A revised chronology and depositional history for the Outer Arumpo lunette, Willandra Lakes Region World Heritage Area, NSW

Quaternary research within the Willandra has focused heavily on understanding the record of landscape change preserved within the Lake Mungo lunette. However, Mungo is just one of the 13 major lakes that comprise the Willandra and, unique among its neighbours, is not directly fed by inflow from the Willandra Creek. The outcome is a biased view of landscape change centred upon one, terminal lake within the system. The stratigraphic record exposed within a deflationary hollow on the Outer Arumpo (OA) lunette, known as Top Hut 1, has been revisited as part on an ARC DECRA project. Here, Bayesian modelling of 52 new single-grain OSL ages, accompanied by a sediment micromorphological analyses, has been used to construct a chrono-stratigraphic framework for lunette development across 7 identified stratigraphic units. The OA basin filled ~80–56 ka ago (Unit 2), with high lake levels maintained until ~44 ka ago (Unit 3). Relative lake level declines ~43–41 ka ago (Unit 4), before fluctuating rapidly ~40–38 ka ago (Unit 5). None of the sediments sampled within the TH1 site date between this 38 ka age and ~150 years ago (Unit 6 and 7). These findings demonstrate that Lakes OA and Mungo have distinct hydrologic histories. The alternating sedimentology of Unit 5 indicates that Lake OA was fluctuating rapidly while Lake Mungo was relatively full and stable ~40–38 ka ago. Critically, these Unit 5 sediments correlate to the ‘Arumpo Unit Type Section’ of Bowler (1998) located ~400 m south of TH1, making the Arumpo Type Section significantly older than the ‘Arumpo-aged’ deposits of the Lake Mungo lunette (~25–18 ka). This conclusion demonstrates that the stratigraphic scheme developed for Lake Mungo is not applicable to other lake basins in the system, given the unique hydrologic and depositional history of each basin.<p></p>