CENOZOIC STRUCTURE, STRATIGRAPHY, AND PALEOGEOGRAPHY OF THE LOWER MAGDALENA BASIN, COLOMBIA

The structural and stratigraphic evolution of the Lower Magdalena Basin (LMB), located in northwestern Colombia, remains controversial with several tectonic models proposed to explain its origin and development. LMB covers a total area of 41,865 km2 of an extensive, flat, and lowlying basin that is traversed by the south-to-north draining Magdalena River, the third largest river in South America. This largely featureless plain is underlain by two large sedimentary sub-basins: the 8km-deep Plato basin in the north and the 7km-deep San Jorge sub-basin to the south separated by the northwest-southeast trending Cicuco high. Using a regional dataset (wells and 2D seismic) provided by Pacific Rubiales Energy, this study defined three tectonic stages in the evolution of the Plato and San Jorge sub-basins since Oligocene to Recent time. Stratigraphic results presented in this thesis for the Plato sub-basin includes a pre-Oligocene igneous and sedimentary basement overlain by six stratigraphic units from Oligocene to Quaternary age that are tied to both wells and the grid of 2D seismic reflection lines. Mapping revealed that the strike of the main normal faults controlling basin subsidence in the Plato sub-basin is northwest-southeast. Biostratigraphic control from wells show that the major period of basin-controlling normal fault movement was from Oligocene to Middle Miocene time. Mapping also shows the presence of Middle Miocene submarine canyon systems that may be the earliest evidence of regional uplift related to the collision of the Panama arc with northwestern South America. The overall evolution of the LMB is summarized as five paleogeographic maps from Late Cretaceous (66-72Ma) to Early Pliocene (5Ma).