Abstract SE Asian carbonate formations have been reviewed with the aim of understanding the influence of tectonics on their development and reservoir potential through the Cenozoic. Regional tectonics, via plate movements, extensional basin formation, and uplift, was the dominant control on the location of carbonate deposits. These processes controlled the movement of shallow marine areas into the tropics, together with their emergence and disappearance. Although ∼ 70% of the 250 shallow marine carbonate formations in SE Asia were initiated as attached features, 90% of economic hydrocarbon discoveries are in carbonate strata developed over antecedent topography, of which more than 75% were isolated platforms. Faulted highs influenced the siting of nearly two thirds of carbonates developed over antecedent topography. Around a third of carbonate units formed in intra- and interarc areas; however, economic reservoirs are mainly in backarc and rift-margin settings (∼ 40% each). Carbonate edifices show evidence of syntectonic sedimentation through: (1) fault-margin collapse and resedimentation, (2) fault segmentation of platforms, (3) tilted strata and differential generation of accommodation space, and (4) modification of internal sequence character and facies distribution. The demise of many platforms, particularly those forming economic reservoirs, was influenced by tectonic subsidence, often in combination with eustatic sea-level rise and environmental perturbations. Fractures, if open or widened by dissolution, enhance reservoir quality. However, fracturing may also result in compartmentalization of reservoirs through formation of fault gouge, or fault leakage via compromised seal integrity. This study will help in reservoir prediction in complex tectonic regions as the petroleum industry focuses on further exploration and development of economically important carbonate reservoirs.

Abstract Porgera is a ~974-metric ton (t) Au, low-sulfidation, alkalic, epithermal gold deposit located in Papua New Guinea. The deposit is spatially associated with 6 Ma stocks of the mafic alkalic Porgera Intrusive Complex, which were emplaced within Cretaceous carbonaceous mudstones in a transpressional orogenic setting linked to continent-island arc collision. As with many other major magmatic-hydrothermal ore deposits in New Guinea, deep-seated, arc-normal transfer structures have been suggested as controls on intrusion emplacement through the creation of a localized extensional environment favorable for magma ascent. Gold mineralization occurred in two distinct phases, both within ≤0.2 m.y. of emplacement of the Porgera Intrusive Complex. Stage 1 mineralization of intrusion-related carbonate-base metal association consists of extensional vein swarms dominated by coarse intergrown pyrite ± galena and sphalerite, generally hosted within or proximal to the intrusive bodies of the Porgera Intrusive Complex. These veins represent the lowest grade and economically least significant mineralization phase. Overprinted high-grade epithermal Stage 2 mineralization consists of roscoelite, pyrite, and quartz veins and breccia veins ± subordinate amounts of barite, marcasite, sphalerite, tetrahedrite, galena, hematite, and tellurides. Gold mineralization is commonly associated with the roscoelite-rich coatings on vein walls or breccia clasts. Stage 2 mineralization is controlled by a deposit-scale extensional fault-fracture mesh and displays a variety of textural styles including: (1) <5-mm veinlets dominated by roscoelite, pyrite, and gold; (2) thicker veins up to 10 cm wide with roscoelite, pyrite, and gold on the margins with central bands of alternating crustiform quartz and thin layers of roscoelite-pyrite-gold; (3) hydrothermal breccias with roscoelite, pyrite, and gold coating breccia margins and internal clasts, with crustiform quartz forming the matrix. The giant endowment of the Porgera gold system is attributed to its favorable tectonic location and local extensional setting, its vertical extent, the oxidized nature of the mineralizing fluids, and highly efficient gold precipitation.

Abstract High-grade metamorphic rocks – marble, charnockite, meta-anorthosite, metapelite, clinopyroxenite and garnet amphibolite – have been found in northwestern Venezuela. They occur as: (a) xenoliths in the Oligo-Miocene lavas of Cerro Atravesado, Central Falcón; (b) possibly olistoliths in Nuezalito Formation, NW Portuguesa; (c) in Cerro El Guayabo, an elongated east–west oriented hill in the Nirgua Complex, Yaracuy; (d) rounded clasts of marble in the basal conglomerate of Casupal Formation, Falcón; (e) rounded clasts of anorthosite and sillimanite gneiss in a conglomerate of Matatere Formation, Lara; and (f) basement cores extracted from La Vela Gulf, Falcón. These high-grade rocks probably suffered a retrograde metamorphism to amphibolite facies of Palaeozoic age, and an even more retrograde event to the greenschist facies during Early Cenozoic, together with strong shearing and hydrothermal alteration. They indicate the possible existence of an extensive high-grade basement, or a mosaic of such blocks, under northwestern Venezuela, especially below the Falcón petroleum basin. Similar rocks crop out extensively in northern and central Colombia, Mexico, Ecuador and Peru. This is the first time they are described from Venezuela. Their high-grade lithology, pre-Mesozoic positions, and the tectonic evolution of Northern South America allow interpretation of a possible Grenvillian affinity, related to the supercontinents of Rodinia and Pangaea.

ABSTRACT The understanding of the plate tectonic interactions between the Caribbean, South America, and Atlantic plates and their integration with the timing of the basin configurations, its source rock deposition, and thermal maturation provides important insights to interpret the Venezuelan petroleum systems. The different tectonic settings in northern Venezuela offered the right environmental conditions for the deposition of world-class–Cretaceous organic-rich source rocks all through its northern margin, allowing the generation, expulsion, migration, entrapment, and geographical distribution for most of the 1.8 trillion bls of original oil in place and 200 TCFG in discovered-proven resources in the 14 main basins of Venezuela. The integrated and comprehensive approach of this study allowed the proposal of an orogenic float partitioning tectonic model that couples the development of the southern Caribbean plate along oblique terrane accretions and subduction below northern South America concurrently with the Atlantic oceanic-crust subduction below the Caribbean plateau. The orogenic float glides on the underlying Caribbean–South American lithosphere coupling, along a basal decollement surface with two deformation fronts that forced a foreland basin to the south in the arc–continent collision (“A” subduction) and coeval forearc basins on Caribbean oceanic-crust subductions under Caribbean terranes or “B” subduction. Right-lateral–strike-slip fault activity along the Oca, San Sebastian, El Pilar, and Arima systems occurs synchronously with the eastward rejuvenation of Caribbean accretion and thrusting. These offsets are the consequence of the oblique convergence between the plates to balance the eastward displacement with the southward thrusting and foredeep subsidence. We report evidence for 100 km (60 mi) of right-lateral displacement along the Oca fault. In our model, the orogenic float used the weakness of the crust along old transform system that formed during the Mesozoic rifting event, to create internal strain-partitioning and displace the arc–continent deformation front along northwest–southeast right-lateral transfer-fault systems of Barquisimeto, Burro Negro, Guárico, Margarita, Urica, and Tobago to name the most important. This succession of tectonic events had implications for basin development north and south of the suture, on the autochthonous side and on the transported terranes. The understanding of the Andean orogenesis as well as the rest of the northern ranges, and the timing and subsidence of adjacent basins, along with the related petroleum systems allowed us to identify and locate from Eocene to present the main oil and gas kitchens for the Cretaceous and Cenozoic source rocks in northern onshore and offshore Venezuela. This facilitated the identification of remaining exploration potential even on mature and explored basins, such as the Cretaceous and Eocene-subcrop plays in Golfo de Venezuela, the foreland subthrust belt play in Ensenada de Barcelona with autochthonous Cretaceous to Paleogene reservoirs, a possible pre-Cretaceous source rock within Espino graben, and several transtensional and transpressional plays in the offshore basins of Blanquilla, Cariaco, Bonaire, and northeastern Falcón basins.