin, andmost of the work is only in the form of older re-ports by previous exploration campaigns. Researchwork in the area has been mostly focused on themacrotectonic evolution of the basin (Pindell, 1991;Benkhelil et al., 1995; Mann et al., 1995), theseismic geometry character of the shelf (Campbell,2005), or the biochemistry and lithostratigraphy oftheODPwells in theDemerara Rise (Meyers et al.,2006).

These studies show that few structures exist inthe basin. Extensional tectonics along the Guyanacontinental shelf were caused by the final drift of theAfrican plate from the SouthAmerican plate duringthe Early Cretaceous, which ceased in the Late Cre-taceous, with normal cooling subsidence (Gouyetet al., 1994). The northeast-southwest Waini archwas interpreted in offshore Guyana byMobil (R. H.Kirk, 1993, personal communication), but no fur-ther studies have been done on its origin and evo-lutionary history. The middle Miocene unconfor-mity is documented over the entire Guyana shelf(Erbacher et al., 2004;Campbell, 2005;Goss et al.,2008), but no correlationwith themiddleMioceneunconformity in Trinidad (Kugler, 2001;Garciacaroet al., 2011) has been established.

A large increase of terrigenous input and pro-gradation occurred in the basin during the post-middle Miocene (Goss et al., 2008). Previousworkers suggest that this rapid progradation is aresponse of paleodrainage rearrangement in north-ern South America as a consequence of the Incaianevent (Andean uplift) during 49 to 37 Ma (Hoornet al., 1995; Golonka, 2002; Campbell, 2005),but no clear correlation has been established be-cause the basin is not sourced by any of the largeriver systems (e.g., Amazon and Orinoco rivers)but instead by localized paleodrainages (e.g.,Corantijn River).

The presence of widespread Turonian–Santonianorganic-rich source rocks is also widely acknowl-edged (Meyers et al., 2006), but until now, moststudies have shown that they are mostly immature(B. Ravanas, 1990, personal communication), and

Figure 1. (A) Location of the GuyanaBasin showing wells with oil and gasshows, oil and gas seeps and Tambaredjoand Calcutta oil fields onshore, andgiant oil and gas fields of eastern Vene-zuela and Trinidad. The passive mar-gin and Demerara Rise are also shown.(B) Guyana onland geology mapshowing the basin’s southeastern limitof the outcropping crystalline Prote-rozoic basement of the Guyana Shield(GEBCO, 2009) and main structuralfeatures, indicating the location of thenortheast-southwest orientation Wainiarch. (C) Free-air gravity map fromSandwell and Smith (2009) showingthe shelf break along the Guyana Ba-sin, the lineament related to the Cre-taceous and Jurassic oceanic crusts,gravity lows offshore suggesting Jurassicgrabens similar to the onland Takutugraben, and the eastern Venezuelaforeland and forebulge.

Yang and Escalona 1341

many questions remain regarding the distribution,origin, migration paths, and maturation patterns ofthe area (Erlich et al., 2003; Meyers et al., 2006;Arndt et al., 2009). Nevertheless, the basin liesnext to the hydrocarbon-rich Eastern VenezuelaBasin with its large heavy oil accumulation thatextends toward the subsurface of theOrinoco deltaand theTrinidadColumbusBasin. In addition, littleattention has been given to the effect of the Ca-ribbean orogeny in the Guyana Basin and the pos-sible connection to the Venezuelan and Trinidadpetroleum systems.

The availability of two-dimensional (2-D) seis-mic data and well data in this area and our currentknowledge on the evolution of the oblique conver-gence of the Caribbean plate with northern SouthAmerica give us the opportunity to improve ourunderstanding of the structure and depositionalhistory of the Guyana Basin into a better regionalcontext and to evaluate the impact on its petro-leum system. Specific objectives are (1) to buildup the regional tectonostratigraphic framework ofthe continental shelf of the Guyana Basin, (2) toevaluate the impact of the oblique collision of theSouth American–Caribbean plates since the Cre-taceous, and (3) to evaluate the petroleum systemand its relationship with the adjacent petroleumsystems.

REGIONAL GEOLOGIC SETTING

The Guyana Basin is located on the edge of thecentral Atlantic continental margin of northeastSouth America, and it lies along the continentalshelf of Guyana and Suriname (Figure 1A). Thebasin’s southeastern boundary is limited by theoutcrop of the crystalline Proterozoic basement ofthe Guyana shield (Figure 1B). The continentalmargin from Guyana to French Guiana is approx-imately 930 km (∼580mi) long and approximately150 km (∼95 mi) wide, and the widest extent isapproximately 380 km (∼240 mi) in the area ofDemerara Rise (Figure 1A). Water depths on thecontinental shelf range from 0 to approximately200m (∼660 ft), and the deep basin reaches depths

1342 Tectonostratigraphic Evolution of the Guyana Basin

ofmore than3000m (9850 ft) (Gouyet et al., 1994;Goss et al., 2008). The free-air gravity map showsclearly the shelf-break margin, which suggests thedifferent plate boundary lineaments such as the Ju-rassic and theCretaceous oceanic plates (Figure 1C).Several gravity lows can also be identified in theshelf, suggesting graben structures similar to theonland Takutu graben located in Guyana and Brazil(Figure 1C). The Takutu graben was formed whenthe central Atlantic Ocean opened during the Ju-rassic (F. D. Crawford, 1985, personal communi-cation). West-southwest–east-northeast–bendingfaults affecting thebasement can also be interpretedclose to the gravity high in eastern Venezuela. Wepropose that this gravity high is the present-dayforebulge formed as a response to the tectonic load-ing of the Caribbean plate over the South Amer-ican plate (Figure 1C).

The tectonic development of the Guyana Ba-sin can be divided into three main tectonic move-ment phases from Late Jurassic (∼200 Ma) topresent (Figure 2). To illustrate the stratigraphicdistribution during the three tectonic phases, a sum-marized stratigraphic column of the Guyana Basinis shown in Figure 3.

Central Atlantic Phase (200∼145 Ma)

The north-south rifting during the Jurassic betweenSouth America and North America, which was ini-tiated in the central Atlantic region, resulted in east-west extension with a large component of dextralshearing (Gouyet et al., 1994) (Figure 2A). Thisrifting event was recorded as grabens developedalong the offshore region of the Guyana Basin andalso onshore in the east-west–oriented Takutu gra-ben (Figure 1C). The Takutu graben is the bestrecord of the Jurassic event in the Guyana Basinregion. In the graben, the Lower Jurassic (∼200Ma)volcanic formation of the lower Apoteri was de-posited (Crawford et al., 1985) and subsequentlycovered by the upper Apoteri and Pirara forma-tions of the Early–Middle Jurassic (Berrangé andDearnley, 1975) (Figure 3). These two formationsconsist of halite and interbedded shale that wasregarded as a matured source rock in the graben.The Upper Jurassic clastic rocks of the Takutu

Formation conformably overlay the previous for-mations. TheTakutu Formation includes the reddish-brown shale interbeds of very fine grained sandstone,siltstone, and micritic limestone sediments devel-oped within the fluvial and coastal facies of theformation and could be a good reservoir (Crawfordet al., 1985).

Africa Rifting Phase (145∼113 Ma)

During the Early Cretaceous, South Africa andSouthAmerica started to rift apart. The rifting eventhappened in the South Atlantic because of thecounterclockwise rotation ofAfrica relative to SouthAmerica (Pindell, 1991; Mann et al., 1995), result-ing in two conjugate margins, the Guinea Rise onthe African margin and the Demerara Rise on theSouth American margin (Figure 2B). Because of

complex plate rotation, a late compressional phaseresulted before final rifting andwas recorded in theDemerara Rise as northeast-southwest en echelonfolds and northwest-southeast–trending normal faults(Gouyet et al., 1994; Goss et al., 2008).

During the Early Cretaceous (Barremian), thebasal-clastic sandstone of the Stabroex Formationwas deposited and overlain by nonmarine silici-clastic deposits of the Potoce Formation (Brouwerand Schwander, 1988) (Figure 3). During rifting ofthe South Atlantic, major erosion affected the re-gion, resulting in a stratigraphic break throughoutthe entire Guyana Basin on top of the Aptian. Thisregional unconformity was then covered by a re-gional flooding event that resulted in the Albian toTuronian shelf marine platform (Canje Formation)(Lindseth and Beraldo, 1985) (Figure 3). This pe-riod correlates well with a global sea level rise event

Figure 2. Plate tectonic evolution of the Guyana Basin using the University of Texas Institute for Geophysics PLATES database andPaleoGIS software. (A) Central Atlantic phase (200–145 Ma). (B) African rifting phase (145–113 Ma). (C) Passive margin phase (113–0 Ma).

Yang and Escalona 1343

Figure 3. Generalized stratigraphic column showing the lithology distribution along the basin dip (left) and along the shelf (right) of the Guyana Basin.

1344Tectonostratigraphic

Evolutionofthe

GuyanaBasin

and a global anoxic event (Erlich et al., 2003). TheCanje Formation is a black shale with average totalorganic content (TOC) between 4 and 7%, withthe highest TOC concentration of 30% in theDemerara Rise (Meyers et al., 2006; Nederbragtet al., 2007).

Passive Margin Phase (113∼0 Ma)

During the Late Cretaceous, Africa drifted awayfrom South America, which formed the main ex-tensional geologic regime in the Guyana Basin andcaused a general collapse of the unstable shelf edgeand slope (Figure 2C). This predominantly trans-current movement occurred mostly from the Al-bian to the Eocene, but is still active at present.Previous workers proposed the creation of a largepull-apart basin with a gentle thermal subsidencecaused by a relatively low heat flow in this trans-current setting (Benkhelil et al., 1995).

In the shelfal areas of the Guyana Basin, theuppermost Cretaceous is a siliciclastic interval in-terpreted as littoral shelf deposits with sand andlagoonal deposits (Lawrence and Coster, 1985) andis found as oil-bearing sediments in the Arapaima-1well in offshore Guyana (Figure 3). The end of theCretaceous is marked by an erosional unconformityoverlain by carbonate shelf deposits (Georgetownand lower Pomeroon formations) of the Paleoceneto the Eocene (Campbell, 2005). Carbonate sedi-mentation ended during the middle Miocene be-cause of an increase of clastic input into the shelfarea (mid-Corentyne Formation) followed by amajor unconformity (Erbacher et al., 2004) thatcan be correlated across the entire Guyana Basin.Above this unconformity, the entire margin be-came completely clastic, dominated by a rapid in-flux of clastic sediments of theCorentyne Formation(Workman, 2000), with a shelf progradation of 50to 60 km (31–37 mi) toward the northeast fromthe lateMiocene to theHolocene. In theDemeraraRise area, the upper Neogene interval is missing.Erosion in this region has been suggested to berelated to glacioeustasy and closure of the PanamaIsthmus, causing global changes in ocean circula-tion patterns (Mosher and Piper, 2007).

DATA AND METHODOLOGY

Two-Dimensional Seismic Data

The data used in this study consist of approximately3000 km (∼1870 mi) of 2-D seismic reflectionlines, which include several surveys acquired in thisregion by the oil industry (Figure 4A). The datawere kindly donated by Christopher Kendall atthe University of South Carolina to the CaribbeanBasins, Tectonics, and Hydrocarbons consortiumat the University of Texas at Austin and the De-partment of Petroleum Engineering at the Uni-versity of Stavanger in Norway. Seismic lines wereavailable in paper and converted to SEGY filesusing Chesapeake Technology’s Image to SEGYsoftware. Most surveys are from the 1970s and1980s, and data quality ranges from bad to good.

Well Data

Information on 16 wells (Figure 4A; Table 1) wasused to correlate the 2-D seismic data interpreta-tion. Eleven wells from published articles (Erlichet al., 2003; Campbell, 2005) and well reports (T.Doran, 1985, personal communication;B.Chevallier,1988, personal communication; A. Noyau, 1991,personal communication) were used to display keygeologic tops to correlate the seismic data and ex-tend the important strata information throughoutthe entire Guyana Basin. In addition, five ODPwells (1257–1261, leg 207) from the Demerararegion were available and used as distal correlationfor the continental shelf (Figure 4A) (Erbacheret al., 2004).

Methodology

The seismic framework follows the conventionproposed by Mitchum et al. (1977), in which seis-mic sequences are bounded by unconformities andtheir correlative conformities. These seismic se-quence boundaries are designated by their strati-graphic ages identified in seismic data and tied to thewells in the basin (Figure 4B). They are correlated

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Figure 4. (A) Topography and bathymetry basemap showing the seismic data and well data used. Red points represent wells used frompublished sources, green points are Ocean Drilling Program (ODP) wells, red lines represent the seismic transects from published articlesthat were used as a reference in the work, and the black lines represent the seismic transects that were interpreted in the work.(B) Correlation between seismic tectonic sequences and the Arapaima-1 well. Locations are shown in (A).

1346 Tectonostratigraphic Evolution of the Guyana Basin

throughout the 2-D seismic survey and correlatedwithin the well sections (Figure 5). Depositionalsystems were defined between flooding surfacesand unconformities, and structural and isochronmaps were constructed from surface subtraction.These maps represent the final interpretation forbuilding up the depositional history of the GuyanaBasin from the Cretaceous to the Pliocene. In ad-dition, Zetaware software was used to build upsubsidence curves from two of the deepest wells toestablish the main subsidence events and the re-lationship between tectonics and sedimentation.The burial history for three wells was completed toanalyze the source rock maturation in the basin.

SEISMIC SEQUENCES AND STRUCTURALINTERPRETATION OF THE GUYANA BASIN

Four seismic sequences were identified by five keyseismic horizons in the study area illustrated onthe seismic well sequences in Figure 4B. Thesehorizons are top basement, top Maastrichtian, topOligocene, top middle Miocene, and top Pliocene.For each sequence, we describe the most signif-icant structural features observed on the structuraland isochron maps. The description of structures

and stratigraphic features is primarily based on theircharacter in map view at different depths. We in-clude key vertical seismic reflection profiles thatsupport our interpreted provenance directions, faultgeometries, and unconformities on the structuraland isochron maps.

Acoustic Basement

We correlated the acoustic basement top in theseismic data with wells in the study area (Figure 4B)and previous regional interpretations from seis-mic data in the adjacent region of the DemeraraRise (Erbacher et al., 2004; Goss et al., 2008) andOrinoco delta and shelf (Di Croce et al., 1999).Two different reflection styles of the basement basedon its seismic response are interpreted (Figures 6, 7A).

Single-Reflector Acoustic BasementThis type of acoustic basement is found in thesoutheastern region mostly covering the largest grav-ity low in the basin that is interpreted as a possibleJurassic graben (Figures 1C, 7D). The basement ischaracterized by a strong reflective surface with cha-otic reflections beneath it. Basement top depths rangefrom 1700 ms toward the mainland in the south-west to about 5000ms in the northeast (Figure 6A).

Reflective Acoustic BasementThis type of acoustic basement is located in thecentral and northwestern parts of the basin. Theseismic depth ranges from approximately 800 msin the central part of the basin to about 3000ms inthe northeast basinward direction (Figure 6B).The basement is characterized by a strong reflec-tion on top followed by pseudoparallel reflectorsasmuch as 3000ms thick, suggesting stratification.These internal reflections pinch out in the land-ward direction and dip gently basinward (∼10° onseismic). The basement character suggests a sim-ilar but gentler characteristic of seaward-dippingreflections interpreted along volcanic marginssuch as the North Atlantic and Gulf of Mexico(Diebold et al., 1999; Kroehler, 2007) or the Nor-wegian Sea continentalmargin (Mutter et al., 1982).Its thickness is quite homogeneous over the shelfregion, but it changes basinward where it develops

Table 1. Wells Data Used in This Study

Well Label

Well Name Company

Arap-1

Arapaima-1 Total Esseq-2 Essequibo-2 Total Berbice-2 Berbice-2 Shell OG-1 Offshore-Guyana-1 Shell Mahai-1 Mahaica-1 Shell Mahai-2 Mahaica-2 Shell Abary-1 Abary-1 Shell CO-1 Coronie-1 Conoco NCO-1 Ncoronie-1 ELF GO-1 Galibi-Offshore-1 Tenneco Well-A Well-A Petróleos de Venezuela, S.A. 1257 ODP-1257 Ocean Drilling Program 1258 ODP-1258 Ocean Drilling Program 1259 ODP-1259 Ocean Drilling Program 1260 ODP-1260 Ocean Drilling Program 1261 ODP-1261 Ocean Drilling Program

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Figure 5.Well cross sections in the Guyana Basin. (A) Well correlation showing the stratigraphic distribution along offshore Guyana Basin. (B) Well correlation section showing thestratigraphic distribution along the Guyana Basin dip. The two cross sections indicate Cretaceous source rock thicknesses of as much as 550 m (1800 ft) and continuous along theshelf. (C) Free-air gravity base map showing the location of cross sections A and B (Sandwell and Smith, 2009).

1348Tectonostratigraphic

Evolutionofthe

GuyanaBasin

tongue shapes across the present-day shelf break(Figure 7A).

High-angle normal faults are interpreted in bothbasement types, as observed in Figures 6B and 8A.These faults have northwest-southeast strike, whichis parallel to the shelf margin (Figure 7B). In thesingle-reflector area, the faults are covered byCretaceous sediments of the Stabroex Formation(Figure 6A), whereas in the reflective basementarea, one can interpret small graben structures thatare covered by the stratified basement (Figure 6B).These faults are interpreted as Jurassic normal faultsas a result of crustal extension related to early riftingbetween the African and South American plates.

Sequence 1: JurassicBasement–Cretaceous Maastrichtian

Seismic CharacterThe thickness of this sequence ranges from 700msin the southeastern part of the basin to 2400 ms inthe northeast (Figure 6A). A clear wedge shapewith divergent reflections basinward is observedwith enhanced amplitude and continuity of seismicreflections toward the main Cretaceous depo-center (Figure 6A). The parallel and continuousreflectors with a high amplitude suggest that car-bonate rocks and marine shales of the Canje, NewAmsterdam, and lower Georgetown formations ofthe Upper Cretaceous exist (Figures 3–5). In thenorthwestern part of the basin, the thickness rangesfrom 500 ms in the southwest to about 600 ms inthe northeast (Figure 6B). The main features inthis area are parallel and continuous reflectors withmoderate to high amplitudes, suggesting an increasein terrigenous sedimentation. In this sequence, thesource rock thickness is as much as 550 m withTOC levels between 4 and 7% (Meyers et al., 2006)(Figure 5).

Structural and Isochron Map InterpretationThe general structure of the Cretaceous intervalreflects a stable shelf region, slope, and basin, witha major depocenter located in the southeasternpart of the basin (Figure 7C). This depocenter rep-resents the area of the single acoustic basement ontop of the gravity low (Figure 7D). The interval is

affected by Miocene listric faults that detach in theUpper Cretaceous shales (New Amsterdam andCanje formations) (Figure 8A). These listric faultshave a northwest-southeast strike, are parallel tothe paleoshelf edge (Figures 7C, 8A), and reflectinstability of the Tertiary prograding wedge.

During the Cretaceous, large amounts of sed-iments were deposited mostly in the southeasternregion. More than 2000-ms thick sediments weredeposited in the main depocenter by a large can-yon system fed by the proto-Berbice and proto-Corantijn rivers in the southern region (Figure 9A).In this area, the shelf progradation reflects a largeclastic input (Figure 9B), whereas in the central andnorthern parts of the basin, the shelf is aggrada-tional, reflecting less clastic input and more car-bonate sedimentation.

Sequence 2: CretaceousMaastrichtian–Paleogene Oligocene

Seismic Sequence CharacterSequence 2 is Paleogene in age and 100 to 600 msthick. The seismic character of this unit consists ofhigh-amplitude and subparallel reflections in theinner region of the shelf break and changes to high-amplitude and discontinuous reflections in the outerregion of the shelf break. The base of the sequenceis defined by the Cretaceous unconformity withclear onlaps, whereas the top of the Oligocene un-conformity is defined by truncations and channelincisions. Basinward, the correlative top of the se-quence is defined byMiocene downlapping on top(Figure 8B). Based on well data, the sequence iscomposed of the middle-upper Georgetown andlower-middle Pomeroon formations. Carbonate de-position that dominated the shelfal regions supportsthe high-amplitude reflections and terrigenous de-position toward the Orinoco delta area. Along theshelf edge, steeper clinoform andmounded shapesindicate the development of carbonates in this area(Figure 8B).

Structural and Isochron Map InterpretationThe structural map of the top of the Paleogene(Figure 10A) clearly shows progradation of theshelf margin relative to the Cretaceous structural

Yang and Escalona 1349

1350 Tectonostratigraphic Evolution of the Guyana Basin

map (Figure 7C). Most of the progradation oc-curred on top of the Cretaceous depocenter in thesoutheastern part of the basin by 60 km (37 mi);whereas in the center and northern parts of thestudy area, progradation was minimal, reflecting alow accommodation space. Similar to sequence 1,listric faults of the Miocene affected this interval,causing collapse of carbonate buildups and sand-stones, resulting in turbidite and debris-flow de-

position in the toe of the slope and deep basin(Figure 8B). This regional faulting along the Paleo-gene shelf edge is expressed in the top of the Pa-leogene as a tilted structure (Figure 8B).

The Cretaceous to Paleogene isochron map(Figure 10B) shows that the southeast depocentercontinued to be the main area of deposition, andthat another localized depocenter started to de-velop to the north, in the area next to the Orinoco

Figure 6. (A) Uninterpreted seismic line and interpreted seismic line showing the main tectonosequences. The depth of the basementtop increases rapidly from 1700 ms in the southwest to about 5000 ms in the northeast. (B) Uninterpreted seismic line and interpretedseismic line showing that the depth of the basement top is 800 ms in the southwest and changes to approximately 3000 ms in thenortheast. A strong parallel reflector can be observed within the basement. This reflection is dipping in a seaward direction andthickening basinward from 500 ms to 1300 ms. Location of the lines are shown on Figure 4A.

Figure 7. (A) Regional isochron map showing the distribution of the two different types of basement interpreted. The black dashed linerepresents the boundary between the two different basements. (B) Regional structural map of the top of the acoustic basement. The purpleline represents the basement shelf edge. (C) Regional structural map of the top of the Cretaceous. Purple line represents the Cretaceousshelf edge, and the dashed black line represents the basement shelf edge showing that the Cretaceous shelf edge moved basinward.(D) Interpreted Cretaceous depocenter on the top of the free-air gravity, suggesting that the Cretaceous depocenter developed on the top ofan inherited Jurassic graben (Sandwell and Smith, 2009).

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Figure 8. (A) Unin-terpreted seismic line andinterpreted seismic lineshowing the Jurassic andMiocene fault families.(B) Uninterpreted seismicline and interpreted seis-mic line also showinglistric faults affecting thePliocene to Cretaceousintervals. Paleogene car-bonate buildups along theshelf edge formed large-scale collapse forming toe-of-slope turbidites. Loca-tions of the lines areshown in Figure 4A.

1352 Tectonostratigraphic Evolution of the Guyana Basin

platform and Columbus Basin region. A mainfeature revealed in the map is major thinning ofthis sequence in the central part caused by west-southwest–east-northeast regional uplift and for-mation of the Waini arch across the entire shelf(R. H. Kirk, 1989, personal communication). Onseismic data, the Waini arch can be identified byonlapping of Upper Cretaceous to lower Miocenerocks against its axis on both sides, indicating itssyndepositional uplift character since the Late Cre-taceous (Figure 11A).

Sequence 3: Lower–Middle Miocene

Seismic Sequence CharacterSequence 3 is approximately 100 to 750 ms thick.The sequence includes high-amplitude continuousparallel to subparallel coherent reflections in thecontinental shelf reflecting continuous prograda-tion of the shelf. The base of the sequence is theOligocene unconformity, and the top of the se-quence is defined by regional erosion with wide-spread incised channels in most of the shelf andby downlap of the upper Miocene to Pliocene se-quence in the slope and basin (Figure 11B). Thesequence is composed of the upper Pomeroon andlower Corentyne formations of the early and mid-dleMiocene. According towell data (Figure 5), theinterval consists of shelfal clastics with isolatedcarbonate rocks toward the shelf edge. Toward theDemerara Rise, the sequence sedimentation be-comes more carbonate rich (Figure 5).

Structure and Isochron Maps InterpretationThe structural map of sequence 3 shows a similarbehavior to the previous sequence, with aggrada-tion and not much sedimentation of the shelf edgerelative to sequence 2 (Figure 12A). Thinning ofthis sequence toward the Waini arch is also inter-preted (Figure 11A). Listric faults affecting thelower sequences were formed during this sequencetime, and most of them end toward the top of thesequence at the middle Miocene unconformity(Figures 8A, 12A).

The isochron map of sequence 3 shows thatthickness ranges from 100 to 750 ms, with themain depocenter located in the southeastern part

of the basin as it was within sequences 1 and 2(Figure 12B). Continuous deposition in the south-eastern depocenter suggests that this region expe-rienced continuous subsidence and was connectedto main onland paleoriver systems. The central andnorthwestern parts of the basin were affected bythe uplifted Waini arch, exposing the paleoshelf,and allowing sediments to bypass toward the deepbasin. Unfortunately, we do not have seismic dataavailable in the deep-water part of the basin to cor-roborate this observation, but the fact that incisedchannels are observed on top of this unit suggestslarge accumulations of clastic sediments in the deepbasin.

Sequence 4: Upper Miocene–Pliocene

Seismic Sequence CharacterThe thickness of sequence 4 is between 200 and2000 ms, and its seismic character consists of mod-erate to poor coherency reflections in the inner-shelf region (Figure 8A). Along the shelf breakregion, reflections become low amplitude and cha-otic to discontinuous (Figure 11B), with large clearsigmoidal clinoforms, suggesting mostly terrigenousinput. This sequence is composed mainly of theupper Corentyne Formation. According to well cor-relations (Figure 5), most sedimentary rocks arethick shelfal sandstones interbedded with thinshale on the shelf, and thick shaly sandstone closeto the southeast depocenter of the basin. The se-quence is not present in the Demerara Rise area(Figure 5).

Structural and Isochron Maps InterpretationThe structural top of sequence 4 (Figure 12C) ischaracterized by a broader and more stable shelfthan previous sequences, by the development of astructural depression toward the Orinoco deltaand Columbus Basin, indicating the developmentof the Caribbean-related foreland basin, and by anelongated depocenter off of and parallel to the shelfedge (Figure 12D). Shelf-edge migration basinwardduring this time is as much as 60 km (37 mi) tothe northeast, indicating a large influx of terrige-nous sediments (Figures 6B, 8B). Two main faultfamilies are affecting this sequence: (1) listric faults

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1354 Tectonostratigraphic Evolution of the Guyana Basin

of the upperMiocene, similar to those that affectedprevious sequences (Figure 8A); and (2) Plioceneshelf-edge shallow northwest-southeast–striking nor-mal faults that parallel the shelf break, formed byrapid sediment loading and instability of the slope(Figures 8B, 12C).

The shelf edge and upper slope depocentercontain asmuch as 1600-ms-thick prograding clasticsediments. Large amounts of clastic sediments weretransferred from inland drainage systems across theshallow shelf toward the slope and basin, wherelarge deep-water fans are inferred.

DISCUSSION

Plate Movement Effect on the GuyanaContinental Shelf

The Guyana continental shelf and basin have de-veloped as passive margins since the Late Jurassicto Early Cretaceous. However, several tectonicevents seemed to have affected this region, result-ing in the development of subtle regional struc-tures, unconformities, and variations in the de-positional patterns. Two different plate tectonicelements seem to be related to the disturbancesobserved on the basin that include oblique riftingwith theAfrican plate during theEarlyCretaceousand oblique convergence of the Caribbean platewith northern South America since the Late Cre-taceous. In this section, we provide a plausible ex-planation of the possible causes of the main eventsobserved in the Guyana continental shelf.

Single-Reflector Versus Reflective BasementThe origin of seaward-dipping reflectors has beendiscussed by Mutter et al. (1982) based on theobservation of wedge-shaped basinward reflectionswithin the basement off the Norwegian Sea mar-gin.Mutter et al. (1982) suggested that this seismicresponse in the basement is caused by a layered

igneous sequence that is produced when crustalaccretion occurs at the subaerial spreading axisduring the earliest phase of ocean-basin genesis. Asimilar case is themagmatic basalt province observedby Hames et al. (2000) on the North Americanmargin and the Carolina Trough, offshore south-eastern United States, where flood basalt devel-oped during the Jurassic rifting between the Afri-can and North American plates (Oh et al., 1995).

The observation of a reflective basement in thecentral and northern parts of the Guyana Basinsupports the idea of seaward-dipping reflectorsformed by subaerial basaltic floods during the LateJurassic to Early Cretaceous rifting between the Af-rican and SouthAmerican plates.Well Arapaima-1drilled gneiss rocks on the upper part of the re-flective basement. This gneiss may be the result ofmetamorphosed basalt, which correlateswithDeepSeaDrilling Project wells 353 and 354 drilled closeto the central ridge of the Atlantic Ocean (Supkoet al., 1977). Basalt flows over the Jurassic base-ment cover graben structures as evidenced by high-angle faults interpreted from seismic data.

Origin of the Waini ArchThe Waini arch was interpreted by Mobil (R. H.Kirk, 1989, personal communication) in the Po-meroon block of offshore Guyana, but there havebeen no further studies on its origin. The arch has awest-southwest–east-northeast–trending fold axisformed from at least the Late Cretaceous until theearly Miocene (Figure 11A). Possible tectonicevents that could have formed the arch include thefollowing:

1. Early Cretaceous rifting between the SouthAmerican andAfrican plates that created a shearzone, resulting in en echelon folding on theDemerara Rise with a northeast-southwest axis(Gouyet et al., 1994; Goss et al., 2008). Thisdirection is similar to the Waini arch axis, in-dicating a similar stress condition. However, the

Figure 9. (A) Regional isochron map of sequence 1 (Cretaceous). The map shows that the main depocenter developed in thesoutheastern Guyana Basin. A main canyon connects this depocenter with onland paleodrainage systems. (B) Uninterpreted seismic lineand interpreted seismic line showing seismic canyon fill facies into the Cretaceous depocenter in the southeastern region of the basin.Location of the line is shown in Figure 4A.

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1356 Tectonostratigraphic Evolution of the Guyana Basin

age of this event, Early to Late Cretaceous, doesnot fit with the syndepositional growth observedon both flanks of the Waini arch from the LateCretaceous to the early Miocene.

2. Caribbean–SouthAmerican oblique convergenceis suggested to be a possible mechanism for theformation of the Waini arch from the Late Cre-taceous to themiddleMiocene (Lugo andMann,1995) (Figure 13A, B, C). The timing and syn-depositional growth of the Waini arch and for-mation of the middle Miocene unconformitycorrelates with timing of the west to east mi-gration of oblique convergence between the Ca-ribbean and South American plates. The long-distance development of the arch relative to themigration of the Caribbean plate may be the re-sult of flexural response of the continental crustcaused by loading, similar to forebulge devel-opment, which has been previously proposedby Pindell and Erikson (1994) along the entiremargin, in the Maracaibo Basin during the Eo-cene (Escalona and Mann, 2003), and in theGuarico Subbasin during the Oligocene (PerezDe Armas, 2005), among others. These previ-ous interpretations of paleoforebulges have ori-entation axes similar to the Waini arch.

Middle Miocene UnconformityA regional middle Miocene unconformity is in-terpreted from seismic and well data across theentire Guyana continental shelf and has been pre-viously interpreted in the region by Erbacher et al.(2004), Goss et al. (2008), and in the Trinidadand Venezuelan regions (Di Croce et al., 1999;Garciacaro et al., 2011).

We attribute the development of the middleMiocene unconformity to the main Caribbeanorogeny in the Trinidad region as the Caribbeanplate continuously moved eastward before strainpartitioning in the area (Escalona andMann, 2011)(Figure 13C). This main tectonic event reacti-vated west-southwest–east-northeast Jurassic nor-

mal bending faults in the eastern Venezuela region(Taboada, 2009) (Figure 1C). We propose that theCaribbean convergence and the development ofthe middle Miocene unconformity in Trinidadwere propagated toward the Guyana Basin area asa regional uplift that exposed most of the con-tinental shelf, forming incised river systems andbypass of sediments toward the slope and deepbasin. Interestingly enough, continuous folding ofthe Waini arch seems to end during this period,suggesting the ending of southeast-directed conver-gence of the Caribbean plate over South Americain the Trinidad margin.

Pliocene ProgradationAs interpreted, a long-distance progradation of theshelf caused large accumulations of sediments andincreased in sediment load over the platform dur-ing the Pliocene (Figure 12C). Similarly, a largeprogradation is also observed south of the studyarea, in the Foz dos Amazonas and northern Bra-zilian margin basins (Campbell, 2005). This large-scale basin infilling along the eastern South Amer-ican plate boundary indicates a regional process.

A possible mechanism for the large increase ofterrigenous influx and progradation of the Guyanacontinental shelf may include the paleodrainagesystem reorganization of northern South America.Before theOligocene, most paleodrainage systemswere north directed and captured into the proto-Maracaibo river system (Escalona andMann, 2011).Sediments were mostly sourced by the Brazilianand Guyana shields and the central and westernCordillera of Colombia (Hoorn et al., 1995; Xieet al., 2010). During the middle and late Eocene,the increase in Andean uplift in western SouthAmerica (Incaian event of Pindell andTabutt, 1995)and emplacement of the Lara nappes in northernSouth America produced major denudation anddeflection of north-directed paleo-drainages to-ward the east (Hoorn, 1993, 1994;Golonka, 2002;Escalona and Mann, 2011).

Figure 10. (A) Regional structural map of the top of sequence 2 (Paleogene). The purple line represents the Paleogene shelf edge, andthe dashed black line represents the Cretaceous shelf edge showing shelf edges progradation in the southeastern region. (B) Regionalisochron map of sequence 2. Two Paleogene depocenters are interpreted toward each end of the basin and separated by a west-southwest–east-northeast regional uplift developed in the central region of the basin (Waini arch).

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1358 Tectonostratigraphic Evolution of the Guyana Basin

During the middle Miocene, a major episodeof Andean tectonic activity and complete blockingof north-directed paleodrainage systems formedthe first west to east transcontinental system of theAmazon and Orinoco river systems (Hoorn et al.,1995; Dobson et al., 2001; Escalona and Mann,2011) (Figure 13C). During the Pliocene (5–3 Ma),theAndes experienced themost rapid uplift (Hoorn,1994; 1995), and both the Amazon and Orinocofluvial systems captured other large drainage sys-tems in the area, acquiring their present appear-ance, and provided large amounts of sediments intothe Atlantic Ocean (Dobson et al., 2001; Latrubesseet al., 2010) (Figure 13D).

The large margin progradation and increaseof terrigenous influx on the Guyana continentalshelf have been influenced by the tectonic evo-lutionary history between the Andean uplift andthe Caribbean collision, which has modified thepaleo-drainage systems in northern South Americasince the Eocene (Figure 13). In addition to thisprocess, glacioeustasy plays an important role in thePliocene shallow-marine continental shelf of theGuyana Basin. Large eustatic sea level fluctuationsfrom the late Miocene to the present most likelyexposed the shelf region and allowed large basin-ward progradation.

Tectonic Phases from Subsidence Analysis

Twowells (Arapaima-1 andEssequibo-2; Figure 4A)drilled close to basement with excellent strati-graphic records were used to build subsidence anal-ysis to understand the relation between accom-modation space and basin fill (Figure 14). Thesubsidence pattern on both wells can be dividedinto five phases:

1. Rifting and passive margin development. Dur-ing the Early Cretaceous, the Guyana conti-nental shelf shows a gradual passive margin

subsidence followed by an abrupt uplift thatresulted in the Aptian breakup unconformity.This event corresponds to drifting of the Africanplate away from South America. The Albian toConiacian rapid subsidence is a result of crustalcooling that affected the region. The increase inwater depth led to major flooding of the basinalong with global anoxic conditions that de-posited world-class marine source rocks duringthe Turonian (Erlich et al., 2003) (Figure 5). Thesubsidence rate during this period increasedfaster in the shallow shelf area (Arapaima-1)than in the deep shelf region (Essequibo-2).

2. Initial Caribbean convergence in western SouthAmerica. This interval covers the period fromthe Santonian to the Campanian of the LateCretaceous and is characterized by a decreasein subsidence (Arapaima 1 well, Figure 14A)and uplift (Essequibo 2 well, Figure 14B). Thischange in subsidence pattern matches the ini-tial formation of the Waini arch.

3. Quiescence and basin fill. This phase covers theperiod from the Late Cretaceous to the middleMiocene. During the Campanian to the Maas-trichtian, it is characterized by rapid subsidencerepresenting a main pulse of clastic sedimenta-tion in theCretaceous platform. Thismain pulseof basin subsidence could have led to majormaturation of Cretaceous source rocks. Duringthe Paleogene to the early Miocene, a decreasein the subsidence rate is characterized by car-bonate sedimentation in the continental shelfand continuous uplift of the Waini arch.

4. Caribbean orogeny. This phase is character-ized by regional uplift, resulting in shelf sub-aerial exposure and development of the middleMiocene unconformity. This event correlateswith the main Caribbean orogeny in the Trin-idad area.

5. Passive margin. This phase is characterized bycontinuous passive margin subsidence in thecontinental shelf ofGuyana. The subsidence rate

Figure 11. (A) Uninterpreted seismic line and interpreted seismic line showing the eastern flank of the Waini arch. Pinch-out against thearch is Lower Cretaceous–middle Miocene. (B) Uninterpreted seismic line and interpreted seismic line showing the character of the middleMiocene unconformity, showing incised valleys that erode large parts of sequence 2. Locations of the lines are shown in Figure 4A.

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Figure 12. (A) Regional structural map of the top of sequence 3 (lower and middle Miocene). Purple line represents the middle Miocene shelf edge, and the dashed black line representsthe Paleogene shelf edge showing slight basinward progradation. (B) Regional isochron map of sequence 3 showing thinning toward the Waini arch and continuous development ofdepocenters at both flanks. (C) Regional structural map of the top of sequence 4 (Pliocene). Purple line represents Pliocene shelf edge, and the dashed black line represents the middleMiocene shelf edge showing considerable progradation of sequence 3. (D) Regional isochron map of sequence 4 showing that the main depocenters are located off the shelf edge.

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GuyanaBasin

Figure 13. Proposed long-distance effect of the Caribbean plate on the Guyana Basin. (A) In the Late Cretaceous (80 Ma), the Caribbean plate started to move eastward and collidedwith South America. The Guyana shield supplied sediments to the Atlantic Ocean during this period. (B) During the end of the Paleogene (30 Ma), continuous west to east Caribbeancollision with northern South America caused uplift of the Cordillera de la Costa and flexural loading, resulting in uplift of the Waini arch. (C) During the early and middle Miocene (14Ma), major convergence in the Trinidad region produced regional uplift that affected the Guyana Basin region. (D) During the Pliocene (5 Ma), rapid uplift of the Andean mountains,development of major paleodrainages, and east-directed erosion of the uplifted Guyana Shield resulted in a large progradation on the Guyana Basin.

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Figure 14. Subsidence analysis on wells of Arapaima-1 (A) and Essequibo-2 (B) showing the main tectonic phases in the Guyana continental shelf.

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Figure 15. Burial history analysis of well (A) Arapaima-1, (B) Essequibo-2, and (C) CO-1.

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Figure 16. (A) Map showingpotential reservoir and traps inthe Guyana Basin. These trapsinclude the Cretaceous canyon,Paleogene turbidites, Wainiarch, middle Miocene incisedvalleys, and Pliocene sand bod-ies. (B) Cross section showingthe petroleum system along theGuyana Basin dip. Matured oilof the deep Cretaceous depo-center could have migrated up-dip along listric faults and in-filled deep-water toe of slopeturbidites, shelf-break carbonatebuildups, and Miocene incisedchannels in the shelf. (C) Crosssection showing the petroleumsystem along the shelf margin.The Waini arch acts as a struc-tural and stratigraphic trapfor hydrocarbons migrating fromthe Guyana, eastern Venezuela,and Trinidad areas. Reservoirscan represent sandstone pinch-outs of both flanks of the archand carbonate buildups.

1364 Tectonostratigraphic Evolution of the Guyana Basin

is larger in the shallow shelf part (Arapaima-1wellarea) than in the deep shelf break (Essequibo-2).

PETROLEUM SYSTEM OVERVIEW OF THEGUYANA BASIN

Source Rock and Maturation

The main source rocks in the Guyana continentalshelf areworld-class Turonian toCampanian organic-rich shale rocks drilled by industry and ODPwellsand are uniformly distributed over the entire region(Figure 5A, B). However, these rocks are mostlyimmature in most of the study area (Erbacher et al.,2004; Meyers et al., 2006). Subsidence and burialhistory analysis using information from existingwells show that the main pulse for source rockburial is during the Late Cretaceous (Figures 14,15). During the Late Cretaceous–middle Miocene,Caribbean collision with northern South Americacaused a reduction of the subsidence rate and up-lift, which affected source rock maturation nega-tively in most of the shelfal region (Figure 14).Nevertheless, Cretaceous source rocks seemed tobe matured in the southeastern depocenter of theGuyana Basin.

Reservoirs, Traps, and Migration Patterns

Based on well correlations and seismic interpreta-tion (Figure 5), a clear evidence of reservoir rocksexists in the Guyana Basin from the Cretaceous tothe Pliocene. Based on our regional interpretation,we classify them as structural and stratigraphictraps (Figure 16A).

Structural TrapsStructural traps are limited to rollover anticlinesand footwall blocks formedby listric faults along thepaleoshelf edge and upper slope and the southwest-northeast–trending anticlinal structure formed bytheWaini arch in the northeastern part of the shelf.Listric faults may be key migration paths from ma-ture source rocks in the deep basin toward the shelfedge and shelf (Figure 16B), but more detailed

interpretation of these structures and basin mod-eling are needed to corroborate this assumption.The Waini arch may play a more important roleboth as a structural and stratigraphic trap. LateCretaceous to lower Miocene sediments pinch outin both directions of the arch and also form anti-clinal traps on top of the arch (Figure 16C). Hy-drocarbons could have accumulated by stratigraphicmigration from the northwest, from the EasternVenezuelan andColumbus basins, and/or from thesoutheast in the Guyana Basin, similarly to theVenezuelan heavy oil belt. More exploration anddrilling in this area are required to test this play.

Stratigraphic TrapsThese are probably the most common and attrac-tive types of trap in the basin. They consist of Cre-taceous canyons in the southeastern part of thebasin, Cretaceous to Miocene debris flows andturbidites in the toe of the slope, Paleogene car-bonate buildups in the shelf edge, middleMioceneincised valleys, and shelfal Pliocene sandstones.We speculate that the presence of hydrocarbonseeps and oil fields along theGuyana and Surinamecoastlines (Figure 1A) are caused by updip mi-gration through Late Cretaceous and middle Mio-cene canyons and incised valleys from the Creta-ceous depocenter and deep basin. If this is true,open possibilities for stratigraphic traps within theshelf and slope of the basin exist.

CONCLUSIONS

The main results of this study follow:

1. Four tectonic sequences from the Cretaceousto the Pliocene are interpreted.

2. Three normal fault families are interpreted inthe basin: (1) Jurassic high-angle normal faultsthat developed on top of the basement as partof the opening of the central Atlantic; (2) mid-dle Miocene listric normal faults that developedon the outer-shelf region and detached in theUpper Cretaceous shales; and (3) Pliocene listricfaults that formed in the shelf edge.

Yang and Escalona 1365

3. We propose that the Late Cretaceous to middleMiocene uplift of the Guyana Basin is related tooblique convergence between the Caribbeanand South American plates.

4. Main source rocks are Late Cretaceous shaleswidely distributed in the basin. In most of thebasin, the rocks are immature, with the excep-tion of the southeastern depocenter.

5. Canyons and incised-valley systems of the Cre-taceous and middle Miocene act as good res-ervoir rocks in the basin, but also are the bestmigration pathways.

6. The Waini arch acts as a potential trap for hy-drocarbons that have migrated toward its flanksboth from the hydrocarbon-rich provinces ofeastern Venezuela and Trinidad to the northand from the Guyana Basin to the south.

7. Most potential reservoirs are stratigraphic trapssuch as carbonate mounds with seal along theshelf edge, incised channels on the shelf, anddeep-water slope and deep-basin turbidites.

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