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Seismic lines C 1422 and C 1412, and C 1413 illustrate the structural configuration of the northern margin of South America, which is an active plate boundary between the Caribbean plate and the American plate.Plate models predict east to west trending strike slip movement along the southern margin of the Caribbean plate but leave little room for differential northward movement of South America.

Seismic profiles across the Caribbean margin, however, display characteristic features of a subduction zone. They show the plunge of the Caribbean basement southward below an accretionary prism of folded and imbricated sediments. The front of the prism forms an arc which extends from western Colombia along the foot of the continental slope to the region of the islands of Curacao and Bonaire.

A similar southward-facing fold belt extends from the Merida range of southern Venezuela to Trinidad along the northern rim of Guyana Craton.

The apparent contradiction between a plate model of global scale and the local geology can be solved by assuming that the Caribbean margin of South America consists of a converging wrench system with predominant east-west slip and a subordinate, north-south compressive component possibly related to the wrench systems in the Andean mobile belt.

The absence of a Benioff zone and the lack of a volcanic arc along the Caribbean margin of South America also indicate that subduction along the Caribbean front has been rudimentary, at least during Tertiary time.

Results of the JOIDES core hole 153, and seismic evidence, suggest that the basement of the Colombia basin in the Caribbean sea is of Late Cretaceous age. It is called Caribbean basement because its thickness and velocity distribution are different to those of a typical oceanic basement. This, however, may be due to the complexities of back-arc spreading.

The geology of the coastal ranges of Colombia and Venezuela is unusually complex. A major orogenic pulse with granitic intrusions and metamorphism in mid-Cretaceous time was followed by repeated tectonic phases, the most important ones being at the base of the Tertiary, during late Oligocene and early Pliocene times. The sediment fill of the coastal basins is of late Oligocene and Neogene age.

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