The Velasquez oil field is in the Middle Magdalena Valley, Colombia, S. A., which is a long, narrow, Tertiary basin. The sedimentary section consists of approximately 8,000 feet of clastic continental beds which rest directly on a crystalline basement. These Tertiary beds increase as much as four-fold in thickness toward the southeast, without any evidence for marine intercalations.

The nearest marine beds are the Villeta formation of Cretaceous age in the Cordillera Oriental which is separated from the Velasquez area by the Belta fault. This fault extends for a great distance along the east side of the Magdalena Valley.

If the Villeta formation is the source of Velasquez oil, it is necessary to postulate migration on the order of several miles and date it as late Tertiary, but prior to the thrusting represented by the Belta fault.

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