Late Neogene passive margin denudation history: cosmogenic isotope measurements from Central Namib desert.

In this paper, we review ideas on the geomorphological history of the southwest African passive margin, focusing on the central Namib sector and presenting new evidence on the late Neogene landscape evolution of this region. The hyperarid central Namib Desert occupies the 100-150-km-wide pediment at the foot of the Great Escarpment and forms part of the southwest African passive margin, which formed after breakup in the South Atlantic at around 118 Ma. Previous apatite fission track (AFT) and cosmogenic isotope studies and numerical models of coupled tectonic-surface processes in the same area suggest that long-term denudation rates of this passive margin (after a period of significant post-rift denudation) have been very low, ∼5 m/my. Aridity of the Namib Desert is generally assumed to have started with the onset of Benguela upwelling in the SE Atlantic at 10-15 Ma and to have prevailed ever since. It has been implied that during this period, the landscape has undergone only marginal change. Here, we present new evidence from in situ cosmogeni