Quantitative approach to extension and fault characterization within the central and northern Llanos basin, Colombia


The early Llanos basin developed during the Paleozoic–Mesozoic in a volcanic back arc, formed by subduction along the northwestern corner of the South American plate. In the Cenozoic, accretion of the Panama arch uplifted the Cordillera and isolated the eastern side of the basin into the current configuration. Two major depocenters were present in the northern and central-western Llanos basin, respectively: the Arauca graben resulted from early Paleozoic rifting, and uplift of the Eastern Cordillera led to flexural depression of the lithosphere. Variations in basin depth between these two depocenters and the eastern forebulge, affected fault populations and the distribution of lateral extension within the basin. Extension was calculated from line length balancing along eight sections across the basin, and the results compared with thickness of basin fill, fault population, and basement structure. This study quantitatively demonstrates that extension is greater in areas of thicker basin fill, yet fault population (principally antithetic faults) increases within thinner sections. Distribution of oil fields apparently follows the areas of high fault population, rather than areas of high lateral extension. Overall, NNE–SSW fault orientations in the Casanare domain provide better seals for oil accumulation than the ENE–WSW fault orientations in the Arauca area.

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Basement structure, Fault population, Lateral extension, Oil fields distribution, Thickness of basin fill