The Botany Sands of southeast Australia: A Quaternary inland dune and swamp system

Abstract

A set of legacy particle-size data confirms that the Quaternary Botany Sands of southeast Australia consist of two elements: inland aeolian sands and organic-rich swamp sediments. Whilst most swamp sedimentation is controlled by groundwater elevation and thus by warm-stage rising sea levels, sand accumulation occurred largely during glacial stages. Across southeast Australia, glacial-stage aeolian activity was restricted to the localised reworking of existing sand bodies. How then was the substantial Botany dunefield able to develop when aeolian deposition elsewhere was so inconsequential? One answer is that deposits of similar age and origin along the eastern margin of the continent have been overlooked. More important is the location of these dunefields along a narrow coastal band extending from central New South Wales into Queensland. This belt experienced onshore winds during at least part of the glacial stage and was located downwind of stores of unconsolidated material exposed along the continental shelf under glacial low sea-level conditions. This explains not only why the dunefields were able to develop, but also why they are confined to such a restricted part of the continent. Such dunefields represent examples of a poorly described depositional environment that may be identified worldwide where suitable receptive basins subject to onshore winds are located adjacent to exposed glacial-stage shelves.