A Middle to Late Miocene Trans-Andean Portal: Geologic Record in the Tatacoa Desert

Integration of several geologic lines evidence reveals the prevalence a lowland trans-Andean portal communicating western Amazonia and westernmost Andes from at least middle Miocene until Pliocene times. Volcanism crustal shortening built up relief in southernmost Central Eastern Cordilleras Colombia, closing this gap. Independent consist first, field mapping Tatacoa Desert with coverage area ∼381 km 2 , 1,165 geological contact traces, 164 structural data points, 3D aerial digital models. This map documents beginning southward propagation tip Cordillera’s west-verging, fold-and-thrust belt between ∼12.2 13.7 Ma. Second, compilation new published detrital zircon geochronology strata shows three distinctive age populations: Miocene, Eocene, Jurassic; first two sourced west Cordillera, latter Magdalena Valley. Similar populations peaks have now been recovered Amazonian strata. These observations, along molecular fossil fish data, suggest that by Serravallian times (∼13 Ma), Northern were separated ∼3°N fluvial system flowed into Amazon Basin through Desert. paleogeographic configuration would be similar to Western Andean, or Marañon Portal. Late flattening subducting Nazca slab caused eastward migration volcanic arc, so starting ∼4 Ma, large composite volcanoes axis today's Andean altering drainage patterns resemble modern configuration.