The effect of lithology on valley width, terrace distribution, and coarse sediment provenance in a tectonically stable catchment with flat-lying stratigraphy

How rock resistance or erodibility affects fluvial landforms and processes is an outstanding question in geomorphology that has recently garnered attention owing to the recognition that the erosion rates of bedrock channels largely set the pace of landscape evolution. In this work, we evaluate valley width, terrace distribution, and sediment provenance in terms of reach scale variation in lithology in the study reach and discuss the implications for landscape evolution in a catchment with relatively flat2
lying stratigraphy and very little uplift. A reach of the 21 Buffalo National River in Arkansas was partitioned into lithologic reaches and the mechanical and chemical resistance of the main lithologies making up the catchment was measured. Valley width and the spatial distribution of terraces were compared among the different lithologic reaches. The surface grain size and provenance of coarse (2-90 mm) sediment of both modern gravel bars and older terrace deposits were measured and defined. The results demonstrate a strong impact of lithology upon valley width, terrace distribution, and coarse sediment provenance and therefore, upon landscape evolution processes. Channel down-cutting through different lithologies creates variable patterns of resistance across catchments and continents. Particularly in post-tectonic and nontectonic landscapes, the variation in resistance that arises from the exhumation of different rocks in channel longitudinal profiles can impact local base levels, initiating responses that can be propagated through channel networks. The rate at which that response is transmitted through channels is potentially amplified and/or mitigated by differences between the resistance of channel beds and sediment loads. In the study
36 reach, variation in lithologic resistance influences the prevalence of lateral and vertical
37 processes, thus producing a spatial pattern of terraces that reflects rock type rather than
38 climate, regional base level change, or hydrologic variability.