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Abstract: Chronostratigraphy and Regional Distribution of the Cretaceous-Tertiary and Upper Cretaceous (Maastrichtian-Campanian) Unconformities, Barinas Basin, Southwestern Venezuela

Clara De Guerra, Zorena De Monroy, Rosa Aquino, Luisa Figueroa

The upper Cretaceous in the subsurface of the Barinas basin unconformably underlies middle Eocene sandstones and carbonates, while it conformably overlies upper Cretaceous clastics (upper Albian). Integration of results from semi-quantitatives analysis of marine and terrestrial palynomorphs, sedimentological analysis from cores, electrofacies, seismic interpretations and third order correlation cycles allowed us to define the chronostratigraphy and regional distribution of two significant unconformities within a more precise geological framework.

The first unconformity is located between the Navay Formation, Campanian in age (83 Ma) and the Maastrichtian Burguita Formation (71 Ma). This hiatus of 12 m.y. represents the unconformable contact between the UZA-3.4 and UZA-4.5 sequences. A possible compressive tectonic event of post-Santonian age could have enhanced this unconformity.

The second unconformity is younger and is found at the Cretaceous-Tertiary boundary. This hiatus of approximately 25 m.y. occurs between the upper Maastrichtian (65 Ma) sandstones of the Burguita Formation and the middle Eocene (42.5 Ma) sandstones of the Gobemador Formation. In almost all the study area, the sequences which are in unconformable contact are the TA-3.4, corresponding to middle Eocene, and UZA-4.5, corresponding to upper Maastrichtian. As in the first unconformity, the last one could have also been enhanced by the tectonics of the area. This unconformity is related to one of the main sandstone reservoirs of the Barinas area.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela