Denudation rates for the southern Drakensberg escarpment, SE Africa, derived from in-situ-produced cosmogenic ³⁶Cl: Initial results

Cosmogenic ³⁶Cl concentrations in basalt samples from the Drakensberg escarpment on the SE African passive margin give quantitative estimates of denudation and scarp retreat rates. Over the 10⁴-10⁶ year timespan addressed by these data, the calculated escarpment retreat rate has been 50-95 m Ma^-1 and the average summit denudation rate 6 m Ma^-1. The scarp retreat rate is an order of magnitude less than previously suggested. The rate of summit lowering is sufficient to prevent the long-term intact survival of erosion cycle surfaces formed in the Mesozoic that were previously inferred for this region.