Late quaternary stratigraphy and chronology of the Riverine Plain, Southeastern Australia

This project examines the Late Quaternary fluvial, aeolian and lacustrine evolution of the Riverine Plain of southeastern Australia during the last glacial cycle since approximately 100 ka. The study employs image interpretation, field mapping, stratigraphic investigations and absolute dating of sediments by thermoluminescence (TL). The present landscape of the Plain is dominated by a variety of palaeochannels subdivided by Pels (1971) into two essentially distinctive sequential categories. TL dating of the palaeochannel stratigraphy shows this interpretation to be simplistic. Oscillations between different channel types occurred repeatedly in the last 100 ka with large sinuous mixed load 'ancestral' type rivers evolving into bedload dominated 'prior type' streams, quite the reverse of Pels' interpretation. The stratigraphic record in the Murrumbidgee sector of the Plain shows that four major palaeochannel phases occurred during the last full glacial cycle commencing with the Coleambally from 105 to 80 ka and progressing through the Kerarbury (55 to 35 ka), Gum Creek (35 to 25 ka) and Yanco (20 to 13 ka) phases. All but the last palaeochannel phase included earlier mixed-load laterally migrating channels and terminal aggrading bedload channels. The mixed-load channel phases carried substantially more bedload than the modern rivers and cannot be regarded as simply larger versions of the latter. The Coleambally and Kerarbury palaeochannel phases coincide with enhanced fluvial activity recorded elsewhere in Oxygen Isotope Stages 5 and 3 respectively. The Kerarbury phase during the Stage 3 Sub-pluvial of Nanson et al. (1992a) was also a time of higher water levels at Lakes Urana and Cullivel and appears to coincide with Bowler's (1986a) Mungo lacustral episode. During Oxygen Isotope Stage 2 the Riverine Plain exhibited enhanced fluvial activity and higher lake levels both immediately before and after the Last Glacial Maximum (LGM) and the evidence is consistent with a short arid interval at the LGM itself. The transition to essentially modern environments occurred near the Oxygen Isotope Stage 2/1 boundary between 15 and 10 ka.