INFLUENCE OF DEFORMED STRATIGRAPHY ON DRAINAGE NETWORK STRUCTURE (Invited Presentation)

Variability in rock erodibility has long been recognized as an important influence on landscape form, but there is a renewed focus within the community on how stratigraphy affects the dynamics of landscape evolution. Prior contributions to this broad effort have emphasized the role of rock strength contrasts and dip of planar contacts on erosion rates within landscapes and the extent to which such a landscape can ever reach an erosional steady-state. Here, we shift to consider folded stratigraphy and the impacts this has on the dynamics of drainage network topology. Specifically, we use a series of landscape evolution models to test the influence of fold amplitude, wavelength, and connectivity along with stratigraphy and the nature of the pre-existing drainage network to assess potential controls on network stability. We evaluate how dynamic the model drainage network structure is, tracking changes in drainage area distribution caused by mobile divides and the degree to which the movement of divides is accommodated by progressive divide motion vs. discrete drainage capture. The main orientation of trunk rivers with respect to fold axes appears to control drainage network stability, with the most change occurring when trunk streams are not all aligned normal to fold axes and the least change when all trunk streams are normal to fold axes. Fold wavelength is not a strong control on drainage network structure, but unsurprisingly, fold amplitude is – drainage networks exhibit less change to their topology as fold amplitude decreases and contacts approach horizontal. Interestingly, we also find that with identical stratigraphy and structure, drainage network change seems more likely to occur by drainage capture, as opposed to progressive divide motion, in models with lower uplift rates. Additionally, drainage networks with an existing trellis pattern similar to the underlying folded stratigraphy experience less drainage network change than initially dendritic networks, but large discrete captures are more common in trellis networks. While contingent on the assumptions inherent in a simple detachment-limited stream power model, our results are broadly consistent with natural examples of rivers eroding through deformed stratigraphy with significant rock-strength contrasts, such as the Appalachians.