Understanding linear dune chronologies: Insights from a simple accumulation model M.W. Telfer ⁎, R.M. Bailey, S.L. Burrough, A.E.S. Stone, D.S.G. Thomas, G.S.F. Wiggs School of Geography and the Environment, University of Oxford, South Parks Road, Oxford, OX1 3QY, United Kingdom abstract article info Article history: Received 14 August 2009 Received in revised form 23 March 2010 Accepted 23 March 2010 Available online xxxx Keywords: Linear dunes Palaeoenvironments OSL dating Accumulation model Dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition, and are thus seen as potential archives of palaeoenvironmental information. Some dune types are more suitable for this purpose than others, and linear dunes (used here synonymously with longitudinal dunes) have been most frequently employed. They are commonly found in dryland and dryland-marginal regions, and they are apparently less migratory than some other dune forms, thereby offering the potential for longer environmental histories. Most recent studies have employed optical (OSL) dating surveys, which directly date the emplacement of dune sands, to attempt to produce a representative history of aeolian accumulation at a dunefield scale; yet such studies have not always given due consideration to the geomorphology of linear dune accumulation. Although linear dunes do not rework their sand as readily as, say, barchans dunes, it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield's surface. For this reason, all dune archives must be assumed to be discontinuous over long timescales. The effect of sediment redistribution on dune preservation, and thus palaeoenvironmental interpretation, is difficult to observe and poorly understood. We present a simplified probabilistic model to replicate deposition/erosion of sand at a linear dune crest, thus simulating the type of profile sampled in many field studies in order to produce a local accumulation history. The modelled sand flux incorporates various feedbacks and the simulations are run with varying boundary conditions in which the simulated surface is assumed to be in equilibrium over the multi- millennial timescales of the model's duration. Periodic instabilities in the landscape are generally well recorded by the modelled dune accumulation history, particularly when the events involve the system as a whole briefly functioning out of an equilibrium state (i.e. the probabilities of deposition and reworking are not equal). However, under forcing conditions where the probabilities are unchanged throughout the duration of the model run, the results can show apparent structure within the data when sample sizes are low, although at large sample sizes the preservation potential decays with burial age according to a power law. The model confirms the importance of rigorous sampling strategies for such studies, but also suggests that if such precautions are taken, the reworking inherent to linear dune aeolian systems does not preclude their use as a Quaternary palaeoenvironmental archive of environmental change. © 2010 Elsevier B.V. All rights reserved. 1. Introduction 1.1. Linear dunes as a palaeoenvironmental tool It has long been recognised that in some regions, particularly those no longer subject to intense aeolian activity, sand dunes are a reflection of past environmental conditions different to the present day, particularly wind and moisture regimes (e.g. Grove, 1969). Linear dunes (used here synonymously with longitudinal dunes), commonly either vegetated or part-vegetated, have proved to be especially valuable archives. Although all dune types are prone to sediment reworking to some degree, and are thus unlikely to preserve a complete sedimentary record, the mode of formation of linear dunes may lend itself to preserving longer-term records than many other dune types (Nanson et al., 1992a; Lancaster, 1995; Munyikwa, 2005). Since the early 1990s, the application of luminescence dating (first as TL, now predominantly utilising OSL) has greatly improved the dating of linear dune sediment sequences (e.g. Nanson et al., 1992a,b; Stokes et al., 1997; Blumel et al., 1998), and recent studies have become more thorough and more sophisticated in their approach to sampling and data interpretation (e.g. Lomax et al., 2003; Fitzsimmons et al., 2007; Telfer and Thomas, 2007; Stone and Thomas, 2008). Such studies now typically involve sampling of dunes at relatively high resolution both laterally and vertically via coring of dune profiles, or where possible, at sections that expose the full dune profile. The correct interpretation of dune chronologies is thus dependent on an understanding of the effects of sediment reworking/removal as well as sediment Geomorphology xxx (2010) xxx–xxx ⁎ Corresponding author. Tel.: +44 (0) 1865 285086. E-mail address: matt.telfer@ouce.ox.ac.uk (M.W. Telfer). GEOMOR-03245; No of Pages 14 0169-555X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2010.03.030 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph ARTICLE IN PRESS Please cite this article as: Telfer, M.W., et al., Understanding linear dune chronologies: Insights from a simple accumulation model, Geomorphology (2010), doi:10.1016/j.geomorph.2010.03.030