Geochronology and evolution of a complex barrier, Younghusband Peninsula, South Australia

Abstract This study examines the southeastern end of the Younghusband Peninsula in South Australia at a location called The Granites in order to gain a better understanding of the processes of formation of the foredune ridge system, and to investigate the drivers that controlled its progradational development during the Holocene. Our findings are based on a morphological analysis, a ground penetrating radar survey, and 14C and OSL dating. The Younghusband Peninsula at The Granites was formed by an initial aggradational phase resulting in a single complex foredune ridge, and which ended around 4.3 ka, and by a regressive (progradational) barrier phase (750 m wide) that developed in the last 4.3 ka, under very low rates of progradation (0.38 to 0.09 m/yr). The last part of this phase shows significant foredune ridge building in the last 1000 years or so. Barrier progradation via foredune ridge development is likely an effect driven by low wave energy that favored conditions for coastal stability and foredune formation. Paleontological and GPR data indicate a maximum sea-level of +1.23 to +1.5 m, respectively, during initial barrier development. The foredune ridge plain of the barrier experienced at least three phases of significant aeolian activity with ages centered at around 3.9, 3.4 and 3.0 ka suggesting their occurrence at 500 to 400-year events. Computer modelling indicates that sediments for the progradational phase of the barrier were provided by the forced regression produced by a sea-level fall over the past 4.3 ka. The large foredune complex formed during the last phase of progradation could be the result of both the very low progradation rate of 0.09 m/yr, and periods of disturbance possibly related to enhanced storm activity.