Tectonostratigraphy of the Cenozoic Tumaco forearc basin (Colombian Pacific) and its relationship with the northern Andes orogenic build up

摘要

The new tectono-stratigraphic setting of the Tumaco forearc basin based on outcrop logging, cutting description from deep oil wells, new biostratigraphy on calcareous nanofossils and sandstone petrography allows a margin scale comparison of the basin response to the Caribbean and Farallon/Nazca subduction under the South American margin. The results are compared to the laterally continuous Ecuadorian Borbon forearc basin and other southern Colombian basins: Patia sub-basin, Upper Magda-lena Valley and southern Putumayo-Caguan basins. The proposed basement of the Tumaco basin is a Colombian Caribbean Oceanic Plateau (CCOP) sliver docked with Santonian-Campanian island arcs that was incorporated into the Colombian Pacific forearc during the Paleocene to Eocene. The filling of the Tumaco basin started with the Oligocene Unidad 1 Sur and the Early-Middle Miocene Cayapas/Viche/Angostura/Formations in a bathyal depositional setting. At Late Miocene to Holocene, a succession of volcaniclastic units was deposited in shallower environments: the Chagui, San Agustin and Cascajal formations, and the recent volcaniclastic fans. The Late Cretaceous evolution of Northern Andes in Colombia was influenced by the collision and fragmentation of the Colombian Caribbean Oceanic Plateau, producing in the west the Tumaco block basement and an oceanic remnant basin in Patia Valley. The convergence between the Farallon/Nazca and South American plates since Paleocene allowed the development of the Pacific forearc as well as shortening leading to the uplift of the Central Cordillera and formation of the foreland basin system, which later was divided into the Upper Magdalena Valley broken foreland basin and the southern part of the Putumayo-Caguan foreland basin. Since Miocene, events in addition to plate convergence as the collision of the Baudo-Panama Arc and the subduction of Carnegie Ridge perturbed the subduction zone in southern Colombia. The integration of all of these tectonic events offers a new improved dynamic framework for the evolution of this region.