Paleocene Segmentation of a Former Passive Late Cretaceous Basin in Northwestern South America: Response to Caribbean Plate Subduction and Magmatism

In the Northern Andes, inversion of extensional structures controlled location of synorogenic successions and dispersal of detritus since Paleocene time. Detailed geologic mapping, tecto-sedimentological studies using provenance, biostratigraphy and termochronological data conducted in several basins with Paleogene strata across the present Eastern Cordillera, Llanos Basin and Perijá Range indicate that reactivation of former normal faults broke the single Upper Cretaceous basin into different depocenters separated by low-amplitude uplifts. Those uplifts exposed dominantly Cretaceous sedimentary cover. In the Paleocene to early Eocene, reverse reactivation broke the syn-orogenic basin into two depocenters. The western depocenter (Magdalena and Rancheria basins) was bounded to the west by eastward-tilted crustal blocks (Central Cordillera and Santa Marta Massif); crustal tilting and Paleocene magmatism were associated to subduction of the buoyant Caribbean plate. Crustal tilting favored reverse reactivation of the western border of former extensional Cretaceous basins. These reactivated structures acted as the eastern boundary of the western depocenter. Terrigenous and magmatic detritus filling the western depocenter were derived mainly from the Central Cordillera and from the uplifts to the east. In Late Paleocene to Early Eocene time, as eastern subduction of the Caribbean plate continued, reactivation of older structures migrated eastward and disrupted the eastern depocenter (presently along the axial zone of the Eastern Cordillera, Llanos foothills, Llanos, Catatumbo and western Maracaibo basin). The Eastern depocenter extended up to the present Llanos basin with minor uplifts, but in the Llanos basin such uplifts could expose Paleozoic metamorphic and sedimentary rocks. However, for most of the eastern depocenter, terrigenous detritus were derived from sources to the west and south, and they included reworking of the western synorogenic clastic wedge and erosion of the Cretaceous sedimentary cover. This Paleocene configuration of low-amplitude uplifts that separated at least two major syn-orogenic depocenters is not similar to the present configuration of the Eastern Cordillera, and differs from the alternative hypothesis of a continuous synorogenic basin that extended from the Central Cordillera to the Guyana shield. Future kinematic restoration of the Eastern Cordillera and Perijá Range requires a deformed stage for Paleocene time.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California