Interpretation of seismic profiles, earthquake fault-plane solutions, radar images, and geometry of structures suggests that two different structural styles are viable alternatives for the Putumayo basin in Colombia. An eastern domain, varying in width from 4 to 13 km, might be characterized by strike-slip faulting parallel to the Andes because it exhibits similar structures to those formed in restraining bend settings, an example is the Orito fold, the largest known oil field in the basin. Correlation of seismic reflections with wells into the Orito fold and foreland indicates a post-Miocene age for this structure. Previous interpretations of contractional dip-slip movement on Andes-parallel structures, as proposed by Portilla (1991) with faults involving basement, are also viable. A 15 km-width western domain is interpreted as a region of foreland-dipping rocks uplifted above their regional level by wedging of pre-Cretaceous (?) rocks beneath known Jurassic rocks. Above the Jurassic rocks thin-skinned deformation occurs inside of the Mesozoic and Cenozoic sedimentary cover, also in the form of wedging. Mesozoic and Paleozoic (?) rocks were injected into of a late Cretaceous-early Paleocene unit composed of shale. The western domain is truncated to the west by a major reverse fault that places Paleozoic rocks over Mesozoic and Cenozoic rocks. / text

Orito Field occupies an area of 31 mi² (80 km²) in the west-central portion of the Putumayo Basin, Colombia and forms part of an extensive littoral system that dominated sedimentation during Albian-Aptian time. The Caballos Formation represents the oldest Cretaceous unit, and was deposited at the beginning of a retrogradational episode immediately above the eroded Triassic-Jurassic surface. The Caballos Formation has an average thickness of 240 ft (73 m) and is largely composed of fine grained, highly compacted quartzarenites, cemented by quartz and kaolinite. A geologic model integrating all the available information allows the definition of four depositional events in the Caballos. The lowest depositional unit is composed of fluvial deposits with minor tidal influence. These fluvial sands grade upward into estuarine deposits formed in tidal channels and tidal flats, that are in turn overlain by tidal channel deposits, and are finally eroded and overlain by tidal mouth bars deposits. The vertical facies association is the product of a retrogradational episode and represents deposition in a tide-modified estuary, inside which diagenetic processes acted differently modifying the petrophysical properties of the facies that compose the Caballos reservoir in Orito field. Historical production trends of the Caballos reservoir correlate with the major depositional axes defined in this study and allow to delineation of high potential areas for future development, by means of targeted infill drilling and workovers.