Piedmont-cove deposits of Dellwood quadrangle, Great Smoky Mountains, North Carolina, USA: Same aspects of sedimentology and weathering
DOI:
https://doi.org/10.26485/BP/1986/30/8Keywords:
periglacial conditions, alluvial fans, debris flows, gelifluctionAbstract
Deposits analogous to alluvial fans occur in many piedmont coves of the southern Appalachian Mountains. In the Dellwood quadrangle of North Carolina these "fans" consist largely of bouldery diamictons lacking sorting or stratification. Because the faris presently seem to be undergoing erosion rather than deposition, many observers have attributed them to an ice-age periglacial regime, perhaps involving gelifluction. Other observers have suggested that they originate as a consequence of debris flows during rare, catastrophic rainstorms, and that climate is not involved. A study of the texture, pebble-roundness, clast-fabric, and sedimentary structures of the fan sediments, however, reveals little evidence of relict gelifluction, although this process cannot be eliminated as a possibility.
Origin by debris flow thus seems more likely, but this does not necessarily imply that the fans are unręlątęd to Quaternary climatic change. At least two ages of fan deposits occur in the study area and a discriminant analysis based on three weathering indices (percent clay, redclest hue, and percent weathered clasts) measured at 28 sites. shows that the younger depdsits form a discrete group separated from the older deposits by a hiatus in weathering intensity and thus presumably also by a hiatus in time. This finding indicates episodic deposition and combined with the fact that the weathering characteristics of the younger deposists are compatible with a late Wisconsin/early Holocene age, suggests that the last episode of deposition may have taken place after climatic amelioration at the end of the Wisconsin, when increased precipitation and an abundance of frost-produced debris at higher elevations propably temporarly incresed the size and frequency of debris flows.
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