Of major importance to geologists was the deposition throughout the sedimentary area in the Late Cretaceous of organic-rich, bituminous shales and limestones which have provided prolific source rocks in all four basins. Subordinate source rocks are found in the Tertiary which is often gas-prone.

PDVSA geologists are also excited by a new play that some believe has the potential to rival that of North African success stories such as Algeria and Sudan. Based on the premise of Venezuela's ancient geological link with North Africa, PDVSA has focused on an under-explored south-west region of Venezuela known as the Western Llanos. Outcrop studies over the last four years have identified some pre-Cretaceous source rocks and oil seepage in the Andean region. Some of the Palaeozoic formations tend to run too deep for commercial purposes but an encouraging trend at about 12,000 feet or less has been identified.

Reservoir rocks in Venezuela range from fractured basement to Late Tertiary and comprise, for the most part, sandstones with subordinate limestones. The sandstone depositional environments range from being open marine through deltaic to fluviatile.

There is a wide variety of traps from those associated with normal faulting on the passive side of basins to complex fold-fault traps where overthrusting has resulted from mountain building at active basin margins. Many traps also have a stratigraphic element in them.

The Maracaibo Basin, with an area of 50,000 sq km, is the most important in Venezuela and almost 40 bn barrels of oil have been extracted from it. In recent years the basin has produced more than half a billion barrels per annum. The centre of the basin is occupied by the shallow waters of Lake Maracaibo.

The main producing areas extend from the shore out into the lake, with the greatest concentration of fields being in the northern portion. The onshore fields contain both heavy and medium oils, while in the offshore medium and light crude oils predominate.

Geology of Northeastern Venezuela

The transpressional plate boundary zone looks like a classical fold and thrust belt with a metamorphic hinterland in the north, the Caribbean Mountain system, and a non-metamorphic foreland fold and thrust belt in the south, the Serran’a del Interior. Recent studies have shown that the time of metamorphism and D₁ deformation in the hinterland is mid-Cretaceous (e.g., Loubet et al., 1985; Stockhert et al., 1995; Ave Lallemant, 1997; Smith, 1996; Smith et al., 1999), whereas the deformation in the foreland is Tertiary (Beck, 1978, 1985; Audemard, 1991). Like the arc, it appears that the metamorphic belts formed far to the west, migrated eastward, and were emplaced onto the South American plate in Tertiary time.

Caribbean Ocean plateau

This model of Caribbean Ocean plateau is extremely complex. Many of its processes lack supporting data and many existing data are ignored or used selectively. It continues to become increasingly complex and its proponents tend to fail to address arguments against it (Pindell et al., 2006). The alternative theory, that the Caribbean plate formed in place between separating North and South America, is supported by a minority of workers only, despite the fact that it accounts for all regional data in the context of simple geological evolution (e.g., James, 2005, 2006).