Tectonic controls and sedimentary evolution of the Gulf of Venezuela

Abstract

The Gulf of Venezuela is located at the boundary between the Cretaceous-Cenozoic deformation zone of the South American and Caribbean plates. It is an underexplored area lying between the hydrocarbon-rich Maracaibo Basin and the emergent plays such as Perla Upper Oligocene to lower Miocene carbonates in the Caribbean plate. Gravity and seismic reflection data reveal three main basement provinces. 1) A western Paleozoic basement with continental affinity similar to those in the Guajira Peninsula and the Maracaibo basin; 2) a central province covering the area of the on and offshore Urumaco trough with Cretaceous metamorphic rocks; and 3) a easternmost province, with Cretaceous Caribbean arc rocks, related to the Leeward Antilles island arc system. The Western flank of the Urumaco trough represents a structural and stratigraphic abrupt change that might be related with the boundary between the Maracaibo and Caribbean affinity province. In addition, right-lateral strike-slip displacement along the Oca-Ancon faults seems to have a relevant role to the present-day basement configuration. It has displaced eastwards and segmented the northern part of the basement provinces, resulting in a more complex distribution that needs to be considered to reconstruct depict the geologic history. Therefore, this region may hold promising opportunities for hydrocarbon exploration, where the Maracaibo Basin petroleum system may extends offshore into the Gulf of Venezuela. Key words: Gulf of Venezuela, Maracaibo basin, Caribbean. Introduction Western Venezuela consists of a complex geological deformation zone as a result of Cretaceous-Cenozoic interaction between the Caribbean and the South American plates. In this regard, the Gulf of Venezuela, located in the northwestern most region of South America, represents an key area to understand the uncertain complex boundary between the hydrocarbon-rich Maracaibo Basin and the emerging condensate and gas province of the Caribbean related basins (Perla Field, upper Oligocene to lowerfault zone northwards, which is interpreted to be the western flank of the Urumaco trough, aligning with the northern Cuiza fault in the Guajira Peninsula (Dewey and Pindell., 1984). This complex system is associated with the main boundary controlling the location of the South America vs Caribbean related rocks during Eocene convergence. An extensive seismic data set of more than 10.000 km of on- and off-shore 2D seismic lines, well information and biostratigraphy reports were used to constrain a tectonostratigraphic evolution model of the Gulf of Venezuela. It ultimately allows us to analyse its geologic relationship with its neighbouring provinces, and its hydrocarbons implications in the region. Preliminary observations Based on gravity and seismic interpretation of the acoustic basement three main basement provinces were identified: 1) A western Paleozoic basement province with continental affinity similar to those in the Guajira Peninsula and the Maracaibo Basin; 2) a central province covering the area of the on- and offshore Urumaco trough with Cretaceous metamorphic rocks; 3) and the most eastern province, with Cretaceous Caribbean arc related affinity (Figure 1). Subsidence Patterns Figure 2 shows three different burial histories displaying total subsidence from key wells in the study area. Well Gua-4 located onland in northwestern region of the Maracaibo Basin (figure 2A) and Atun-1X located in the Maracaibo province of the Gulf of Venezuela (figure 2B) show a steady subsidence pattern from Early to Late Cretaceous. Spanning from Paleocene to Early Miocene, the subsidence curve shows a steeply subsidence pattern and Cretaceous rocks were therefore deeply buried (Escalona and Mann, 2005). During the Oligocene, a tectonic uplift interrupted the subsidence phase. Most recently, an increase in subsidence is observed starting in the Late Oligocene to recent. Subsidence curves Miocene carbonates; 16 TCF of non- associated gas, Castillo et al. 2017). Regional tectonic plate models and paleogeographic maps indicate large uncertainties about the exact location of the Caribbean and South America plate boundary. Gorney et al. (2007) identified three main basement provinces: 1) Paleozoic with continental affinity revealed in the Guajira Peninsula and the Maracaibo Basin; 2) the northwestern Falc.n region with Cretaceous metamorphic rock with continental affinity; and 3) the Cretaceous Caribbean Arc, which is related to the Leeward Antilles Arc system (Figure 1). In contrast, Castillo et al. (2017) defined two geologic provinces: the autochthonous Dabajuro platform to the west and the Urumaco trough to the east related with an allochthonous arc block. The geological configuration of the region, based on onshore data, shows a transition zone defined by the 40-km — wide Urumaco trough. It separates the Paleozoic continental basement to the west (Maracaibo Basin stratigraphy) from the Cretaceous related provinces to the east (Gorney et al., 2007). Cenozoic right-lateral slip along the Oca-Ancon fault system might have resulted in a more complex configuration that transported eastward basement blocks to the north by more than 80 km (Gorney et al., 2007). Arguments supporting this configuration include the possible extension of the Burro Negro fault zone northwards, which is interpreted to be the western flank of the Urumaco trough, aligning with the northern Cuiza fault in the Guajira Peninsula (Dewey and Pindell., 1984). This complex system is associated with the main boundary controlling the location of the South America vs Caribbean related rocks during Eocene convergence. An extensive seismic data set of more than 10.000 km of on- and off-shore 2D seismic lines, well information and biostratigraphy reports were used to constrain a tectonostratigraphic evolution model of the Gulf of Venezuela. It ultimately allows us to analyse its geologic relationship with its neighbouring provinces, and its hydrocarbons implications in the region. Preliminary observations Based on gravity and seismic interpretation of the acoustic basement three main basement provinces were identified: 1) A western Paleozoic basement province with continental affinity similar to those in the Guajira Peninsula and the Maracaibo Basin; 2) a central province covering the area of the on- and offshore Urumaco trough with Cretaceous metamorphic rocks; 3) and the most eastern province, with Cretaceous Caribbean arc related affinity (Figure 1). Subsidence Patterns Figure 2 shows three different burial histories displaying total subsidence from key wells in the study area. Well Gua-4 located onland in northwestern region of the Maracaibo Basin (figure 2A) and Atun-1X located in the Maracaibo province of the Gulf of Venezuela (figure 2B) show a steady subsidence pattern from Early to Late Cretaceous. Spanning from Paleocene to Early Miocene, the subsidence curve shows a steeply subsidence pattern and Cretaceous rocks were therefore deeply buried (Escalona and Mann, 2005). During the Oligocene, a tectonic uplift interrupted the subsidence phase. Most recently, an increase in subsidence is observed starting in the Late Oligocene to recent. Subsidence curves on figure 2A and B display similar patterns and timing the Maracaibo foreland basin; these observations are in accordance with Escalona and Mann, 2011. The different phases observed on the subsidence plots for well GUA-4 and Atun-1X are the response to major geological events: (1) An initial passive margin (Late Cretaceous- Paleocene); (2) A burial foreland phase, associated with the oblique collision between Caribbean and South American plates (Paleocene- Early Eocene); (3) Isostatic rebound (Oligocene) triggered by the Maracaibo basin uplift; and (4) Tectonic loading related with the uplift of the Sierra the Perija and Merida Andes. An important increase in subsidence is observed in well Atun-1X during Early Oligocene. It is probably associated with the opening of the Urumaco trough and Leewards Antilles basins. Well Perla-1X, located in the Caribbean province (figure 2C), shows a subsidence curve which are relatively different from the other two provinces and three main phases are observed. This geological trend resembles that of the Caribbean basins described by Escalona and Mann, 2011. During the Oligocene, a subsidence phase (a) is seen. It coincides with the (initial subsidence phase proposed by Escalona and Mann, 2011. Following, a short-lived uplift (b) occurs around 25 Ma and corresponds to the inversion phase of Escalona and Mann, 2011. Spanning from the Late Oligocene until Middle Miocene, constant subsidence took place. This steady subsidence appears to be related to the Urumaco trough opening. Starting in the Late Miocene, subsidence has been interrupted by short-lived periods of uplifts. Figure 2. Subsidence curves showing the different phases present in the Caribbean and Maracaibo province. A) Well Gua-4X located in the northwestern region of the Maracaibo basin. B) Atun-1X located in the Maracaibo province and C) Perla-1X located in the Caribbean province. The numbers 1-4 are related with the phases described by Escalona and Mann in 2011 for the Maracaibo foreland basin deformation. Letters a-c represent the phases described by Escalona and Mann in 2011, for the Caribbean deformation. Fault Families Based on seismic interpretation five (5) fault families were defined. Fault type and timing of formation were used as the main criteria to define fault families. . Fault family 1: Eocene-Recent / major northwest striking tear faults. . Fault family 2: Eocene- Middle Miocene / north-northwest striking normal faults. . Fault family 3: Cretaceous—Middle Miocene / east-southeast striking normal faults reactivated as strike slip. . Fault family 4: Cretaceous—Miocene/ north-west striking normal faults. . Fault family 5: Early Miocene-Holocene/ northwest striking normal faults. From families 1 to 4, faults penetrate the basement. By contrast, fault family 5 is related with thin-skinned deformation. Fault Family 1, bounds the SE-NW elongated depocenter. This mega-structure seems to be an offshore extension of the Urumaco trough described onshore by Maceralli, 1995 . One member of this family represent an abrupt boundary between the Urumaco trough infilled by Eocene to recent sediments and the Maracaibo province containing Cretaceous to recent sediments. In addition, the east-west-oriented strike-slip fault system interpreted in Paraguana and La Vela bay (Blanco et al., 2017; Audemard, 2011; Maceralli, 1995,) seems to continue towards the Gulf of Venezuela, where it coincides with fault (Family 3), segmenting the Urumaco trough. Normal faults are the most common fault type observed across the study area (Family 2, 4 and 5). However, some of them were reactivated as reverse faults during the Oligocene and Middle Miocene. Conclusion Within the western province (Maracaibo province), sequences from Cretaceous to Recent were interpreted. This stratigraphic framework seems to be similar to the one in the Maracaibo Basin. In contrast, the Eocene-Oligocene sequences in the Urumaco and Caribbean provinces rest directly on the acoustic basement. The Maracaibo petroleum system might be present in the western region of the Gulf of Venezuela (north of Oca-Ancon faults) based on the strong stratigraphic resemblance. Burial histories also support this assumption, showing in Gua-4X and Atun-1X the typical deformation patter for this province. Fault family 3 might be related with the monocline of La Sierra de Perij., therefore part of the Maracaibo basin could extend north and be present in the Maracaibo province. These features are presently located towards the east due to Cenozoic right-lateral strike-slip along the Oca-Anc.n fault which has segmented the northern part of the Maracaibo basin. The extension of the Maracaibo province towards the Gulf of Venezuela opens promising exploration opportunities similar to those plays found in the north-western corner of the Maracaibo Basin.

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018