Ngarrawa (mound spring) sediments as archives of Holocene environmental change in arid central Australia: Insights from Itrax XRF scanning

ABSTRACT

Central Australia's ngarrawa, or ‘mound springs’, are unique hydrological systems that serve as some of the only near‐permanent sources of water and continuous sediment deposition in Australia's arid interior. As such, they hold significant potential as palaeo‐climate and ‐environmental archives in a region where many aspects of past climate remain uncertain. To date, few studies have investigated the potential of these sediments, including their stratigraphic integrity or if they can be radiocarbon‐dated. In this study, Itrax X‐ray fluorescence (XRF) scanning was performed on a series of sediment cores taken at Maka (Warburton Springs) to determine sediment integrity at mm scale for sediments that do not clearly show visual structures. Radiocarbon dating was also attempted using different materials, including plant macrofossils, charcoal, one bone remain and an insect carapace. The different materials returned a wide range of potential ages, with the plant macrofossils, which we tentatively consider to be the most robust indicator of sediment age, suggesting that the sediment records extend back to ~700 cal. yr BP at Maka. Highly variable XRF‐inferred elemental profiles indicate that sediments at the ngarrawa are heterogeneous, not heavily mixed, with a trend towards increasingly organic sediments up‐core. The elements Fe, K, Si and Ti are interpreted to reflect different detrital sources throughout the sediments with increasing Fe concentrations, suggesting increased dust mobilisation during recent times. These findings suggest that the XRF data from ngarrawa have potential as palaeoenvironmental archives to support future research into the climate and ecological history of these important desert oases, but still require more robust chronological constraints.