WEATHERING RINDS AND THE EVOLUTION OF PIEDMONT SLOPES IN THE SOUTHERNBLUE-RIDGE MOUNTAINS

The piedmont slopes on the west side of Rich and Snake mountains in th e 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 de posits are rich in amphibolite clasts, the weathering rinds of which a llowed fan surfaces to be classified into six relative-age categories on the basis of rind thickness. The presence of reversed remanent magn etism in one old fan deposit indicates an age of at least 780 ka. Howe ver, the magnetization appears to reside in secondary hematite produce d by weathering rather than in original magnetite grains, so that a mi nimum age on the order of 1 Ma is more likely. Transverse profiles sur veyed across 15 fans and fan remnants show that old surfaces may attai n heights as great as 30 m above younger surfaces, but that a better i ndex of age is the convexity of the profile. Young surfaces show only slight transverse convexities but old surfaces show pronounced ones. M ap patterns, stream locations, and transverse profiles of fans suggest a cycle of fan development not previously described, in which narrow drainageways expand laterally to become young fan surfaces, eventually becoming fan remnants that may survive several million years before b eing removed by lateral erosion.