Apparent gibbsite growth ages for regolith in the Georgia Piedmont

Carbon bound in gibbsite, collected from a residual weathering profile developed on a Paleozoic granite in the Georgia Piedmont, was examined for its C-14 content and found to be geologically young. The study site, located at the Panola Mountain Research Watershed, has developed a granite-saprolite-soil regolith in which C-14-gibbsite model ages deep within the profile (C-horizon) average about 8000 years. Near the surface (A- and B-horizon) C-14-gibbsite model ages range from 2100 to 4200 years. Quartz has acquired Al-26 and Be-10 inventories suggesting a near-surface residence time of at least 90,000 years. This age disparity supports the notion that secondary minerals undergo significant recrystallization as weathering fronts propagate into the landscape. Combining the results of C-14, Al-26, and Be-10 analyses offers the potential to assess differential rates of chemical weathering and continental denudation to understand better the links between rates of silicate rock weathering, climate, and soil residence times. Copyright (C) 2001 Elsevier Science Ltd.