May, J.-H.1,2, Marx, S.2, Cohen, T.2, Schuster, M.3 & May, S.M.4
1School of Geography, University of Melbourne, Melbourne, Australia, 2GeoQUEST Research Centre, University of Wollongong, Wollongong, Australia; 3Institut de Physique du Globe, University of Strasbourg, France; 4Institute of Geography, University of Cologne, Cologne, Germany
Lake Callabonna is one of four large connected playa lakes northwest of the Flinders Ranges in South Australia. These lakes are now mostly dry but would have joined to form mega-lake Frome that existed until ~45 ka. Although interrupted by major highstands, lakes declined in size since then and became successively disconnected. While this would significantly alter lake hydrology over time, the pronounced variability in lake levels also must have had a profound impact on the ways in which sediment were (i) supplied to the lakes by fluvial processes, (ii) distributed and deposited in various parts of the lake basin by lacustrine and coastal processes, or (iii) re-activated to be exported from the playa lake system by aeolian processes. In this spatially and temporally highly dynamic system, source-bordering lunettes play a particularly significant role by linking these different depositional and erosional environments. Despite the important clues these landforms may therefore hold in assessing mechanisms, timescales and controls on landscape-scale sediment flux in drylands, existing models of lunette formation are still very limited and often oversimplified. To contribute new data and discussions towards a better understanding the dynamically evolving landscapes around dryland playa lakes, we therefore explore the use of ‘source-to-sink’ perspectives in unravelling the palaeoenvironmental potential of desert lunettes, and specifically discuss geomorphic, sedimentary and geochronological data from Lake Callabonna in South Australia.
Multiple lunettes were identified around Lake Callabonna and occur in various shapes, sizes and orientations reflecting significant variability in sediment source and/or aeolian transport processes over time. We here present new data from a small km-scale lunette adjacent to the Moppa-Colina delta in the northwestern corner of the lake. Lunette texture is dominantly sandy and implies depositional processes analogous to coastal foredunes. Sedimentary architecture, however, is characterized by laterally continuous and finely interbedded intercalations of well-sorted fine and loamy sands, respectively. These observations are inconsistent with foredune formation, and rather point to processes of frequent and alternating processes of extensive aeolian sand accretion (i.e. draping) across the landscape. Our topographic and new chronological constraints suggest that sustained sediment supply in a late Holocene seasonally active deltaic environment at the interface between fluvial, lacustrine, coastal and aeolian process domains may best explain the observed morpho-stratigraphic data. In contrast to its growth over more than two millennia, the lunette has been actively eroding over the last few centuries from the combined effects of wind and water. In combination, our observations and preliminary results imply that in addition to variations in wind speed and direction, or the source and supply of sandy sediment, changes in vegetation cover (e.g. pre vs post-European land use) have to be considered when discussing the depositional and post-depositional mechanisms involved in sandy lunette formation as well as their potential for recording late Quaternary palaeoenvironmental conditions and pathways of sediment transport in drylands.
Dr Jan-Hendrik May is a Physical Geographer. Following from his PhD in Bern, Switzerland, he worked on several postdoctoral and assistant positions in Australia, China and Germany, and is now senior lecturer in Melbourne. His research interests are Quaternary climate-driven sedimentary dynamics in arid Central Australia and the Central Andes.