GPR SIGNATURES OF THE GIANT PODZOL SEQUENCES ON THE SAND DUNES OF GREAT SANDY NATIONAL PARK, QUEENSLAND, AUSTRALIA

Great Sandy National Park, coastal southeast Queensland, Australia, is home to the world’s largest sand island and massive dune fields that are currently stabilized by vegetation. Previous work suggests the dune field has periods of activity and dune building over the past million years when the entire region had active aeolian processes. The area is also home to soil sequences that are greater than 30 m deep. The soils, developed in aeolian-derived sands, are classified as podzols and exposed on eroding coastal bluffs. The repeated sequences of exposed podzols with white, yellow, orange, red, and black-brown colors provide the name “Rainbow Beach” to one of the area’s beaches.

Over 200 km of ground penetrating radar has been acquired to elucidate the evolution of the area. Lines were acquired along firebreaks, sand roads and paths of the National Park. The surveys identified facies that relate to various aeolian landforms and soil sequences. The A and O horizons are minimal to absent on most firebreaks and sand roads of the area due to use and maintenance. The E horizon appears as bleached white (10YR 8/1 – 5Y 8/1 white) and is of variable thickness; on GPR it appears transparent or has discontinuous reflections. The B horizon appears as yellow to orange or brown (2.5Y 7/4 pale yellow to 7.5YR 7/8 strong brown) with various degrees of cementation; on GPR it is generally chaotic with increasing hyperbolic reflections as cementation increases. The C horizon appears buff to tan (10YR 7/3 very pale brown to 2.5Y 7/3 pale yellow) with primary sedimentary structures related to aeolian deposition; on GPR various internal reflections related to primary sedimentary structures are visible.

The surveys revealed stacked podzol sequences, reflecting sequential periods of dune building, stabilization and podzolisation, partial erosion of upper soil horizons, and dune rebuilding. In places, the E horizon was over 30 m thick in one continuous unit, indicating long periods of dune stabilization and extended or intense podzolisation; while in others, thin E-B sequences were repeated 5 to 8 times within 30 m depth, indicating short dune stabilization and podzolisation and/or extensive erosion of upper soil horizons. Identification of various podzol sequences has enabled the research team to target units for dating and geochemical analysis.