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Abstract: The Importance of High Resolution Calcareous Nannofossil Biostratigraphy for the Eocene Misoa C Sands Studies, Lake Maracaibo, Venezuela

J. Munoz, G. Nicolas, Walter W. Wornardt

The mature Lake Maracaibo Bloque I oil field has recently been subjected to a comprehensive and truly integrated multidisciplinary study with 3D seismic interpretation, sequence stratigraphy, sedimentology, organic geochemistry, petrophysics, well log analysis and correlation. For the C Sands of Bloque I East and Horst this study resulted in a new important sedimentary model which supports a tide dominated shallow marine shelf and delta front in a restricted gulf embayment, where 75% of the C section constitutes transgressive systems tracts. The previous conceptual model of the same sequence favored a fluvial dominated deltaic paleoenvironment. Fifty-seven core and cutting samples selected from the main MFS intervals of 6 wells were analyzed to investigate if any marine p anktonic microfossils were present. No benthic or planktonic foraminifera were found. Calcareous nannofossils were found at depths associated with the Misoa C Sands, conclusively supporting a general shallow marine paleobathymetry for the sequence. A checklist of each calcareous nannofossil slide is shown on a correlation chart based on the peaks of the histograms, important fossils, and on sequence stratigraphic principles. The upper and lower peaks probably represent the 48.0 and/or 49.0 Ma MFS of the Global Cycle Chart, associated with the latest Early Eocene to Early Middle Eocene NP14 calcareous nannofossil zone. A more detailed analysis would produce a statistically sound correlation chart and would help in defining a "less marine to more marine" eustatic curve for the Misoa sequen e.

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