Internal sedimentary structures of a recent transgressive dunefield in South Australia

Dune sediments packages, their sedimentary structure and bounding surfaces can provide an excellent record of deposition/erosion cycles and can be used for reconstructing dune evolutionary history and morphodynamics. Several studies have described transgressive dunefield development and evolution over different time scales, but the internal structures and evolution on a relatively short-term period has not been extensively explored and can provide interesting insights about how coastal dunes respond to short term environmental changes. In this study Ground Penetrating Radar (GPR) was utilized to examine sedimentary structures near Tea Tree Crossing and at 41.5 Mile on the Younghusband Peninsula, South Australia. The latter site, located in the middle of a new aeolian transgressive dune phase provides a modern example of dunefield development. Topography collected via LiDAR in 2008 and 2018, and RTK surveys in 2021, combined with GPR surveys from 10 to 17 m depth, allowed the identification of three distinct cross-shore patterns: (1) an erosion zone, (2) a stable/aggradation zone, and (3) landward progradation zone/dominated by slip face strata. LiDAR surveys are in line with high amplitude GPR reflections which indicate previous exposed surfaces with paleo-soils before the dune field became unstable followed by considerable geomorphic change and dune migration inland. Combination of LiDAR data and GPR surveys portray detailed stratigraphic information of the dune field that adds to an understating of transgressive dune field evolution and formation processes and sediment volume changes in the short term, which informs the development of an initial model of stratification in transgressive dunefields with typical GPR radarfacies.