Towards more robust chronologies of coastal progradation: Optically stimulated luminescence ages for the coastal plain at Moruya, south-eastern Australia

Abstract

Accurate chronologies are fundamental for detailed analysis of palaeoenvironmental conditions, archaeological reconstructions and investigations of Holocene coastal morphological changes. Chronological data enable estimation of rates of shoreline progradation, and provide appropriate context for forecasting future coastal changes. A previously reported radiocarbon chronology for the Moruya coastal plain in south-eastern Australia indicated a decelerating overall rate of progradation with minimal net seaward shoreline movement in the past ~2500 years. Single-grain and multi-grain aliquot optically stimulated luminescence (OSL) analyses demonstrate that marine sands from this region have excellent luminescence characteristics. A series of OSL ages across this coastal barrier indicates a remarkably linear trend of Holocene shoreline progradation. The linear trend of seaward shoreline movement indicates that the barrier has grown at an average rate of 0.27 m/yr with successive ridge formation every ~110 years. The oldest ridge on the barrier appears to correspond to cessation of rapid post-glacial sea-level rise, and the large foredune at the seaward margin of the barrier is <400 years old. The contrast between the existing radiocarbon chronology and the OSL ages reported in this study implies the need for a more cautious interpretation of coastal barrier chronologies, in Australia and around the world, where they have been based on radiocarbon dating of shell hash.