Soil‐Geomorphic Relations on the Blue Ridge Front: I. Regolith Types and Slope Processes

Abstract

AbstractRegolith distributions and characteristics were related to slope processes along two transects in mica gneiss and mica schist terrane on the Blue Ridge Front of North Carolina. Regolith types are saprolite, soil residuum, and colluvium. Saprolite is thickest on low slope positions, where throughflow moisture promotes weathering and overlying colluvium protects the saprolite from mass wasting. Saprolite is thinnest on shoulders and backslopes, where mass wasting and rapid runoff inhibit its formation. Rock outcrop is most common on backslopes. Soil residuum, present on most landscape positions, comprises the entire regolith above saprolite only on the broad, nearly level ridge top. The pedogenic transformation of saprolite to soil residuum resulted in higher clay contents and redder hues through in situ weathering and illuvial accumulations. On sloping terrain, saprolite or soil residuum is overlain by colluvium. Lower slopes contain thick deposits of landslide colluvium. Colluvium from slope wash and soil creep comprise the upper 10 to 20 cm of regolith on all sloping surfaces. Colluvial deposits, excluding A and E horizons, are uniform in color, the result of homogenization during transport. Mass movement has also served to physically break down chemically weathered mica grains, releasing secondary minerals into finer size fractions. Knowledge of slope processes assists interpretation of regolith weathering history, which is important for understanding soil parent materials.