Structural Evolution of the Sinu-Lower Magdalena Area (Northern Colombia)

The Lower Magdalena Valley of northern Colombia can be subdivided into two very distinct structural provinces separated by the Romeral fault system. The Sinu–San Jacinto Province, located west of the Romeral fault, is a Paleocene to Oligocene accretionary wedge floored by Cretaceous oceanic crust. The Plato–San Jorge Basin is a back-arc basin filled by Oligocene to Pliocene sediments. The basin is structured into several northwest-southeast-trending structural highs and lows controlled by transtensional and transpressional faults that evolved through geologic time. The basement of the Plato–San Jorge Basin is a Paleozoic metamorphosed oceanic crust. Paleocene-Eocene siliciclastic series including shale, sandstone, and mostly conglomerate and breccia unconformably overlie the basement close to the Romeral fault. A widespread deltaic sandy section referred to as Cienaga de Oro Formation overlies this section. The Cienaga de Oro sandstone (locally, Cicuco Limestone) represents the main reservoir of the area and is overlain by deep-water shale with interbedded sandstone (i.e., Porquero Formation). The Sinu–San Jacinto area is the onshore part of the northern Colombia accretionary prism, related to the subduction of the Caribbean Plate underneath the South American Plate. The onshore part of the wedge is dominated by west-vergent imbricates involving Cretaceous oceanic crust (Cretaceous ophiolitic series) and Cretaceous to Oligocene sediments. The Cretaceous sedimentary section (i.e., Cansona Formation) consists of organic-rich shale, limestone, and chert. The Paleocene-Eocene section consists of deep-water shale and turbiditic sandstone, except in the Tol area where it is made up of shallow-water sandstone, conglomerate, and reefal limestone (La Risa Reef). The Miocene section is composed mostly of flysch-type deposits (i.e., Floresanto Flysch), which can be reservoir rock. Seismic and geologic data suggest that the Romeral fault is a major strike-slip fault that offsets the obduction suture.