Lunette dunes of Lake Torrens and their significance as paleoenvironmental indicators

Abstract

This paper aims to provide an understanding of the variability of the lake level at Lake Torrens and use this as a proxy for climate throughout the last 50,000 thousand years (ka). Australia's climate has evolved throughout the Quaternary, with the Holocene experiencing much more variable episodes of wetness, however questions remain due to most previous works focused on different climatic regimes. Dunes characteristic of high clay content, known as lunettes, form adjacent to dry lakes in unique environmental settings and therefore can offer important information of lake hydrological phases. These dunes are useful climatic indicators as they form in response to prevailing winds during the middle to latter part of the dry season after water table lowering has occurred. A complex lunette system has formed on the eastern margin of Lake Torrens which has been found to record paleoenvironmental indicators through its mineralogical, textural and morphological characteristics. This study analysed this lunette system through mapping of surficial geomorphology and construction of a digitally elevated modal based on aerial photometry, sediment characterization for grain size, elemental and mineralogical composition and dating by optically stimulated luminescence (OSL). The key results suggest that the formation of two lunette units, indicating variable lake levels. These clay rich units were dated at ~40 ka and ~20 ka which agree with lake levels found from neighbouring Lake Frome. These results offer new insights and understanding of the climate variability in southern arid Australia, with significance for interpreting the mechanisms of multi-millennial climate change and associated hydrological response in the southern hemisphere arid continents.