MIOCENE DELTAIC SEDIMENTATION IN THE FALCON BASIN AND ITS RELATION TO CLIMATE AND CARIBBEAN TECTONICS

The Falcon Basin is an east-west trending depression developed in Northwestern Venezuela over the accreted Cretaceous and Paleogene rocks of the Lara Nappes, related to the interaction of the Caribbean and South American plates. The Opening of the basin started in the Early Eocene and since that time sedimentation has been almost continuous until the early Pliocene.

During most of the Miocene a thick deltaic succession, up to 8000m, was accumulated in western Falcon, punctuated by marine transgressions. Early Miocene deltaic sedimentation is characterized by fluvio-dominated deltas, while sedimentation in the Middle and Late Miocene represent prograding delta-strand plain complexes with the development of extensive wetlands in the delta plain.

The vertebrate fauna of the Middle and Late Miocene Socorro and Urumaco formations have been correlated biogeographically with the modern Orinoco River system, and other Neogene Fauna in Colombia and Brasil, which has allowed to interpret the origin of the deltaic successions in the Falcon Basin as the product of the proto-Orinoco delta system, a large river that drained the South American Craton and the Colombian Andes, running in a south-north direction before the major rise of the Merida Andes in the Early Pliocene. An alternative paleogeographic interpretation, indicates that the axis of the proto-Orinoco river was diverted to the northeast at the end of the Oligocene, so that all the Miocene deltaic sequences in the Basin were sourced from intrabasinal drainage.

Here we present an integrated provenance study including data on petrography, detrital Zircon geochronology and heavy minerals analysis for sandstone in the Miocene succession that suggest a major input from the accreted Cretaceous metamorphic and Paleogene Sedimentary rocks of the Lara Nappes and the adjacent northern most Andean massifs including the Perija and Merida Andes Ranges. This study suggest that the deltaic Miocene deposits of the Falcon Basin are the product of small deltas draining low-relief mountains and the tropical weather may be driving the high input of sediment similar to the tropical deltas of the South East Asia islands.