CLAY MINERAL CONCENTRATION WITH DEPTH AND LAND USE HISTORY IN THE CRITICAL ZONE IN CALHOUN, SOUTH CAROLINA

History of Land Use at the Critical Zone Observatory (CZO) in Calhoun, South Carolina has been well documented and studied. Land use, climate, biotic factors and topography all contribute to rates of chemical denudation (mass loss) and chemical weathering (mineral transformations). This comparative study contrasts clay mineral assemblages in a hardwood plot, which has not had recent anthropogenic influence, and an adjacent reforested pine plot that has been historically farmed. Methods used to characterize the soil cores taken from the respective plots include X-ray diffraction of oriented clay fraction with treatments of K-, Mg-, and Na- saturation in the air-dried, ethylene glycol (EG), and heated (100^O, 330^O, and 550^OC) states. Based on weathering intensities, early end member minerals with little weathering are biotite and muscovite, while the other end member is thoroughly weathered kaolinite soils. Bedrock at the Calhoun Experimental Forest is Neoproterozoic gneiss, which shows a progression of micas, interlayered vermiculite, vermiculite, smectite, interlayered kaolin-smectite, and kaolin with increasing depth. In shallow depths of older profiles, kaolin-smectite interlayering should be apparent due to the long time for weathering and erosion. Smectite should be seen at greater depths of younger profiles using the same reasoning. From 240 XRD patterns of varying depths and methods, smectite interlayering begins at 40 centimeters at the hardwood site and at 100 centimeters at the pine site. This data is consistent with the predictions of where smectite interlayering should be found.