Oil occurs in intensely fractured pre-Cretaceous igneous and metamorphic rocks, as well as in overlying Cretaceous limestones of the La Luna and Cogollo formations, along the La Paz-Mara uplift in the northwest Maracaibo basin, Venezuela. The accumulations are believed to have a common origin in the La Luna beds. Migration into the basement rocks may have taken place as a result of hydrostatic pressure gradients established by dilatancy accompanying fracturing.

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