The Eastern Llanos Basin is located in eastern part of Colombia. Its boundaries are the Barinas Basin to the north, the La Macarena Range and Vaupés arch to the south, Guaicaramo fault system to the west and the Guyana Shield to the east.
The geological history of this basin starts in the Paleozoic with an extensional phase (rifting) that allowed accumulation of siliciclastic sediments on Precambrian crystalline basement. During Jurassic to late Cretaceous times, the basin constituted the eastern end of a big extensional system covered by shallow marine deposits. Since the Maastrichtian it became a foreland basin. From the Miocene to present, huge volumes of molassic sediments have been accumulated.
Regarding maturity, the source rocks have ranges from immature to the east, with increasing maturity to the west, due the frontal thrusting of the Eastern Cordillera. The main reservoirs are late Cretaceous and Paleocene siliciclastic units. Separate component analyses of the migration systems are complicated due to the constant varying lateral thickness of the section.