The optically stimulated luminescence (OSL) dating method was used to determine the geochronology of seven relict beach ridges that sit immediately behind the modern beach at Beachmere, a low-energy sandy coast within Moreton Bay, Queensland. Between 2600 ± 400 and 1700 ± 130 years ago, the shoreline eroded and foreshore sediment was deposited over the older beach deposit. Subsequently, there was a 1500-year period of shoreline progradation: the shoreline advanced 0.16 m/y between 1700 ± 130 and 1140 ± 80 years ago; and 0.41 m/y between 1140 ± 80 and around 200 years ago. Shortly after 690 ± 60 years ago, a series of well-developed regularly spaced beach ridges gave way to an intertidal flat and then deposition of a set of lower amplitude, closely spaced beach ridges. The younger ridges were deposited between 230 ± 40 and 140 ± 50 years ago, at a rate of around 1.06 m/y. During the last several decades, much of the Beachmere shoreline has eroded into these younger relict ridges. Drivers of these changes in shoreline sedimentary regime are yet to be accurately determined; however, it seems likely they are related to switches that occur in the nearshore sand transport pathway. Our results demonstrate the utility of the OSL method for providing insights into coastal change that occurred in the historical and recent geological period. Better understanding the tempo of shoreline change in the recent past is particularly relevant for assessments of vulnerability to erosion of rapidly developing, low-lying sandy coasts such as northern Moreton Bay.
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Vol. 2008 • No. 243