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Insights Into the Occurrence of Intraplate Strike-Slip Deformation in the Foreland Llanos Basin, Colombia

Abstract

The Colombian-foreland Llanos basin is a prolific hydrocarbon province where oil discoveries are associated with numerous low-displacement high-angle faults. These faults are broadly distributed across the basin, and predominately display a NE-SW trend parallel to the Eastern Cordillera deformation front. The steeply dipping faults have been generally described as normal faults with either foreland (E) or hinterland (W) vergence. In addition to the normal faulting, tectonic inversion is also identified as a result of the episodic advance of the deformation front. This inversion is evident and well documented in the foothills of the Eastern Cordillera, the westernmost part of the Llanos basin and its occurrence decreases towards the East.

The origin of these faults have been attributed to the foreland flexure due to tectonic loading associated to the uplift of the Eastern Cordillera during the Cenozoic. However, detailed seismic interpretation of various 3D seismic datasets for reservoir management purposes, has allowed us to identify fault geometries related to a consistent right-lateral strike-slip component. Typical geometries include the occurrence of vertical faults deep-rooted into basement rocks, which change dip slightly at the interface with Meso-Cenozoic rocks. ā€œVā€ shape geometries (pop-up/pull-apart) are often associated with the vertical alignment of fluvial channels throughout the Miocene to Recent section, evidence of fault control, although sometimes without vertical displacement. Associated secondary faults seem to control hydrocarbon accumulations and may cause the late field compartmentalization. In plain view, these faults display typical Riedel trends which correspond to a regional dextral displacement.

Broadly distributed dextral deformation might be explained from the far-field tectonic stresses that affect the NW corner of South America, where the northern expulsion of the Andes along oblique boundaries (e.g. Algeciras Fault) is partially transferred into the foreland region. A preliminary hypothesis suggests that closer to the deformation front dextral transpression controls the deformation whereas dextral transtension dominates the Eastern sector. In any case, the analysis of this strike-slip component of deformation is an important step to understand the complex compartmentalization of reservoirs within the Llanos basin, and their implementation will improve the success of future development plans and exploratory campaigns.