Discrimination of depositional environments using sedimentary characteristics in the Mega Kalahari, central southern Africa

Africa, the 'Mega Kalahari', extending far beyond the Kalahari Desert of today. Relic aeolian, lacustrine and fluvial landforms indicate that in the Quaternary the Kalahari sand has been deposited and reworked by a variety ofprocesses. Large areas of the sand have no identifiable andform associations, and because of this, sedimentological studies are necessary for a better interpretation of the palaeoenvironmental his ory of the Mega Kalahari. To this end, almost 200 Kalahari sand samples, in and not in identifiable landform associations, were collected and analysed in order to: investigate sedimentological characteristics; determine whether different processes have imparted distinct sedimentological characteristics to the sand; and thereby attempt to determine the depositional environments of samples without prior knowledge of the landform associations. Three methods have been used: (1) standard sedimentological techniques of grain size and shape determination; (2) multivariate discriminant analyses, to determine whether depositional environments could be better distinguished by considering rain size and shape parameters in combination; and (3) scanning electron microscope analyses of samples which lie centrally in any group identified by statistical analyses. Results indicate that aeolian processes have dominated the environmental history of the Kalahari sand, with only limited modification by subsequent processes. Multivariate discriminant analysis achieved only limited success in differentiating process environments. SEM investigations best identified the subtle modification of sand characteristics bynon-aeolian processes, because individual grain textures are more readily adjusted than overall sample fabrics, andmay therefore be the best echnique for elucidating palaeoenvironments from sediment characteristics. Unconsolidated Kalahari sand covers an area of 2.5 million km 2 in central southern Africa (Cooke 1964), extending from humid tropical Zaire to semi-arid Botswana (Fig. 1). This area has been termed the 'Mega Kalahari ' (eg Thomas 1986a and b) in order to distinguish it from the smaller area known today as the Kalahari Desert (e