Upper Crustal Control of Deformation and Hydrocarbon Traps Along Upper Magdalena Valley, Colombia

K. Butler, S. Schamel

The compressive tectonic history of the Upper Magdalena Valley (UMV) is dominated by three Tertiary cratonward-verging deformation phases: (1) an early to middle Eocene uplift of the Central Cordillera, (2) a late Oligocene climax to this uplift and emplacement of crustal-rooted thrusts along the eastern flank of the Central Cordillera, and (3) the Miocene-Pliocene development of the Eastern Cordillera.

Uniquely, each of these distinct deformation episodes displays similar structural trends despite exhibiting varying convergences and emplacement along strike. In one case, the late Oligocene San Francisco anticline, a ramp-style basement fold, is bounded by a low-angle thrust and an adjacent crustal-driven thin-skinned thrust belt, but in a span of 30 km the anticline changes into a simple propagating basement thrust and fold that shows a Miocene fault reactivation. The Eastern Cordillera developed as a west-verging fold belt along the UMV but still exhibits the same fault trends as the east-verging Central Cordillera structures. The Eastern Cordillera deformed these older structures. The eastern flank of the Eastern Cordillera verges eastward, which gives the western flank the appear nce of a backthrust sequence.

Previously, interpretations of this region focused on a single, possibly transpressional, Andean-age deformation. Based on this reexamination, two distinct climactic events are seen in the Central and Eastern Cordillera structures, which are similar because Eocene-Pliocene compressive deformation was controlled by an older regional upper crustal fabric. These multiple episodes match deformation phases seen elsewhere in the northern Andes and thus may lend evidence for a regional tectonic relationship to the Andean deformed belts.

These deformational phases and their associated depositional packages indicate that the UMV has undergone at least two periods of oil generation and migration. This history is similar to that of the structures seen in the Middle Magdalena Valley and draws an additional parallel in the pre-Andean structural development of this area of Colombia.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.