Parent Material of Upper‐ and Middle‐Coastal‐Plain Soils in North Carolina

Abstract In the upper‐ and middle‐Coastal Plain of North Carolina, Paleudults are on the old landscapes; Hapludults, with low base status, are on the young valley side slopes. This distribution of soils suggests a parent‐material control of soil development. X‐ray and petrographic analyses of samples of the surficial sediments showed kaolinite to be the dominant clay mineral below the solum and quartz to be the primary sandsized mineral. Weatherable minerals such as feldspar are rare. The effective exchange capacity of the clay is less than 15 meq/100 g. Aluminum is the predominant cation, and the pH ranges from 4.2 to 4.8. The percent base saturation by the sum of cations is < 35% both within and below the solum. The surficial sediment is most clayey at the surface and gradually becomes coarser with depth. The Paleudults are thus developed in the most clayey part of the sedimentary unit. These facts suggest the parent material was composed primarily of quartz sand and kaolinitic clay, with a low pH and with aluminum the dominant exchangeable cation. As a consequence only Ultisols developed; the original character of the parent material has strongly influenced such things as the mineralogy, base saturation, and vertical clay distribution.