Abstract

Seismic-stratigraphic analysis of multichannel seismic-reflection profiles indicates that the sedimentary section in the western Colombian Basin comprises five principal units. The deposition of these units was strongly influenced by the basement relief of an oceanic plateau. The five units define three depositional episodes, the middle three units defining a single episode. The depositional history of the western Colombian Basin supports plate-tectonic models of this area based on the insertion of Pacific lithosphere.

The first depositional episode is interpreted to be an extended period of biogenic pelagic sedimentation before and during the insertion of Pacific lithosphere. It is characterized by accumulation of a thick (0.5 km) layer of pelagic deposits on the crest of the plateau, above the carbonate compensation depth. These deposits probably correlate with similar rocks of Late Cretaceous to Eocene age bounded by reflection horizons A″ and B″ in the Venezuelan Basin.

The second depositional episode represents a major change in sedimentation with the influx of a large volume of clastic sediment transported mainly by unconfined turbidity flows. This episode is inferred to span Eocene through Miocene time. Sediments were derived from sources north and west of the basin. Resuspension of some of these sediments in nepheloid layers probably led to hemipelagic deposition on topographically elevated areas. Pervasive internal deformation and physical properties suggest that this hemipelagic layer is undercompacted. The beginning of this episode apparently corresponds to initiation of predominantly eastward motion of the Caribbean Plate relative to the Americas.

The final depositional episode began in the late Miocene epoch and extends to the present. It is characterized by deposition of turbiditefan complexes, including a large fan dominated by leveed-channel systems offshore of Costa Rica. Development of this fan was in response to uplift and increased volcanism in southern Central America caused by the collision between the Panama arc and South America.

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