Quaternary Sea-Level Changes and Coastal Evolution of the Coorong Coastal Plain, Southern Australia

Abstract

The sea level record of the Coorong Coastal Plain in southern Australia provides a chronicle of interglacial and interstadial sea-level highstands extending back in time for over the past 1 million years. East Naracoorte Range, one of the oldest and most landward coastal barriers considered in this book is at least of MIS 25 age but could be older (MIS 31). In a global context, the record is unique for its degree of preservation of relict coastal barrier landforms, as well as the number of interglacial events preserved in the stratigraphical record. The relative sea-level record from the coastal plain reveals that successive interglacial sea levels returned to a broadly common datum ranging between 9 m BPSL (Baker Range) to 3 m APSL (Harper Range). The inferred palaeosea-level record reveals no evidence for interglacial sea levels higher than the last interglacial maximum during the Middle Pleistocene. The record also reveals that MIS 11 is characterised by a more prolonged period of barrier development consistent with oxygen isotope records which indicate a longer duration for this interglaciation. Based on currently available geochronological evidence, Baker, Lucindale, Ardune and East Avenue Ranges all formed during the ‘super-interglacial’ MIS 11 with inferred palaeosea-levels ranging between 9 m BPSL for Baker Range and 2 m BPSL for the Ardune Range and East Avenue Range. Inferred relative sea levels for MIS 11 from the Coorong Coastal Plain are in accord with the EPICA Dome C ice core record which indicates larger ice volumes (lower sea levels) in MIS 11 than in MIS 5e. Over the past 1 Ma the coastal plain has prograded by over 90 km in its widest section in response to gradual epeirogenic uplift and sequential glacio-eustatic sea-level changes. Up to 20 coastal barriers formed during this period at times of high sea level. Quaternary volcanism (Early Pleistocene) created an archipelago of volcanic islands which influenced the geometry of the barriers in plan-view.