The birth of longitudinal rivers in orogenic systems

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Large river systems in mountain belts exert important controls on erosion, sediment flux to oceans, as well as the distribution and evolution, of species. These rivers are highly mobile systems and understanding the processes that modulate their development and evolution are fundamental questions in earth surface processes. This proposal will address the timing and factors that caused the growth of major longitudinal river systems in the northern Andes Mountains of Colombia by studying the modern and ancient sediment transported by these rivers. Data from this project will form the foundation for a new course at the University of Oklahoma. Exercises will be designed to introduce students to transferable skills including basic coding, plotting, and use of geospatial software. These exercises will be available online (at no charge) for others to use or modify in teaching or research. Additionally, this project will support and train undergraduate and graduate students and a postdoctoral scholar, and continue to enhance collaborations with international scientists. More specifically, this proposal will address growth of the Magdalena and Cauca Rivers in the northern Andes Mountains using combination of modern geomorphology, source characterization, and basin analysis. Geomorphic indices will be used to identify areas of modern drainage instability, and 10Be erosion rates will allow for assessment of along-strike variations of erosion rates over notable knick-points. Unique sediment sources in three sub-parallel mountain ranges (Western, Central, and Eastern Cordilleras) facilitate the use of provenance to track shifts in drainage networks through time. These distinctive sediment source regions will be characterized using provenance proxies on modern river sands. Provenance records will also be obtained in upper Miocene-Pliocene strata. Interbedded volcanic and volcaniclastic materials in the sedimentary intervals of interest will enable development of a robust chronostratigraphy. The refined chronostratigraphic framework and new provenance datasets will allow identification of upstream shifts in drainage networks through time. Integration of modern geomorphic proxies and provenance records will test the principal hypothesis that structural diversion led to the birth of longitudinal rivers in the northern Andes. A subset of the samples will be the basis for a series of teaching modules, which will be publicly available to the broader geoscience community as teaching tools.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.