Late Cretaceous-Cenozoic basin evolution and structural compartmentalization along the Middle Magdalena Valley to Eastern Cordillera transition (5–6°N), Colombian Andes

Topographic development of the northernmost Andes is recorded by Mesozoic to Cenozoic clastic basin fill along the structural transition between the Middle Magdalena Valley and Eastern Cordillera fold-thrust belt of Colombia. The Caceres syncline region (5.5−6.0°N) displays diverse fold-thrust structures that pre-date and post-date a regional Eocene angular unconformity. Contrasting clastic sedimentary successions above and below the unconformity define a major shift from organic-rich marine deposition of regional extent to more localized coarse-grained fluvial and alluvial fan deposition with significant lateral variations. New detrital zircon U-Pb geochronological results reveal stepwise provenance changes in response to a temporal transition from post-extensional thermal subsidence to retroarc flexural subsidence. A latest Cretaceous-Paleogene provenance switch from eastern Andean basement and cratonic sources to principally western forearc and magmatic arc sources reflects early Andean deformation and uplift in Colombia. This phase of basin reorganization is associated with arc magmatism and initial exhumation of western sources such as the Central Cordillera during shortening, transpression, crustal-scale tilting, and integrated basin development in the Magdalena Valley. This retroarc basin system was then partitioned by multiphase fold-thrust deformation, which generated the Eocene angular unconformity and led to eastward advance and topographic growth of the Eastern Cordillera during progressive Andean shortening and orogenic wedge evolution.

Vitrinite reflectance results for Cretaceous-Paleocene units indicate spatial variations in thermal maturity related to compartmentalization of deformation along different fault-bounded blocks and associated folding before and during unconformity development. The U-Pb maximum depositional ages (MDAs) for stratigraphic units bounding the unconformity support an ∼5−10-m.y.-hiatus of early to middle Eocene age. The MDAs also constrain the timing and potential geometry of upper crustal shortening and basin reorganization during earliest topographic construction of the Eastern Cordillera. Integration of detrital zircon U-Pb provenance and vitrinite reflectance results with cross-cutting structural and stratigraphic relationships indicates that Cretaceous extension and post-extensional (thermal sag) basin subsidence were followed by Paleogene shortening and selective basin inversion during early Andean orogenesis. This study helps constrain the kinematic history of deformation and genetic linkages between uplift and sediment dispersal across the Middle Magdalena Valley and flanking Eastern Cordillera and Central Cordillera during early mountain building, with attention to the role of tectonic inheritance in shaping the stratigraphic and structural architecture of the Colombian Andes.