SHEDDING LIGHT ON RECENT EVENTS: ASSESSING THE TIMING OF GULLY EROSION AND SEDIMENT DEPOSITION ON THE AUSTRALIAN TABLELANDS USING A PORTABLE OSL READER

Gully erosion and sediment deposition associated with rapid population expansion, such as European colonialism, result in widespread losses of topsoil and native environments. The southeast Australian Tablelands are unique among landscapes subject to population growth due to well-documented depictions of the pre-colonised landscape by early surveyors and explorers, yet specific causes and the timing of degradation remain controversial. Surficial deposits of coarse-grained sediment tens of centimetres thick are exposed in stream gully-walls throughout the Tablelands, commonly overlying organic-rich, finer-grained sediments thought to be associated with swampy meadow environments. The overlying sandy deposits are typically associated with elevated rates of soil erosion after the arrival of Europeans; however, the conditions under which these sediments were deposited are not well understood, nor is the timing well constrained. We utilise recently developed techniques in luminescence analysis of sediment to determine the exact depth in gully-wall sediment profiles which corresponds to the onset of sediment deposition and thus the onset of landscape change. These data allow us to select sites from which sediment samples can be collected for burial-age dating using optically stimulated luminescence (OSL). This work quantifies when sedimentation, and thus gully erosion, began and evaluates the likelihood of natural versus anthropogenic causes of erosion on the Australian Tablelands. Results from this study will provide new ways of assessing the impacts of population growth on a landscape and increase our knowledge of landscape response to population growth where no historical accounts exist.