Abstract
Interpretations of regolith and soil thickness in the context of landscape evolution are typically based on the notion that thickness is controlled by the interaction of weathering rates and erosion and tuned to topography. On slideslopes of the Quachita Mountains, Arkansas, however, there is a high degree of local spatial varibilty that is largely unrelated to topography. This indicates nonequilibrium in the sense that there is no evidence of balance between rates of weathering and removal, as is postulated in some conceptual models geomorphology and pedology. Johnson's soil thickness model is applied as an alternative to interpret local variations in regolith thickness. At the study sites, regolith thickness is not generally related to slope, curvature, elevation, or pedogenic development in the in the solum. This indicates that varibility in thickness is related chiefly to processes and controls acting in the lower regolith, below the solum. The primary controls of varibility are local lithological variation, variable structural resistance associated with fractures and bedding planes in strongly tilted Paleozoic sedimentary parent material, and point-centered pedological influences of trees. A steady state regolith may be relatively rare. Results of this study suggest that an equilibrim regolith thickness is most likely in uniform lithology with a high degree of lithologic purity, less likely in interbedded sedimentary rocks, and more unlikely still if the latter are tilted and fractured. Equilibrium thickness would also be more likely where the effects of bioturbation are more areally uniform (as opposed to the point-centered effects of individual trees) and where the biomantle is above the weathering front.
Citation
Phillips, Jonathan D.; Marion, Daniel A.; Luckow, Kenneth; Adams, Kristin R. 2005. Nonequilibrium regolith thickness in the Ouachita Mountains. The Journal of Geology, Vol. 113, pp. 325-340 (2005)
