TESTING EROSION POTENTIAL OF HETEROGENEOUS LITHOLOGIES TO UNDERSTAND ATYPICAL VALLEY MORHPOLOGY IN THE BUFFALO NATIONAL RIVER WATERSHED, AR

Within the Buffalo National River watershed, a wide river valley carved through limestone gives way to a narrower valley as the river incises into a more resistant sandy dolostone. This atypical valley morphology has been credited to the variability in lithologic resistance of the primary rock units within the river valley - the Everton Formation and the Boone Formation. Field and laboratory testing has shown that the Everton, an interbedded dolostone, limestone and sandstone, has a statistically similar mechanical resistance, but significantly lower solubility than the Boone Formation, a thick sequence of cherty limestone and a thin-bedded bioclastic limestone referred to as the St. Joe Limestone Member. To further examine the differences in erosion potential, abrasion mill experiments were paired with dissolution test for samples from each of these units as well as the Batesville Sandstone, a very-fine grained calcite-cemented sandstone found at higher elevations in the watershed. During 5 runs in an abrasion mill the St. Joe sample lost approximately 15.4% thickness on average and mass decreased 12.8% as compared to the Batesville sample which lost 28.6% thickness and decreased 39.7% in mass. Solubility was 89.7% and 2.9% respectively. The Everton and Boone samples are still in process. The Batesville sample mechanically eroded more than the St. Joe. However, the St. Joe sample was significantly more susceptible to chemical erosion. Preliminary results suggest that mechanical erosion should dominate in the sandstone units, while chemical erosion is dominate in the limestone reaches. While these data support the conclusion that differences in chemical resistance influences valley morphology, it also suggests that resistance to mechanical erosion cannot be discounted.