Kalahari Pans: Quaternary Evolution and Processes of Ephemeral Lakes

Abstract

Pans, playas and similar morphological structures occur across all continents. They are small, closed sediment sinks that are characteristic of arid and semi-arid regions with low relief. In the Kalahari Basin, small pans are widespread and they function as ephemeral lakes and sedimentary sinks. They are characterised by their flat, salty to clayey surface and slightly elevated surroundings. Some principle sedimentary processes are distinctive for pans. Showers during the short rainy season deliver siliciclastic material by runoff from the local catchment. During the dry season, evaporites precipitate by evaporation of the surface water and supersaturated pore water and groundwater. Additionally, fine-grained sediments are transported on the dry pan surface by strong wind regimes (long-term) or by vortices/eddies from thermal uplifts (short-term). The marginal lunette dunes, a characteristic feature of many small Kalahari pans, resulted from temporary phases of significant aeolian sediment transport. However, there is no hint of longer sedimentation gaps or significant periods of erosion. The prevailing depositional processes contradict the former assumption that deflation is the most prominent process in salt pan formation. The pans contain sediment sequences that are several decimetres to metres in thickness, which reach back until the Late Pleistocene. They contain different kinds of proxy information that can be used for environmental reconstruction and climate modelling throughout the pans’ history.