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Dengo, Carlos A., Exxon Exploration Company, Houston, Texas

Abstract: Tectonic Architecture of the Subandean Fold and Thrust Belt: Structural Style Variations and Occurrence of Hydrocarbon Traps

The Subandean fold and thrust belt and associated foreland basins of South America represent one of the world’s most prolific hydrocarbon provinces. Improved seismic data coverage and quality, and structural models validated by recent drilling, have increased our understanding of the hydrocarbon trap styles, their variations, and remaining untested potential. Along the entire length of the Subandean system, earlier structures formed in a variety of tectonic settings now share a common overprint of late Miocene–Holocene compressional deformation. The result is a segmented fold belt comprised of distinct hydrocarbon systems and contrasting trap styles. This segmentation is clearly exemplified by variations in stratigraphy, which control source type and distribution, structural detachment levels, and reservoir quality.

The Subandean in Venezuela and Colombia has structures that result from reactivation of Jurassic rifting by compressional/transpressional deformation, and are locally influenced by Early Cretaceous evaporites. Recent movement along basement-involved reverse faults modified thin-skinned fault-ramp folds. From southern Colombia to northern Peru, structures are dominated by basement-involved reverse faults, some possibly inherited from Permian–Triassic back-arc extension and locally influenced by Late Triassic evaporites. Regional uplift, interpreted to be the result of a gently dipping oceanic subducting plate, has exhumed giant oil accumulations and arrested the maturation of source rocks and generation of hydrocarbons. From central Peru to northern Argentina, the Subandean is characterized by large thin-skinned fault-ramp folds, a function of the relatively continuous Paleozoic stratigraphy and detachment horizons. Back-thrusting is prevalent and has dissected migration pathways. Thin-skinned and basement-involved deformation is observed in the southern Subandean fold and thrust belt. Many structures had their origin in the tectonics related to terrain accretion during middle Paleozoic and subsequent reactivation during Late Jurassic to Early Cretaceous opening of the South Atlantic.

AAPG Search and Discovery Article #90934©1997-1998 AAPG International Distinguished Lecturers