THE MULTIPART EVOLUTION OF THE LANDSCAPE IN FOLDED STRUCTURES: LITHOLOGY RULES

The persistence of high topography in active and inactive orogens has been the subject of study for nearly a century. Once rock uplift wanes, the rate of erosion also declines with time as hillslopes are smoothed and rivers reach dynamic equilibrium, explaining why high topography can be found in old orogens like the Appalachians. Lithology is a determining factor in the persistence of topography and the evolution of the drainage network, since lithological heterogeneity can delay the erosional response to rock uplift in a landscape and serve to maintain high topography by modifying erodibility. We test such a proposition in the Oiba-Arcabuco anticline (Colombian Eastern Cordillera), a topographic high that persists in the axial plateau of the range despite waning rock uplift rates since the Andean Orogeny. By gathering a dataset of around 1,200 Schmidt hammer rebounds from 34 stations from which we computed erodibility per geological unit, river profile analysis and channel steepness, and empirical erosion rates, we probe the hypothesis that the folding and exhumation of quartz sandstones at the anticline core boosts the residence time of high topography. Conversely, the anticline limbs, where weaker rocks are present, have been eroded, and the topography has been smoothed out. Drainage network reorganization is a byproduct of the differential erosion process as the drainage network is modified sequentially from a longitudinal to a trellis and finally, a transverse pattern. Studying the residence time of high topography matters to know how the landscape is transformed early in the life of a relaxing topography. Our work also emphasizes the need of including spatio-temporal variations in erodibility to improve the predictability and reliability of landscape evolution models.