New Insights on the Jurassic Rift Succession of the Merida Andes, Venezuela: Implications for New Petroleum Systems in Northern South America
The Jurassic succession in Venezuela is found either in rifts preserved under Cretaceous to Tertiary basins (Ipire beds in Eastern Venezuela) or exhumed in outcrops (La Quinta Formation) along the Perija and Merida mountains. In general, it is described as red beds and subordinate volcanics, with few references to sparsely distributed non-red facies.
A more complete graben fill style is described in a Jurassic depocenter exposed near the town of Jají, in the central Merida Andes. The structure is viewed as a half-graben that was reactivated and rotated as part of the Mio-Pliocene uplift of the Serranía La Culata. The measured rift column is 500m thick, with the lower 240m made of fluvial channel and overbank red bed deposits, followed by 200m of dark, organic-rich lacustrine shales and micrites that contain ostracods, estherids, bryozoans and pollen of Tithonian age. This lacustrine section is capped by 60m of gray-colored and well bedded shallow marine shales, also of Tithonian age, that are inferred to be in angular relation with the cretaceous of the Maracaibo Basin.
These La Quinta “dark” facies compare with other late-rift sequences found in the region, such as the marine Kimmeridgian Cuiza shales of the Guajira peninsula. With this new evidence, exploration models in northern South America should consider effective source rocks of pre-cretaceous age that may have formed effective petroleum systems additional to those already known in the Cretaceous and Paleogene successions.
New or Poorly Proven Petroleum Systems
2004 AAPG International Conference and Exhibition Technical Program