Cenozoic Tectono-Stratigraphic Relationships between the Cesar Sub-Basin and the Southeastern Lower Magdalena Valley Basin of Northern Colombia

Alejandro Mora and Alberto García
Drummond Ltd. Colombia, Bogotá, Colombia

The boundary between the Cesar Sub-basin and the Lower Magdalena Valley Basin comprises a poorly-understood area that has been controlled mainly by the activity of the Santa Marta-Bucaramanga Fault System. Recent interpretations of 2D seismic data in the Cesar Sub-basin and towards the eastern Lower Magdalena Valley suggest that the Santa Marta-Bucaramanga Fault System is a mature stage wrench zone that was active until the Eocene, that underwent erosion in the Late Eocene and that was finally “fossilized” with the deposition of Oligocene to Recent tectonosequences. This means that presently the Santa Marta -Bucaramanga Fault System isn't a physical boundary between the Cesar Sub-basin and the Lower Magdalena Valley Basin- as it has been considered in most of the previous work-, since both basin areas have been connected from the Oligocene to our days. By contrast, at deeper levels intense structural deformation related to this fault system is affecting pre-Oligocene units, indicating that it was an active boundary between both basins, especially during the Eocene. The Santa Marta-Bucaramanga Fault System exhibits notorious changes in configuration and activity along its trace, probably related to the influence of other major oblique faults (Palestina Fault?) and of the basement structure. This interpretation of the evolution of the Santa Marta-Bucaramanga Fault System during the Tertiary, based on the tectono-stratigraphic relationships between the Cesar Sub-basin and the eastern Lower Magdalena Valley, has to be integrated to the paleo-tectonic and paleo-geographic reconstructions in northern Colombia, and also implies that most of the previous reconstructions have to be re-evaluated.