FIGURE 3. Major hydrological changes and main archaeological and megafaunal features of sites.

a, Synthetic stratigraphic section (from Fig. 2, right-hand column). See the key in Fig. 2 for meanings of symbols. b, The artefact frequency distribution is that determined from the Mungo B trench excavations¹⁷, and indicates maximum occupational density between 45 and 43 kyr. Megafaunal extinction is shown to occur at about 46 kyr (refs 14, 15), which is shortly after initial human arrival at Lake Mungo and coincident with fluctuations between lake-full and regionally dry conditions. c, Low lake levels are identified by weak soils that contain clay and silty sand blown from the partly exposed lake floor. The three Lower Mungo gravel bands were formed during three high water stands, when the lake overflowed, after the sand barrier had emerged above lake level³. During Upper Mungo time, when the system was dry for long intervals (thereby permitting clay deflation from the lake floor), detailed lake oscillations are difficult to specify. A brief return to high lake levels is suggested by cessation of deflation at about 30 kyr. d, The record of desert dust accession constructed from microscopic analysis of Wüstenquarz grains²⁴ (grains cm^-2 counted in thin-section) shows several weak soil-forming episodes between 48 and 42 kyr with major accession after 40 kyr. Grain counts are not significant beyond 150 grains cm^-2. While lake level changes reflect hydrologic controls in the southeastern highlands, the dust index is a response to erosion of the westerly dunefields. These two independent lines of evidence indicate a major climatic change of regional extent at 40 kyr.