Bachelor of Arts
Caribbean, Venezuela, Andes
The Caribbean Mountains of Venezuela reach from the Venezuelan Andes to the Northern Ranges of Trinidad. Upper Cretaceous and Paleocene flysch units deposited in a marine euxinic basin are crucial in unraveling the evolution of the mountains. Two formations in the Acarigua region (near the termination in the Venezuelan Andes), the Rio Guache and Nuezalito formations, are the most complete sections of these flysch sequences. A sedimentary petrologic study was undertaken to determine the source areas for these formations, to put age brackets on the timing of uplift and rotation of portions of the Caribbean Mountains.
The mountains are divided into five tectonic divisions: The Cordillera de la Costa Belt, the Tinaco Belt, the Paracotos Belt, the Villa de Cura Belt and the Flysch Basins. The remnants of an island arc system connected with the evolution of the mountains lies off the coastline. Plutonic clasts from the Nuezalito formation indicate that deposition occurred in a basin bounded on the north by the Tinaco and Villa de Cura belts, a Tinaco Belt correlative which now forms the Guajira Peninsula and possibly the island arc system. The southern margin of the basin was formed by the continental platform. Uplift, plutonism and metamorphism of several belts had already occurred by the time of deposition of the Nuezalito formation.
The Rio Guache formation was deposited under similar conditions. More abundant metamorphic clasts suggest that uplift of the Cordillera de la Costa Belt occurred after the Nuezalito and before the Rio Guache formations were deposited. Analysis of graywackes from the two formations shows differences in composition attributable to depositional factors, but no clear variation in maturity which might indicate whether the Rio Guache formation was derived in part from recycled older sediments such as the Nuezalito formation. Comparison of monocrystalline to polycrystalline quartz ratios in the two formations shows the Rio Guache formation to be more mature, but this may have little statistical validity.
Recent theories for evolution of the Caribbean Mountains speculate that the island arc, rotating to the south as a result of eastward movement of the Caribbean plate, collided with the continental craton, causing orogenesis to occur. Paleomagnetic data suggests that the Tinaco and Villa de Cura as well as the Guajira Peninsula also rotated. The Nuezalito basin rotated with these belts; consequently the timing of rotation cannot be fixed by the provenance of clasts in the Nuezalito formation.
Changes in the style of orogenesis in the Caribbean Mountains are reflected in the clast types present in the Rio Guache and Nuezalito formations. A theory proposed by Crook (1974) states that graywackes reflect three different types of geotectonic terrains. The data collected from graywacke and pebble clast analysis indicates that this model is overly simplistic, and that perhaps the model should be replaced by more exact theories.
Meyer, Steve A., "Two Upper Cretaceous Flysch Sequences in the Caribbean Mountains of Venezuela and Their Relationship to Caribbean Tectonics" (1979). Honors Papers. 718.