Provenance of Cretaceous-Oligocene Sedimentary Strata of the Floresta Basin, Eastern Cordillera, Colombia and Tectonic Implications

We use integrated detrital zircon U-Pb geochronology, sandstone petrography, sedimentary facies analysis, and paleocurrent measurements from a Mesozoic-Cenozoic clastic succession preserved in the northern Andean fold-thrust belt to address foreland-basin disruption in the Paleogene. The Floresta basin is situated along the axis of the Eastern Cordillera of Colombia. Detrital zircon U-Pb ages and sandstone petrography indicate that the Floresta basin first received sediment from the eastern craton (Guyana shield) in the Cretaceous-early Paleocene and then from the western magmatic arc (Central Cordillera) starting in the mid-Paleocene. The upper-crustal magmatic arc was replaced by a metamorphic basement source, which we identify as Magdalena valley basement equivalent, in the middle Eocene. This, in turn, was replaced by an upper-crustal thrust-belt source in the late Eocene which persisted until Oligocene truncation of the Cenozoic section by the eastward advancing Soapaga thrust. This upper crustal source is interpreted to represent uplift of the western flank of the Eastern Cordillera. The combined provenance data indicates that sediments were derived from eastward-migrating sources. Throughout the Paleogene, paleocurrent and sediment provenance data point to a uniform western or southwestern sediment source with no evidence of the complex sourcing or sediment dispersal patterns emblematic of a broken foreland basin. Therefore, these data show that the Floresta basin existed as part of a laterally extensive, unbroken foreland basin connected with the western (Magdalena) basin from Cretaceous to late Eocene time, when it was isolated by uplift of the western flank of the Eastern Cordillera. The Floresta basin was also connected with the eastern (Llanos) basin from the Cretaceous until its late Oligocene truncation by the advancing thrust front.