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

Cosmogenic Cl-36 concentrations in basalt samples from the Drakensberg esca rpment on the SE African passive margin give quantitative estimates of denu dation and scarp retreat rates. Over the 10(4)-10(6) year timespan addresse d by these data, the calculated escarpment retreat rate has been 50-95m Ma( -1) and the average summit denudation rate 6m Ma(-1). The scarp retreat rat e is an order of magnitude less than previously suggested. The rate of summ it lowering is sufficient to prevent the long-term intact survival of erosi on cycle surfaces formed in the Mesozoic that were previously inferred for this region.