Campanian–Miocene tectonostratigraphy, depocenter evolution and basin development of Colombia and western Venezuela

Abstract

The position of the central axis of deposition over Colombian and Venezuelan continental crust has varied markedly through time. The axis migrated from west to east from Late Cretaceous to Oligocene but at times, secondary drainage divides were established by local uplift events. In Oligocene times with initial inversion of the Eastern Cordillera the central axis of deposition was divided into two main axes, the proto-Magdalena and the proto-Orinoco systems. The west to east migration of the central axis of deposition had a tectonic origin and it occurred in combination with tectonically driven changes in accommodation space. Depocenter evolution can be divided as follows. (1) The axis of the Campanian and early Maastrichtian depocenter was located few km east of the present position of the Central Cordillera of Colombia; it migrated east with gradual uplift of the Central Cordillera. (2) The central axis of late Maastrichtian deposition is positioned approximately over the present-day western foothills of the Eastern Cordillera, possibly crosses the Eastern Cordillera over the Santander Massif and continues into the Maracaibo Lake in western Venezuela. Accommodation space decreased from Campanian to Maastrichtian times. In Cretaceous–Tertiary boundary times parts of the eastern margin of the Eastern Cordillera were uplifted by an initial phase of inversion of deeply rooted Jurassic and Early Cretaceous normal faults. (3) In Paleocene times the central axis of deposition was located along the spine of the Eastern Cordillera and extended into the Maracaibo Basin, and accommodation space continued to decrease. (4) In latest Paleocene times the central axis of deposition shifted to eastern regions of the Eastern Cordillera and accommodation space decreased. (5) The Early Eocene central axis of deposition was located along the present-day eastern foothills of the Eastern Cordillera; accommodation space continued to decrease and the regional Middle Eocene unconformity began to develop. In Middle Eocene times a regional unconformity developed, marking the climax of the pre-Andean Orogeny. Deposition during these times was dominant in the Maracaibo Basin area where large amounts of sediment derived from vast exposed areas accumulated. (6) The Late Eocene central axis of deposition was confined to the present position of the Llanos foothills. Late Eocene deposition reflects a regional increase in accommodation space. In Oligocene times the initial uplift of the Eastern Cordillera divided the main depocenter into two central axes. Accommodation space diminished in uplifted regions but continued to increase in the depocenters allowing sporadic marine ingressions into the present position of the Llanos foothills. As uplift of the Eastern Cordillera continued, the eastern depocenter axis (proto-Orinoco) migrated east and the western depocenter axis (proto-Magdalena) migrated west. This process continued through the rest of the Cenozoic.