Hydroclimatic interpretation of Quaternary shorelines on south Australian playas

The catchment of Lake Lyre is one of the world's largest internally drained basins. The playas near its depocentre, the driest region of Australia, co ntain a partial record of Quaternary climatic and hydrologic events for the last full glacial cycle, and probably beyond. Ancient beach-ridges margina l to lakes Eyre, Frome, Callabonna and Blanche have been dated using thermo luminescence (TL) to provide evidence for major changes in the hydrological regime of the basin. Beach ridges around Lake Lyre provide evidence of hig h-lake stands up to 27 m above the present lake floor during what probably corresponds to the middle to latter part of Marine Oxygen Isotope Stage 5. There is evidence also for even higher lake stands associated with earlier isotope stag:es. Three TL dates identify a period of aeolian activity durin g Stage 4 and a further 5 TL dates from lakes Lyre and Frome indicate that high lake stands occurred between about 55 and 40 ka, corresponding with St age 3. The Stage 5 and Stage 3 high stands both relate to periods of enhanc ed fluvial activity previously identified in the Lake Lyre basin and elsewh ere in Australia. In contradiction with other work, a few TL dates from som e playas suggest a possible major episode of high lake levels immediately p receding or at the start of the Last Glacial Maximum (LGM) (26-22 ka). This may relate to a sharp temperature suppression and an increase in runoff by rivers fed from monsoons in the north. While a set of relatively low-eleva tion late Holocene beaches have been dated on two of the playas, a period o f enhanced precipitation and stream flow in the early to mid-Holocene appea rs not to have formed higher beaches, possibly due to high temperatures and evaporation rates at that time. The filling of Lake Eyre during and since Stage 5 appears to have been to no more than to a level of similar to 12 m Australian height datum (AHD), possibly due a spillway at about this elevat ion in the form of the Warrawoocara Channel connecting Lake Lyre with playa s to the southeast (lakes Gregory, Blanche, Callabonna and Frome). Such ove rflows from one large basin to another would have had a major impact on the hydrology of the region. In addition to enhanced runoff, essential for the maintenance of high lake levels must have been local temperatures and evap oration rates significantly reduced from present day levels. (C) 1998 Elsev ier Science B.V. All rights reserved.