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BOESI, T., R. HIGGS, M. A. LORENTE, L. MOMPART, B. MURAT, and TESTAMARCK, Maraven S.A., Caracas, Venezuela, and R. FALCON, Universidad Central de Venezuela, Caracas, Venezuela

ABSTRACT: Facies and Sedimentary Environments of the Cretaceous La Luna Formation in San Pedro Del Rio Section, Venezuelan Andes: A Multidisciplinary Study

Vertical variations in facies and sedimentary environments in an outcrop of the La Luna Formation in the Venezuela Andes were evaluated with an integrated study of sedimentology, micropaleontology, palynology, visual kerogen, organic geochemistry and field geology. Up to now, the La Luna Formation, main hydrocarbon source rock in the Maracaibo Basin, has been considered for calculations of oil generation as an homogeneous interval with similar properties across the basin. However, this study reveals important vertical variations in organic facies and sedimentary environments.

The microfacies range from almost pure carbonate (recrystallized) mudstone to almost pure shale, with a varying organic content. An overall upward change from oxic to anoxic environments can be recognized, culminating in a chert-rich interval (Ftanita de Tachira Member). The total organic carbon content is high throughout, with the exception of low to moderate values in the chert. The organic matter is mature to postmature. Phosphatic intervals are also developed, supporting a model of platform-edge upwelling and high organic productivity. The presence of rare volcanic grains suggests contemporaneous volcanic activity within adjacent areas (Colombiam Andes?).

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.