THE MORPHOLOGY, SEDIMENTOLOGY AND PALEOENVIRONMENTAL SIGNIFICANCE OF TWO PAN-LUNETTE CLUSTERS IN THE SOUTH WESTERN CAPE OF SOUTH AFRICA

Two clusters of small pans and associated lunette dunes are distinct landscape features in the Swartland and Agulhas Plain regions of the southwestern Cape of South Africa. While occurring in geographic proximity within the winter rainfall region, each of the pan-lunette clusters is hosted by different substrates, subjected to different coastal climate regimes and exhibits different morphology, orientation of features, and sedimentological characteristics. Not only are geomorphic characteristics at variance between regions, but also the alignment of lunettes on the leeside of pans, parallel within the cluster, is at variance with predominant modern wind direction and seasonality of precipitation at both sites, although the difference is more pronounced at Agulhas. In order to elucidate the occurrence and formational processes of these features, a dual-scale approach was employed: a regional cartographic study coupled with detailed local sedimentological analyses. The geomorphic characteristics of these features were quantified using aerial photography and orthophotographic maps. Dry season paleo-wind direction was inferred from the regional analysis. Sedimentological and geochemical analyses were applied to investigate the pan-lunette sediments at Voelvlei, in the Agulhas cluster, and at Droevlei East, in the Swartland cluster, in order to clarify the processes responsible for their formation. The characteristics of sediments in both lunettes indicate a primary control by parent material with little post-depositional diagenesis. Sedimentological characteristics of many of the lunettes suggest differences in timing of formation; radiocarbon dates confirm this. Although dunes within each cluster appear to have been initiated at different times, the dune-building activity at Agulhas (8000 BP) was initiated, on average, prior to the activity in the Swartland (11800 BP). Without further chronological constraints to elucidate the timing of dune-building periods, the lunettes may be seen as a cumulative product of at least the past 8000 years of windy arid seasons. The comparative relationships of the pan and lunette features in the Swartland and Agulhas offer insights into the shifting palaeoenvironment of the winter rainfall region of South Africa.