CATENA vol. 20, p. 515-527 Cremlingen 1993 } Present Day Lunette Sediment Cycling at Witpan in the Arid Southwestern Kalahari Desert D.S.G. Thomas, D.J. Nash, P.A. Shaw & C. Van der Post Summary Witpan is a pan depression in the south- western Kalahari Desert. The pan fling- ing lunette dune has a number of no- table characteristics: a highly active crest; the lower lunette pediment is ce- mented; and the lower lunette supports a highly developed and active gully sys- tem. Geomorphological and sedimento- logical considerations are used to evalu- ate the interaction of wind and water in shaping contemporary lunette processes. It is considered that like other pans in the area, groundwater activity influ- ences pan floor sediment availability and transport, that the present highly sea- sonal climatic regime permits the inter- action of aeolian transport of sediment to the dune and its return to the pan floor by water during storm events, cre- ating a cycling process favoured by sedi- mentary properties that promote surface runoff. 1 Introduction Pans are small closed depressions, of- ten containing ephemeral lakes, that are characteristic of low relief areas of many ISSN 03,11-8162 (~)1993 by CATENA VERLAG, 38162 Cremlingen-Destedt, Germany 0341-8162/93/5011851/US$ 2.00 + 0.25 semi-arid and arid environments (Shaw & Thomas 1989). Their origins have proved controversial (Goudie & Thomas 1985) and it is probably the case that the features to which the name has been applied have developed by various mech- anisms both from region to region and in some cases within a single area. De- flation, leading to the formation of pan fringing lunette dunes has often been re- garded as a major formative process (e.g. Lancaster 1978), though there is grow- ing evidence that pan development is controlled by groundwater activity. The groundwater table acts as a base down to which deflation occurs, or as a control on weathering processes where pans are developed in bedrock rather than uncon- solidated sediments (Bowler 1986, But- terworth 1982, Farr et al. 1982, Lan- caster 1986, Shaw 1988). Bowler (1986) has shown that depres- sion development and morphology can be considered in terms of positive and negative surface water balances. De- flation is a consequence of basin pro- cesses rather than a major formative influence, with lunettes not necessar- ily formed from sediment deflated di- rectly from the basin floor but also dur- ing pan full stages from sediment trans- ported to the downwind margin of the water body by wave action, analogous to coastal dune development. Lunettes can CATENA--An Interdisc|pl|nary Journal of SOIL SCI~NC~--H~/DROLOG~/--GEOMORPHOLOGY