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RULL,V., and M. A. LORENTE, PDVSA Exploration, Caracas,Venezuela

Abstract: Ecostratigraphy: a New Tool for High Resolution Dating of Terrestrial Sections: Two Case Histories from the Maracaibo and Falcon Basins, Venezuela

Ecostratigraphy or the stratigraphy of ecosystems deals with evolution at the community level, in order to apply the ecological advances to Geochronology. Ecostratigraphy is a challenge for traditional biostratigraphy, but it is a more realistic approach to the community behavior in time. Palynocycles are among the new tools involved in ecostratigraphy. Palynocycles are recurrent palynological sequences reflecting vegetational changes determined by cyclic sea level oscillations and the association climatic variations.

The present work shows the results of a study on wells from Maracaibo and Falcón basins. For these studies new ecological groups were statistically established. Time control was provided by pollen, foraminifers or nannoplankton, depending on data availability. Cycles of Haq et al. (1987) were used as reference framework. For the first case, 13 Oligo-Miocene palynocycles were defined in the Falcon Basin. Five Oligocene palynocycles (PCY9 to PCY13) were correlated with cycles TA4.4 to TB1.3.

Miocene, eustatic cycles TB1.4 to TB3.3 are represented by palynocycles PCY15 to PCY21, however,TB1.5,TB2.1 and TB2.6 have not been recorded. Therefore, two significant palynological hiata, not reported before, have been found in the Early and Middle Miocene of the basin.

In the second case, western Maracaibo Basin, nine palynocycles were defined. These seven Oligocene and two Early Miocene palynocycles provided high resolution dating and allowed the calculation of the variation in the sedimentation rates, documenting the evolution of the Perijá foredeep, during the Oligocene and Early Miocene. The tectonic influence of the Perijá range uplift, interrupted the regularity of the palynocycles, showing the impact of tectonic on eustatic sea level cycles.

AAPG Search and Discovery Article #[email protected] International Conference and Exhibition, Birmingham, England