Australia: The Land Where Time Began

A biography of the Australian continent 

Strzelecki & Tirari Deserts in Australia – Characterisation of Aeolian Sediments

Aeolian sediments are a major source of potential palaeoenvironmental information in arid environments that are dominated by desert dunes. However, it is unclear to what extent the sedimentology of dunes can be used in the reconstruction of palaeoenvironments. In this paper Fitzsimmons, Magee & Amos present the results of their assessment of the value of dune sediments as indicators of palaeoenvironments by investigating the sedimentological characteristics of linear dunes in the Strzelecki and Tirari Deserts of central Australia. To characterise the sediment that occurs within the dunefields of the region they used thin section microscopy, analysis of particle size and X-ray diffractometry (XRD) mineralogy, and examined the stratigraphic record in the context of the preservation of dunes and the reworking of sediment. They found that to reconstruct environmental change from the past in the dunefields of the desert purely on the basis of sedimentological evidence is rarely possible. Limited palaeoenvironmental information is, however, preserved within the sediments in dunes with which it is possibly to combine additional arid zone proxies and geochronological techniques to enable reconstruction of conditions in the past that is most reliable.

The most informative and unambiguous palaeoenvironmental indicators within dune sediments are provided by palaeosols which act as markers of relative environmental stability. Pedogenic carbonates and gypsum, and illuviated clays in the form of coating on grains, characterise palaeosols. For the reconstruction of palaeoenvironments a critical consideration is the potential for incomplete stratigraphic preservation within dunes, the preservation of palaeosols, however, indicates that in this region the dunes have not been reworked completely. Important evidence for pedogenesis is provided by the coatings on grains when they are intact, and for aeolian reworking when they are partially abraded. Across the region studied abraded cutans are ubiquitous. In the Strzelecki and Tirari Deserts mineralogy of linear dunes is dominated by quartz, with minor feldspar and clay minerals, the latter of which is in the form of on grain coatings and aggregates. It is indicated by the occurrence at several sites of intact sand-sized aggregates that are composed of clay and silt particles that incipient rather than peak aridity, and may, within this geomorphic context, indicate reduced discharges of streams. A regional bias is shown by grain size, though it is most likely that silt-sized material has been deposited as long-travelled dust. The regional grain size characteristics, together with the local occurrence of rock fragments and high feldspar content, suggest that the sediments are derived mostly from local sources.

Sources & Further reading

Fitzsimmons, K. E., J. W. Magee and K. J. Amos (2009). "Characterisation of aeolian sediments from the Strzelecki and Tirari Deserts, Australia: Implications for reconstructing palaeoenvironmental conditions." Sedimentary Geology 218(1–4): 61-73.