Using radiometric data to identify æolian dust additions to topsoil of the Hillston district, western NSW

Abstract

The identification and characterisation of æolian dust additions to Australian soil profiles has been attempted using a wide range of analytical techniques. Such techniques are often reliant on specialised equipment and operator expertise, but do not necessarily yield information on the spatial distribution of deposited dust across the landscape. An airborne geophysical technique which measures naturally occurring gamma-rays may now assist in the rapid assessment of dust accumulation sites at the catchment scale. This technique, known as gamma ray spectrometry or radiometrics, assesses the potassium (K), uranium (U), and thorium (Th) contents of the Earth's surface, and may potentially distinguish æolian sediments from the underlying rock or in situ developed soil profile by their differing K, U, and/or Th-bearing mineral suites. This paper summarises a study of this technique for identifying æolian dust in topsoils of the Hillston district in western New South Wales. Using airborne with follow-up ground-based radiometric data, a variable relationship was established between large K signatures and apparent topsoil dust accumulations, which were identified as containing appreciable feldspar and illite. The previously established correlation between topsoil clay content and eTh (equivalent Th) concentration was also observed in this region, indicating that the technique may allow for rapid identification of landform features with significant clay and silt enrichment, as often occurs with dust accession. Despite the ubiquity of æolian sediments in this region, the radiometric data were moderately effective in discriminating different dune systems and may therefore represent a useful initial technique for discerning likely areas of dust accumulation in this environment. However, in areas influenced by fluvial sediments, the radiometric signatures were not necessarily indicative of the topsoil dust content.