A Holocene–late Pleistocene aeolian record from lunette dunes of the western Free State panfield, South Africa

Abstract

The greatest concentration of pans in southern Africa occurs in the western Free State province, South Africa. A feature of many Free State pans is their fringing lunettes, located on the southern and south-eastern margins. Lunette dunes associated with pans in the neighbouring and presently drier Kalahari region show depositional ages, determined by optically stimulated luminescence (OSL) dating, primarily in the Holocene. However, to date, the precise timing of Free State lunette accumulation has not been investigated. The morphology, sedimentology and age of lunettes at five pan sites in the western Free State panfield are reported here. The lunettes form distinct topographic features, with heights up to 5 m above the pan floor, and all have been dissected by gully erosion. Sediment in the sand size class dominates in the lunettes, often overlying clay-rich basal or pan floor sediments. The intra- and intersite data consistency of 46 OSL ages is interpreted as reflecting regional causal factors responsible for lunette accretion, with phases of lunette building at 12—10 ka, 5.5—3 ka, 2—1 ka and 0.3—0.07 ka ago. These are in good agreement with the findings from pan-fringing lunettes in the southwest Kalahari and consistent with established records of palaeocirculation and wind direction over central southern Africa during the late Pleistocene. Lunettes in the western Free State are currently not in a major accretion phase. They are subject to degradation by localized fluvial erosion, with sediment being recycled into the pans.