Apparent gibbsite growth ages for regolith in the Georgia Piedmont

Carbon bound in gibbsite, collected from a residual weathering profile deve loped 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 lea st 90,000 years. This age disparity supports the notion that secondary mine rals undergo significant recrystallization as weathering fronts propagate i nto the landscape. Combining the results of C-14, Al-26, and Be-10 analyses offers the potential to assess differential rates of chemical weathering a nd continental denudation to understand better the links between rates of s ilicate rock weathering, climate, and soil residence times. Copyright (C) 2 001 Elsevier Science Ltd.