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

Abstract

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.