Sedimentary Megasequences of Colombian Basin, Offshore Colombia

Abstract

The Colombian Basin is located in the northern Colombian Caribbean Sea and overlies a large portion of the Caribbean plate. It is the largest of several Caribbean basins with an average depth of about 3.5 km. The tectonics of the Caribbean region are complex and the Caribbean Plate itself has been interpreted both as an oceanic plate that migrated from the Pacific and as having evolved “in situ” after the separation of South and North America. Given its location, insights into the geology of the Colombian Basin play an essential role in informing our understanding of these controversies. Previous geophysical studies such as gravimetric, refraction and reflection studies showed that the basin is partly underlain by anomalously thickened oceanic crust that corresponds to the Caribbean Oceanic Plateau, adjacent to areas of typical oceanic crust as occurs in the Eastern Venezuela basin. However, previous data acquired does not cover most of the central and eastern parts of the Colombia basin. This thesis evaluates a total of 6390 km of newly available multichannel 2D seismic reflection data acquired in the deep-sea Colombian Basin by the Colombian Agency of Hydrocarbons (ANH); the seismic data cover most of the central and eastern parts of the Colombian Basin and permit expansion of earlier studies that focused on the western Colombian Basin. The seismic reflection data was tied to well DSDP 153 from the Deep Sea Drilling Project and seven horizons were tracked throughout the area, and three main mega-sequences were identified, which record the evolution of the basin. Two different types of basement crust (thickened oceanic plateau or thin oceanic crust) were mapped, and it is apparent that the differential nature of oceanic crust controls overlying thicknesses of Late Cretaceous to Middle Miocene sedimentary rocks and the subduction angle beneath the South Caribbean Deformed Belt. Initial increases in the thickness of trench-filling sedimentary units in the Eocene confirms the initiation of subduction by this time. Since the Middle Miocene, sedimentary rock units of the Magdalena fan have had a dominant role in the sediment supply of the basin and these sedimentary rocks record the eastward migration of the Caribbean Plate and avulsion processes of the Magdalena river. After the late Miocene, channel-levee complexes (CLC) and very large mass-transport complexes (MTC) are identified and mapped in the study area. A Pleistocene mass transport complex has been mapped, and its area and calculated volume showed that it is larger than 95% of the mass-transport complexes compiled from the geological record around the world.