QUANTIFYING CHEMICAL EROSION IN THE LITHOLOGICALLY HETEROGENOUS APPALACHIAN VALLEY AND RIDGE

Understanding how lithologically heterogeneous landscapes take shape in response to environmental forcings requires untangling the relative roles of chemical and physical erosion. The Appalachian Valley and Ridge geographic province, which is underlain by a mix of sandstones, shales, and carbonate units, is an ideal region in which to test the relative dominance of chemical and physical erosion across varying rock types. Normalized molar ratios derived from USGS stream water data show heterogeneity within the rock units of the Valley and Ridge, where Ca/Na molar ratios range from 0.01-237.9 and Mg/Na molar ratios range from 0.01-53.8. The Valley and Ridge exhibits topographic variations that broadly co-vary with lithology, leading to the hypothesis that differing efficiency of chemical erosion rates between siliciclastic and carbonate units governs the iconic topography. Previous studies focused on the Appalachian Valley and Ridge Province have determined 10-Be denudation rates from stream sediment; we seek to complement those data by adding a detailed dataset of chemical erosion measurements.

We present preliminary results from an analysis of stream water within the Valley and Ridge in which we use USGS water chemistry data calculate chemical erosion rates and compare them to published 10-Be denudation rates. We use stream water cation and anion concentrations to calculate the total chemical weathering flux, and therefore the chemical erosion rate, of both siliciclastic and carbonate units. Recycling USGS water chemistry data will allow the creation of a region-wide map of silicate and carbonate chemical erosion rates across the Valley and Ridge province, enabling future testing of the controls on chemical weathering in tectonically inactive, lithologically heterogeneous regions. Ongoing work will compare total weathering fluxes with previously determined 10-Be denudation rates to assess the variability in the relationship between physical and chemical erosion across our lithologically variable study region.

Erosion drives topographic change, but in lithologically heterogenous, the influence of physical and chemical erosion must be untangled. Gaining a broader understanding into the relative roles of physical and chemical erosion will allow for improved understanding of how landscapes respond to environmental signals.