LATE GLACIAL AND HOLOCENE ENVIRONMENTS OF PLAYAS IN SOUTHEASTERN AUSTRALIA

Southwestern New South Wales is significant because it lies on the boundary of the arid and semi-arid climatic zones. Contractions and expansions of the Australian arid core are reflected in the landforms and biota of this transition belt. Playas in the region are sensitive to hydrological changes and minor differences in elevation between basins have caused them to respond differently to fluctuating water-tables.

The playas were dry and source-bordering dunes were emplaced between 21-16 ka, corresponding to the height of aridity at the global Last Glacial Maximum. Deglaciation appears to have been rapid, with lacustrine conditions returning to some basins by 16-14 ka. However, a hiatus in lake sediment accumulation after 14 ka, and the mobilization of dunes from 13-11 ka, suggests an arid interlude at the Pleistocene termination. This correlates with the Antarctic Cold Reversal.

Conditions were wetter after 11 ka and pollen records show that woodland replaced herbfields and shrublands over the early Holocene. Falling water-tables at some playas indicate aridity at 7-6 ka, although lakes were at their highest during the mid-Holocene. The presence of bull-oak, a woodland taxon now only found in higher rainfall zones, shows that the high groundwater levels correspond to an increase in local precipitation.

Woodland contracted after 4 ka, with bull-oak disappearing from the flora. The Holocene was most arid from 3-1 ka, when some playas dried and wind eroded their exposed floors. Aeolian sand was deposited in the lakes that persisted during this phase. Their pollen records show further decline of woodland taxa, particularly of drought-sensitive native pine.

Water-tables rose during the past millennium, reactivating many previously dry playas. Human population densities increased regionally over the late Holocene, but the playa environments were not particularly hospitable at this time and the archaeological record indicates occupation was limited to brief visits.