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Paper No. 5
Presentation Time: 1:30 PM-5:35 PM
A SOIL CHRONOSEQUENCE STUDY ON TERRACES OF THE CATAWBA RIVER NEAR CHARLOTTE, NC
Despite their utility in Quaternary geologic studies, relatively few soil chronosequences exist for the Piedmont of the southeastern United States. Here we present a chronosequence of soils on alluvial terraces from the Catawba River near Charlotte, NC. The Catawba River is characterized in the Charlotte area by a broad meandering morphology with five well-expressed unpaired fluvial terraces ranging from 3 to 42 meters elevation above the modern channel. Five soil pits were excavated and described, together with five auger borings, on the terrace sequence. Pits were sampled by horizon and the <2mm fraction analyzed for particle size (pipette method) and extractable iron (oxalate and citrate-dithionite method). Tentative ages are assigned to the terrace units through comparison with regional terrace elevation/age curves (Mills, 2000). The elevations (and inferred ages) of the terraces above the modern channel are: 3m (4 kyr BP), 10m (50 kyr BP), 14m (128 kyr BP), 28m (610 kyr BP), 42m (1,470 kyr BP). Redness, iron oxide and clay content recorded good positive trends with increasing terrace elevation and therefore age. Color hue, Fed and maximum clay content of the B horizon increased from 10YR to 2.5YR, 3.6% to 6.4%, and 25% to 63% respectively, from the lowest (Qt5) to highest (Qt1) terrace unit. Theses values are consistent with those described in other regional chronosequence studies. Redness, Fed and percent clay reach steady state conditions on older (Qt1-2) terrace units. Feo/Fed ratios, while decreasing with soil age from 0.75% to 0.61% for the oldest three terraces (Qt1-3), also record a break in soil development (between Qt3-4), which coincide with an observed change in sedimentology. Channel deposits consisting of rounded quartzite gravels and cobbles were found on the upper two terraces (Qt1-2). No coarse deposits were found on other units suggesting a change in fluvial transport capacity between 128-610 kyr BP if age-elevation correlations are accurate.