Late Quaternary lunette dune sedimentation in the southwestern Kalahari desert, South Africa: luminescence based chronologies of aeolian activity

Abstract

Through the application of luminescence dating techniques, great advances have recently been made in the understanding of the late Quaternary histories of many dryland regions, including southern Africa. Here, this work has largely applied optical dating to sediments from the extensive linear dune systems which dominate the Kalahari region of the central southern African interior. Relatively little attention has been given to localised aeolian accumulations such as lunette dunes, despite their wide distribution over many parts of the region, in particular the arid southwest Kalahari. To redress this, we consider the palaeoenvironmental significance of pan margin lunettes, and investigate the timing of lunette dune development in the southwest Kalahari through the application of optical dating to sediments from lunette dunes associated with four closed basins (pans). Ages show that localised aeolian activity occurred frequently throughout the past 18 ka, indicating that the factors controlling lunette sedimentation are markedly different from those determining regional linear dune development. It is proposed that the mechanisms controlling sediment supply to lunette dunes are controlled at both the regional and local (pan-specific) scales by factors such as groundwater levels. Where pans support more than one discrete lunette, the time since any individual lunette crest received significant accumulations of sediment increases with distance away from the pan margin. Outer and inner lunette sequences may be chronologically disparate features. Inner lunette formation may arise in response to modifications to the local atmospheric boundary conditions by the presence of large, downwind outer lunette features, or by shifts in sediment supply.