Marien Parra¹, Lorena Moscardelli², Maria A. Lorente³

(1) Universidad Central de Venezuela, Caracas, Venezuela
(2) Universidad central de Venezuela, Caracas, Venezuela
(3) PDVSA, Caracas, Venezuela

ABSTRACT: Tectonic And Paleoenvironmental Changes At The End Of La Luna Formation Sea And Its Exploration Implications

The Tres Esquinas Member is a phosphorite unit glauconite rich associated with the changes that took place in Western Venezuelan Basin at the end of the Late Cretaceous. It marked the end of La Luna Formation sedimentary cycle. We present the results of a study carried out in samples from an outcrop section in the Andes Range (Río Guaruríes ) and a subsurface interval in the Perijá foothill combined with seismic information.

In Río Guaruries outcrop section, four sedimentary microfacies were defined based on allochemical and mineral distribution: Orthocarstenia and Bolivinoides wackstone(OBW); Orthocarstenia and Bolivinoides phosphatized grainstone and ooids(OBPG); Orthocarstenia and Bolivinoides phosphatized grainstone with glauconite and dolomite(OBPGG) and Glauconitic mudstone(GM).

In the Perijá area three different associations characterized by a poor allochemical portion and foraminifer fauna, along with important carbonate matrix development and poor definition of mineral facies were defined: Foraminifer and intraclastic wackstone(FIW); Glauconitic and Dolomitic wackstone(GDW); Glauconitic wackstone(GW) and Planktic foraminifer mudstone(PFM).

The microfacies analysis reveals reworking and erosion processes as part of Tres Esquinas Member sedimentation dynamic. This elements can be associated to paleoenvironmental and tectonic changes that took place at the end of La Luna Formation deposition. This high energy condition would be related to the geodynamic framework developed in the western boundary of South American plate during Late Cretaceous. This modification of the Cretaceous epicontinental shelf configuration control the erosion and deposition processes creating a new stratigraphic play at the Colon - La Luna formation contact.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado