Eastward extent of the Late Eocene-Early Oligocene onset of deformation across the northern Andes: constraints from the northern portion of the Eastern Cordillera fold belt, Colombia

New geologic information supports an interpretation of the initiation of tectonic uplift in the eastern margin of the Eastern Cordillera of Colombia and the onset of deformation across the northern Andes during the Late Eocene-Early Oligocene. The eastern edge of Late Eocene-Early Oligocene deformation was located at the present site of the eastern margin of the Eastern Cordillera. This uplift can be linked to tectonic events already described for the western margin of the Eastern Cordillera. On the basis of an interpretation of geologic maps, a new regional balanced cross-section across the region, seismic reflection profiles, remote sensing images, and biostratigraphic data, three major deformation events are invoked to describe the evolution of this fold belt. The first event occurred early during the Late Eocene-Early Oligocene and formed a NE-vergent imbricate fan. This imbricate fan was eroded and covered by Late Oligocene deposits, which formed a major angular unconformity. A subsequent compressional event in Miocene-Pliocene times (Andean orogeny) reactivated preexisting thrust faults and created new ones that folded those formed during the earlier event. These younger thrust faults also offset and folded the angular unconformity. Finally, a more recent tectonic event refolded the structures from the previous events. The thin-skinned thrust system of the northeastern margin of the Eastern Cordillera of Colombia can be linked to a foot wall shortcut of the inverted Servita fault formed during the Late Eocene-Recent inversion of a Jurassic-Cretaceous extensional basin. (C) 2003 Elsevier Ltd. All rights reserved.