--> ABSTRACT: Fault Patterns in Part of Orinoco Heavy Oil Belt, Eastern Venezuela Basin, by R. L. Countryman and D. M. Flores; #91030 (2010)

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Fault Patterns in Part of Orinoco Heavy Oil Belt, Eastern Venezuela Basin

R. L. Countryman, D. M. Flores

Faults in a 2,500 km2 block of the Orinoco heavy oil belt in the Eastern Venezuela basin show two major trends: one east-northeast, the other north-northwest. Earlier work interpreted both trends as normal faults that trapped hydrocarbons in "trap-door" structures at their intersections. Recent mapping provides an alternative interpretation.

The mapped region is a homocline dipping north at 2°-3°. It is cut by a major east-northeast normal fault system and a younger north-northwest right-lateral fault system. Trapping of hydrocarbons occurs where faults cut segments of fluvial-deltaic sands. The east-northeast normal faults dip shield-ward 40°-60°S, with throws up to 200 ft near basement. Fault planes are undulatory and commonly splayed. The shield-ward orientation and lack of observed sediment thickening on the down side argues against syndepositional growth faulting. Instead, episodic postdepositional movement in response to craton downwarping is suggested.

The north-northwest-trending faults are almost purely translational and offset the east-northeast faults. They are planar, nearly vertical, and do not have splays. Horizontal offsets to 0.5 km and vertical throws to 12 m have been mapped. Faulting may extend to the surface as numerous rivers and topographical features appear aligned or offset along faults, suggesting recent movement.

The observed fault systems may reflect the transition of the Eastern Venezuela basin from a downwarped basin formed by convergent-margin tectonics to one presently being overprinted by transform-margin tectonics. This transformation is the result of continued convergence and rotation of South America with respect to the North American and Caribbean plates.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.