The Peripheral Bulge of the Interior Range of the Eastern Venezuela Basin and its Impact on Oil Accumulations

Abstract

The peripheral bulge of the Eastern Venezuela Basin is located along the Orinoco Heavy Oil Belt. The forebulge developed as a direct result of flexure of the continental lithosphere in Eastern Venezuela that resulted from the load of the overriding plate, the Interior Range. The Eastern Venezuela foreland basin lies mostly over crystalline basement that has been affected by three distinct phases of crustal evolution. The southernmost region, south of the Merey Fault, is Archean crystalline basement covered by thin late Paleogene to Neogene sediments. Archean crystalline basement and late Precambrian allochthonous terrains dominate the region between the Merey Fault and the Pirital Fault. This region underwent crustal attenuation during late Precambrian rifting. Jurassic rifting associated with the area north of the Pirital fault trend further attenuated the crust. Variations in thickness of lithosphere subjected to elastic deformation control the amount of flexure in the basin and the position of the peripheral bulge. The Pirital trend acted as a buttress to the southern migration of the principal thrusts. As a result, the peripheral bulge did not migrate significantly. Uplift on the bulge was episodic and slow. Fluvial systems from the shield had sufficient time to maintain their course and, as a result, continued to flow north across the slowly rising peripheral bulge but were focused in specific north-south-trending depressions. By latest Miocene/Pliocene an east-west-trending back-bulge depozone formed south of the Heavy Oil Belt and presently forms the Orinoco River valley. During most of the Miocene, the peripheral bulge acted as a major trap for the hydrocarbons generated along the northern portions of the Eastern Venezuela Basin.