Regional Geology and Oil Potential of the Guajira Peninsula

NW Venezuela and Aruba

EGI E nergy & Geoscience Institute at the University of Utah

I00204 I00204

The Regional Geology and O

il Potential of the G

uajira Peninsula - N

orthwestern Venezuela and A

ruba

EGICoastal View of NW Venezuela

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Energy & Geoscience Institute at the University of Utah

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Raymond A. Levey, Ph.D., – Director

presence of arenaceous forms (assemblage of Valvulina flexilis). These faunas

are interpreted to have inhabited a bathyal environment below carbonate

compensation depth (CCD) (possibly over 1000 m). The upper interval alsoindicates very deep water deposition (1000-1500 m), although somewhat

shallower in the uppermost portion of the formation (Diaz de Gamero, 1977a).

The Pedregoso Formation is mostly limited to the southern and south-

western margins of the Serrania de San Luis (Fig. 30). Lithologically, it is

characterized by shales interbedded with sandstones and bioclastic limestonesin beds less than one meter thick. The sandstone and limestone intercalations

have been interpreted as proximal turbidites (Diaz de Gamero, 1977a).

The Pedregoso Formation is 124 meters thick at the type section in the Rio

Mitare (Fig. 24). The formation thickens to the west as it grades into the

__Castillo Formation and a maximum thickness of 938 meters is found in

Fig. 31. Typical landscape resulting from exposures of the Pecaya Shale in the centralportion of the Falc6n Basin.

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Fig. 33. Erosional contact between underlying shales of the Agua Clara Fro and wellbedded sandstones of the Cerro Pelado Fm exposed along the Coro-Barquisi-meto road near the Rio Coro. This contact marks the passage from Cycle C toCycle B.

Fig. 34. Closer view of Fig. 33 showing the erosional contact betwen Cycles C and Band iron-stained crossbedded sandstones at the base of the Cerro Pelado Fm.Large-scale channels are observed above this contact. The outcrop is -10mhigh.

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Fig. 35. Close-up of Figs. 33 and 34 showing marked facies change between shales ofthe Agua Clara Fro and crossbedded sandstones of the Cerro Pelado Fm.

Formation, and in the sandstone-conglomerate facies of the GuarabalFormation (Gonzalez de Juana et al., 1980) (Figs. 29, 30, 32).

The San Luis Formation consists of massive, dense to finely crystalline,gray reef limestones. These rocks contain large foraminifera, algae, and,locally, large brain corals and bivalves (Wheeler, 1963). The maximumgrowth of the reef is restricted to the eastern portion of the Serrania de SanLuis where some of these bodies are more than 100 meters thick (Diaz deGamero, 1977a). To the west, the individual reefs are smaller and are inter-calated with shales, marls, and few thin coal beds.

The northern portion of the reefal complex contains more clastic facies.Here, the reefal facies developed on top of a sandy to conglomeratic unit richin detrital fragments of igneous origin. A cyclic development of the reef andback-reef facies is characteristic, with shales passing upward to branching

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sandstones. The sandstones are usually crossbedded and contain ripple

marks; lignite beds up to one meter thick are also found in this formation(Gonzalez de Juana et ai., 1980). In several localities - including the Que-brada Patiecitos, Quebrada Hombre Pintado, and in the Rio Coro - the base ofthe Cerro Pelado Formation has a basal sandstone, approximately 20 meters

thick (Liddle, 1946). The sandstones are welllithified, have a reddish ferru-

ginous patina, and are crossbedded, with individual crossbedding sets of ap-proximately 30 cm separated by thin (- 3 cm) intercalations of gray shale. Athin ironstone (- 5 cm thick) is found in the lowermost portion of the formation,

delimiting the erosional contact with the underlying Agua Clara shales (Figs.33-35). In the Quebrada Hombre Pintado (western Falcon), the basal sand-

stones are followed by 400 meters of micaceous ferruginous sandstones, inter-

Fig. 38. Panorama looking south, taken north ofCoro. The first hills south ofCoro arecomposed of middle-late Miocene and Pliocene rocks of Cycle B (Cerro Pelado,Socorro, Caujarao, La Vela, and Coro Fms). The most distant hills arecomposed of rocks of Cycle C (Oligo-Miocene limestones of the San Luis Fro;Serrania de San Luis). -

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Steeply dipping and deformed sandstones, siltstones, and shales of the Cau-jarao Fm, near the town ofCaujarao south ofCoro.

Fig. 39.

Toward the west, in the Urumaco Trough area, the Caujarao is replaced bythe Urumaco Formation (Figs. 10, 36). This unit, which represents moreproximal facies than the Caujarao Formation, is also divided into three mem-bers. A lower interval comprises brown to varicolored shales of marine andnon-marine origin, with minor proportions of fossiliferous limestone. Theshales contain silicified wood fragments and thin coal veinlets (Ministerio deMinas, 1970). The middle member has a similar lithology, but contains amore abundant marine molluscan fauna. The upper member displays a re-newed continental influence with thicker sandstone beds and coaly intervals.The uppermost portion of the Urumaco Formation has a widely distributedbed containing abundant turtle fragments (~ortuga" Beds). The UrumacoFormation is approximately 1675 meters thick (Ministerio de MInas, 1970;

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Gonzalez de Juana et aI., 1980), and it is conformable with the underlyingSocorro and the overlying Codore formations.

The La Vela Formation conformably follows the Caujarao Formation in

the La Vela de Coro area (Figs. 37, 40). This formation includes calcareous

sandstones with intercalations of shales reflecting a beach environment in thebase to an estuarine complex towards the top (Gonzalez de Juana et aI., 1980).

Two members are distinguished in this formation. The lower member is 192

meters thick, and consists of 70% clays and 30% coarser sediments. The claysare bluish gray, but weather to reddish colors, and are occasionally fossili-

ferous and calcareous. The sandstones are impure, micaceous, calcareous,

fossiliferous, and range in color from dark gray to maroon to yellowish.

Conglomeratic sandstone intercalations, intervals with Ostrea banks and.Pecten sp. are observed within this formation.

Fig. 40. Yellowish silts and calcareous sandstones with Ostrea banks of the La VelaFm, Coro-La Vela road near La Vela. .

..

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Fig. 42. Typical exposure of the Capadare Limestone northwest of Tucacas, easternFalcon Basin.

Linda rests conformably on top of the Casupal Formation and is disconfor-mably overlain by the Capadare limestones (Gonzalez de Juana et al., 1980).

Cycle A (Pliocene)

During the Pliocene, sedimentation was reinitiated along the northern and

eastern margins of the Falcon Basin. At this time, large portions of the basinhad already been uplifted; thus, conglomeratic facies are common -particularly in the northwestern and north-central portions of the basin.

In the northwestern portion of the basin, Cycle A rocks are represented by

silts and sandstones that pass upward into conglomerates (San Gregorio For-mation). In the north-central portion of the basin, south of Coro, these

sediments are predominantly conglomeratic (Coro Formation), whereas in the=-

low lands of the Paraguana Peninsula and the coastal area east of Cumarebo,

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Fig. 43. Steeply dipping alluvial fan deposits of the Coro Formation exposed im-mediately south ofCoro.

mostly unfolded sequence equivalent to that of the anticlinorium. A north-south cross-section of the basin presented in Figure 45 shows the structural

relationship between the Falcon Anticlinorium and the coastal plain area.

Muessig{1984) distinguished six structural trends within the Falcon Anti-clinorium (Fig. 46):

1) East-west transcurrent faults. These are right-lateral faults of clear

surface expression (Oca, San Sebastian). Evidence for right-lateral dis-

placement along the Oca Fault has been presented by Feo-Codecido

(1972) and Tschanz et al. (1974), among others. Isopach maps presentedlater in this work provide aditional evidence for this displace~ent.

2) East-u,rest normal faults. Several normal faults with this orientation arefound in the Falcon Basin. The most conspicuous is the Ancon Fault,

located south of the Oca Fault in western Falcon. The south coast of

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unpublished studies on shales obtained from a water well demonstrated thepresence of middle and late Miocene faunas in the Paraguana Peninsula(Hunter, pers. comm, 1986). The Cantaure Formation is correlated with theCerro Pelado Formation of the Falcon Basin and represents Cycle B in theParaguana Peninsula (Figs. 10,36).

The Paraguana Formation comprises the large majority of sedimentsexposed in this Peninsula. The type locality is located 5 km east of PuebloNuevo where the road to Adicora cuts the low hills formed by these beds (Fig.50). In this locality, the section is subdivided into a lower interval of shalesand siltstones (EI Hato Member) and an upper interval of limestones (AmuayMember). The EI Hato Member is at least 30 meters thick and is composed ofcream-colored marine shales bearing an abundant foraminiferal fauna, whichare followed by more silty beds that form a laminated sequence of gray

Fig. 50. Type section of the Paraguana Fm, 5 km east of Pueblo Nuevo on the road toAdicora (Fig. 11). The lithology includes light gray shales weathering toyellowish and reddish colors, with intercalations of sandy, silty. limestonesbearing an abundant mollusc fauna (Glycimeris sp~, Ostrea sp., and pectinids).

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~

Contact between the lower (ELHato) and the upper (Amuay) members of theParaguana Fro exposed along the road between Adicora and Pueblo Nuevo.The basal unit of the upper member consists of a massive fossiliferouslimestone.

Fig. 51.

Fig. 52. Close-up of Fig. 51 showing the trace fossil Ophiomorpha indicative of shallowwater deposition.

.

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