Weathering Rinds and the Evolution of Piedmont Slopes in the Southern Blue Ridge Mountains

Abstract

The piedmont slopes on the west side of Rich and Snake mountains in the Blue Ridge province are composed of dozens of fans and fan remnants of various ages. The fans consist of a few meters of flood and debris flow deposits overlying saprolite and deeply weathered bedrock. The deposits are rich in amphibolite clasts, the weathering rinds of which allowed fan surfaces to be classified into six relative-age categories on the basis of rind thickness. The presence of reversed remanent magnetism in one old fan deposit indicates an age of at least 780 ka. However, the magnetization appears to reside in secondary hematite produced by weathering rather than in original magnetite grains, so that a minimum age on the order of 1 Ma is more likely. Transverse profiles surveyed across 15 fans and fan remnants show that old surfaces may attain heights as great as 30 m above younger surfaces, but that a better index of age is the convexity of the profile. Young surfaces show only slight transverse convexities but old su...