The Last Interglacial – Other Inland Lakes

Australia: The Land Where Time Began

The Last Interglacial – Other Inland Lakes

During MIS 5 a stronger, more active monsoon is reflected in the palaeohydrology of Lake Eyre, Smith saying it is therefore not surprising that other inland lakes, especially in northerly Australia, also display this imprint. Lake Gregory and Lake Woods, on the northern margins of the desert, have palaeoshorelines indicating both were much larger perennial lakes about 100-96 ka (Bowler et al., 1998; Bowler, Wyrwoll and Lu, 2001). At the present both are active ephemeral lakes that are fed by inflows from the northern subtropics. Smith suggests these are likely to have been freshwater systems: the remains of beds of Velesunio mussels confirm this at Lake Gregory.

The Willandra Lakes on the southeastern margin of the desert, which are fed by runoff from southeastern Australian highlands, match the northern lakes. It appears that these lakes also had high lake levels during the MIS 5, which is represented by the Golgol Unit at Lake Mungo, though this has been only poorly dated, >126-98 ka, or defined (Bowler & Price, 1998). It appears all of these lakes were reactivated, to a varying extent, early in MIS 3 (50-45 ka), which would have made them an obvious focus for hunter-gatherer groups that moved into the desert (e.g. Bowler et al., 1998; Veth et al., 2009).

During the last interglacial Lake Amadeus in Central Australia was a hypersaline playa, though the regional water table was higher than it is at the present. Prior to 82 ka and from 60 ka to 45 ka, the deposition of shoreline gypsum indicates that the waters of the lake were mainly saturated brines, which was subject to seasonal drought, and from near-shore seepage zones, deflation of sand-sized CaSO₄, to form local dunes (Chen et al., 1993). A similar pattern is shown by Lake Lewis, which is nearby, which displays a similar pattern (English et al., 2001). This was a groundwater-controlled basin by 80-70 ka that had shallow lake waters, high salinity levels, and precipitation of carbonates and sulphates (Chen, Chappell and Murray, 1995; English et al., 2001).

Lake Frome, to the southeast of Lake Eyre, appears to have been a perennial standing body of brackish water during the last interglacial, the mega-lake being termed Lake Millyera by Callen (Callen, 1984), this lake drying towards the end of MIS 5. This was seen by Callen as recording the demise of permanent lakes of brackish water in the northeast of South Australia (Callen, 1984: 172). Recent research has shown that about 70-60 ka and 48-45 ka Lake Frome refilled again (Cohen et al., 2012), and since that time, with the fluctuating levels and salinities since then (De Deckker, Magee and Shelley, 2011). The lake became saline and ephemeral from 30 ka, with occasional flushes of freshwater and, as it was mostly a saline, groundwater-controlled playa after 20-15 ka. According to Smith this shows that fluvial and lake systems on the southeaster margins of the desert responded to shifts in winter rainfall and reduced evaporation and that they may possibly have different histories from lakes further to the north. Lake Callabonna is part of a chain of saltlakes that link Lake Eyre and Lake Frome. Sediment that was inside a crania of a Diprotodon that was excavated has been dated by OSL to 75 ± 9 ka (Roberts et al., 2001) which suggests it was towards the close of MIS 5 that this system last carried water. Smith suggests that the presence of skeletons on the surface and the preservation of trackways of Diprotodon on the lake floor (Tedford, 1984) indicate there cannot have been significant reactivation of this lake since that time.