Landscape evolution and palaeoenvironment reconstruction of the Lake Mulurulu Lunette, Willandra Lakes World Heritage Area, NSW.

Tegan Kelly, Rainer Grün, Ian Moffat, Maxime Aubert and Tim Barrows

Research School of Earth Sciences, Australian National University, Canberra, ACT  0200, Australia

Figure 1. a) An otolith (fish ear bone) in cross-section, showing growth lines. b) ?18O isotope ratios along a transect of an otolith, measured using the SHRIMP II. The increasing values indicate increasing evaporation and hence aridity, while the fish was growing. c) The transect that these data represent. (Courtesy of Maxime Aubert)

The Willandra Lakes are a dry lake system consisting of a number of ancient lakes in the western region of the Murray basin. The area has significant scientific value, providing detailed palaeoenvironmental and palaeoclimatic records of arid, ice-age Australia as well as a rich and unique archaeological record. Lake Mungo, resting place of Australia's oldest dated aboriginal remains, has been a popular lake for study, while Lake Mulurulu, the northern-most lake in the system, is relatively understudied, despite its abounding potential. The aim of the current study is to combine isotope palaeoecology, geochronology, stratigraphy and sedimentological techniques to study the Mulurulu Lake lunette, thus creating a detailed geomorphological and palaeoenvironmental history of the lake, putting the aboriginal occupation of the area into an environmental context.

Techniques being utilised in the study include stable isotope analyses of wombat teeth, mollusk shells, emu egg shells and fish otoliths to provide palaeoenvironmental records of the area (e.g. Fig 1). This information is put into a geochronological context through ESR dating of wombat teeth, radiocarbon dating of mollusk shells and otoliths and AAR dating of egg shells. Detailed stratigraphic and sedimentological analyses (e.g Fig 2) further provide information about the history of the lake, and are also put into a geochronological context, through OSL dating of sediments.

Research questions being addressed include the history of the current deflation regime at the site, past seasonality and wetting-drying cycles in the region, climate change, timing and reasons for local species extinctions and how these factors relate to the human occupation of the area. Additionally, by utilising independent methods of palaeoenvironment reconstruction (i.e. stratigraphy and geochemistry) and geochronology (i.e. ESR and OSL), the competency and reliability of the techniques are tested.

The study is backed by an ARC-Linkage grant and is being conducted in collaboration with a number of other researchers from ANU, Latrobe, Bond and UQ universities as well as the local aboriginal groups (3TTG inc.) from the area. Associated work is being conducted on other lake lunettes in the region and the overall project integrates geological, geochronological, archaeological, palaeontological and palaeoenvironmental research at the Willandra Lakes World Heritage Area, providing a thorough analysis and understanding of one of Australia's most significant and unique areas of cultural and environmental history.

Figure 2. An example profile of the Mulurulu lunette. Approx. 5x vertical exaggeration.