Linear dune accumulation chronologies from the southwest Kalahari, Namibia: challenges of reconstructing late Quaternary palaeoenvironments from aeolian landforms A.E.C. Stone * , D.S.G. Thomas School of Geography, Oxford University Centre for the Environment, South Parks Road, Oxford OX13QY, UK article info Article history: Received 19 March 2008 Received in revised form 18 June 2008 Accepted 19 June 2008 abstract The linear dunes of the southern Kalahari dunefield constitute one of the major palaeoenvironmental proxies in the region. The application of optically stimulated luminescence (OSL) dating since the1990s and advancements in the depth of sampling using augering equipment over the past few years have permitted the reconstruction of linear dune accumulation chronostratigraphies for entire dune profiles from base to crest. These methods are applied to four dunes in the Mariental–Stampriet region of the southern Kalahari dunefield, sampled at predominantly 0.5 m intervals. Individual dunes record multiple phases of dune construction, but with only a few phases recorded consistently between two or more of the dunes. Results from the 48 OSL ages produced here extend the aeolian accumulation record for the southern Kalahari dunefield through the last three glacial–interglacial cycles with two ages from the early part of MIS6. A synthesis of all existing luminescence ages for the southern Kalahari reveals that the dunefield has been partially active throughout much of the past 120 ka. There are no clear clusters of ages within OSL age errors. This is in contrast to previous syntheses of ages for this region. In addition, these new data from Mariental–Stampriet dunes show that clusters in grouped dune OSL ages can be spuriously produced as a function of reducing the sampling frequency with depth within the dunes, from 0.5 to 1 mintervals. This has significant implications for previous conclusions regarding discrete phases of aeolian accumulation based on sampling at 1 m intervals and less vertically intensive sampling tech- niques. The total luminescence data set of 136 ages for the southern Kalahari implies that this dunefield has been close to the threshold of reactivation throughout much of the late Quaternary. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Reconstructing late Quaternary Kalahari environmental and climatic change Palaeoclimatic conditions in the southwest Kalahari and interior of southern Africa have to date largely been inferred from geomorphological proxy evidence, such as linear dunes and lake shorelines (Thomas and Shaw, 2002). This reflects the paucity of palaeoecological evidence, owing to poor preservation of pollen and insect material in semi-arid environments, and the limited number of sites preserving geochemical proxies, such as those in speleothems and groundwater aquifers. Geomorphological archives will continue to constitute the major environmental proxy in this region, such as in the recent reconstruction of positive hydrological excursions in the middle Kalahari by systematic optically stimulated luminescence dating (OSL) dating of beach ridges marking the former shorelines of mega-lakes in Makga- dikgadi, Mababe and Ngami basins (Burrough et al., 2007). In the southwest Kalahari linear dunes are the dominant land- form, extending from 23 to 29  S, and covering areas of northern South Africa, southern Botswana and eastern Namibia (Fig. 1). The longest and most reliable records of dune accumulation collected so far come from the Witpan area in northern South Africa (crossed circle, Fig. 1)(Telfer and Thomas, 2007). These geomorphological proxies are not without their challenges and limitations as palae- oenvironmental and palaeoclimatic archives. Particular issues surround providing reliable OSL accumulation chronologies, and the palaeoclimatic interpretation of those chronologies. This paper first examines the nature and limitations of dune records before presenting and analysing new data from the western edge of the northern part of the southern Kalahari linear dunefield, in the Mariental–Stampriet region, thereby dramatically extending the record for the Namibian portion of the region. It also addresses whether similar aeolian accumulation chronologies are preserved in this region of the dunefield, as compared to the records to the * Corresponding author. Tel.: þ44 (0) 1865 285070; fax: þ44 (0) 1865 275885. E-mail address: abigail.stone@ouce.ox.ac.uk (A.E.C. Stone). Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev 0277-3791/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2008.06.008 Quaternary Science Reviews 27 (2008) 1667–1681