Whole-rock aminostratigraphy of the Coorong Coastal Plain, South Australia: towards a 1 million year record of sea-level highstands

The Coorong Coastal Plain in southeastern South Australia preserves a long Quaternary record of cool-water, temperate-carbonate sedimentation in the f orm of high wave energy, barrier shoreline deposits and associated back-bar rier lagoon facies that formed during successive sea-level highstands. Whol e-rock samples of bioclastic skeletal carbonate sand with subordinate quart z were collected from aeolian facies (modern and relict foredunes) of a Hol ocene embayment fill and from ten Pleistocene barriers across the coastal p lain in a transect from Robe to Naracoorte. The extent of leucine racemizat ion (total acid hydrolysate and Free amino acids) in the Pleistocene skelet al carbonate sand (63-500 mum) increases monotonically with age and is cons istently higher than for entire fossil molluses from the same allostratigra phic units, reflecting the lengthy residence time for bioclasts in this hig h wave energy environment, and sediment recycling from the erosion of older barriers. The extent of racemization in the whole-rock samples conforms wi th a model of apparent parabolic racemization kinetics and the calculated a ges largely agree with previously determined luminescence ages. Apart from a possible reinterpretation of the significance of the West Naracoorte Rang e, the coastal plain succession indicates that interglacial sea levels did not deviate by more than 6 m of present sea level for the Mid- and Late Ple istocene thus providing an important framework for quantifying ice volume d uring sea-level highstands and calibrating the oxygen isotope record.