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Integrating millennial and interdecadal shoreline changes: Morpho-sedimentary investigation of two prograded barriers in southeastern Australia

Academic Article


Abstract


  • Progradedbarriers are distinctive coastal landformspreservingthepositionof past shorelines as lowrelief, shore- parallel ridges composed of beach sediments and commonly adorned with variable amounts of dune sand. Prograded barriers have been valued as coastal archives which contain palaeoenvironmental information, how- ever integrating themillennial timescale geologicalhistoryof barriers withobserved inter-decadalmodernbeach processes has proved difficult. Technologies such as airborne LiDAR, ground penetrating radar (GPR) and optical- ly stimulated luminescence dating (OSL)wereutilised atBoydtownandWonboyn, in southeasternAustralia, and combinedwith previously reported radiocarbon dates and offshore seismic and sedimentological data to recon- struct themorpho-sedimentary history of prograded barrier systems. These technologies enabled reconstruction of geological timescale processes integrated with an inter-decadalmodel of ridge formation explaining the GPR- imaged subsurface character of the barriers.Both theBoydtown andWonboyn barriers beganprograding ~7500– 8000 years agowhen sea level attained at or near present height along this coastline and continued prograding until the present-day with an initially slower rate of shoreline advancement. Sources of sediment for progradation appear to be the inner shelf and shoreface with a large shelf sand body likely contributing to progradation at Wonboyn. The Towamba River seems to have delivered sediment to Twofold Bay during flood events after transitioning to amature estuarine systemsometimeafter ~4000 cal. yr BP. Someof thismaterial ap- pears to have been reworked onto the Boydtown barrier, increasing the rate of progradation in the seaward 50% of the barrier deposited over the past ~1500 years. The GPR imaged beachfaces are shownto have similar geom- etry to beach profiles following recent stormevents and a model of ridge formation involving cut and fill of the beachface, and dune building in the backshore, explains the character of the preserved beachface record and the morphology of the ridges. This model is applicable to future management of individual beaches where such beaches are subject to ongoing cut and fill, dune building processes and inherited sediment budget conditions.

Publication Date


  • 2017

Start Page


  • 129

End Page


  • 147

Volume


  • 288

Abstract


  • Progradedbarriers are distinctive coastal landformspreservingthepositionof past shorelines as lowrelief, shore- parallel ridges composed of beach sediments and commonly adorned with variable amounts of dune sand. Prograded barriers have been valued as coastal archives which contain palaeoenvironmental information, how- ever integrating themillennial timescale geologicalhistoryof barriers withobserved inter-decadalmodernbeach processes has proved difficult. Technologies such as airborne LiDAR, ground penetrating radar (GPR) and optical- ly stimulated luminescence dating (OSL)wereutilised atBoydtownandWonboyn, in southeasternAustralia, and combinedwith previously reported radiocarbon dates and offshore seismic and sedimentological data to recon- struct themorpho-sedimentary history of prograded barrier systems. These technologies enabled reconstruction of geological timescale processes integrated with an inter-decadalmodel of ridge formation explaining the GPR- imaged subsurface character of the barriers.Both theBoydtown andWonboyn barriers beganprograding ~7500– 8000 years agowhen sea level attained at or near present height along this coastline and continued prograding until the present-day with an initially slower rate of shoreline advancement. Sources of sediment for progradation appear to be the inner shelf and shoreface with a large shelf sand body likely contributing to progradation at Wonboyn. The Towamba River seems to have delivered sediment to Twofold Bay during flood events after transitioning to amature estuarine systemsometimeafter ~4000 cal. yr BP. Someof thismaterial ap- pears to have been reworked onto the Boydtown barrier, increasing the rate of progradation in the seaward 50% of the barrier deposited over the past ~1500 years. The GPR imaged beachfaces are shownto have similar geom- etry to beach profiles following recent stormevents and a model of ridge formation involving cut and fill of the beachface, and dune building in the backshore, explains the character of the preserved beachface record and the morphology of the ridges. This model is applicable to future management of individual beaches where such beaches are subject to ongoing cut and fill, dune building processes and inherited sediment budget conditions.

Publication Date


  • 2017

Start Page


  • 129

End Page


  • 147

Volume


  • 288