We put to scrutiny a tectonic model for the Cenozoic of the Middle Magdalena Valley Basin (MMVB) and bounding Andean ranges in Colombia that differs markedly from generally accepted models. It is supported by new field information, collected within the MMVB, provenance analyses, subsurface correlation and structural interpretations. Previous models, extrapolated from neighboring regions, suggest that the MMVB was part of a Paleogene foreland basin generated by uplift of the Central Cordillera to the West and transformed to a Miocene-Pliocene intermontane basin during deformation of the Eastern Cordillera to the east.

Our data indicate that, during the Early Paleogene, the MMVB was a broken or composite foreland basin sourced by the Central Cordillera, intrabasinal highs, and the Eastern Cordillera whose uplift began in the Early Paleogene and not in the Miocene as previously assumed. Thus, a paleogeographic barrier separated the MMVB from the Llanos Foothills Basin to the east. Growth-stratal geometries suggest that a second phase of deformation of the Eastern Cordillera began during the Late Paleogene. Overfilling of the MMVB may have produced communication with the Llanos Basin between these pulses of Paleogene deformation. The principal uplift of the Eastern Cordillera resulted from Miocene-Pliocene out-of-sequence thrusting. Pre-Cenozoic crustal structure produced a heterogeneous pattern of crustal thickness and mechanical properties; consequently, spatially varying flexural response to Cenozoic tectonic loading may have determined the MMVB geometry.

This interpretation has implications for the prediction of reservoir facies trends and hydrocarbon maturation and migration histories in the oil-producing MMVB.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas