224-8 Detecting drainage basin rearrangements due to lithologic heterogeneity

Session: From the Cosmos and Back: Quantifying Processes and Rates of Landscape Change (Posters)

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Abstract:

Drainage divides are key features in landscape evolution, separating river networks and regulating the movement of water, sediment and nutrients. These features are dynamic and can monotonically migrate due to across-divide erosional imbalances or rapidly via river capture events. Commonly, tectonically quiescent landscapes are mistakenly thought to be at or near equilibrium due to slow erosion rates, steady and/or spatially uniform precipitation rates. In areas with lithologic heterogeneity, the variability of rock erodibility causes perturbations of base level and can be a first order influence on drainage divide migration, even in divides situated away from the lithologic contacts. While it is straightforward to identify tectonic and/or climatic influences of divide migration, the role of lithology is less well understood. In this study, we aim to identify drainage network reorganization due to lithologic perturbations of base level. Based on numerical modeling of landscape evolution, when hard rocks outcrop, large drainage basins crossing them tend to expand at the expense of neighboring, parallel-flowing smaller drainage basins. Therefore, the distribution of drainage area for basins upstream of the lithologic transition (soft-to-hard in the downstream direction) systematically varies as a function of time since the outcropping of the hard rock, with small basins disappearing over time. Furthermore, the loss of drainage area drives wholesale surface uplift of the shrinking basins, producing positive relationships between drainage area and elevation during the transient phase. Here, we examined the drainage areas and their relationship with elevation and relief in the San Rafael Swell and the Appalachian Plateau. These areas are marked by soft-to-hard lithologic transitions in the downstream direction. We observe positive relationships between drainage area, relief, and elevation, consistent with the numerical modeling results. The observations suggest that drainage basins in these landscapes are systematically changing size in response to the lithologic control of base level. Our results suggest that drainage area distributions can reveal drainage network reorganizations in response to lithologic heterogeneity.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11294

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