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

Abstract

The Coorong Coastal Plain in southeastern South Australia preserves a long Quaternary record of cool-water, temperate-carbonate sedimentation in the form of high wave energy, barrier shoreline deposits and associated back-barrier lagoon facies that formed during successive sea-level highstands. Whole-rock samples of bioclastic skeletal carbonate sand with subordinate quartz were collected from aeolian facies (modern and relict foredunes) of a Holocene embayment fill and from ten Pleistocene barriers across the coastal plain in a transect from Robe to Naracoorte. The extent of leucine racemization (total acid hydrolysate and free amino acids) in the Pleistocene skeletal carbonate sand (63–500 μm) increases monotonically with age and is consistently higher than for entire fossil molluscs from the same allostratigraphic units, reflecting the lengthy residence time for bioclasts in this high wave energy environment, and sediment recycling from the erosion of older barriers. The extent of racemization in the whole-rock samples conforms with a model of apparent parabolic racemization kinetics and the calculated ages largely agree with previously determined luminescence ages. Apart from a possible reinterpretation of the significance of the West Naracoorte Range, 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 Pleistocene thus providing an important framework for quantifying ice volume during sea-level highstands and calibrating the oxygen isotope record.