IMPLICATIONS TOWARD PAST AND FUTURE CLIMATE – THE SPATIAL AND STRATIGRAPHIC RELATIONSHIPS BETWEEN SUB-TROPICAL FENS, BEACHES AND DUNES OF THE SOUTHEAST QUEENSLAND COAST, AUSTRALIA

Fraser and North Stradbroke islands are the two largest sand islands in the world. Fraser Island, a UNESCO World Heritage Site and North Stradbroke Island, an Australian National Park, are located on the southeast coast of Queensland with vegetated dune complexes that reach 240 m in elevation and date to the mid-Pleistocene. The margins of the islands have been reworked through coastal processes and show evidence of relict environments that may relate to the previous interglacial; where prograding beach ridge complexes, low-elevation aeolian dunes and large wetland systems presently dominate the low-lying coastal plains. Previous research has identified the only examples of sub-tropical pattern fens within the wetland systems.

During 2012 and 2013, a series of GPR lines were acquired on Fraser and North Stradbroke islands to elucidate the spatial and stratigraphic relationships between the beach, aeolian and wetland facies. We collected 25 km of 250 and 500 MHz ground penetrating radar profiles in each of the three environments where we identified a series of sub-facies and established a conceptual and relative chronology based on stratigraphy of the facies and previous research.

The radar data acquired on the coastal plains suggests a series of modern environments that have been deposited during the last glacial period that overlie erosional remnants of a previous coastal plain that may relate to the last interglacial period. The present-day coastal plain consists of a series of beach ridges that interfinger with wetland deposits and grade to beach deposits toward the shoreline. The beach deposits show evidence of large storm impacts while the wetland deposits contain sediment-rich layers that are spatially continuous across the wetland at various depths. The wetland complexes grade into coastal deposits or lap on remnant coastal plain or Pleistocene dunes. The beach deposits and margins of wetland complexes are blanketed by an aeolian drape that is inferred to be mid to late Holocene.

The spatial and temporal relationships of the environments, while still under development, will yield vast quantities of climate, ecologic and process-based information that will assist our future studies and enhance understanding of the impacts of past climate and events on the landscape of southeast Queensland's coast.