Complex Holocene lunette dune development, South Africa: Implications for paleoclimate and models of pan development in arid regions

Abstract

Closed depressions (pan or playa basins) are very common landscape features in arid or formerly arid regions. Many have associated downwind dune assemblages (lunettes) that have been explained in terms of deflation of sediments from the basin. These widespread features have also been used as proxies of late Quaternary rainfall and atmospheric circulation change. We use a detailed program of optically stimulated luminescence dating at Witpan, South Africa, to show that lunette construction may be rapid and spatially complex. This study presents 33 ages from 9 sample sites on the dune that show how accumulation of the present dune largely occurred over the past 2 k.y., but with marked sectoral variability in accumulation rates and timing. Variability is attributed largely to local sediment supply factors. Geochemical analysis shows that primary deflation from the pan has not contributed significantly to the construction of much of the current lunette; most sand is derived from recycling of older lunette sediments, preserved today at only a few locations, and from neighboring linear dunes. These findings, if representative of lunettes in other localities, have marked implications for the types of paleoclimatic information that these features may yield.