Geomorphology, stratigraphy and thermoluminescence dating of the lunette dune at Lake Victoria, western New South Wales

Abstract

Abstract Lake Victoria, 13 km long and 10 km wide, is the largest lunette lake attached to the Murray River in southeastern Australia. The lake occupies the western part of a larger basin at least twice the size of the present lake. The larger basin has been incised nearly 30 m into the regional sand plain surface and into the early-middle Pleistocene Blanchetown Clay. Within the larger basin (east of the lunette of the present Lake Victoria), various landforms have developed, including alluvial terraces, salt pans, small dry basins and multiple small lunettes. Among these, an arcshaped sand ridge, possibly an old lunette, was dated by TL as 82 ka. The present lunette of Lake Victoria is up to 40 m high and consists of 3 units: Nulla Nulla Sand (30 m thick), Talgarry Sand (up to 10 m thick) and the reworked Dunedin Park Sand. The Nulla Nulla Sand consists dominantly of pure medium to fine-grained sand sequences with a few red palaeosols, indicating long-standing high lake levels with a few lunette stable intervals. Deposition of the Nulla Nulla Sand ended around 20 ka, starting at least 40 ka ago and probably much earlier. The Talgarry Sand, overlying a prominent red palaeosol on top of the Nulla Nulla Sand, consists of pure sand horizons interbedded with at least 3 gypseous clayey silt layers. The gypseous sediments indicate a major change of hydrologic conditions in the lake basin, fluctuation of lake levels and periodically high salinity. The Talgarry Sand was deposited from 17 to 10 ka as dated by TL and previous 14C dates. After 10 ka, lunette accretion stopped, possibly the result of incision of the Murray River channel, reducing the water and sediment input to the basin. However, erosion and deflation of the lunette formed an apron of sediment on the lower lake-facing slope and sand transport to the lee-side long slope, leaving “islands” of old sediment along the lunette crest zone.