ABSTRACT We present seven paleogeographic maps from the Late Cretaceous to Pliocene for the circum-Caribbean region. The maps represent a comprehensive integration of data (e.g., well, outcrop, seismic, maps, etc.) from our own study and published data. The interpretations were conducted interactively using mapped data and spatial databases ( Watson and Escalona, 2021 ) alongside the construction of a quantitative plate model based on paleogeographic information systems ( Escalona et al., 2021 ). The maps reproduce the variation of sedimentary-facies distribution though time. In particular, the wide coverage of the study area provides insights into the onshore and offshore timing and filling of basins, subsidence patterns, and development of paleodrainages from large catchment areas, such as the northern margin of South America, to smaller source of sediments, such as the Great Arc of the Caribbean and the Central American Arc. Paleogeographic maps also illustrate how the various fault systems conditioned the capture and redirection of sedimentation through time.

ABSTRACT This chapter focuses on a structurally complex area, the southern Gulf of Paria, which straddles the boundary between eastern Venezuela and Trinidad. Using a combined seismic and well data set crossing the political border between Trinidad and Venezuela, the objective of this work is to provide an overview of the structural provinces present in the study area and to describe how they control the different tectono-sequences in the subsurface, the timing of events, and ultimately the implications for the petroleum systems. Five structural provinces were defined based on the main structural elements and tectonic setting: eastern Venezuela passive margin, southeast-directed fold-and-thrust belt (FTB), lateral ramp, pull-apart (PA) basin, and north-directed FTB. Four main tectono-sequences were interpreted and mapped from Cretaceous to present. Because of data quality and structural complexity, the oldest sequences are difficult to map, and interpretations are of higher uncertainty in the PA province (northern part especially) and the highly deformed areas of the FTB provinces. Regarding petroleum systems, conceptual models of the dominant trapping styles in relation to structural provinces are presented.

ABSTRACT Tectonic interactions in the Caribbean region are driven by two main processes: eastward motion of the Caribbean plate relative to North and South America, with subduction of Atlantic oceanic crust toward the west; and subduction of the Cocos and Nazca plates along the Mexico–middle America trench. This geometry has been maintained since the Eocene. Prior to this, the Caribbean plate entered the space between North and South America (the “proto-Caribbean”) from the Pacific causing polarity reversal of the arc (the Great Arc of the Caribbean) that separated the Pacific–Farallon plates from the proto-Caribbean. This latter region of oceanic crust was created by seafloor spreading between North and South America that started in the Early Jurassic; included in this early motion was the opening of the Gulf of Mexico by independent motion of Yucatan. Although this overall tectonic scheme has been well established for some time, only one quantitative plate model has been published before. This chapter updates that with a larger set of plate polygons and tectonic features in GIS format, along with a set of Euler poles that describe motion of about 350 tectonic elements, which make up the Caribbean and surrounding plates. Constraints on quantitative motions of these blocks comes almost entirely from geologic and geophysical data and a large database compilation of previous work from the Caribbean Basins, Tectonics, and Hydrocarbons and the PLATES consortia; the only well-constrained plate motion vectors come from seafloor spreading magnetic isochrons that record motion between North America and Africa, and between Africa and South America. A less-reliable magnetic chron data set is used to constrain post-Eocene motion of the Caribbean plate along the Cayman Trough. Geologic data used to constrain motion of the smaller blocks include stratigraphy, geochronology, structural mapping, and potential field data. The motion of individual blocks is adjusted until all these data combine to allow for a uniform progression of motion that honors local data as well as interactions among neighboring blocks.

ABSTRACT The Barbados Island is the topographically highest part of the Barbados Ridge and the only subaerially exposed part of the accretionary prism. Oil production from the Woodbourne field and the presence of migrated petroleum in outcropping rocks prove the existence of a working petroleum system. Detailed geochemical analyses suggest that petroleum onshore Barbados was derived from a Cretaceous deep marine shale source rock deposited under oxic-to-dysoxic conditions with varying contributions of marine and land plant-derived organic matter. This petroleum can be categorized into two groups. Group A petroleum was generated and expelled at the early oil window (0.72%Rc–0.77%Rc) from an interval of the shale source rock containing predominantly marine organic matter. By contrast, petroleum in group B was generated at the peak of the oil window (0.87%Rc–0.94%Rc) from a more proximal interval of the same source rock containing comparatively higher input of terrestrial-derived organic matter. These observations suggest the existence of the shale source rock at different maturities within a possible multiple-stacked source rock system. Reservoirs at the Woodbourne field have received at least two charges of hydrocarbons recognizable at present day. A first filling event is interpreted to have charged the reservoirs with the lower maturity petroleum (group A) after the middle Miocene uplift of the Barbados Ridge. Oils in reservoirs above 1000 m (3280 ft) depth are heavily biodegraded, whereas more deeply buried oils are moderately biodegraded. The second more recent charge consists exclusively of light hydrocarbons ( n -C3 to n -C9) expelled from the source rock at maturity levels similar to those determined for group B petroleum (0.86%Ro–1.05%Ro). These light hydrocarbons probably separated from their parental oils and migrated upward through faults or partially leaking seals, reaching reservoirs that contain early mature degraded oils above and below 1000 m (3280 ft). This charging event is inferred to be triggered by the Pliocene–Pleistocene tectonic event. A comparison using facies-sensitive biomarkers indicates that Barbados petroleum was not derived from carbonate facies typical of the La Luna Formation or its eastern equivalent, the Querecual Formation. This comparison shows that Barbados petroleum was sourced by clastic facies similar to those sourcing petroleum in the northern part of the Eastern Venezuelan basin, Gulf of Paria, and Trinidad. It implies that Barbados-type source rocks were deposited over vast areas along the Cretaceous passive margin of northern South America. These organic-carbon rich strata were probably incorporated into the western margin of the Barbados prism during the early stages of accretion (Paleocene–Eocene). Although speculative, the aforementioned observations suggest that significant petroleum potential may be present within the Barbados accretionary prism, but also further south within several offshore basins of Venezuela, Trinidad, and Tobago.

ABSTRACT This chapter presents an overview of the geochemical composition of 15 heavy oils from producing and exploration wells onshore Suriname aiming to determine the organic facies generating them. The inferred facies are integrated with the geologic framework of the Guyana Basin in a two-dimensional basin model to further assess their thermal history in the shelfal area of the basin. Detailed biomarker and carbon isotope geochemistry indicates that two compositional groups occur onshore Suriname. Oils produced from Cenozoic reservoirs (Group A) possess compositional attributes characteristic of oils generated from a distal marine shale. Their composition suggests the Upper Cretaceous shales of the Canje Formation as their possible source. In contrast, oil shows in the Upper Cretaceous strata (Group B) have biomarker relationships diagnostic of oils derived from a proximal marine depositional system rich in terrestrial organic matter. Uncertainty exists as to the age and spatial distribution of this organic facies. A Late Jurassic–Early Cretaceous age is provisionally proposed. Oil-maturity estimates indicate generation from source rocks at the mid-oil window for all the sample set. Thermal maturity modeling suggests that generation from the Upper Cretaceous (Canje Formation) and Upper Jurassic–Lower Cretaceous source rock facies started in the early Oligocene. The Upper Cretaceous clay-rich facies has only transformed 30% of its potential in the shelf with expulsion starting in the middle Pliocene. Accordingly, entrapment of Canje-generated oils in the onshore Tambaredjo trapping structure is suggested to be younger than the middle Pliocene. The Upper Jurassic–Lower Cretaceous facies in most of the shelf area has nearly reached peak generation with expulsion commencing in the late Miocene given the input parameters. In the shelf area, updip migration of hydrocarbon expelled from these two organic facies is dominant and terminates around the onshore Tambaredjo area.

ABSTRACT Two-dimensional seismic reflection data from offshore Barbados are combined with existing stratigraphic and geophysical data to reconstruct the Late Cretaceous–Cenozoic tectono-stratigraphic evolution of the western Barbados Accretionary Prism and the easternmost extension of the Tobago Basin. Three geological provinces are recognized in the study area: the Barbados Accretionary Prism (BAP), the Barbados Ridge (BR), and the Tobago Basin (TB). Eight fault families and five seismo-stratigraphic sequences bounded by unconformities or correlative conformities are interpreted and mapped. A four-phase evolution model is constrained using these combined interpretations. (1) Late Cretaceous–Paleocene normal faults affected the Cretaceous forearc crust and deep-marine shales deposited within half grabens. In the Paleocene, the accretionary prism started to build as a univergent wedge north of the Maracaibo Basin, whereas the proto-Maracaibo delta acted as a point source and delivered deepwater turbidites. (2) Northeast striking thrust faults, formed during the early stages of accretion, steepened and became inactive. Uplift along the South American margin disconnected the area from the proto-Maracaibo delta and late Eocene to Miocene deep-marine pelagics blanketed the study area. (3) Backthrusting of the BR over the TB commenced during the middle Miocene and the accretionary wedge became divergent. Because of thickening, the ridge surpassed the critical taper angle and a listric normal fault developed along its eastern margin. The rising ridge delivered reworked sediments to both the TB and the BAP. Compression along the southern boundary of the Caribbean plate reactivated thrusting and shale tectonics dominated within the southern subprovince of the prism forming deep piggyback basins. (4) Backthrusting of the BR continued and gave way to an imbricate fan system of thrusts accompanied by shale tectonics in the southern part. Subduction of a seamount beneath the northern subprovince of the prism caused uplift of the Barbados Island and subjected the region to flexure, expressed as extensional tectonics. In the early Pliocene, fluvio-deltaic deposition in the Columbus Basin sourced by the proto-Orinoco River fed deepwater sediments in the tectonically active southern subprovince of the prism. The rest of the study area has been a site of deep-marine pelagic and distal turbidite deposition. Geochemical work indicates that source rocks are Cretaceous and Paleogene marine shales. Reservoir–seal pairs are the Paleocene–Eocene, Eocene–Oligocene, and Miocene–Pliocene deposits. Viable structural traps were formed by normal faulting in the TB, thrusting in the BAP, and backthrusting of the BR.

Abstract Previous studies along the Andean subduction zones of South America have shown that forearc basins can develop over shallow-dipping the subduction zone dips horizontally or up to 15°, and that these shallow-dipping subduction zones can alternate with more steeply dipping (>30°) subduction zones over distances of 400–1500 km (249–932 mi). This study describes the Cenozoic structural and depositional history of the Lower Magdalena Basin (LMB)—an Oligocene to Recent forearc basin covering an area of 42,000 km 2 (16,216 mi 2) and overlying a zone of shallow subduction (the depth to the top of the Caribbean slab ranges from 30 km to 90 km [19 to 56 mi] beneath the LMB). Using 7000 km (4350 mi) of two-dimensional (2-D) seismic reflection lines tied to 33 wells, we describe the initial Oligocene subsidence of the forearc basin along a radial array of 70°- to 110°-striking normal faults that remained active until the early Miocene. During this period, the LMB was underfilled by 1–3 seconds two-way-time (TWT) (1500 m [4921 ft]) of shallow-marine and deep-marine facies. During middle Miocene the LMB remained underfilled with marine sediments deposited in water depths of 200–2600 m (656–8530 ft). An angular unconformity spanning the interval of 11–7 Ma marks a shortening and uplift affecting the Sinu accretionary prism west of the LMB that became emergent to form a prominent forearc high along the western edge of the LMB. The regional structure of the LMB is a broad syncline that folds all units older than early Miocene and produces an asymmetrical shape—in profile—with the western edge of the LMB (against the Sinu accretionary prism), steeper than the eastern edge of the LMB. After the late Miocene–Pliocene, the forearc high continued to elevate and separate the LMB from the outer Sinu accretionary prism. During this period, the LMB overfilled with terrigenous sediments of shallow marine facies that spilled offshore into the Caribbean Sea to form the proto-delta of the Magdalena Fan; these spilled sediments led to rapid tectonic accretion and growth of the offshore Sinu accretionary prism from 5 Ma to present. During the period of Oligocene to middle Miocene, different structural styles and subduction-related magmatic intrusions suggest that the Caribbean slab was subducting at an angle greater than 30° with a discontinuous volcanic arc. The decrease in the dip of the Caribbean slab to its modern dip angles of 4–8° occurred during the late Miocene and is interpreted as the entry of thicker Caribbean oceanic plateau crust into the subduction zone. Comparison of the segmented dip of the 400-km-long (249-mi-long) subducting Caribbean slab is consistent with the upper, 220-km-long (137-mi-long) shallow-dipping part subducting at rates of 2 cm/yr (0.78 in/yr) from 11 Ma (late middle Miocene) to Recent. We propose that this change from the steeper to shallower-dipping slab in the middle Miocene led to (1) increasing elevation of the forearc high of the Sinu prism along the eastern edge of the LMB; (2) the regional synclinal structure of the LMB in profile; and (3) the possible elevation of the entire LMB after 11 Ma as it changed from underfilled, deep-water marine environments to overfilled, shallow-water marine and fluvial environments.